Emily LakdawallaSep 02, 2008

Rosetta's zeroing in on Steins

As of midnight last night (UTC, so that's about 17 hours ago now) ESA's Rosetta spacecraft has all its science instruments on, getting ready for its first close encounter with an asteroid. The closest approach to 2867 Steins happens at 18:37 UTC on Friday, September 5, at a distance of 800 kilometers. It's still too early for the spacecraft to actually be gathering much in the way of scientific data on the asteroid; currently it's warming up and calibrating its instruments, getting ready for the action-packed encounter. Meanwhile, the OSIRIS and navigational cameras have been snapping images of the asteroid -- still an unresolved point of light -- for a month.ESA's blog is now live, with posts about the upcoming encounter; I'll be watching that and the Rosetta website for news, and reporting it here, all week. I'll also watch Daniel Muller's website for a realtime countdown of events. I understand that the first images are planned to be released (assuming all goes well) on Saturday, September 6, at a press event at the European Space Operations Centre at 12:40 CEST (10:40 UTC); hopefully they'll be released on the Internet concurrently with that, and I'll find them when I wake up on Saturday morning. In the meantime, I'll repost my science timeline here.

Aug 4
OSIRIS and NAVCAM begin optical navigation campaign
Sep 1
Other science instruments switched on
Initially, the other science instruments will be occupied with calibration, decontamination, and other "warming-up" routines. Meanwhile, the cameras will continue taking images for optical navigation purposes.
Sep 2
Trajectory Correction Maneuver
This and the following two maneuvers may be canceled if optical navigation results indicate that the spacecraft is on the proper course for the encounter.
Sep 4
Trajectory Correction Maneuver
16:00End optical navigation campaign
The data must be returned to Earth quickly if the final Trajectory Correction Maneuver is to be performed.
Sep 5
Trajectory Correction Maneuver
08:00Attempt to put cameras into tracking mode
17:57Begin spacecraft flip
The spacecraft must rotate into a particular orientation in order to track Steins throughout the flyby while also keeping sensitive parts of the Philae lander out of direct solar illumination. The flip takes about 20 minutes to complete; during this time, the cameras should still be tracking the asteroid.
18:18Entry into Asteroid Fly-By Mode
The spacecraft will now perform automatic tracking of the asteroid based upon information from the navigation cameras.
18:27End telemetry from Rosetta
The geometry of the flyby will result in the spacecraft's high-gain antenna pointing away from Earth. Earth will be out of communication with Rosetta for about an hour.
18:35Rosetta views Steins at "zero phase"
Rosetta will pass almost directly between the Sun and Steins, an unusual geometry that provides immensely valuable data on the way that the asteroid's surface reflects sunlight. The entire "globe" of Steins will be fully lit by the Sun.
18:37Asteroid (2867) Steins Closest Approach (800 kilometers)
19:37End Asteroid Fly-By Mode; start high-gain antenna rotation
Control of the spacecraft's orientation will be handed back from the optical navigation system to the spacecraft's internal sequences. At the same time, the high-gain antenna will begin to rotate back towards Earth. The rotation will take 25 minutes to complete. It is possible that the spacecraft will remain out of communication with Earth for 22 of those minutes, until 22:02.
20:25Resume telemetry transmission with Earth
NASA's Goldstone radio antenna will receive Rosetta's communications.
21:25Earliest possible start of scientific data reception on Earth
The first five hours of downlink will contain data from the OSIRIS and VIRTIS instruments. Then two more hours of VIRTIS, followed by data from the rest of the science instruments.
Sep 6
End first downlink

From September 6 to 14, there will be daily communications passes with ESA's New Norcia station and NASA's Goldstone station to relay more data from the encounter. After that, communications passes continue with the New Norcia station only through October 5.

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