Frequently Asked Questions
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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
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!