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OSIRIS spots Philae drifting across the comet

245 points by lentil_soup 12y ago

netcan 12y ago
This layer of soft dust in low gravity is hard for me to get my head around.
- robin_reala 12y ago
  It‘s just time, and low rather than no gravity. It helps that there’s no air resistance to blow it off either.
3rd3 12y ago
It seems to me that this shot is missing: http://blogs.esa.int/rosetta/2014/11/16/philae_spotted_after_first_landing/ http://blogs.esa.int/rosetta/2014/11/16/philae_spotted_after... However, there seems to be a confusion about the time. If it’s indeed one hour after touchdown the bright and dark blobs are probably just dust.
- grey-area 12y ago
  The pic you linked to was taken with a different camera (NAVCAM), the pictures in this article (OSIRIS) are much better, and clearly show the lander before and after touchdown along with marks where it first landed/bounced. What they don't show unfortunately is the final resting place, but that's a bit tricky because of comet rotation, comet shape (not a flat surface), and the parabolic trajectory of the lander. What's the confusion about the time? Touchdown was at 15:34 UTC (NB UTC), I doubt anyone at ESA is confused about the time, though some of the commenters seem pretty confused on the ESA blog post this BBC article is based on: http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet/ http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-...
  - 3rd3 12y ago
    It says below the article that they confused the time due to fatigue.
    - grey-area 12y ago
      That's an older article about old pics though isn't it, not these new pics? It was just a label on the website blog which the web team got wrong and was corrected soon after posting. The pics in the article you link are 4 mins before and 1 minute after landing, not 1 hour after, and they are corroborated by these new images, so no real confusion over timings.
      - deleted 12y ago
        [deleted]
Pxtl 12y ago
Hindsight is 20/20, but it really looks like the lander descended too quickly, at least at the final stage. I mean, any smaller bounce would have prevented the shadow landing. But then, there are probably risks associated with a last-second deceleration, and the odds of both the top-thruster and the clamps failing were probably small.
- m-app 12y ago
  Note that the final image in this mosaic (labeled 15:43) is not the final resting place for Philae. They still do not know exactly where it landed.
- mikeash 12y ago
  The only way to make it hit at a lower speed would be to have some sort of thruster on the bottom, which could have failed just as the one on the top did. Additional redundancy may have helped, but that would have reduced useful payload for other things, and since the top thruster is more versatile then you may as well go for redundant top thrusters rather than top and bottom.
lisper 12y ago
I wonder if there's a reason they didn't design the lander with some sort of energy-absorbing material (something analogous to the crush zone in a car) on the bottom of the landing pads to prevent bounces. I thought I'd "wonder out loud" here because someone on HN might actually know the answer.
- shawabawa3 12y ago
  From the article it seems they assumed the comet surface would be a soft layer of dust, absorbing the impact
  - Tloewald 12y ago
    in the initial race to the moon it was widely speculated that the moon was covered in a deep layer of ultrafine dust, and any spacecraft landing on it would be liable to sink. Arthur C. Clarke's novel "A Fall of Moondust" was based on this thinking. It seems astronomers have a bias towards assuming dust will cover stuff. Perhaps this says something about their office space.
    - hnal943 12y ago
      I thought they calculated the amount of dust that based on the current rate dust accumulation and extrapolating based on the believed age of the universe. It's a little surprising we have not corrected that thought since the moon landing.
      - Tloewald 12y ago
        Who's to know why they were wrong — it's just amusing to see the same error come up again. I prefer the theory that they look around their offices and extrapolate ;-)
        dandelany 12y ago
        They weren't wrong, there's plenty of dust on the comet. The first photo of the initial landing site is visible precisely because of the shadow cast by a giant cloud of dust kicked up by the lander.
madaxe_again 12y ago
If there's one plus in all of this (notwithstanding the data already returned!) it's that if there wasn't a thick enough coating of dust to absorb the shock of a light impact in the absence of the harpoons or retro-thrusters, and the surface was hard enough to break the thermometer... there may also not be enough dust to cover the panels as 67P nears the sun, which means we may not have heard the last from Philae.
- markcerqueira 12y ago
  How long is Rosetta going to orbit 67P? Indefinitely? We need Rosetta to be able to talk to Philae.
- jlgaddis 12y ago
  markcerqueira, you, sir, are hellbanned.
Osmium 12y ago
Any news on if the drill managed to pick up anything useful? Curious to find out if the Ptolemy data that came back was of anything useful (as I understand it, Ptolemy's task was to measure isotope ratios so that we could see if the water composition on the comet was at all similar to that on Earth).
- codeulike 12y ago
  I hear some of the instruments were owned by private research institutes rather than European taxpayers (who funded the vehicle) so for some areas may take a while to publish. Might have to wait for proper papers etc
  - Osmium 12y ago
