I watched this documentary called "To catch a comet" about the Rosette/Philae mission to comet Churyumov–Gerasimenko. The achievement of getting to the comet and landing Philae, like many other achievements in space, is really phenomenal. So many things could've gone wrong, but the fact that the worst was Philae bouncing and getting stuck in a dark place (and not being able to perform fully) is a huge success beset by an issue of a smaller magnitude.
The description of the documentary says [1]:
> Unable to carry enough fuel owing to weight restrictions, the Rosetta scientists devised a delicate cat and mouse trajectory to reach their distant destination. In the ten years Rosetta had been in space she flew around the Earth three times, Mars once and the asteroid belt twice, to gain the momentum she needed to reach her destination. In the months before landing, the team navigated Rosetta safely to a world never before observed at such distances or accuracy. Rosetta orbited the comet before releasing Philae onto the surface.
Quoting from the article of this thread:
> “We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour.”
This brings a much better ending for the people who worked on the mission for more than 30 years. [1] We tend to anthropomorphize things like spacecrafts, landers, rovers and many other inanimate objects. I think for the team (and many others following this news), this photo would be like being able to see a dear friend one last time, say goodbye in their minds and have some kind of closure.
The Wikipedia article, and especially the section titled "Landing and surface operations" [2], is also quite interesting to read.
I tried to find the full version of the PBS "To catch a comet" about the Rosette/Philae mission but came up empty handed. Searching google, I was able to find a talk by Mark McCaughrean (ESA) called "Rosetta: to Catch a Comet". Been watching it for about 30 minutes and it's awesome. So, for anyone else looking for something to watch, this worked out great. Pretty amazing talk!
There's also the argument for doing things a better way. Our propulsion systems suck, which is why we're having to send robots to comets instead of humans. Humans don't get stuck in cracks. Robots get stuck in cracks because they have no clue how to measure things they've never seen before.
What exactly is your point? Better propulsion would solve a ton of problems with space flight all at once, but how do you achieve it? This is nearly as bad as saying that gravity sucks, if we could just turn it off then it would all be so much simpler.
Again, clearly not true. Crewed implies habitable implies need for O2 implies more complexity. This complexity could not be carried on the budget, schedule, and risk allocated for this asteroid lander.
You could say the same thing about safety, and the need for return.
But use of such a system requires development, testing, and flight qualification, affecting cost, schedule, and risk. It will also affect other variables, like volume.
Focusing on a point solution like "propulsion" is not even the right kind of question to answer "why not solve this problem with humans?".
> development, testing, and flight qualification, affecting cost, schedule, and risk
These are all a lot easier if you are not worried about mass anymore. Just give all your structures a 3x safety factor like a bridge, and bring extras of anything complicated. Heck bring a mechanic and tools, too.
Of course this is all fantasy, which was the point of this subthread under kordless, in the first place.
EDIT
> Focusing on a point solution like "propulsion" is not even the right kind of question to answer "why not solve this problem with humans?".
To be more clear: I agree with you. I'm just playing the idea of "what if we had much better propulsion." But of course we don't, so in real life, we do need to carefully consider the factors you mention.
That's a fair point. That's like saying "we have the best medical facilities in the world for any treatment imaginable, but the hospital is five miles away. How will we carry you there in time to be treated?"
With our current understanding of physics, chemical rockets have one giant engineering advantage: the same mass that is consumed for energy production is also the reaction mass. So anything better for imparting large delta-Vs has to be non-newtonian and our current understanding of physics does not allow existence of any such thing.
That's a big oversimplification. Project Orion-style propulsion is certainly not ruled out by our current understanding of physics. There's no non-Newtonian mechanics involved, just the substitution of a nuclear reaction instead of a chemical one. Not to mention that we have lots of evidence of non-Newtonian mechanics (e.g. Special and general relativity), even if whether GR can assist in space travel is an open question.
If look at it the other way around: burning the reaction mass is the only source of energy you use to accelerate the reaction mass — it doesn't sound obviously optimal.
