S
 

Exploration Architecture with Quantum Inertial 
 

Gravimetry and In-situ ChipSat Sensors
 

NIAC Phase I Final Report
 

April 28, 2015
 

NIAC Fellow: Brett Streetman, Ph.D. (Draper) 
 

 

 

 

 

Dual Exploration Architectures
 

NIAC Phase I Final Report 

April 28, 2015
 

Contributing Authors: Joe Shoer (Draper), Rick Stoner (Draper), Mason Peck (Cornell), Zac 

Manchester (Cornell), Lorraine Weis (Cornell) 

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Executive Summary 

The Dual Exploration Architecture is a mission concept that combines remote sensing and in-situ 

observations into a single mission to answer planetary science questions that can only be 

answered with both types of data. Adoption of dual exploration architectures may short circuit 

the long, slow cycle of missions to inaccessible bodies by eliminating the need for separate 

precursor and follow-up missions. Additionally, the dual architecture possesses inherent 

flexibility that enables the design of adaptive, event-driven missions that are very different from 

traditional, largely pre-planned missions. Five key observations about the state and trends of 

planetary science exploration lead us to the dual architecture: increasing complexity of 

observations, scarcity of future mission opportunities, desire to capture transitory events, 

continued miniaturization of spacecraft components, and the Mars exploration cycle. Our goal in 

this study is to explore missions that can only happen using the dual architecture concept and 

find technology development needs that must be filled for those missions to compete. 

A survey of historical and current missions finds that opportunities for exploration are becoming 

less frequent, causing the flexibility and dual-nature elements of each mission to become more 

common. The dual exploration architecture takes these trends to their far conclusion, attempting 

to eliminate precursor and follow-up missions while still returning more scientific payoff. A 

study of the future of planetary science goals through the decadal survey reveals broad 

applicability of dual missions to solve mysteries that cannot be answered with a traditional 

mission architecture. These missions fall into three broad classes: choosing a local target from a 

global survey, dynamic/reactive science, and global in-situ networks. Two example missions of 

each class are notionally described. 

A deeper look at these dual architecture classes reveals four technology development needs that 

must be addressed for wide adoption of dual missions: passive landers, guided atmospheric 

probes, robust sensing packages, and small, precise orbital instruments. This study pursues a 

specific focus on two examples of such enabling technologies: the ChipSat and cold atom 

gravimetry. The ChipSat is a fully functional spacecraft-on-a-chip system that has broad 

versatility in the dual architecture mission space. Initial studies show that ChipSats could 

survive as passive impactor landers on bodies up to the size of Europa. Furthermore, COTS 

components could provide an in-situ senor suite that readily answers a number of pressing 

planetary science questions. Cold atom gravimetry uses inertial sensors based on light-pulse 

atom interferometry in a small form factor to map the gravity field of a body to precision 

equaling what would normally require two full spacecraft to achieve. The cold atom gravimeter 

provides an example of how advanced remote sensing capability can enable dual missions by 

providing greater returns in a significantly smaller package. 

Using the above two technologies, we study an example dual architecture mission to both 

characterize and sample the subsurface oceans at Europa. The greatest scientific return in terms 

of detecting extraterrestrial life is in those regions where Europa’s ice crust is thin. The 

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identification of regions with thin ice should therefore precede the selection of surface targets 

and dispatch of probes to those targets. This two-step process, if accomplished by separate 

flagship-scale missions, might take decades. As a result, a combined mission to both identify thin 

areas of Europa’s ice and follow up with surface observations at those regions is a good 

candidate for the dual exploration architecture. This example mission consists of an orbiter 

spacecraft carrying a cold atom gravimeter capable of sensing or inferring the ice thickness on 

regional to local scales, along with a number of ChipSat probes capable of landing on the moon. 

The small size and weight of the ChipSats allows large numbers of them to be carried, ensuring 

that enough can be dropped to ensure survival of a minimum number of probes and potentially 

allowing for the in-situ sampling of multiple locations on the moon. 

The example missions and Europa case study show that amazing scientific return can obtained 

from dual exploration architecture missions with a single launch by breaking the long timescales 

of planetary exploration and providing the flexibility to capturing transitory events and collect 

data across the local, regional, and global scales. 

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Executive Summary........................................................................................................................ 3
 

1 Introduction and Motivation.................................................................................................... 6
 

2 Background and Significance.................................................................................................. 8
 

2.1 Historical Perspective....................................................................................................... 8
 

2.2 Other Missions with Dual Features.................................................................................. 9
 

2.3 Survey of Decadal Survey Topics.................................................................................. 11
 

3 Dual Mission Classes and Technology Needs....................................................................... 13
 

3.1 Dual Mission Classes and Examples.............................................................................. 13
 

3.2 Technology Needs for Dual Missions............................................................................ 16
 

3.3 Technology Example: ChipSats..................................................................................... 18
 

3.4 Technology Example: Cold Atom Gravimeter and Gravity Gradiometer ..................... 24
 

4 Europa Case Study................................................................................................................. 31
 

4.1 Mission Goals and Science ............................................................................................ 31
 

4.2 Gravity Mapping Phase.................................................................................................. 33
 

4.3 In-situ Sampling Phase................................................................................................... 35
 

5 Appendices ............................................................................................................................ 42
 

5.1 Historical Mission Data.................................................................................................. 42
 

5.2 Decadal Survey Question Classifications ...................................................................... 45
 

6 References ............................................................................................................................. 56
 

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1	 Introduction and Motivation 

The Dual Exploration Architecture is a mission concept that combines remote sensing and in-situ 

observations to answer planetary science questions that can only be answered with both types of 

data. The combination produces a mission with the ability to examine details shortly after 

identifying them. As such, the dual exploration architecture also can short circuit the long, slow 

cycle of missions to inaccessible bodies by eliminating the need for separate precursor and 

follow-up missions. Additionally, the dual architecture possesses inherent flexibility that enables 

the design of adaptive, event-driven missions that are very different from traditional, largely preplanned missions 

Five key observations about the state and trends of planetary science exploration lead us to the 

dual architecture: 

1.	 Increasing complexity of observations: as solar system exploration matures, the data sets 

required to answer new questions naturally become more complex. A single observation 

becomes less and less likely to fully solve an open question as we return to bodies or classes 

of bodies that we have visited before. Increasingly, combinations of remote sensing and 

ground truth data or body-wide, coordinated in-situ measurements are required. Complex 

questions need to be examined on local, regional, and global scales to gain full 

understanding. 

2.	 Increasing scarcity of mission opportunities: as further described below in Sec. 2.1, 

opportunities to visit bodies of interest have become scarcer in recent decades, and that trend 

is projected to continue. As such, any mission needs to return significantly more science 

payoff if we want to push planetary science forward at a comparable speed to today. 

3.	 Desire to capture transitory events: as we continue to visit solar system bodies, their static 

qualities (such as mass, baseline composition, etc.) become better known and we need to start 

capturing dynamic and transitory events (such as jets/volcanoes, trace gas concentrations, 

weather patterns, etc.) to fully understand them. Some events whose timing cannot be 

predicted far beforehand drive important processes. Studying such events is hard to do with 

current exploration paradigms 

4.	 Miniaturization of spacecraft components: as with most industries, spacecraft components 

continue to become smaller and more capable over time. Although launch vehicle 

capabilities have not significantly increased, the miniaturization of components and systems 

allows for more capability within the same launch mass. This miniaturization needs to be 

exploited to increase scientific returns multiplicatively rather than additively. 

5.	 The Mars cycle and its failure beyond Mars: Mars exploration tends to work in cycles of 

remote survey and in-situ sensing. Mars Global Survey and Mars Odyssey did planet-wide 

studies. With this global data, interesting sites could be selected for the Mars Exploration 

Rovers. With new, more-detailed information from the Mars Reconnaissance Orbiter, a new 

interesting landing site for the Mars Science Laboratory was chosen. For Mars exploration, 

this cycle works well, as there are launch windows every two years and travel time can be 

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measured in months rather than years. Resources, enthusiasm, interest, and expertise do not 

have time to significantly diminish between missions. For more inaccessible targets, the 

cycle of remote followed by in-situ does not always close. For example, the Galileo mission 

made many exciting and unexpected 

discoveries at Europa, resulting in an almost 

universal desire to revisit the moon with an insitu probe. However, due to resource and time 

constraints, such a probe has been often 

proposed but never built. As the delay between 

visits to Europa widens, expertise and 

enthusiasm brought on by Galileo slowly 

wanes, making it ever harder to close the 

exploration cycle. 

Our goal in this study is to explore missions that 

can only happen using the dual architecture concept 

and find technology development needs that must 

be filled for those missions to compete. In Section 

2, we expand upon the above drivers that justify the 

dual exploration architecture by both looking 

backwards at past trends in planetary science and 

looking forward with the planetary sciences 

decadal survey. This allows us in Section 3 to 

broadly classify dual missions, generate dual 

mission concepts, and explore the technologies that 

enable them. We have a specific focus on two examples of such enabling technologies: the 

ChipSat and cold atom gravimetry. The ChipSat is a fully functional spacecraft-on-a-chip 

system that has broad versatility in the dual architecture mission space. Cold atom gravimetry 

uses inertial sensors based on light-pulse atom interferometry in a small form factor to map the 

gravity field of body to precision equaling what Figure 1. Conceptual stage of a Europa dual 

exploration architecture would normally require two full spacecraft to 

achieve. Using these two technologies we develop 

a dual exploration mission case study in Section 4. In this example mission we explore both 

fully mapping the ice crust thickness at Europa and then obtaining an in-situ sampling of ocean 

material within a single mission. 

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60 

J 

Cumulative number of missions launched 50 

40 

30 

20 

10 

0 

Moon 

Mars 

upiter 

Saturn 

195519601965197019751980198519901995200020052010 

Year 

 

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2 Background and Significance 

2.1 Historical Perspective 

NASA planetary science launch trends 

Figure 2. Cumulative number of NASA missions launched to several different solar system bodies 

versus launch date. Human, robotic, successful, and unsuccessful missions are all included. 

Figure 2 shows the cumulative number of NASA missions launched to various planetary science 

targets as a function of launch date. Both manned and unmanned missions are included, as well 

as both successful and unsuccessful missions. A list of the specific missions counted as raw data 

for this plot appears in Appendix 5.1. Three features are evident from this figure. First, the 

number of spacecraft launched to the Moon ramped up dramatically in support of the Apollo 

human exploration program. Science missions to other solar system bodies, especially the outer 

planets, did not begin until later. Second, there is a period around the 1980s in which a hiatus of 

almost all planetary science launches occurs. Third, after the hiatus the cadence of launches to 

many solar system bodies is lower than before the pause (with the exceptions of launches to 

Mars, which coincide with the familiar two-year launch window both before and after the hiatus, 

and asteroid/cometary exploration, which did not pick up until the 1990s). In fact, the cadence of 

lunar launches is 80% lower between the hiatus and present than it was between the first lunar 

launch and the 1980s. Jupiter exploration launches happen 50% less frequently after the hiatus 

than before the hiatus. 

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From Figure 2, we draw the conclusion that launches to various solar system exploration targets 

are happening at a generally decreasing cadence over time. Indeed, the number of NASA 

missions projected to launch in the future is smaller still: before 2030, InSIGHT and Mars 2020 

may launch to Mars, Europa Clipper to Jupiter, and OSIRIS-REx and a potential human mission 

to asteroids. Few other programs, if any, have started. (Of course, future smaller-scale missions 

such as Discovery-class missions may not be predicable this far in advance.) The drop in launch 

cadence is likely due to a number of factors, several of which revolve around the Apollo 

program. Not only did the Space Race result in sustained high funding levels for NASA, but 

NASA maintained a steady focus on lunar exploration to support the eventual human landing. It 

is not until the end of the Apollo program in 1972 that NASA launched any missions to the outer 

solar system at all. After the pause in the 1980s, NASA began to split its attention between a 

larger number of science targets than before – with a smaller bank of funds to divide between 

them. 

With science and exploration missions launching at a slower pace as time passes, it will be 

imperative to formulate missions that maximize science returns. A natural reaction to this drive 

would be to pack as much functionality as possible into each individual mission to a given 

exploration target. However, it is likely that the data from such a mission will raise even more 

questions, leaving the scientific community without fresh data for ever-longer periods of time. In 

such an environment, there may be great value to exploration architectures capable of responding 

to scientific targets of opportunity. 

2.2 Other Missions with Dual Features 

A number of other missions have included elements of the dual-mode responsive exploration 

architecture. However, despite some commonalities, these past missions fall short of achieving 

the revolutionary objectives of the proposed approach. Table 1 lists a number of historical 

missions, indicating which include the three key elements of the architecture: remote survey 

measurements (such as from an orbiter), in-situ science (for example, from a lander or 

penetrator), and whether or not the remote science data informed the choice of in-situ science 

target. We view this last point to be crucial to the dual exploration architecture: that the mission 

responds to scientific targets of opportunity that may not have been known to the mission 

definition team. 

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Table 1. Other missions with dual exploration architecture-like features. 

Launch 

year 

Mission Remote 

science? 

In-situ 

science? 

Choose target 

from survey? 

Notes 

1975 Viking Orbiter + 

Lander 

Yes Yes No* * Mission operators re-targeted Viking 2 

Lander based on Orbiter images 

1995 Galileo + Probe Yes Yes No 

1996 NEARShoemaker 

Yes No* Yes * Landed on asteroid at end of mission 

as a demonstration 

1997 Cassini + 

Huygens 

Yes Yes No 

2004 Rosetta + Philae Yes Yes Yes Closest to this exploration concept! 

2005 Deep Impact + 

Smart Impactor 

Yes No* No *Impactor not designed to survive and 

record measurements 

1999 Stardust-NEXT Yes No No* *Mission re-targeted to respond to Deep 

Impact mission science needs 

2016 OSIRIS-REx Yes Yes* Yes *Sample return; no in-situ science 

performed on board 

Some of the most obvious comparisons of historical missions to the dual exploration architecture 

are the Galileo mission to Jupiter and the Cassini-Huygens mission to Saturn. In both cases, the 

mission consisted of an orbiter spacecraft and a lander or probe, and so each might seem similar 

to the dual exploration concept. However, both the Galileo Probe and Huygens lander separated 

from their mother spacecraft before any science return was available from the orbiters. Neither 

in-situ probe was designed to target a site identified from remote sensing data. In effect, the 

probes’ missions were independent of the orbiter mission. 

