JuanCastillo29/space-mission-intelligence-data huggingface dataset:
[Table: Table 4 lists concepts for interstellar propulsion and power. The tactic taken here is to first sort the prospects as a one-part or two-part system (just the spacecraft, or the spacecraft plus some base support, like laser systems). Thereafter sorting is by thrusting method, and then by major power source. To reveal systems with multiple stages that are not captured by the concepts' more familiar name, columns will be included to encompass those elements.
The final version of this table (spreadsheet) will include:
• Sorting Category • Concept Name, & Abbreviated Description • Concept Date • Reference Citation • Interstellar Era (see Section 8.1 for definition)
1. Era of Precursors 2. Era of Infrastructure 3. Era of Breakthroughs • Propulsion Type Analysis, IP-OM, RP-OM, RP-XM, IP-XM, see Section 8.4

– – – These remaining columns will be added to the Stage II work – – –

• Base System, when applicable
o Source of power (Earth based electrical grid, in-space solar, or nuclear) o Energy conversion method o Output power to spacecraft o Thermal radiators • Intermediate Base System Components (lens, beamed particles) • Spacecraft System
o Power receiver (if applicable)
� Conversion to thrust � Conversion to operating power � Thermal radiators o Onboard power source
� Propellant self energy (chemical fission, fusion, antimatter) � Separate primary power generator (e.g., Beamed power receiver, RTG, Fission reactor) � Thermal radiators o Thruster type
� Energy conversion � Key components (e.g., magnetic nozzles) � Thermal radiators • Other system performance measures (see variables list, table 6) • Technology Readiness Levels (TRL) of system elements performance as proposed (list of elements) • Comparative TRL-6 performance levels of those same elements (if not at TRL-6)
Devising a means of sorting the information was a challenge. All of the following initial sorting methods were attempted with difficulties encountered with each. This final system (one- or two-part system, then thrusting method, then power) is still not free of confusions, but it was the least problematic of the following sorting methods:]

• Traditional Concept Discipline: (where the breakouts starts at the level of sails {solar or beamed}, rockets {chemical, electric, nuclear} and propulsion physics {spacedrives, FTL}). Though familiar, it only draws attention to one key element, rather than reflecting on the broader functionality.
• Primary Power Source: This gets ambiguous when there are two power conversions (e.g., solar-to-laser, laser-to-sail). • Primary Power to Spacecraft: This gets ambiguous for concepts whose key elements are a power source in one mode and a reaction mass in another concept (e.g., solar photons).
• Thrusting Method First: Ambiguities encountered with crossover of power source and reaction mass, especially between onboard and externally supplied systems.
pg 24 of 69

Millis 2018 Grant NNX17AE81G_for_CR.docx Primary Reaction Mass:
1,000

Milestone, 1000 AU (TAU) Hills Cloud (Torus) (?) 0.032 2,000 20,000 0.316 5% VLIM 0.033 2,063 0.000 5% Very Local Interstellar Medium [McNutt 2016] LISM 0.047 3,000 20,000 0.316 5% Local Interstellar Medium [McNutt 2016] Oort Cloud sphere (?) 0.16 10,000 200,000 3.163 15% Far enough to compare parallax to Hubble red-shift distance (basic physics) G-Cloud ?? 0.60 3.8E+04 0.7 ly 5% Next transition into local interstellar medium ?
Interstellar Medium Interstellar
6.3E+05

Milestone, 10 light-years Epsilon Eridani 10.5 6.6E+05 80% K2 star, similar planetary system to a young Sun. Unconfirmed exoplanet (b) Procyon 11.5 7.2E+05 10% Binary system with white dwarf star Tau Ceti 12.0 7.6E+05 80% Closest lone star similar to sun  Unconfirmed 2 of 5 planets in HabZone (e, f) GJ 273 12.4 7.8E+05 80% M3.5 star. 1 of 2 planets in HabZone (b) Gliese 191 (Kapteyn b) 13.0 8.2E+05
85%
.67 b M1.0 star. 1 of 2 planets in HabZone (b) Wolf 1061 13.8 8.7E+05 80% M3.5 star. 1 of 3 planets in HabZone (c) Gliese 687 14.7 9.3E+05 80% M3V star. 1 of 1 planets in HabZone Gliese 876 15.3 9.7E+05 80% M4V star. 2 of 4 planets in HabZone (b,c)
1.0E+06

