ESA selects targets for asteroid-deflecting mission Don Quijote (Forwarded)

European Space Agency
Press Release No. 41-2005
Paris, France 26 September 2005

ESA selects targets for asteroid-deflecting mission Don Quijote

Based on the recommendations of asteroid experts, ESA has selected two
target asteroids for its Near-Earth Object deflecting mission, Don Quijote.

Don Quijote is an asteroid-deflecting mission currently under study by
ESA's Advanced Concepts Team (ACT). Earlier this year the NEO Mission
Advisory Panel (NEOMAP), consisting of well-known experts in the field,
delivered to ESA a target selection report for Europe's future asteroid
mitigation missions, identifying the relevant criteria for selecting a
target and picking up two objects that meet most of those criteria. The
asteroids' temporary designations are 2002 AT4 and 1989 ML.

With this input and the support of ESA's Concurrent Design Facility
(CDF) experts, the Advanced Concepts Team has now completed an extensive
assessment of suitable mission architectures, launch strategies,
propulsion system options and experiments.

The current scenario envisages two spacecraft in separate interplanetary
trajectories. One spacecraft (Hidalgo) will impact an asteroid, the
other (Sancho) will arrive earlier at the target asteroid, rendezvous
and orbit the asteroid for several months, observing it before and after
the impact to detect any changes in its orbit.

Industrial studies are now about to start; it will be down to European
experts to propose alternative solutions for the design of the low-cost
NEO precursor mission. This will be the first step towards the
development of a means to tackle asteroid impacts -- one of the few
natural disasters that our technology can prevent.

A near miss?

While the eyes of the world were on the Asian tsunami last Christmas,
one group of scientists were watching uneasily for another potential
natural disaster -- the threat of an asteroid impact.

On 19 December 2004 MN4, an asteroid of about 400 m, lost since its
discovery six months earlier, was observed again and its orbit was
computed. It immediately became clear that the chances that it could hit
the Earth during a close encounter in 2029 were unusually high. As the
days passed the probability did not decrease and the asteroid became
notorious for surpassing all previous records in the Torino and Palermo
impact risk scales -- scales that measure the risk of an asteroid impact
just as the Richter scale quantifies the size of an earthquake.

Only after earlier observations of the object were found and a more
accurate trajectory was computed did it become clear that it would not
impact the Earth -- at least not in 2029. Impacts on later dates, though
unlikely, have not been totally ruled out. It is extremely difficult to
tell what will happen unless we come up with a better way to track this
or other NEOs and if necessary take steps to tackle them.

Most world experts agree that this capability is now within our reach. A
mission like ESA's Don Quijote could provide a means to assess a
threatening NEO and take concrete steps to deflect it away from the Earth.

But every good performance needs rehearsing and in order to be ready for
such a threat, we should try our hardware on a harmless asteroid first.
Don Quijote would be the first mission to make such an attempt. The big
question was: which asteroid and what should it be like?

Looking for the perfect target

The NEO population contains a confusing variety of objects, and deciding
which physical parameters are most relevant for mitigation
considerations is no trivial task. But the NEOMAP experts took on the
challenge and in February 2005 provided ESA with their recommendations
on the asteroid selection criteria for ESA's deflection rehearsal.

People might wonder whether performing a deflection test, such as that
planned for Don Quijote, represents any risk to our planet. What if
things go wrong? Could we create a problem, rather than learn how to
avoid one?

Experts world-wide say the answer is no. Even a very dramatic impact of
a heavy spacecraft on a small asteroid would only result in a minuscule
modification of the object's orbit. In fact the change would be so small
that the Don Quijote mission requires two spacecraft -- one to monitor
the impact of the other. The second spacecraft measures the subtle
variation of the object's orbital parameters that would not be
noticeable from Earth.

Target objects can also be selected so that all possible concerns are
avoided altogether, by looking into the way the distance between the
asteroid's and the Earth's orbits changes with time. If the target
asteroid is not an 'Earth crosser', as is the case with NEOs in the
'Amor' class (which have orbits with perihelion distance well in excess
of 1 AU), testing a deflection manoeuvre represents no risk to the Earth.

