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 l.jpg

Pekka Janhunen

Finnish Meteorological Institute,

(Kumpula Space Centre)

ESA/ESTEC

May 19, 2008

Electric SailTechnology Status Review


Contents l.jpg

P.Janhunen, www.electric-sailing.com

Contents

  • 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 l.jpg

P.Janhunen, www.electric-sailing.com

Tether 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 l.jpg

P.Janhunen, www.electric-sailing.com

Wire 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 l.jpg

P.Janhunen, www.electric-sailing.com

Tether manufacture

  • Prof. Edward Haeggström, Univ. Helsinki, Electronics Research Lab

    • Presented by Henri Seppänen


Tether reels l.jpg

P.Janhunen, www.electric-sailing.com

Tether 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 l.jpg

P.Janhunen, www.electric-sailing.com

Electron 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


Main properties of designed guns l.jpg

P.Janhunen, www.electric-sailing.com

Main properties of designed guns



Electron gun summary l.jpg

P.Janhunen, www.electric-sailing.com

Electron 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 l.jpg

P.Janhunen, www.electric-sailing.com

Tether 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 l.jpg

P.Janhunen, www.electric-sailing.com

Tether 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 l.jpg

P.Janhunen, www.electric-sailing.com

Mechanical simulations

  • Numerola Ltd company, Jyväskylä, Finland, together with P. Janhunen


Orbital calculations l.jpg

P.Janhunen, www.electric-sailing.com

Orbital calculations

  • University of Pisa, prof. Giovanni Mengali, Alessandro Quarta


Integration of components l.jpg

P.Janhunen, www.electric-sailing.com

Integration 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 l.jpg

P.Janhunen, www.electric-sailing.com

Control

  • 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 l.jpg

P.Janhunen, www.electric-sailing.com

Flight 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 l.jpg

P.Janhunen, www.electric-sailing.com

Technical 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 l.jpg

P.Janhunen, www.electric-sailing.com

Demonstration 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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