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Space

After Four Days, Philae Team Gets to Rest 88

The Associated Press reports on one happy consequence of the inevitable shutdown of the Philae lander, after its incredible landing on Rosetta: the team that was in control of the lander here on earth finally gets to take a well-deserved break, after four nearly sleepless days and nights. It seems unlikely -- though it's not impossible -- that Philae will get enough solar energy to briefly wake up again; its bouncy landing and harpoon malfunction mean that the craft is in shadow rather than the sunlight that it was hoped to bask in. From CNN: Originally, it was supposed to have seven hours of light per comet day -- which lasts just 12.4 hours. Now it is exposed only 1.5 hours a day. That's likely not enough to juice up Philae's rechargeable secondary battery, ESA said. There is one last hope. "Mission controllers sent commands to rotate the lander's main body, to which the solar panels are fixed," ESA says in on its blog. "This may have exposed more panel area to sunlight."
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After Four Days, Philae Team Gets to Rest

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  • by Anonymous Coward

    Using an RTG would have eliminated this problem. Just saying...

    • Re:RTG (Score:4, Insightful)

      by Ken_g6 ( 775014 ) on Sunday November 16, 2014 @03:05PM (#48397907) Homepage

      It took ten years to get the Rosetta mission to the comet. By then a RTG would be fairly depleted too.

      • That would depend heavily on the radioactive material used, no? For example, Wikipedia lists Pu238 to have just a ~16% drop in output after 20 years.

        I'm guessing cost and weight were the key factors for picking solar over an RTG.

      • Re:RTG (Score:5, Informative)

        by Dan East ( 318230 ) on Sunday November 16, 2014 @07:21PM (#48399179) Journal

        It took ten years to get the Rosetta mission to the comet. By then a RTG would be fairly depleted too.

        That isn't a legitimate reason to not use RTG for Philae. The lander only uses 32 watts of power. The MMRTG used in Curiosity provides 125 watts of power initially, and 100 watts after 14 years. The mass of that specific RTG (the MMRTG) would be too great for use in Philae, but then it also produces 3 times more energy than needed (even after 14 years). RTGs have been made in many sizes for many different applications, so it would simply have been a matter of designing an RTG that produces 40-45 watts of power after 10 years.

        However, one of the main uses of the 32 watts of power required by Philae is just to keep the batteries warm so they don't fail. RTGs produce more "waste" heat than they do electricity. For example, the MMRTG used in the Curiosity rover produces 2 kW of heat, of which 125 W is converted to electricity. The extra heat is used to keep the various temperature-sensitive parts of the rover nice and warm so they don't fail. With Philae, a good portion of the 32 watts of the solar power it requires is just to keep the battery warm. So if an RTG were used, it wouldn't even need to produce 32 watts of electricity since it can keep the lander warm directly.

        Looking at the mass and wattage produced, the RTGs ("SNAP-19") in the Pioneer probes would have been just about perfect for Philae. They produce 40 watts of power and weigh 13.6 kg. Philae's current electrical system weighs 12.2 kg, so that's at least in the ballpark. The RTGs on the surface of the moon, as manually placed by Apollo astronauts's would have been a bit heavy at 20 kg. One of those RTGs was still producing 90% of its power after 10 years.

        Regardless, the fact that the Philae mission would last more than 10 years is not a reason to not have used RTG. Other issues (obtaining the radioactive material, environmentalists throwing a fit, inexperience of the ESA with that kind of power source, delays in production, etc) certainly dictated that an RTG wasn't used, but it was most certainly not due to any technical limitation.

      • No. The Voyagers were launched in the late 1970's and are still functioning.

    • Re:RTG (Score:4, Funny)

      by YrWrstNtmr ( 564987 ) on Sunday November 16, 2014 @03:11PM (#48397939)
      Thank you, Mr. Comet Lander designer guy! I'm sure, for the next one, they will bring you in as a consultant.
    • Re: (Score:2, Troll)

      Pretty sure having working landing gear would have solved the problem.