In several cases, a mission deviated from its initial definition in a way that aligned with the dual 

exploration architecture. The earliest such example is Viking 2, which consisted of the Viking 2 

Orbiter and Lander. Mission planners selected a landing site for the Lander in advance, but upon 

review of images returned from the Orbiter, they decided to re-target the Lander. In some sense, 

then, the Lander mission responded to remote sensing data. Another prominent example is the 

NEAR-Shoemaker mission, which launched as a mission to survey an asteroid from orbit. As a 

demonstration, the spacecraft ended its mission life by touching down on the asteroid surface, at 

a point selected from available science data. Finally, some missions include attempts to visit 

more than one target, sometimes responsively: after the Deep Impact mission, operators retasked the Stardust spacecraft to perform follow-up studies of Comet Tempel 1. 

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The European Space Agency’s Rosetta and Philae spacecraft represent the closest match of any 

past or present mission to the dual exploration architecture proposed in this study. The mission 

consisted of an orbiter and a lander spacecraft, with the orbiter performing a survey of the target 

comet 67P/Churyumov–Gerasimenko before deploying the lander. The team scientists selected 

the landing site from remote sensing results. Furthermore, the Rosetta science team did not know 

what to expect at the comet. Rather than sending two different missions, though, with Philae as a 

follow-up to Rosetta, the two spacecraft were launched together with the intention that the lander 

would immediately follow on the science from the orbiter. 

In a sense, there is already a trend towards the dual-phase exploration architectures this study 

suggests. The need to maximize science return from less frequent missions, combined with 

increasing experience with autonomous landers and proximity operations, is evident in the 

progression from Galileo and Cassini-type missions to more recent mission concepts such as 

Rosetta and OSIRIS-REx. Rather than sending multiple missions to perform initial survey and 

then follow-on studies of a target, these missions combine both efforts. The exploration 

architecture put forward in this study embraces and encourages this trend. 

2.3 Survey of Decadal Survey Topics 

The planetary sciences decadal survey is the guiding document for NASA’s planetary science 

agenda for the next decade.[1] In addition to prioritizing objectives and missions, the decadal 

survey gives a concise summary of lines of research for planetary science in the form of a large 

number of unanswered questions about our solar system. This set of questions provides a rich 

set of data for us to examine what types of missions and data sets are required to advance 

planetary science in the near-term, mid-term, and far-term periods. 

We have parsed these questions to determine what kind of mission is needed for an answer, and 

they fall into three distinct categories: 

1.	 Remote observation or in-situ observation only questions: these are questions which 

we both know how to ask and how to answer. We know where to go and what to look 

for. These questions are the “low hanging fruit,” so to speak, which we could answer in 

5-10 years (given the resources). This category represents 84 of 161 questions (52%) 

asked within the decadal survey. However, this category is likely overrepresented as 

these are the types of decade-scale questions that the survey is prioritizing. One example 

of this category is “How does the atmosphere of Venus respond to solar-cycle 

variations?” This is a pure remote observation question that can be answered with a 

spacecraft very similar to the MAVEN mission to Mars. We know where to go and what 

to do when we get there. An example of an in-situ only question is “How do the 

compositions of presolar grains and organic molecules vary among different comets?” 

Again, we know what data we need, we just have to go get it. 

2.	 Dual Architecture questions: the “high-hanging fruit” requiring both In-situ and 

Remote observations. We know how to answer these but they push the boundaries of 

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traditional mission architectures and have a 10-20 year horizon. These are the questions 

that seem to fall within the NIAC charter and are what we focus on in this report. With 

traditional single mission architectures, two separate missions or spacecraft would be 

needed to answer these questions, potentially pushing the final answer out several 

decades for hard to reach targets. This category represents 19% of the explicitly asked 

questions. An example from the decadal survey is “What can the significant differences 

among ring systems teach us about the differing origins, histories, or current states of 

these giant planet systems?” We need both a planetary-scale view to see the overall ring 

structure and an in-situ view to get to resolve the fine detail within the rings to answer 

such a question. This begs for a dual architecture mission that can fully satisfy the 

question in a single mission rather than two missions likely separated by decades. A 

second dual architecture example question from the decadal survey is “What is the fourdimensional wind structure of the Martian atmosphere from the surface boundary layer to 

the upper atmosphere?” This question, and several others that are meteorological in 

nature, requires global atmospheric data, coupled with a global network of in-situ 

sensors, something that can only be accomplished using a dual architecture. 

Figure 3. Breakdown of decadal survey question types 

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3.	 Theoretical questions: This group of inquiries is looking for deeper answers. These are 

generally questions we do not know how to ask precisely enough to properly answer, and, 

thus, they have very long time horizons. Often such questions would require precursor 

missions. We posit that the inherent flexibility of dual architecture missions could 

effectively short circuit the long timeline by providing better precursor data, or by 

providing the opportunity for an immediate response to precursor data. Theory questions 

represent 29% of questions. An example of such a deep question is “Can evidence of life 

be found on Mars?” We have to agree on what evidence of life would look like before 

we can design a mission to find it, but a dual mission that searched for hotspots of certain 

compounds from orbit before deploying a lander could provide a faster answer. A second 

example is “What do the crater populations on the satellites reveal about the satellites’ 

histories and subsurface structure and about the populations of projectiles in the outer 

solar system and the evolution thereof?” This is much more of a modeling question, but 

will require lots of data from around the solar system to corroborate the model. 

All of the decadal survey questions and classifications are shown in Section 5.2. 

Pursuing dual architecture missions allows us to skip ahead, so to speak, on the second and third 

categories, using designed-in flexibility to greatly reduce the need for precursor missions or 

repeated visits to planetary bodies. 

3	 Dual Mission Classes and Technology Needs 

3.1 Dual Mission Classes and Examples 

Looking deeper at the Dual Exploration Architecture questions posed by the Decadal Survey, we 

create dual mission scenarios to answer these questions with a single mission instead of multiple 

visits. Upon completing this exercise, three broad classes of Dual Architecture mission are 

evident: 

1.	 Global Survey Chooses Local Site: The first dual mission class involves choosing the 

right landing or sampling location after mapping a quantity of interest remotely. This 

class is appropriate when we know there is a spot of particular interest on a planet or 

body, but we can’t know exactly where it is until we arrive. An example is our case 

study, Example Mission 1 in Table 2: Gravimetry of an icy body to determine the 

locations of thinnest ice or most likely spot to gain access to subsurface material, 

followed by landing small in-situ sampling probes at the most promising location. This 

mission allows us to determine both the ice thickness and subsurface ocean composition 

with the same mission, something that would likely take decades otherwise. Another, 

different example is Example Mission 2, which explores Saturn's (or other body's) rings 

from both a global and local perspective to achieve understanding of their structure at all 

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scales. Such a mission would include both survey-class instruments and small probes 

that actually enter the ring system. 

2.	 Dynamic/Reactive Science: The second class of dual architectures involves capturing 

transitory events on other bodies. Certain events are ephemeral, with hard to predict start 

and end times. A dual mission can operate with the flexibility to wait for these events to 

occur. An example of this type of mission is Example Mission 3: a reactive orbiter that 

waits for active volcanoes and then releases probes to fly through the plume. We know 

these events are occurring at a body, but we cannot predict ahead of time where and when 

we need to be to capture them. Thus, instead of a traditional mission that will follow a 

prescribed trajectory and timeline; we need an orbital platform that watches and waits for 

the transitory event and then releases a separate probe to capture it. A second example of 

this class, Example Mission 4, is a global weather satellite that monitors for new storms 

on a giant planet and then sends a probe into the eye of the storm. 

3.	 Global In-situ Networks: The third class of dual mission involves deploying and 

communicating with global sensor networks. Many measurements of interest require a 

global network of in-situ samples. Generally a global asset is required to both deploy and 

communicate with the distributed network. Our first example of this class, Example 

Mission 5, is a seismic network at a small body. A global “mothership” deploys a 

network of seismic sensors to map internal composition of asteroids or KBOs. A second 

example of this class, Example Mission 6, is a global Martian LIDAR wind measurement 

network with reserved nodes deployed into active large scale dust storms detected from 

orbit. 

Table 2 gives presents these six example missions and gives further description of the questions 

asked in the decadal survey to inspire each mission. Figure 4 show a breakdown of the dual 

mission classes, their examples, and the technology development needs for each example 

mission. 

Table 2. Example dual-phase missions to answer questions posed in the Decadal Survey. 

Example 

Mission Mission Idea(s) Decadal Survey Question 

Decadal 

Chapter Class 

Technology 

Development Needs 

1 

Gravimetry of an icy body to 

determine the locations of thinnest 

ice or most likely spot to gain 

access to subsurface material 

followed by landing small in-situ 

sampling probes at the most 

promising location 

Are volatiles present at the 

surface or in the ice shell of 

Europa that are indicative of 

internal processing or 

resurfacing? And many other 

Europa questions 

Ch8 1 

Small scale gravimeter, 

Passive landers 

(impactors) 

2 

Explore Saturn's (or other body's) 

ring from both a global and local 

perspective to achieve 

understanding of their structure at 

all scales. Include small probes 

that actually enter the ring system 

What is the mechanical process of 

accretion up to and through the 

formation of meter-size bodies? 

Plus other ring related questions 

Ch4, 

Ch7 1 Small, cheap, disposable camera/sensing package 

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G

ple 

ons 

am

ssi

Ex

Mi

 

 

 

(1) 

Europa 

ravity 

and Ocean 

Dual 

Exploration 

Architecture 

Global 

Chooses 

Local 

Dynamic/ 

Reactive 

Science 

Global 

In-situ 

Network 

Sampler 

(2) Saturn 

Ring 

Explorer 

(3) Venus 

Volcanic 

Plume 

Sampler 

(4) Giant 

Planet 

Hurricane 

Hunter 

(5) 

Asteroid 

Seismic 

Network 

(6) Mars 

Weather 

Network 

Mission 

Classes 

S 

I 

A 

Lander: Small Body 

Lander: Atmospheric 

Lander: Impactor 

Guided Atmospheric Probe 

Robust Sensing Package 

Small Orbital Instrument 

I S A 

Technology 

Needs 

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3 

Reactive orbiter that waits for 

active volcanoes and then 

releases probes to fly through the 

plume 

What are the inventories and 

distributions of volatile elements 

and compounds (species 

abundances and isotopic 

compositions) in the mantles and 

crusts of the inner planets? Plus 

other volcanism questions 

Ch5, 

Ch8 2 

Guided atmospheric 

probes, remote eruption 

sensor 

4 

Global 'weather' satellite that 

monitors for new storms on a giant 

planet and then sends a probe 

into a the eye of the storm 

What are the natures of periodic 

outbursts such as the global 

upheaval on Jupiter and the 

infrequent great white spots on 

Saturn? 

Ch7 2 Guided atmospheric 

probes, storm sensor 

Seismic networks at small bodies. 

5 A global 'mothership' deploys a 

network of seismic sensors to map 

What are the internal structures of 

Trojans and KBOs? Ch4 3 Passive landers (small body), Seismic sensor 

internal composition 

Global Martian LIDAR wind 

What are the processes 

controlling the variability of the 

present-day climate? What is the 

four-dimensional wind structure of 

6 

measurement networks with 

reserved nodes deployed into 

active large scale dust storms 

detected from orbit 

the Martian atmosphere from the 

surface boundary layer to the 

upper atmosphere? What are the 

primary causes behind the 

occurrence of global dust events? 

What are the processes coupling 

the CO2, dust and water cycles? 

Ch6 3 

Weather sensors, 

Passive landers 

(atmospheric) 

Figure 4. Dual exploration classes, mission examples, and technology needs 

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3.2 Technology Needs for Dual Missions 

From the three classes of dual architecture mission and their examples listed in Table 2, four 

major technology categories appear that need more development to make these mission possible: 

1.	 Passive Landers: Needed for getting from orbit to the in-situ environment with minimal 

packaging. These landing technologies must be robust enough to ensure mission success. 

However, an importation distinction between traditional mission architectures and many 

of our example missions is robustness through numbers: single in-situ sensors are 

unimportant as long as enough survive to complete the mission. Three distinct versions of 

landers are needed: 

a.	 Small body, for asteroids/comets. These impact with very low speeds, but must 

remain on the body (i.e. not bounce back off), which can be the most challenging 

aspect of design as the Rosetta mission demonstrated. 

b.	 Atmospheric, for large bodies with significant atmospheres. The presence of 

atmosphere can help with passive landing, especially for very small probes. At 

the extreme some designs with very low area-to-mass ratios can survive with no 

heat protection at all [2] 

c.	 Impactors, for moons and other significant bodies without atmosphere. As bodies 

grow larger without an atmosphere, passive landers must survive larger and larger 

impact velocities, bringing in new design challenges. A sufficient number must 

survive the impact such that the mission still succeeds. 

2.	 Guided Atmospheric Probes: Needed for sampling specific places in an atmosphere or 

landing on specific surface spots. Passive landers are designed to land where they may, 

but many missions require passage through or landing on a specific spot. These missions 

tend to occur on atmospheric bodies, with goal of sampling things like volcanic plumes, 

storm regions, or areas with a higher concentration of a gas species of interest. 

