Collision course

The European Space Agency has unveiled details of the advanced engineering needed to meet one of space technology’s ultimate challenges — deflecting an asteroid from a collision course with Earth.

ESA is planning a mission to launch a spacecraft at an asteroid to see for the first time whether it is possible to deflect one from its path.

The Don Quixote mission will involve launching two separate spacecraft on two different trajectories. The first, Hidalgo, will impact the asteroid, while the other, Sancho, will target the asteroid and circle it for several months, observing it before and after impact to detect any changes in orbit.

Sancho will be launched in March 2011, to arrive at the asteroid in 2015. Its systems, which will remain dormant for the journey, would then start up again and it will begin monitoring the asteroid. Later that year Hidalgo will be launched to arrive in June 2017 at a speed of around 10 km/s to crash into the 500m-wide asteroid.

ESA’s scientists expect that the asteroid will be moved from its path by at least 100m due to the highspeed collision, a change in orbit that would be sufficient to eventually change its trajectory by many thousands of kilometres.

According to Andres Galvez, the technical director of ESA’s Advanced Concepts Team, the most challenging aspect of the mission is that the spacecraft must be able to work autonomously.

‘In both the orbiter and the impacter the most important part is the onboard intelligence,’ he said. ‘There is a very difficult part of the mission where the orbiter has to perform autonomous navigation via its onboard system without any control from the ground. That is extremely tricky. At ESA we have nicknamed it the William Tell project — it is that hard.’

Two asteroids have been shortlisted as possible candidates for the mission. One target asteroid, 2002AT4, is smaller, which makes it easier to deflect but harder to hit. The second possibility is asteroid 1989ML. This is larger so it is easier to target, but harder to deflect. It is also closer and so the cruise phase of the spacecraft before it reaches the target and during which all the systems lie dormant would be shorter, making it technically more feasible.

Don Quixote will enter a detailed feasibility stage in January once the winner of the open call tendering process for the design of the spacecraft has been announced.

EADS Astrium is one of the European space technology groups bidding to develop the spacecraft. The company’s UK base in Stevenage will, if successful, be developing the sophisticated electric propulsion system for Sancho.

The orbiter will use solarpowered ion thrusters to manoeuvre itself around the asteroid. Steve Eckersley, a senior missions systems engineer at Astrium UK, said that using these state-of-the-art thrusters would be a good option, particularly for the orbiter.

‘They have the advantage of being extremely efficient as they use only small amounts of ionised gas that are blasted at extremely high speeds to provide the craft’s propulsion,’ he said.

As well as using a series of infrared cameras and seismic monitoring equipment, the orbiter could also carry a package of scientific equipment — the Autonomous Surface Package (ASP) — that it would attempt to hurl into the crater left by the impacter. After this industrial feasibility study, which runs to the end of 2006, ESA will formally apply for EU funding for the mission.