IPB

Welcome Guest ( Log In | Register )

95 Pages V  « < 88 89 90 91 92 > »   
Reply to this topicStart new topic
Philae landing on the nucleus of Comet 67P C-G
Sherbert
post Apr 18 2015, 11:44 PM
Post #1336


Member
***

Group: Members
Posts: 153
Joined: 20-December 14
From: Eastbourne, UK
Member No.: 7372



QUOTE (scalbers @ Apr 17 2015, 11:50 PM) *
The outer solar diurnal arc shows the sun's track for the present time and looks quite a bit more favorable to get more insolation on the panels.

Nicely done Scalbers.

It took me a bit to get orientated, but indeed putting this together with Stephan's comments, at the moment Philae's top plate is probably receiving it's best illumination and even if power is not increasing enough, the temperature inside Philae should. It was mentioned there are also heat absorbers on the top plate. This also shows how Philae is slightly tilted backwards towards the cave wall behind. As 67P approaches its equinox the angle of the sun will no longer be perpendicular to the top plate but start to illuminate the side panels more. There might be a fly in the ointment from the large cliff below "Spider Hill". This sits slightly below Philae's alcove and so nearer Perihelion its shadow may be cast "up" the comet and across Philae. This could also be a blessing, as "Perihelion Cliff" has proved to be, protecting Philae from the heat at the height of Perihelion.
Go to the top of the page
 
+Quote Post
dvandorn
post Apr 19 2015, 12:15 AM
Post #1337


Senior Member
****

Group: Members
Posts: 3419
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



As far as the temperature of Philae goes, if the surface upon which it rests is extremely cold, wouldn't that tend to encourage any heat it develops within the lander to follow the second law and basically flow to the cold surface?

It would very much depend on how much of Philae's structure is in direct contact with the surface, and the thermal characteristics of both that portion of Philae's structure in contact as well as the thermal characteristics of the surface. But I know that if you set a metal box on a very cold surface, heat it draws in from above will flow into that surface and keep the temperature in the metal box colder than if it box was not in contact with that cold surface. Would heat be depleted faster from Philae into the comet's surface than it would radiate into vacuum?

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
Gerald
post Apr 19 2015, 10:58 AM
Post #1338


Senior Member
****

Group: Members
Posts: 2252
Joined: 7-December 12
Member No.: 6780



QUOTE (Sherbert @ Apr 19 2015, 12:44 AM) *
This could also be a blessing, as "Perihelion Cliff" has proved to be, protecting Philae from the heat at the height of Perihelion.

Overheating isn't considered as a risk anymore.
But there is no information about what's above Philae, including a possible ceiling.
From ROLIS images it's known, that the final turn has been successful.
At the moment Philae might be able to boot (at about 4 W) and to execute "blind" commands, but not necessarily able to send before June (more than 19 W needed).
Temperatures of the environment after landing have been about -145 °C, -45 °C are necessary for boot.
The -145°C are no problem for the exposed exterior instruments, but it's well below the design temperature of the thermally insulated interior electronics and instruments. So there is some risk due to thermal stress.
Go to the top of the page
 
+Quote Post
fredk
post Apr 19 2015, 02:57 PM
Post #1339


Senior Member
****

Group: Members
Posts: 3933
Joined: 17-January 05
Member No.: 152



QUOTE (dvandorn @ Apr 19 2015, 01:15 AM) *
As far as the temperature of Philae goes, if the surface upon which it rests is extremely cold, wouldn't that tend to encourage any heat it develops within the lander to follow the second law and basically flow to the cold surface?

Considering the ultra-low gravity, the legs may be contacting the surface only just barely, ie only a very small surface area would need to be in contact to hold up the lander. So thermal conduction to the ground may be very poor.
Go to the top of the page
 
+Quote Post
scalbers
post Apr 19 2015, 03:28 PM
Post #1340


Senior Member
****

Group: Members
Posts: 1349
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



I clarified the wording a bit in my post #1334 from yesterday. My present solution has the initial tilt of Philae at around 80 degrees toward Perihelion Cliff, so the top panel was pointed just above the northern horizon. The CIVA images are including the zenith in the field of view and it looks clear, so there isn't an overhang directly overhead.

The ROLIS images suggest a clear southern horizon, so it seems that in summertime there wouldn't be much shadowing, depending on the azimuth of the cliff below Spider Hill. I'm assuming Perihelion Cliff is the large obstruction to the north and east, so it is blocking the sun at landing time and would be out of solar arc near perihelion.

Perhaps green dots could be added with the post-rotation solar panel orientations in the existing panorama. The ROLIS images should help to specify the rotation event more quantitatively.