    • Two problems. ESA does not have access to the plutonium as i understand it. The second issue is that it would have made the unit much heavier and so needed a bigger rocket to be able to meet the timelines.

  • 1. As the comet approaches the sun, is it likely that the angle of or proximity to the sun will provide enough light to make a difference?

    2. I assume we've measured whether Rosetta is rotating, even slightly. Is there a chance that this will help (or hurt) Philae's chances at coming back on line?

    3. As the comet gets closer to the sun, I imagine that it will start melting/vaporizing (this being what makes a comet look like a comet in the first place). Since Philae is not firmly anchored (and that might not

    • by duck_rifted ( 3480715 ) on Sunday November 16, 2014 @03:19PM (#48397967)
      First things first.

      We've been calling this comet "Rosetta" thanks to the media, but it's actual name is 67P/Churyumov–Gerasimenko. Rosetta is the name of a probe that photographed it. But it does have a certain ring to it that may better stick in the minds of your average news reader.

      The comet has a rotation period of about twelve and a half hours. Its orbit lasts 2,398 days. We may be calling that a "Rosetta year" soon. To actually calculate whether the comet's orientation will allow sunlight to strike the main panels for longer stretches, we'd need to know more about the cliff it's under. The ESA is no doubt crunching those numbers now, but it's possible that if this situation will resolve itself then it will take years.

      A smaller panel got sunlight when the drill was used to rotate the probe. So, if it is powered down and we wait, it should eventually charge back up. Each time that happens, the ESA can work at getting it into a better position, little by little.

      It's not dead; it's just napping. It will eventually be back online. The big question is, when? If the ESA knew for sure, they'd probable tell us. So, we wait.
      • Just 'pining for the fjords' does have a certain sensibility about it in this case.

      • by rvw ( 755107 )

        If it has 90 minutes a day sunlight, while it was expected to be 7.5 hours, wouldn't it just take five times longer? So maybe they could only use it once every five days (or whatever time unit they use). I'm not trying to be clever, just wondering why this doesn't seem to be an option.

        • by Lord Crc ( 151920 ) on Sunday November 16, 2014 @03:32PM (#48398029)

          As I understand it, the problem is that the batteries must be at 0 degrees C to accept charge. The limited sun it's getting now isn't enough to heat the batteries (surface temperatures are about -70C IIRC).

        • by confused one ( 671304 ) on Sunday November 16, 2014 @03:42PM (#48398091)
          It's not quite that simple. It takes a certain amount of power to keep the computer running, even in low power standby mode. It also requires some energy to run the onboard heaters, which keep the battery and electronics from failing due to the extreme cold. The amount of energy they were receiving in the 90 minutes, before the attempt to turn the probe, was insufficient to supply the heaters, run the computer in low power standby and charge the battery. I don't know if they left the heaters running, because there was concern that the heaters alone were enough to prevent the battery from charging. If not, the battery may freeze solid before charging to a level that's able to restart the computer. It's hoped that that won't be the case... we'll have to wait and see.
      • We've been calling this comet "Rosetta" thanks to the media, but it's actual name is 67P/Churyumov-Gerasimenko.

        Man, anyone who'd name their kid "67P" is just asking for that kid to be picked on. No wonder it prefers to go by "Rosetta".

      • A smaller panel got sunlight when the drill was used to rotate the probe. So, if it is powered down and we wait, it should eventually charge back up. Each time that happens, the ESA can work at getting it into a better position, little by little.

        Unfortunately, it doesn't work like that. A significant amount of power goes into heating the batteries up, which is necessary to get a significant amount of power out of (and in to) the batteries.

        Batteries are, as I'm sure you realise, chemical devices.

        All chemi

    • by mbone ( 558574 )

      1. As the comet approaches the sun, is it likely that the angle of or proximity to the sun will provide enough light to make a difference?

      2. I assume we've measured whether Rosetta is rotating, even slightly. Is there a chance that this will help (or hurt) Philae's chances at coming back on line?

      3. As the comet gets closer to the sun, I imagine that it will start melting/vaporizing (this being what makes a comet look like a comet in the first place). Since Philae is not firmly anchored (and that might not make a difference in any case), what do we expect to happen, and when?

