We all know that Gravity is a work of fiction and the Hubble telescope didn’t really get hit with debris from a defunct satellite. As students from the University of Leister pointed out in a recent paper, though, there is a defunct satellite that could pose a threat to current real-life space missions: Envisat.
Envisat was a 30 foot long, £1.8 billion dollar satellite first launched by the European Space Agency in 2002. It was used to observe and monitor the Earth’s atmospheres, oceans, and ice caps, but the ESA lost contact with the satellite in April of 2012 and gave up on the mission soon after. Now it’s roaming around the Earth willy nilly at an altitude of about 790 km, which is where the largest amounts of space debris are currently located.
This is actually a lot more dangerous than you might think, as Envisat is expected to remain in space for another 150 years, and about two objects a year are expected to pass Envisat to within about 200 meters, to the point where spacecrafts sometimes have to deliberately move out of its way. If one of these objects were to collide with the satellite, it could lead to a situation known as the Kessler Syndrome, where clouds of fast-moving debris cause other collisions with orbiting bodies around Earth. You don’t need to have seen Gravity to know that this is probably not a very good thing at all, because pretty much everything that gets sent up into space is ridiculously expensive and really doesn’t do well getting collided with by other things in space.
Speaking of which, it would probably be ridiculously expensive to get Envisat back down to Earth, which is why no one is really considering that as an option. In a recent peer-reviewed student journal from the University of Leister’s Department of Physics and Astronomy, a fourth year student suggested that if the satellite were moved to an altitude of 700 km, it would be able to return to the planet in approximately 25 years. However, doing that would require 2.7 billion joules of energy, or 143.1kg of hydrazine fuel, and refueling a satellite that was never meant to be refueled in the first place would prove incredibly difficult and would no doubt costs hundreds of millions of dollars.
Ultimately the team behind the paper (entitled De-orbiting Envisat) suggest that a full analysis beyond the scope of  Journal of Physics Special Topics would be worth pursuing, since their journal is only meant to teach students about peer review and scientific publishing. “The students are encouraged to be imaginative with their topics, and find ways to apply basic physics to the weird, the wonderful and the everyday,” course professor  Dr Mervyn Roy.
Still, they’ve got a point. We’ve got a lot of stuff up in space that could possibly do this thing where it hits other stuff and explodes. Let’s get on that problem, guys.
(via Phys.org, image via Gravity)
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