micro asteroid prospector

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Micro Asteroid Prospector Powered byMicro Asteroid Prospector Powered by

Energetic Radioisotopes: MAPPEREnergetic Radioisotopes: MAPPER

Steven D. HoweSteven D. Howe

Gerald P. JacksonGerald P. Jackson

Presented at the NIAC Review MeetingPresented at the NIAC Review Meeting

March 23, 2004March 23, 2004


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Topics PresentedTopics Presented

Goals and objectivesGoals and objectives

Target characterizationTarget characterization-- Main Belt AsteroidsMain Belt Asteroids

SubSub--SystemsSystems

Preliminary optimization calculationsPreliminary optimization calculations

IssuesIssues

ConclusionsConclusions


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Goals and ObjectivesGoals and Objectives

Purpose: Catalogue the resources of the Main BeltPurpose: Catalogue the resources of the Main Beltasteroids for future explorationasteroids for future exploration

Goal: Design a lightGoal: Design a light--weight, inweight, in--expensive spacecraftexpensive spacecraftso that a fleet can cruise autonomously through theso that a fleet can cruise autonomously through the

Belt for 20 yearsBelt for 20 years

Objectives:Objectives:

Determine mass, power, and number of spacecraft forDetermine mass, power, and number of spacecraft forcharacterizing a signif icant fraction of the Main Beltcharacterizing a significant fraction of the Main Beltasteroidsasteroids

Identify major issues and future goalsIdentify major issues and future goals


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Main Belt AsteroidsMain Belt Asteroids

The Asteroid Belt may be the most valuable future resourceThe Asteroid Belt may be the most valuable future resourcein the solar systemin the solar system

The asteroid belt is estimated to contain 100 bill ion objects.The asteroid belt is estimated to contain 100 bill ion objects.

The total mass is calculated to be around 1/1000 of EarthsThe total mass is calculated to be around 1/1000 of Earthsmassmass -- equivalent to breaking the top 1.3 miles of the Earthsequivalent to breaking the top 1.3 miles of the Earths

crust into piecescrust into pieces

Diameters range from a few kilometers to a few metersDiameters range from a few kilometers to a few meters

Most of the asteroids are silicon dioxide, some are iron andMost of the asteroids are silicon dioxide, some are iron andother metals, a lesser number are carbonaceousother metals, a lesser number are carbonaceous chondriteschondriteswith up to 10 % water by weight, and a few may be heavywith up to 10 % water by weight, and a few may be heavyprecious metals.precious metals.

Average separation distance is 2.3x10Average separation distance is 2.3x1044 km forkm for DminDmin=20m=20m


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The main belt asteroid sizeThe main belt asteroid size--frequencyfrequency

distribution approximately follows a power lawdistribution approximately follows a power law

Ntot=2.88e06 D-2.27

(Adapted from(Adapted from FarinellaFarinella and Davis, 1994)and Davis, 1994)


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The asteroids in the belt are notThe asteroids in the belt are not

uniformly distributed but form bandsuniformly distributed but form bands


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SubsystemsSubsystems

Th MAPPER i hTh MAPPER t i th


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The MAPPER concept requires theThe MAPPER concept requires the

integration of many subsystemsintegration of many subsystems

A power supply to provide electrical power to a platform thatA power supply to provide electrical power to a platform thatcancan propulsivelypropulsively cruise between targetscruise between targets

A radiation detector system that can measure elementalA radiation detector system that can measure elemental

constituents at a standoff distance,constituents at a standoff distance,

A heating system that can extract and store volatiles forA heating system that can extract and store volatiles forpropulsion,propulsion,

A tagging method to label the target for future generations.A tagging method to label the target for future generations.

A method of absolute coordinate location determination viaA method of absolute coordinate location determination viastar tracking or interstar tracking or inter--communication with Earth or a fixedcommunication with Earth or a fixedbeacon.beacon.

Radar system sufficient to provide guidance to the nextRadar system sufficient to provide guidance to the next

target and avoidance of smaller objectstarget and avoidance of smaller objects A communication link to EarthA communication link to Earth


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POWERPOWER


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232232U offers high specific powerU offers high specific power

The decay sequence ofThe decay sequence of 232232UUreleases 25% of the energy perreleases 25% of the energy peratom of a nuclear reactor butatom of a nuclear reactor butrequires no critical massrequires no critical mass

55 W(th)/gW(th)/g peak is 10 timespeak is 10 timesPu238Pu238

Power scales linearly with massPower scales linearly with mass

Relatively flat over 20 yearRelatively flat over 20 year

periodperiod Production:Production:

Available in spent fuelAvailable in spent fuel

Fast neutron irradiate UFast neutron irradiate U--233233

Accelerator irradiate ThAccelerator irradiate Th--232232 Uses tuned PV conversionUses tuned PV conversion

High gamma activity requiresHigh gamma activity requiresstandoff from platformstandoff from platform

ISSUE: l ifetime of tuned PVISSUE: l ifetime of tuned PV

Preliminary estimates of power source activityPreliminary estimates of power source activity