      1.) Maybe.

      2.) If you mean Comet P/67, maybe.

      3.) Maybe, pretty much anything up to and including ejecting Philae away from the comet for good. As for when, maybe around perihelion (13 August 2015) when activity is highest. Or, maybe before then. Or after then.

      Glad I could help clear things up!

      • 2. I assume we've measured whether Rosetta is rotating, even slightly. Is there a chance that this will help (or hurt) Philae's chances at coming back on line?

        The comet is actually rotating a lot, once every twelve hours. Since the comet acts as a gyroscope its axis of rotation keeps pointing towards the same distant star while the comet goes around the sun, and because the axis is tilted, different parts of the comet will receive light. The comet has seasons.

  • A simple calculatoin:
    Current amount of energy from panels is a quarter of what's needed
    current distance from the sun is 3 earth units, it will go down to 1.3.
    That means energy flux no the panels will increase (3/1.3)^^2 or more than 5 times.
    If all the rest remains the same(er, what?), that should be enough.
    And if the system can handle currents five times as high.

  • While the Philae team is sleeping, nefarious malefactors are busy selling Philae on eBay [ebay.co.uk]. It's up to five pounds sterling as I write. Maybe we should wake them up.

  • The article said it landed on Rosetta, if this was the case it wouldn't have been much use. Instead it landed on Comet 67P Churyumov-Gerasminko
  • Landing gif (Score:5, Funny)

    by SternisheFan ( 2529412 ) on Sunday November 16, 2014 @03:52PM (#48398137)
    This ESA blog link has a Gif of the landing from Rosetta... http://blogs.esa.int/rosetta/2... [esa.int]
  • From Valerie Lommatsch, an engineer at the Lander Control Center at DLR in Germany [planetary.org] :

    "It is very unlikely right now. We have 1.5 hours [of sunlight] at less than 1 watt, and 20 minutes of 3 or 4 watts. The lander needs 5 watts to boot....In order to charge the secondary battery, we have to heat it to 0 degrees Celsius. We need about 50-60 watt-hours a day in order to reach 0 degrees and still have daylight left to charge the battery. So it doesn't look that great. What we could hope for is if we are closer t

    • by Thagg ( 9904 )

      Sadly, while the "weight" is very small on the comet, it's mass (and therefore inertia) is substantial. You're not going to blow it over.

      It wouldn't surprise me if they land Rosetta on the comet toward the end of the mission.

      • by mbone ( 558574 )

        It wouldn't surprise me if they land Rosetta on the comet toward the end of the mission.

        That is indeed under discussion.

      • by mbone ( 558574 )

        Sadly, while the "weight" is very small on the comet, it's mass (and therefore inertia) is substantial. You're not going to blow it over.

        I am going to ignore for now any issues of damage from nearby thruster firings.

        Rosetta has 24 bipropellant 10 N thrusters and is 2.8 x 2 m, not counting solar panels. Philae is 1 x 1 x 0.8 m. Suppose Rosetta fires a thruster from 3 meters away - Philae is then 1/3 of a radian across, or about 0.1 steradians. Suppose the thruster has a exit angle of 2 pi steradian (i.e., the whole hemisphere away from the spacecraft, which is surely conservative). So, I would expect Philae to experience a force of 10 N x 0

    • The risk to Rosetta would not make such a maneuver worth trying. Use of propellant would also shorten Rosetta's life.
      • Not to mention that they don't know where the lander is.
        • by mbone ( 558574 )

          Not to mention that they don't know where the lander is.

          I think it is a safe bet it will be found. They have the photos from the surface, they have the CONSERT triangulation, and of course they have a great desire to find it (and the comet isn't that big). It will be found.

        • I think they've found it already, to a couple of Philae-diameters.
    • by f3rret ( 1776822 )

      I wonder if they couldn't get Rosetta near Philae, and use the reaction jets on Rosetta to move it (i.e., by blowing on it). Philae only weighs about as much as ping-pong ball; it wouldn't take much to move it away from where it is.