    Ptolemy's PI is Ian Wright at the Open University: http://www.open.ac.uk/science/pssri/research/missions/rosetta/ptolomy.php http://www.open.ac.uk/science/pssri/research/missions/rosett... But your point stands; I know a lot's under embargo right now, I was more wondering if we knew if the drill had successfully retrieved a bit of comet or not rather than specific experimental results which will take some time!
  - privong 12y ago
    > I hear some of the instruments were owned by private research institutes rather than European taxpayers (who funded the vehicle) so for some areas may take a while to publish. Might have to wait for proper papers etc It is not immediately obvious to me why who owns the instrumentation would be a driving factor in the time to see results. Both private research institutes and public institutes would want to get results out as quickly as possible, to capitalize on the PR effect. But that is moderated by the need to perform sufficienly accurate and detailed analysis, which takes time. Those pressures are the same for both public and private research institutes. If anything, the private institues would feel more pressure to publish results quickly, to improve their chances of obtaining future funding. I cannot tell if you are comparing the quickness of this press release with the lack of results from the scientific packages on Phile, but I will address the (potential) comparison, just in case... Part of reason this press release (with the image of Philae bouncing) was out so quickly is that it does not require a very detailed and specific analysis (requiring roughly the equivalenth of image stictching in photoshop), and the results are fairly straightforward. Additionally, it is not really providing much in the way of new scientific information and so does not have as high a burden of proof. Additionally, the OSIRIS imager has been used to collect data for a while now, so presumably the OSIRIS team has a decent understanding of the real-world operation of the equipment, enabling them to quickly release images in which they were confident. In contrast, the Philae lander's instruments had not provided actual data before the landing, so the instrument teams still need to do the careful calibrations and analysis to understand the systematics.
jessmartin 12y ago
Is it just me, or did Jonathan Amos slip a subtle Star Wars homage into the article? "It's a trap" is one of the section headings.
- ebbv 12y ago
  That's about as subtle of a Star Wars reference as slicing someone's arm off with a light saber.
brianbreslin 12y ago
It amazes me that we take for granted the sheer complexity of hitting a moving target like a comet at such an incredible distance in space. Navigation in space has to be so incredibly complex because you are moving in so many planes. It's like firing a gun and hitting a quarter that was thrown miles away.
- netcan 12y ago
  I don't think "we" do take it for granted. It's just that those of us who don't can't think of much more to say than "Woah! on a comet?! wow." This is incomprehensibly amazing to me.
- acqq 12y ago
  If you haven't already, do watch which orbit changes of Rosetta were needed to deploy the lander: https://www.youtube.com/watch?v=4a3eY5siRRk https://www.youtube.com/watch?v=4a3eY5siRRk Must watch. The video was made by ESA.
  - bronson 12y ago
    That is astonishing. Goes to show how simple stuff can turn into hellish soup once all the requirements are in.
  - kens 12y ago
    The video is very cool. But I find it hard to imagine how to orbit something that has hardly any gravity - the orbiter must be getting just milligrams of force.[1] The scale isn't clear from the video: are they orbiting really slowly? And it seems like it would be very hard to enter orbit around something that has hardly any pull without flying right past it. On the positive side, the orbit changes in the video would require almost no propulsion, right? [1] milligrams isn't a unit of force, but hopefully you know what I mean; milli-ounces sounds too weird.
    - seanflyon 12y ago
      9.8 micronewtons is the correct way of saying one milligram of force.
grey-area 12y ago
The original blog post is here: http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-... There's a nice image[2] which shows this in context linked to in the comments [3]. ESA seem to think the lander ended up somewhere over in the dark cliffs of the large crater filling the right hand side of this image. [2] http://i.imgur.com/4m4WqAN.png http://i.imgur.com/4m4WqAN.png [3] http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet/#comment-201918 http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-...
udev 12y ago
Philae's landing is commonly represented as a vertical descent. In fact, it seems there was considerable lateral velocity. My guess is that Philae landed tumble-weed style, jumping, and rolling until it hit a wall, in this case, the cliff that shadows it.
- TheBiv 12y ago
  How did you come to this conclusion? The images shown may just be a matter of perspective and the lander still could've had a vertical descent
- chockablock 12y ago
  You can't tell that from this sequence of photos, since the orbiter was not viewing the descent from directly 'above' the landing site. After releasing Philae, Rosetta performed a maneuver to establish a new orbit. There are some nice plots of these trajectories here: http://www.bis-space.com/2014/11/12/13849/about-landing-on-a-comet http://www.bis-space.com/2014/11/12/13849/about-landing-on-a...
- udev 12y ago
  Philae is 1km away from the original landing site. There must've been lateral velocity.
  - ChuckMcM 12y ago
