Lots of number crunching. There are very simple transfers they could do like the Hohmann transfer. Realistically, the mass of the comet is so small, and conserv

Lots of number crunching. There are very simple transfers they could do like the Hohmann transfer. Realistically, the mass of the comet is so small, and conservation of fuel is so important that they are probably doing a significantly more complicated transfer that utilizes the gravity of other orbital bodies to slingshot the lander. Some wikipedia pages you may find interesting: http://en.wikipedia.org/wiki/N-body_problem http://en.wikipedia.org/wiki/N-body_problem http://en.wikipedia.org/wiki/Interplanetary_Transport_Network http://en.wikipedia.org/wiki/Interplanetary_Transport_Networ... Ideally they would have an orbit that would have a really low intercept velocity, so the deceleration burns would require the least amount of fuel possible. Once they get close, they burn to get into a stable orbit around the comet. I found one article covering the math behind the deceleration orbit: http://blog.wolframalpha.com/2014/08/04/rosetta-first-mission-to-orbit-and-land-on-a-comet/ http://blog.wolframalpha.com/2014/08/04/rosetta-first-missio...