I. Introduction

The Artemis missions will land astronauts on 

the lunar surface to leverage the unmatched 

capabilities of human explorers. These landings 

will commence long-term exploration and 

utilization of the Moon by NASA, industry, and 

international partners for the benefit of all. 

With humanity’s impending return to the lunar 

surface, precision landing of human spacecraft 

on the Moon’s surface is a fundamental 

challenge. The ability to land in proximity to 

the specific sites with demonstrated value for 

exploration, commerce, and science will be 

critical to achieving our Moon to Mars Objectives. 

Precision landings will enable spacecraft to 

avoid hazardous features, promote crew safety, 

co-locate infrastructure, and increase science 

and exploration returns.

This paper introduces the mechanics of and 

methodologies for precision lunar landing and 

explains critical aspects of landing, including 

vehicle navigation capabilities, plume-surface 

interactions, geospatial considerations, and 

science-related needs. 

2. Safe and Precise Landing:

What Does it Mean?

Precision landing generally refers to the process 

of navigating a spacecraft to a safe landing 

location in close proximity to a specified target. 

For example, a precision landing could be 

qualified as a requirement to safely touch down 

within 50 to 100 meters of a given target on the 

lunar surface. 

Precision landing is often coupled with hazard 

avoidance, resulting in the term “precision 

landing and hazard avoidance” (PL&HA). 

Implementing PL&HA systems on a spacecraft 

enables the landing of multiple assets within a 

targeted surface region or landing zone while 

avoiding collisions and limiting damage to 

existing surface assets. This mitigates the risk of 

unsafe touchdown for new landers and reduces 

post-landing travel distances between surface 

assets.

Literature on PL&HA often conflates precision 

landing to also imply safe and/or accurate 

landing. While both precision and accuracy are 

measurements of error in landing, precision 

is the measurement of how close landings 

are to one another, whereas accuracy is a 

measurement of how close they are to their 

intended target. 

Both accuracy (offset error from truth) and 

precision (uncertainty of the offset) are crucial 

for ensuring successful lunar missions, as they 

allow scientists and engineers to select specific 

landing sites of interest that better meet science 

or resource exploration objectives. For the 

remainder of this paper, the terms “precision 

landing” and “PL&HA” will be synonymous with 

safe, precise, and accurate landing.

3. Science Purpose and Needs

Landing at precise locations will help NASA 

meet lunar science objectives by guiding 

explorers closer to scientifically rewarding 

areas on the lunar surface. The Apollo Program 

demonstrated that landing human explorers 

near specific geologic features dramatically 

improves science return. The Apollo missions 

resulted in paradigm-shifting science discoveries 

that transformed our understanding of the 

Universe.

Proximity increases efficiency, effectively 

utilizing precious crew time and enhancing 

the quality and accuracy of data collection. 

That improvement in data collection enables 

researchers to gain deeper insights into the 

Moon’s history, composition, and geology. 

With the limited duration of extravehicular 

activities, landing in regions that meet 

illumination and communications requirements 

and optimizing proximity to areas of scientific 

interest will be critical to returning precious 

lunar samples to Earth for further analysis. 

Furthermore, precision landing near resourceand volatile-rich zones will help us understand 

and utilize the Moon’s resources. 

National Aeronautics and

Space Administration

2023 Moon to Mars Architecture Concept Review 1white paper 2023 Moon to Mars Architecture

Safe and Precise 

Landing at Lunar Sites
2023 Moon to Mars Architecture Concept Review 2

In addition, coupling precision landing with a hazard 

detection and avoidance system enables the lander to 

more accurately maneuver clear of hazardous obstacles. 

An effective PL&HA system could select landing sites 

with more benign surface conditions to improve lander 

touchdown stability. 

Such a system could also offer mitigation strategies for 

plume-surface interactions (PSI), where the exhaust 

from a lander kicks up lunar dust, or regolith. This could 

help minimize the hazard that ejected regolith poses to 

surface assets and prevent contamination of scientific 

areas of interest.

4. Surface Architecture

Precision landing can enable aggregation of surface 

assets in closer proximity, improving efficiency and risk 

posture. Whether using robotics or crew members to 

transfer logistics items, a reduction in distance means a 

reduction in transfer time and risk.

As an example, landing a logistics module closer to 

a habitat module would ease the transfer of items 

from one module to the other. Keeping assets within 

extravehicular activity walking distances or within rover 

mobility distances enables efficiency of time spent on 

science and utilization. 