3.	 Robust Sensing Packages: Needed for reliably operating away from a mothership in 

highly challenging environments (rings, high radiation zones, etc.). These sensing units 

are thought of as somewhat disposable with perhaps even planned destruction. They go 

to places where a main spacecraft asset cannot and must reliably capture and return data 

before succumbing to the environment. By acting away from the main orbital asset, they 

protect the overall mission. 

4.	 Small, Precise Orbital Instruments: The ideal dual mission provides the benefits of 

both modes of exploration in the same scale package. In addition to the in-situ 

technologies listed above, this requires the continued miniaturization and improvement of 

remote sensing units. 

Development in the above categories improves the overall TRL of all of our example missions. 

However, given the inherent flexibility designed into the dual exploration architecture, these 

technologies have wide ranging uses and applications. For space exploration, each could serve 

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as either the focal point of a small mission or a hosted payload/instrument on a large mission. 

The technology set also have many applications terrestrially, some of which are noted in Table 3. 

Table 3. Potential Earth Applications of the Dual Mission Technology Needs 

Technology Class Potential Earth Applications 

Passive Landers 

Small Body Sensor deployment from a low altitude, low velocity UAV 

Sensors able to land on a moving vehicle 

Atmospheric 

Deployment of widely dispersed sensor networks from orbit 

Sampling of mesosphere and atmospheric layers 

unreachable by balloons or traditional spacecraft 

Measuring radiation environment in near space and within 

auroras 

Impactor 

Development of electronics robust to extreme g-loading, 

e.g. gun-launched sensors 

Gun-launched spacecraft for inexpensive, high-cadence 

suborbital (or, perhaps, orbital) access 

Other gun-launched devices? E.g. law enforcement launch 

a GPS tag at a getaway car 

Sensors to monitor road and rail condition subject to 

vehicles driving over them 

Guided Atmospheric Probes 

Return of small sample capsules from LEO 

Return of data from LEO in physical form factor ('thumb 

drive from space') 

Sampling of volcanic plumes 

Gather in situ data from hurricanes 

Oceanic sensor networks with individuals that hold station in 

ocean currents (to listen for airliner "black box" pings, track 

subsurface oil spills, monitor climate variables like dissolved 

CO2) 

Sea-floor probes that target a particular landing site (deepsea vents, wreckage, coral reef, search-and-rescue sites) 

Robust Sensing Packages 

Sensor networks covering glaciers or ice caps 

Sensor networks for high radiation environments 

Sensor networks for high pressure environments 

Sensor networks for other dangerous environs (high 

temperature, toxic, etc.) 

Small, Precise Orbital Instruments Move instruments that used to require large spacecraft into 

CubeSats 

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3.3 Technology Example: ChipSats 

The ChipSat architecture represents a core that can be adapted to meet many of the technology 

needs discussed in the previous section. Designed as extremely small standalone spacecraft, they 

readily fill the role of robust sensing packages and can readily be used as small body and 

impactor landers. With small aerodynamic surfaces attached, ChipSats can become the core of 

atmospheric landers as well.[2] 

A revolutionary characteristic of 

ChipSats is that they are both very 

small and relatively inexpensive to 

produce in volume. Because of these 

unique features, a modest-size 

primary satellite (even a smallsat, less 

than 180 kg) can store and deploy 

hundreds to thousands of ChipSats in 

a single launch. Their sheer numbers 

enable mission planning to be based 

on a high-confidence statistical model 

of success, very different from the 

probabilistic reliability models used 

for single spacecraft. 

ChipSats have several target 

applications and more will surely 

follow as the technology matures. One of the target missions is in-situ detection. ChipSats can be 

equipped with temperature, pressure, magnetic, and other sensors to measure phenomena on a 

planetary surface. Another scientific objective for ChipSats would be testing for the presence of 

particular chemistry, specifically those related to organic compounds and life. 

The Sprite spacecraft is the first instance of a ChipSat, motivated originally by a 2006 NIAC 

study. Each weighs approximately 5 g. 1000 of them would represent a 5 kg payload. Each 

contains solar cells (on both sides), a radio transceiver, and a microcontroller. In 2011 three 

prototypes flew on the MISSE-8 experiment. They survived three years in LEO and continue to 

function today. In April 2014, 104 Sprites ware launched from a 3U CubeSat satellite bus called 

KickSat. These two technology-demonstration missions establish the feasibility of 

communicating across large distances with low power—10 mW reaches over 1000 km with 

suitable forward-error correction, requiring only a laptop and a hand-held antenna. Increasing 

this range requires only trivial changes, primarily an increase in the length of the pseudorandomnoise sequence that represents a single bit transmitted from the Sprite. We are confident that 

lightweighting the current design can result in a roughly 1 g Sprite equivalent, and advancing this 

Figure 5. A Sprite spacecraft 

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technology may reduce the mass to below 100 mg. The roadmap for doing so is based on 

exploiting thin-film solar-array technologies, custom ASICs, and antenna structures mounted or 

printed on a thin-film Kapton substrate. 

The communications architecture enables simultaneous reception of a large number of signals, 

one from each Sprite, with a guarantee that the source of the signal (i.e. the identity of a single 

Sprite) is unambiguous. So, the data can be correlated spatially and temporally to suit the 

mission needs. Furthermore, the communications hardware on the spacecraft side can be quite 

simple. These important objectives are accomplished with a Code-Division Multiple Access 

(CDMA) strategy that was demonstrated in 2011. It has since been flown on Sprite prototypes 

on ISS, where the technology successfully survived three years on the MISSE-8 experiment, 

exposed to the space environment. An additional communications technology, forward error 

correction, increases the signal-processing gain at the expense of data bandwidth, allowing the 

mission architecture to accommodate an optimal combination of data rate and signal-to-noise 

(SNR), analogous to gain. 

Each Sprite communicates a single data bit via a unique pseudorandom-noise (PRN) sequence. 

This PRN is in fact a so-called gold code, mathematically orthogonal to that of every other 

Sprite. Matched filtering essentially allows the energy in the entire PRN code to be summed and 

treated as a single data bit, providing an increase in SNR equal to the code length. For the 2014 

KickSat mission, a family of PRN codes 640 chips long is being used, providing a “code gain” of 

about 28 dB for a very robust link margin. Aside from improving SNR, matched filtering also 

makes possible CDMA. By assigning each Sprite a different PRN, the receiver can “tune” to a 

particular spacecraft’s signal by correlating against its unique code. This allows all the Sprites on 

a particular mission to share the same allocated frequency, simplifying receiver hardware and 

eliminating the need for clock synchronization that would otherwise be required for the Sprites to 

alternate transmitting on the same frequency. CDMA has been used for many years in the 

cellular telephone industry and the global positioning system. It has proven in practice to be the 

most efficient channel access method when a large number of users must be accommodated. We 

conclude that the Sprite technology enables a wide range of survey tasks that require spatial 

and/or temporal distribution of in-situ sensors. 

For this study, we adapt this proven design to the science needs of a dual-mission architecture. 

Chief among these adaptations is the sensor technology. Sprite spacecraft will have to be 

outfitted with suitable small-scale sensors. The size of the spacecraft restricts the kinds of 

sensors that are appropriate for this technology concept, as does the available power. This study 

considers state-of-the-art, COTS components to establish feasibility. With this existence proof in 

place, we argue that extending the capability or further reducing mass is entirely feasible. 

Companies such as Systron Donner Inertial, Colibrys, ST Microelectronics, Bosch, and Texas 

Instruments have developed entire product lines of microelectromechanical systems (MEMS) 

sensors that fit Sprite’s design parameters. Inevitable advancement in sensing technology will 

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represent additional design margin or further opportunities for NASA missions in the longer 

term. 

Sprites may be able to reveal information about the gravitational field and composition of the 

celestial body by measuring their inertial behaviors in orbit and as they impact the surface. A 

combination of MEMS gyroscopes and accelerometers can achieve this goal. They can be used 

as two independent sensors or together. Some COTS IMUs combine the two products into one 

small MEMS unit. Advancements in MEMS technology have enabled these gyros to provide 

suitable performance, including low noise, miniature size, wide bandwidth and temperature 

ranges, and high reliability, as shown in Tables 1 through 3. 

Table 4: Systron Donner Inertial Gyroscopes 

Product 

Name Size [mm] Input voltage 

[V] 

Input 

current 

[mA] 

Standard range 

[°/sec] Scale factor Bandwidth 

[Hz] 

Noise 

[°/sec/√Hz]

QRS11 Ø 37.9 x 13.46 ± 5 < 80 ± 100 < 1% of value > 60 < 0.01 

QRS116 Ø 37.9 x 13.46 ± 5 < 20 ± 100 < 1% of value > 60 < 0.002 

SDG1400 40.6 x 35.6 ± 10 to 16 < 15 ± 200 

0.025 

VDC/°/sec 50 ± 10 < 0.0017 

SDG500 32.5 x 32.5 ± 10 to 15 < 20 ± 100 

0.050 

VDC/°/sec 60 ± 15 < 0.005 

53.1 x 25.7 x 9 to 18, ± 9 to ± 50, 100, 200, < 0.05, < 

QRS14 25.7 18 < 20, < 25 500 ± 2% of value > 50 0.02 

HZ1 

58.3 x 25.3 x 

25.3 8 to 15 < 20 ± 90, 100 < 2% of value > 18, > 60 < 0.025 

Table 5: Colibrys inertial sensors 

Product 

Name Size [mm] Full-scale 

[g] 

Scale factor 

[mV/g] 

One year 

bias 

stability 

[mg] 

One year SF 

stability 

[ppm] 

Bandwidth 

[Hz @ -3dB] 

Noise 

[μV/√Hz]

MS8002.D 14.2 x 14.2 ± 2 1000 1.5 300 > 200 18 

MS8010.D 14.2 x 14.2 ± 10 200 7.5 300 > 200 18 

MS8030.D 14.2 x 14.2 ± 30 66.6 22 300 > 200 18 

MS8100.D 14.2 x 14.2 ± 100 20 75 300 > 200 18 

MS9001.D 8.9 x 8.9 ± 1 2000 < 1 300 > 100 18 

MS9002.D 8.9 x 8.9 ± 2 1000 1.5 300 > 100 18 

MS9005.D 8.9 x 8.9 ± 5 400 3.75 300 > 100 18 

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MS9010.D 8.9 x 8.9 ± 10 200 7.5 300 > 100 18 

MS9030.D 8.9 x 8.9 ± 30 66.6 22 300 > 100 18 

MS9050.D 8.9 x 8.9 ± 50 40 37.5 300 > 100 18 

MS9100.D 8.9 x 8.9 ± 100 20 75 300 > 100 18 

MS9200.D 8.9 x 8.9 ± 200 10 150 300 > 100 18 

Note: The sensors operate from a single power supply voltage (between 2.5 V and 5.5 V) with low current 

consumption (< 0.5 mA at 5 V). The output is a radiometric analog voltage that varies between 0.5 V and 4.5 V for 

the full-scale acceleration range at a voltage supply of 5 V. They operate over temperature range of -55 °C to 125 °C 

and can withstand shocks up to 6000 g. 

Table 6: Colibrys tilt sensors 

Product 

Name Size [mm] Full-scale 

[g] 

Scale factor 

[mV/g] 

One year 

bias 

stability 

[mg] 

One year SF 

stability 

[ppm] 

Bandwidth 

[Hz @ -3dB] 

Noise 

[μV/√Hz]

RS9002.B 8.9 x 8.9 ± 2 1000 10 < 300 > 200 30 

MS9001 8.9 x 8.9 ± 1 2000 0.75 300 > 100 18 

MS9002 8.9 x 8.9 ± 2 1000 1.5 300 > 100 18 

MS9005 8.9 x 8.9 ± 5 400 3.75 300 > 100 18 

MS9010 8.9 x 8.9 ± 10 200 7.5 300 > 100 18 

MS9030 8.9 x 8.9 ± 30 66.6 22 300 > 100 18 

MS9050 8.9 x 8.9 ± 50 40 37.5 300 > 100 18 

MS9100 8.9 x 8.9 ± 100 20 75 300 > 100 18 

MS9200 8.9 x 8.9 ± 200 10 150 300 > 100 18 

Note: The sensors operate from a single power supply voltage (between 2.5 V and 5.5 V) with low current 

consumption (< 0.5 mA at 5 V). The output is a radiometric analog voltage that varies between 0.5 V and 4.5 V for 

the full-scale acceleration range at a voltage supply of 5 V. They operate over temperature range of -55 °C to 125 °C 

and can withstand shocks up to 6000 g. 

Conceivable surface measurements include tectonic activity and magnetic fields, and potentially 

weather on the few bodies with atmospheres. There are a number of MEMS options that can be 

outfitted on the Sprites for these purposes including seismic, geomagnetic, humidity, pressure, 

and temperature sensors. Once again, there are also some units that integrate the multiple 

weather sensors into one small product. Vibration sensors with a low noise, high resolution, and 

large dynamic range offer a solution to seismic monitoring. They are designed to detect natural 

movements that are characterized by low amplitude signals. Geomagnetic sensors measure 

external magnetic fields in three axes and can be integrated with a three-axis accelerometer to 

detect the planet-fixed direction of the magnetic field by compensating for the sensor’s tilt. For 

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general weather measurements, e.g. on surface of Titan, a combination of humidity, pressure, 

and temperature sensors can be used on the Sprites. These would also be useful from a science 

perspective and for monitoring spacecraft health. 