    This is my understanding from reading the web site and some of the proposal papers associated with the mission. The plan was that Philae would come in at net 0,0 velocity with respect to the normal of the landing site. That involved putting it into an orbit which intercepted the landing site. This was made a bit more challenging as the top thruster on Philae failed to fire, which meant it was unable to circularize its interception orbit. And that resulted in some horizontal motion at the time of landing. That said, the motion seems to have been well within the safely margin of the harpoon system from what I can read about that subsystem. Since we aren't on the comet we can only guess what happened but one speculation I've read that seems plausible is that the harpoons "fired" but did not "release", which is to say they tried to move and did not. Imparting a delta-v that was vertical with respect to the surface normal of the landing spot. That delta-v, combined with the landers imperfect alignment, contributed to the sideways journey. It did confirm that you really do want something like harpoons to hold you to the comet (and potentially to asteroids if you're doing missions to them).
sliverstorm 12y ago
Is it completely out of the question to reflect light onto Philae using Rosetta (once they locate the probe of course)?
- anigbrowl 12y ago
  That sounds too complicated for the amount of light you'd get, although I get your point - I'm sometimes surprised by the light/heat that reaches my greenhouse from a reflection on a window as the sun is setting. On a related note, though, perhaps future missions will transmit power via laser rather than relying on solar panels. Of course solar panels have also had 10 years to improve since the mission was launched...
  - MichaelGG 12y ago
    Or future missions could just stick an RTG on it, right?
    - chx 12y ago
      Please read http://nucleardiner.com/2014/11/15/wasnt-philae-given-rtg/ http://nucleardiner.com/2014/11/15/wasnt-philae-given-rtg/
      - MichaelGG 12y ago
        Those sound distinctly non-technical.
  - sliverstorm 12y ago
    I agree that it sounds like a math/astrophysics/trajectory nightmare, but I remind myself that is the kind of thing these agencies are really good at. Remember, they just shot a comet some 400 million miles away.
modzu 12y ago
are these photos in B&W or is the comet really that gray?
- matheweis 12y ago
  Probably B&W. Even color images (aka like you see from the MER mission) are just a B&W imager multiple exposures - each with a different color filter.
  - modzu 12y ago
    we're running spectrographic analysis etc but we don't know the color of the surface? it strikes me as strange we don't have color photos. is it to save bandwidth?
    - clarkmoody 12y ago
      The imaging sensors themselves will be monochromatic (B&W), so there are no color-detecting pixels. Some space imagers slide multiple colored filters in front of a single B&W camera to get colored frames. Those frames are later composited into color photos.
    - grey-area 12y ago
      They have some colour photos (taken with filters), they've already stated the colour of the surface (black or grey, it's really just not colourful).
    - dandelany 12y ago
      We will get color photos eventually - they're being taken, they're just subject to a 6-month embargo.
- Pinckney 12y ago
  "Some light contrast enhancements have been made to emphasise certain features and to bring out features in the shadowed areas. In reality, the comet is extremely dark – blacker than coal. The images, taken in black-and-white, are grey-scaled according to the relative brightness of the features observed, which depends on local illumination conditions, surface characteristics and composition of the given area." http://www.esa.int/Our_Activities/Space_Science/Rosetta/Highlights/Top_10_at_10_km http://www.esa.int/Our_Activities/Space_Science/Rosetta/High...
unclebucknasty 12y ago
I have to say this. I have been as amazed as anyone by the feat of engineering that this entire mission represents. It is absolutely mind-blowing and I have been sharing it with others, including my kids. But, something puzzles me. That is, why didn't they use better camera technology? That's a lot of miles traveled and a lot of effort. Seems the mission would have been much better served by better imaging, both from a scientific perspective and from a public interest perspective (which can help engender support for future exploration). Frankly, the fact that it even happened amazes me. But, the images disappoint me. I know it sounds like a nit, given the overall accomplishment, but that's all the more reason to wonder why not ensure that something presumably as simple as the images we capture be as stunning as possible?
- wldcordeiro 12y ago
  My guess would be latency, a higher quality camera feed would take longer to transmit.
- seccess 12y ago
  Bear in mind it left Earth more than 10 years ago, I'd imagine they did send state of the art tech for the time.
  - rosser 12y ago
    It might not quite have been state of the art; launch-contemporary technology probably wasn't also radiation-hardened.
- Xylakant 12y ago
  The wifi reception is really shitty up there. Jest aside: More pixels, more bandwidth needed and if you think about how much bandwidth wifi systems were capable of achieving 10 years ago, they're probably at the edge of what they could use without resorting to cutting edge tech. You also have to transmit the data from the lander to the orbiter in a reasonably short timeframe since the lander is not always visible from the orbiter. Maybe they have higher res pictures still on the orbiter that will download later when there's bandwith left.