Nuclear thermal, and nuclear/solar electric (aka ion) rockets achieve better specific impulse despite carrying separate weight for power.
Some nuclear designs (e.g. Orion as johncolanduoni said) do have overlap between reaction mass and energy source mass.
Solar sails, ground lasers, and gravity assists avoid some of the need for carrying reaction mass.
All these are perfectly newtonian.
Chemical does win among currently working designs at accelerating quickly, which is critical for human exploration, and to some degree for getting to orbit. There is no inherent physical reason alternatives can't achieve that.
I must recommend the extremely fun Project Rho site though I'm just started reading it:
http://www.projectrho.com/public_html/rocket/enginelist.php
It's not always clear where existing science ends and Sci-Fi begins, but that's generally on technology barriers (e.g. we haven't yet managed break-even contained fusion), not mythical "entirely new understanding of physics".
And the amount of actual science — detailed papers, prototypes etc — on diverse and bizzare drive designs is way more than I expected!
I didn't get why this was important and the article didn't reveal it upon skimming. Since it seems to get people very enthusiastic I gave it a proper read. After 11 paragraphs, the actual news is revealed:
> “This [...] means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!”
Also, the third paragraph shows why it was relevant:
> The images also provide proof of Philae’s orientation, making it clear why establishing communications was so difficult following its landing on 12 November 2014.
Mostly the curiosity of the public and more importantly the scientists who worked so hard on the project only to have their lander not land properly.
Otherwise the fact that Philae was lost almost immediately upon landing has been a huge story line this past year. I believe the blog assumed the readers would know this. A CNN article would typically provide back story but this is original source from ESA.
There were a couple of mechanisms intended to hook it upright to the surface upon landing. Instead it bounced 2 or 3 times and landed tilted in some rocks. The battery was only sufficient for a few hours of pictures and other experiments. If it had landed upright and charged by solar panels it could have operated a long time, perhaps until now. The hope was that some of the solar panels were exposed it might revive after a couple of weeks. There was a hint it called the orbitor at least once, but no more data.
It is scientifically useful, but mostly people are just pleasantly surprised that the proverbial needle in the haystack was actually found before the mission of Rosetta itself ends, and happy to get closure for the story of the little probe that went MIA. It's an emotional response first and foremost, just being human.
Scientifically speaking, a successful mission is one where you've gathered all the data for analysis and can work with it long after the mission is over.
It's like, if SpaceX launches a rocket and it explodes - a real failure would be if they captured no telemetry and had no idea what happened vs knowing everything that happened and being able to replay the mission after the fact. Often times the data is far more important than the outcome.
The SpaceX comparison is bad because they don't do science missions. SpaceX do commercial launches for paying customers. Mission success is defined by whether the payload gets to its intended orbit, unharmed. Even if SpaceX learn a lot from a mission, if the payload is lost then the mission failed. While one can learn from failures, when the mission is not a test, learning is not enough for the mission to be called a success.
> they don't do science missions
true, but they do R&D like most large for-profit entities. However I agree with you that the comparison is not compelling. R&D is not SpaceX's main objective, hence the situation described doesn't compare to a scientific mission where you send a lander on a comet and you actually get the data from the lander.
1. Launch contracts for paying customers where mission success was defined as "unharmed payload to correct orbit".
2. Test/demo missions with mass simulator instead of payload where mission success was defined as "unharmed payload to correct orbit" (two missions: Falcon 1 Flight 4 [0] and Falcon 9 Flight 1 [1]).
3. Rocket landing development flights with Grasshopper where mission success was defined as advancing the ability to land the booster.
SpaceX did R&D on all flights (for example they unsuccessfully tried parachute recovery), but for all flights of Falcon 1 and Falcon 9 (not Grasshopper), they always stated that mission success is to get the customer's payload unharmed to the correct orbit, or to demonstrate the ability to get the customer's payload unharmed to the correct orbit. If they defined mission success as anything else, a potential customer might think SpaceX would sacrifice the payload to advance SpaceX's own goals (like recoverability R&D), and this customer would not fly with SpaceX.