Table 7: Colibrys vibration sensors 

Product 

Name Size [mm] Full-scale 

[g] 

Scale factor 

[mV/g] 

Bandwidth 

[Hz @ -5%] 

Bandwidth 

[Hz @ -3dB] 

One year 

stability 

[mg] 

Noise 

[μV/√Hz]

VS9002.D 8.9 x 8.9 ± 2 1000 > 250 > 800 1.5 25 

VS9005.D 8.9 x 8.9 ± 5 400 > 700 >1700 3.75 25 

VS9010.D 8.9 x 8.9 ± 10 200 > 1000 > 3000 7.5 25 

VS9030.D 8.9 x 8.9 ± 30 66.6 > 1000 > 3000 22 25 

VS9050.D 8.9 x 8.9 ± 50 40 > 1000 > 3000 37.5 25 

VS9100.D 8.9 x 8.9 ± 100 20 > 1000 > 3000 75 25 

VS9200.D 8.9 x 8.9 ± 200 10 > 1000 > 3000 150 25 

MS9100 

Ø 15.55 x 

3.9 ± 2 10 n/a 800 2 7 

MS9200 8.9 x 8.9 ± 10 50 n/a 650 10 7 

Note: The VS series sensors operate from a single power supply voltage (between 2.5 V and 5.5 V) with low current 

consumption (< 0.5 mA at 5 V). The output is a radiometric analog voltage that varies between 0.5 V and 4.5 V for 

the full-scale acceleration range at a voltage supply of 5 V. They operate over temperature range of -55 °C to 125 °C 

and can withstand shocks up to 6000 g. The MS series sensors operate from a single power supply voltage (between 

2.5 V and 5.5 V) with low current consumption (< 0.2 mA at 3 V). The output is a radiometric analog voltage that 

varies between 0.5 V and 2.5 V for the full-scale acceleration range at a voltage supply of 3 V. They operate over 

temperature range of -40 °C to 125 °C and can withstand shocks up to 6000 g. 

After impacting the surface, the detection of organic compounds and gases is one of the principal 

goals. MEMS sensor technology in this field has not progressed as rapidly as others, but there are 

a few technologies that fit the Sprite design requirements and the dual-mission concept. For a 

Solar System body that has even a thin atmosphere, a gas chemical sensor can be used to 

measure the composition. Electrochemical sensors can only detect and measure a specific gas, so 

the type of sensor would have to be determined before the ChipSats are built and launched. The 

target gasses include nitrogen dioxide, ammonia, hydrogen, and volatile organic compounds, 

among others. Water quality (e.g. on Europa) can even be monitored by measuring the pH, or the 

concentration of hydrogen ions in solution. Conversely, non-dispersive infrared (NDIR) sensors 

are not confined to a specific gas and are able to make various measurements, but they also 

require more hardware to operate as a complete system. 

The simplest ChipSats are designed to be impactors, in that they do not have a method of 

slowing their descent. The size of the planetary body and the presence of an atmosphere greatly 

22
 
Impact velocities on objects in Solar System 

50
 

45
 

40
 

35
 

Frequency 30 

25 

20 

15 

10 

5 

0 

102030405060708090

100200300400500600700800900

1000200030004000

50006000700080009000

100002000030000400005000060000 

Impact velocity (m/s) 

 

 

 

 

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affect the landing conditions of the Sprites. The gravity on larger bodies causes the satellites to 

approach at very high velocities, likely incurring fatal damage upon impact. Heavy atmospheres 

can cause the satellites to burn up upon entry unless their mass is below 100 mg, where 

aerothermal heating is never sufficient to cause demise. With no active landing system, these two 

factors constrain the target bodies to minor planets, certain moons, and asteroids/comets. 

Nevertheless, this wide range of applicability enables future mission architectures based on an 

in-situ site survey. 

Impacting a body the size of Europa or Earth’s moon is only barely survivable—on the order of 

1% of impacting ChipSats remain functional, as discussed below. For smaller bodies, the 

survival rate can be much higher, approaching 100% for impact velocities on the order of 1 m/s 

or lower. These speeds correspond to a large number of bodies in the solar system, as shown in 

Figure 6. These velocities are based on cases with no atmospheric drag, which is representative 

of virtually every body under consideration, and the minimum impact velocity is equal to the 

escape velocity. However, 20% additional velocity appears in these results, in order to account 

for variations in the deployment from the spacecraft and unmodeled orbital perturbations. The 

figure is a histogram showing the impact velocities for over 250 planetary bodies in the Solar 

System (note the varying scale on the x-axis). The impact velocities of Earth, Mars, the Moon, 

Europa, and Itokawa are 9,493, 4,266, 2,017, 1,719, and 0.10 m/s, respectively. 

Figure 6. Impact velocities for various Solar System objects 

The significant savings in technology-development effort by omitting explicit Entry, Descent, 

and Landing (EDL) hardware, as well as the versatility that this ChipSat concept offers, make it a 

valuable element of the dual-mission architecture. 

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3.4 Technology Example: Cold Atom Gravimeter and Gravity Gradiometer 

Atom interferometry is a powerful tool for precision metrology [see, e.g., 3, 4, 5, 6, 7], and 

represents an example of the small, precise orbital instrument category of technology that 

enables dual exploration architectures. Light pulse atom interferometry (LPAI) has been 

successfully used to measure gravity [8] and gravity gradients [9, 10] at high precision. To 

realize its technological potential outside the laboratory, methods must be developed for 

After time T

Proof mass released at rest

Proof mass is displaced

Acceleration

Acceleration

Figure 7. Acceleration sensing with free particles. A proof mass is released from rest in the 

reference frame of the sensor. Measurement of the particle displacement during a known time 

interval will enable determination of the average acceleration. 

operating atom interferometers in adversely dynamic environments and within constraints of 

reduced size, weight, and power (SWaP) [11, 12, 13, 14]. We have carried out a design study for 

a LPAI-based gravity gradiometer for space science applications, with an eye towards 

gravitational survey of Jovian moons. The proposed gradiometer 

will exploit Raman LPAI beamsplitter technology intended for use 

in dynamic environments and in physically compact sensors: 

specifically, LPAI at short interrogation times using large 

momentum transfer (LMT) technology [15,16]. 

Figure 7 illustrates the method for measuring acceleration using 

free particles. LPAI uses this scheme, with atoms as proof masses. 

The use of particular atoms (in this case, alkali) allows for 

application of laser cooling and trapping for creation of a proof 

mass, and LPAI as a means for measuring proof mass 

displacements with very high precision. LPAI exploits laser beams 

as highly precise “rulers” to measure non-uniform motion of free 

particles in a sensor reference frame. The Gaussian mode structure 

of the laser beams can be thought of as a “transducer” between frequency and Figure 8. Two-photon transfer 

between ground states. 

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distance: the frequency-stabilized lasers provide exquisitely precise and accurate position 

references. 

An LPAI accelerometer (or gravimeter) uses a pair of oppositely directed, phase-coherent laser 

beams, prepared such that the difference in the laser frequencies coincides with the energy level 

splitting of an alkali atom [17]. The laser beam pair induces the atom to simultaneously change 

its internal state while absorbing a 2-photon momentum “kick” from the light (Figure 8). The 

result is a so-called entangled state in which the atom is a coherent superposition of conflated 

internal and center of mass momentum states [18,19]. The atom is thus “split” into two 

wavepackets that tend to separate along the laser beam direction. 

Probability of 

detecting atom in 

lower output 

[1 cos( )]

2

1

P = − Δφ

Mach-Zehnder Atom Interferometer Interference fringes

2 Δφ = keff aT

i eff i i Use laser phase as ruler: φ = k z −ωt  Atoms “store” this 

information % of atoms

-2π 0 

2π 

Contrast 

Figure 9. Acceleration measurement with atom interferometry. Three pulses are applied to an atom 

that is initially stationary in the sensor reference plane. Under acceleration (solid line), the 

fractional population of the ground states varies sinusoidally; the period of the sinusoid decreases 

with increasing time T between pulses, because the inertially induced deflection of the atom 

increases. 

A series of laser pulses can be applied in order to carry out inertial sensing. A three pulse 

sequence from a single laser beam pair can be used to measure acceleration: Figure 9 depicts the 

motion of atomic wavepackets during the three pulse sequence (a so-called Mach-Zehnder 

interferometer). The difference of optical phases of the two lasers is imprinted on the atomic 

wavefunction during each pulse. The result is a sinusoidal variation in the probability of 

occupation of the two ground states at the end of the measurement sequence (interferogram), 

which depends on the applied acceleration. The interferometer phase is defined as the relative 

phase of the interferogram with the interferogram measured with zero inertial input. 

25
 
 

 

 

 

 

 

 

 

b

T

N

C

Ta μK

SNR1 shot

−1 C−1 

. SNR1 shot

(2N +1) k 2 

effT frep 

ε com

ε com δ a1 sec

b 

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It is possible to carry out a measurement of gravity gradient by applying a single pair of laser 

beams to two atom clouds prepared at a known separation, as depicted in Figure 10. A difference 

in the phase registered by the two interferometers then is a measure of the difference in 

acceleration at the sites of the two atom clouds. This method has the advantage that many 

sources of noise are common to the two measurements; thus, when the difference is taken, there 

is a significant reduction in the net noise signal, as compared to the individual acceleration 

measurements. 

Table 8. Gravity gradiometer design parameters and performance goals 

Quantity Value Description/Discussion 

1 meter Baseline separation between accelerometers 

Δb 70 μm Maximum variation in gradiometer baseline 

50 msec Measurement time 

3 LMT index (12 “augmentation” pulses: [16]) 

( )

2 2 1 N eff + k T

2.58e5 

sec 2 /m 

Individual interferometer scale factor (factor to 

convert acceleration to phase shift) 

0.10 Individual accelerometer contrast 

1.2 Atom cloud temperature 

600 Per shot SNR 

rep

f 8 Hz Rate of accelerometer measurements 

2.3 nano-g 

/sqrt(Hz) Individual accelerometer noise density 

0.1 Common mode noise rejection factor 

2.3 E 

/sqrt(Hz) Gradiometer noise density 

26
 
b

Cloud 2

Cloud 1

Raman Beams

0 1 2 3 4

0

0.2

0.4

0.6

0.8

1

Pe

θ

p

π

0 1 2 3 4

0

0.2

0.4

0.6

0.8

1

Pe

θ

p

π

Accelerometer 1

Accelerometer 2

Δφ

Population Transfer Population Transfer

 

 

 

 

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Figure 10. Gravity gradiometry. A difference in the gravitational acceleration (along the beam axis) at 

sites separated by baseline b induces an interferometer phase difference Δφ. Common mode noise 

processes cause simultaneous phase variations in the two interferograms, leaving Δφ unaffected. 

Atom 

Orbital Radius 

Orbital Track 

t 

Δrshear 

t+T t+2T

Probability Amplitudes 

Partial Overlap 

Figure 11. Raman interferometry in orbit. Raman pulse interferometry operates by splitting 

individual atoms into spatially separated wavepackets. If the wavepackets are separated 

along the radial direction, they orbit at slightly different altitudes during the measurement 

and thus slightly different speeds. When the wavepackets are recombined, they no longer 

overlap perfectly and the atomic interference is reduced. Spatial coherence length for atoms 

at 10 micro-K are of order 50 nm. The wavepacket separation increases with T as 

2

shear Δ ∝ r T .
 

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We propose to apply our dynamic environment sensing modality (high repetition rate with LMT 

interferometry) to achieve a highly robust, noise-immune gradiometer with sensitivity adequate 

to perform important science goals. 

A serious challenge to high precision atom interferometry in an orbital environment is “orbital 

shear” (Figure 11), wherein atomic wavepackets separated in a radial direction (with respect to 

the body being orbited) will effectively orbit at different speeds in the sensor reference frame, 

when the sensor is rotating to maintain a fixed orientation to the orbital radius. Maintaining a 

fixed orientation with respect to the radial direction would be important in a gradient survey 

campaign; the “shear” is a pseudo-force arising from operation in the rotating frame. Table 8 

summarizes the design goals of a cold atom gravity gradiometer designed for gradient surveys of 

Jovian moons. 

Figure 12 depicts a possible 

physics package for a Jovian 

moon gradiometer system. The 

gradiometer comprises a pair of 

LPAI accelerometers connected 

by a magnetically shielded, 

evacuated drift tube that would 

provide optical access for a 

single Raman laser beam pair to 

excite both atom clouds (Figure 

10). We note that a layer of 

Figure 12. Design concept for flight capable interferometer. magnetic shielding surrounding Each accelerometer unit is magnetically shielded, as is the the gradiometer will likely be vacuum drift tube connecting them. 

necessary. Of particular 

importance for a Jovian moon orbital operation is the fact that Raman LPAI sensors are 

intrinsically radiation hard: the proof masses (clouds of atoms) are totally impervious to ionizing 

radiation. The bulk of the apparatus would require little or no additional radiation shielding 

beyond that provided by magnetic shields. Only sensitive electronics and lasers would need to be 

shielded. These components would occupy but a small volume, reducing the mass needed for 

radiation shielding. Draper has carried out radiation effects testing on typical LPAI-capable 

DFB lasers, and shown that with suitable shielding, they would be capable of sustained operation 

in Europa’s orbit for weeks or months with little performance degradation [20]. 