Other considerations related to the orbit of the target asteroid are
also important, especially the change of orbital velocity that is
required by the spacecraft to 'catch up' with the target asteroid -- the
so-called 'delta V'. This should be sufficiently small to minimise the
required amount of spacecraft propellant and enable the use of cheaper
launchers, but high enough to allow the same spacecraft to be used with
a number of possible targets.

Navigation and deflection measurements requirements set some heavy
constraints on the target selection. The shape, density, and size are
all important factors, but are often poorly known. A spacecraft orbiting
an asteroid needs to know about the object's gravitational field in
order to navigate. The 'impactor spacecraft' must know the position of
the centre of mass to define the point it is aiming for.

Asteroids come in all sort of flavours, but as far as composition is
concerned two main types dominate. Our still rudimentary knowledge of
the abundance of asteroids of different types in the near-Earth asteroid
population indicates that the next hazardous asteroid is more likely to
be a 'C-type', than an 'S-type'. C-types have dark surfaces with a
carbonaceous spectral signature, while S-types have brighter surfaces,
their spectra matching closely that of silicates. The surface properties
of the target asteroid -- and in particular the percentage of light that
it reflects -- are a critical factor in the final phase of the impactor
spacecraft navigation. The brighter it looks the easier it is to aim at.
However for a rehearsal the target should not be too easy.

ESA has selected asteroids 2002 AT4 and (10302) 1989 ML as mission
targets because they represent best compromise among all the (sometimes
conflicting) selection criteria. A decision on which of the two will
become the final destination of both Sancho and Hidalgo spacecraft will
be made in 2007.

Don Quijote -- the knight errant rides again

The phase of internal studies on the Don Quijote mission is now over,
and it is time for the space industry to suggest suitable design
solutions. ESA has made an open invitation to European space companies
to submit proposals on possible designs. The selection of the most
promising ones will take place towards the end of the year. In early
2006, two teams should start working on their interpretations of this
technology demonstration mission. A year later, once the results are
available, ESA will select the final design to be implemented, and then
Don Quijote will be ready to take on an asteroid!

Note for editors:

Don Quijote is a NEO deflection test mission based entirely on
conventional spacecraft technologies. It would comprise two spacecraft
-- one of them (Hidalgo) impacting an asteroid at a very high relative
speed while a second one (Sancho) would arrive earlier at the same
asteroid and remain in its vicinity before and after the impact to
measure the variation on the asteroid's orbital parameters, as well as
to study the object.

Asteroid 2004 MN has now been given an official designation, (99942)
Apophis. Recent observations using Doppler radar using Arecibo radio
telescope in Puerto Rico have reduced the impact probability during
future encounters to very small levels, though they have not totally
ruled out an Earth impact. In 2029, the asteroid will have the closest
approach ever witnessed for an object of this size, swinging by the
Earth at a distance of around 32,000 kilometres. Its trajectory will be
well within the geosynchronous orbit used by most telecommunications and
weather satellites, and the object will be visible to the naked eye.
Further radar measurements are expected in 2013.

Don Quijote target asteroids 2002 AT4 and (10302) 1989 ML do not
represent any danger to our planet.

For more information, please contact:

ESA Media Relations Division
Tel: + 33(0)1.53.69.7155
Fax: + 33(0)1.53.69.7690

Andrés Gálvez
Advanced Concepts Team, ESTEC
Noordwijk, The Netherlands
Tel +31–71-565-3118
Fax: +31-71-565-8018

More information

* Don Quijote mission
http://www.esa.int/gsp/NEO/quijote/quijote.htm
* NEO Space Mission Preparation
http://www.esa.int/gsp/NEO/
* Advanced Concepts Team
http://www.esa.int/gsp/ACT/index.htm
* CDF
http://www.esa.int/SPECIALS/CDF/

Related articles

* CDF NEO study
http://www.esa.int/SPECIALS/CDF/SEMOC4D3M5E_0.html

[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEML9B8X9DE_index_1.html ]