author: none
Nov 11, 2014
astro RosettaOver tonight and tomorrow morning the European Space Agency (ESA) will attempt to land a probe on a comet.
The Rosetta spacecraft and her little sister Philae were launched from Earth in March 2004. They have flown by the Earth three times and Mars once in four orbits round the Sun .. each fly-by has transferred a little energy to the spacecraft to pump Rosetta’s orbit high enough to intercept a comet called 67P/Churyumov-Gerasimenko (67P, or Chury, for short) which is diving towards the Sun. They met in August, about five times further that the Sun than the Earth is, when Rosetta started surveying the comet for a place for Philae to land.
Chury is a very odd shape, about 4Km long, its gravity is tiny .. not enough to pull it together into a sphere. It has two bulbous ends connected by a thick neck and Philae is aimed to land on one end. Chury and Philae will be just over 22Km apart when Rosetta dive-bombs Chury .. Philae will be released at 4am Wednesday, and Rosetta will divert back to orbiting Chury. Philae will take about 7 hours to fall onto Chury, landing gently sometime around 11am Wednesday (give or take about 20 minutes).
As mentioned Chury has little gravity so Philae (about the size of a dishwasher) will fire two harpoons into the icy surface of the comet, then drive three screws from its landing pads to stop it bouncing and keep it upright. What excites me about this landing is that, unlike putting down on Mars which a violent event (“seven minutes of terror!”), this will be very gentle. Chury is blacker than coal, traveling at 18Km/sec; Rosetta is flying alongside and will ‘throw’ Philae at a small spot 22Km away on Chury. Philae has no means of steering and it will drift across the gap at walking pace.
I’m watching the activity in the ESA Ops Center, where it’s after midnight as I type this and there’s almost nobody there, but will start to change in a couple of hours. Philae is ready, Rosetta is ready .. about 1am, our time, Rosetta will turn and aim itself at Chury. Three hours later, Philae will be dropped off and will photograph Rosetta as it drifts away .. about ten minutes later, when Rosetta is a safe 100 meters distant, Philae will deploy its landing struts and rotate to a feet-down attitude, and Rosetta will stop its own descent and resume orbiting Churny, ready to gather Philae’s data through descent and landing.
Photo taken by Philae from its perch on Rosetta, looking past one of Rosetta’s solar panels at Chury, 16Km away