Sample Fetching Rover Lightweight Rover...
Transcript of Sample Fetching Rover Lightweight Rover...
ASTRA 2011 – ESTEC – 14 April 2011
Sample Fetching Rover-
Lightweight Rover Concepts for Mars Sample Return
Elie Allouis, [email protected]
T.Jorden, N.Patel, A.Ratcliffe
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Astrium Satellites, EOS.
SFR StudyASTRA 2011 ESTEC - 14 April 2011 Contents
Scope
Introduction
The SFR mission Concept SFR and the MSR Mission Architecture SFR Mission Operational Baseline Rover System Design Drivers Rover Design Philosophies
Selected System concepts: Mobility Locomotion System GNC
Baseline Down-Selection
Conclusion & Wrap-up
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Introduction Scope
Introduce the SFR mission concept, design drivers and mass reduction philosophies Concentrate on Mobility issues and first preliminary concepts
Study objectives To carry out an assessment study of a lightweight rover for fetching
cached samples on Mars and return them to a Mars Ascent Vehicle (MAV)
. Challenges
Very stringent mass constraints: target 60 kg, (ExoMars is ~ 300kg) Compact 1 x 1 x 0.7m stowed envelope Must traverse 15 km in 180 sols mission
Design Highlight interleaved aspects of environmental and operational
requirements Identify and thoroughly understand of “ripple effects” through the sub-
systems design. Identify enabling technologies and future developments
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Introduction - The Team
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 MSR Mission Architecture
NASA/ESA Joint Mars Exploration Programme The caching rover will collect and deposit a sample cache onto the
Martian surface to be collected by SFR.
2018 2022-2024
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 MSR Mission Architecture
Baseline Architecture : MAV and SFR deployed together
Rover begins operations in September 2025 ≈ Ls 133 NASA concept allocates 150 kg to a single purpose fetch rover The rover shall fit in a 1 x 1 x 0.7 m envelope to transfer to Mars
Need to investigate alternative deployment concepts in case of MAV mass growth (ESA Mars Precision Lander)
NASA
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Mission Operational Baseline
Mission Nominal Operational Scenario : Navigate and traverse to the location of a sample cache deposited by a previous
rover mission Retrieve the sample cache Deliver it to the MSR Ascent Vehicle and cooperate in transferring the sample
cache to the MSR lander
A compressed mission timeline : 180 sol mission Accounting for post landing operations, checkouts and dust storm contingencies… Only 125 sols remaining for egress Minimum traverse of 120m/sol for a 6-month mission If mission is to be done before the dust season ~170m/sol
Cache
MAX-C Start
MAX-C End
MSR Lander
Traverse Distance = 14
km straight line
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SFR StudyASTRA 2011 ESTEC - 14 April 2011
Environment Similar to ExoMars/Caching Rover Same location, however
Mission operation from Ls 133 to 212 shortly before Dust seasonDifferent illumination conditions and thermal environment
Terrain Conditions At worst, SFR should be compatible with
ExoMars terrain, At best, the cache is deposited in a more
benign location (fewer/smaller rocks and slopes, better characterised terrain, etc)
Mission Environment
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 SFR Rover
- Rover System Design Drivers -
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SFR StudyASTRA 2011 ESTEC - 14 April 2011
Structure
Locomotion Navigation
Deployable Mast
Thermal Control
Power
HarnessData Handling
Communication
Rover System Design Drivers
The SFR design presents significant challenges in the areas of
Mass : Target mass for the rover platform is 60 kg
- 1/5 Exomars The four major contributors to mass (90%) are
locomotion, structure, power and harness.
Performance : Accumulated ground track of at least 15km Nominal 180 sol mission baseline 125 sol
traverse SFR highly dependent on robust mobility system.
Risk : Overall MSR mission architecture high degree
of risk. No Rover return No samples
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Rover System Design Drivers
SFR Design Drivers, Dependencies and Ultimate Impact on Mass
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Approaches to Design Evolution
Remove the need for the solution from the designNot usually practical – severe loss of functionality
Remove the need for a solution
Displacement
Novel architecture & technologyInnovative & ground breakingFull Validation and qualification reqd –usually high risk
Thinking out of the boxRadical
Same functions but re-development from scratchDesign needs validation and qualification
New developmentSame functions
Alternative
Based on heritage itemmedium uncertainty / risk
Altered heritage solutionModified
Optimisation of heritageLow risk / high confidenceGood retention of TRL
Optimise existingHeritage
Comments / issuesApproachSolution Type
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Proposed Rover Design Philosophies
Stripped out approach Removes any mass that is not essential for the
achievement of the major goals of the mission. Each element of the rover is pared down to its minimum
required functionality/performance. Sub-systems can be de-scoped and performance traded
to achieve a lower mass solution, but component redundancy must be maintained.
Ready-To-Go Seeks to remove any deployments or mechanisms that
are not essential i.e. utilisation of fixed solar arrays, fixed mast, no wheel deployment etc.
This approach removes rover complexity reducing risk during the commissioning phase.
The gain of removing mechanisms must be carefully traded against the impact on performance and the reciprocal effects on the system design.
E.g. a rover with a fixed solar panel may have a small total array size due to the constraints imposed by the lander.
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Proposed Rover Design Philosophies
Cold Skeleton The rover is stripped down to it fundamental structures and
uses minimum thermal control to save structure mass and packaging
Involves the use of cold electronics and mechanisms Limited by battery temperature requirements
Locomotion Optimisation The design is driven by the optimisation of the locomotion
system. Potential to alleviate GNC load Rover is designed around the Locomotion Sub-System
ensuring mobility is not compromised at any stage in the design.