As the number of government and commercial landers 

on the surface increases, there will be a critical need to 

ensure that associated keep-out zones are respected. 

Precision landing capabilities can help achieve this. 

Additionally, knowing the final, accurate location of the 

landed asset will enable planning for landing additional 

assets.

While enabling co-location of surface assets can be 

beneficial, there are also potential risks. The larger the 

engine, the higher the potential for PSI events that could 

damage existing surface assets. There is little lunar 

atmosphere to slow PSI ejecta during landing, and lunar 

regolith is essentially shrapnel from meteors impacting 

the surface without the weathering that takes place on 

Mars or Earth. While precision landing and close asset 

aggregation reduce transit times, surface assets will have 

to mitigate against PSI ejecta, which may require asset 

hardening.

5. Navigation Capabilities

Consider a typical lunar deorbit, descent, and landing 

trajectory. A deorbit burn inserts the lander from a low 

lunar orbit to a transfer orbit with a low periapsis (e.g., 

15–20 kilometers). Powered descent initiation occurs at or 

near periapsis and begins with a braking phase designed 

to reduce lander velocity as efficiently as possible. 

During powered descent, the lander transitions to an 

approach phase where attitude and altitude ranges 

permit the use of landing sensors and pilot visual contact 

with the landing site. At the end of the approach phase, 

the vehicle is directly above the target landing site and 

terminal descent begins, with the lander approaching the 

lunar surface until touchdown. 

Throughout these phases, the onboard navigation system 

must provide accurate and precise estimates of lander 

position, velocity, and attitude so that the guidance and 

control algorithms can plan and execute maneuvers that 

deliver the vehicle to a safe touchdown in close proximity 

to the target site. 

Navigation systems can include an assortment of 

components: software algorithms, onboard sensors, 

celestial navigation tools, maps of terrain features, 

and other devices for external measurements. Over 

the years, NASA has performed numerous studies and 

developed many relevant technologies[1] for precision 

landing through projects such as Autonomous Landing 

and Hazard Avoidance Technology (ALHAT)[2] and Safe 

and Precise Landing – Integrated Capabilities Evolution 

(SPLICE).[3] 

The ongoing SPLICE project has been tasked with 

advancing the technology readiness levels of key deorbit, 

descent, and landing guidance, navigation, and control 

systems. The project is also implementing simulation tools 

for conducting navigation sensitivity and performance 

studies for autonomous precision landing.

Findings from focal SPLICE navigation studies[4,5] 

demonstrate how improved physics-based engineering 

simulations and modeling fidelity can enable rapid, 

detailed assessments of the integrated performance of 

these systems. These simulation tools can evaluate the 

effectiveness of different navigation sensors on overall

Figure 1. : Sensor Assumptions Modeled from Lunar Orbit to Vertical Descent [2]. Acronyms: DSN (Deep Space Network), 

NDL (Navigation Doppler Lidar) velocimeter, TRN (Terrain Relative Navigation), IMU (Inertial Measurement Unit)
2023 Moon to Mars Architecture Concept Review 3

system performance. Sensors that can be integrated into 

these analyses include an array of inertial and relative 

sensors on which navigation systems would rely, such 

as accelerometers, gyroscopes, star trackers, altimeters, 

velocimeters, terrain relative navigation systems, and 

hazard detection systems. Figure 1 shows active sensors 

during particular deorbit, descent, and landing phases in 

an example scenario.

Powered descent is a short-duration event (approximately 

10 minutes). Utilizing Earth-based ground tracking 

updates for vehicle navigation during powered descent 

is not feasible due to the turnaround time required to 

process Earth-based tracking measurements and then 

communicate them up to the spacecraft. Instead, this 

phase relies on a lander’s onboard sensors.

Terrain relative navigation matches real-time observations 

of the lunar surface (e.g., camera images for passive 

navigation and lidar/radar surface contours for active 

navigation) to pre-flight maps stored onboard. Terrain 

relative navigation capabilities can improve lander state 

knowledge from the initial deorbit and braking burns.

Onboard maps are derived from orbital reconnaissance 

imaging and digital elevation models generated prior 

to a mission. Verification and validation of these preflight maps are critical to the success of terrain relative 

navigation. Passive approaches utilize cameras that 

require surface illumination from the Sun, as well 

as surface maps obtained or rendered with similar 

illumination conditions. Active approaches utilize a 

sensor like lidar or radar that do not require solar surface 

illumination for imaging; this approach obtains contour 

maps during descent that are then matched against 

onboard digital elevation models.

