Rosetta’s operators will begin changing the trajectory in August ahead of the grand finale such that a series of elliptical orbits will take it progressively nearer to the comet at its closest point.
“Planning this phase is in fact far more complex than it was for Philae’s landing,” says Sylvain Lodiot, ESA Rosetta spacecraft operations manager. “The last six weeks will be particularly challenging as we fly eccentric orbits around the comet – in many ways this will be even riskier than the final descent itself.”
“The closer we get to the comet, the more influence its non-uniform gravity will have, requiring us to have more control on the trajectory, and therefore more manoeuvres – our planning cycles will have to be executed on much shorter timescales.”
A number of dedicated manoeuvres in the closing days of the mission will conclude with one final trajectory change at a distance of around 20 km about 12 hours before impact, to put the spacecraft on its final descent.
The region to be targeted for Rosetta’s impact is still under discussion, as spacecraft operators and scientists examine the various trade-offs involved, with several different trajectories being examined.
Broadly speaking, however, it is expected that impact will take place at about 50 cm/s, roughly half the landing speed of Philae in November 2014.