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Preliminary estimates of power source activityPreliminary estimates of power source activity(3e04(3e04 CiCi) are well below past launch history for) are well below past launch history for

the USthe US


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Power levels and mass of the power system varyPower levels and mass of the power system vary

strongly with average cruise velocity andstrongly with average cruise velocity and IspIsp


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PROPULSIONPROPULSION

Mi d i h ff h i l


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Microwave driven thrusters offer the potentialMicrowave driven thrusters offer the potential

of long life due to low surface interactionsof long life due to low surface interactions

(courtesy of(courtesy of http://www.islandone.org/APC/Electric /04.html)http://www.islandone.org/APC/Electric /04.html)
http://www.islandone.org/APC/Electric/04.html)http://www.islandone.org/APC/Electric/04.html)http://www.islandone.org/APC/Electric/04.html)


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RefuelingRefueling


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Refueling sequenceRefueling sequence

Cruise

vector

Neutron probe

Water = Yes then decelerate

V = cruise velocity

T = Taccel

Return to asteroid in 1.4 Taccel days

Accelerate for distance and decelerate

for distance

Accelerate up to

Vcruise in Tacceldays

Water = NO

Then radar

search andcourse correct


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Microwaves couple toMicrowaves couple to regolithregolith

In 1985, Dr. T. Meek of theIn 1985, Dr. T. Meek of theLos Alamos NationalLos Alamos National

Laboratory (LANL)Laboratory (LANL)demonstrated the ability todemonstrated the ability toextract water from simulatedextract water from simulatedlunar soil using 2.45 GHZlunar soil using 2.45 GHZmicrowaves.microwaves.

According to Meek, usingAccording to Meek, usingconventional means to heatconventional means to heatthe soil would require 10,000the soil would require 10,000

times more energy thantimes more energy thanusing the microwaves tousing the microwaves toselectively heat the water inselectively heat the water inthe soil.the soil.

2.45 GHz microwaves for 15 s2.45 GHz microwaves for 15 sonto lunar soil sampleonto lunar soil sample


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DETECTIONDETECTION


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Neutron SourceNeutron Source

Original concept usedOriginal concept used 232232U plus Beryllium to makeU plus Beryllium to makeneutrons via (neutrons via (,n,n) reaction) reaction 44 sourcesource

Created too much backgroundCreated too much background

Irradiated componentsIrradiated components

Required close approach, i.e. < one diameterRequired close approach, i.e. < one diameter

Propose H(Propose H(66Li,n) mini acceleratorLi,n) mini accelerator 13.213.2 MeVMeV 66LiLi

1010oo

cone of emissioncone of emission Pulsed, intense source fired during flyby closest approachPulsed, intense source fired during flyby closest approach

Optimum standoff distance is 3 X diameterOptimum standoff distance is 3 X diameter

Flight qualified neutron detector hasFlight qualified neutron detector has


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Flight qualified neutron detector hasFlight qualified neutron detector has

been flown to find water on the Moonbeen flown to find water on the Moon

Designed and built atDesigned and built at

LANL by W. FeldmanLANL by W. Feldman

Weight: 8 lbsWeight: 8 lbs

Electrical powerElectrical power reqdreqd: 3: 3

ww

33He tubesHe tubes

Returned neutronReturned neutron

spectrum dependsspectrum depends

strongly on hydrogenstrongly on hydrogen

contentcontent

Issue: lifetime

Howe problem

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

neutron energy

flu

x

3%water

water

10%

Issue: lifetime

Flight qualified gammaFlight qualified gamma--ray detector hasray detector has


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Flight qualified gammaFlight qualified gamma-ray detector hasray detector has

been flown measure gammas on the Moonbeen flown measure gammas on the Moon

Designed and built atDesigned and built at

LANL by W. FeldmanLANL by W. Feldman

Weight: 3 lbsWeight: 3 lbs

Electrical powerElectrical power reqdreqd: 2: 2

ww

BGO crystalsBGO crystals

Gamma rays identifyGamma rays identify

heavy metalsheavy metals

CdZnTeCdZnTe oror HgIHgI maymay

provide better resolutionprovide better resolution


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TAGGING and COMMUNICATIONTAGGING and COMMUNICATION


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Smart Dust sensors developed at Berkeley low massSmart Dust sensors developed at Berkeley low mass


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Smart Dust sensors developed at Berkeley low massSmart Dust sensors developed at Berkeley low mass

and long lifeand long life

ProPro

Low massLow mass

Broadcast widely, i.e.Broadcast widely, i.e.44

Reasonable rangeReasonable range

ConCon--

Power neededPower needed

Less secureLess secure

Limited lifeLimited life

Radiation mayRadiation maydegradedegrade

(courtesy of(courtesy of

http://http://robotics.eecs.berkeley.edu/~pister/SmartDustrobotics.eecs.berkeley.edu/~pister/SmartDust /)/)

Communications back to Earth rely onCommunications back to Earth rely on


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Communications back to Earth rely onCommunications back to Earth rely on

demonstrated technologiesdemonstrated technologies

Galileo transmissions required 400 w onGalileo transmissions required 400 w on

board powerboard power Platform will determine location from splitPlatform will determine location from split

field of view star sensors (field of view star sensors (

StarNavStarNav

II)II)

