The European Space Agency (ESA) is contemplating smashing a spacecraft into an asteroid.

The proposed mission, called AIDA (for "Asteroid Impact and Deflection Assessment"), would consist of a pair of spacecraft (sadly, not named Armageddon and Deep Impact) flung at the near-Earth asteroid 65803 Didymos. Didymos is actually a binary object consisting of a large primary mass and much smaller secondary satellite mass. The idea with the AIDA mission, which would take place near the end of 2022, is to accelerate a small kinetic impactor spacecraft to a relative velocity of 6.25 kilometers per second and crash it into the secondary Didymos mass. A second spacecraft would hold off a short distance away and measure the orbital deflection imparted by the more than 300kg impactor spacecraft.

The two spacecraft halves of the mission are sponsored by two different agencies. The impactor spacecraft is called DART, for Double Asteroid Redirection Test, and is designed by the US Johns Hopkins Applied Physics Laboratory. The observer is called AIM, for Asteroid Impact Monitor, and is designed by ESA. DART is a mostly uninstrumented craft, equipped with only a single imager for targeting itself at Didymos, while ESA's AIM spacecraft contains a suite of sensors designed to help it observe Didymos before, during, and after DART's impact.

A crash at 6.25km/second qualifies as a "hypervelocity" impact. At that kind of speed, materials involved in the impact aren't just deformed or displaced, but rather are actually vaporized, transforming into glowing plasma. ESA's announcement page notes that in addition to simply understanding the mechanics of impact, doing it at "hypervelocity" gives the added bonus of being able to study in miniature the conditions that might have existed in the earlier stages of our solar system. The smaller Didymos satellite into which the DART spacecraft will crash has a diameter of 150 meters and a measured density of about 1.7g/cm3; assuming that the asteroid is a perfect sphere (which it obviously isn't), this gives us a rough upper bound of about 3×109kg for the smaller asteroid's mass, or about 3 million metric tons. Smashing 300kg of spacecraft into the asteroid won't "blow up" the asteroid or anything dramatic, but it will greatly help scientists understand how asteroid deflection might work—or if it's even practical.

The study's stated goals are merely the beginning of the project, though. ESA is publishing all the AIDA materials now and is calling for public comment on the mission, seeking suggestions for additional experiments which could be done with the spacecraft, either ground-based or space-based. The formal call for experiments will be issued on February 1, 2013 on ESA's Near Earth Object page.