SHEPHERD* - A Concept for Gentle Asteroid Retrieval with a Gas-Filled Enclosure

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Dan Lesterarchivelist.htm

Dan Lester

Dan Lester

Introduction: Asteroid 2008 TC3

20h advanced warning 1.2kT; 4m

Spin/precession period: 99.0/97.0 sec.

2008 October 7

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ARM option A E:O%#5$7"#)U%M%,6588%VWM6%F(56"#"$%5)#"$=(F%M%/F"588;%5'%('#"$")#('7%='"%+9$(6(#(X"1%

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Strength in atmospheric entry

Rubble pile asteroid

" Gravity & Rotation: Surface gravity of 180-m sized asteroid = 0.00001 G (micro G); fast rotating 360-m 1999 KW4: 25 Pa)

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Asteroid mining

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Asteroid mining

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SHEPHERD: capture & handling

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Feasibility " Up to 10 metric ton Xe as fuel

! Use 2 metric ton in 20-m enclosure, 0.1 atm (10 kPa) pressure " Internal energy of gas: 6 x 10^7 J

! Spin kinetic energy of 100-1000 metric ton asteroid: 1 x 10^3 J; Tumble kinetic energy ~1 x 10^3 J

! Gas is not heated significantly if turbulent dissipation ! Turbulent dissipation to 1% of gas in enclosure, drag power is

0.5 J/s > about 7h needed for dissipation " Apply force to enclosure to gently dissipate angular

momentum ! Gas may start co-rotating, dissipate to enclosure: dissipate with

external engine ! Increases time for angular momentum dissipation (order of

magnitude longer?)

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Gentle ARM option A -'7('""$('7%3?588"'7")%6"#U%M%

15-m , 0.1 atm balloon (ULD1)

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SHEPHERD: soft structure vs rigid

Outer and inner envelopes separated by air beams supporting ductwork and blisters with lighting, cameras I_%

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Key issue: how to seal enclosure T)"%)#(3*;%

SHEPHERD: capture

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SHEPHERD: alternative to sealing

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Other issues: power generation, thermal management

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SHEPHERD: re-direct 4$(X('7%!?5)"U%75)%g=H%5'F%$"3;38('7%

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Feasibility " 1.5 N of force applied to enclosure by SEM

! To transfer 1.36 N to asteroid requires flow velocity of about 2 m/s if directed to 1 m2 area (4-know wind, light breeze)

! Stable in sense that undersupply of force will drift asteroid closer to gas outlet, oversupply will drift asteroid away

! Requires pumping about 2 m^3/s of Xe gas for duration of cruise phase

" Gas loss during cruise phase ! Operational pressure much lower than 0.1 atm. ! Micrometeoroid impacts can cause leaks (in 5-y mission,

largest meteoroid to hit would be about 0.2 cm ) " Other forces

! Solar radiation pressure on enclosure much less than supplied force

! Force due to gas leaks, can be compensated by gas thrusts into enclosure

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Key issue: autonomous control LIDAR for proxops

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Blister: thruster,

return vent, lighting, camera

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Bring asteroid in-tact to Earth

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Future in-space operations for asteroid mining: CO gas mineral extraction, electroforming

(Mond process)

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Volatiles capture, condensation, separation

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Liquid phase biosphere harvesting consumables

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Contact: Petrus.M.Jenniskens@nasa.gov

bdamer@digitalspace.com JJ%