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

[Voidryder]

Great news. And congratulations to the Engineers who designed and built such a tough spacecraft.

[sgt_flyer]

Do they know what condition its in? Is it an 'acceptable' landed position? Laying on its side? Upside down? Did it sustain any damage?

Granted, I know the 'collision' with the comet when the harpoon failed was probably an extremely slow-motion process, give that the comet's finite gravity was enough to hold onto it, but then, things like solar panels aren't what I would call durable.

It's hard not to picture it being crushed like a beer can while it was bouncing across the surface.

And I at least thought the harpoon was needed to keep it tethered to the comet while using the drill, but apparently even that isn't the case.

From the pictures philae took and transmitted during the 60hours after landing, ESA thinks philae landed on it's side, with one feet towards space.

As for the drill unit, you can see it being deployed at around 2:10 in this video.

http://www.esa.int/spaceinvideos/Videos/2014/08/Philae_s_mission_at_comet_67P

Though, if the lander landed on the side, i guess they are going to have some problems. (don't know how much degrees of freedom the drill deployement system has to help in positioning the drill vertically towards the surface)

Without harpoons / feet anchors securing the lander and on the side, philae's drill might not be able to devellop enough force to drill through (if trying to drill at an angle, they might be ripping the drill's head across the surface instead of drilling)

Edited June 14, 2015 by sgt_flyer

[Vanamonde]

Merged into the existing thread for this subject.

[LittleBlueGaming]

Saw this earlier today... I remember watching someone at TED talking about the landing and their projected search area. Glad it woke up, that's great news whenever you spend a billion dollars trying to get somewhere.

[PakledHostage]

I remember watching someone at TED talking about the landing and their projected search area.

Here's the TED video for anyone who hasn't seen it:

Also, does anyone have any updates? One report that I read earlier today said that data links between Rosetta and Philae were possible every 12 hours and 30 minutes. There should have been at least two windows by now since the first one. Are they getting more data or has Philae stopped transmitting again?

[Streetwind]

Rosetta is not in a favorable orbit for communicating right now (which is also why it took so long to catch the signal even though Philae has been awake or days). They're looking into a plane change maneuver, but in the meantime, there's only a few minutes of contact for each pass. Philae has a huge amount of diagnostics data buffered, which they need to slowly grab piece by piece with every pass. It'll take a couple of days to download it all, and then it still needs to be analyzed and a plan of action formed.

But then again, there's no hurry. With 24 W available, 19 of which is required for communication, Philae isn't exactly doused in power. It's enough to charge the batteries, but slooowly so. Once the batteries are full, then you can have a burst of high activity and run experiments and stuff.

[Hcube]

surely a plane change is not very Delta-V expensive in orbit around such a light parent body... The low mass of the comet combined with a good bi-elliptical plane change should be somehow easily feasible, right ? How much DeltaV does Rosetta have left after arriving in orbit around 67P ? What was the total mass and hydrazine mass at launch anyway ? Just wondering...

Glad it woke up, that's great news whenever you spend a billion dollars trying to get somewhere.

Yeah, actually i'm pretty sure that Rosetta/philae is the most expensive probe the ESA has ever flown. Must have been quite a bit of good news for the responsibles of the mission and the for the investors !

Edited June 15, 2015 by Hcube

[Streetwind]

Rosetta is regularly changing orbits anyway to get a good look from all sides as the comet is changed by the sun. It's designed into the mission. Not a problem of dV, more a problem of when and where - and what other observations (if any) will not be possible from the new orbit.

Maneuvering around the comet is indeed cheap. They're often rating maneuver dV costs in cm/s.

[Hcube]

Maneuvering around the comet is indeed cheap. They're often rating maneuver dV costs in cm/s.

Wow, are hydrazine thrusters even this precise ? what's the shortest burn possible with those ?

[Spock1108]

Moment ago came the news of a new contact with the lander last night versole 21:30 GMT!

http://www.bbc.com/news/science-environment-33135603

[Camacha]

Wow, are hydrazine thrusters even this precise ?

They will need to be if you are orbiting a body from which an astronaut could escape by jumping. Escape velocity is 1 m/s, so if your engine will not do less you are gone quite quickly

[Nuke]

you can always make a smaller thruster. there are probibly lower limits to what you can accomplish, but those limits are far below what is needed for manuvering around a comet. they can get thrusters down to mems scale devices now, thruster on a chip type devices.

[LordFerret]

They will need to be if you are orbiting a body from which an astronaut could escape by jumping. Escape velocity is 1 m/s, so if your engine will not do less you are gone quite quickly

Being its gravity is so low, couldn't the craft just come really close to the surface and retro and stop its motion and let the comet's gravity pull it in to a landing?

[Meithan]

From an old post in Rosetta's blog:

Rosetta is equipped with 24 bi-propellant 10-Newton thrusters. Over half the launch weight of the entire spacecraft was taken up by propellant (just over 1700 kg).

These thrusters are extremely robust and use mature technology provided by European industry (EADS Space & Defence, formerly, Astrium); they are designed for precision attitude, trajectory and orbit control of large satellites and deep-space probes.

[...]

For delta-v manoeuvres, Rosetta will use only four thrusters, called the axial thrusters, because they are aligned with the spacecraft’s Z-axis (i.e. along the same direction in which the instruments are pointing, although the thrusters are mounted on the other side of the main body).

And here's the technical specs page for the thrusters. To get a sense of size, that nozzle's diameter is only 35 mm (1.38 inches)!

Edit: 40 N applied to 2000 kg of mass gives an acceleration of 2 cm/s^2.

Edited June 15, 2015 by Meithan

[*Aqua*]

Why should it land there? Atm the surface is a no-go zone for a space craft. All that dust and vapor can easily obstract or even permanently block the sensors. They already have problems with the star tracker thinking dust particles are stars. Rosetta should stay out of the coma by a good margin.