In a commercial sense, you're right, but if they have telemetry from the recent mishap which allows them to identify and fix a serious design flaw, then it absolutely is beneficial to their R&D. Especially when you consider that they're winding up for manned missions. Losing a satellite on the launch pad is not so much of an issue compared with losing an ISS crew.
Science is not a white/black min/max field. Failure in science is to end up not knowing more about why your original idea or theory is either wrong or right. It's the literal equivalent to a sealed glass of water containing the same exact (to the molecule) amount of volume after a period of time attempting to change it through external forces. You've learned nothing.
When a rocket explodes on a launch pad, and you've gathered petabytes of telemetry data and sensory data from all of it's systems, you can study and research that data to figure out what went wrong and put procedures and systems in place to mitigate that in the future. You learn from the mistakes, thus the outcome of the failure is a success. This doesn't mean we should stand in the viewing area of SpaceX's control center and cheer them on for their work in making a rocket explode. They still failed their mission, but they can make their future missions more safe and more robust because of what they learned in a real world failure situation.
I'm surprised at how rugged the surface looks in these high-res images. Especially compared to the imagined flat landing areas we were used to seeing in the run up to the landing [1]. Just shows how difficult a task it was to land and keep the craft the right way up.
It was aimed at a flat spot, but when it failed to attach to the surface it bounced and floated for almost 2 hours, hitting the surface again 1 km away[1][2]. Its speed of 38 cm/s during that time was below escape velocity but not by much.
> it failed to attach to the surface it bounced and floated for almost 2 hours, hitting the surface again 1 km away[1][2]. Its speed of 38 cm/s during that time was below escape velocity but not by much.
These numbers sound completely ridiculous, unless you've played Kerbal Space Program, and know the visceral pain of bouncing above Minmus with a pixel of monopropellant left in the tanks.
There is no atmosphere and thus no wind (let alone flowing water), so no natural forces to smooth it out. On a related note, moon dust is apparently incredibly sharp for the same reason.
From Wikipedia about the comet: "One of the most outstanding discoveries of the mission so far is the detection of large amounts of free molecular oxygen (O
2) gas surrounding the comet. Current solar system models suggest the molecular oxygen should have disappeared by the time 67P was created, about 4.6 billion years ago in a violent and hot process that would have caused the oxygen to react with hydrogen and form water. Molecular oxygen has never before been detected in cometary comas. In situ measurements indicate that the O
2/H
2O ratio is isotropic in the coma and does not change systematically with heliocentric distance, suggesting that primordial O
2 was incorporated into the nucleus during the comet's formation. Detection of molecular nitrogen (N
2) in the comet suggests that its cometary grains formed in low-temperature conditions below 30 K (−243.2 °C; −405.7 °F)." [1]
"At 2.7 km, the resolution of the OSIRIS narrow-angle camera is about 5 cm/pixel, sufficient to reveal characteristic features of Philae’s 1 m-sized body and its legs, as seen in these definitive pictures."
I looked at the pictures and the human eye can barely see the lander. Considering that the chances of losing these landers is not that low, I don't understand why they don't make them visually more distinctive.
Andrew Ng gave a talk recently where he talks about designing the autonomous cars not for aesthetics, but predictability (via visual distinctiveness). [1] In the same spirit, shouldn't there be efforts to make these spacecraft modules more visually distinctive?
"the human eye can barely see the lander" is a bit exaggerated. It's not immediately obvious where in the image the lander is (it took me a few seconds to find it), but well visible once you've got the position.
"Considering that the chances of losing these landers is not that low" - most of the time, when the mission fails, they don't make it to the surface, though. As far as I know, Beagle 2 is the only lander that was lost and later found. The Mars Polar Lander likely dropped onto the surface from some 40m up, maybe a wreckage could be found there. But other than that, I'm not aware of any landers that could be found with a camera in orbit. Debris is hard to find, even on earth - it took over 20 hours to find a crashed fighter jet in Switzerland last week, and another day to find the pilot's body.
