This viewgraph presentation reviews the work towards technology that will result in an autonomous landing on the lunar surface, that will avoid the hazards of lunar landing. In October 2005, the Exploration Systems Mission Directorate at NASA Headquarters assigned the development of new technologies to support the return to the moon. One of these was Autonomous Precision Landing and Hazard Detection and Avoidance Technology now known as ALHAT ALHAT is a lunar descent and landing GNC technology development project led by Johnson Space Center (JSC) with team members from Langley Research Center (LaRC), Jet Propulsion Laboratory (JPL), Draper Laboratories (CSDL) and the Applied Physics Laboratory (APL

Epp, Chirold

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Autonomous Landing Hazard Avoidance Technology (ALHAT)
Page 1 STAIF 2008
Autonomous Landing and Hazard 
Avoidance Technology (ALHAT)
Dr. Chirold Epp
ALHAT Project Manager
Johnson Space Center
https://ntrs.nasa.gov/search.jsp?R=20080009586 2019-08-30T03:43:20+00:00Z
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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OUTLINE
• ALHAT BACKGROUND
• ALHAT VISION STATEMENT
• ALHAT MISSION PHASES
• TERMINAL DESCENT PHASE
• SAFE AND PRECISE LANDING
• LIGHTING
• LANDER TOLERANCE
• HDA TERRAIN SENSORS
• HDA SENSOR PERFORMANCE
• CREWED LANDINGS
• SUMMARY
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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ALHAT BACKGROUND
• In October 2005, the Exploration Systems Mission 
Directorate at NASA Headquarters assigned the 
development of new technologies to support the return to 
the moon.
• One of these was Autonomous Precision Landing and 
Hazard Detection and Avoidance Technology now 
known as ALHAT
• ALHAT is a lunar descent and landing GNC technology 
development project led by Johnson Space Center (JSC) 
with team members from Langley Research Center 
(LaRC), Jet Propulsion Laboratory (JPL), Draper 
Laboratories (CSDL) and the Applied Physics Laboratory 
(APL)
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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ALHAT VISION STATEMENT
• Develop and mature to 
TRL 6 an autonomous 
lunar landing GN&C and 
sensing system for 
crewed, cargo, and 
robotic lunar descent 
vehicles. The System will 
be capable of identifying 
and avoiding surface 
hazards to enable a safe 
precision landing to 
within tens of meters of 
certified and designated 
landing sites anywhere 
on the Moon under any 
lighting conditions.
ALHAT
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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ALHAT MISSION PHASES
Powered Descent
NOTE –
Not to scale
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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TERMINAL DESCENT PHASE
• PDI maneuver guidance targets an altitude and velocity at 
approximately 1.5 km from the landing site to execute the pitch-up 
maneuver and begin the final phase of landing with crew viewing out 
the window
• This phase requires hazard knowledge and the ability to identify a 
safe landing site
– ALHAT assumes no a priori knowledge of surface hazards
– Unclear what hazard resolution to expect from LRO but definitely will not 
have a priori surface hazard knowledge globally
• Most challenging and difficult landing phase
• Most important information is hazard elevation relative to the 
surrounding surface (above or below)
• Also important to maintain a good surface relative navigation state 
during this phase
• Following slides discuss major factors affecting this phase 
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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SAFE AND PRECISE LANDING
• The ALHAT project has accepted the challenge 
of global access to the moon
– Global access is interpreted to mean any terrain 
where there exists an area certified for landing within 
the tolerance of the lander
– Implies any lighting conditions because of places like 
the south pole where the maximum sun elevation 
angle is 1.5º
• Requires real-time hazard information 
• Requires real-time surface relative navigation to 
land relative to a surface feature in a safe 
hazard-free area
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LIGHTING
• CA0046-PO The Constellation Architecture shall conduct 
Lunar Sortie missions so that surface stays are 
conducted during periods of lunar daylight. [ARDIG]
– Not a specific landing lighting requirement but could be 
interpreted to mean no dark landings
– If the landing destination is Shackleton area this could mean 
landing with sun elevation angle of 0.5º and launching from the 
surface with sun elevation angle of 0.5º for a 7 day stay
• Daylight and what one can see with the human eye or 
cameras is an open question for places like Shackleton
Crater where daylight has a sun elevation angle of -1.5º
to +1.5 degrees.
– Opinions vary. 
– Apollo requirements were for the sun to have a view angle that 
differed from the sun angle by more than 2º in both elevation and 
azimuth 
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LIGHTING
Kaguya North Pole Image
1.5º sun elevation
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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Apollo 14
11° Tilt 
(12° Limit)13.5"
clearance
However….
LANDER TOLERANCE
Some hazards recognizable during pre-flight 
planning….
Apollo 17
….some are not.
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LANDER TOLERANCE
Apollo 15 set down on the rim of a small crater, 
damaging the engine bell and tilting at ~10º
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LANDER TOLERANCE
• Apollo limit was to tolerate rocks, holes and 
slopes that did not produce a vehicle that was 
more than 12º from the vertical
• Vehicle footprint and this kind of constraint 
defines the hazards that need to be tolerated
• ALHAT is using very conservative requirements 
for mininum detectable hazards until something 
definite is given
– 30 cm hazards (rocks and holes) and 5º slopes
– If the ALHAT system can work for these requirements 
it will work for less conservative requirements
– The probability of finding a safe site improves rapidly 
with more tolerant requirements
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LANDER TOLERANCE