Additional architecture systems such as orbital 

communications relays, Global Navigation Satellite 

System (GNSS) signals, ground references, or surface 

beacons can also help support navigation capabilities for 

precision landing.[6,7]

6. Geospatial Aspects and 

Hazard Detection & Avoidance

The lack of an Earth-like atmosphere on the Moon means 

that even small meteorites impact the surface. This 

results in regolith heavily covered with impact craters and 

ejecta of varying sizes. These impact craters, ejecta, and 

other surface features (e.g., exposed uneven bedrock) 

present hazards to landers, which typically will have 

some maximum hazard size and surface slope that can 

be accommodated by landing systems (e.g., landing gear/

mechanisms, footpads).

Lunar surface geospatial data and analysis play a pivotal 

role in mitigating these hazards. Coordinated data fusion 

of relevant planetary mission datasets enables detailed 

evaluation of candidate landing sites. Mapping increases 

the likelihood that a safe landing can occur in a given 

surface region. 

These analyses examine data to assess terrain types, 

identify hazards, and evaluate surface illumination 

conditions. Current knowledge of surface features based 

on direct observations at proposed Artemis landing sites 

remains at the scale of meters per pixel. High-resolution 

mapping techniques such as shape-from-shading[8] may 

be used to enhance imagery and improve landing site 

characterization for hazard avoidance planning. 

Every lander has engineering constraints related to the 

size and characteristics of potential hazards that can 

be overcome during a safe landing. Given enough data 

from landing site observations and lander capabilities, an 

informed trade between pursuing further site knowledge 

versus investing in further lander robustness can be 

made. 

The trades between lander robustness — a local hazard 

accommodation size for a given lander — versus site 

knowledge — the available resolution of features and 

hazards at a desired landing site — can be summarized 

as follows:

1. Improved hazard size accommodation by the lander 

(e.g., through a landing gear redesign)

2. Improved orbital mapping resolution of the desired 

landing site to identify smaller hazards (e.g., through 

better or increased orbital observations of the area)

3. Implementation of an onboard hazard detection and 

avoidance system

The first two options are often constrained by program 

resources, schedule, and vehicle margins (e.g., maximum 

size and mass of the lander given launch vehicle 

constraints or remaining propellant onboard a lunar 

orbiter for obtaining closer images of targeted landing 

regions). The third option may be relatively lower cost 

since it does not require a vehicle redesign or additional 

mapping from orbiting assets. 

A balanced mix of all three options will aid in achieving 

NASA’s Moon to Mars Objectives. Observations by NASA’s 

Lunar Reconnaissance Orbiter and other missions 

have characterized the lunar surface environment very 

well. These data can inform hardware design choices 

quantitatively.

Figure 2. Site Knowledge vs. 

Lander Tolerance Continuum[7]
NASA has identified a need for a continuous lunar 

observation capability to preserve and enhance Lunar 

Reconnaissance Orbiter capabilities. These would be 

provided through follow-on NASA and/or commercial 

missions, enabling continued surface situational 

awareness for planned lunar activities. In addition, 

international partner missions are collecting valuable 

datasets that can be leveraged as more nations conduct 

lunar surface observations.

Hazard detection and avoidance systems can be passive 

or active, consisting of either:

1. An optical camera able to passively image illuminated 

localized hazards and indirectly detect them 

via shadow detection and feature identification 

algorithms.

2. A lidar able to actively image illuminated, shadowed, 

or unlighted hazards and directly detect them from 

point-cloud range data. An onboard hazard avoidance 

system would use this information to determine 

a safe landing location within lander performance 

margins. 

Hazard detection may also be coupled with terrain 

relative navigation systems, either by sharing imaging 

hardware or through software algorithms.

The needed capability to process orbital lunar surface 

data to a resolution that provides adequate pre-mission 

hazard mapping varies by location on the Moon. Some 

regions will require a lander to have a higher hazard 

tolerance or higher hazard avoidance capability than 

others — even with tightly resolved features — due to 

the size of the hazardous features on the surface. The 

Moon to Mars Lunar Surface Data Book [9] describes 

the process to resolve features, assumptions made, and 

modeling analyses. 

With the variability of surface crater and hazard size and 

distribution on the lunar surface, geospatial analyses 

generally focus on identifying zones with relatively safe 

landing conditions. In general, greater precision landing 

capabilities enable access to more surface sites, since 

smaller areas can be assessed to determine if hazards 

are present. 

