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Dienstag 13.03.07, Mühlleithen:

Workshop „Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen“

Horst W. Löb

RAUMFLÜGE MIT ELEKTRISCHEM RAUMFLÜGE MIT ELEKTRISCHEM RAUMFLÜGE MIT ELEKTRISCHEM RAUMFLÜGE MIT ELEKTRISCHEM ANTRIEB UND ANTRIEB UND ANTRIEB UND ANTRIEB UND EINE STUDIE ÜBEREINE STUDIE ÜBEREINE STUDIE ÜBEREINE STUDIE ÜBERDIE LANDUNG AUF DEM DIE LANDUNG AUF DEM DIE LANDUNG AUF DEM DIE LANDUNG AUF DEM JUPITERMOND EUROPAJUPITERMOND EUROPAJUPITERMOND EUROPAJUPITERMOND EUROPA

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Bepi-Columbo:

Start: Aug. 2013

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Deep Space 1,

Start: Okt. 1989

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NSTAR,

30 cm Kaufman-Triebwerk

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ARTEMIS,

Start: Juli 2001

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4 NSSK-Triebwerke:

2 UK-10

2 RIT-10

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SMART-1:

Start: Sept. 2003

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PPS-1350 :

Halleffekt-Triebwerk

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MUSES-C:

Start: Mai 2003

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4 Mikrowellen-Ionentriebwerke

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DAWN, Start: Sommer 2007(?)

3 NSTAR-Kaufman-Triebwerke

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JIMO(NEP, Prometheus)

Jupiter Icy Moons Orbiter

Expected 2017

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• 1. Referenz-Mission: FORTUNA

Vergleich NASA-Flug „DAWN“ zu Vesta/Ceres (Orbiter)

CONSEP-Studie : Round Trip zu Fortuna (Sample Return)

DAWN: 3 NSTAR + 10 kW GaAs-Panel, Mars Gravity Assist

CONSEP: 3 RIT-22 + 19 kW Si-Panel, keine Gravity Assist

DAWN: Startmasse 1,24 to, Missionsdauer 8 Jahre

CONSEP: all-SEP 1,54 to, 4,6 Jahre

hybrid 2,05 to, 4,1 Jahre

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SEP FOR A LANDER MISSION TO THE JOVIAN MOON EUROPA

H.W. Loeb and K.-H. Schartner, Giessen University

Wolfgang Seboldt, Bernd Dachwald, and Joern Streppel , DLR Cologne

Hans Meusemann and Peter Schülke, German Aerospace Center Bonn

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• Europa is the second Galilean Moon of Jupiter(Jupiter distance: 9.4 RJ).

• Beneath a ca. 20 km thick icy shell,a deep, warm, salty-water ocean is supposed.

• In such a habitable environment:Is there a biological evolution?

• Tectonic activities caused fractures of theicy crust, subsurface material intrudedand reached the surface causing long "bands".

• There, in-situ measurements may trace outorganic-chemical compounds.

EUROPA – A HIGHLY INTERESTING TARGET

Photo: NASA

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• SEP-task: transport a chemical cruise & landing vehicleinto a high circular orbit around Jupiter(e.g. 80 RJ altitude), with SEP-payload ratio ca. 25 %

• BOM: SEP-spacecraft has escape velocity from Earth, but C3 = 0,no interplanetary GA

• Challenges:

EUROPA-MISSION TASK AND PROBLEMS

- very high analytical ∆v-requirement: interplanetary 16.7 km/s + spiraling-down4.7 km/s

- decrease of solar constant at Jupiter by factor 27.0,using LILT-solar cells: factor 19.4 (incl. degradation)

- severe radiation environment near Europa: 1 Mrad/month (even with4 mm Al-shielding) prohibits SEP operation

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• Solar power plant:

SEP-STRATEGY

- panels with triple junction GaAs-cells (LILT), high efficiency (> 25 % at BOM)

- flat mirror concentrator (tilted by 50 deg.); stepwise deployment

• Two-stages EP-system:- 1st stage: to save propellant and launch mass (Ziolkowsky):

cluster of high-Isp ion thrusters

- 2nd stage: to shorten transfer time at reduced solar power (F/P~1/Isp):cluster of low-Isp thrusters

• In favour of a "mission performance quality factor" Q (launch mass x EP-thrusting time), the 1st stage is jettisoned after its burn out;analyses show the related Q-advantage over single-stage versions withthrusters of optimized Isp = const and HIsp-LIsp-combinations (see paper).

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MISSION PROFILE – LARGE & SMALL-SCALE VERSIONS

• Large-scale version "Europa-L": maximum science return

- 50 kg instruments on Europa's surface + 35 kg in SEP-bus

- launch mass of chemical vehicle in Jupiter orbit (80 RJ): 1350 kg

- solar power plant at BOM: 67 kWe

- 6 HIsp + 4 LIsp ion thrusters

- SEP launch mass: 5.47 to (analytical) and 5.25 to (numerical)

• Small-scale version "Europa-S": BOM-mass fits e.g. to medium classlauncher- all masses, solar power, number of ion thrusters are halved:

25 kg scientific equipment on Europa, 33.5 kWe at BOM, 3 + 2 ion thrusters

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MISSION PROFILE – EUROPA-L

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MISSION OPTIMIZATIONS (EUROPA-L)

• Calculation procedure: standard using classical ∆vEP-formula (see paper)

• Inputs: chemical vehicle 1350 kg, bus 800 kg, two solar wings 804 kg, RIT-22 clusters

• Optimizations:- beam voltage (Isp) of the first-stage RIT-22 engines

- beam voltage (Isp) of the second-stage RIT-22 engines

- Sun distance at EP-stages separation (jettison of 1st stage)

