Philae landing on the nucleus of Comet 67P C-G Options

[tanjent]

Strictly speaking...Spirit and Opportunity bounced quite a few times in their airbags...

[elakdawalla]

Just a quick check-in from Darmstadt. What a ride it's been today. It's been occasionally frustrating in the media room -- ESA are always much more focused on the VIPs than the wretched news media (we were actually 2 floors down from the room where they were doing updates). But it was fun anyway.

I anticipate little news coming out of the mission except maybe in the form of the kinds of tweets we just saw from ROMAP before the 2pm CET briefing. Everybody is just too tired. Even the news media. We all need to sleep in.

Except I have one more interview on BBC World News tonight

[pmetschan]

So just to be clear? Do we know if the lander is stationary on the surface of the comet?

[JTN]

Tidbit of news from elakdawalla (who I thought was already totally done for the night, but just blogged -- thanks!) that I hadn't noticed mentioned already:

The most-anticipated data was from the ÇIVA panoramic imager. Although the imaging sequence executed, there was a problem with the data that was returned to Earth; it had black stripes or bars or was just black. It's unclear what went wrong, especially since ÇIVA worked great during descent. They may ask Philae to re-run the ÇIVA sequence while the rest of the science sequence is executing (they can apparently do this in parallel) in order to try to get this important image observation acquired and on the ground.

[fredk]

Wow, three landings. I'm amazed it made it past the second - after two hours I'd expect the lander could have drifted into any orientation relative to the surface and been damaged on the second landing. But clearly it survived if we have telemetry from ROMAP for the third landing. I don't know if we have confirmation of any telemetry after the third landing, so it's current status is unclear.

Still, I suppose we may get telemetry even if the lander came down upside down. That's got to be a very real possibility now. I wonder how much science could still be done in that scenario.

About drifting between landings, that depends strongly on the ratio of horizontal to vertical velocity after the first landing, and that's clearly very uncertain now. For a short bounce, zero horizontal velocity means no drift, even though the comet is rotating. For a higher bounce, Coriolis effects due to the rotation should become important, but it's not clear off the top of my head what drift might result.

[spacearch]

I don't know if we have confirmation of any telemetry after the third landing, so it's current status is unclear.

Ulamec said two hours after the first touchdown signal, the indications of "turning" due to the flywheel stopped, but that they still had a radio link and data past that point. Sounded like it was gone as expected by the time of the media briefing.

Since the fluctuations of the signal were so visible during the turning, I wonder if that means the lander finally settled right side up? I don't know anything about the radiation pattern of Philae's antenna, but wouldn't the signal be weaker if it were on the side or top plate?

[nprev]

Just got home from work, and have only been able to follow events sporadically. Question/thought: If the lander is indeed upright, would it be possible to firmly secure Philae by just embedding the sampling drill without retrieving a sample?

Fully understand that would be a MAJOR sacrifice in science return, but the trade-off would presumably be allowing the rest of the instruments to execute a full campaign.

Not anyone's preferred option, obviously. But is this an option at all?

[MarsInMyLifetime]

Just got home from work, and have only been able to follow events sporadically. Question/thought: If the lander is indeed upright, would it be possible to firmly secure Philae by just embedding the sampling drill without retrieving a sample?

It's a chicken-and-egg problem: you need the other anchoring in place to be able to use the drill. Used by itself, the drill might spin/rattle the body around instead. If the craft is upright after next contact, they'll assess the use of the screws again and possibly the harpoon, depending on ability to reuse them. There is plenty of contact, imaging, and sounding science to be done while they can.

[MarsInMyLifetime]

I don't know anything about the radiation pattern of Philae's antenna, but wouldn't the signal be weaker if it were on the side or top plate?

Possibly, but it only needs to reach Rosetta, since the craft are set up as a relay system. The main problem in this case would be that most of the instruments and cameras would be pointed the wrong way. Hope for the best!

[spacearch]

The main problem in this case would be that most of the instruments and cameras would be pointed the wrong way.

I realize that. I was just trying to find comfort in the fact that Ulamec thought it worthwhile to mention the fluctuating signal during the bounce, but didn't mention anything about the final steady signal being weaker than what they had been seeing during descent. Again, though, I guess the significance of that depends on whether or not the antenna's radiation pattern varies with orientation.

[nprev]

I imagine that the actual location of the lander is another variable that might affect expected signal strength.

EDIT: MarsInMyLifetime, I forgot to add that my drill idea assumes at least one footpad anchor was embedded (somewhat, anyhow).

[MarsInMyLifetime]

I imagine that the actual location of the lander is another variable that might affect expected signal strength.

EDIT: MarsInMyLifetime, I forgot to add that my drill idea assumes at least one footpad anchor was embedded (somewhat, anyhow).

That does make a difference. But in that case, if they were able to drill with only one anchor, I wonder why not finish the sampling? Was anchoring required for any other tests? I hope that the bounces did not break off or compromise the other instruments that depended on contact/compression data.

[anticitizen2]

The ice screws use the energy from impact to drive into the surface - Reference
Maybe they were able to dig in at the third landing.

The harpoons use a gas generator, so they are certainly single-use.
Dr. Ulamec seemed certain at first touchdown that they had fired. So they are probably not an option, unless he was mistaken.


Edit: Someone asked for info on SD2, here is a paper on it
 SD2.pdf ( 399.24K ) Number of downloads: 1933

[MarsInMyLifetime]

Thank you for that link. It answers many questions and reminds us why anchoring is critical. Fingers crossed!

[rlorenz]

A dual landing is special indeed, and make this another unintended first.

For comets specifically, yes, but not planetary landings. A lot of landers bounce (Pathfinder especially);
Huygens bounced/skidded out of the hole it made. But more to the point one of the Surveyors bounced a bit IIRC,
and one Surveyor was even commanded to take off again and hop a little to one side.