Dealing with threatening space rocks (Forwarded)

ESA News
http://www.esa.int

20 September 2007

Dealing with threatening space rocks

Every now and then a space rock hits the world's media -- sometimes almost
literally. Threatening asteroids that zoom past the Earth, fireballs in the
sky seen by hundreds of people and mysterious craters which may have been
caused by impacting meteorites; all make ESA's planned mission Don Quijote
look increasingly timely.

The uncertainty surrounding whether a meteorite impacted in South America
recently highlights the need to know more about these pieces of natural
space debris and their trajectories. ESA has always been interested in such
endeavours and conducted a number of studies into how it might best help.

Those studies showed that it is probably the smaller pieces of rock, at most
a few hundred metres across, rather than the larger ones that we should be
more worried about for the time being. A worldwide network of astronomers is
currently cataloguing most of the larger objects, those above 1 km in
diameter. A number of survey telescopes have taken up the challenge to
detect as many as 90 percent of all near Earth objects down to a size of 140
metres by around 2020. Only after this time will we know whether space-based
observatories will be needed to find the rest.

Part of the trouble with these small chunks of rock is fixing their orbits.
From the ground, it is very difficult -- sometimes impossible -- to
determine their trajectory with enough precision to rule out impacts with
our planet in the years to come. So, ESA have been concentrating on a
mission to actually 'mark a cross' on small asteroids and check the state of
the art of our technology. The Don Quijote mission is a project based on two
phases. In the first phase, a spacecraft would rendezvous with an asteroid
and go into orbit around it. It would monitor the asteroid for several
months, precisely determining its position, shape, mass and gravity field.

In the second phase, another spacecraft would slam into the asteroid at a
speed of around 10 km/s, while the first spacecraft watches, looking for any
changes in the asteroid's trajectory. In this way, a mission involving two
spacecraft would attempt to be the first to actually move an asteroid.

In preparation for dealing with small asteroids, ESA's Don Quijote is also
starting small. In its current design, the first spacecraft, Sancho, could
reach any one of 5 or 6 small, nearby asteroids. Each one is no larger than
a few hundred metres in diameter. At present, the mission planners have
chosen to concentrate on Apophis, a small asteroid that can swing
dangerously close to Earth on the outwards stretch of its orbit around the
Sun.

If it becomes a reality, Don Quijote could launch sometime early in the next
decade. Sancho would take some 25 months to reach its target. Once there, it
would begin its groundbreaking study -- both literally and metaphorically.

"The idea is to get the technology ready before you really need it," says
Ian Carnelli, Technical Officer for the Don Quijote mission at ESA.

In 1908, a 20-metre asteroid impacted the uninhabited Tunguska forest in
Siberia, toppling trees and causing total devastation over an area of two
thousand square kilometres. Scientists predict this type of event to occur
about every 150 years. Next year's 100th anniversary of that impact will be
yet another reminder of the need to learn about and become ready to deal
with asteroids -- even the small ones.

For further information contact:

Ian Carnelli
Don Quijote Technical Officer
Tel: +31 71 56558117
Email: ian.carnelli @ esa.int

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