--------------------
Go to the top of the page
 
+Quote Post
mcgyver
post May 7 2015, 10:29 AM
Post #1341


Member
***

Group: Members
Posts: 107
Joined: 1-August 14
Member No.: 7227



QUOTE
At the end of May even more detailed images will be released in the NAVCAM image browser and in the Planetary Science Archive. This release will again cover two months – this time October and November – and therefore cover the transition from the 30 km mapping phase down to just 10 km from the comet’s surface. In addition, the image release will cover the exciting period leading up to and during the landing, including the days in which Philae was operating on the surface of Comet 67P/C-G.

http://blogs.esa.int/rosetta/2015/04/29/ma...s-800-to-30-km/
Go to the top of the page
 
+Quote Post
scalbers
post May 7 2015, 11:01 PM
Post #1342


Senior Member
****

Group: Members
Posts: 1349
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



I see this French news story that Rosetta will start to listen for Philae beginning tomorrow.

A similar story appears in Nature.


--------------------
Go to the top of the page
 
+Quote Post
MahFL
post May 8 2015, 01:50 PM
Post #1343


Forum Contributor
****

Group: Members
Posts: 1235
Joined: 8-February 04
From: North East Florida, USA.
Member No.: 11



QUOTE (scalbers @ May 8 2015, 12:01 AM) *
I see this French news story that Rosetta will start to listen for Philae beginning tomorrow.


They already had one listening period, but nothing was heard, as expected. This next one might have a better chance as Philae warms up.
Go to the top of the page
 
+Quote Post
climber
post May 8 2015, 05:19 PM
Post #1344


Senior Member
****

Group: Members
Posts: 2822
Joined: 14-February 06
From: Very close to the Pyrénées Mountains (France)
Member No.: 682



So they know where it is within 50 metres! Not enough anyway to modelize the exact environment where it ended up (or down)


--------------------
Go to the top of the page
 
+Quote Post
brellis
post May 8 2015, 08:51 PM
Post #1345


Member
***

Group: Members
Posts: 747
Joined: 9-February 07
Member No.: 1700



Hypothetical/theoretical (certainly not practical) question here: if contact isn't established with the lander during the Rosetta mission, could Philae revive itself in the future? Could we send another spacecraft out to the comet to re-attempt contact in six years? If it doesn't get bumped around by an outgassing from the comet, how long can it remain re-bootable?

Go to the top of the page
 
+Quote Post
polaris
post May 10 2015, 02:26 PM
Post #1346


Junior Member
**

Group: Members
Posts: 23
Joined: 3-May 04
From: mes pieds à Paris, mon coeur dans les Pyrénées, mon esprit dans l'Espace
Member No.: 72



At last, we found Philae ! She has landed in front of the Grand Palais, in Paris. rolleyes.gif



More pictures :
https://plus.google.com/photos/112434140547...=CJTm7qGD4oiMTg
Go to the top of the page
 
+Quote Post
kato
post May 10 2015, 08:11 PM
Post #1347


Newbie
*

Group: Members
Posts: 1
Joined: 29-August 14
Member No.: 7251



Pity they'll take that exhibit down again in two weeks...

(couldn't they wait another three till i'm there?)
Go to the top of the page
 
+Quote Post
Paolo
post May 29 2015, 07:27 AM
Post #1348


Senior Member
****

Group: Members
Posts: 1682
Joined: 3-August 06
From: 43° 35' 53" N 1° 26' 35" E
Member No.: 1004



a nice interview (in French) with the guy in charge of operations at the Philae control cemter here in Toulouse. there is a new communication window opening


http://www.cnes.fr/web/CNES-fr/11924-gp-le...l-de-philae.php
Go to the top of the page
 
+Quote Post
Gerald
post May 29 2015, 07:56 PM
Post #1349


Senior Member
****

Group: Members
Posts: 2252
Joined: 7-December 12
Member No.: 6780



Interesting, they've completely redesigned the scientific activities to work without charging the rechargeable battery, but using the solar power directly, a way to operate which hasn't been anticipated before landing:
QUOTE
Nous nous préparons donc à travailler uniquement pendant le jour local, en utilisant l’énergie solaire en direct, sans passer par une phase de stockage. Il s’agit d’un mode de fonctionnement que nous n’avions pas anticipé avant l’atterrissage et il a fallu redéfinir toutes les activités scientifiques en prenant en compte ces nouvelles contraintes.
Go to the top of the page
 
+Quote Post
pitcapuozzo
post Jun 11 2015, 02:08 PM
Post #1350


Junior Member
**

Group: Members
Posts: 65
Joined: 19-November 14
From: Milan, Italy
Member No.: 7340



Rosetta has identified a "promising candidate" for Philae

http://blogs.esa.int/rosetta/2015/06/11/th...-find-philae-2/

Pros:

- visibile only in post-landing images, not in pre-landing ones
- good size match
- good solar illumination match
- good radio visibility match
- region was poorly illuminated -> relatively inactive -> unlikely that it's something "natural"
- current shape model isn't perfect, so the landing ellipse could be slightly adjusted and include this spot
- it's visible in two images, so it's a real feature, not a dust grain or an image artifact

Cons:
- 7 weeks between images, plenty of time for a rock to fall off a cliff or something
- just outside landing ellipse
Attached thumbnail(s)
Attached Image
 
Go to the top of the page
 
+Quote Post

95 Pages V  « < 88 89 90 91 92 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 21st August 2019 - 09:00 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.