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E-sail Test Mission – Reaching the Solar Wind With a CubeSat

1st Interplanetary CubeSat Workshop

Cambridge MA, USA

29-30 May 2012

Jouni Envall, Petri Toivanen, Pekka Janhunen

Finnish Meteorological Institute

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Electric Solar Wind Sail (E-sail)● Uses solar wind for spacecraft propulsion.

● Coulomb interaction between solar wind and long, thin, positively charged tethers (10-20 km, 25-50 μm wire, +20-40 kV).

● 1 N thrust from 100-200 kg system: 100-1000 times more efficient in a 10-year mission than chemical rockets and ion engines.

● Maximum speed > 50 km/s.

● Fastest and largest man-made device.

● Developed to TRL 4-5 in ESAIL FP7 (2011-2013).

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ESTCube-1

- Origin: Estonia.

- 1U CubeSat, polar LEO orbit.

- Measures E-sail force by 10 m tether, ±450 V voltage.

- Launch 2013.

Aalto-1

- Origin: Finland.

- 3U CubeSat, polar LEO orbit.

- 100 m tether, attempt to de-orbit.

- Launch 2014.Aalto-1

ESTCube-1 and Aalto-1 Test Missions

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Life after LEO• After the demonstrations at LEO the next logical step is to

perform tests in solar wind plasma.

• Simplified E-sail craft is taken to solar wind, tethers are deployed and E-sail thrust is observed.

• Preferred orbit: highly eccentric Earth orbit with apogee in solar wind.

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Solar Wind Test• Piggyback launch to a suitable starting orbit, e.g. GTO.

• Apogee raised with a dedicated thruster.

• Spinning commenced with a separate thruster.

• E.g. four 1-km main tethers, no auxiliary tethers.

• Several methods to observe E-sail thrust.

– Change in orbital parameters.

– Bending of tethers (on-board cameras).

– Direct measurement of acceleration.

Main craft

Tether

Tip mass

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CubeSat-SWEST: Example Setup• 3U CubeSat platform assembled from COTS parts.

• Ion thruster for apogee raise.

• Cold gas thrusters (Nanospace Ltd, Sweden).

– Attitude control during apogee raise.

– Thrust for spin-up in tether deployment phase.

• Four 250-meter tethers, 10 kV voltage.

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CubeSat-SWEST: Example Setup (2)

Aalto-1 tether reel system

Ion thruster beamCold gas thruster beams

Tether

Solar panel

Deployable solar panel

Tether reel system

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Mission Parameters• Satellite mass 4 kg (3U CubeSat).

• Orbit averaged power 10 W.

• Orbit perigee ~1000 km, apogee ~160 000 km.

• Thrusting phase 9 months (from GTO).

• Operations phase 3 months. Month 0

Month 12

Month 9

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Example Mass Budget

Item Mass, g

Structure 570

ADCS 248

EPS 398

COM 185

OBC 70

“Payload” 1985

Total, wet 3456

Margin 15% 518

Total with margin 3974

Item à mass N Total

Tether reel system 140 4 560

Electron gun 5 4 20

Ion Thruster, wet 630 1 630

CG Thruster, wet 300 1 300

High Voltage Source 160 2 320

Camera 30 4 120

Accelerometer 35 1 35

Total 1985

Masses for satellite platform are as stated by a commercial supplier.

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Remaining Challenges• Radiation.

– Many of the key subsystems available rad hardened.

– Mass budget is flexible (e.g. leave out one HV source, scale up to 6U etc.), → plenty of room for shielding.

– Not a major concern IMHO.

• Communications.

– Data dumps possible near perigee.

– Small amounts of data (~3 MB per orbit) will suffice.

– Equator vs Finland. Partner needed.

• Launch.

– Getting a piggyback to GTO not that trivial.

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Conclusions• 3U CubeSat could carry out an E-sail solar wind test mission

in 12 months.

• Launch into GTO.

• Apogee raised to 160 000 km (25 RE) with ion thruster.

• Satellite spun with CG thrusters, four 250-m tethers deployed, 10 kV voltage applied to tethers.

• Thrust observed 1) as change in orbital parameters, 2) directly with an accelerometer and 3) by imaging the tethers.

• CubeSat platform introduces its challenges for such mission, but no show stoppers appear to exist.

Jouni.Envall@fmi.fi www.electric-sailing.com