28
 
 

 

 

 

 

 

 

 

 

 

k r eff Δ shear,mean

dg (2 1 N + ) k

z 2 

eff b T

dz

(2 1 N + Ω )k

22 

eff b y T

2(2N +1)k

2 

eff ΔvxΩyT

−3(2N +1)k

23 

eff ΔvzΩy T

dg 

−(2 1 N + ) k

z 3 

eff ΔvzT

dz 

7 dg (2 1 N + ) k

z 24 

eff b y 

T

6 dz 

Ω

2 7 ⎛ ⎞ dg (2 1 N + ) k

z 4 

eff b T ⎜ ⎟ 12 ⎝ ⎠ dz 

( )

1

3 2 7.18 10 sec y π

−

Ω = ×

2 1

2

z

y

dg

dz

Ω =

0 Ω ≅y

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Table 9. Gravity gradiometer phase shifts in a Europa orbital environment 

Phase Shift Value 

(mrad: N 

= 3) 

Fractional 

Size 

Description 

380 -6.01 “Gravity shear” mean phase for the 

two accelerometers (strongly 

common mode—see entry below) 

-63.2 1 Mean gradiometer phase difference 

31.6 -0.5 Gradiometer phase due to 

“centrifugal force” induced by 

rotation 

0.723 -0.011 Error arising from rotation-induced 

displacement from discrepant initial 

cloud velocities in x-direction 

50 km + 1 meter 50 km 

eff shear shear k r r 

⎛ ⎞ ⎜ ⎟ Δ − Δ

⎝ ⎠

2.37e-4 -3.75e-6 “Gravity shear” (rotation-induced) 

phase difference between the two 

radially separated accelerometers: 

gravity shear errors are common 

mode to 1e-6 fractional level 

-1.90e-5 3.00e-7 “Centrifugal force” error arising from 

discrepant initial cloud velocities in 

z-direction 

1.26e-5 -2.00e-7 Phase difference between two 

accelerometers induced by discrepant 

initial cloud velocities in z-direction 

coupling to the z-comp. of the gravity 

gradient 

-2.26e-8 3.57e-10 “Centrifugal force” error arising from 

difference in gravitational 

acceleration of the two clouds in zdirection 

1.13e-8 -1.79e-10 Phase difference between two 

accelerometers induced by discrepant 

velocities in z-direction induced by 

gravity gradient, coupling to the zcomp. of the gravity gradient 

Notes: 

• Phase shift values are computed assuming an orbit 50 km above the Europa surface. 

Orbital frequency is approximately , and the gradiometer is 

rotated synchronously to maintain radial orientation. Note that when radial orientation 

is maintained, . If the gradiometer is oriented normal to the orbital track 

and the orbital radius, . 

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• The accelerometers are separated by b = 1 meter . The mean gravity gradient 

1532 E z dg 

dz 

= − is the value at the mean orbital altitude. 

• Velocity differences ,

z x Δv Δv are estimated differences in release velocities from the 

atom traps of the two accelerometers, i.e., mean velocities of the respective atom 

clouds. 

• “Orbital shear” displacement phase and phase difference are estimated assuming the 

formula below for the final cloud separation slip Δr

• ( )

2 3 2 1 

2 

eff 

slip y 

Cs 

k 

r N T 

m 

Δ = Ω +

• Parameter values: 3 

2 20 msec; ; 3; 0.001 cm/sec 

7.18 10 sec 

T y N z x v v 

π

= Ω = = Δ = Δ =

×

• Adapted from D.M.S. Johnson, “Long Baseline Atom Interferometry”, p. 31, Ph.D. 

thesis, Stanford (2011) 

We have made a preliminary assessment of systematic gradiometer errors that would be realized 

in a Europa orbital environment; a tabular summary of those errors is displayed in Table 9. These 

errors serve to guide the definition of performance requirements and resultant design for a flight 

gradiometer. It is interesting to note that the largest phase signature (for radial gradiometer 

orientation) is a so-called separation phase arising from the “gravity shear” error mechanism, 

arising from orbital rotation, described earlier. This phase is highly common-mode and should be 

rejected to a few parts per million. We also note that the mean gradiometer phase difference (that 

would be produced by a perfectly spherical Europa) is exactly twice the magnitude and of 

opposite sign to a centrifugal force error arising from gradiometer rotation when radial 

orientation is preserved. This can be interpreted as a net reduction to this gradient background, 

but does require control (or at least measurement) of the gradiometer rotation rate at the 0.01°/hr 

level of accuracy in order to correctly account for rotation in determining the net gradient 

signature. The last major error mechanism arises from rotation induced displacement occurring 

when the atoms are inadvertently released with different initial velocities. For a velocity 

discrepancy of 10 mm/sec, an error of roughly 15 E occurs in a radial gradiometer orientation; 

the degree to which this error can be controlled will probably determine if radial gradiometer 

orientation will permit high accuracy operation (1 E or below). The remaining errors are all at or 

below the desired long term stability (0.1 E). 

We can contrast the single axis gravity gradiometer of Figure 12 with the hardware suites 

comprising high performance systems like those used in GRACE [21] or GOCE [22]. GRACE 

derives gravitational information by highly precise measurement of the relative positions of a 

leader-follower pair of nearly identical satellites in a polar near-earth orbit, in conjunction with 

careful accounting for the effects of non-inertial motional effects through use of exquisitely 

sensitive ONERA Star accelerometers [23]. GOCE was a single spacecraft mission that exploited 

an array of six ONERA accelerometers in a configuration to enable measurement of all 

components of the gravity gradient tensor; the accelerometer signals were also used to control 

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thrusters for achievement of drag-free operation. The ONERA electrostatically suspends a 

parallelepiped-shaped titanium proof mass, and the measured electrostatic restoring forces 

provide the inertial input signal. A single ONERA sensor measures acceleration and rotation 

along all three axes. GRACE and GOCE provided highly accurate, global, and homogeneous 

measurements of the Earth’s geoid to very high precision, over a period of years and at a cost 

enumerated in hundreds of millions of dollars. The satellites used had mass on order of a metric 

ton. 

Such systems possibly could, and perhaps should, ultimately be deployed for study of the Jovian 

moons, but cost considerations would demand a comprehensive justification—framed by 

compelling preliminary data that could be provided by a “first look” survey carried out by a 

relatively low-cost, low mass, relatively simple cold atom gradiometer operating from a ChipSat 

launch platform. The proposed cold atom gradiometer is a cost/performance compromise vis-àvis an ONERA-based gradiometer system. The cold atom gradiometer has no moving parts and a 

minimum of critical mechanical alignments; has sensitivity roughly comparable to a pair of 

ONERA Star accelerometers; could reasonably be guessed to be order 10X lower cost and mass 

than an ONERA accelerometer pair; could have ~30X higher bandwidth; but can only sense a 

single component of the gravity gradient tensor at a time, whereas a pair of ONERAs could 

simultaneously sense three tensor components (out of five independent components). We believe 

that a cold atom gravity gradiometer has the simplicity, robustness, and level of performance 

needed to observe key phenomena that could motivate a more comprehensive subsequent 

exploration. Applications of the design to the study of Europa are summarized in Section 4.2. 

4 Europa Case Study 

4.1 Mission Goals and Science 

Jupiter’s icy moon Europa is an enticing target for planetary exploration, due to the potential 

habitability of its subsurface ocean.[24] Perhaps the greatest challenge facing a mission to 

determine whether any kind of life actually exists on Europa is the limited access to the ocean. 

The ice shell, which completely covers the moon, has an unknown thickness. Some researchers 

estimate that the ice may be on the order of a few kilometers thick[25] while other groups 

suggest that the crust could have a thickness of tens of kilometers.[26] The ice thickness has 

implications not only for habitability but also for what engineering solutions might be necessary 

to penetrate through to liquid water. Without new data since the Galileo mission, the ice crust 

thickness is an open question in the scientific community. Fortunately, Europa has surface 

features that planetary scientists interpret as marking thin ice or even direct exposure of the 

ocean to space.[27] These locations might even be habitable.[24] 

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Clearly, the greatest scientific return in terms of detecting extraterrestrial life is in those regions 

where Europa’s ice crust is thin. The identification of regions with thin ice should therefore 

precede the selection of surface targets and dispatch of probes to those targets. This two-step 

process, if accomplished by separate flagship-scale missions, might take decades. As a result, a 

combined mission to both identify thin 

areas of Europa’s ice and follow up with 

surface observations at those regions is a 

good candidate for our dual-phase 

exploration architecture. 

Such a mission would consist of an orbiter 

spacecraft carrying instruments capable of 

sensing or inferring the ice thickness on 

regional to local scales, along with a 

number of probes capable of landing on the 

moon. A sensitive gravimeter is a potential 

instrument for determining the ice 

thickness; cold-atom interferometers 

provide the required sensitivity with a 

relatively small baseline suitable for 

packaging as a spacecraft instrument. For the 

surface probes, we suggest taking advantage of the enabling technology of ChipSats to send a 

very large number – perhaps thousands – of small vehicles with our notional mission. A 

particular advantage of sending such a large number of surface probes is that they can be 

deployed to many locations on Europa, allowing the mission to repeat landing events rather than 

banking on the success (in terms of both the probe itself and the target selection) of a single 

vehicle. Each ChipSat is a centimeter-scale, self-contained spacecraft including power, 

computation, communication, and science subsystems. The science instruments on a ChipSat 

may be only a lab-on-chip device designed to detect a single chemical biomarker, and the 

communication need only be one way from the ChipSat back to the orbiter. 

The concept of operations of this mission to detect life on Europa, after its arrival in the Jovian 

system, would be as follows: 

1.	 The main spacecraft inserts into a mapping orbit around Europa. 

2.	 The cold-atom interferometer commences gravimetry of Europa. The mission downlinks 

science data to Earth for analysis. 

3.	 Based on the gravity map of the moon, correlated to image or other data, scientists 

identify regions of interest corresponding to locations where the ice crust may be thin or 

the subsurface ocean may be exposed. 

Figure 13. Basic steps for Europa example mission 

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4.	 The orbiter deploys a large number of ChipSats to a target region. The deployment time, 

altitude, and other parameters are selected to scatter the ChipSats across a landing zone 

with some known statistics. 

5.	 ChipSats impact the surface of Europa in the landing area. Some fraction of the ChipSats 

will be destroyed on impact; the number of ChipSats in the initial deployment is selected 

to achieve a desirable survivability rate for science return. 

6.	 The ChipSats’ science instruments collect data. 

7.	 ChipSats signal the orbiter spacecraft with the results from their science packages. 

8.	 The orbiter collects all the science data and relays it to Earth. 

9.	 Steps 4 through 8 may be repeated for other targets of interest. 

On Earth, the collection of signals from all the ChipSats forms the basis for the scientific return 

of the mission. In this example, suppose the orbiter deploys a population of 2000 ChipSats, each 

of which signal “1” to indicate the detection of a biomarker and “0” to indicate non-detection. If 

the survival rate of the ChipSats after impact is 1%, and half of the survivors are positioned in an 

attitude to power their instrument and communicate back to the orbiter, then scientists will 

receive 10 data points as to whether the biomarker is at the landing site. The number of “1”s in 

the data set will contribute to scientists’ confidence that the biomarker is present at the target 

site. Every additional 2000 ChipSats deployed to the same site will provide, on average, 10 more 

data points. 

The following sections describe the enabling technologies for this mission with greater 

specificity. 

4.2 Gravity Mapping Phase 

The performance characteristics of the gravity gradiometer concept described in Sec. 3.4 are 

based on the requirements for addressing key science questions pertaining to a gravitational field 

survey of Europa. In this section we outline analyses of some key elements of a gravity survey. 

To define the types of accelerometer accuracies a cold-atom gradiometer would need to explore 

some of the more compelling science questions surrounding icy moons such as Europa, a series of 

numerical experiments were done by researchers at Georgia Tech [28]. 

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Figure 14. Simulated gravity gradients from possible sea floor 

topography, as observed from a 100 km orbital altitude. 

For Europa, the combination of a sub-surface ocean, along with variations in the sea-floor 

topography and potential density variations in the external ice shell (currently estimated to be 30­

100km thick), makes for a very complex and dynamic gravitational field. The largest gravitational 

features of interest, besides the central body terms, would be those of the ice shell and sub-surface 

ocean. 

To explore potential sea-floor variations, Figure 14 shows the gravity gradient from the same 

accelerometer pair (1m radial at 100km altitude) for features that lie 100km below the ice shell. 

Since no information exists on Europa’s sub-shell topography, a Mars gravity field was used as a 

proxy, scaled down to the size of Europa. As expected, the gravity variations are smaller, but still 

in the 1-5 E 

To address potential variations in ice shell density, specifically the existence of water pockets, a 

simple “slab” geometry was numerically analyzed comprising a square volume of 100 x 100 x 5 

km with a density ~8% that of water (corresponding to a water pocket surrounded by ice). Figure 

15 shows gravity gradients for the same 1m separated accelerometers at an altitude of 50km, flying 

directly over the center of the slab. Sensing the presence of such a water pocket would require 

sensitivity at the level of a few E in the radial direction. 

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50 km 

dgz/dz

dgx/dx

dgy/dy

x

z

Ice

Water Pocket

1 m 

x (km)

-200 0 200 2.0

1.0

0

-1.0

-2.0

-3.0

Gradient (1e-9/m)

( ) , , 1 z

g x y z m +

( ) , ,

z

g x y z

( )

( )

, , 1

, ,

z

z

z

dg g x y z m

dz g x y z

⎧ ⎫ ⎪ ⎪ +

≅ ⎨ ⎬ ⎪ ⎪ −⎩ ⎭

Figure 15. Gradiometer oriented along orbital radius, overflying the center of a water pocket at an 

altitude of 50 km. The gradient is the difference in gravitational acceleration sensed by the two 

component gravimeters. Three components of the gravity gradient are plotted as a function of 

gradiometer position relative to the water pocket. 

We conclude that the proposed gravity gradiometer technology would be capable of addressing 

important Europa science questions and would comprise a critical component of the dual mission 

architecture. 

4.3 In-situ Sampling Phase 

ChipSats offer a unique opportunity in the context of a dual-mission architecture: they can land 

on the surface of a small-enough celestial object with a certain statistical guarantee of survival, 

despite not having an explicit entry, descent, and landing (EDL) technology on board. 

Deploying a sufficient number toward the surface offers confidence in this statistical survival of 

impact with the surface. This unusual approach is well-suited to the dual-mission concept 

because it enables operators to decide where and how to send ChipSats without needing to 

implement EDL hardware and software before launch. The result is a flexible science 

architecture suitable for a wide range of celestial bodies, from the smallest asteroids to moons the 

size of Europa. 