[Camacha]

Being its gravity is so low, couldn't the craft just come really close to the surface and retro and stop its motion and let the comet's gravity pull it in to a landing?

You mean Philea? It pretty much did that, as it simply got pushed from Rosetta, not even actively propelled. Still it bounced like it did.

[Kilmeister]

So It looks like they're going to prioritize Philae's lander mission over Rosetta's orbiter even though it's going to be limited what Philae can still can accomplish while laying on it's side. I can't imagine the Rosetta orbital science team put up too much of an opposition against this though.

http://www.theguardian.com/science/2015/jun/15/rosetta-spacecraft-to-change-orbit-in-bid-to-strengthen-philae-communication

[Streetwind]

Keep in mind that the orbiter team has had nine full months of constant work now. They've already produced mountains of data that will keep the scientists busy for years to come. Additionally, even if Rosetta's orbit is shifted to cater to the lander, it can still perform science from that orbit too. Maybe it doesn't get all the angles all the time anymore, but it's not like it needs to stop working. It'll still do 90% of what it did before.

The one big risk is getting too close to the dust trail and getting the navigation unit confused, but that's a recoverable error (it has happened several times already).

[Shpaget]

I'm trying to find a representation of Rosetta's orbit in relation to Philae position, but I'm not successful. Does anybody have some link?

[gogozerg]

^^^ I was looking for information about Rosetta's orbits too, but couldn't find anything detailed.

I was at a conference held by mission control people a few months ago, I remember them saying a natural elliptical orbit was not possible or inapproriate because of gravity being much too low. That's why the probe was maintained on a succession of flat hyperbolic orbits with thrusters around the comet, flying in squares like a fly.

Any graphical document about today's orbit in some ESA report?

Edited June 17, 2015 by gogozerg

[Meithan]

Ok, here's the story of the orbits as far as I've been able to determine.

Earlier in the year they transitioned from close "stable" orbits to flyby orbits to get closer looks at parts of the nucleus:

http://www.esa.int/spaceinvideos/Videos/2015/02/Rosetta_s_close_flyby

Now, since 67P is getting closer to perihelion (which will happen on August 3 of this year), its activity is increasing. This means that during these close flybys Rosetta was flying into increasingly denser environments of dust and comet emission. This was measured as larger drag being applied to the orbiter as early as February 17.

During the March 28 flyby of the nucleus, dust and emission from the nucleus confused Rosetta's star trackers which are used to accurately determine its attitude (when that fails, it falls back to gyros, but they seem to build up error over time). The result of this issue with the star trackers was that Rosetta entered a safe mode. It took mission controllers two days to restore it to normal operating conditions.

As a result of this safe mode, Rosetta was left in a hyperbolic trajectory that reached 400 km from the nucleus. Then, they executed a series of maneuvers starting on April 1st to bring it back to about a 140 km orbit by April 8. Since then, they've been much more cautious about getting close to the nucleus and Rosetta has been executing "pyramid orbits" (legs of nearly-straight hyperbolic trajectories forming triangles) since. To get a sense of scale, each of these legs takes about one week to complete, so one full "pyramid orbit" takes about three weeks.

After contact with Philae was reestablished on June 13 (with a second, briefer contact on June 14), ESA planners have been planning further orbit changes to maximize the chances of communication with Philae. So far contact with Philae has not reoccurred, and the initial contacts were weak, so the first priority if Philae is to resume operations is to strengthen its link with the orbiter, and thus Earth. Rosetta is currently about 230 km from the nucleus on one of these hyperbolic legs. It seems they'll bring down Rosetta below 200 km, which was the altitude on which Philae was first contacted.

[LordFerret]

I'm trying to find a representation of Rosetta's orbit in relation to Philae position, but I'm not successful. Does anybody have some link?

^^^ I was looking for information about Rosetta's orbits too, but couldn't find anything detailed.

I was at a conference held by mission control people a few months ago, I remember them saying a natural elliptical orbit was not possible or inapproriate because of gravity being much low. That's why the probe was maintained on a succession of flat hyperbolic orbits with thrusters around the comet, flying in squares like a fly.

Any graphical document about today's orbit in some ESA report?

If you'll check out the JPL/NASA HORIZONS site, you'll find you can pull up the ephemeris data for Rosetta.

The HORIZONS System

Direct link to the HORIZONS ephemerides generation page ... just select "Rosetta" from the spacecraft list, modify the rest of the parameters as you wish..... and make sure you make note of -

NOTE: To generate an ephemeris of Rosetta with respect to comet 67P, set the

coordinate center to "@1000012". Such relative data is available only

over 2014-Jan-1 to 2015-Apr-04, currently based on CORB_DV_093_02_00157.

Due to the spacecraft's close proximity to the comet and the comet's

irregular shape, some quantities such as sub-solar/center latitude and

longitude may not be meaningful.

Edited June 17, 2015 by LordFerret
clarification

[SuperFastJellyfish]

^^^ I was looking for information about Rosetta's orbits too, but couldn't find anything detailed.

I was at a conference held by mission control people a few months ago, I remember them saying a natural elliptical orbit was not possible or inapproriate because of gravity being much low. That's why the probe was maintained on a succession of flat hyperbolic orbits with thrusters around the comet, flying in squares like a fly.

Any graphical document about today's orbit in some ESA report?

NASA's Eyes on the Solar System has a KSP-like map view(with time warp) that shows Rosetta. I just followed its trajectory from '04 up until a few days from today.

[Shpaget]

Thanks guys, awesome links.

[Meithan]

Just installed Eyes on the Solar System and spent 30 minutes following the trajectory of Rosetta around 67P. Amazing! Thanks for the link!