a reusable design for precision lunar landing...

Lunar Access Program: A Reusable Design for Precision Lunar Landing Systems Slide 1 September 20, 2005

The Lunar Access Program:

A Reusable Design for Precision Lunar Landing Systems

International Lunar Conference 2005

Linda Fuhrman Steve Paschall

September 20, 2005

[email protected]

[email protected]


Outline

• Executive Summary

• Project Objectives, Challenges, and Plans

• Navigation Issues

• Preliminary Findings

• Conclusions


Executive Summary

• President of the U.S. outlined the new Vision for Space Exploration in January, 2004

– Extend human presence beyond Low Earth Orbit (LEO)

– Earth’s moon as a test bed

– Mars, asteroids, and beyond

• Challenges of the next generation of lunar exploration:– Long-duration surface stays (multiple landers)– Polar and far side landings

• Lunar Access Program– Draper-led, 4-year technology maturation program to enable safe

access to the lunar surface

– Team includes ARES Corp., Doreen Evans Associates, Honeywell Inc., JPL, MIT, Payload Systems Inc., Starcraft Boosters Inc., USfalcon


Project Objectives

• To develop the Precision Landing System (PLS) design to meet performance requirements for the next generation lunar lander

– Reusable design– Fully autonomous to operator-in-the-loop

– “Anytime, anywhere”– Precision 10 – 100 m– Landing system safety

• To develop a Lunar Access Test Bed (LATB) to instantiate and validate the PLS design

– Feed forward capability (modular, open, upgradeable)

– Real-time, Hardware-in-the-loop (HWIL), Human-in-the-loop (HITL)

LSAM

Prop

Com

ECLSS

P/L

C&DH

Infr

astr

uctu

re

PLS

LandingGN&C

LandingH-SI

HDA

Crew DisplaySW

HDA SW

GN&C SW

Cre

w In

terf

ace

CPS

LATB Operator I/F

Stubs

Sensors

Env.

Sim.

Vehicle

LATBdefinitions

Sensors

CrewStation

Proc.


Key Project Challenges

• Complexity of mission requirements– Maintaining precision and safety for all mission scenarios

• Light & dark; polar & equatorial; robotic & human; first & following

• Realism of design and approach– Designing system & algorithms today anticipating a 2015+ flight

hardware & infrastructure

– LATB implementation choices that allow flexibility for future upgrades

• Design solutions that minimize the need for new technology developments and infrastructure investments– Single solution with gradual implementation / maturation path

• From early robotic precursors to later human missions

• Capability growth and demonstration path

– Solution that does not require extensive ground operations, infrastructure, precursor missions

• Focus on currently available technologies and planned capabilities


Key System Issues

• Mapping– A priori map resolution for both landing site selection and navigation– Planned maps for 2010+ may not be sufficient to address both issues

• Map-tie• Resolution and accuracy• Global coverage

• Infrastructure & Ground Support– Minimize infrastructure (no lunar “GPS”) – Minimize ground ops support (not like Apollo)

• Vehicle Configuration– New technologies produce fewer constraints– No Apollo-type viewing constraints

• Hazard Detection & Avoidance (HDA)– Hazard tolerance (slopes, rocks, craters, and combinations) of vehicle drives

detection sensing needs– HDA enables much larger selection of viable landing zones

• Without HDA, only large zones certifiably free of hazards can be considered

• Precision– Extended-stay missions imply multiple landers in a landing zone– High precision capability enables more safe landings in a zone– High-interest science sites may be very small compared to Apollo


Key Enabling Technologies

• Several areas are critical in achieving the objectives of the Precision Landing System:

– Guidance & Control

– Navigation

– Lunar terrain mapping

– Hazard detection & avoidance

• The remainder of this presentation will focus on highlights of the NAVIGATION issues related to Lunar Access


Navigation Issues


What is a Navigation system?

• An onboard system that uses an inertial measurement unit (IMU) in conjunction with external sensor measurements to estimate the vehicle’s current position, velocity, & attitude (i.e. vehicle state).

• Its performance is a function of the:– initial estimated state precision – sensor measurements errors– trajectory profile– gravity field uncertainty


Precision Landing System

Guidance ControlSensorData

EffectorCommandsNavigation

AccelerationCommands

Vehicle State(Low Rate)

Vehicle State (High Rate)

Mission Objectives

How the Nav System Fits into the PLS

Navigation – determines the position/velocity/attitude state of the vehicle at the current time

Guidance – determines acceleration commands necessary to meet landing requirements

Control – maneuvers spacecraft as needed to achieve Guidance commanded accelerations

Human System Interface – a.) receives data from GN&C, and b.) may alter mission objectives via re-designation


Reference Lunar Landing Trajectory

1. The vehicle begins in a parking orbit about the moon (~100 km altitude)

2. A de-orbit burn occurs to lower the periapse (to ~18 km)and begin the landing sequence

3. A large braking burn occurs near the periapse to null horizontal velocity (burn termination at ~2km)

4. A final descent burn occurs to null the remaining vehicle velocity and achieve a soft landing (burn initiation at ~800m)

dede--orbit burnorbit burn

braking burnbraking burn

descent burndescent burn

parking orbitparking orbit


Bounds of this Navigation Problem

• The navigation system begins operation in the initial parking orbit upon receiving an estimated vehicle state from the JPL DSN (Deep Space Network).