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This principle has been verified through simulations of ChipSat landings at Europa, for a 

ChipSat architecture that closely resembles the TRL 7 design launched on KickSat in 2014. A 

key difference is that the mechanical substrate is not FR-4 (the common fiberglass circuit-board 

material) but Kevlar, a tough material that custom board-fabrication service providers use today, 

although very infrequently. Also, these ChipSats are lightweighted to 3 g (a 40% reduction from 

the current baseline), are 2 cm square, and 1.57 mm thick. These specifications represent an 

adaptation of the current Sprite platform, but nothing of sufficient technology-development risk 

to contribute to the risk associated with the broader objectives of this NIAC study. 

A key factor for ChipSat swarm mission success is how the swarm’s orbit mechanics evolve in 

time, after deployment from a spacecraft. This numerical simulation represents the trajectory 

propagation of a swarm released with some probabilistic distribution in position and velocity 

around a nominal initial condition. The simulation models an arbitrarily large number of 

ChipSats near small or irregular bodies. It uses available spherical harmonic gravity coefficients 

to calculate accelerations in spherical coordinates and integrates for extended trajectories. The 

integration stops when the trajectory has intersected the sphere circumscribing the object, or 

when it has exited an approximate Hill sphere. The surface contact velocity and incident angles 

are then analyzed for survival statistics. The regolith or ice on the surface is assumed to be half 

as stiff as the Kevlar. So, about 80% of the impact energy is absorbed in the planetary surface. 

A mission to Europa is a stressing case, with impact velocities above 1 km/s. For this case, we 

simulate a direct approach at 1.2 times escape velocity, and initialize at varying altitudes with the 

same distribution about the nominal trajectory. The figures show varying landing zones, spread 

in impact velocities, and incident angles. The incident angle accounts for the fact the surface is 

rotating, and is banded because of numerical round-off. 

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Figure 16. Impact attitude distribution 

Figure 17. Total incident angle and speed relative to surface for high-speed impact 

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Figure 18. Statistical distribution of impact stress in Kevlar material 

Figure 19. Statistical distribution of impact stress in Kevlar material 

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Figure 20. Statistical distribution of impact stress in Kevlar material 

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Figure 21. Summary of survivability: green region indicates 

survival 

For the extreme case of Europa impact, approximately 1% of the incident ChipSats survive. This 

small fraction nevertheless may represent tens of individual sensors with various scientific and 

technological uses. 

A compelling example of an in-situ sensor is a microfluidic lab-on-chip system that determines 

the chirality of amino acids. Virtually all life that we understand forms chiral compounds as one 

or another enantiomer. Enantiomers are isomers for which the left- and right-handed forms are 

mechanically identical but react differently with other chiral molecules. In contrast, for most 

chemical processes that do not take place within an organism, left- and right-handed molecules 

form in equal amounts because chirality is random. Odds are that unless some special chiral 

reagent is present, this randomness produces just as many right- as left-handed compounds. On 

Earth, all amino acids in biologically produced proteins are of the same chirality, so-called “L.” 

All of the sugars in nucleic acids happen to have the opposite spatial relationship and are 

designated “D”. Assuming that this principal extends to all life, a survey of the chirality of 

organic compounds can point to the presence of life as the source of a chirality bias in these and 

other compounds. 

In 2011, Nagl, Schulze, and others [29] reported the development of a microfluidic sensor for 

determining chirality. Figure 22 shows the results from a technology demonstration, 

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Figure 22. Left: synthesis and analysis chip for enzyme screening and chiral separation. Right: 

Electropherograms after on-chip separation for determination of mutant biocatalyst 

enantioselectivity. Enantioselectivity is expressed vie the E value. Adapted from [30] 

This technology, implemented on board a ChipSat, may represent a means to perform an in-situ 

detection of biomarkers on a surface with organic matter. In Europa’s case, the ChipSat would 

need sufficient power to melt a very small (micrograms) sample, ingest it into the microfluidic 

chirality sensor by wicking the liquid water along thin-polymer fibers extending from the Sprite, 

and transmit the binary result. This prospect in an exciting example of what can be done at the 

small scale, leveraging a dual mission architecture to answer a high-priority planetary-science 

decadal question. 

Overall, the Europa mission shows the power of using next generation technologies and a dual 

exploration architecture to produce amazing scientific results without the decades-long wait 

between visits to this exciting moon. At its heart, the dual architecture concept is designed to 

speed the progress of planetary science by operating in leaps and answering questions with a 

single mission that would require multiple missions under traditional architectures. 

41
 
 

 

 

 

 

 

 

Name Launch date 

Pioneer 0 17 August 1958 

Pioneer 1 11 October 1958 

Pioneer 2 8 November 1958 

Pioneer 3 6 December 1958 

Pioneer 4 3 March 1959 

Pioneer P-3 26 November 

1959 

Pioneer P-30 25 September 

1960 

Pioneer P-31 15 December 

1960 

Ranger 3 26 January 1962 

Ranger 4 23 April 1962 

Ranger 5 18 October 1962 

Ranger 6 30 January 1964 

Ranger 7 28 July 1964 

Ranger 8 17 February 1965 

Ranger 9 21 March 1965 

Surveyor 1 30 May 1966 

Explorer 33 1 July 1966 

Lunar Orbiter 1 10 August 1966 

Surveyor 2 20 September 

1966 

Lunar Orbiter 2 6 November 1966 

Lunar Orbiter 3 5 February 1967 

Surveyor 3 17 April 1967 

Lunar Orbiter 4 4 May 1967 

Surveyor 4 14 July 1967 

Explorer 35 19 July 1967 

Lunar Orbiter 5 1 August 1967 

Surveyor 5 8 September 1967 

Surveyor 6 7 November 1967 

Surveyor 7 7 January 1968 

Apollo 8 21 December 

1968 

Apollo 10 18 May 1969 

Apollo 11 16 July 1969 

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5 Appendices 

5.1 Historical Mission Data 

5.1.1 Missions launched to the Moon 

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Apollo 12 14 November 

1969 

Apollo 13 11 April 1970 

Apollo 14 31 January 1971 

Apollo 15 26 July 1971 

PFS-1 26 July 1971 

Apollo 16 16 April 1972 

PFS-2 16 April 1972 

Apollo 17 December 1972 

Explorer 49 10 June 1973 

ISEE-3 12 August 1978 

Clementine 25 January 1994 

PAS-22 24 December 

1997 

Lunar Prospector 7 January 1998 

SMART-1 27 September 

2003 

ARTEMIS 17 February 2007 

SELENE 14 September 

2007 

Lunar Reconnaissance 18 June 2009 

Orbiter 

LCROSS 18 June 2009 

GRAIL 10 September 

2011 

LADEE 7 September 2013 

 

Name Launch date 

Mariner 3 5 November 1964 

Mariner 4 28 November 

1964 

Mariner 6 25 February 1969 

Mariner 7 27 March 1969 

Mariner 8 9 May 1971 

Mariner 9 30 May 1971 

Viking 1 20 August 1975 

Viking 2 9 September 1975 

Mars Observer 25 September 

1992 

Mars Global Surveyor 7 November 1996 

Mars Pathfinder 4 December 1996 

Mars Climate Orbiter 11 December 

1998 

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5.1.2 Missions launched to Mars 

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Name Launch date 

Pioneer 10 March 72 

Pioneer 11 April 73 

Voyager 1 September 

77 

Voyager 2 August 77 

Ulysses October 89 

Galileo October 90 

Cassini October 97 

New Horizons January 06 

Juno August 11 

Name Launch date 

Pioneer 11 April 73 

Voyager 1 September 77 

Voyager 2 August77 

Cassini October 97 

Name Launch date 

Galileo October 89

Clementine January 94 

NEAR February 96 

Shoemaker 

Cassini October 97

Deep Space 1 October 98

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Mars Polar Lander 3 January 1999 

Deep Space 2 3 January 1999 

Mars Odyssey 7 April 2001 

Spirit rover 10 June 2003 

Opportunity rover 8 July 2003 

Mars Reconnaissance 12 August 2005 

Orbiter 

Phoenix 4 August 2007 

Dawn 27 September 

2007 

Curiosity rover 26 November 

2011 

MAVEN 18 November 

2013 

5.1.3 Missions launched to Jupiter 

5.1.4 Missions launched to Saturn 

5.1.5 Missions launched to asteroids 

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Stardust February 99 

Dawn September 

07 

 

Name Launch date 

ICE August 78
 

Deep Space 1 October 98
 

Stardust February 99
 

CONTOUR July 02
 

Deep Impact January 05
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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5.1.6 Missions launched to comets 

5.2 Decadal Survey Question Classifications 

All question copied from Visions and Voyages[1] 

5.2.1 Chapter 4 –Primitive Bodies 

Important Questions: 

Remote 

Component 

In-situ 

Component Both Theory 

Chapter 4 - Proto bodies 

How do the presolar solids found in chondrites relate to 

astronomical observations of solids disposed around young 

stars? 0 0 1 0 

How abundant are presolar silicates and oxides? Most of the 

presolar grains recognized so far are carbon (diamond, 

graphite) phases or carbides. 0 1 0 0 

How do the compositions of presolar grains and organic 

molecules vary among different comets? 0 1 0 0 

How much time elapsed between the formation of the various 

chondrite components, and what do those differences mean? 0 1 0 0 

Did evaporation and condensation of solids from hot gas occur 

only in localized areas of the nebula, or was that widespread? 0 0 0 1 

What are the isotopic compositions of the important elements in 

the Sun? 0 0 1 0 

Which classes of meteorites come from which classes of 

asteroids, and how diverse were the components from which 

asteroids were assembled? 0 0 0 1 

How variable are comet compositions, and how heterogeneous 

are individual comets? 0 0 1 0 

What are the abundances and distributions of different classes 

of asteroids, comets, and KBO? 1 0 0 0 

How do the compositions of Oort cloud comets differ from those 

derived from the Kuiper belt? 1 0 0 0 

To what degree have comets been affected by thermal and 

aqueous alteration processes? 0 0 1 0 

How well can we read the nebular record in extraterrestrial 

samples through the haze of secondary processes? 0 0 0 1 

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What is the relationship between large and small KBOs? Is the 

small population derived by 

impact disruption of the large one? 1 0 0 0 

How do the impact histories of asteroids compare to those of 

comets and KBOs? 1 0 0 0 

How do physical secondary processes such as spin-up result 

from non-gravitational forces, 

the creation and destruction of binary objects, and space 

weathering? 0 0 0 1 

Did asteroid differentiation involve near-complete melting to 

form magma oceans, or modest 

partial melting? 0 1 0 0 

How did differentiation vary on bodies with large proportions of 

metal or ices? 1 0 0 0 

Were there radial or planetesimal-size limits on differentiation, 

and were KBOs and comets 

formed too late to have included significant amounts of live 

26Al as a heat source? 1 0 0 0 

What are the internal structures of Trojans and KBOs? 0 0 1 0 

What are the chemical routes leading to organic molecule 

complexity in regions of star and 

planet formation? 0 0 0 1 

What was the proportion of surviving presolar organic matter in 

the solar nebula, relative to 

the organic compounds produced locally? 0 0 0 1 

What roles did secondary processes and mineral interactions 

play in the formation of organic 

molecules? 0 0 0 1 

How stable are organic molecules in different space 

environments? 0 0 1 0 

What caused the depletions in volatile elements, relative to 

chondrites, observed in 

differentiated asteroids and planets? 0 0 0 1 

What kinds of surface evolution, radiation chemistry, and 

surface-atmosphere interactions 

occur on distant icy primitive bodies? 0 0 1 0 

How is the surface composition of comets modified by thermal 

radiation and impact 

processes? 1 0 0 0 

Are there systematic chemical or isotopic gradients in the solar 

system, and if so, what do 

they reveal about accretion? 0 0 0 1 

Do we have meteoritic samples of the objects that formed the 

dominant feeding zones for the 

innermost planets? 0 0 0 1 

How did Earth get its water and other volatiles? What role did 

icy objects play in the 

accretion of various planets? 0 0 0 1 

What is the mechanical process of accretion up to and through 

the formation of meter-size bodies? 0 0 1 0 

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Which classes of asteroids participated in the late heavy 

bombardment of the inner planets and the Moon, and how did 

the current population of asteroids evolve in time and space? 0 0 0 1 

What are the sources of asteroid groups (Trojans and 

Centaurs) that remain to be explored by spacecraft? 0 0 0 1 

How are objects delivered from the Kuiper belt to the inner 

solar system? Specifically, by what mechanisms are Jupiter 

family comets resupplied to the inner solar system? 0 0 0 1 

5.2.2 Chapter 5 – Inner Solar System 

Important Questions: 

Remote 

Component 

In-situ 

Component Both Theory 

Chapter 5 -Inner Solar System 

What are the proportions and compositions of the major 

components (e.g., crust, mantle, core, atmosphere/exosphere) 

of the inner planets? 1 0 0 0 

What are the volatile budgets in the interiors, surfaces and 

atmospheres of the inner planets? 1 0 0 0 

How did nebular and accretionary processes affect the bulk 

compositions of the inner planets? 0 0 0 1 

How do the structure and composition of each planetary body 

vary with respect to location, depth, and time? 0 0 1 0 

What are the major heat-loss mechanisms and associated 

dynamics of their cores and mantles? 1 0 0 0 

How does differentiation occur (initiation and mechanisms) and 

over what timescales? 0 0 0 1 

What are the major surface features and modification 

processes on each of the inner planets? 0 0 1 0 

What were the sources and timing of the early and recent 

impact flux of the inner solar system? 1 0 0 0 

What are the distribution and timescale of volcanism on the 

inner planets? 1 0 0 0 

What are the compositions, distributions, and sources of 

planetary polar deposits? 0 0 1 0 

How are volatile elements and compounds distributed, 

transported, and sequestered in nearsurface environments on 

the surfaces of the Moon and Mercury? What fractions of 

volatiles were outgassed from those planets’ interiors, and what 

fractions represent late meteoritic and cometary infall? 0 0 1 0 

What are the chemical and isotopic compositions of hydrogenrich (possibly water ice) near the Moon’s surface? 0 1 0 0 

