space resources roundtable vii

COLORADO SCHOOL OF MINESPILOT Project

SSR, Houston, 10-26-05 p1 of 18

SPACE RESOURCES ROUNDTABLE VII

Evaluation of Lunar-Regolith Excavator Concepts for a Small, ISRU Oxygen Plant

R. H. King, M. B. Duke, and L. Johnson Colorado School of Mines

Supported by the NASA/Lockheed Martin ProjectIntegrated In-Situ Resource Utilization for Human

Exploration – Propellant Production for the Moon and Beyond

akaPrecursor In-situ Lunar Oxygen Testbed - PILOT



Multi-criteria Decision Analysis with Uncertainty

1. Specify the design. 2. Develop a hierarchy of criteria.3. Generate alternative concepts. 4. Develop a conceptual spec sheet) for each

concept.5. Weight each criterion with the pair-wise

comparison method. 6. Evaluate with a decision matrix. 7. Revise the concepts (eliminate, combine, modify).8. Re-evaluate.

Method



Purpose and Characteristics

Purpose– Oxygen production– Habitat berms and other structures – Exploration

•Productive•Capable•Low mass•Power efficient•Reliable•Maintainable

•Mobile•Telerobotic•Stable•Integrateable•Cost effective•Multi-functional

Enabling Characteristics



Functional Requirements & Constraints

Excavator

100 kg/24 hrs6 batches

5.0 cm depth 10m x 10m or 11.5-m diameter

Sojourner - 11.5 kg<50 kg total0.63m x 0.48m x 0.23m30 W peak power

Lift System

ReactorPhoenix-class Lander



Functional Requirements/Constraints (cont.)

• simple and reliable• deploy and operate untended• modifiable to excavate 500 kg/hr • modifiable to excavate up to 1m deep• develop sufficient excavation reaction forces • navigate the lunar surface• handle material internally• transfer material to the reactor• dispose of reactor waste• build habitat berms• explore• avoid rocks• navigate slopes up to 20° fully loaded.• operate in the equatorial lunar thermal environment• be modifiable to the polar lunar thermal environment• maintainable suited or via robotic maintenance vehicle



Evaluation Criteria

Productive100 kg/24hrsExpandable to 500 kg/hr

CapableHorizontal reaction forceVertical reaction forceExcavate at least 1m deepEase of internal material handlingHandle particles up to 0.25 inReject particles over 0.25 in

Power efficientPeak powerTotal power per excavation cycle

Maintainable - maintainable suited or via robotic maintenance vehicle

Telerobotic - operate untended for long periodsStable - tipping forces when loaded



Evaluation Criteria (cont.)

Integrateable - ease of material transferCost effectiveMulti-functional

Dispose of reactor wasteSupport habitat

ReliableOperate in the equatorial lunar thermal environmentModifiable to the polar lunar thermal environmentSolar radiationNumber of major subsystemsNumber of motorsNumber of sealsNumber of moving partsProven technologyMaterial plugging pointsControl complexityDust generation



Pairwise Comparison Weighting

PAIRWISE COMPARISON Pr

oduc

tive

Capa

ble

Relia

ble

Powe

r Effi

cien

tM

aint

aina

ble

Cont

rolla

ble

Stab

leIn

tegr

atea

ble

Cost

Effe

ctiv

eM

ulti-

func

tiona

lTo

tal

Primary Criteria Ranking & WeightingPrimary Criteria Score Score +1 WeightProductive C R P P CO S I P P 4 Capable 9 10 17Capable C C C C C C C C 9 Integrateable 7 8 14Reliable R R R R S R I R R 7 Reliable 7 8 14Power efficient PE CO S I CE PE MF PE 3 Stable 7 8 14Maintainable CO S I MF CE MF 0 Controllable 5 6 10Controllable S I CO CO 5 Productive 4 5 8Stable S I S S 7 Cost effective 3 4 7Integrateable I I 7 Multi-functional 3 4 7Cost effective MF CE 3 Power efficient 3 4 7Multi-functional 3 Maintainable 0 1 2

1.7 scaling



Hierarchical Weighting

Seco

ndar

y W

eigh

t

Prim

ary

Wei

ght

CriteriaPrimary Secondary

Capable 17Horizontal reaction force 40Vertical reaction force 40excavate at least 1m deep 5ease of internal material handling 5Maximum Particle Size 5Sizing Capability 5

Integrateable ease of material transfer 14Reliable 14

operate in the equatorial lunar thermal environment 5modifiable to the polar lunar thermal environment 5solar radiation 5number of major subsystems 20number of motors 20proven technology 15material transfer points 10control complexity 10dust generation 10

Stable tipping forces when loaded 14Controllable telerobotic 10Productive 9

Cycle Time 75expandable to 500 kg/hr 25

Cost effective 7Multi-functional 7

dispose of reactor waste 50support habitat construction 25explore 25

Power efficient 7peak power 50total power per excavation cycle 50

Maintainable suited or robotic 2Total



Baseline Specifications

0.5 kgBuckets Mass4 kgBoom and auger Mass0.9 kgAuger mass

6 kgBucketwheel Boom Assembly Mass

2.3 kgTransfer Bed Mass

11 kgMobility Platform Mass

30 minDump Bed Exchange

17 min.One-way Travel Time0.33 m/minTravel Speed



Baseline Specifications (cont.)