seccess 12y ago
I haven't seen any discussion of the possibility of Philae receiving light to its solar panels as the comet tumbles through space. Is there no chance of the comet turning to a point where the sun can reach the lander?
- zak_mc_kracken 12y ago
  It's estimated to take between 6 and 14 months but still not guaranteed to produce enough current to recharge the lander.
  - deleted 12y ago
    [deleted]
- sp332 12y ago
  Philae is getting 1 hour of sunlight about every 12 hours. Right now, it's so cold that it has to warm up the batteries before charging them, and it's getting so little light that it can't even do that. It's possible that the rotation might change, but because the probe is surrounded on 3 sides, that's not likely to help. So we'll have to wait for the temperature to get higher and/or the sunlight to get a lot stronger.
  - disputin 12y ago
    Can Rosetta not be angled to reflect sunlight to Philae, Iridium style? How close can Rosetta be placed to the comet?
    - jessaustin 12y ago
      This is probably not feasible, but in order for reflection to help much Rosetta would have to be much farther from the comet, so that its orbit would be comet-synchronous. Actually I doubt Rosetta has any surface reflective enough to help with this anyway. If it were used this way it would probably not be pointing its transmitter toward Earth.
    - dandelany 12y ago
martijn_himself 12y ago
I associate 'bouncing' with a certain amount of elasticity. If the comet's surface is much harder than expected, I would expect the lander to be smashed to bits. Where is the flaw in my thinking? Is this to do with it being very small forces exerted over a long time period?
- ergzay 12y ago
  The gravity and forces we're talking about are tiny. The craft hit the ground moving slower than 1 m/s and then bounced up over 1km before landing again. The forces involved with something moving that slowly and stopping are minuscule.
  - martijn_himself 12y ago
    This is fascinating. I imagine they probably ran simulations with different margins and as a few bounces would have been one of the expected outcomes i.e. it would have been factored into the design of the craft?
    - estel 12y ago
      The craft had a small thruster on its top side to gently push it into the surface of the comet, but this seems to have been faulty and couldn't be primed prior to Philae's separation. It sounds like the sort of equipment that might have mitigated such a bounce!
    - prawn 12y ago
      In the end, the speed at which Philae left the comet after the initial bounce was not far off reaching the escape velocity of the comet! The thrusters and harpoons failed, and I don't think the ice screws have really had a chance.
- 4ad 12y ago
  Philae hit the comet at around 0.5m/s. 0.5m/s is a very small velocity. The probe is definitely much elastic than the comet, for start, the legs were designed to be elastic.
ck2 12y ago
Remember the old lunar lander game? Someone needs to make a Philae Lander game. for those that weren't around in 1979: https://www.atari.com/arcade/lunarlander/play#!/arcade/lunarlander/play https://www.atari.com/arcade/lunarlander/play#!/arcade/lunar... (js version http://www.somethinghitme.com/projects/jslander/ http://www.somethinghitme.com/projects/jslander/ )
- iliis 12y ago
  You can always reenact it in Kerbal Space Program ;)
  - marvin 12y ago
    Landing on Gilly, the asteroid orbiting Eve in KSP, will give an idea of the challenges of the low-gravity environment Rosetta/Philae are operating in. The Rosetta comet has lower gravity, though, by two orders of magnitude. http://wiki.kerbalspaceprogram.com/wiki/Gilly http://wiki.kerbalspaceprogram.com/wiki/Gilly
    - iliis 12y ago
      Indeed, KSP gives a good intuition about orbital mechanics and space travel. It makes you appreciate the skills of NASA/ESA/... engineers even more! Also, KSP now has 'real' asteroids! http://wiki.kerbalspaceprogram.com/wiki/Asteroid http://wiki.kerbalspaceprogram.com/wiki/Asteroid
martijn_himself 12y ago
Does anyone know if the highly irregular shape of the comet would cause a wild variation of the strength of the gravitational field near the surface of the comet? (as opposed to a 'perfect' spherical planet). I'd imagine that would cause quite interesting dynamics and make it potentially quite difficult to calculate where it will end up?
- maaku 12y ago
  Yes, yes it would.
  - jessaustin 12y ago
    You move from calculations using little-g to calculations using big-G (i.e. the acceleration due to gravity varies significantly since the distance between centers of mass is varying significantly), but this is still a straight-forward problem of one body moving in a gravitational field.
    - narag 12y ago
      Original question said: when moving near the comet. So ISTM that it's not so straightforward. Some months ago someone posted a gravity simulator here and it was very instructive playing with it and seeing how unstable a small object's orbit is around two bigger objects rotating around their center of gravity, situation that seems similar to the "duck". Edit: http://www.nowykurier.com/toys/gravity/gravity.html http://www.nowykurier.com/toys/gravity/gravity.html Try creating two big objects in a circular orbit and experiment launching smaller objects with the same direction and speed. Some of them will crash, some others will escape.
      - jessaustin 12y ago
        My impression is that although it is not spherical, the core of the comet is a single object. It may therefore be treated as a point mass for these purposes.

