Philae may have scraped a crater during its landing

[Buster's Uncle]

Philae may have scraped a crater during its landing
The Week
Meghan DeMaria 10:46am ET



When the Philae lander touched down on comet 67P/Churyumov-Gerasimenko last month, it may have scraped the rim of a crater with its landing gear.

Russian scientists suspect that the lander grazed a comet after it was deployed from the Rosetta spacecraft on Nov. 12. The Philae lander bounced multiple times before attaching itself to the comet, and its location is now unknown.

Magnetic field data from the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP), which is mounted on the Philae lander, suggests that the legs of the lander scraped what may have been a crater rim after its first bounce. The scrape may have sent the lander spinning away from its intended landing site. The Philae lander is now in a low-power hibernation mode, and scientists are working to determine its exact location.

Malcolm M. Campbell   @m_m_campbell 
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Happy accident.
@Philae2014's lucky tumble.
http://news.discovery.com/space/philae-may-have-grazed-a-crater-and-tumbled-over-comet-141202.htm … #CometLanding #astronomy by @JPMajor

10:19 AM - 2 Dec 2014

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 "It was not a touchdown like the first one, because there was no signature of a vertical deceleration due to a slight dipping of our magnetometer boom as measured during the first and also the final touchdown," ROMAP co-principal investigator Hans-Ulrich Auster said in a statement. "We think that Philae probably touched a surface with one leg only — perhaps grazing a crater rim — and after that the lander was tumbling."
   

http://theweek.com/article/index/272902/speedreads-philae-may-have-scraped-a-crater-during-its-landing

[Geo]

Tumbling how - head over heel, or spinwise?

[Unorthodox]

Tumbling how - head over heel, or spinwise?

Yes.

[Geo]

Both directions? I mean head over heel, and around on its plane?

[Unorthodox]

Would almost have to be all directions. 

[Geo]

Then its almost a miracle the lander finished its trajectory in a more ir kess uoright position. At least, I assume it did because it could use its drill equipment.

[Buster's Uncle]

I'm not sure it could; all the reports I've seen -quite a few- are mum about drilling attempt results.

[Unorthodox]

There was some preliminary chemical analysis, thought that was from a drill sample? 

It's a miracle this thing was in any kind of working order, really.  The landing thruster malfunctioned, the anchors didnt fire, and the tumble over the crater.   

[Buster's Uncle]

There was some sort of spectroscopic gas analysis or something at first touchdown.

It fell 1,500 feet to the second touchdown - that had to be a non-trivial impact, even at trivial gees.

[Unorthodox]

"Fell" is probably relative at that point.  "Traveled" 1500 feet is probably more accurate, and it could be very trivial depending on relative velocities. 

[Buster's Uncle]

Well, it traveled for over an hour - a long time to build acceleration even at very low gee.

[Unorthodox]

It bounced, which means it had SOME upward momentum gravity had to overcome before it started falling, so the time difference can be misleading.  Then the irregular shape of the thing, and the fact we don't know where it is, real hard to judge how "hard" it fell with the given information.  It could even be at a higher relative altitude than the first touchdown.  Don't really know, too little to go on at present. 

Think of a basketball, each bounce is a little softer than the last.  The second landing HAD to be softer than the first without some significant additional force applied to the thing.  I don't know how hot the thing went in on first touchdown, but I doubt the gravity was enough to rebuild that velocity. 

[Buster's Uncle]

Hmm.  And the lander was designed to survive several G at takeoff from Earth, at that...

[Geo]

Well, it traveled for over an hour - a long time to build acceleration even at very low gee.

The lander wasn't supposed even to be capable of acceleration after touch down...

[Unorthodox]

Gravity causes acceleration. 

As for the tumbling, the length between it starting to spin at the bounce and landing was probably critical.  There was almost certainly some kind of guidance that was able to at least partially correct it's orientation prior to the second landing.