Fermi space telescope fires thrusters to avoid explosive collision

Two satellites colliding in Earth’s orbit would potentially be disastrous. Not only because of the loss of the crafts, but also because of the lethal debris it would create that could damage or destroy other satellites circling the globe.

At the end of March last year NASA discovered that its Fermi Gamma-ray Space Telescope was on course to pass within 700 feet of the decommissioned Russian Cosmos 1805 satellite. 700 feet sounds like a lot, but NASA only works off position estimates and has been out by more than that in the past. It also didn’t help that only a week’s warning was given about the near pass.

As the days went by it became clearer that the two craft would be passing extremely close to each other. The most accurate estimate put Fermi and Cosmos 1805 at the exact same location within 30 milliseconds of each other. That’s too close for comfort, especially as Cosmos 1805 weighs 3,100 pounds and is travelling at 27,000mph relative to Fermi. It was calculated that a collision would destroy both craft and release energy the equivalent of 2.5 tons of high explosives. In other words, action needed to be taken to ensure they didn’t hit at any cost.

Fermi’s project scientist Julie McEnery decided to use the telescope’s thrusters, previously reserved for use only when Fermi is set to end its mission and leave orbit. Having never been tested, using them while Fermi’s mission was still in progress was a huge risk, but there was no choice. NASA fired the thrusters on April 3 for just one second and avoided the collision. They also ensured doing so would not put Fermi in danger of colliding with anything else.

Such drama in space doesn’t happen very often, but it reminds us we do have a growing problem of potential collisions and the consequences they would bring. And saving Fermi was very important as it is performing an all-sky study using the on board Large Area Telescope (LAT). Since launching in 2008 it has discovered a pulsar in the CTA 1 supernova, observed the largest yet recorded energy release from the Carina constellation, discovered antimatter occurs naturally on Earth, found two massive gamma-ray and X-ray bubbles around the Milky Way, and observed the highest energy light ever seen from the Sun. Nice save, NASA