Figure 3 includes an example of hazard avoidance by 

reducing the radius from 100 meters to 50 meters. In 

the image, the 100-meter-radius ellipse contains one 

large crater with potentially unsafe landing conditions. 

However, the 50-meter-radius ellipses can remain safely 

outside the large crater while still allowing a close enough 

distance for trips to the crater region, if desired.

7. Plume-Surface Interaction (PSI)

PSI results from rocket engine exhaust interacting with a 

planetary surface during descent, landing, or ascent. 

The Apollo missions experienced regolith ejections that 

obscured views of the landing site during final approach 

and touchdown. Apollo 12 sandblasted the Surveyor 3 

lander located 155 meters away. Apollo 15 landed on 

a crater slope, very nearly violating the tilt limit for safe 

ascent and sustaining structural damage to its descent 

engine bell, which would mean not being able to re-use 

that engine for ascent. 

The Mars Science Laboratory eroded significant craters 

with its Skycrane engines. Mars 2020 Perseverance’s 

descent and landing footage showed high-velocity debris 

and dust that completely obscured the cameras during 

touchdown. Both the Mars Science Laboratory and 

Perseverance showed evidence of debris impact damage. 

These past missions indicate that PSI can impact safe, 

precise landings and negatively affect landing sensor 

performance. Potential risks from PSI vary with lander 

configuration, concept of operations, and landing site. 

Many new lunar lander designs use the same vehicle to 

descend to the surface and later ascend back to orbit (i.e., 

single-stage) and are significantly larger in size than those 

flown by Apollo. They also have very different operations, 

which could result in a very different induced-hazard 

potential from Apollo. 

NASA currently lacks direct in-situ measurements of PSI 

phenomena, leaving predictions largely qualitative and 

uncertain. Validation and model improvements require 

ground testing and in-situ data.

NASA has conducted small-scale vacuum tests with 

different types of simulated regolith and plans to conduct 

more complex testing in the coming years to reducing 

PSI risk for the Human Landing System. The tests would 

allow the agency to improve models that currently rely on 

Apollo flight reconstructions.

2023 Moon to Mars Architecture Concept Review 4

Figure 2. : r=100m Landing Ellipse vs. 

r=50m Landing Ellipse (Artemis Geospatial 

Data Team)
2023 Moon to Mars Architecture Concept Review 5

References

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Technology from Concept through Flight-Tested Prototypes,’ AIAA SciTech 2015 Forum, AIAA 2015-0324, doi: 

10.2514/6.2015-0324

3. Carson, J., Munk, M., et al., (2019), ‘The SPLICE Project: Continuing NASA Development of GN&C Technologies for 

Safe and Precise Landing,’ AIAA SciTech 2019 Forum, doi:10.2514/6.2019-0660

4. Collicott, B. and Woffinden, D., (2020) ‘Lunar Navigation Performance Using the Deep Space Network 

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citations/20205010306

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a Generalized Simulation Framework,” https://doi.org/10.2514/6.2022-0609

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7. Anzalone, E., Woffinden, D., (2022), ‘Architecture Options for Navigation in Cislunar Space for Human Landing 

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8. Alexandrov, O., & Beyer, R. A. (2018). ‘Multiview Shape-From-Shading for Planetary Images. Earth and Space 

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citations/20230007818

In addition, upcoming Commercial Lunar Payload 

Services missions aim to capture PSI data using stereo 

cameras. These cameras will image the area under the 

landers during descent and touchdown. 

These observations represent a first step in understanding 

ejecta size and velocity on the lunar surface, which will 

be crucial to understanding surface asset proximity 

limitations, what risks exist, and how to mitigate those 

risks. Various technology efforts are planned or underway 

across NASA, industry, academia, and international 

partners for PSI testing, in-situ sensor development, and 

modeling advancements. 

8. Conclusion

Precision lunar landings have become increasingly important as space agencies and 

private companies aim to establish a robust, long-term presence at the Moon. Though 

there are many technical challenges to overcome, precision landings represent a pivotal 

advancement in space exploration technology. The potential benefits include enhanced 

safety for crewed missions, optimal targeting of scientifically valuable sites, and 

minimizing site contamination risks. Precision lunar landings will empower scientists to 

better study specific geological features, conduct experiments, analyze lunar soil, and 

gather valuable data about the Moon’s composition, history, and potential for future 

human exploration or resource utilization.