The European probe Rosetta has been chasing comet 67P/Churyumov-Gerasimenko for more than 10 years. This spring it’s finally catching up. But not so fast. To reach its target, the spacecraft must now slow down to match the comet’s speed. After such a long journey, it would be a shame if Rosetta overshot its objective.
Mission controllers are working this spring to throttle back the spacecraft’s speed by firing its rocket thrusters. On May 20, Rosetta did a burn for nearly 8 hours to reduce its speed relative to the comet by 650 mph (1,046 km). In space, rocket fire pushes against the spacecraft, slowing it down.
A second burn is planned for today June 4 when Rosetta’s speed will be reduced by another 606 mph. More ‘delta-v’ burns (shorthand for ‘change in velocity’) through the end of July will gradually drop the distance between the two until the spacecraft achieves orbit. Each firing is part of a well-choreographed dance to bring them together.
“Upon arrival in early August, we should be at a 62-mile (100 km) distance and 2.25 mph (3.6 kph) relative velocity,” says Sylvain Lodiot, Spacecraft Operations Manager.
Meanwhile, the comet is doing anything but twiddling its thumbs as the clock ticks toward August. 67P has gone from a tiny, inactive point of light to a classic fuzzy blob with a bullet-shaped coma or atmosphere now estimated at 808 miles (1,300 km) across. It’s looking like a real comet now as recent photos taken by Rosetta attest.
Amazing to think that the spacecraft will secure its orbit around Churyumov-Gerasimenko in August and then land a separate probe named ‘Philae’ on the surface later this fall. Can humans really do such things? Yes we can.