- parking orbit of SEP-mothership in Jupiter system = launch altitude of chemical craft)

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Isp OPTIMIZATION OF FIRST EP-STAGE

U+1 = 4.0 kV → Isp = 6600 s

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Isp OPTIMIZATION OF SECOND EP-STAGE

U+2 = 1.25 kV → Isp = 3700 s

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OPTIMIZATION OF DISTANCE FROM SUNAT STAGE SEPARATION

U+1 = 4.0 kV

U2 = 1.25 kV

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OPTIMIZATION OF SEP-PARKING ORBIT IN JUPITER SYSTEM

• Hohmann-trajectories of chemical craft includes single GA at Callisto and Ganymed

• Instruments on-board SEP-mothership map Jupiter's outer magnetosphere duringspiraling-down

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CHEMICAL TRANSFER & LANDING VEHICLE (EUROPA-L)

• Trajectory:80 RJ → 1 Callisto GA → 1 Ganymed GA →Europa capture

• 1 – 2 weeks reconnaissance + remote sensingfrom circular 100-km orbit, thenlanding and 2 weeks in-situ measurements

• propulsion unit 115 kg: Babakin's study for"BepiColombo" 2002975 kg MMH + NTO, Isp = 330 s

• scientific instrumentation 50 kg:- ground penetrating radar system(ESA: "JME" 2005)

- ultrasonic corer on robotic arm and chemistry labsfor sample ("Cadmus", Georgia Inst. Techn. 2004)

- pancam, descent imager, seismometer, spectrometer, etc.

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EUROPA-L SPACECRAFT

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ION THRUSTERS RIT-22

• RIT-22 (EADS-ST) has been chosen forcalculation because

- it is already under qualification (U+ ≤ 2.1 kV),

- the absence of discharge electrodes guaranteesa reliable operation and long lifetime,

- the thrust control only by Prf (at given ) simplifies cluster operation,

- a suited modification of grid systemenables operation at Isp ≤ 7000 s.

m&

• Following a test campain of EADS-ST (April 2005),Giessen team modelled the thruster for variable Isp.A 4.0-kV grid system has been sketched.

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HIsp- AND LI sp-DATA OF RIT-22

*) approximately constant up to a throttling of about 65 %**) related to lifetime limit

47021.3

19044.7

max. propellant consumption, in kg**)mass of propulsion unit, in kg

33.730.926

21.700.335

thrust-to-power ratio, in mN/kW*)

propellant flow per power, in mg/kWs*)

4.02135.5

11.11241

PSCU power consumption, in kWthrust (nominal), in mN

1.253704

4.06591

beam voltage, in kVspecific impulse, in s

RIT-22 LIspRIT-22 HIsp

Maximum propellant consumption during lifetime (γ = sputtering rate):

)U()k V1.2(

sm g7 2.3h r s0 0 0,2 3m a xm

+γγ⋅⋅=

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TWO-STAGE PROPULSION MODULE (EUROPA-L)

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EP-PERFORMANCE DATA

151.5272.5303545total stage mass (dry), in kg

42.534

75**)

13438.5100

8568

150**)

26877

200

mass of propulsion units, in kgtank mass, in kgstructure mass, in kg

0.2718.037.44

0.7233.3211.16

0.54216.0714.88

1.4566.6322.31

nominal thrust, in Nnominal PSCU-consumption, in kWnominal propellant consumption, in mg/s

2 LIsp45.1

3 HIsp85.4

4 LIsp45.1

6 HIsp85.4

number of thrusters and typeload of thruster per lifetime, in %*)

2nd2nd2nd2ndstagestagestagestage

1st 1st 1st 1st stagestagestagestage

2nd 2nd 2nd 2nd stagestagestagestage

1st 1st 1st 1st stagestagestagestage

EuropaEuropaEuropaEuropa----SSSSEuropaEuropaEuropaEuropa----LLLL

*) all thrusters are symmetrically loaded by cluster switching; **) integrated in the bus

load of thrusters per lifetime: m a x

TmNmß

⋅=

with mT = propellant mass

N = number of thrusters

mmax = maximum propellant consumption

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COMPARISON OF EUROPA-L AND EUROPA-S PERFORMANCES

3.78 + 1.763.78 + 1.76thrusting time, in yrsinterplanetary + spiraling down

0.880.912.74

1.761.825.47

burn-out mass of SEP-spacecraft*), in toXe-propellant mass (two stages), in toSEP-launch mass, in to

250.675

501.35

scientific equipment on Europa's surface, in kglaunch mass of the chemical vehicle, in to

Europa-SEuropa-L

*) after launch of the chemical vehicle and jettison of the 1st EP-stage

NOTE: All specified data of launch mass, propellant mass, and thrusting/transfer-time are based on the classical EP-computation of ∆v.Trajectory optimizations show, however, that all the data are significantlysmaller because the trajectories are not narrow spirals.

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SPIRALING-DOWN IN JUPITER SYSTEM

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INTERPLANETARY TRANSFER TRAJECTORY

140 days coasting

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CONCLUSIONCONCLUSIONCONCLUSIONCONCLUSION

• A SEP-mission to Jupiter with landing a chemical vehicle on Europa is well feasible if- stage principle is introduced into EP,- the solar array is equipped with concentrators, deployed step by step, - the propulsion strategy is carefully optimized.

• A large SEP-ship of 5.25 tons launch mass is capable to deposit 50 kg of scientific instruments onto Europa's surface.The masses may be scaled down e.g. by a factor of 2.

• The total transfer time to Europa could be kept within about 6 yrs.

• The scientific return comprises the mapping of Jupiter's outer magnetosphere, remote sensing of and in-situ measurement on Europa.

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Jupiter to Europa:“ Look, a SEP-spacecraft“