      That's a Kerbal solution if I ever read one.

    • I know everyone hates armchair rocket scientists, but I'd like to leave this [nanomedicine.com] here:

      A ~0.2 kg block of pure Gd148 (~1 inch^3) initially yields ~120 watts, sufficient in theory to meet the complete basal power needs of an entire human body for ~1 century ...

      They could've had 120W of heat free for the asking with 200g of Gd148 (a pure alpha emitter). Use 50W of that to keep the wee beastie warm, and the other 50-ish Watts might've been enough to power the lander.

  • by Anonymous Coward

    seven hours of light per comet day -- which lasts just 12.4 hours. Now it is exposed only 1.5 hours a day.

    So 7 hours of light should provide enough energy for ~12 hours of operation, which it was planned would allow it to function every day.

    Surely though the 1.5 hours will be enough for it to wake up for a short period of time? Long enough to upload some new instructions.

    If they leave the lander in sleep mode for several comet days they can gain enough energy for a longer period of operation. Sleeping for 5 comet days will give the equivalent of charging for 5x1.5 = 7.5 hours, roughly what they expected in a si

  • Wait, everyone was like that? How can one/1 work like that? :/

    • If you have worked for a couple decades on a project I imagine it would nearly impossible to sleep.

    • The key word is "nearly" ; most people who haven't had to do it on a regular basis are surprised to learn that you can function on quite small amounts of sleep. You do still need some sleep, and your performance degrades over time, but it's not too drastic.

      My normal working day is 18-19 hours, but when we're in critical operations I go down to working about 03:00 to 12:00, have a nap after lunch, then am back on shift from 13:00 to about midnight ; lather, rinse repeat. After a week, you're really looking

      • by antdude ( 79039 )

        So, you do this daily?

        • When I'm at work, and we go from routine operations (where I have a lot to do) to evaluation operations (where I have a lot to do and can't delegate chunks of it to my night-shift/trainee, because they're a trainee) then yes, I have to do this regularly. Bouts of 4-5 days are normal; up to 8 days not uncommon, but deeply draining. Then there will unavoidably be 1-2 days of engineering/ maintenance work, and then the cycle repeats. Bouts like this happen a couple of times a month, then I'm rotated back to sh
          • by antdude ( 79039 )

            Wow, how long have you been doing this? Is it worth it? I used to work long hours and even worked about a month nonstop (no days off). It wasn't worth it. Ugh.

            • I've been doing this since 1987, to varying degrees. Some years I've been down to about 1500 hours work (though we bill by the day, or part of, door to door), some years pushing 3000 hours, and utterly exhausted. The intensity increases with time, because you get sent to jobs with absolute greenhorn (instead of being the greenhorn yourself). And sometimes you do have to just dump raw data upstream for assessment there, but even then you need to verify that the collection parameters were recorded appropriate
  • ESA doesn't have its own RTGs yet. Access to plutonium is a problem and the use of americanium 241 for future EU RTGs is planned. Since US nuke regulations forbid to sell such technology unless it is installed at the last moment on US soil which would imply US acces to EU industrial secrets and a launch from US soil with a US rocket it is out of the question for ESA to buy a RTG on the shelf.

    Plus ESA has a much lower budget than ESA and doesn't have as many deep space missions As the NASA. Yet.

    • by tomhath ( 637240 )
      The design of Philae was fine, it would have had enough power if the landing had gone as planned. The main thing they need to look at is why the attachment mechanism didn't work; fix that and there's no need for an RTG.
    • RTGs were considered and rejected as too heavy for the power needed. You'll note that the large majority of the science programme was carried out, despite the unintended changes to operations.
  • by Anonymous Coward on Sunday November 16, 2014 @06:37PM (#48399001)

    ...who will be heckeled by feminazis until they find someone or something else to attack.

    • by Anonymous Coward

      I'd like to show support for the man that did this comet landing thing.
      Anybody know where I can get a copy of his shirt?

  • > After Four Days, Philae Team Gets to Rest

    Thank god. I have this comfy shirt I've been meaning to wear...

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