[http://www.jsc.nasa.gov/aiaa/lal/lljun01/][http://www.jsc.nasa.gov/aiaa/lal/lljun01/]

Information burst will include location,Information burst will include location,

measured gammameasured gamma--ray and neutronray and neutronspectra, and ship status dataspectra, and ship status data


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GUIDANCEGUIDANCE

The architecture depends on the averageThe architecture depends on the average


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e a c ec u e depe ds o e a e agep g

velocity of the craftvelocity of the craft i.e. cone of acceptabilityi.e. cone of acceptability

A light weight radar is required but does notA light weight radar is required but does not


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A light weight radar is required but does notA light weight radar is required but does not

yet existyet exist

Needs to see 156,000 km outNeeds to see 156,000 km out

Correlate distance with return signal strength (RSS) andCorrelate distance with return signal strength (RSS) and

target sizetarget size Indicate water content (i.e.Indicate water content (i.e. albedoalbedo) with RSS) with RSS

Determine relative velocity with multiple returnsDetermine relative velocity with multiple returns

May require power accumulator to operate in highMay require power accumulator to operate in high--powerpowerbut pulsed modebut pulsed mode

Determines required deltaDetermines required delta--VV

Enables target choiceEnables target choice

Issues:Issues: baseline needed for Synthetic Aperture Radar ?baseline needed for Synthetic Aperture Radar ?

power level?power level?

OptimizationOptimization


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OptimizationOptimization

DeploymentDeployment Nuclear Thermal RocketNuclear Thermal Rocket


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DeploymentDeployment Nuclear Thermal RocketNuclear Thermal Rocket

Current NASA program, Prometheus, isCurrent NASA program, Prometheus, isinterested in recovering the NTR to fulfill the newinterested in recovering the NTR to fulfill the new

Presidential space exploration directionPresidential space exploration direction NTR is considered to be a demonstratedNTR is considered to be a demonstrated

technology that could be recovered within atechnology that could be recovered within a

decadedecade Assumed operating parametersAssumed operating parameters

5000 lb thrust engine5000 lb thrust engine

T/W = 3T/W = 3 IspIsp= 950 s= 950 s

HohmannHohmann transfer orbittransfer orbitsum ofsum of VsVs= 9.52 km/s= 9.52 km/s

Reusable for N missionsReusable for N missions

Preliminary optimization calculationsPreliminary optimization calculations


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y p

are positiveare positive

Power level is dictated by the propulsion systems need toPower level is dictated by the propulsion systems need toaccelerate over a short period (variable)accelerate over a short period (variable)

The same power level is sufficient for communications backThe same power level is suff icient for communications backto Earth, water extraction, neutron generation, and the radarto Earth, water extraction, neutron generation, and the radarsystems.systems.

The average cruise velocity,The average cruise velocity, IspIsp, time of acceleration, and, time of acceleration, andinterception velocity are independent variablesinterception velocity are independent variables

Propellant requirements for initial acceleration to cruise,Propellant requirements for initial acceleration to cruise,intercepts, and refueling are determinedintercepts, and refueling are determined

Power system mass including waste heat radiator is found forPower system mass including waste heat radiator is found forthe tuned PV methodthe tuned PV method

Ship characteristics depend strongly onShip characteristics depend strongly on


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the average cruise velocitythe average cruise velocity

Significant surface area can be scannedSignificant surface area can be scanned


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by reasonable cruise velocityby reasonable cruise velocity

Optimum specific impulse lies withinOptimum specific impulse lies within


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achievable valuesachievable values

Preliminary cost optimization indicatesPreliminary cost optimization indicates


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lower than expected cruise velocitylower than expected cruise velocity

Phase II will strive to resolve severalPhase II will strive to resolve several


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issuesissues

LifetimesLifetimes-- Power conversionPower conversion scintillatorscintillator

RFRF taggerstaggers Microwave generatorMicrowave generator

detectorsdetectors

Need time dependent simulation to developNeed time dependent simulation to developguidance, control algorithms, andguidance, control algorithms, and VVinterceptintercept

RadarRadar mass and powermass and power

Earth communicationsEarth communications PackagingPackaging-- is the platform volume limited oris the platform volume limited or

mass limitedmass limited

C l i


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ConclusionsConclusions

A host of small platforms can survey a significantA host of small platforms can survey a significantfraction of the asteroid population in a 20 yearfraction of the asteroid population in a 20 year

intervalinterval The land area surveyed could be equal to aThe land area surveyed could be equal to a

major fraction of the Earths surface areamajor fraction of the Earths surface area

The energetic radioisotope power supplyThe energetic radioisotope power supplyappears adequate for the mission needsappears adequate for the mission needs

Most subsystem hardware has currentMost subsystem hardware has current--dayday

examples that can be improvedexamples that can be improved A timeA time--dependent simulation is needed for flightdependent simulation is needed for flight

profile demonstration and targeting algorithmprofile demonstration and targeting algorithmdevelopmentdevelopment

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