Milestone, 1-Million AU Observable Biomarker? 16.0 1.0E+06 N/A Predicted 2030 astronomy biomarker detection range [51] GJ 682 16.6 1.0E+06 80% M3.5V star. 1 of 2 planets in HabZone (b) HD 20794, 82 G Eridani 19.8 1.3E+06 80% G8V star. 1 of 3 planets in HabZone (d) Gliese 581 20.3 1.3E+06 80% M2.5V star. 1 of 5 planets in HabZone (g) Gliese 832 21.0 1.3E+06 80% M1.5 star. 1 of 2 planets in HabZone (c) Gliese 667 22.0 1.4E+06
95%
.84 Cc M1.5 V (3-star system). 4 of 7 in HabZone (.84 Cc, .77Cf, .60 Ce) 3-ESI's GJ 1132 39.3 2.5E+06 90% M3.5 star. 1 of 1 planets in HabZone (b) Trappist-I 39.5 2.5E+06
95%
.85 e M8V star. 3 of 7 planets in HabZone ? (.85 e, .68 f, .58 g) MULTIPLE LHS 1140 40.7 2.6E+06
95%
.68 b M4.5 star. 1 of 1 planets in HabZone (b) Nearest hab exoplanet? 70.0 4.4E+06 Highest probable distance of nearest habitable planet [Maccone 2010]
Habitable? Inhabited? In Solar
The challenge of the science instrumentation, in addition to the mass and power efficiencies already stated, is that they need to measure phenomena at the destination that will not be possible to measure by Earth-based astronomy, even after decades more of astronomy advancements. For example, from a lecture by M. Kasper of the European Southern Observatory (ESO), given at the Technical University of Dresden in the summer of 2017, it was predicted that by 2030, the ESO will be able to detect biomarkers as far out at 16 ly [51]. That calendar year is decades before StarShot reaches its destination and almost five decades sooner than StarShot will have finished transmitting its data.
The next challenge for the science instruments is that they need to be able to acquire their data at distances from the target that might be between 1 and 100 AU (depending on aiming, navigation and limited maneuvering propulsion) and at flyby speeds as high as 20% lightspeed.
6.3E+07

Milestone, 1000 light-years Kepler 442 1115 7.1E+07 100% .84 b Kepler 62 1200 7.6E+07 100% .67 f ET Civilization? 2000 1.3E+08 100% Probable distance of nearest extraterrestrial civilization [Maccone 2010] To Center of Galaxy 25000 2E+09
* ESI = Earth Similarity Index: http://phl.upr.edu/projects/habitable-exoplanets-catalog/results ** In comparison, Voyager is ≈ 3.5 AU/yr, and Juno ≈ 15.5 AU/yr Yellow refers to distance numeric milestones
pg 14 of 69

