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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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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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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- 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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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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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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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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- 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

Sample Fetching Rover Lightweight Rover...

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