245 points by lentil_soup 12y ago

netcan 12y ago

This layer of soft dust in low gravity is hard for me to get my head around.

robin_reala 12y ago
It‘s just time, and low rather than no gravity. It helps that there’s no air resistance to blow it off either.

3rd3 12y ago

It seems to me that this shot is missing: http://blogs.esa.int/rosetta/2014/11/16/philae_spotted_after_first_landing/ http://blogs.esa.int/rosetta/2014/11/16/philae_spotted_after... However, there seems to be a confusion about the time. If it’s indeed one hour after touchdown the bright and dark blobs are probably just dust.

grey-area 12y ago
The pic you linked to was taken with a different camera (NAVCAM), the pictures in this article (OSIRIS) are much better, and clearly show the lander before and after touchdown along with marks where it first landed/bounced. What they don't show unfortunately is the final resting place, but that's a bit tricky because of comet rotation, comet shape (not a flat surface), and the parabolic trajectory of the lander. What's the confusion about the time? Touchdown was at 15:34 UTC (NB UTC), I doubt anyone at ESA is confused about the time, though some of the commenters seem pretty confused on the ESA blog post this BBC article is based on: http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet/ http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-...
- 3rd3 12y ago
  It says below the article that they confused the time due to fatigue.
  - grey-area 12y ago
    That's an older article about old pics though isn't it, not these new pics? It was just a label on the website blog which the web team got wrong and was corrected soon after posting. The pics in the article you link are 4 mins before and 1 minute after landing, not 1 hour after, and they are corroborated by these new images, so no real confusion over timings.
    - deleted 12y ago
      [deleted]

Pxtl 12y ago

Hindsight is 20/20, but it really looks like the lander descended too quickly, at least at the final stage. I mean, any smaller bounce would have prevented the shadow landing. But then, there are probably risks associated with a last-second deceleration, and the odds of both the top-thruster and the clamps failing were probably small.

m-app 12y ago
Note that the final image in this mosaic (labeled 15:43) is not the final resting place for Philae. They still do not know exactly where it landed.
mikeash 12y ago
The only way to make it hit at a lower speed would be to have some sort of thruster on the bottom, which could have failed just as the one on the top did. Additional redundancy may have helped, but that would have reduced useful payload for other things, and since the top thruster is more versatile then you may as well go for redundant top thrusters rather than top and bottom.

lisper 12y ago

I wonder if there's a reason they didn't design the lander with some sort of energy-absorbing material (something analogous to the crush zone in a car) on the bottom of the landing pads to prevent bounces. I thought I'd "wonder out loud" here because someone on HN might actually know the answer.

shawabawa3 12y ago
From the article it seems they assumed the comet surface would be a soft layer of dust, absorbing the impact
- Tloewald 12y ago
  in the initial race to the moon it was widely speculated that the moon was covered in a deep layer of ultrafine dust, and any spacecraft landing on it would be liable to sink. Arthur C. Clarke's novel "A Fall of Moondust" was based on this thinking. It seems astronomers have a bias towards assuming dust will cover stuff. Perhaps this says something about their office space.
  - hnal943 12y ago
    I thought they calculated the amount of dust that based on the current rate dust accumulation and extrapolating based on the believed age of the universe. It's a little surprising we have not corrected that thought since the moon landing.
    - Tloewald 12y ago
      Who's to know why they were wrong — it's just amusing to see the same error come up again. I prefer the theory that they look around their offices and extrapolate ;-)
      - dandelany 12y ago
        They weren't wrong, there's plenty of dust on the comet. The first photo of the initial landing site is visible precisely because of the shadow cast by a giant cloud of dust kicked up by the lander.

madaxe_again 12y ago

If there's one plus in all of this (notwithstanding the data already returned!) it's that if there wasn't a thick enough coating of dust to absorb the shock of a light impact in the absence of the harpoons or retro-thrusters, and the surface was hard enough to break the thermometer... there may also not be enough dust to cover the panels as 67P nears the sun, which means we may not have heard the last from Philae.

markcerqueira 12y ago
How long is Rosetta going to orbit 67P? Indefinitely? We need Rosetta to be able to talk to Philae.
jlgaddis 12y ago
markcerqueira, you, sir, are hellbanned.

