On Wings of Light

Solar Sails and the Starships of the 3rd Millennium

Talk given at WAS on 17 Dec 2003 by Stuart Clark

      Is it possible to design spaceships that need take no fuel, no engine, can travel anywhere in the solar system and are re-usable and cost efficient? Are Solar Sails the answer?

The idea was considered by Kepler as he watched a comet with its great tail. The tail, he thought, must be shaped by a kind of Solar wind. If there is a wind then why not sail in the wind?

It is radiation pressure that shapes emission nebulae.  In the Orion nebula just one new star is producing all the radiation. We see the cavity that has formed with its opening in our direction. Behind is the glowing emission gas, which has become compressed, triggering new star formations.

NASA found that radiation pressure blows spacecraft slightly off target.  Subsequently radiation pressure was used on the Mariner 10 mission to Mercury. Fins were fitted to keep the craft pointing straight at the sun. If the craft rotated slightly, radiation pressure on the fins caused it to turn gently back into line. This is a good example of the advantage of Solar sails.

The Russian, Tsiolkovsky envisaged mirrors to reflect radiation and hence obtain thrust.  The spacecraft would be pushed by radiation and pulled by gravity. It would mostly travel in orbit around the sun. However, by varying the angle of the sails, the craft can move closer or further from the Sun on spirals. It can also climb up from the plane of the ecliptic. With cunning, it can transfer to the gravity of a planet.

The European Space Agency see Solar Sails as central to strategic planning. So far plans have been very ad-hoc, but It might be possible to investigate problems such as asteroids on near-earth orbits. Fifty or more cheap Solar sails could visit many of these objects to give us a much better idea of what they are. So far only a very few have been investigated. What is the statistical probability of it being a solid body, a dead comet nucleus or a collection of rubble? If a bomb were exploded near the solid body, it could deflect it. As a comet nucleus is light and porous a bomb would shatter it and the earth would get showered; a worse effect than a single impact. If the asteroid were just a collection of rubble, a bomb would have very little effect as the explosion would be absorbed. Therefore we really need to know much more about asteroids if there is to be an effective solution. It would have been rather the same with Beagle on Mars. It could have only sampled one area.

One of NASA’s early plans in the 1970s was to rendezvous with Halley’s comet. Originally it was going to use an ion-engine. This is a very complicated device that shoots accelerated electrons out backwards and therefore accelerates forward albeit very slightly.

Because of its anti-planetary motion, Halley is very difficult to approach. Ion-engines or Solar Sails would be a good way to get there, taking either 8 or 4 years respectively. The Apollo missions had been very expensive and costs had to be scaled down. NASA allowed development of both types of propulsion which became highly competitive. The crucial problem to be solved for the Solar Sail was deployment. If the whole space craft is packed into something the size of a washing machine for launching, it then has to be opened out to form an enormous sail. The mechanism required must not fail. One idea was to spin the craft so that the sail gets flung out. Another idea was to have 4 arms, long and narrow to give the same area. However they would have to be 10km in length!  Eventually, NASA decided to use an ion-engine.

The ESA have built an ion-engine which is on its way to the Moon now. Whereas Apollo took 3 days to get there this experimental ion-engine will take 18 months!

Solar Sails have had a run of bad luck including cancelled missions and it has not yet been possible to prove that they work. Many of the problems of deployment can now be overcome using new materials. One material can be rolled up into a cylindrical shape and stay that way without problems. Then with a lightly applied pressure, it can be triggered to completely unroll into another stable shape, with no tendency to roll up again. It is rumoured that this material is going to be used to make T-shirts with short sleeves that unroll themselves up in cool weather!

In the next decade, a new mission called Solar Orbiter is planned to take a close look at the Sun. Although Solar Sails are the obvious choice of propulsion, because it is still unproven, ion-engines have been selected. But maybe that can be changed. A private investor is about to test his design soon, which if successful, may make NASA think again.

Further out in the Solar system the radiation pressure decreases, to just 4% of its strength at the earth. There is now an idea to drive a Solar Sail from Earth, using a powerful laser. The craft would be able to change its sail so that it either accelerated or decelerated.

This was a very interesting talk but a little sad to think that Solar Sails have not yet got going!

Joan Grace


      The next meeting of the Society is on Wednesday January 21st  2004 when the speaker will be R. F. Turner.  His subject that evening will be either “The Sun in Ha (Hydrogen-alpha)” or “Hubble Start of the Universe” 

      As usual, the meeting will be held in the Drama Studio at Uplands College.  The doors open at 7.15 and the meeting starts at 7.30 prompt.





      There will be Observing Sessions on the following Fridays:

23rd January

20th February

19th March

23rd April

      The sessions meet at 7.30 pm in the Crow and Gate pub, about a mile south of Crowborough on the A26 main Uckfield road.  Then at 8.00 pm the group move onto Ashdown Forest.



      A committee meeting has been arranged to take place at the Abergavenny Arms in Frant at 7.30 pm on Wednesday 28th of January.



      The Treasurer’s Annual Report was available at the last meeting of the Society, and again copies will be available for members to pick up at the next meeting.

        Annual Subscriptions were due on 1st November last year for the year 2003-04. The committee would be very grateful if members who may have overlooked the payment could either send a cheque made payable to Wadhurst Astronomical Society, to the Treasurer at Broadwater Lodge, Stone Cross Road, Wadhurst, E Sussex, TN5 6LR or  pay Ian Reeves or Joan Grace, (membership secretary) at the Society meeting. The subscription for the 2003-2004 session is £15 for individual membership and £20 for joint membership.

Membership: There are still vacancies on the committee for ladies and for gentlemen to take their turn in helping to run the Society. There are only four meetings each year each lasting about 1 hour and are held in a mutually convenient and comfortable hostelry. The present team was elected en bloc for 2 years just over 2 years ago and one or two members have already had to vacate their position.


      Quite a number of members receive their Newsletter by email, but after sending out the December Newsletter, a number were returned with a note saying that they could not be delivered.  This may be because Anti-virus filters have been set to accept emails originating from Peter Bamlett but not from Geoff@rathbone007.fsnet.co.uk   I therefore sent the newsletter on to these members by post, but will still keep trying to send them via email first for a time.





Chairman: Murray R. Barber        01892 654618


Treasurer: Ian Reeves                        01892 784255

Editor:        Geoff Rathbone           01959 524727


Publicity &

Web Site:  Michael Harte              01892 783292


Dir. of

Obs:    Sean Tampsett                       01892 667092