0.25 min90° Swing 0.4 mBoom Length50 kg/hrAuger Capacity

0.8 kgMotor/Gear Assembly Mass

12.8 N (2.9 lbf)Horiz Force from32 N (7.2 lbf)Vertical Force

0.4Traction Ratio = Horiz/Vert Force

19.8 kgEmpty Mass

0.04 minExcavation Time per Bucket

120Buckets/Bed

0.14 kgBucket Material Mass

0.000086 m3Bucket Material Volume (-10%)

0.000095 m3Bucket Volume

0.04 kgEmpty Bucket Mass

0.6 kgWheel Mass



Alternative Concepts

Bucket WheelAugerBackhoe w/ Fork LiftBackhoe & TruckBoom Excavator w/ Fork LiftBoom Excavator & TruckBucket ChainBucket Ladder Bucket Wheel

Front-end Loader w/ Fork LiftFront-end Loader & TruckFront-end Loader & RakeOvershot LoaderPneumatic SystemScraperShovel w/ Fork LiftShovel & TruckThree-point Dragline



Alternative Concept Base Assumptions

Mobility Platform

Power - On-board batteries

Material transfer to reactor – dump bed

Waste material disposal – dump bed



Example Alternative Concepts

Auger and Scraper Shovel, Backhoe, and Loader



Example Alternative Concepts (cont.)

Dragline, Bucket Ladder, 3 pt. Boom & Pneumatic



Spec Sheets Developed for All Concepts

5Material Transfer Points15Motor/gear assemblies:6Subsystems:2.3 N (0.5 lbf)Vertical Reaction Force12.7 N (2.9 lbf)Horizontal Reaction Force19.6 kgSystem Mass - Unloaded134 minProduction Cycle:

Summary Specs for Bucket Chain



Decision Matrix

Seco

ndar

y W

eigh

t

Prim

ary

Wei

ght

Buck

et W

heel

Auge

rBa

ckho

e w/

For

klift

Back

hoe

& Tr

uck

Boom

Exc

avat

or w

/ For

klift

Boom

Exc

avat

or &

Tru

ck

Buck

et C

hain

Fron

t-end

Loa

der w

/ For

klift

Fron

t-end

Loa

der &

Tru

ck

Fron

t-end

Loa

der &

Rak

e

Over

shot

Loa

der

Scra

per

Shov

el w

/ For

klift

Shov

el &

Tru

ck

CriteriaPrimary Secondary

Capable 17 16 13 16 14 16 14 15 16 13 15 13 7.5 16 14horizontal reaction force 40 39 36 40 37 40 37 38 40 37 38 37 20 40 37vertical reaction force 45 42 33 45 31 45 31 38 44 29 38 29 20 45 31ease of internal material handling 5 3 5 5 5 5 5 4 5 5 5 5 2 5 5maximum particle size 5 5 0 5 5 5 5 5 5 5 5 5 0 5 5sizing capability 5 5 2 2 2 2 2 2 2 2 2 2 2 2 2

Integrateable ease of material transfer 14 14 14 10 7 10 7 14 10 7 7 14 14 10 7Reliable 14 12 11 13 11 12 11 13 13 11 9 13 11 13 11

number of major subsystems 30 15 23 23 23 23 23 23 23 23 15 23 30 23 23number of motors 30 28 29 27 16 27 15 29 29 18 17 29 30 27 16proven technology 20 20 10 15 20 10 15 10 15 20 10 15 10 15 20material transfer points 15 12 0 15 15 15 15 15 15 15 15 15 0 15 15dust generation 15 12 15 15 8 15 8 15 12 6 6 12 12 15 8

Stable tipping forces when loaded 14 14 14 6 8 6 8 14 10 12 12 14 14 6 8Controllable telerobotic 10 10 10 8 4 8 4 10 6 2 2 8 8 8 2Productive cycle time 8 8 8 4 4 4 4 8 4 4 4 6 6 4 4Cost effective 7 6 6 6 4 6 4 6 6 4 4 7 7 6 4Multi-functional 7 5 4 6 7 6 7 5 6 7 7 6 4 6 7

dispose of reactor waste 50 40 40 40 50 40 50 40 40 50 50 40 40 40 50support habitat construction 25 10 5 20 25 20 25 10 20 25 25 20 5 20 25explore 25 15 5 20 25 20 25 15 20 25 25 20 5 20 25

Power efficient 7 6 7 6 4 6 4 7 7 4 4 7 7 6 4Maintainable suited or robotic 2 2 2 2 1 2 1 2 2 1 2 2 2 2 1Total 100 93 88 77 64 77 63 93 79 66 66 89 81 77 62



Results

Bucket Chain (93)Bucket Wheel (93)

Overshot Loader (89)

space resources roundtable vii

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