ESA Rosetta Night Time Excursion to reduce orbit to 20Kms

For the last two weeks, ESA's Rosetta has been orbiting comet comet 67P/C-G at a distance of about 30 km on the “Global Mapping Phase” (GMP), and is now set to go even lower.

The aim of the GMP was to gather high-resolution science data to help characterise the potential landing sites for Philae, while also continuing to monitor how the spacecraft responds to the environment of an active comet, before getting closer still.

The Rosetta team discussed whether to fly one complete orbit, the spacecraft conducted two seven-day-long half orbits at about 30 km, in different planes.

That is, on 10 September, the spacecraft was at the terminator plane (the boundary between day and night, which is itself the 06:00/18:00 plane), and performed a thruster burn to insert onto the 30-km circular orbit.

The orbital plane was then 60 degrees away from the Sun’s direction, such that the spacecraft orbited over areas of the comet in their ‘morning’ hours.

Seven days later, when the spacecraft was again on the terminator plane, it conducted another thruster burn to change the orbital plane such that it had the same characteristics as the previous orbit, but instead was flying over ‘afternoon’ areas of the comet.

Thus, from 18 September, the spacecraft was in a 28 km x 29 km orbit around the comet with an orbital period of 13 days 14 hours 59 minutes.

Check out the ESA Rosetta team blog here