Lunar Landing GN&C and Trajectory Design Go For Lunar Landing: From Terminal Descent to Touchdown Conference Panel 4: GN&C Ron Sostaric / NASA JSC March 5, 2008 National Aeronautics and Space Administration

Slide 2 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Introduction ALHAT is a NASA project developing technologies needed to improve landing capability –Autonomous Precision Landing and Hazard Detection and Avoidance Technology Project The objective of the project is to develop and deliver an autonomous GN&C hardware and software system and certify it to Technology Readiness Level (TRL) 6 through analysis and testing –Functional on robotic, cargo and human missions –Place humans and cargo safely, precisely, repeatedly and autonomously anywhere on the lunar surface under any lighting conditions within 10’s of meters of certified landing sites –Detect surface hazards with the capability to re-designate to hazard free landing areas –Extensible to other missions

Slide 3 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Approach Phase Hazard Detection and Avoidance Hazard Relative Navigation Braking Maneuver Terminal Descent Phase Pitch-up Maneuver Deorbit maneuver Powered Descent Phase Powered Descent Initiation (PDI) ~15 km ~30 m ~300 to ~600 km NOTE – Not to scale Transfer Orbit Phase (coast)‏ Hazard Detection Human Interaction Hazard Avoidance Parking Orbit ~100 km Braking Phase Terrain Relative Navigation ~1 to ~2 km Orbit1 Coast2 Braking3 Approach4 Vertical Descent5 TRAJECTORY PHASE # --- ~ 55 min ~ 6 - ~10 min ~30 - ~180 sec ~ 30 sec TIME ALLOCATION De-orbit Maneuver Powered Descent Maneuver Pitch Up Maneuver Vertical Descent Maneuver Touchdown ~ 1 hour Total Time Allocation Descent Trajectory

Slide 4 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Trajectory Design Drivers for Approach and Landing How to shape the approach and landing trajectory, and why? Trajectory design drivers during Approach –Minimize propellant usage –Trajectory design must be representative of what crew would be willing to fly –Provide reasonable operating conditions for sensor (and/or crew member) to scan landing area for hazards –Allow time for interpreting sensor scan information and crew decision making –Allow enough margin for maneuvering to avoid hazards –Provide enough margin to account for dispersion control Approach Phase Hazard Detection and Avoidance (HDA) Terminal Descent Phase ~30 m Hazard Detection Human Interaction Hazard Avoidance ~1 to ~2 km

Slide 5 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Trajectory Interaction With Conditions for Hazard Detection Too shallow for sensor Too steep for window view Too far for sensor scan Trajectory path Meets constraints

Slide 6 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Trajectory: Slant Range for Hazard Detection Need to be within range of landing site for sensor scan, crew viewing Spending more time sensing/viewing closer to the landing site is preferred for sensing and viewing This has a trade-off with propellant usage The relationship of time during approach and landing with propellant usage is about 10 kg for each second –Assuming low throttle, Altair-size lander

Slide 7 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Trajectory: Path Angle During HDA The trajectory path angle directly affects the angle for sensing/viewing Shallower approach ideal for window viewing –Landing area moves “up” in the window as path becomes more shallow –Apollo flew ~16 deg approach HDA sensor performance degrades at shallow approach angles –Shallow approach causes stretching of samples, partial or complete obstruction of small and medium size hazards behind large ones ALHAT working to fully characterize the trade space and better understand path angle effects Other considerations –Lighting conditions –Cameras, light tubes, or augmentation systems may affect the path angle constraint –These things (and others) under investigation

Slide 8 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Hazard Avoidance Hazards must be detected early enough that they can be avoided –for a reasonable amount of propellant and –without exceeding tipover limits or other vehicle constraints The required divert distance capability can be sized by relating it to the size of the hazard scan area –The hazard scan area is determined by a probalistic terrain analysis to determine the amount of area needed to ensure a safe landing The required divert distance drives the point at which divert must be initiated m/s Hazard Avoidance (HA) Last point with “full” HA redesignation capability Final Descent Divert to edge of scan area Scan area 180 m 80 m The maximum divert for a 180 m scan area is 80 m Vehicle footprint assumed to be 20 m (10 m radius)

Slide 10 5 March 2008 Ron SostaricNASA Johnson Space Center, Aeroscience and Flight Mechanics Division Introduction to Safe and Precise Landing Safe Landing –A controlled touchdown within tolerance on vehicle state while avoiding any hazards Hazards are defined as rocks, craters, holes, slopes, or other obstructions that exceed the vehicle hazard tolerance –Safe Landing is by primarily accomplished knowing about all hazards prior to the mission, or by providing a real-time method of hazard detection, and by having the capability to avoid hazards Precise Landing –Landing accurately enough inertially as required for mission design and also precisely enough locally to achieve a safe landing (avoid any hazards) –Precision Landing is primarily accomplished by providing accurate enough state knowledge early enough to fly out dispersions, and accurate enough state knowledge near touchdown to avoid hazards