Bjørn Sørheim wrote:
On Thu, 13 Nov 2014 15:08:50 -0000, "Mike Dworetsky"
wrote:

Bjørn Sørheim wrote:
Philae on Comet 67P/Churyumov-Gerasimenko.

And then no discussion about it on sci.astro??
What have this ng turned into? More or less a sesspool of
destructive people?

Pretty much. It should perhaps be renamed sci.psych.abnormal.

;-)

Was there anything specific you wanted to know about Philae?

Apparently the lander bounced three times before coming to rest on
the surface of the comet, and I suspect the initial "silence" from
ESA was due to not being able to figure out why some of the readings
were varying unexpectedly such as IR and magnetometer right after
touchdown. A few images from the surface have now been received.
The lander seems to be up against some sort of vertical rock on one
side which may be shading the solar cells. They need to know more
about the exact geometry before attempting to move it, as doing
something now might make matters worse.

I watched the press confrence today (with some difficulty - NASA is
better than ESA in this respect, for shure).

So most questions were answered in that press briefing.
Philae is currently in a very dire situation on the surface, with one
leg sticking apperently into space up against a 'rock' face. Do this,
do that, as was the plan, and Philae will tip over or leave the comet
again.
This is close to catastrophe, on the other hand close to a success.
The life-giving solar panels (on the top) are receiving currently only
1.5 hours of expected 6-7 hours pr. rotation. Most experiments, at
least the mechanical ones, are not possible to do right now, because
of uncharted consequences. At least let's hope they will get some good
images before it could be over. As stated in the press conference, the
top main priority is being able to investigate and analyse the
material of the comet, which never have been done on a comet before.
Alas, this is almot impossible with the current tilt and position of
Philae, as it is placed right now.

It seems like landing on a comet with such very low gravity needs a
very sophisticated landing mechanism (which must work) and very
controled automatic operation. This didn't work this time around for
ESA. The causes must be studied carefully.

B.S.

Hindsight is usually clearer than foresight. When the lander was designed
and built (around 15 years ago) it was not possible to use techniques that
might be possible now. The original plan was to launch in 2003 but a
previous failure of the Ariane 5 launch system delayed the launch by a year
and changed the choice of destination comet. And the design and
construction started several years before that.

The main requirement would seem to be an ability to slow the descent speed
to near zero just before surface contact. This requires radar and a rocket
engine that can be throttled. Both add mass to the lander, so one or more
scientific experiments would probably need to be removed to accommodate it.

--
Mike Dworetsky

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