pekka janhunen finnish meteorological institute kumpula space centre esa estec may 19 2008
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Pekka Janhunen Finnish Meteorological Institute, (Kumpula Space Centre ) ESA/ESTEC May 19, 2008 Electric Sail Technology Status Review Contents Tether manufacture Edward Haeggström et al., Univ. Helsinki, Electronics Res. Lab Tether reels Lutz Richter, DLR-Bremen Electron gun

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pekka janhunen finnish meteorological institute kumpula space centre esa estec may 19 2008
Pekka Janhunen

Finnish Meteorological Institute,

(Kumpula Space Centre)

ESA/ESTEC

May 19, 2008

Electric SailTechnology Status Review
contents
P.Janhunen, www.electric-sailing.comContents
  • Tether manufacture
    • Edward Haeggström et al., Univ. Helsinki, Electronics Res. Lab
  • Tether reels
    • Lutz Richter, DLR-Bremen
  • Electron gun
    • Mikhail Zavyalov et al., IKI-Moscow
  • Tether Direction Sensors
    • Greger Thornell et al., ÅSTC-Uppsala
  • Dynamic Tether Simulations
    • Numerola Oy company & PJ
  • Orbital Calculations
    • Giovanni Mengali et al., Univ. Pisa
  • Integration of components
tether material tech selection
P.Janhunen, www.electric-sailing.comTether material & tech selection
  • Initial material & technology study was made by Prof. S.-P. Hannula et al. at Helsinki Univ. Tech.
  • Technology options covered:
    • Laser-cut tether from metal sheet (efficiency? quality?)
    • Metal-clad fibres (CTE? radiation?)
    • Wire-wire bonding
      • Laser welding
      • Ultrasonic welding
      • Soldering (temperature range? CTE?)
      • Glueing (reliability? CTE?)
      • Wrap wire (not done at 20 um scale?)
  • Ultrasonic welding selected, others are fallbacks
wire metal selection
P.Janhunen, www.electric-sailing.comWire metal selection
  • Requirements: Good yield strength, preferably at least steel-class conductivity
  • No brittle-ductile transition at cold temperature
  • Generally: Alloying can improve yield strength, but usually destroys conductivity
  • Good-conductivity alloys:
    • 90% Cu, 10% Ag: Tensile strength 1000-1600 MPa, Density 9 g/cm3
    • 99% Al, 1% Si: Tensile strength ~300 MPa, Density 2.7 g/cm3
  • Dense metal has better micrometeoroid tolerance?
tether manufacture
P.Janhunen, www.electric-sailing.comTether manufacture
  • Prof. Edward Haeggström, Univ. Helsinki, Electronics Research Lab
    • Presented by Henri Seppänen
tether reels
P.Janhunen, www.electric-sailing.comTether reels
  • Preparatory work by Lutz Richter, DLR-Bremen
  • Baseline plan
    • Spinning reel, maybe with capstains
    • Outreeling only, or reeling both in and out
    • Ordinary or magnetic bearing
  • Other ideas also considered
  • Plan for proceeding
    • TRL 4 level work can commence when at least few metre piece of tether is available (either final-type or mockup, this is TBD)
electron gun
P.Janhunen, www.electric-sailing.comElectron gun
  • Prof. Mikhail Zavyalov, Pavel Tujrujkanov, E.N. Evlanov, Space Research Institute IKI, Moscow
  • Three new designs produced, based on IKI heritage hardware:
    • 300 V low-voltage gun for ionospheric testing
    • 20 kV/2kW baseline model for solar wind
    • 40 kV/2kW enhanced voltage model for solar wind
electron gun summary
P.Janhunen, www.electric-sailing.comElectron gun summary
  • 40 kV, 2 kW, 50 mA gun: Mass 3.9 kg including power supply (2 kg) and radiator (0.9 kg)
  • LaB6 cathode lifetime: theoretically should be at least 10 years in high vacuum
  • Overall, electron gun situation looks good: gun which actually exceeds our power requirement (~400 W) several times has <4 kg mass. Could have more than one gun for redundancy.
tether direction sensors
P.Janhunen, www.electric-sailing.comTether Direction Sensors
  • Greger Thornell, Henrik Kratz, Ångström Space Technology Center, Uppsala
  • Status: Preliminary TRL 3 -level analysis done in collaboration with ÅSTC and PJ
  • Initially, also Univ. Liege (P. Rochus et al.) looked at the topic
  • Main idea: Detect tethers optically with stereo camera, Reconstruct 3-D directions from images onboard
  • Purpose: Tether lengths must be actively fine-tuned to avoid their collisions. One must first detect them.
tether direction sensors12
P.Janhunen, www.electric-sailing.comTether Direction Sensors
  • TRL 3 analysis done, basically
  • Modest-sized cameras enough unless >10-15 AU distance
  • May have to mat-finish wires to create diffuse reflectance
  • Seeing root of tether enough to determine its direction
  • Seeing the tip would be good as tether breakage alarm
mechanical simulations
P.Janhunen, www.electric-sailing.comMechanical simulations
  • Numerola Ltd company, Jyväskylä, Finland, together with P. Janhunen
orbital calculations
P.Janhunen, www.electric-sailing.comOrbital calculations
  • University of Pisa, prof. Giovanni Mengali, Alessandro Quarta
integration of components
P.Janhunen, www.electric-sailing.comIntegration of components
  • General approach
    • Design whole s/c around electric sail
    • Add electric sail to existing s/c design
  • Spinup strategy
    • Spinup rockets
    • Siamese Twins
  • Placement of reels
    • At outer edge of s/c disk
    • At deployable booms at ends of solar panel arrays
  • High voltage path design (grounding plan)
    • Whole s/c at high positive potential
    • Only reels and electron gun at high positive potential
control
P.Janhunen, www.electric-sailing.comControl
  • Tethers have two degrees of freedom: in spinplane and perpendicular to spinplane
  • Thus we need two controls: potential (controls solar wind force) and length (controls angular speed)
  • Length fine-tuning strategies:
    • Reel in and out (needs reliable reeling of partly damaged tether or thicker monofilament base tether)
    • Reel out only (must have enough spare tether)
flight algorithm
P.Janhunen, www.electric-sailing.comFlight algorithm
  • Inputs (partly redundant):
    • Pointing direction of each tether (direction sensor)
    • Spacecraft potential (electron detector)
    • DC current flowing in each tether
    • Thrust (accelerometer)
  • Output commands:
    • Overall thrust (electron gun current and voltage)
    • Individual tether potentials (potentiometers)
    • Tether length fine-tuning (reel motors)
  • Running in parallel:
    • S/C body spin state control so that it conforms with tethers (star sensor and ACS)
technical status summary
P.Janhunen, www.electric-sailing.comTechnical Status Summary
  • Tether manufacture: Progressing well, required before test mission can fly
  • Tether reels: No serious problems seen, but must be done to demonstrate reeling of final-type tether
  • Electron gun: Straightforward (could use spare cathodes/guns for redundancy)
  • Tether direction sensors: Should be straightforward
  • Dynamic tether simulations: No problems seen, but should be done more comprehensively still
  • Orbital calculations: OK
  • Overall design: OK
demonstration goals
P.Janhunen, www.electric-sailing.comDemonstration goals
  • Reel to reel tether production (10 m, 100 m, 1 km, 10 km) with quality control
  • Reliable reeling of the tether
  • After these, one can make decision to build test mission. Technological development risk remaining after this is small.
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