What are the inventories and distributions of volatile elements 

and compounds (species abundances and isotopic 

compositions) in the mantles and crusts of the inner planets? 0 0 1 0 

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What are the elemental and isotopic compositions of species in 

Venus’s atmosphere, especially the noble gases and nitrogen-, 

hydrogen-, carbon- and sulfur-bearing species? What was 

Venus’s original volatile inventory and how has this inventory 

been modified during Venus’s evolution? How and to what 

degree are volatiles exchanged between Venus’s atmosphere 

and its solid surface? 0 0 1 0 

Are Venus’s highlands and tesserae made of materials 

suggestive of abundant magmatic water (and possibly liquid 

water on the surface)? 0 0 1 0 

What are the timescales of volcanism and tectonism on the 

inner planets? 0 0 0 1 

Is there evidence of environments that once were habitable on 

Venus? 0 1 0 0 

How are planetary magnetic fields initiated and maintained? 0 0 0 1 

What are the mechanisms by which volatile species are lost 

from terrestrial planets, with and without substantial 

atmospheres (i.e., Venus versus the Moon), and with and 

without significant magnetic 

fields (i.e., Mercury versus the Moon)? Do other loss 

mechanisms or physics become important in periods of high 

solar activity? 1 0 0 0 

What are the proportions of impactors of different chemical 

compositions (including volatile contents) as functions of time 

and place in the solar system? 0 0 0 1 

What causes changes in the flux and intensities of meteoroid 

impacts onto terrestrial planets, and how do these changes 

affect the origin and evolution of life? What are the 

environmental effects of large impacts onto terrestrial planets? 0 0 0 1 

What are the influences of clouds on radiative balances of 

planetary atmospheres, including cloud properties: 

microphysics, morphology, dynamics and coverage? 1 0 0 0 

How does the current rate of volcanic outgassing affect 

climate? 1 0 0 0 

How do the global atmospheric circulation patterns of Venus 

differ from those of Earth and Mars? 1 0 0 0 

What are the key processes, reactions and chemical cycles 

controlling the chemistry of the middle, upper and lower 

atmosphere of Venus? 1 0 0 0 

How does the atmosphere of Venus respond to solar-cycle 

variations? 1 0 0 0 

What is the history of the runaway greenhouse on Venus and is 

this a possible future for Earth’s climate? 0 0 0 1 

What is the relative role of water on the terrestrial planets in 

determining climate, surface geology, chemistry, tectonics, 

interior dynamics, structure, and habitability? 0 0 1 0 

What is the history of volcanism and its relationship to interior 

composition, structure and evolution (e.g., outgassing history 

and composition, volcanic aerosols and climate forcing)? 0 0 0 1 

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How has the impact history of the inner solar system influenced 

the climates of the terrestrial planets? 0 0 0 1 

What are the critical processes involved in atmospheric escape 

of volatiles from the inner planets? 0 0 0 1 

Do volatiles on Mercury and the Moon constrain ancient 

atmospheric origins, sources and loss processes? 0 0 0 1 

How similar or diverse were the original states of the 

atmospheres and the coupled evolution of interiors and 

atmospheres on Venus, Earth, and Mars? 0 0 0 1 

How did early extreme ultraviolet flux and solar wind influence 

atmospheric escape in the early solar system? 0 0 0 1 

5.2.3 Chapter 6 – Mars 

Important Questions: 

Remote 

Component 

In-situ 

Component Both Theory 

Chapter 6 - Mars 

Which accessible sites on Mars offer the greatest potential for 

having supported life in the past? How did the major factors 

that determine habitability—duration and activity of liquid water, 

energy availability, physicochemical factors (temperature, pH, 

Eh, fluid chemistry), and availability of biogenic elements—vary 

among environments, and how did they influence the 

habitability of different sites? 1 0 0 0 

Which accessible sites favor preservation of any evidence of 

past habitable environments and life? How did the major factors 

that affect preservation of such evidence—for example 

aqueous 

sedimentation and mineralization, oxidation, radiation—vary 

among these sites? 1 0 0 0 

How have the factors and processes that give rise to habitable 

conditions at planetary and local scales changed over the long 

term in concert with planetary and stellar evolution? 0 0 1 0 

Can evidence of past (or present) life in the form of organic 

compounds, aqueous minerals, cellular morphologies, 

biosedimentary structures, or patterns of elemental and 

mineralogical abundance be found at sites that have been 

carefully selected for high habitability and preservation 

potential? 0 0 0 1 

Do habitable environments exist today that may be identified by 

atmospheric gases, exhumed subsurface materials, or 

geophysical observations of the subsurface? Does life exist 

today, as evidenced by biosignatures, atmospheric gases, or 

other indicators of extant metabolism? 0 0 1 0 

What are the processes controlling the variability of the 

present-day climate? What is the four-dimensional wind 

structure of the martian atmosphere from the surface boundary 

layer to the upper atmosphere? What are the primary causes 

behind the occurrence of global dust events? What are the 

processes coupling the CO2, dust and water cycles? 0 0 1 0 

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What is the distribution of chemical species in the atmosphere 

and what are their sources and 

sinks? Do unexpected short-lived trace gases indicate a 

subsurface activity or even the presence of life, 

currently or in the past? What was the role of volcanic gases 

and aerosols in controlling the atmospheric 

composition? What is the role of photochemical reactions? Are 

we missing key chemical or physical 

processes in our models? 1 0 0 0 

Is there an observable change in martian climate on the 10- to 

1,000- years timescale? If so what causes it? Which processes 

control the evolution and stability of the residual carbon dioxide 

ice cap? 1 0 0 0 

How do the climate and especially the water cycle vary with 

orbital and obliquity variations? What is the global history of ice 

on Mars? How and when did the polar layered deposits form? 

What is the origin of the latitude-dependant ice mantle? 1 0 0 0 

What was the nature of the early martian climate? Were the 

conditions suitable for liquid water episodic or stable on longer 

time scales? What processes enabled such conditions? 0 0 0 1 

How and why did the atmosphere evolve? Which process did 

and still do control the escape and the outgassing of the 

atmosphere? 0 0 0 1 

How, when, and why did environments vary through Mars’s 

history and were these environments habitable? What was the 

origin and nature of the diverse sedimentary units and inferred 

aqueous environments, what are their ages, and how did 

significant accumulations of layered sediments form? What is 

the mineralogy of the regolith and how did it form? 0 0 1 0 

Are reduced carbon compounds preserved and, if so, in what 

geologic environments? What is the origin of the reported 

methane? What is is the martian carbon cycle? 0 0 0 1 

What is the petrogenesis and character of the igneous rocks, 

how old are they, and what does this tell us about martian 

crustal and mantle processes and formation of the core? How 

do martian meteorites relate to the martian surface? 0 0 0 1 

What is the geologic record of climate change? How do the 

polar layered deposits and layered sedimentary rocks record 

the present-day and past climate and the volcanic and orbital 

history of Mars? 0 1 0 0 

What is the interior structure of Mars? How are core separation 

and differentiation processes related to the initiation and/or 

failure of plate tectonic processes on Mars? 0 0 1 0 

When did these major interior events occur, and how did they 

affect the magnetic field and internal structure? What is the 

history of the martian dynamo? What were the major heat flow 

mechanisms that operated on Early Mars? 0 0 0 1 

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What is Mars’s tectonic, seismic, and volcanic activity today? 

How, when, and why did the crustal dichotomy form? What is 

the present lithospheric structure? What are the martian bulk, 

mantle and core ompositions? How has Mars’s internal 

structure affected its magmatism, atmosphere, and habitability? 1 0 0 0 

5.2.4 Chapter 7 – Giant Planets 

Important Questions: 

Remote 

Component 

In-situ 

Component Both Theory 

Chapter 7 GIant Planets 

What is the energy budget and heat balance of the ice giants, 

and what role do water and moist convection play? 1 0 0 0 

What fraction of incident sunlight do Uranus and Neptune 

absorb and how much thermal energy do they emit? 1 0 0 0 

What is the source of energy for the hot coronas/upper 

atmospheres of all four giant planets? 1 0 0 0 

What mechanism has prolonged Saturn’s thermal evolution? 0 0 0 1 

Does helium rain play a role in reducing the H/He in Saturn’s 

molecular envelope? 0 0 0 1 

Why and how does the atmospheric temperature and cloud 

composition vary with depth and location on the planet? 1 0 0 0 

Which processes influence the atmospheric thermal profile, and 

how do these vary with location? 0 0 1 0 

How did the giant planet atmospheres form and evolve to their 

present state? 0 0 0 1 

What are the current pressure-temperature profiles for these 

planets? 0 0 1 0 

What is the atmospheric composition of the ice giants? 0 0 1 0 

What are the pole precession rates for giant planets? 0 0 0 1 

How much do they constrain models of the internal structure of 

the giant planets? 0 0 0 1 

How do giant planets respond to extreme heat balance 

scenarios, both in terms of thermal structure and global 

dynamic state? 1 0 0 0 

How is energy dissipated within giant planets? 1 0 0 0 

What is the nature of the displaced and tilted magnetospheres 

of Uranus and Neptune, and how do conditions vary with the 

pronounced seasonal changes on each planet? 1 0 0 0 

What is the detailed plasma composition in any of these 

systems, particularly for ice giants? 0 0 1 0 

What causes the enormous differences in the ion to neutral 

ratios in these systems? 0 0 0 1 

What can our understanding of the giant planet 

magnetospheres tell us about the conditions to be expected at 

extra-solar giant planets? 0 0 0 1 

What can the significant differences among ring systems teach 

us about the differing origins, histories, or current states of 

these giant planet systems? 0 0 1 0 

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Can the highly structured forms of the Uranus and Neptune ring 

systems be maintained for billions of years, or are they 

“young”? Are their dark surfaces an extreme example of space 

weathering? 0 0 1 0 

What drives orbital evolution of embedded moonlets; how do 

they interact with their disks? 0 0 1 0 

What drives mass accretion in a ring system? 0 0 1 0 

How and why do elemental and isotopic abundances vary as a 

function of distance from the Sun? 0 0 0 1 

How and why do the abundances of the heavy elements and 

their isotopes, the D/H ratio, the H/He ratio and noble gases 

differ between the two classes of giant planets represented in 

the solar system? 1 0 0 0 

What is the current impact rate on Jupiter? 1 0 0 0 

To what extent can Jupiter’s current atmospheric composition 

be utilized as a record of the impact history? 0 0 0 1 

What are the characteristics of bolides and large airbursts on 

Jupiter, and how do they compare with known bolides and 

airbursts on Earth? 1 0 0 0 

What are the flux, size distribution, and chemical composition of 

the various populations of impactors, from late-stage 

planetesimals 4 billion years ago to present-day interplanetary 

dust? 0 0 0 1 

What are the surface modification mechanisms for lowtemperature smaller icy targets? 0 0 0 1 

What processes drive the visible atmospheric flow and how do 

they couple to the interior structure and deep circulation? 0 0 1 0 

What are the sources of vertically propagating waves that drive 

upper atmosphere oscillations and do they play a role on all 

planets? 0 0 0 1 

Are there similar processes on Uranus and Neptune, and how 

do all these compare with Earth’s own stratospheric wind, 

temperature and related abundance (ozone, water) variations? 1 0 0 0 

How does moist convection shape tropospheric stratification? 0 0 0 1 

What are the natures of periodic outbursts such as the global 

upheaval on Jupiter and the infrequent great white spots on 

Saturn? 0 0 1 0 

How far have the various satellites evolved outwards from their 

sites of formation? 0 0 0 1 

To what extent do the observed eccentricities and inclinations 

of satellites reflect this evolution? 0 0 0 1 

How do magnetospheres interact with the solar wind? 0 0 0 1 

How is surface material modified exogenically (e.g., processes 

such as magnetospheric interactions and impacts) versus being 

pristine or relatively unmodified? 0 0 1 0 

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5.2.5 Chapter 8 – Moons 

Important Questions: 

Remote 

Component 

In-situ 

Component Both Theory 

Chapter 8 - Moons 

Why are Titan and Callisto apparently imperfectly differentiated 

whereas Ganymede underwent complete differentiation? 1 0 0 0 

Why did Ganymede form an iron-rich core capable of 

sustaining a magnetic dynamo? 1 0 0 0 

What aspects of formation conditions governed the bulk 

composition and subsequent evolution of Io and Europa? 0 0 0 1 

In what ways did the formation conditions of the saturnian 

satellites differ from the conditions for the jovian satellites? 0 0 0 1 

Can we discern any evidence in the uranian satellites of a very 

different origin scenario (a giant impact on Uranus for example) 

or is this satellite system also the outcome of a process 

analogous to the other giant planet satellite origins? 1 0 0 0 

What features of Triton are indicative of its origin? 1 0 0 0 

In what ways do the highly volatile constituents differ between 

Callisto and Ganymede? 1 0 0 0 

Are volatiles present at the surface or in the ice shell of Europa 

that are indicative of internal processing or resurfacing? 0 0 1 0 

How, and to what extent, have volatiles been lost from Io? 1 0 0 0 

What does the plume material from Enceladus tell us about the 

volatile inventory of that body? 0 0 0 0 

Why does Titan uniquely have an exceptionally thick 

atmosphere? 0 0 0 1 

What does the volatile inventory of Titan tell us about its 

history? In particular, how is the methane resupplied, given its 

rapid photochemical destruction in the upper atmosphere? 1 0 0 0 

What is the history of the resonances responsible for the tidal 

heating and how is this heating accomplished? 0 0 0 1 

How does this heat escape to the surface? 0 0 0 1 

How is this heat transfer related to the internal structure 

(thickness of an outer solid shell, or composition of the interior) 

and formation? 0 0 0 1 

How hydrostatic are the satellites? 0 0 0 1 

Does Io have a magma ocean and what is the compositional 

range of its magmas? 1 0 0 0 

What is the origin of the topography of Io? 1 0 0 0 

What is the magnitude and spatial distribution of Io’s total heat 

flow? 1 0 0 0 

What are the thickness of Europa’s outer ice shell and the 

depth of its ocean? 1 0 0 0 

What is the magnitude of Europa’s tidal dissipation, and how is 

it partitioned between the silicate interior and the ice shell? 0 0 0 1 

What is the relationship between Titan’s surface morphology 

and internal processes, particularly for the history of the 

methane budget and lakes or seas and possible replenishment 

of methane from the interior or subsurface? 1 0 0 0 

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Does Titan have an internal liquid water ocean? 1 0 0 0 

