Philae update: First of four "go-no-go" decisions is a GO!

It's been a day of calm before the storm here at the European Space Operations Centre in Darmstadt, as we get ready for the big event tomorrow: Philae's hoped-for landing on a comet.

There have been two press briefings today. The second one is actually going on right now, but the most important piece of news was shared at the start: the first of four "go-no-go" decisions has been made, and it's a "go." Mission navigators have gotten data back from Rosetta that indicates that the spacecraft is on the correct trajectory to deliver Philae to the comet. At any of the later "go-no-go" points, they could abort the landing; if they did that, it would take two weeks to bring the spacecraft back to the right position with respect to the selected landing site. One down, three to go. The next three decisions happen at 0:00, 01:35, and no ater than 07:35 UT.

This morning's press briefing was just a preview, mostly benefiting people who haven't been paying close attention to the mission; but there were a few interesting tidbits.

• Spacecraft operations manager Andrea Accomazzo said that yesterday there had been an anomaly on Philae; they switched it on last night, and it did not switch on correctly. They restarted the computer and it now seems ready.
• Mission manager Fred Jansen emphasized the risky nature of the attempted landing. If you want to land on an object that you know nothing about, he said, then you run risks. After analyzing the surprising terrain of the comet, he says the team figures they have about a 75% chance of success.
• ESA science advisor Mark McCaughrean and Rosetta project scientist Matt Taylor talked about how great the results of Rosetta have been so far, and reminded the audience that regardless of what happens tomorrow, Rosetta will continue its scientific work at the comet all next year, through its perihelion in July.

Clearly, the risk of the landing and the uncertainty of success is weighing on everyone's minds now. To make an editorial comment, I think ESA missed an opportunity this week: there should have been a big press release on Monday, coordinated with the gorgeous results presented at the Division for Planetary Sciences meeting. The resulting "Rosetta is a great scientific success!" message would have been a matter of public record, no matter what happens with Philae. I say this knowing full well that there are political considerations (both within the mission's science teams and outside ESA) that prevented ESA from doing the big splash that I am sure they would have liked to do -- ESA is not the reason that there was no Rosetta science press release this week. But I think it's a shame. Hopefully Philae will be a fantastic success and there will be no repercussions. But if Philae fails, it will be hard to correct the public impression that the whole mission is a failure. ESA has seen that, with Mars Express: it's a fantastically successful mission, but the failure of Beagle 2 strongly influenced public perception of Mars Express success.

More from the morning press briefing:

• During Philae's descent, we should get CONSERT and ROMAP data, as well as the farewell images from ÇIVA. (Note: this camera's name is pronounced "Shiva.") It's still not clear to me whether any ROLIS images of the surface of the comet will get transmitted from Philae before the moment of touchdown.
• The ÇIVA images will be released to the Web between 13:40 and 14:30 CET tomorrow (assuming ESA gets them as expected); this is hours before the landing (which is expected at 17:03).
• One journalist inquired about whether there would be any public release of OSIRIS science camera images. Fred Jansen said "We definitely intend to squeeze some of these out tomorrow."

The next media event is tomorrow at either 7 or 8 am, local time. I'm told that ESA expects 400 journalists here. It's clearly straining their capacity. I expect fistfights over electrical outlets. One way or another I'll find a spot to report from, and keep bringing you the latest news!

I've updated my timeline with one or two corrections, and I'll keep doing that as I follow events on the mission. Stay tuned...

Edited to add: at the end of the day, this happened. This is Klim Churyumov, one of the comet's co-discoverers, with a 3D model of Churyumov-Gerasimenko.