Scientific Mission Applications
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Transcript of Scientific Mission Applications
22.04.23
Scientific Mission Applications
P. K. Toivanen, P. Janhunen, and J.-P. Luntama
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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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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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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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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
Optimal operation of the sail
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Optimal operations andreal 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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Solar wind variations andsail 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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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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Wind speed variations #1
Acceleration is regulated:
• Solar wind speed drive not linear:
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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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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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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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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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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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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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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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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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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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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 150-200 kg)
• Minimal instrument set only to study the target
• Fast travel time
• Fast flyby, data into memory and slow downloading
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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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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