My entirely uneducated guess is that a layer of paint would impede the cooling of electronics that depend on the housing to dissipate heat.Paint would also absorb more solar heat than plain metal.
A dye bomb is used for aerial crash/rescue. That would contaminate a surface, but also provide a possible visual marker. Maybe several launched away from the lander, but which could be used to triangulate it, in the rare case that might actually be of interest.
I suspect there's a lot of re-thinking of how to land on a comet going on as well.
Certainly I started thinking about better ways once this image made it clear what we (humans) are dealing with here.
I can imagine a cage-like outer shell where the robot inside is able to rotate on two axes under power. Let it tumble any which way and then use sensors to determine the correct orientation and right itself.
That's pretty much what Spirit and Opportunity's airbag landing system was, although a lot simpler --- it was set up so that no matter what way up it was after it came to a rest (after bouncing and rolling!), when the bags deflated it would automatically roll the right way up so that when the deployment mechanism finally opened, the rover could just drive out.
I've tried to find a video showing it happening, but while there's lots of animations of bouncing, rolling, and the final opening up, they all miss the critical moment. Also, car safety videos are really badly poisoning the search results...
> I looked at the pictures and the human eye can barely see the lander. Considering that the chances of losing these landers is not that low, I don't understand why they don't make them visually more distinctive.
If it was hot pink it would have made no difference, it ended up in a bad spot with limited solar power.
Finding the lander made a difference. Now they can put the the data into context (“[...] we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context [...].”).
ESA is lucky it had a high-resolution camera to distinguish the lander from the terrain. If you only have low-res cameras, it might be useful to have a visually distinguished lander so you find it despite of poor resolution (1 bright pixel).
A naive solution might be to make future landers reflect a certain wavelength and use a tiny camera that is tuned to capture that wavelength. Finding the lander should be much easier then.
But then you probably have a camera that has exactly one use – finding the lander – which doesn't necessarily yield the same quality of scientific results than having a camera that is more useful to the actual goals of the mission. Yes, finding Philae is nice, but not finding it wouldn't have been that bad, and the camera surely generated worthwhile data even without finding Philae.
If they didn't have a high res camera and could only identify the lander as a brightly colored speck it would not provide any "context" for their data other than it did not vanish into space.
The suggestion, I think, is to have both, under the assumption that one extra low-res single-purpose camera would be relatively easy to add. Once you find it with one camera, you can find it with the other.
> A naive solution might be to make future landers reflect a certain wavelength and use a tiny camera that is tuned to capture that wavelength. Finding the lander should be much easier then.
That's a complicated way of saying "paint it like barricade tape", isn't it?
If they were to commit resources to this situation, a simple, tiny, low power radio beacon would be an option.
Rather than search for it, let it tell Rosetta where it is.
The problem with this is that even though the beacon could be only a few grams and use micro-watts (1 milliwatt transmission 1/1000th of the time?) of energy, Rosetta would need a receiver capable of picking it up.
I assume Rosetta has something like software defined radio but due to when it was designed, not sure if this is the case. In any case Rosetta is loaded with really sophisticated radio gear probably it could be build such that there is no weight or energy penalty for this.
Wish more NASA folk would read hacker news and could chime in
It seems that the beacon is not necessary. They already have radio localization. The problem is confirmation from imagery.
> Radio ranging data tied its location down to an area spanning a few tens of metres, but a number of potential candidate objects identified in relatively low-resolution images taken from larger distances could not be analysed in detail until recently.
Ah hah... good spotting. Using radio to locate down to 10's of meters is a heck of an achievement. Makes me wonder how many other amazing things are hidden under the surface of this effort that are similarly amazing but don't see the light of day.
I believe he is talking about an autonomy-enabled region, which is full of autonomous cars. It includes things such as modifying even the road infrastructure.
At some point in the future, someone is going to fly to that comet, land, get out of their vessel and walk over to Philae and smile, give it a pat on the head, and then take it home; someone in the future is going to be lucky enough to experience that task and become a part of its history.
