Deflecting asteroids

The UK’s first engineering feasibility study into missions for deflecting asteroids has begun, with joint research undertaken by the Universities of Glasgow and Strathclyde.

The Engineering and Physical Sciences Research Council (EPSRC) is funding a new three-year study into interception and deflection strategies for asteroids found to be on a collision course with Earth. Although there have been similar studies in the past, Dr. Gianmarco Radice, of the Department of Aerospace Engineering at the University of Glasgow, and Professor Colin McInnes, of the Department of Mechanical Engineering, University of Strathclyde, are approaching the subject in a new way.

“We will be looking at this as engineers, so we want to investigate the practicality of different deflection strategies,” explained Professor Colin McInnes. “In other words, it is no use having a brilliant deflection scheme if no one can build it with current technology.”

Although Hollywood blockbuster films have popularised the idea of using nuclear weapons to blow up asteroids, the study will investigate more realistic alternatives such as space mirrors. Such mirrors would be angled to focus sunlight onto the incoming object, and the intense heat would boil away a section of the asteroid, creating a natural rocket that pushes the asteroid in the opposite direction. The study will also look into high-speed collisions to literally knock an asteroid out of the way using no explosives, just a ‘battering ram’ spacecraft.

Asteroids have widely differing compositions, ranging from pure rock or even metal to ice and snow. Knowing what an asteroid is made from, and therefore its likely strength, is the crucial first step in determining the best way to divert it without shattering it. “One of the main objectives of this study is to try to associate a particular deflection strategy with a particular type of asteroid that has to be deviated,” explained Dr. Gianmarco Radice.

The internal arrangement of Near Earth Objects (NEOs) can critically affect the deviation strategy. Some asteroids, known as rubble piles, are not solid slabs of rock but loose assemblages. Slamming an object into a rubble pile would not be very effective in altering its course, because the rubble would absorb the energy of impact rather like a crumple zone on a car absorbs a crash. Instead, scenarios which melt part of the surface, such as space mirrors, producing jets of gas that gradually ease the object into a new orbit, are favoured.

The study is however more than just diverting asteroids, no matter how critical that need may one day become. The biggest part of the research is concerned with how to intercept such targets. In conventional space exploration, everything is precisely worked out beforehand and targets are chosen that have well-known orbits. The exact technique is how NASA recently hit comet Tempel 1 with its Deep Impact mission.

A dangerous object is likely to be newly discovered and that means its orbit will be poorly known. “We would probably have to launch a deflection mission without a clear idea of where we are aiming,” said Dr. McInnes. “The study will seek to find the best strategies for launching space missions into approximate intercept orbits that can be adjusted later.”

The study will therefore investigate the additional fuel that such a spacecraft would require. As fuel is heavy, spacecraft are traditionally designed to carry little extra which will have to change with this new approach to space exploration, thus resulting in more versatile spacecraft and enabling better responses to a variety of unexpected situations.

As well as fuel considerations, the team will investigate ‘general purpose’ orbits and flexible navigation strategies that keep a spacecraft’s options open for longer, before committing it to a final destination.