Osmium 12y ago

Any news on if the drill managed to pick up anything useful? Curious to find out if the Ptolemy data that came back was of anything useful (as I understand it, Ptolemy's task was to measure isotope ratios so that we could see if the water composition on the comet was at all similar to that on Earth).

codeulike 12y ago
I hear some of the instruments were owned by private research institutes rather than European taxpayers (who funded the vehicle) so for some areas may take a while to publish. Might have to wait for proper papers etc
- Osmium 12y ago
  Ptolemy's PI is Ian Wright at the Open University: http://www.open.ac.uk/science/pssri/research/missions/rosetta/ptolomy.php http://www.open.ac.uk/science/pssri/research/missions/rosett... But your point stands; I know a lot's under embargo right now, I was more wondering if we knew if the drill had successfully retrieved a bit of comet or not rather than specific experimental results which will take some time!
- privong 12y ago
  > I hear some of the instruments were owned by private research institutes rather than European taxpayers (who funded the vehicle) so for some areas may take a while to publish. Might have to wait for proper papers etc It is not immediately obvious to me why who owns the instrumentation would be a driving factor in the time to see results. Both private research institutes and public institutes would want to get results out as quickly as possible, to capitalize on the PR effect. But that is moderated by the need to perform sufficienly accurate and detailed analysis, which takes time. Those pressures are the same for both public and private research institutes. If anything, the private institues would feel more pressure to publish results quickly, to improve their chances of obtaining future funding. I cannot tell if you are comparing the quickness of this press release with the lack of results from the scientific packages on Phile, but I will address the (potential) comparison, just in case... Part of reason this press release (with the image of Philae bouncing) was out so quickly is that it does not require a very detailed and specific analysis (requiring roughly the equivalenth of image stictching in photoshop), and the results are fairly straightforward. Additionally, it is not really providing much in the way of new scientific information and so does not have as high a burden of proof. Additionally, the OSIRIS imager has been used to collect data for a while now, so presumably the OSIRIS team has a decent understanding of the real-world operation of the equipment, enabling them to quickly release images in which they were confident. In contrast, the Philae lander's instruments had not provided actual data before the landing, so the instrument teams still need to do the careful calibrations and analysis to understand the systematics.

jessmartin 12y ago

Is it just me, or did Jonathan Amos slip a subtle Star Wars homage into the article? "It's a trap" is one of the section headings.

ebbv 12y ago
That's about as subtle of a Star Wars reference as slicing someone's arm off with a light saber.

brianbreslin 12y ago

It amazes me that we take for granted the sheer complexity of hitting a moving target like a comet at such an incredible distance in space. Navigation in space has to be so incredibly complex because you are moving in so many planes. It's like firing a gun and hitting a quarter that was thrown miles away.

netcan 12y ago
I don't think "we" do take it for granted. It's just that those of us who don't can't think of much more to say than "Woah! on a comet?! wow." This is incomprehensibly amazing to me.
acqq 12y ago
If you haven't already, do watch which orbit changes of Rosetta were needed to deploy the lander: https://www.youtube.com/watch?v=4a3eY5siRRk https://www.youtube.com/watch?v=4a3eY5siRRk Must watch. The video was made by ESA.
- bronson 12y ago
  That is astonishing. Goes to show how simple stuff can turn into hellish soup once all the requirements are in.
- kens 12y ago
  The video is very cool. But I find it hard to imagine how to orbit something that has hardly any gravity - the orbiter must be getting just milligrams of force.[1] The scale isn't clear from the video: are they orbiting really slowly? And it seems like it would be very hard to enter orbit around something that has hardly any pull without flying right past it. On the positive side, the orbit changes in the video would require almost no propulsion, right? [1] milligrams isn't a unit of force, but hopefully you know what I mean; milli-ounces sounds too weird.
  - seanflyon 12y ago
    9.8 micronewtons is the correct way of saying one milligram of force.

grey-area 12y ago

The original blog post is here: http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-... There's a nice image[2] which shows this in context linked to in the comments [3]. ESA seem to think the lander ended up somewhere over in the dark cliffs of the large crater filling the right hand side of this image. [2] http://i.imgur.com/4m4WqAN.png http://i.imgur.com/4m4WqAN.png [3] http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-drifting-across-the-comet/#comment-201918 http://blogs.esa.int/rosetta/2014/11/17/osiris-spots-philae-...

udev 12y ago

Philae's landing is commonly represented as a vertical descent. In fact, it seems there was considerable lateral velocity. My guess is that Philae landed tumble-weed style, jumping, and rolling until it hit a wall, in this case, the cliff that shadows it.