45m x 45m Hazard Map Area
0.00
0.20
0.40
0.60
0.80
1.00
1.20
15 16 17 18 19 20 21 22 23 24 25
lander diameter (m)
2
4
6
8
10
% area
covered 
by rocks
• Only rocks considered based on published statistical rock distribution models  
• 30 cm rock is considered a hazard
Monte Carlo Analysis by Dr. Andrew Johnson, JPL, 2007
Probability of finding one safe landing area
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LANDER TOLERANCE
• Only rocks considered based on published statistical rock distribution models
• 30 cm rock is considered a hazard
Monte Carlo Analysis by Dr. Andrew Johnson, JPL, 2007
Probability of finding one safe landing area
180m x 180m Hazard Map Area
0.00
0.20
0.40
0.60
0.80
1.00
1.20
15 16 17 18 19 20 21 22 23 24 25
lander diameter (m)
2
4
6
8
10
% area
covered 
by rocks
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LANDER TOLERANCE
• Only rocks considered based on published statistical rock distribution models 
• 30 cm rock is considered a hazard
Monte Carlo Analysis by Dr. Andrew Johnson, JPL, 2007
Probability of finding one safe landing area
360m x 360m Hazard Map Area
0.00
0.20
0.40
0.60
0.80
1.00
1.20
15 16 17 18 19 20 21 22 23 24 25
lander diameter (m)
2
4
6
8
10
% area
covered 
by rocks
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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LANDER TOLERANCE
Based on published statistical rock distribution models
Monte Carlo Analysis by Dr. Andrew Johnson, JPL, 2007
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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HDA TERRAIN SENSORS
• Human eye 
– Requires some light
– Unclear about the ability to define hazards and hazard 
elevations, particularly holes and slopes, with significant 
shadows and contrast problems like expected at Shackleton
Crater
– Current analysis and research underway to better understand 
this capability
• Infrared sensing systems and low light enhancing 
systems
– Usefulness of these systems at the lunar surface is not well 
understood and there exist some disagreements
– Current analysis and research underway to better understand 
this capability
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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HDA TERRAIN SENSORS
• Optical cameras 
– Requires some light
– Provides 2-D image with adequate light
– Limited ability to define hazards and hazard elevations, particularly 
holes and slopes, with lighting conditions expected at Shackleton Crater
• With image processing for comparison with preflight maps of 
hazards
– If preflight maps of hazards are good enough this approach could be 
used for hazard relative navigation
– Requires significant data processing
– Data available for display in near real-time (few seconds)
• Stereo cameras
– Requires large baseline
– Not considered a viable option for real-time imaging from altitudes 
between 500m and 1000m
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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HDA TERRAIN SENSORS
• Flash LIDAR 
– Digital camera which carries its own light source and able to measure 
time of flight for light striking each pixel (thus elevation data)
– Data independent of surface lighting conditions
– Provides Digital Elevation Map of the surface thus identifying rocks, 
holes and slopes
– Data utilized for hazard relative navigation to safe landing site
– Requires significant data processing
– Data available in near real-time (few seconds)
• Scanning LIDAR
– Similar to flash LIDAR except uses scanning beam
– Technology slightly more mature than flash
– Time required for data collection and processing is higher than for flash
– More moving parts than flash
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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HDA SENSOR PERFORMANCE
• Must support landing without surface or orbiting 
navigation aids (supports sortie and first down outpost)
• Sensors required to provide real-time surface hazard 
elevation information
• Factors effecting sensor performance
– Range at which sensor capability provides required hazard 
resolution
• Higher the better
• Allows time to analyze, divert and fly efficiently to safe site
– Time required to obtain hazard information and define safe 
landing site
• Depends on range from target site data and deceleration rate
• Approximately 1.0 to 1.5 minutes to collect the data, process it, do 
analysis to pick safe site and divert to the safe site
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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CREWED LANDINGS
• ALHAT has been challenged to analyze a crewed mission to a 
landing site with polar lighting conditions with no navigation aids and 
utilizing the crew’s capabilities to maximum extent possible to 
determine the “minimum” suite of navigation/sensor equipment to 
land safely on the lunar surface. 
• Based on the ALHAT Team current research and analysis 
knowledge, we believe a LIDAR provides the best option to meet 
safe landing requirements
– Considered to be a good sensor for determining real-time elevation 
information
– Additional development required to improve capability and resolution at 
higher altitudes and improve efficiency, robustness, reliability and space 
qualification
– Real-time LIDAR data requires high volume and high speed processing
• As our knowledge base increases it is possible that we will find other 
systems that can meet safe landing requirements
– Considering options such as infrared sensors, flood lights with crew 
capability, cameras, etc.
Autonomous Landing Hazard Avoidance Technology (ALHAT)
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SUMMARY
• The trade space of the ALHAT technology 
development includes a number of options
– Plan to have considerable analysis and test data by 
the end of FY08 that will narrow down the trade space 
and better define what is required for safe landing 
anywhere on the moon
• ALHAT is investigating human capability and 
aids to help humans detect hazards is part of the 
ALHAT development
• Important to continue to develop promising low 
TRL technologies that assure safe landing for 
crewed and autonomous vehicles for outpost 
and sortie missions


Autonomous Landing and Hazard Avoidance Technology (ALHAT)

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