scientific mission applications

22.04.23

Scientific Mission Applications

P. K. Toivanen, P. Janhunen, and J.-P. Luntama

22.04.23Ilmatieteen laitos / PowerPoint ohjeistus 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


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


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


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


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…


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


Density variations

Acceleration limited:

• Electron current to the tethers increases

• Electron gun power limited by the given solar panel power

• Tether voltage drops


Wind speed variations #1

Acceleration is regulated:

• Solar wind speed drive not linear:


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


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)



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



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


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


Electric sail and science missions

High delta-v for small payloads

Interplanetary Heliospheric Probe (IHP)

Kuiper/Centaur flyby mission

Asteroid tour


Other missions

Near-solar missions

Planetary missions


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


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


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


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


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



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

scientific mission applications

Documents

solar wind speed drive

occursolar wind speed

small wind speed values

limited tether voltage

small power values

month averaged thrust

largefor large power

initial acceleration