Spaceship approaching comet this week

This video is called CHASING A COMET – The Rosetta Mission.

How Rosetta arrives at a comet

1 August 2014

After travelling nearly 6.4 billion kilometres through the Solar System, ESA’s Rosetta is closing in on its target. But how does a spacecraft actually arrive at a comet?

The journey began on 2 March 2004 when Rosetta was launched on an Ariane 5 from Europe’s Spaceport in Kourou, French Guiana.

Since then, Rosetta has looped around the Sun five times, picking up speed through three gravity-assist swingbys at Earth and one at Mars, to enter an orbit similar to that of its destination: comet 67P/Churyumov–Gerasimenko.

This icy target is in an elliptical 6.5-year solar circuit that takes it from beyond the orbit of Jupiter at its furthest point, and between the orbits of Mars and Earth at its closest to the Sun.

Rosetta’s goal is to match the pace of the comet – currently some 55 000 km/h – and travel alongside it to within just 1 m/s between them, roughly equivalent to a walking pace.

Since early May, Rosetta’s controllers have been pacing it through a tightly planned series of manoeuvres designed to slow its speed with respect to the comet by about 2800 km/h, or 775 m/s, to ensure its arrival on 6 August.

ESA’s experts are playing a crucial role, having worked extensively behind the scenes to develop a series of ten orbit-correction manoeuvres that use Rosetta’s thrusters to match the spacecraft’s speed and direction with that of the comet.

“Our team is responsible for predicting and determining Rosetta’s orbit, and we work with the flight controllers to plan the thruster burns,” says Frank Dreger, Head of Flight Dynamics at ESA’s Space Operations Centre, ESOC, in Darmstadt, Germany.

The burns were carried out every two weeks in May and June and, after a short test, the three subsequent manoeuvres were some of the longest ever performed by an ESA spacecraft – exceeding seven hours.

These first burns dramatically reduced Rosetta’s speed with respect to the comet by 668 m/s of the necessary 775 m/s required by 6 August, when Rosetta will ‘arrive’ at a distance of just 100 km from the comet.

Throughout July, the burns were made on a weekly basis, and will culminate in two short orbit insertion burns set for 3 and 6 August.