Setting sail on a solar mission

The European Space Agency is investigating the use of large solar sails to propel spacecraft on its future missions to the outer planets.

The agency is working with the German Aerospace Centre (DLR) to develop a 20m x 20m demonstrator solar sail made of a very thin plastic material coated with a sheet of aluminium. The pressure of photons from the sun on the sail would provide the spacecraft with propulsion.

ESA does not yet have any missions planned for the technology, but it could be used to enable spaceships to explore far-off planets, said Pedro Cordero Perez, head of the agency’s technology research and development division.

Accurate navigation

‘Usually inter-planetary travel is not propelled at all, you use gravitational laws. What we are trying to do is optimise trajectories and to navigate more accurately to travel to our targets.’

Solar sails are attracting increasing attention as spacecrafts do not need to carry any fuel, and can travel at high speeds for a very long time, at a fraction of the cost of existing rockets. The ESA-led research team is designing a spacecraft to determine how the sails should be packaged to allow them to be deployed effectively in orbit, said Stephane Lascar, head of the technology harmonisation and strategy division at ESA.

‘We will need to launch and deploy a sail, which means we need to be able to deploy booms which are 15m long, and unwrap the sheet. We are looking in the medium to long term, but we must start now because there are many elements to the technology we need to consider,’ he said.

The solar sail and carbon-fibre boom could be rolled up into a 1m3 hub.

Production of the prototype spacecraft is due to begin early next year, if a project review planned for this December gives the scheme the go-ahead.

The team is then aiming to launch the vehicle into orbit within two years, using an inter-continental ballistic missile fired from a Russian submarine, according to Dr Wolfgang Seboldt at the German Aerospace Centre’s Institute of Space Science.

The researchers have previously deployed the system on the ground, and hope to demonstrate that it works in orbit. ‘This will not really be a demonstration of solar sailing, because it is extremely small and structurally too heavy [to be propelled by photonic acceleration],’ said Seboldt. To demonstrate that a spacecraft can be accelerated by light pressure the sails must be at least 40-50m, he said.

Autumn launch

A privately funded space mission, Cosmos 1, led by a team including the Planetary Society and the Babakin Space Centre near Moscow, is planning to launch a spacecraft with a 30m solar sail this autumn.

But the project has suffered delays in the past, and there is scepticism in the industry that it will meet this deadline, while the sail’s relatively small size means it is also unlikely to demonstrate true solar sailing.