Superthin wire for electric sail space propulsion engineered

An one kilometer long electric sail (ESAIL), which is meant to interact with the solar wind (charged particles from the sun) to produce long-distance propulsion power for a spacecraft, has now successfully been manufactured for the first time, announced the Electronics Research Laboratory at the University of Helsinki this week.

Experts considered it impossible until now to weld together the extremely thin wires needed, measuring just 25-50 micrometer in diameter.

But with a fully automated, precision mechanical device under computer control, using ultrasonic welding, developed and constructed by the team at the Kumpula Science Campus in Helsinki, it became possible. The achievement proves that manufacturing full-size ESAIL tethers is possible, and even realistic and relatively cheap.

Invented by Dr. Pekka Janhunen at the Finnish Kumpula Space Centre in 2006, the ESAIL consists of long, thin (25-50 micron) electrically conductive tethers manufactured from aluminum wires. A full-scale sail can include up to 100 tethers, each 20 kilometers long.

The electric field of the charged tethers will extend approximately 100 meters into surrounding solar wind plasma. Charged particles from the solar wind crash into this field, creating an interaction that transfers momentum from the solar wind to the spacecraft.

A spacecraft like this also needs to contain a high-voltage source and an electron gun that creates a positive charge in the tethers.

Compared with other methods, such as ion engines, the electric sail produces a large amount of propulsion considering its mass and power requirement. Since the sail consumes no propellant, it has, in principle, unlimited operating time.

The deployed tethers are kept straight in space by centrifugal force, generated by simply spinning the spacecraft with its extended wires around its axis.

The electric sail is raising a lot of interest in space circles, but until now it has been unclear whether its most important parts, i.e. the long, thin metal tethers, can be produced. It took 4 years of development, and the produced 1 km wire contains no less than 90,000 ultrasonic welds. And it will be tested ion space very soon, first by the ESTCube-1 satellite, an Estonian small satellite to be launched in March 2013. It will deploy a 15-meter-long tether in space and measure the force it is subjected to. One year later, a finnish satellite, the Aalto-1 nanosatellite from Aalto University, will deploy a 100-meter-long tether - it is scheduled to be launched in 2014,

According to the Electronics Research Laboratory, a 1000 kg spacecraft with 100 electric-sail wires, each 20-km long, could produce acceleration of about  1 mm per square second. After acting for one year, this acceleration would produce a final speed of 30 km/s (67108 miles per hour), and would continue to accelerate.

Several wires would be needed for an ESAIL tether, because micrometeoroids present everywhere in space pose a risk to cut it. So the tether must be manufactured from several wires in parallel, joined together every centimeter; which will allow micrometeoroids to only cut individual wires without breaking the entire tether.

The EU funding contribution to the ESAIL project is 1.7 million euros.