The Microlight Solar Sail

Introduction

Originally the brainchild of Oxford inventor and SEDS member Colin Jack, this project is seem as a way to cheaply (total cost is projected to be of the order of ten thousand pounds) and quickly demonstrate the feasibility of solar sails, whilst simultaneously gaining valuable scientific knowledge. Instead of sail designs covering many square kilometres that have surfaced in the past (many think these would be virtually undeployable and uncontrollable), this would only be a few square metres in size.

Technical Information

The solar sail control and instrument package would be totally solid state thus reducing the risk of failure, using off-the-shelf technology such as thin film amorphous silicon solar cells and a miniaturised CCD camera developed at Edinburgh university. A directional radio antenna for telemetry and data downloading is to be etched into the surface of the sail itself. Different attitude control mechanisms have been investigated, such as using liquid crystal films to alter the reflectivity and hence photon pressure on different portions of the sail; or utilising the variation of pressure on a solar cell according to the power it draws.

A variant on the sail, the solar kite, has also been proposed. This could either carry a small payload, or singly or multiply be used to generate a towing force, eg. to change satellite orbits.

Mission Opportunities

Possible missions are manifold, but two of the most exciting are:

1) Steering the sail into a lunar polar orbit, then angling the sail to reflect sunlight into deep, perpetually dark craters could reveal the presence of volatile materials such as water by the reflections they make.

2) A rendezvous with an asteroid or comet. Steered close to such a body, the craft could fire a tiny harpoon on a retractable line to take a physical sample. Returning to Earth, the sail acts as an ideal re-entry parachute and re-entry heat would be re-reradiated so effectively that the sail temperature need not exceed 100'C. So the sample could be recovered, if a small insulating container (made of a material such as glass foam) was used. If the container is mounted behind the sail, to shield it from sunlight in transit, even low temperature volatiles like methane ice from the surface of a comet could be recovered, in pristine condition. Such a flight would also generate valuable experience in dynamic control of solar sails, for later application to larger models.

Conclusions

The solar sail could easily be built by a semi-amateur body such as a student group, and nowadays the possibilities of obtaining "piggyback" launches with major payloads could reduce launch costs to a very reasonable amount. It is for this reason, that UK-SEDS decided that this would be a viable project to undertake. This is a project which is low cost, yet highly educational. The means to construct a microlight solar sail are within the reach of UK-SEDS, however further progress is dependent on any form of funding becoming available.

Bibliography & References

Starsailing: Solar Sails and Interstellar Travel - Louis Friedman, John Wiley & Sons, 1988.
The Starflight Handbook - Eugene F. Mallove & Gregory L. Matloff, John Wiley & Sons, 1989.
The Interstellar Solar Sail: Optimization and Further Analyses - Eugene F. Mallove and Gregory L. Matloff, JBIS Volume 36, pages 201-209
Interstellar Solar Sailing: Consideration of Real and Projected Sail Material - Gregory L. Matloff, JBIS Volume 37, pages 135-141
The State of the Art Solar Sail and the Interstellar Precursor Mission - Gregory L. Matloff, JBIS Volume 37, pages 135-141

Solar Sail Web Links

IslandOne Solar Sail Information
Solar and laser Driven Lightsails
Solar Sails
The Canadian Space Society Solar Sail Project
DLR's Solar Sail pages

Status

The first feasibility studies on a microlight UK-SEDS solar sail commenced in 1993, by a group of postgraduate students at the then Cranfield Institute of Technology (now Cranfield University). In 1994, some further work followed at Kingston University and the University of Kent at Canterbury, at both institutions, the work being undertaken by undergraduates.

The solar sail work went into abeyance late in 1994, and has been on hold ever since. Nevertheless, much of the design work has been done - the documentation and calculations are waiting to be used!