<Micro-propulsion> IFP ESTEC, 8th July 2011 Prepared by the ICPA / CDF* Team

EuLISA

(*) ESTEC Concurrent Design Facility

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Micro-thrust Propulsion Subsystem (MPS)

Requirements and Design Drivers

‒  Basic requirements coming from LISA Pathfinder MPS specification although: ‒  Larger thrust noise accepted (two order of magnitude

higher for cold gas) ‒  Slower thrust response time accepted (cold gas)

‒  Overall mass budget: to be optimized (cold gas) ‒  Overall power budget: to be optimized (electric

propulsion) ‒  Overall accommodation: to be optimized (cold gas

tanks)

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MPS options for LISA

–  MPS based on 12 Caesium FEEP thrusters design (LPF baseline)

–  MPS based on 12 miniRIT thrusters design, optional and under assessment for LPF

–  MPS based on 12 GAIA type cold gas thrusters, optional and under assessment for LPF

Cs FEEP

Mini RIT

Cold Gas thrusters

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Caesium FEEP MPS architecture

—  LPF FEEP MPS is composed by 3 elements (MPA), each comprising: — One Power Control Unit (PCU) each

commanding/controlling 4 thrusters — One LPF Neutralizer Assembly with 2

units (1 cold redundant) — One cluster structure hosting 4 FEEP

thrusters each equipped with its own tank filled with Cs propellant

— Tank size needs to be increased to host propellant load necessary to achieve LISA total impulse

—  Nominal FEEP arrangement has therefore 12 thrusters in 3 clusters, fully symmetric.

—  They are all 12 nominally operating. If one fails => 11 operating

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Cs FEEP MPS wet mass budget

LPF Caesium load per tank = 90g

LISA Caesium load estimated considering worst single thruster total impulse

Consequently, tank mass and cluster mass increase

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miniRIT MPS architecture ‒  LISA mini RIT MPS is composed by:

‒  3 Power Control Unit (PCU) each connected to 4 thrusters

‒  3 LPF Neutralizer Assembly with 2 units (1 cold redundant)

‒  3 cluster structure each hosting 4 mini RIT thrusters and 4 RFG

‒  Common xenon storage and feeding system with the high pressure part of the xenon distribution placed on the panel hosting the tank (tbc)

‒  Nominal miniRIT arrangement has therefore 12 thrusters in 3 clusters, fully symmetric.

‒  8 out of 12 are nominally operating. If one fails => change to different set of 8 thrusters

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miniRIT MPS wet mass budget

Xenon load computed considering 8 thrusters firing at 5µg/s for 5 years

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GAIA proportional COLD GAS MPS architecture

–  LPF cold gas MPS is composed by: –  2 MPE each commanding/controlling 6

thrusters –  3 clusters each hosting 4 cold gas

thrusters –  Common N2 storage and management

system with the high pressure part of the N2 distribution placed on a panel near the tanks (tbc)

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Cold gas MPS wet mass budget

The 2 tanks can be replaced by single 178litre tank (0.7mD; 39.5kg)

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Total impulse, propellant load —  ASU/ESA model based on:

— Minimum thrust capability —  Thrust noise level —  Number of thrusters operating —  S/A size —  Cant angle —  Solar radiation pressure net

force per area —  Model has been optimized mainly

for cold gas to reduce propellant load and number of tanks to be accommodated

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MPS Power Budget

— ESA model based on: — miniRIT MPS power consumption — results from miniRIT breadboard test performed in February 2011 — thruster EOL condition of 10% increase in RFG power — Assumed fixed power loses at PCU level — LISA sizing case: EOL LTP science with 8 thrusters at 20 µN — miniRIT MPS power architecture: 1 PCU operating 4 thrusters and no neutraliser plus 2 PCU's each operating 2 thrusters and one neutraliser

— MPS power budget:

— BOL = 155W — EOL = 164W

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Micro-propulsion Total Impulse

(Ns)

Dry mass (kg)

ISP (sec)

Propellant load (kg)

Total Mass with

margins (kg)

Volume constraints

(m3)

TRL MPS EOL Power (W)

FEEP 52771 (6m2 SA, canting 45°) 7000Ns worst single thruster for tank sizing

53 2300 (test) 4600 (LPF spec) 6000 (redesign)

3.7 (320g on each tank) Caesium

56.7 3 x LPF PCU volumes

5 (qual. shall resume on June 2012)

214W (EOL LTP science 12 x 20µN, Iacc =0 .8mA) 158W (EOL LTP science 8 x 20µN, Iacc = 0.5mA )

miniRIT 67222 (6m2 SA, canting 45°)

42 Propellant load computed as xenon flow of 5microg/s consumed by 8 thrusters for 5 years

6.3 xenon

52.7 3 x LPF PCU volumes 1 tank 0.56X0.168D

4 to 5 (subsystem PDR planned Jan 2012 LPF)

164W (EOL LTP science 8 x 20µN)

GAIA cold gas

23182 (optimized canting 25°, 5m2 SA)

71 45 54.5 nitrogen

127 2 tanks 0.88X0.425D (alternatively 1 tank 0.7D ITAR) 2 x GAIA MPE boxes

7 (qualified for GAIA, not flown)

<51

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MPS conclusion

— All 3 MPS options can be used for LISA: — LISA CDF study system budget assumes worst case for:

— Mass budget => Cold Gas MPS — Power budget => MiniRIT/FEEP MPS

— LISA CDF study configuration assumes the need to accommodate up to 2 cold gas tanks — accommodation is very tight — further analysis is needed to confirm/reduce Total Impulse

— Confirmation is needed that cold gas thrust noise and response time are accepted for LISA