Rosetta, Philae and Comet 67P/Churyumov-Gerasimenko.

[softweir]

The CONCERT instrument mounted on the lander is a high-gain, multi-spectral, low-bandwidth transponder. It isn't used for communications: all it can do is re-send signals it receives directly back to Rosetta so Rosetta can measure propagation delay as well as attenuation. The transmitter Philae uses to transmit to Rosetta is entirely different, and it is this which is only working intermittently. That CONCERT works is independant of this, and discussion of how it can transmit through the comet is irrelevant to discussion of the communications problems.

[YNM]

The transmitter problem seems to be due to illumination - it said that the lander only receive 90 min of sunlight out of ~12 hour rotation.

[Frida Space]

Yes, the main problem is still Philae's energy, not the communication link itself. On Rosetta's side, they've done what they could to optimize the orbit, but it's clear that the orbiter's great distance from the nucleus is a problem too (it first detected a signal at 200 km of distance, then at 206 or so km it couldn't detected anything anymore so it had to be lowered to 177 km if I recall correctly), however because of that navigation glitch it can't go much further down -- in fact, I read they are experiencing the first signs of this glitch even at the current altitudes.

[LordFerret]

Any chance there's a map yet indicating the locations of the newly named features?

Edit:

Only thing I've found so far is this -

http://astrobob.areavoices.com/2015/04/14/dwarf-planet-ceres-a-more-colorful-view/

A topographic map of Ceres with provisional names given to each quadrangle. Ceres’ craters are named for agricultural gods; other features after world agricultural festivals. Credit: NASA / JPL / UCLA / MPS / DLR / IDA / JohnVV / Emily Lakdawalla - See more at: http://astrobob.areavoices.com/2015/04/14/dwarf-planet-ceres-a-more-colorful-view/#sthash.9tbk5gA6.dpuf

Edited July 11, 2015 by LordFerret

[Brotoro]

Yumyum?

[Frida Space]

It looks like Philae transmitters are not working properly.

[LordFerret]

Oh, great.

[Frida Space]

So, big - and mostly bad - news:

- it's confirmed, one of Philae's two transmitters isn't working properly;

- plus, one of Philae's two receivers is "damaged", whatever that means

- changes in the illumination of each solar panel suggest Philae might have been moved by a jet

- Rosetta is experiencing the same problem as a few months ago: increasing dust, star trackers getting confused, Rosetta not knowing where she is. For safety reasons, the s/c's altitude has been raised from 153x180 km to 170x190 km.

[PB666]

So, big - and mostly bad - news:

- it's confirmed, one of Philae's two transmitters isn't working properly;

- plus, one of Philae's two receivers is "damaged", whatever that means

- changes in the illumination of each solar panel suggest Philae might have been moved by a jet

- Rosetta is experiencing the same problem as a few months ago: increasing dust, star trackers getting confused, Rosetta not knowing where she is. For safety reasons, the s/c's altitude has been raised from 153x180 km to 170x190 km.

Wow its sounds like she landed someplace hostile, like an active comet ..... oh wait, that was the plan, whoops.

[Camacha]

I guess this shows why rocket science is synonymous with things that are hard to do. This is not easy at all.

[LordFerret]

So, big - and mostly bad - news:

- it's confirmed, one of Philae's two transmitters isn't working properly;

- plus, one of Philae's two receivers is "damaged", whatever that means

- changes in the illumination of each solar panel suggest Philae might have been moved by a jet

- Rosetta is experiencing the same problem as a few months ago: increasing dust, star trackers getting confused, Rosetta not knowing where she is. For safety reasons, the s/c's altitude has been raised from 153x180 km to 170x190 km.

Wasn't this probe anchored down with its harpoons? Then again, if blasted by a jet, I suppose that could take out a receiver and muck up the solar panels. Yes, bad news. :/

[jfull]

None of the anchoring systems were able to deploy correctly

[Godot]

Poor Philae ... only a short while awake again and already in big trouble

[KerikBalm]

Wasn't this probe anchored down with its harpoons? Then again, if blasted by a jet, I suppose that could take out a receiver and muck up the solar panels. Yes, bad news. :/

No... and that was the whole problem... it bounced.... and bounced again.... and ended up really far from where they intended it to land (which would have given it enough sunlight.

