Frequently Asked Questions
Q : How are Earth Entry Capsules recovered?
A : The capsule has a target landing ellipse where it is expected to land. This landing area will be in a specialised recovery zone, usually in a military area as the military have useful equipment for tracking and recovering the capsule. Once its beacon is located, the capsule is tracked by radar to its landing site, then the helicopters are sent to pick up the capsule. Often the capsule has to be ‘safed’, ie: the electronics and pyrotechnics disconnected before the capsule is removed to the facility where it will be stored by aircraft. If the capsule contains material from a body where there is a possibility of life, then the samples will already be in a special biocontainer within the spacecraft to seal in any biological organisms and will have special recovery measures in order to protect the Earth.
Q : Why doesn’t the capsule burn up on re-entry?
A : Capsules come in through the Earth’s atmosphere at a great velocity. They get very hot as they pass through the atmosphere. They have a special shield called an ‘aeroshell’ which protects the sensitive samples from the heat of re-entry. The shield is made from ‘ablative’ material whose surface vapourises as it travels through the atmosphere.
Q : Have extraterrestrial samples already been returned from space or
are they still science-fiction at this stage?
A : Yes, the first such missions were the Apollo missions, the very
ones which brought men to the Moon and during which a total of 382 kg
of lunar rocks were collected. The automated Soviet Luna probes also
brought back 326 g of lunar regolith (the powdery covering of the
lunar surface) around that time. This long remained the only
sample-return missions of the Space Age. In 2006, dust particles from
comet Wild 2 collected by the Stardust probe on a flyby were returned
in a capsule on Earth. Shortly before that time, a Japanese probe
called Hayabusa had scratched the surface of asteroid Itokawa,
sampling grains that were returned to Earth in 2010. More
sample-return missions are planned or have already started ; this is
only the beginning!
Q : Are sample-return missions the only way to obtain extraterrestrial
samples?
A : No. Each year, stones from interplanetary space of all size, from
microscopic to many meters in diameter, rain down on Earth. Their
rapid entries in our atmosphere are marked by fiery phenomena known as
meteors or shooting stars, and surviving fragments impacting the
ground are called meteorites. Meteorites have been studied for more
than two centuries, most of them originating from asteroids, some
likely from comets, with rare samples from Mars and the Moon having
also been recognized.
Q : If space comes to us that way, why would we need sample-return missions?
A : Sample-return missions indeed have a substantial cost, and their
combined crops will never compete with the mass of meteorites in
Museum collections, however rare these are in an absolute sense. Yet
meteorites as they are found on Earth have no context and one cannot
tell their parent body (whether an asteroid, a comet or a planet).
Even in cases where their falls have been recorded by cameras, the
extrapolated pre-impact orbit has usually been modified by
interactions with planets to such an extent that their original
provenance is irreversibly blurred. This is a serious obstacle to
decipher the clues that meteorites contain about the history of the
solar system. Imagine trying to reconstitute the history of Rome on
the sole basis of mislabelled ruin debris! But this will change with
sample-return missions. They will provide us with samples from duly
identified celestial bodies, with no alteration from interplanetary
transit or terrestrial sojourn. Not only will we gain a precious and
unparalleled knowledge of the specific bodies sampled, also we will be
able to understand how laboratory analyses of samples correspond to
remote observations of their parent bodies. That way, we will be able
to make the link between meteorites and other celestial bodies that
are only remotely observed. A few sample-return missions will thus
enable us to exploit the full potential of our meteorite collections.
It may also well be that some returned samples will turn out to be
completely unlike any known meteorite, that is, that the mission was
actually the only mean to sample the celestial body in question, and
glean qualitatively new insights on the solar system!