The Rosetta probe has woken up ...

Beelzebuddy said:
Yeah, no, that scale is wrong. Eyeballing google maps, the financial district (that bunch of skyscrapers) is about a mile wide, so the comet should be less than 2x that, since we're not looking along its long axis.
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I was wondering about that, and the article linked seemed to both confirm and deny the scale. It's a very cool picture nonetheless.
 
There is a good summary of the Rosetta information on the ABC StarStuff podcast for August 6. The guest being interviewed (around 20:00) states that the original powered orbits of the comet are triangular at about 100 km and diminishing until a hoped for Keplerian un-powered orbit.
 
Olowkow said:
There is a good summary of the Rosetta information on the ABC StarStuff podcast for August 6. The guest being interviewed (around 20:00) states that the original powered orbits of the comet are triangular at about 100 km and diminishing until a hoped for Keplerian un-powered orbit.
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Yes, first we have the "triangles" on the dayside of the comet. These are used to map the surface with OSIRIS, to find a good landing spot for Philae, AND the flybys give us Doppler measurements from which the gravitational pull of the comet on the spacecraft can be determined, and thus the mass (see the ESA blog on this topic: http://blogs.esa.int/rosetta/2014/08/21/determining-the-mass-of-comet-67pc-g/). We are planning for both bound and open orbits, which are dependent on the mass and on the activity of the comet, and will be selected at the appropriate time. The mission is split up in to numerous planning spread sheets, where each is either 1 month or 2 weeks, for "medium term planning".
 
Rosetta selfie

Lovely

Man, I can't admire this mission enough. An actual landing would just be a huge bonus.

eta: Hadn't even scrolled down to see the detail of the surface. Amazing and also difficult.
 
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The smooth areas remind me of sand dunes. Given the low gravity, that could be very fine dust, which probably presents its own set of landing hazards.

The part of the peanut that is closest to the camera has some roundish rocks jutting out. I keep wondering just how solid the thing might be - or might not be. Not much gravity to make things stick together.
 
GlennB said:
Lovely

Man, I can't admire this mission enough. An actual landing would just be a huge bonus.

eta: Hadn't even scrolled down to see the detail of the surface. Amazing and also difficult.
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That Rosetta selfie with 67P in the background deserves to be displayed. Very historic photograph.

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It would be fun to free climb those cliffs. :)
Five possible landing sites were chosen last month. They were selected because they appeared to be relatively flat and smooth. But as the spacecraft has neared the comet, its rocky jagged surface which can be clearly seen in this picture has come sharply into focus.
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GlennB said:
Lovely

Man, I can't admire this mission enough. An actual landing would just be a huge bonus.

eta: Hadn't even scrolled down to see the detail of the surface. Amazing and also difficult.
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Staggeringly beautiful images - icons for the future.

Yuri
 
Olowkow said:
It would be fun to free climb those cliffs. :)
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I think you'd be struggling to find firm hand-holds-- to hold you down!

The estimate is 1/10000 earth's gravity: a 70 Kg person would weigh 7 grams. I expect you could easily do push-ups with your pinkie, as long as you do them slowly so as to not launch yourself.
 
Pulvinar said:
I think you'd be struggling to find firm hand-holds-- to hold you down!

The estimate is 1/10000 earth's gravity: a 70 Kg person would weigh 7 grams. I expect you could easily do push-ups with your pinkie, as long as you do them slowly so as to not launch yourself.
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Breaking into a brisk jog would put you into orbit. For some reason, I find this mental image amusing.
 
thedopefishlives said:
Breaking into a brisk jog would put you into orbit. For some reason, I find this mental image amusing.
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This means that "landing" on the asteroid is going to take on a very different meaning, right?

The landing bot is going to have to be pretty much synched up with the movement, because they aren't going to be able to use gravity to help it in much at all, can they?
 
thedopefishlives said:
Breaking into a brisk jog would put you into orbit. For some reason, I find this mental image amusing.
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Originally Posted by tusenfem
... there are bound orbits, which last about a week for one revolution. The latest estimate of the mass that I could find was MCG ≈ 3.14±0.21 ⨯ 1012 kg.
....
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I used some on line calculators a while back and got these results. No one has corrected me, so hopefully these numbers are in the ballpark.

Olowkow said:
Assuming a radius of 2 km:
  • gravitational acceleration (a)=5.24-5 meter/sec2
  • escape or critical speed (ve)=0.46 meter/second
That is:

  • (a)=0.002"/sec2
  • (ve)=18"/sec
Source for calculations:
http://www.ajdesigner.com/phpgravity/gravity_acceleration_equation.php

ETA: I wonder what the altitude for a one week orbit would be.
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Since the comet is not even close to being spherical, I imagine the Newtonian orbit would have to be pretty far out to avoid any chance of a collision.
 
pgwenthold said:
This means that "landing" on the asteroid is going to take on a very different meaning, right?

The landing bot is going to have to be pretty much synched up with the movement, because they aren't going to be able to use gravity to help it in much at all, can they?
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Part of the reason for the delay in getting to this point is getting Rosetta into a non-powered orbit. Now that it has settled into a predictable orbit that can launch the lander and understand how it approaches the comet. This is definitely a case when slowly-slowly makes for a more sure result.
 
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