1
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
2
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).
3
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
4
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.
5
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
6
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.
7
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
8
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
9
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.
10
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.
11
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.
[email protected] www.electric-sailing.com