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

[vikingmars]

Now, it's time to open a new section devoted to the landing of the Philae lander itself on the nucleus of Comet 67P C-G.

Also to answer better the earlier post,
http://www.unmannedspaceflight.com/index.p...st&p=212943
and for your information, here is the quick summary (as a "pdf" file) of the events that are expected to occur during landing on the nucleus and after : it's the timeschedule on which we are working to set up our EPO event in Paris.
 Sequence_ATTERRISSAGE10_UMSF.pdf ( 263.81K ) Number of downloads: 4561

The landing itself should occur around November 11th.

We'll keep you informed

[Malmer]

There are several measures of surface roughness,

Thank you Gerald for all the good info!

Isn't an anaglyph enough? It is already aligned and I can extract images from it with StereoPhotoMaker.
http://www.esa.int/var/esa/storage/images/...ull_image_2.png

You can obviously build a disparity map from that image. (I made a shape-model of that very anaglyph a while back) but you will not know the actual height of anything unless you also know the camera positions. you get only relative heights.
you can download that old one from here if you like:
http://classic.syndicate.se/image/space/Landingsitemodel.zip

Is it available to the public?

The new one is much better. I have the camera positions and all that good stuff reverse enginnered so it is an absolute map. (it matches my Global shapemodel) will post it when it is more finalized.

What do you mean by "centre of rotation"? What point do you point the gravity vectors to?

I suppose that for these purposes, and without a mass distribution model, you could choose that point such that some average slope over the area of the plot is close to zero. Of course that may not be very accurately true.

I'm simply aiming my gravity vector towards the center of mass of the comet (the point it is rotating around)

I did some simple tests with my global shape model. I fill it with particles and let them gravitationally affect an external point. At the top of the comet the gravity vector is pointing mostly towards the center of gravity of the comet anyway. There are areas in the neck area that have gravity vectors pointing slightly of to one side or the other but it is not by a huge deal. (I'm assuming a homogeneous comet with no mass concentrations because of lack of data) I also did not factor in the spinning. (to much math for one night)



I'm so excited about the landing. I really hope it works out well. There is so much science to be gained if it works as planned.
I made my maps to try to get a feel for the chances. I think it looks really promising. There are very few really steep slopes in the area. And there are big areas of very few boulders. (at the scale of this picture)

About those flat dust plains. Is there any reason to fear that the dust would be very soft and that the lander would just sink?

[fredk]

I'm simply aiming my gravity vector towards the center of mass of the comet (the point it is rotating around)

A body doesn't rotate around a point, it rotates about an axis. So you have to decide where on that axis your gravity vectors point to.

The centre of mass (COM) calculated assuming uniform density is probably a good first approximation to the gravitational field direction. It would be very interesting to see how close the uniform-density COM is to the rotation axis. That would tell you something about how good the uniform-density approximation is, since (I believe) the COM will lie on the rotation axis for a body that actually has uniform density.

[Malmer]

A body doesn't rotate around a point, it rotates about an axis. So you have to decide where on that axis your gravity vectors point to.

Thats true, I stand corrected...

Anyway, I did not factor in rotation... so then the center of mass was the simplest point to choose.

I also did not calculate my own center of mass. I used the center of the coordinate system that ESA used for this VIRTIS map as my center of mass...

http://mattias.malmer.nu/wp-content/upload...IS_LAT_LONG.jpg

I will try to do a new map where I calculate the effects of rotation and local gravity. then I can do a dot product between the vectors and see if the difference is much to talk about... (the J site is almost on the equator so the rotation should not make all that much difference. J has most of the mass centered under it so the deflection of the gravity vector is not going to be too aggressive either.)

Interesting stuff...