Millis 2018 Grant NNX17AE81G_for_CR.docx A mission takes longer than just the time to reach its destination.
There is also the time-of-flight for the return signals to reach Earth, and the time it takes to finish transmitting the data. This last duration, transmit time, is not trivial. For example, at the extremely low power levels envisioned for the Breakthrough StarShot mission, it has been estimated that it will take 20 years to transmit the data [40]. Hence, the total mission duration for Breakthrough StarShot is roughly 46 years (22 yr trip, 4 yr signal delay, 20 yr transmit time).
For this study, "Total Mission Duration," Tm, is defined as the sum of the "trip time," Tt, to reach the destination, the "signal time," Ts, for the data to begin to reach Earth, and the "transmit time," Tx, to send the acquired data. Figure 3 shows a comparison between the projected timescales for precursor missions, the StarShot mission, and the mission suggested in the 2016 congressional language [17].
The timescales of some historic technological breakthroughs are shown for comparison on figure 3. For example it took only six decades from the discovery of natural radioactivity to having a nuclear power plant on the electrical grid (1890-1950). It took a little over two decades from the creation of the rocket equation to the first liquid rocket, and another four decades before humans walked on the moon (1903-1926-1969). Another fitting example is the 1-century between the steam power era, when Jules Verne wrote his fictional depiction of a Moon mission (1865) and the first actual lunar landing (1969). If scientists and engineers of the steam era were contemplating Moon missions, would they have debated which steam cycle to use, or perhaps even considered Verne's cannons? What was missing at that time was the undiscovered future of electrical power, liquid rockets, and nuclear power. What is next in our undiscovered future?
Since the timescale for revolutionary technological developments are comparable to interstellar mission durations, the potential impact of future advancements are considered as part of this study. While it is not possible to predict the future with certainty, the historic patterns of technological revolutions can be used as guides for this study [41].
Trip time is a function of propulsion energy and payload mass. Higher speeds or greater spacecraft mass demand more energy. Following the kinetic energy equation (KE = ½mv2) as the lowest bound on required energy (where propellant mass and inefficiencies are ignored), doubling the spacecraft mass at least doubles the required propulsive energy. Doubling the velocity at least quadruples the required propulsive energy, since energy goes as the square of the velocity. Note, relativistic effects do not become significant (> 1.0%) until past 14% lightspeed.
One of the largest impediments to starflight is the gap between the energy required for propulsion and the energy available, regardless of the choice of propulsion. Calculations that compared the rate of humanity's growing energy prowess to the energy required for propulsion suggest that perhaps two centuries remain before sufficient energy is likely to be available [21]. This estimate took into consideration that only a portion of total world energy would be allocated for space missions. By comparing the Space Shuttle launch history to the US energy capacity over the same years, an estimate for that allocation is found to be one-millionth. Granted, such a rough estimate could be off by an order of magnitude or two, which should be taken in consideration. Figure 4 shows that comparison from the 2010 paper (with revisions & corrections).
For an example of the magnitude of propulsion energy, consider the 1-gram StarShot spacecraft traveling at 20% lightspeed. Just its kinetic energy is approximately 2 TJ. When calculating the propulsive energy in terms of the laser power and beam duration, (100 GW for minutes) the required energy spans 18 to 66 TJ, for just one probe. The full suite of 1,000 probes would be 1,000 times that span. For comparison, the energy for that suite of 1,000 probes is roughly the same as 1-4 years of the energy consumption of New York City (NYC @ 500 MW).
If instead of a 1 g spacecraft, the kinetic energy is calculated using the mass of a Voyager type spacecraft (≈ 1,000 kg) traveling at 10% lightspeed, then the kinetic energy becomes 4.5 x 105 TJ. For comparison, this is about one-thousandth of the total world energy consumption in 2016 (5.5 x 108 TJ [46, 47]).
pg 16 of 69

Millis 2018 Grant NNX17AE81G_for_CR.docx 1.E+19

|  |  |  |  |  | (6 |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  |  |  |  |  |  | (6 | ) Rocket Rendezvous |
|  |  |  |  |  | (5 |  |  |
|  |  |  |  |  |  | (4 | ) Probe Rendezvous |
|  | H igher G row th 3.6% | A v erag e G ro w th | 1 .9 % |  | (3 |  |  |
|  |  |  |  |  |  |  | ) Ten Starshot Beam |
|  |  |  | L o w e r G ro w | th 0 .2 % | (2 | (2 |  |
|  |  |  |  |  |  |  | ) Ten StarShot Kinetic |
|  |  |  |  |  | (1 | (1 |  |

1.E+18
Interstellar precursor missions that are based on existing technology do not need new infrastructure, but anything beyond that will. For example, even the 1 g StarShot probe will require the construction of a 100 GW laser array, estimated to span 1 km2, and require one million 100 kW lasers.
While the StarShot infrastructure is considered to be built on Earth, other interstellar concepts envision using future in-space infrastructure. For example, the laser lightsail concepts of Robert Forward required a 26 TW laser, firing through a 1,000 km diameter Fresnel lens placed beyond Saturn (around 10 AU), aimed at a 1,000 km diameter sail with a mass of 800 MT [48]. The Project Daedalus study envisioned needing 50,000 MT of Helium 3 mined from the atmospheres of the gas giant planets [49]. This not only requires the infrastructure for mining those propellants, but also processing and transporting that propellant to the assembly area of the spacecraft.
Thus, it is an inescapable requirement that missions beyond the era of precursors will need substantial infrastructure. Section 8.3 describes how the infrastructure growth will be predicted and methods to compare the interstellar dependence of planned missions.
pg 18 of 69

Millis 2018 Grant NNX17AE81G_for_CR.docx Though the focus of this study is on propulsion technology, the payload challenges are also addressed because they significantly affect the propulsion requirements, and hence the ultimate success of an interstellar mission.
the systems needed to deliver that mass to the destinations.

