'Spider webs' would help propel future space probes

London, April 25 : A team of scientists in Finland has woven a new type of spider web-like solar sail, with positively charged wires, that might be able to repel positive ions in the solar wind and thus propel itself through space.

According to a report in New Scientist, the 'spider webs' are designed to catch the wind of ionised gas that blows from the Sun, carrying spacecraft to the outer reaches of the solar system, or letting them tack back and forth through the asteroid belt on exploration or mining missions.

Thus, the new sail differs from the more conventional type of solar sail, which is designed to use the gentle pressure of sunlight to move a spacecraft.

Instead of catching sunlight, the new sail is aiming to sail with the solar wind, a tenuous plasma of electrons and positive ions blowing out through the solar system at speeds of hundreds of kilometres per second.

Pekka Janhunen of the Finnish Meteorological Institute in Helsinki, who designed the sail, plans to reel out long wires from a spacecraft and pump a positive electric charge into them, so that they repel the heavy positive ions in the solar wind.

That way a wire only microns across can feel the force of a broad swath of passing plasma, behaving like a sail many metres across.

Though one problem with the sail is the high-velocity micrometeoroids shooting through interplanetary space, the design team would make them more robust by weaving each section of sail from four strands of wire.

Janhunen and his team have now crafted a sample of this structure in the lab, using ultrasound to weld the gossamer strands together. Their hand-sewn ribbon of sail is only 30 centimetres long, so the next stage is to work out a way to automate its manufacture.

A test mission, to see whether the method works, might involve eight ribbons about a kilometre long, towing a small spacecraft carrying an accelerometer.

Janhunen then envisages full-scale missions with up to 100 ribbons, each 20 km long, which would have a combined mass of about 20 kilograms.

Because the solar wind is so tenuous, these huge solar sails would still only feel a fairly gentle force, but over a year it could accelerate a 200-kilogramme payload up to a brisk 30 kilometres a second.

That could save a lot of propellant, and therefore money.

"We benefit from the fact we can't run out of fuel," said Janhunen.

ANI