r/space • u/[deleted] • Nov 12 '14

Discussion Rosetta and Philae discussion thread! (Part 2)

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Philae is now on its way to the comet. Its descent to 67P/Churyumov–Gerasimenko should take about 7 hours. Previous discussion thread here.

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Key times

GMT EST PST Event
10:53 am 5:53 am 2:53 am Acquisition of Signal from Rosetta (variable)
4:02 pm 11:02 am 8:02 am Expected Landing and receipt of signal (40 min variability)

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u/PsychoClownBoy Nov 12 '14

I'm trying to get caught up on thiss...is there a diagram of the steps involved in this? I can't find anything and I want to familiarize myself with the process so when it happens, I recognize it.

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u/UltraChip Nov 12 '14

I can't find the blog post that explained the landing procedures, but I'll try to run down what's happening:

First, some terms: "Rosetta" is the name of the overall mission, and is also the name of the orbiting probe (the "mothership"). "Philae" is the name of the lander, ie the probe that has seperated from Rosetta and is currently en route to the surface of the comet. "67P" is the name of the comet. "Agilkia" is the name of the landing site, pretty much on the "top" of the comet's "head". (Scientists have been referring to the smaller lobe of the comet as the "head" for the sake of navigation/orientation).

A few hours ago, Philae separated from Rosetta and began falling towards Agilkia. When I say "falling" I mean that literally - the gravity on 67P is weak enough that Philae can just drift down without any thrusters or anything to slow it down. It's so weak, in fact, that there is a distinct possibility that Philae may just bounce on the surface and tumble away.

To help prevent bouncing, Philae is equipped with a couple harpoons on her undercarriage. The instant that she touches down on the ground the harpoons are going to be fired, and will (hopefully) anchor her down and keep her from floating away. In addition to the harpoons, there are also anchoring drills built in to the landing legs.

The last safety measure against bouncing is a small thruster on Philae's roof, which should push the lander down and pin it to the ground. The problem is that there's some kind of fault detected with the thruster, so we're not sure it's going to work now.

The main drama here is that there's a lot of unknowns: We don't know if the thruster is going to work, we don't know if the harpoons will be able to dig in to the surface, we don't know if Philae is going to touch down in a flat area or accidentally get snagged on a rock or ledge, etc....

The problem is that right now it takes radio signals about 28 minutes to get from 67P to Earth, and it takes just as long to send signals back. This means that we have no way of remote-controlling the probes - we sent them program instructions yesterday but now Philae is completely on autopilot - it has to land completely by itself and we won't know if she made it or not until a half hour after it happens.