Considering the force of gravity on the probe is said to be less than the weight of a sheet of paper... it doesn't take a very strong "jet" to move it

[kurja]

Considering the force of gravity on the probe is said to be less than the weight of a sheet of paper... it doesn't take a very strong "jet" to move it

It may not weigh very much where it is but it's mass is still 100kg, right?

[*Aqua*]

Yep, it's mass is still 100 kg. But it's weight is about 0.3 grams which is less than most feathers weight on Earth.

[PB666]

Here is a link

http://www.bbc.com/news/science-environment-33596274

[YNM]

Next time they should put a full size claw, maybe ?

[lajoswinkler]

Jets on comets aren't tiny.

They originate from very wide areas sublimating into space. Imagine a town square with a pillar of light above it, visible only if your eyes adjust to the darkness. That would be the experience of standing on it.

Philae is a 100 kg box the size of a washing machine. Yes, its weight is tiny, but you need lots of energy to accelerate it. In my opinion, there's a greater chance of it tilting or making a roll because of the instability of the crumbly terrain giving off volatiles, than it being pushed. If there were such concentrated jets appearing all over the comet, like in Deep Impact here:

The surface of the comet would be shrouded when looked from orbit. It would look fluffy, foggy.

Edited July 21, 2015 by lajoswinkler

[pincushionman]

This is one of those rare situations in space where the mass is irrelevant and the weight matters greatly. Yes, a force can only accelerate it a small amount, but it only needs a small acceleration to send it sloooooowly tumbling across the surface.

[softweir]

This is one of those rare situations in space where the mass is irrelevant and the weight matters greatly. Yes, a force can only accelerate it a small amount, but it only needs a small acceleration to send it sloooooowly tumbling across the surface.

Indeed and exactly, except it is hardly rare - it takes only microscopic forces to change the orbits of small bodies!

With minimal gravity to hold it down, any force on the lander greater than its local weight will move it, no matter how slowly. Mass doesn't stick things in place, it just slows itself down. It's the weight that sticks things to planets. Even a tiny force could lift accelerate the lander away from the surface, far enough that it could turn over or fall into a deeper crevice than it was already stuck in.

[lajoswinkler]

You do realize the forces of gases sublimating (total pressure is almost interplanetary vacuum) are negligible, otherwise, when applied to the whole area of the comet that's sublimating, it would cause the thing to behave analogous to an oxygen tank when you forcibly remove its valve by an axe.

[PakledHostage]

I'm with Lajos. Bear in mind that Philae is generating heat that would conduct into the comet through any contact points with the comet's surface. It also has a reflective surface that will reflect the incoming solar radiation back onto some areas of 67P/Churyumov-Gerasimenko's surface while shading it in others. Philae is very likely shifting as those effects cause the surface that it is sitting on to sublimate away at uneven rates. We know that Philae came to rest in an uneven location to begin with. It is unlikely that that uneven surface would sublimate away uniformly.

[softweir]

You do realize the forces of gases sublimating (total pressure is almost interplanetary vacuum) are negligible, otherwise, when applied to the whole area of the comet that's sublimating, it would cause the thing to behave analogous to an oxygen tank when you forcibly remove its valve by an axe.

That is an assumption. However: a) The existance of jets implies that this is not the case - if the surface of the comet was sublimating then it would be surrounded by a uniform halo of sublimating gas. the velocity of the jets and the fact they can carry dust off the comet further suggests that this is not mere sublimation.

It should also be remembered that the ices are not on the surface of the comet, which is largely dust and grit. This would generate small amounts of resistance to the exit of sublimating gasses, increasing the pressure above the zero of vacuum. And if any of the gasses are sourced from deep inside the comet quite non-negligible pressures could build up.

The reference to a bottle of oxygen is irrelevant. There is an entire continuum of circumstances from ices sublimating in vacuum through ices sublimating under a thin layer of dust all the way up to ices evaporating in bubbles of less volatile ice bursting their way out breaking the comet in half. Given the behaviour of the comet, I feel we are still at the low end of that continuum.

I agree that any forces being exerted on the lander by a gas jet will be tiny, but so long as they are larger than the local weight of the lander (which is also tiny) then the jet would still be able to move it.

[lajoswinkler]

Jets are sublimation.

We're seeing highly exposed images of the comet. This is not Halley's comet or some sungrazer. Nothing wild happening there.