And it might still work. One of the neat things about Philae is that it's rated to withstand temperatures down to −60 °C. Most other space probes(and electronics in general) are not rated for such low temperatures and will experience solder joint failures if such temperatures are reached. Most space probes stay above their failure temperature with heaters, if said heaters fail, the space probe dies and won't function even if it warms back up. This happened to the Mars Exploration Rover Spirit.
We don't know just how low Philae can go, however, there is a good chance it's electronics won't break below the rated temperature.
Worth mentioning is that objects keep their thermal energy for much longer in a vacuum since there is nothing that can conduct the heat away, so the heaters does not have to output that much energy.
You're assuming that's a technological challenge that hasn't been overcome, despite the fact the person flying the vessel is was indeed flying a vessel capable of landing in the first place, and returning home :P
The XKCD already updated the live comic about this subject [1].
All panels are available at its sister wiki [2]
In my opinion it is a beautiful work of art, pushing the limits of what the media allow the artist to do (the media in this case being comic strips in the webcomic format.
Wow. I had only mild interest in the news and was about to close this tab after I learned what the hell Philae is (without opening TFA), but this comic series made me excited about the project and made me check out the article. Good job, Randall, and thanks!
Not sure how accurate it is, but an article found via cursory Googling[0] makes it seem like a true-color photo doesn't have as much scientific value as other spectrum recording photography - different filters over the monochrome camera can make it easier to see heat, minerals, radiation, etc.
Goes on to mention producing a true-color photo is kind of a pain in the ass for these probes.
Cameras often have wavelength filters to allow recording only certain wave lengths, that can be switched. So taking a colour photo requires three different exposures. Depending on how long you can take a single picture and how much changes in between you may not really get a useful result. A Bayer filter like in common digital cameras these days would also reduce resolution and restrict you at the sensor level to colour photos.
About the only use for colour photos in space is PR with non-scientists anyway. That was one major obstacle the Hubble Space Telescope had to face. It's a useful component, to be sure, but not one to justify adding much more weight or cost to a planned mission in all cases.
In case of Rosetta/Philae the probe was very weight-restricted, taking even a very long course towards the comet to save fuel since it didn't have much.
it's not worth it scientifically to use a bayer filter. if there's a color shot, it's usually false color or three successive shots with a R/G/B filter separately. this spacecraft may not have such filters available as the comet is expected to be about as colorful as a lump of coal.
Anular velocity might also be too high to get a suitable impression. Three separate scans would be shifted leaving a rainbow-blurred image. Still lifes are easier (e.g., geostationary shots of Earth, Mars rover shots).
Also the picture may not be "black" and "white", it's just captured at a single frequency [or a small spectrum], and readings are for that particular frequency.
Combine multiple spectrum and you get a color image.(Though comets don't have too much change across the spectrum.)
Some decisions are made about what is going to be observed. For example, if the objective is to study the methane atmosphere (as it's being done on Jupiter), you calibrate your camera and filters for that. Then photo is taken, with whiter points indicating more emission or reflection on that wavelength. Black and white is how we see "more / less emissions"
Yes, they knew it landed, they got data back and then other than the last burst, never heard from it again. That's from the article and other news sources.
Nice to know that it was still there after the last burst, that it hadn't been swept into space. And from the pictures it's going to be on there for awhile.
Then RYFC: "it's good to know that Philae hadn't bounced off into space." does not correlate with someone who had bother to read the article before commenting. You can't "bounce" from a stationary position, but glad to see you've now caught up.
NASA and ESA's recent push to land things on comets and asteroids makes me pause and wonder if they have in the last decade or so calculated the orbit of an object that concerns them.
Why did it take so many months for the orbiter to get a photo?
Compared to the rest of the achievements of this mission, it seems like this should have been relatively easy: 67P is all of like 2.5 miles wide and the orbit is at like 10 miles. You'd think that a few high res photos in a single orbit would capture nearly every inch of the entire rock.
Unless other parts of the comet is more flat, that landing gear design seems clearly wrong. It included bolting itself to the surface, if I remember correctly, but it seems almost impossible to fixate three legs with almost no gravity on that surface.
