Hidalgo impacts with the asteroid

On 9 July 2004, the Near-Earth Object Mission Advisory Panel recommended that ESA place a high priority on developing a mission to actually move an asteroid. The conclusion was based on the panel’s consideration of six near-Earth object mission studies submitted to the Agency in February 2003.

Of the six studies, three were space-based observatories for detecting NEOs and three were rendezvous missions. All addressed the growing realisation of the threat posed by Near-Earth Objects (NEOs) and proposed ways of detecting NEOs or discovering more about them from a close distance.

A panel of six experts, known as the Near-Earth Object Mission Advisory Panel (NEOMAP) assessed the proposals. Alan Harris, German Aerospace Centre (DLR), Berlin, and Chairman of NEOMAP, says, “The task has been very difficult because the goalposts have changed. When the studies were commissioned, the discovery business was in no way as advanced as it is now. Today, a number of organisations are building large telescopes on Earth that promise to find a very large percentage of the NEO population at even smaller sizes than visible today.”

Artist's impression of the Don Quijote mission

As a result, the panel decided that ESA should leave detection to ground-based telescopes for the time being, until the share of the remaining population not visible from the ground becomes better known. The need for a space-based observatory will then be re-assessed. The panel placed its highest priority on rendezvous missions, and in particular, the Don Quijote mission concept. “If you think about the chain of events between detecting a hazardous object and doing something about it, there is one area in which we have no experience at all and that is in directly interacting with an asteroid, trying to alter its orbit,” explains Harris.

The Don Quijote mission concept will do this by using two spacecraft, Sancho and Hidalgo. Both are launched at the same time but Sancho takes a faster route. When it arrives at the target asteroid it will begin a seven-month campaign of observation and physical characterisation during which it will land penetrators and seismometers on the asteroid’s surface to understand its internal structure.

Sancho will then watch as Hidalgo arrives and smashes into the asteroid at very high speed. This will provide information about the behaviour of the internal structure of the asteroid during an impact event as well as excavating some of the interior for Sancho to observe. After the impact, Sancho and telescopes from Earth will monitor the asteroid to see how its orbit and rotation have been affected.