Catching Stardust by Natalie Starkey

Author:Natalie Starkey
Language: eng
Format: epub
Publisher: Bloomsbury Publishing

Chapter 6

Taking the Science to Space

Having established that the distances to even the closest comets and asteroids are vast means that visiting them in their natural habitat is technically challenging, financially costly, time consuming and requires patience, as well as technical expertise. Of course, some of these objects come a little closer to Earth as NEOs, which makes them slightly easier and cheaper to reach as they transit the inner Solar System after they’ve been diverted from their normal orbits in the Kuiper Belt, Oort Cloud or asteroid belt. Studying space objects in the near-Earth environment still has its challenges, but their relative proximity to Earth has some benefits, as they are easier to get to with space missions and they can also be studied using less powerful telescopes, including amateur ones. Nevertheless, intercepting NEOs using spacecraft is still technically demanding because these inner Solar System visitors arrive on trajectories that are challenging to approach with a spacecraft, and at speeds that are hard to achieve with a direct launch from Earth. It certainly isn’t a case of launching a spacecraft from Earth and heading in a straight line to meet the asteroid or comet. Often it will take a space mission many years just to catch up with an orbiting NEO, because it has to perform gravitational slingshots around the rocky planets and the Sun to build up enough speed, and to get on to the correct orbit as the object it’s trying to catch. In fact, on its 10-year journey to catch up with comet 67P/C-G, the Rosetta spacecraft performed three gravitational slingshots of Earth and one of Mars after launch in order to gain enough speed to catch up and approach the comet from behind, before braking to cruise alongside it at the same speed.

An added issue is that comets and asteroids are small in comparison to planets, so they have very little gravitational attraction. This makes approaching and orbiting around one no easy matter, requiring a powered craft capable of manoeuvring itself to achieve an intercept without the benefit of a large gravitational pull from the object it’s approaching.

Another of the many complications of approaching NEOs is that comets, in particular, but also some asteroids depending on their composition, tend to be very active in the inner Solar System. If the object is rich in volatiles, it will affect how much material streams off it in the form of rock dust particles and gas as the volatiles inside it are gradually heated up as the object approaches the Sun. The dusty activity produced by the object is enough, by itself, to bombard and cover space instruments in dust, rendering them useless in this situation. Solar panels, for example, obviously won’t work very well if they are covered in dust as it blocks the Sun’s rays. Some high-speed particles could easily even puncture spacecraft panels or instruments as the process of dust leaving a comet isn’t always gentle – some dust leaves its parent body rather explosively in a powerful jet.

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