It's pretty hard to see the details of a cometary surface from earth. And there isn't much you could do with no gravity and an all-rubble surface either way.
> It included bolting itself to the surface, if I remember correctly, but it seems almost impossible to fixate three legs with almost no gravity on that surface.
Philae had a harpoon for anchoring itself to the surface (with a thruster on the other side to compensate). The harpoon failed to fire. The legs were not intended for fixation, only to dampen the landing.
Maybe they should put it into a very very close orbit and wait for the micro gravity doing it's work. Maybe large harpoons tangling on sticks every side. It's easy for me to talk at this point, but it's their job to expect that surface. I don't think other comets passing closer by have better surfaces.
I'm following this mission almost from the beginning, amazed by the success despite Philae's short lived life on comet, and think the science aspect of it all is unbelievably great. But that landing moment made all the difference, and it failed to fix it on the surface, hence the criticism.
Would we consider Curiosity mission success if landing put it upside down?
INANE (I Am Not A NASA Engineer), but perhaps 4 or better yet more legs arranged in a tetrahedron or analogous polyhedron would better ensure the lander did not get stuck inside a crevasse; an inner rotating body could then bring the lander into a working position. The more the legs, the higher the chance the lander could 'roll' to a lower ground when initially bouncing off the surface, but the optimal number of legs could be determined in advance by simulating the terrain (you wouldn't want it to roll all the way down a slope, ending at the bottom of a crevasse etc.).
Harpoons protruding from each leg could be fired automatically as soon as a stable enough position was detected, or manually when deemed safe; having more legs available could only improve chances of getting a safe fixation.
Philae had a harpoon to anchor itself to the surface, but ended up malfunctioning. I assume had it actually fired, the engineers balanced the need for extra landing gear and scientific instruments quite well.
There were three aspects to fixing the landing, to my understanding.
Legs keep it oriented, give a stable platform, and cushion the initial landing.
Top thruster pushes it into the surface, damping any bounce back from the impact.
Harpoons attach to the surface, affixing it permanently.
The top thruster was reported to not work at all, and the harpoons were unable to work by themselves. It's not clear if they would have worked if the top thruster was working as well.
I am assuming you don't want to know why the whole mission is important (that should be obvious), and that instead you want to know why taking a photo of Philae is important.
It is important because Philae did made measurements and sent the data to us, but we didn't knew what the measurements measured, now we know.
It would be like throwing a ball that can tell about how much a place is wet in a random direction, and conclude that some place is 90% wet... Then, what place it was? A lake? A swamp? A beach? And then you find a picture of it in a bog, and conclude the bog was 90% wet.
> “This wonderful news means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!” says Matt Taylor, ESA’s Rosetta project scientist.
Philae did send data for three days (unless i miss-remember). Knowing where that data was taken helps put it into context. So quite important for the mission.
#/media/File:Rosetta%27s_Philae_on_Comet_67P_Churyumov-Gerasimenko.jpg){kind=link}
The description of the documentary says [1]:
> Unable to carry enough fuel owing to weight restrictions, the Rosetta scientists devised a delicate cat and mouse trajectory to reach their distant destination. In the ten years Rosetta had been in space she flew around the Earth three times, Mars once and the asteroid belt twice, to gain the momentum she needed to reach her destination. In the months before landing, the team navigated Rosetta safely to a world never before observed at such distances or accuracy. Rosetta orbited the comet before releasing Philae onto the surface.
Quoting from the article of this thread:
> “We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour.”
This brings a much better ending for the people who worked on the mission for more than 30 years. [1] We tend to anthropomorphize things like spacecrafts, landers, rovers and many other inanimate objects. I think for the team (and many others following this news), this photo would be like being able to see a dear friend one last time, say goodbye in their minds and have some kind of closure.
The Wikipedia article, and especially the section titled "Landing and surface operations" [2], is also quite interesting to read.
[1]: http://www.pbs.org/program/catch-comet/
[2]: https://en.wikipedia.org/wiki/Philae_(spacecraft)#Landing_an...