Rosetta space mission - Philae probe due to land on comet on 12th Nov 2014
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coley
Well-Known Member
2hats
Dust.
On Wednesday (12 Nov) separation of orbiter and lander will occur at 09:03:20 UTC (signal arrival in earth time frame*) during a 94 second window (ie could occur up to one and half minutes later and still be within limits). Philae will take farewell shots of Rosetta but these won't be available until some time after 1200UTC as Rosetta won't be able to start downlinking data until 1053UTC (navigation/engineering/sequencing data will have priority).
The lander is planned to touch down at 16:02:20 UTC (signal arrival in earth time frame*). Mission managers have said they hope to be able to circulate images within one or two hours (the data bit rate is a little under 30kbps - recall this mission hardware is actually early 90's vintage).
However they are allowing for touchdown at any time, due to a number of variables, in a window 40 minutes either side of the planned landing time. Due to the distance the entire sequence is automated and there is no human intervention/decision making involved once the final GO is given (0735UTC on the day).
* one way light time on the day will be 28m20s
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hiraethified
I think we should make you science editor of urban75. I love your posts!
coley
Well-Known Member
Good idea
farmerbarleymow
I'm Petee's spirit animal
It's quite exciting to think we're only two days away from potentially landing on a comet. Human ingenuity is ace.
2hats
Dust.
All still running to plan. Philae didn't fully wake up on schedule last night so was rebooted as a precautionary measure but is reported to be powered up and working correctly now. Rosetta's velocity was fine tuned by 3mm per second and a final orbit determination should be made about 1930 tonight when the first GO/NOGO is given for proceeding to the lander release.
weltweit
Well-Known Member
Shit, I hope Philae isn't running windows!!
2hats
Dust.
The CPU is 16 bit with no OS (as such) - it runs bespoke code written in a mix of assembler and Ada.
2hats
Dust.
Just bear in mind that earlier in the year, prior to the nucleus being discovered to be 'duck' shaped, when it was assumed that it was probably some sort of irregular sphere of some description, the mission manager, Fred Jansen, reckoned that the chance of a successful landing was around 70-75%... I think it is rated at about 50% now.
2hats
Dust.
The 'sound' of the interaction of the comet with the solar wind (frequency upshifted by a factor 10000 to make it audible to us) picked up by a magnetometer on Rosetta:
https://soundcloud.com/esaops/a-singing-comet
https://soundcloud.com/esaops/a-singing-comet
weltweit
Well-Known Member
It does make me wonder how they will orient the lander wrt the comet so that it comes down on the target area which is itself moving. Kudos if they manage it.
2hats
Dust.
A momentum flywheel on the lander provides stabilisation and reference (6.2 Nms at 9600 rpm). The magnetometers will also be used as a cross check. They have also been carefully mapping the gravitational field so can model where the lander will be at any time after a known starting position.
e2a: The single cold gas thruster (+z up direction only) can also be employed for correction though is primarily to counter rebound at touchdown. Philae may purposefully put itself into a slow rotation during the descent if a slight axis offset is picked up (to null such arising from gas drag in the coma).
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TheHoodedClaw
acknowledging ur soup leg
Crispy
The following psytrance is baṉned: All
0.0067 mphThat's a pretty amazing level of control
Stream is up:
https://new.livestream.com/esa/cometlanding
ETA: man checking all the mice has a boring arse jumper on.
https://new.livestream.com/esa/cometlanding
ETA: man checking all the mice has a boring arse jumper on.
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Limejuice
Well-Known Member
Such a tiny and precise adjustment.
I think it's easier to grasp if you convert it to sensible measures: 18.0096 furlongs per fortnight.
2hats
Dust.
That's a pretty amazing level of control
The range error to the orbiter is around 1 metre and the error on the rate of change of range is on the order of 0.1 mm per second (ie with reference to Earth).
The positional error in the plane of the sky, however, is typically a few km. But this isn't quite as bad as it sounds since the position of the comet itself in the solar system isn't known to that degree of accuracy (prior to rendezvous it was maybe 100km or so).
Ultimately a combination of radio distance, angle and rate finding, orbital modelling and positional measurement through optical navigation with reference to the overall position of and individual features on the nucleus is used to position Rosetta and hopefully bring the lander Philae down to within a few hundred metres of the intended location (though landing descent rate, orbiter visibility for data uplink and position for radio science are somewhat greater concerns).
2hats
Dust.
The few hundred metres is the landing error ellipse on the surface of the comet. The lander won't end up x metres above the surface because it will just keep descending until it reaches the surface - at which point the lone on board thruster will help pin it to the surface, then the two harpoons will fire to draw it in closer, before the ice screws bolt it down (unless the surface is really soft, in which case it should hopefully settle down sinking up to the baseplate of the craft). The various science experiments on board (including a camera) will contribute to determining whether it has reached the surface.
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hiraethified
Look at these amazing images from 10km!
http://astronomynow.com/2014/11/11/top-ten-rosetta-images-from-10km/
http://astronomynow.com/2014/11/11/top-ten-rosetta-images-from-10km/
2hats
Dust.
If you imagine that each of smaller boulders (~10 pixels) in each image are around the size of a typical house then that might give you some sense (a human standing on the surface would just, barely, be resolvable).
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