TheBiv 12y ago
How did you come to this conclusion? The images shown may just be a matter of perspective and the lander still could've had a vertical descent
chockablock 12y ago
You can't tell that from this sequence of photos, since the orbiter was not viewing the descent from directly 'above' the landing site. After releasing Philae, Rosetta performed a maneuver to establish a new orbit. There are some nice plots of these trajectories here: http://www.bis-space.com/2014/11/12/13849/about-landing-on-a-comet http://www.bis-space.com/2014/11/12/13849/about-landing-on-a...
udev 12y ago
Philae is 1km away from the original landing site. There must've been lateral velocity.
- ChuckMcM 12y ago
  This is my understanding from reading the web site and some of the proposal papers associated with the mission. The plan was that Philae would come in at net 0,0 velocity with respect to the normal of the landing site. That involved putting it into an orbit which intercepted the landing site. This was made a bit more challenging as the top thruster on Philae failed to fire, which meant it was unable to circularize its interception orbit. And that resulted in some horizontal motion at the time of landing. That said, the motion seems to have been well within the safely margin of the harpoon system from what I can read about that subsystem. Since we aren't on the comet we can only guess what happened but one speculation I've read that seems plausible is that the harpoons "fired" but did not "release", which is to say they tried to move and did not. Imparting a delta-v that was vertical with respect to the surface normal of the landing spot. That delta-v, combined with the landers imperfect alignment, contributed to the sideways journey. It did confirm that you really do want something like harpoons to hold you to the comet (and potentially to asteroids if you're doing missions to them).

sliverstorm 12y ago

Is it completely out of the question to reflect light onto Philae using Rosetta (once they locate the probe of course)?

anigbrowl 12y ago
That sounds too complicated for the amount of light you'd get, although I get your point - I'm sometimes surprised by the light/heat that reaches my greenhouse from a reflection on a window as the sun is setting. On a related note, though, perhaps future missions will transmit power via laser rather than relying on solar panels. Of course solar panels have also had 10 years to improve since the mission was launched...
- MichaelGG 12y ago
  Or future missions could just stick an RTG on it, right?
  - chx 12y ago
    Please read http://nucleardiner.com/2014/11/15/wasnt-philae-given-rtg/ http://nucleardiner.com/2014/11/15/wasnt-philae-given-rtg/
    - MichaelGG 12y ago
      Those sound distinctly non-technical.
- sliverstorm 12y ago
  I agree that it sounds like a math/astrophysics/trajectory nightmare, but I remind myself that is the kind of thing these agencies are really good at. Remember, they just shot a comet some 400 million miles away.

modzu 12y ago

are these photos in B&W or is the comet really that gray?

matheweis 12y ago
Probably B&W. Even color images (aka like you see from the MER mission) are just a B&W imager multiple exposures - each with a different color filter.
- modzu 12y ago
  we're running spectrographic analysis etc but we don't know the color of the surface? it strikes me as strange we don't have color photos. is it to save bandwidth?
  - clarkmoody 12y ago
    The imaging sensors themselves will be monochromatic (B&W), so there are no color-detecting pixels. Some space imagers slide multiple colored filters in front of a single B&W camera to get colored frames. Those frames are later composited into color photos.
  - grey-area 12y ago
    They have some colour photos (taken with filters), they've already stated the colour of the surface (black or grey, it's really just not colourful).
  - dandelany 12y ago
    We will get color photos eventually - they're being taken, they're just subject to a 6-month embargo.
Pinckney 12y ago
"Some light contrast enhancements have been made to emphasise certain features and to bring out features in the shadowed areas. In reality, the comet is extremely dark – blacker than coal. The images, taken in black-and-white, are grey-scaled according to the relative brightness of the features observed, which depends on local illumination conditions, surface characteristics and composition of the given area." http://www.esa.int/Our_Activities/Space_Science/Rosetta/Highlights/Top_10_at_10_km http://www.esa.int/Our_Activities/Space_Science/Rosetta/High...

unclebucknasty 12y ago

I have to say this. I have been as amazed as anyone by the feat of engineering that this entire mission represents. It is absolutely mind-blowing and I have been sharing it with others, including my kids. But, something puzzles me. That is, why didn't they use better camera technology? That's a lot of miles traveled and a lot of effort. Seems the mission would have been much better served by better imaging, both from a scientific perspective and from a public interest perspective (which can help engender support for future exploration). Frankly, the fact that it even happened amazes me. But, the images disappoint me. I know it sounds like a nit, given the overall accomplishment, but that's all the more reason to wonder why not ensure that something presumably as simple as the images we capture be as stunning as possible?

wldcordeiro 12y ago
My guess would be latency, a higher quality camera feed would take longer to transmit.
seccess 12y ago
Bear in mind it left Earth more than 10 years ago, I'd imagine they did send state of the art tech for the time.
- rosser 12y ago
  It might not quite have been state of the art; launch-contemporary technology probably wasn't also radiation-hardened.
Xylakant 12y ago
The wifi reception is really shitty up there. Jest aside: More pixels, more bandwidth needed and if you think about how much bandwidth wifi systems were capable of achieving 10 years ago, they're probably at the edge of what they could use without resorting to cutting edge tech. You also have to transmit the data from the lander to the orbiter in a reasonably short timeframe since the lander is not always visible from the orbiter. Maybe they have higher res pictures still on the orbiter that will download later when there's bandwith left.

seccess 12y ago

I haven't seen any discussion of the possibility of Philae receiving light to its solar panels as the comet tumbles through space. Is there no chance of the comet turning to a point where the sun can reach the lander?