– 1-σ errors on the order of 100’s of meters in position and 10’s of cm/s in velocity just prior to deorbit burn)

• The navigation system estimates the vehicle state throughout the landing trajectory to the point of touchdown

dede--orbit burnorbit burn

braking burnbraking burn

descent burndescent burn

parking orbitparking orbit


Sensor Suite

• Baseline Suite:– DSN

• Provides initial state estimate via Earth radio antenna ranging and Doppler

– MIMU IMU• Uses accelerometers and gyros to measure vehicle accelerations and

rotations

– Star camera• Provides periodic inertial attitude updates

– RADAR Altimeter• Provides terrain-relative range measurements using radio beams

– Scanning LiDAR• Scans a LASER beam across the terrain to measure range to many points

on the terrain below• This data is used to build up a map of this terrain• The constructed map can be correlated to an a priori terrain map to provide

terrain-relative position and/or analyzed to characterize the terrain hazards


Sensor Use Scenario

– IMU for dead-reckoning navigation begins in lunar orbit following the final DSN navigation state update

– Star camera periodically provides inertial attitude updates during orbit and descent.

– As the vehicle trajectory nears the surface, the RADAR and LiDARinstruments begin providing data.

• The RADAR provides range and/or range-rate to the average terrain below.

• The scanning LiDAR builds a map of the terrain below to provide terrain-relative position

• Near touchdown the LiDAR will evaluate the terrain for hazards and provide any necessary target redesignation

Sen

sor

Op

erat

ion

Alt

itu

de

100 km

0 kmIMU Star

camera

. .

.

RADAR LIDAR


Alti

tude

Sensor Use Scenario

100 km

0 km

RADAR Range

LIDAR Range

800 m (~30 sec till touchdown)

Braking Burn

(~1 min till touchdown) 2 km

Freefall (Nominal)

Terminal Descent Burn

Downrange

(~1 hour till touchdown)

Deorbit Burn


Additional Sensors

• Other sensors will also be considered for the Precision Lunar Landing System:

– Optical cameras

– Doppler RADAR

– Ground Beacons

– Orbital Beacons


Navigation Analysis


Analysis Approach

Step 1) Linear covariance (LINCOV) analysis– performed in order to validate the baseline sensor suite and

other sensors under consideration. LINCOV analysis allows for relatively quick comparative navigation analysis of a wide variety of sensor suites and configurations.

Step 2) Monte-Carlo analysis– performed using a deterministic, 6-DOF (degree-of-freedom)

simulation. This will provide a higher-fidelity analysis that better captures the dynamics of the lunar landing problem.


Preliminary Linear Covariance Results

• Preliminary results based on use of IMU, Star Tracker, LIDAR, and Radar Altimeter

• Results shown are for a nominal polar trajectory

Time Direction

± 600 m

± 2200 m

± 500 m

3-σ Uncertainty at 5 km(IMU & Star Tracker)

± 600 m

± 1000 m

± 60 m

3-σ Uncertainty at 5 km(IMU, Star Tracker, &

Radar )

Crossrange

Downrange

Altitude


Conclusions

• Lunar Landing Navigation Analysis:

– Preliminary LINCOV analysis shows that additional terrain-relative sensors (i.e. LiDAR) are necessary to achieve the required lateral landing precision on the order of 10-100 m

– Terrain relative measurements would be necessary even with perfect error-free inertial navigation due to map-tie errors and resolution limits to the a priori lunar terrain map


Backup Charts


PLS

LSAM

Prop

Com

LifeSupport

Payload

C&DH

Infr

astr

uctu

re

PLS

Sensors

CrewStation

Proc.

LandingGN&C

LandingH-SI

HDA


LATB

Crew DisplaySW

HDAAlgorithms / SW

LandingGN&C

Algorithms / SW

Cre

w In

terf

ace

CPS

LATB Operator I/F

Stubs

Sensors

Environment

Simulation

Vehicle

LATB


Backup – Acronyms & Abbreviations

C&DH – Command and Data HandlingCom – CommunicationsCPS – Computing Platform SubsystemDSN – Deep Space NetworkECLSS – Environmental Controls and Life

Support SystemGN&C – Guidance, Navigation, and ControlHDA – Hazard Detection & AvoidanceHITL – Human in the loopH-SI – Human-System InterfaceHWIL – Hardware in the loopI/F – InterfaceJPL – Jet Propulsion LaboratoryLATB – Lunar Access Test BedLEO – Low Earth OrbitLSAM – Lunar Surface Access ModuleMIT – Massachusetts Institute of TechnologyP/L - PayloadPLS – Precision Landing SystemProc. - ProcessorProp – PropulsionSim. - SimulationSW - Software

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