April
2007
Electric sails0
Links to free teaching resources for the story on electric sails
Teaching resources (UK US) designed specifically for this story at www.realscience.org.uk
The Sun produces a solar wind — a continuous flow of charged particles — that can affect us on Earth. It can disrupt communications, navigation systems and satellites, and cause power outages such as the Canadian blackout in 1989. In this video segment adapted from NASA, learn about solar storms and their effects on Earth.
Centauri Dreams is the place to go for the latest news, made easy to understand, on all aspects of space travel. This latest posting provides more insight than the press release, but teachers should be careful of letting young kids loose on it, because of a little bad language in one of the comments.
An electric sail has not yet been built. But a related method of propulsion powered the NASA mission Deep Space 1, which did fly. “An ion engine is much the same as what you experience when you pull hot socks out of the clothes dryer on a cold winter day. The socks push away from each other because they are electrostatically charged, and like charges repel.”
Gain a feel for the distances involved in space travel by creating scale models.
How do vessel design, navigation, and propulsion affect exploration? This lesson compares vessel design, navigation, and propulsion used by early Jamestown explorers to those used by NASA. Students use maps and coordinate planes to demonstrate the Global Positioning System and to compare 17th-century mapmaking to modern technology. They conduct experiments about sails and other propulsion systems.
Latest news on solar sails.
Background and animation on the electric sail.
Links to more
The new electric sail research paper.
The story:
Electric sail
Space travel is difficult for two main reasons: Very high speeds are needed to get anywhere at all, because space is enormous. And high speeds usually mean high energy and high costs.
But some sources of energy come free or at least very cheap. One of these is solar sails, which use the feather-touch of sunshine on vast sheets of fabric to shift a spaceship.
Another idea is to harness the energy in the solar wind, through its effect on electrically charged wires. This electric sail concept has now been studied in detail by scientists in Finland. Their work has just been published in Annales Geophysicae.
The solar wind consists of high-energy, charged particles thrown out by the sun. These travel across space at speeds from 300-800 kilometres per second. On Earth they power the aurorae, the stunning displays of light in the sky, which have many other names such as the “northern lights”.
On average the pressure of the solar wind is 2 nano-pascal, which is just a fifth of a gram weight on each square kilometre. (One gram is the weight of a paperclip.)
To use such a weak pressure to propel a spacecraft you need a very large area of sail. Larger than a solid surface can provide. So the electric sail uses the idea of forming an electric field around a thin, charged wire.
This wire is kept at high voltage by a solar-powered electron gun on board the spacecraft. A 20-km long tether, made of wire thinner than human hair, can fit into a small reel. But it provides a square kilometre of effective area when stretched out in space and charged up.
In the Annales Geophysicae paper the scientist describe 2-dimensional simulations they ran on a supercomputer. These calculated the thrust per meter of tether length. Different solar wind conditions and tether voltages were studied. The aim was to test if the whole approach could work.
Theoretical analysis and one-dimensional simulations were used to validate the results.
These show that around 50 nano-newtons force per meter of wire can be achieved in a normal solar wind.
This could accelerate a light spacecraft up to final speeds in the range 50-100 kilometres per second. This is 10 to 20 astronomical units (1AU) a year. One AU is the distance from earth to the sun.
At such high speeds a craft powered by the electric sail could reach Pluto in less than four years. It could fly out of the heliosphere into interstellar space in less than 15 years.
The electric sail needs no propellant or other consumables. So one of the possible applications is cheap transportation of raw materials. These include water mined from asteroids and used to make fuel for other spaceships.