The "top 10 challenges" of interstellar flight are listed below. These are not in priority order, since determining such priorities is what the study aims to determine later. Many of these are payload technologies:
• Communication* • Navigation* • Instrumentation to collect information at the destination that Earth-based astronomy cannot* • High-density and long duration energy storage • Long duration and autonomous spacecraft operation (plus survive cosmic radiation and dust impingement) • Propulsion that can achieve 400 times greater ∆V than chemical rockets • Energy production sufficient to enable that high-velocity propulsion • High efficiency energy conversion • Braking and maneuvering at destination
• Infrastructure creation in affordable increments

*For those marked with an asterisk, there is a possibility of shared technology elements. For example, could a telescope intended to study the destination also be used for optical communication? Could a dish used for navigation also be used for communication?
A typical starting point for planning a mission is determining the mass of the payload, since this significantly affects the propulsion and other system requirements. The payload mass is a combination of:
• Science instruments that acquire data at the destination • Communication system to send that data back to Earth • Power supply for that instrumentation, communication system, and rest of spacecraft system • Attitude control system (ACS) • Guidance navigation and control (GNC) • Command and data handling (C&DH) • Power management and distribution (PMAD) • Excess heat radiators

The basic challenge is how to provide all those functions with the least amount of power, energy, and mass. While continued miniaturizations will improve the situation, some functions will have a finite lower limit (e.g. antenna size to match long wavelengths). Even with miniaturization, there will be some lower limit eventually reached (one molecule per pixel?).
The power and mass for the communication system are perhaps the most significant drivers for the payload, and the data rate is a significant driver of the communication system. The data rates are a function of the transmitter power and aperture. The power (and mass) requirement can be reduced by more efficient technology or by reducing the data transmission rate. Since reducing the data rate can add years to the total mission duration, this is a significant technical challenge (StarShot uses 20 years to transmit the data [40]).
Note: the concept of using a stream of smaller trailing spacecraft to relay signals at lower power is considered here as being part of the whole spacecraft system, instead of individual spacecraft. Part of the reason for this stance
Millis 2018 Grant NNX17AE81G_for_CR.docx

pg 19 of 69 is that such a string of relay spacecraft would only be useful to the one mission ahead of it and inaccessible to any other missions sent in different directions.

To reduce the mass of the power supply, higher-density energy sources are required (J/kg, W/kg). This challenge should be pursued in concert with very long term energy storage. The power supply must still produce enough energy at the end of the mission for operating the science instruments and data transmission. As mentioned previously, interstellar missions will probably span a minimum of four decades when considering both the trip time and data transmission time. Batteries do not hold their charge for anywhere near that duration. Radioisotope thermal generators (RTGs), like those on Voyager, have demonstrated the ability to function for over four decades, but also have less power as time progresses due to their radioactive decay.
Similarly to communication, any navigation equipment must also be as energy and mass efficient as possible. While one approach is to remove the navigation system altogether—for those approaches whose probes lack any propulsion to make course corrections—there will still be need for equipment to discern when the probe is nearing its destination and then aim the scientific instrumentation.
The navigation system will traverse roughly three orders of magnitude farther than all prior missions. To appreciate the scale of this challenge, consider aiming with an accuracy of 1 AU after traveling 270,000 times that distance. Emerging navigation techniques involve using x-ray pulsars [50].
Speed
To convey the challenge of reaching 10% lightspeed, consider the improvements between the 1977 Voyager and the 2011 Juno missions. In roughly three decades there was a four-fold increase in speed. At that rate, it would take another 130 years to reach 10% lightspeed. The gap between achieved speeds and the goal of 0.1c is a factor of 400 (Juno achieved 0.00025c). Hence, the technical challenge is to increase spacecraft ∆V by at least 400 times more than presently possible with chemical rockets.
The energy challenges of interstellar propulsion are two-fold. First there is the challenge of producing and controlling large amounts of energy, and second, to use that energy efficiently to minimize waste heat.
Under ideal circumstances and velocities below roughly 20% lightspeed, energy requirements scale linearly with spacecraft mass and are a squared function of spacecraft speed. Thus, for the Juno spacecraft, the additional energy needed to reach 10% lightspeed is at least 1600 times more than its Jupiter mission velocity. For rockets, the energy scales roughly as an exponential of speed, far in excess of a squared function (eq 1) [13, p 145].
pg 20 of 69

Millis 2018 Grant NNX17AE81G_for_CR.docx ⎛

⎞
Δv
E = 1
2 e
⎜ ⎜
⎟ ⎟
ve −1
( )
2 m ve
Eq. 1 ⎝
⎠ Where m = Mass of spacecraft without propellant (kg) ve = Exhaust velocity (m/s) ∆v = Change in velocity (m/s)