What is the spatial distribution of Enceladus’s heat output, and 

how has it varied with time? 1 0 0 0 

Does Enceladus have an ocean or some other means of 

providing large tidal dissipation, and to what extent is its 

behavior dictated by its formation conditions (e.g., presence or 

absence of a differentiated core?) 1 0 0 0 

What does the diversity of the uranian moons tell us about the 

evolution of small to mediumsized icy satellites? What drove 

such dramatic endogenic activity on Miranda and Ariel? 0 0 0 1 

What powers past or possible ongoing activity on Triton, which 

currently has negligible tidal heating? 0 0 0 1 

One of the key missing pieces in our understanding of satellite 

surface geology is adequate knowledge of the cratering record 

in the outer solar system.21 What are the impactor populations 

in the outer solar system, and how have they changed over 

time, and what is the role of secondary cratering? 0 0 0 1 

What are the origins of tectonic patterns on Europa, including 

the ubiquitous double ridges (Figure 8.4) and chaos regions? 1 0 0 0 

How much non-synchronous rotation has Europa’s ice shell 

undergone, and how have the resulting stresses manifested at 

the surface? 1 0 0 0 

How is contraction accommodated on Europa? 1 0 0 0 

Has material from a subsurface Europa ocean been 

transported to the surface, and if so, how? 0 0 1 0 

What caused Ganymede’s surface to be partially disrupted to 

form grooved terrain, and is the grooved terrain purely tectonic 

or partly cryovolcanic in origin? 1 0 0 0 

Did Ganymede suffer a late heavy bombardment that affected 

its appearance and internal evolution? 1 0 0 0 

What is the age of Titan’s surface, and have cryovolcanism and 

tectonism been important processes? Have there been secular 

changes in the surface methane inventory? 0 0 1 0 

Why is Enceladus’s geology so spatially variable, and how has 

activity varied with time? 0 0 0 1 

What geological processes have created the surfaces of the 

diverse uranian moons, particularly the dramatic tectonics of 

Miranda and Ariel? 0 0 0 1 

Has viscous extrusive cryovolcanism occurred on icy satellites, 

as suggested by features on Ariel and Titan? 1 0 0 0 

What geological processes operate on Triton’s unique surface, 

how old is that activity, and what do its surface features reveal 

about whether it is captured? 1 0 0 0 

What mechanisms drive and sustain Enceladus’s plumes and 

active tiger stripe tectonics? 1 0 0 0 

What are the magnitude, spatial distribution, temporal 

variability, and dissipation mechanisms of tidal heating within 

Io, Europa, and Enceladus? 

Is there active cryovolcanism on Titan? 1 0 0 0 

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What are the eruption mechanisms for Io’s lavas and plumes 

and their implications for volcanic processes on early and 

modern Earth? 1 0 0 0 

What is the temporal and spatial variability of the density and 

composition of Io’s atmosphere, how is it controlled, and how is 

it affected by changes in volcanic activity? 1 0 0 0 

What are the relative roles of sublimation, molecular transport, 

sputtering and active venting in generating tenuous satellite 

atmospheres? 1 0 0 0 

Do the large organic molecules detected by Cassini in Titan’s 

haze contain amino acids, nucleotides and other pre-biotic 

molecules? 0 0 1 0 

What processes control Titan’s weather? 1 0 0 0 

What processes control the exchange of methane between 

Titan’s surface and the atmosphere? 1 0 0 0 

Are Titan’s lakes fed primarily by rain or by underground 

methane-ethane “aquifers”? 0 0 1 0 

How do Titan’s clouds originate and evolve? 1 0 0 0 

What is the temperature and opacity structure of Titan’s polar 

atmosphere, and what is its role in Titan’s general circulation? 1 0 0 0 

What is Triton’s surface distribution of molecular nitrogen and 

methane, and how does it interact with the atmospheric 

composition and dynamics? 1 0 0 0 

Is Io’s intense magnetospheric interaction responsible for its 

volatile depletion? 0 0 0 1 

How is the strong ionosphere of Triton generated? 0 0 0 1 

How do exogenic processes control the distribution of chemical 

species on satellite surfaces? 0 0 0 1 

How are potential Europa surface biomarkers from the 

ocean/surface exchange degraded by the radiation 

environment? 0 1 0 0 

What do the crater populations on the satellites reveal about 

the satellites’ histories and subsurface structure and about the 

populations of projectiles in the outer solar system and the 

evolution thereof? 0 0 0 1 

Why is Jupiter’s magnetosphere dominated by charged 

particles whereas Saturn’s magnetosphere is dominated by 

neutral species? 0 0 0 1 

What fraction of the material in Jupiter’s magnetosphere 

originates from Europa and other icy satellites? 1 0 0 0 

Is the reconnection in Ganymede’s magnetosphere steady or 

patchy and bursty? 1 0 0 0 

How rapidly does Saturn’s magnetosphere react to the 

temporal variability of Enceladus’s plume? 1 0 0 0 

Do other saturnian icy satellites such as Dione and Rhea 

contribute measurable amount of neutrals or plasma to Saturn’s 

magnetosphere? 1 0 0 0 

What is the nature of Triton’s inferred dense neutral torus? 1 0 0 0 

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What are the depths below the surface, thickness and 

conductivities of the subsurface oceans of the Galilean 

satellites? The depth of the ocean beneath the surface is 

important because it controls the rate of heat loss from the 

ocean, and the probability of material exchange with the 

surface. The thickness indicates the likely ocean lifetime, and 

for Ganymede and Callisto constrains the ocean temperature. 1 0 0 0 

Which satellites elsewhere in the solar system possess longlived subsurface bodies of liquid water? Titan and Enceladus 

are obvious candidates, but other mid-sized icy satellites, 

including those of Uranus and Neptune, could in theory have 

retained internal oceans to the present day.43 Triton in 

particular, with its geologically young surface and current 

geysering, is another interesting candidate. 1 0 0 0 

For all satellites, what is the lifetime of potential oceans? Ocean 

lifetime is a key to habitability. If Enceladus is only intermittently 

active, for instance, as suggested by several lines of evidence, 

and thus only intermittently supports liquid water, it is less 

attractive as a potential habitat.44 0 0 0 1 

What is the nature of the atmospheric processes on Titan that 

convert the small organic gasphase molecules observed in the 

upper atmosphere (such as benzene) into large 

macromolecules and ultimately into solid haze particles? 0 0 0 1 

What is the fate of organics on the surface of Titan and their 

interaction with the seasonally varying lakes of liquid 

hydrocarbons? 0 0 0 1 

Are organics present on the surface of Europa, and if so, what 

is their provenance? 0 1 0 0 

What is the source of the organic material in the plume of 

Enceladus? 0 0 1 0 

What is the nature of any biologically relevant energy sources 

on Europa? 0 0 0 1 

What are the energy sources that drive the plume on 

Enceladus? These may lead to understanding the possibilities 

for biologically relevant energy sources. 0 0 0 1 

On Titan, how is chemical energy delivered to the surface? 0 0 0 1 

Does (or did) life exist below the surface of Europa or 

Enceladus? 0 1 0 0 

Is hydrocarbon-based life possible on Titan? 0 0 0 1 

6 References 

1 National Research Council, “Visions and Voyages for Planetary Science in the Decade 2013-2022,” National 
 

Academies Press, 2011.
 

2 Atchison, J. A., Manchester, Z. R. and Peck, M. A., “Microscale Atmospheric Re-Entry Sensors,” International 
 

Planetary Probe Workshop 2010 (IPPW-7), Barcelona, Spain, 2010.
 

3 Peters, A., Chung, K. Y., and Chu, S., “High-precision gravity measurements using atom interferometry”,
	 

Metrologia Vol. 38, No. 1, 2001, pp. 25-61 (2001)
 

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4 Bodart, Q., Merlet, S., Malossi, N., Pereira Dos Santos, F., Bouyer, P., and Landragin, A., "A cold atom pyramidal 

gravimeter with a single laser beam," Applied Physics Letters Vol. 96, no. 13, 2010), pp. 134101-132104 

5 Snadden, M. J., McGuirk, J. M., Bouyer, P., Haritos, K. G., and Kasevich, M. A. , “Measurement of the Earth's 

gravity gradient with an atom interferometer-based gravity gradiometer” , Physical Review Letters Vol. 8, No. 5, 

1998, pp. 971-974 

6 McGuirk, J. M., Foster, G. T., Fixler, J. B., Snadden, M. J., and Kasevich, M. A., “Sensitive absolute-gravity 

gradiometry using atom interferometry”, Physical Review A, Vol. 65, No.3, 2002, 033608 

7 Gustavson, T. L., Landragin, A., and Kasevich, M. A., “Rotation sensing with a dual atom-interferometer Sagnac 

gyroscope”, Classical and Quantum Gravity, Vol. 17, No. 12, pp. 2385-2398 

8 Peters, A., Chung, K. Y., and Chu, S., “High-precision gravity measurements using atom interferometry”, 

Metrologia Vol. 38, No. 1, 2001, pp. 25-61 (2001) 

9 Snadden, M. J., McGuirk, J. M., Bouyer, P., Haritos, K. G., and Kasevich, M. A. , “Measurement of the Earth's 

gravity gradient with an atom interferometer-based gravity gradiometer” , Physical Review Letters Vol. 8, No. 5, 

1998, pp. 971-974 

10 McGuirk, J. M., Foster, G. T., Fixler, J. B., Snadden, M. J., and Kasevich, M. A., “Sensitive absolute-gravity 

gradiometry using atom interferometry”, Physical Review A, Vol. 65, No.3, 2002, 033608 

11 Butts, D. L., Kinast, J. M., Timmons, B. P., and Stoner, R. E., “Light pulse atom interferometry at short 

interrogation times”, Journal of the Optical Society of America B, Vol. 28, No. 3, 2011, pp. 416-421 

12 McGuinness, H. J., Rakholia, A. V., and Biedermann, G. W. , “High data-rate atom interferometer for measuring 

acceleration”, Applied Physics Letters, Vol. 100, No. 1, 2012, 011106. 

13 Rakholia, A. V., McGuinness, H. J., & Biedermann, G. W. , “Dual-Axis High-Data-Rate Atom Interferometer 

via Cold Ensemble Exchange”, Physical Review Applied, Vol. 2, No. 5, 2014, 054012. 

14 Wu, X., “Gravity gradient survey with a mobile atom interferometer”, Ph.D. thesis, 2009, Stanford University 

15 McGuirk, J. M. , Snadden, M. J., and Kasevich, M. A., “Large area light-pulse atom interferometry”, Physical 

Review Letters, Vol. 85, No. 21, 2000, pp. 4498-4501 

16 Butts, D., Kotru, K., Kinast, J., Radojevic, A., Timmons, B., and Stoner, R., “Efficient broadband Raman pulses 

for large-area atom interferometry”, Journal of the Optical Society of America B, Vol. 30, No. 4, 2013, pp. pp. 922­

927 

17 Kasevich, M. and Chu, S., “Atom interferometry using stimulated Raman transitions”, Physical Review Letters, 

Vol. 69, No. 2, 1991, pp. 181-184 

18 Young, B., Kasevich, M., and Chu, S., “Precision atom interferometry with light pulses”, in Atom Interferometry, 

edited by Paul R. Berman (Academic, San Diego, CA), 1997, pp. 363–406 

19 Stoner, R., Butts, D., Kinast, J., and Timmons, B., “Analytical framework for dynamic light pulse atom 

interferometry at short interrogation times”, Journal of the Optical Society of America B, Vol. 28, No. 10, 2011, pp. 

2418-2429 

20 B. Timmons and R. Stoner, “Radiation Exposure of Distributed-Feedback Lasers for Use in Atom Trapping and 

Atom Interferometry”, IEEE Trans.Nuc.Sci. 58, 490 (2011) 

21 B.D. Tapley, S. Bettadpur, M. Watkins, “The gravity recovery and climate experiment: mission overview and 

early results”, Geophys.Res.Lett. 31, L09607 (2004) 

22 M. van der Meidje, R. Pail, R. Bingham, and R. Floberghagen “GOCE data, models, and applications: a review”, 

Intl.J.Appl.Earth Obs. & Geoinformation 35, 4-15 (2015) 

23 P. Touboul, E. Willemenot, B. Foulon, and V. Josselin, “Accelerometers for CHAMP, GRACE, and GOCE 

space missions: synergy and evolution”, Boll.Geofis.Teor.Appl. 40, 321-327 (1999) 

24 Richard Greenberg, “Tides and the biosphere of Europa,” American Scientist, v.89 p. 48-55. 2001. 

25 Richard Greenberg, Paul Geissler, B. Randall Tufts, and Gregory V. Hoppa, “Habitability of Europa's crust: The 

role of tidal-tectonic processes,” Journal of Geophysical Research: Planets, Volume 105, Issue E7, pages 17551– 

17562, 25 July 2000. 

26 Paul Schenk, “Thickness constraints on the icy shells of the galilean satellites from a comparison of crater 

shapes,” Nature 417, 419-421 (23 May 2002). 

27 Richard Greenberg and Paul Geissler, “Europa’s dynamic icy crust,” Meteoritics and Planetary Science, v. 33, p. 

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28 B. Davis and B. Gunter, private communication (2014) 

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