zak_mc_kracken 12y ago
It's estimated to take between 6 and 14 months but still not guaranteed to produce enough current to recharge the lander.
- deleted 12y ago
  [deleted]
sp332 12y ago
Philae is getting 1 hour of sunlight about every 12 hours. Right now, it's so cold that it has to warm up the batteries before charging them, and it's getting so little light that it can't even do that. It's possible that the rotation might change, but because the probe is surrounded on 3 sides, that's not likely to help. So we'll have to wait for the temperature to get higher and/or the sunlight to get a lot stronger.
- disputin 12y ago
  Can Rosetta not be angled to reflect sunlight to Philae, Iridium style? How close can Rosetta be placed to the comet?
  - jessaustin 12y ago
    This is probably not feasible, but in order for reflection to help much Rosetta would have to be much farther from the comet, so that its orbit would be comet-synchronous. Actually I doubt Rosetta has any surface reflective enough to help with this anyway. If it were used this way it would probably not be pointing its transmitter toward Earth.
  - dandelany 12y ago

martijn_himself 12y ago

I associate 'bouncing' with a certain amount of elasticity. If the comet's surface is much harder than expected, I would expect the lander to be smashed to bits. Where is the flaw in my thinking? Is this to do with it being very small forces exerted over a long time period?

ergzay 12y ago
The gravity and forces we're talking about are tiny. The craft hit the ground moving slower than 1 m/s and then bounced up over 1km before landing again. The forces involved with something moving that slowly and stopping are minuscule.
- martijn_himself 12y ago
  This is fascinating. I imagine they probably ran simulations with different margins and as a few bounces would have been one of the expected outcomes i.e. it would have been factored into the design of the craft?
  - estel 12y ago
    The craft had a small thruster on its top side to gently push it into the surface of the comet, but this seems to have been faulty and couldn't be primed prior to Philae's separation. It sounds like the sort of equipment that might have mitigated such a bounce!
  - prawn 12y ago
    In the end, the speed at which Philae left the comet after the initial bounce was not far off reaching the escape velocity of the comet! The thrusters and harpoons failed, and I don't think the ice screws have really had a chance.
4ad 12y ago
Philae hit the comet at around 0.5m/s. 0.5m/s is a very small velocity. The probe is definitely much elastic than the comet, for start, the legs were designed to be elastic.

ck2 12y ago

Remember the old lunar lander game? Someone needs to make a Philae Lander game. for those that weren't around in 1979: https://www.atari.com/arcade/lunarlander/play#!/arcade/lunarlander/play https://www.atari.com/arcade/lunarlander/play#!/arcade/lunar... (js version http://www.somethinghitme.com/projects/jslander/ http://www.somethinghitme.com/projects/jslander/ )

iliis 12y ago
You can always reenact it in Kerbal Space Program ;)
- marvin 12y ago
  Landing on Gilly, the asteroid orbiting Eve in KSP, will give an idea of the challenges of the low-gravity environment Rosetta/Philae are operating in. The Rosetta comet has lower gravity, though, by two orders of magnitude. http://wiki.kerbalspaceprogram.com/wiki/Gilly http://wiki.kerbalspaceprogram.com/wiki/Gilly
  - iliis 12y ago
    Indeed, KSP gives a good intuition about orbital mechanics and space travel. It makes you appreciate the skills of NASA/ESA/... engineers even more! Also, KSP now has 'real' asteroids! http://wiki.kerbalspaceprogram.com/wiki/Asteroid http://wiki.kerbalspaceprogram.com/wiki/Asteroid

martijn_himself 12y ago

Does anyone know if the highly irregular shape of the comet would cause a wild variation of the strength of the gravitational field near the surface of the comet? (as opposed to a 'perfect' spherical planet). I'd imagine that would cause quite interesting dynamics and make it potentially quite difficult to calculate where it will end up?

maaku 12y ago
Yes, yes it would.
- jessaustin 12y ago
  You move from calculations using little-g to calculations using big-G (i.e. the acceleration due to gravity varies significantly since the distance between centers of mass is varying significantly), but this is still a straight-forward problem of one body moving in a gravitational field.
  - narag 12y ago
    Original question said: when moving near the comet. So ISTM that it's not so straightforward. Some months ago someone posted a gravity simulator here and it was very instructive playing with it and seeing how unstable a small object's orbit is around two bigger objects rotating around their center of gravity, situation that seems similar to the "duck". Edit: http://www.nowykurier.com/toys/gravity/gravity.html http://www.nowykurier.com/toys/gravity/gravity.html Try creating two big objects in a circular orbit and experiment launching smaller objects with the same direction and speed. Some of them will crash, some others will escape.
    - jessaustin 12y ago
      My impression is that although it is not spherical, the core of the comet is a single object. It may therefore be treated as a point mass for these purposes.