1. Scientific Mission Applications
P. K. Toivanen, P. Janhunen, and J.-P. Luntama

2. Outline Example mission to Mars Optimal orbit to Mars
Optimal operation of the sail
Optimal operations and real solar wind
Solar wind variations and sail performance
Density variations
Wind speed variations
Average performance
Tether voltage and navigation
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3. Electric sail and science missions About mass budget of electric sail
About economics of electric sail missions
Interstellar Heliospheric Probe (IHP)
Kuiper/centaur flyby mission
Asteroid tour
Space weather monitoring
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4. Optimal orbit to Mars Mengali, Quarta, and Janhunen:
Journal of Spacecraft and Rockets, 2008.
Solar wind speed, 400 km/s
Density, 7.3 cm-3
Electron temperature,12 eV
Radial scaling laws for the solar wind parameters
Total mass 200 kg
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5. Optimal operation of the sail
Optimal solution includes:
Initial acceleration of about 0.5 mm/s2 (Earth)
Coasting phase (shading)
Constant thrust angle of 20 deg
Acceleration at Mars of about 0.3 mm/s2
Travel time of 600 days
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6. Optimal operations and real solar wind
Varying density and speed:
Acceleration varies about 40% around the average
Mars missed!
But s/c kind of got there…
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7. Solar wind variations and sail performance
Some severe weather conditions:
Densities higher than 30 cm-3 may occur
Solar wind speed may be higher than 1000 km/s
Variations in acceleration far more mellow than those of the solar wind driving the sail
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8. Density variations Acceleration limited:
Electron current to the tethers increases
Electron gun power limited by the given solar panel power
Tether voltage drops
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9. Wind speed variations #1
Acceleration is regulated:
Solar wind speed drive not linear:
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10. Wind speed variations #2
For small wind speed values:
Solar wind kinetic energy less than the tether electric potential
Dynamic pressure term dominates
For large wind speed values:
Solar wind kinetic energy larger than the tether electric potential
Solar wind penetrates to the tether potential structure
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11. Average performance #1 3-month averaged thrust in cases of:
Limited tether voltage (40 kV, thick)
No tether voltage limitation (thin)
Variations relatively small around average at 70 nN/m
Missions can be desinged for the minimum thrust (dotted) without missing much of the maximum thrust (dashed)
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12. Average performance #2 Thrust vs. solar panel power:
For small power values, difference between the maximum and minimum thrust not large
For large power values, the minimum thrust saturates
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13. Average performance #3 Thrust vs. averaging window:
Down to averaging over about ten days, difference between maximum and minimum thrust does not change dramatically
Averages below ten days are not relevant in mission time scales
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14. Tether voltage and navigation
Simple navigation procedure:
Onboard accelerometer
Time-integrate measured acceleration for spacecraft speed, Vsc
Compare hourly Vsc with speed at optimal orbit, V0
If Vsc < V0, increase tether potential by 5kV for the next hour
If Vsc > V0, decrease tether potential by 5kV for the next hour
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15. Electric sail and science missions
High delta-v for small payloads
Interplanetary Heliospheric Probe (IHP)
Kuiper/Centaur flyby mission
Asteroid tour
Space weather monitoring
Other missions
Near-solar missions
Planetary missions
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16. Electric sail propulsion system
100 X 20 km aluminium four-fold Hoytether
Tethers: 7.3 kg (20 µm)
Reels: 22.0 kg (3 X tethers)
Electron gun + radiator: 1.5 kg (40 kV & 1kW)
High-voltage power source: 2.0 kg
Avionics + tether direction sensor: 7.0 kg
Solar panels: 6.0 kg (1.1 kW)
Battery Li-ion: 1.0 kg (8 Ah)
S/c frame with thermal isolation: 4.5 kg
AOCS thrusters: 1.0 kg
Total: 52.3 kg
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17. About economics of electric sail missions
Payload more expensive than the launch
Soyuz-fregat: 1.3 ton payload to escape orbit
Electric sailer with 1.3 ton payload accelerates slowly
Smaller booster saves no that much
4-6 electric sailers per launch
Piggybag
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18. Interstellar Heliospheric Probe
Fast flight to interstellar medium:
Formation of the heliosphere
Pioneer anomaly
Present proposed mission time is tens of years
Electric sailer is an enabling technology
Reduced travel time
Weight issue
Use of several electric sailers
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19. Kuiper/centaur flyby mission
Properties of primoidal objects:
Group of flyby probes, target per probe
One launch with Siamise Twins spin-up for each pair
Small payload (total mass kg)
Minimal instrument set only to study the target
Fast travel time
Fast flyby, data into memory and slow downloading
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20. Asteroid tour More for the same money:
Single electric sailer can visit several asteroids
Water/hydrogen on asteroids
Mineral composition
Morphology
Imager, radar, and spectroscope (infrared, neutron, and gamma)
Shoot bullet with a railgun
Laser heating
Micrometeor flashes on dark side
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21. Space weather monitoring
Off-Lagrange point monitoring:
Propellantless operation needed
Longer than the 1-hour time delay to Earth (solar wind)
Solar wind monitoring for other planet missions (as a piggybag)
Tether voltage cycled:
off during monitoring
on during orbit control
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