For laser sails, the low conversion efficiencies ramp up the energy requirements. Prior examples of interstellar propulsion energy spanned the low end of tera-joules to tens of thousands of tera-joules (Section 3.3).
€
With those large amounts of energy, conversion efficiencies become a more critical issue. For example, even a 99% efficient energy conversion of 100 GW still produces 1 GW of waste energy that needs to be radiated. On Earth this is less of a challenge than in the vacuum of space. Radiating excess heat in space is more difficult and likely to become a significant portion of the whole system. In addition to improving efficiencies, the related technical challenge is to create more effective radiators, with lower specific mass (kg/W).
Another technical challenge is to find propulsion methods that can slow down at the destination. Virtually all prior interstellar mission concepts are envisioned as a flyby. The shorter the trip time, the shorter the time that the spacecraft will be in range of the target to acquire its mission data. For example at 20% lightspeed, a spacecraft would only be within ± 1 AU of the target for less than 90 minutes. Even relaxing that to only 1% lightspeed and a range of ± 2 AU, the spacecraft will only be in that range for 56 hours. (See table 8 in Section 7.2.1 for more examples.)
Most interstellar mission concepts rely on substantial infrastructure in our solar system to build, power, and launch their vehicles. Further, many of those concepts also assume that this infrastructure is already there, ready to be used. Presently, there are no commonly accepted predictions of the rate of infrastructure growth to determine when the infrastructure will be ready to begin the construction of interstellar hardware. Estimating the growth of infrastructure is addressed in Section 8.3.2.
The infrastructure will be providing service to more than just the interstellar missions, so the system level consideration of that infrastructure is relevant. For example, could the same laser arrays envisioned for an interstellar mission be an integral part of the infrastructure—beaming power to remote segments of infrastructure? If so, then there is the need for system level trade studies at the infrastructure level.
What is seldom addressed, however, is how to begin the construction of that infrastructure. Many concepts for space solar power assume that one large investment will create a functional infrastructure as one project. Even though space solar power is usually conceived as sending the energy to Earth, it is analogous to the scale of energy needed for an in-space infrastructure. What is missing are concepts for building the in-space infrastructure in affordable increments. This challenge remains open.
Millis 2018 Grant NNX17AE81G_for_CR.docx

pg 21 of 69 system level mission concepts, there are key technologies that will have to be solved, and of those, many will need significant further research.
[Table: Table 2 lists major historic exploration missions as a baseline comparison for data, payload, and spacecraft speed. This also serves as a starting point for the Stage II analysis of comparative rates of advancement. At this point, the table is only partially populated with data, but does show key relevant factors. The missions are listed in order by launch date, and the columns thereafter are listed roughly in order of the questions for designing a mission, per Section 7.] [Table: Table 2. Historic Exploration Mission Baselines]
Build

Launch Data Volume
Data Rate Xmit duration
Spacecraft Power (W)
Power Supply
Payload
Spacecraft
Tm (yrs)
km
(%c) Mission
Mass
empty mass (kg)
s
Dev, Tdev,
(mo)
(kg)
(kg)
(yrs)
Luna 3 1959 1MB <1 Mariner 4 1964 1MB Mariner 9 1971 2GB 16 kbps 0.4 1 Voyager 1 1977 160 bps 450 (1977) 105 723 >40 178 (2025) Galileo 1989 7.7 kpps 600 2380 14
17.3 0.006
Ulysses 1990 56 (11kg Pu-238) Cassini-1997 635GB 800 5600 Huygens Deep 1998 2,500 374 Space 1 Kepler 2006 4.3 Mbps
11.3 0.004
Mbps Dawn 2007 10,000 30 1250 New 2009 50GB 15 200 30 585 Horizons 7GB (?) 478 Juno 2011
73.6 0.025
Ambiguities encountered between energetic propellants and reaction masses that
require a separate source of power to accelerate them.
•
Technical Maturity: This is not a constant. This is a factor to track over time with each concept.
•
Performance Level: There is no accepted ranking on performance level since those are mission specific as
well as being a non-constant discriminator.

Millis 2018 Grant NNX17AE81G_for_CR.docx

pg 25 of 69

[Table: Table 4. Interstellar Power & Propulsion Prospects]
Electric Sail & Stellar Winds 2005 Pekka Janhunen 1 IP-XM Magnetic Sail & Stellar Winds 2000 Winglee 1 IP-XM Plasma Magnet & Stellar Winds 2013 Slough 1 IP-XM Alfven-wave plasma propulsion 1996 Moore, R. IP-XM Plasma Wave 2013 Gilland IP-XM Interstellar Ramjet 1960 Bussard IP-XM