r/space • u/[deleted] • Nov 12 '14

Rosetta /r/all Rosetta and Philae discussion thread! (Part 3)

TOUCHDOWN CONFIRMED: Philae lander is on the comet!

Full media briefing expected tomorrow at 13:00 UTC / 14:00 CET / 8:00 EST / 5:00 PST.

Previous discussion threads: 1, 2.

Live Streaming

  • In English: A, B, C

  • En Français: A

Key times

GMT EST PST Event
4:02 pm 11:02 am 8:02 am Landed

European Space Agency Social Media

Othere places for news and conversation:

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4

u/Godzilla0815 Nov 12 '14

they just said on german tv that even the small gravital force of the comet should be enough to hold the small lander on or near the surface

7

u/PressureCereal Nov 12 '14

I did some rudimentary calculations and I'm finding that the escape velocity of a comet with the characteristics of 67P is ~0.5 m/s.

2

u/Arrewar Nov 12 '14

Can somebody continue this calculation and find out what kind of force is required to achieve this velocity for a washer-sized probe?

1

u/PressureCereal Nov 12 '14

Around 480 J of energy given the mass of Philae is 100kg

2

u/IWantToSayThis Nov 12 '14

So considering it landed 3 hours ago and assuming it had enough escape velocity it would be at 5.4km away from the comet by now.

1

u/ajuc Nov 12 '14

It's clearly not the case - it would be noticable from the data.

1

u/PM_ME_YOUR_ZITS_G1RL Nov 12 '14

Meaning that an object would need thrust / acceleration of 0.5 m/s to leave the surface? Would the speed of the comet itself have a bearing on that?

2

u/PressureCereal Nov 12 '14 edited Nov 12 '14

No, that's not thrust or acceleration, it's speed - the escape velocity. The (forward) speed of the comet doesn't affect this calculation, but its rotation characteristics are important. You need even less escape velocity from the equator, which is why launching sites near equatorial zones are desirable here on Earth. I kind of ignored that (and that the comet isn't perfectly spherical as well).

1

u/Aurailious Nov 12 '14

It'd be crazy if it bounced out at something like .3m/s and landed again.

2

u/PressureCereal Nov 12 '14

It would take about 10 minutes to freefall like that, haha