Scientific Mission Applications P K Toivanen P Janhunen

Scientific Mission Applications P. K. Toivanen, P. Janhunen, and J. -P. Luntama 28. 10. 2021

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 2

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 3

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 e. V • Radial scaling laws for the solar wind parameters • Total mass 200 kg Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 4

Optimal operation of the sail Optimal solution includes: • Initial acceleration of about 0. 5 mm/s 2 (Earth) • Coasting phase (shading) • Constant thrust angle of 20 deg • Acceleration at Mars of about 0. 3 mm/s 2 • Travel time of 600 days Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 5

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… Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 6

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 7

Density variations Acceleration limited: • Electron current to the tethers increases • Electron gun power limited by the given solar panel power • Tether voltage drops Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 8

Wind speed variations #1 Acceleration is regulated: • Solar wind speed drive not linear: Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 9

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 10

Average performance #1 3 -month averaged thrust in cases of: • Limited tether voltage (40 k. V, thick) • No tether voltage limitation (thin) • Variations relatively small around average at 70 n. N/m • Missions can be desinged for the minimum thrust (dotted) without missing much of the maximum thrust (dashed) Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 11

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 12

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 13

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, V 0 • If Vsc < V 0, increase tether potential by 5 k. V for the next hour • If Vsc > V 0, decrease tether potential by 5 k. V for the next hour Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 14

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 15

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 k. V & 1 k. W) High-voltage power source: 2. 0 kg Avionics + tether direction sensor: 7. 0 kg Solar panels: 6. 0 kg (1. 1 k. W) 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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 16

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 17

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 18

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 150200 kg) • Minimal instrument set only to study the target • Fast travel time • Fast flyby, data into memory and slow downloading Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 19

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 20

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 Ilmatieteen laitos / Power. Point ohjeistus 28. 10. 2021 21