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Proposed Rover Design Philosophies
24/7 Rover – Not Possible A perpetual power supply the rover Achieved by a power system not constrained by solar flux
such as RTG and SRG But Very low TRL and energy density of current
radioisotopes too low for small rovers The SFR Mission currently baselines photovoltaics
Day Rover – Not Possible The rover only operates during daylight and only from the
power of the solar arrays No battery – Some mass saving and lower thermal
requirements as per Cold skeleton But Mission requires a night communication window
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 SFR Rover
- Locomotion Sub-System -
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Locomotion Overview
Terrain topography and its physical properties play a critical role in the design and performance of the LSS The soil properties - rover slope traverse capability, power requirements, grousers size,
number of wheels. Size of the rocks - design of the suspension system, the wheel size, power
requirements. Rock distribution - mean free path of the rover which influences GNC. Slope - minimum gradeability, the static stability of the rover and power requirements.
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Locomotion System Options
Extensive locomotion system concepts review 20 configurations 4,5,6,8 wheels Preliminary trade-off:
Mechanical and actuation complexity, Ground clearance Redundancy, Risk and TRL, Stowage and deployment, .…
Wheel Types and Constructions Rigid Semi-rigid Flexible
NASA
NASA
AMSTL
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Locomotion System Candidates
Heritage and redundancy
6WD – 3 bogies
Simpler, lower mass
4WD +diff
Lowest mass, Lowest TRL
4WD
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 SFR Rover Concepts and Trade-Offs
- Guidance Navigation and Control -
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 GNC Sub-System
Functional specification Key to rapid traverse (15km-120m/sol) However
Unlike past missions a wealth of local terrain data will be potentially available to the platform
Key design drivers
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 GNC Sub-System
Navigation Options:
Stop-Go Stop to image the way ahead and process the
data to derive a safe path Used on MER and ExoMars Requires heavy processing, Provide careful
path planning and dead-reckoning Holds up the progress of the traverse
(Processing power limitations)
Continuous Drive Set off in the target direction and avoid
obstacles along the way Can be time (and therefore power) inefficient
as the navigation seeks a path continuously through obstacles
SLAM and Obstacle Avoidance
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 GNC Sub-System
An alternative Navigation Concept: Hybrid Architecture
Current missions are relying on direct-drive with some operational autonomy for obstacle avoidance
In the timeframe of SFR Wealth of data gathered of the ExoMars and MSR landing sites
Unprecedented opportunity to perform a preliminary route mapping to the cache Obital imagery, altimetry and shape from shading may identify obstacles
- HiRISE already provides 0.3m pixel sizes on the ground It is possible to envisage that high resolution digital terrain models (DTM)
will be available
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 GNC Sub-System
GNC architecture – Using High res DTMs
Localisation: Visual feature matching
Navigation and Path planning:- Identification of all the main obstacles in the path large scale nav map (uploaded
in manageable chunks. However, specific terrain data such as the soil condition will be missing. On-board
replanning required to find altrenative path.
Control: The DTM could be used in conjunction of the Structure from Motion techniques to
improve the control and accuracy of the rover along the prescribed path.
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 SFR Rover
- Baseline Downselection -
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Baseline Candidates - Discussion
Candidates mass comparison The concepts range from ~72kg (4WD_diff) to ~79kg (Exomars based, flexi
wheels) Mainly relates to mass savings in:
Locomotion System OBDH mass reduction scheme
However: Not as large a difference as initially anticipated Limited by
Power sub-system and Solar Array Size and deployment Structure Mass
SFR Baseline Candidates Mass
68
70
72
74
76
78
80
ExoLight ExoEvo 4WD_diff 4WD_XLW_300 4WD_XLW_400
Mas
s [k
g]
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Preliminary Baseline
Based on Trade-off exercise, a 6WD 3 bogies configuration selected
Higher redundancy than 4WD concepts Heritage in a “smaller” package evolution of the ExoMars
configuration (not necessarily implementation) 1.4m2 array (configuration TBC) Large area in the front for Cache Acquisition System Stowed envelope fits into the allowable volume Footprint deployed – 1500x1000mm ~75kg (with 300mm spoke/mesh wheels)
However: Mass > target of ~60kg, but will be optimised in next phase Alternative locomotion formula and their performance will be
investigated i.e. from 6x6x6 down to 6x4x4 Wheel construction and dimensions TBC
Rigid Vs flexible, 250-300+mm Innovative lightweight solutions for collateral systems to be
investigated e.g. OBDH, Comms, Power…
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 SFR Rover Concepts and Trade-Offs
- Conclusion & Wrap-up -
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SFR StudyASTRA 2011 ESTEC - 14 April 2011 Conclusion
This activity is looking at a wide range of architecture, system and sub-system options for the Sample Fetch Rover Mobility subsystem critical to mission success
Based on the current mission constraints and following this preliminary review and trades: None of the concepts proposed currently fit into the 60kg target mass envelope
(~75kg). Preliminary analysis showed that it is difficult to drastically reduce the mass of
the main mass drivers further, but other system may be optimised Rover must be compatible with ExoMars environment drives locomotion and
power systems
The preliminary rover concept draws on heritage, but leaves open a number of options for actual implementation
The next phase Will see further definition and mass optimisation of the rover subsystems Careful evaluation of GNC scheme and Locomotion system sizing. Preliminary design of the rover concept
ASTRA 2011 – ESTEC – 14 April 2011
Sample Fetching Rover-
Lightweight Rover Concepts for Mars Sample Return
Elie Allouis, [email protected]
T. Jorden, N.Patel, A. Ratcliffe