http://nextbigfuture.com/2008/09/solar-electric-sail-developments-and.html
A simplified picture of the electric sail. An actual system would have 50 to 100 or more 20 kilometer wires.
100 kg spaceships could be accelerated to final speeds of 40-100 km/second. [Further refinement can
enable a 800km/s top speed - the top solar wind speed]
This site has identified the solar electric sail as one of the top ten near term space developments that
would have the most impact in increasing capabilities in space.
The preparation of components for an actual deployment in space of an electric sail is proceeding.
There was an electric sail workshop by ESA ESTEC (European Space Agency) on May 19, 2008
A powerpoint where progress on electric sail work was presented.
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
-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.
Commercial Uses of E-sails
Electric Sail is a propellantless non-impulsive propulsion method, suitable for small
and medium payloads
œ Electric Sail does not produce much thrust inside the magnetosphere, i.e. at Earth orbit
œ Water mining and transporting from asteroids, for producing chemical propellant, is a
way to use the E-sail to the utility of any space activity
Asteroid mining schemes
œ Water
– Mine water at ice-containing asteroid (KY-26 ?)
– Transfer to Earth orbit by E-sailer
– Water customers at LEO, GTO or MEO:
œ ISS
œ Electrolysis spacecraft (Orbital Transfer Service for satellites)
œ Platinum group metals:
– Challenge: mining
– Transfer by E-sailer to Earth reentry
– PGMs are rare on Earth (differentiated planet), needed as catalysts (fuel cells + other “green” tech's)
œ Structural materials (bricks, stones, basic trusses)
How to mine water
œ Straightforward way: Dig out material one piece at a time. Put piece into container,
close the lid and heat. Container fills with vapour. Open pipe
into cold trap where let H2O condense.
œ Another way: Enclose whole asteroid in gold covered bag so that it gets heated.
Install pipe to a cold (white) bag where ice condenses. Might be feasible for small
asteroid such as KY-26.
Benefit: insensitive to type of asteroid material.
Getting to Earth orbit from asteroid
œ E-sailer used to get payload to Earth-Moon system rendezvous
œ Lunar capture used to kill incoming delta-v (up to 1.5 km/s) ==> get into high elliptic orbit (stable for ~1 year)
œ Use aerobrakings to lower apogee (using solar panels, like Mars missions do) until at GTO or LEO
œ E-sailer can detach before Moon ==> no need to fly with E-sail through near-Earth region
Mining platinum group metals
œ Many benefits and one big challenge
œ Benefits:
– Easy to store in space during E-sail transportation
– Easy to sell once dropped to Earth
– Precious enough (> 10,000 eur/kg)
– Guaranteed, growing market (automotive industry)
œ Challenge:
– Mining (enrichment) at asteroid is probably not simple
– Can be done, since can be done at Earth; but at what initial cost?
E-sail logistics chain. How to use that capability?
œ Cheaper launch to GEO, MEO and make space operations beyond LEO cheaper
Is E-sail required for asteroid mining ?
œ If icy asteroids exist nearby, water can be fetched by electrolysis rockets without losing too much on the way.
But E-sail is more lightweight than any
electrolysis rocket.
œ “Dry” ores reasonable to fetch by electrolysis rocket only if water is also mined nearby.
E-sail is not dependent on any fuel supply.
œ E-sail has better thrust/power ratio than ion engines, plus needs no propellant
Tether Material and Technology selection was made
Technology options covered:
-Laser-cut tether from metal sheet (efficiency? quality?)
-Metal-clad fibres (CTE? radiation?)
-Wire-wire bonding
---Laser welding
---Ultrasonic welding [This was chosen, others are fallback]
---Soldering (temperature range? CTE?)
---Glueing (reliability? CTE?)
---Wrap wire (not done at 20 um scale?)
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
Tether Reels
Baseline plan
-Spinning reel, maybe with capstains
-Outreeling only, or reeling both in and out
-Ordinary or magnetic bearing
-Other ideas also considered
TRL 4 level work can commence when at least few metre piece of tether is available.
http://nextbigfuture.com/2008/09/solar-electric-sail-developments-and.html
