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After Four Days, Philae Team Gets to Rest
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."
It took ten years to get the Rosetta mission to the comet. By then a RTG would be fairly depleted too.
(T>t && O(n)--) == sqrt(666)
Thank you, Mr. Comet Lander designer guy! I'm sure, for the next one, they will bring you in as a consultant.
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.
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.
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.
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!
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).
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.
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
This ESA blog link has a Gif of the landing from Rosetta... http://blogs.esa.int/rosetta/2...
We are suffering from a severe shortage of Pu238 already. It's already one of the main limiting factors to NASA/ESA long range space exploration efforts.
That's possible, but the real issue is that the electronics are likely to be damaged by extremely cold temperatures.
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 0.1 / 2 pi ~ 0.2 N. It has a mass of ~ 100 kg, so that would impart a thrust of 2 x 10^-3 m/sec^2. (I am assuming Rosetta has a thruster firing on the opposite side too, so it's not moving.) That is actually greater than the 67/P gravity, so Philae could move. If this were done for say 10 seconds, Philae would have a velocity of ~ 1 cm/sec afterwards and maybe a total flight time of 30 seconds. Now, it wouldn't move far, but it might get to a little flatter terrain and maybe more sunshine.
It's worth pointing out that the cause of this shortage is a political issue rather than a technical one. It started with a non-proliferation bill during the Carter era.
Do what thou wilt shall be the whole of the Law
All they have, before they release the probe, was a series of GO / NO GO checklist, on the few chosen "preferred landing spot" on that comet
There was no contigensy plan for the many "what ifs" that may happen
Do you have any reason to believe this, any actual evidence that there wasn't a long list of contingencies, or are you just making it up? Because I certainly don't know all the inner workings of the ESA, and since you've provided no links then I somewhat doubt that you do either.
...who will be heckeled by feminazis until they find someone or something else to attack.
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.
Better known as 318230.
If you have worked for a couple decades on a project I imagine it would nearly impossible to sleep.
I love Jesus, except for his foreign policy.
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.
No, if it's properly designed energy goes where the controller sends it. However, temperatures are low enough to freeze the battery, bringing it below the point where it will function. There are many electronic components that just won't work at -100C; or, will be damaged by deep cold. Heaters are critical to operation of most of the components on a deep space probes.
I dig this one: "Buyer must collect item from its storage location on Comet 67P."
Table-ized A.I.
It's amazing what they blame on Carter: A dead probe 40 years after his term.
Table-ized A.I.
assumed that they could land the probe on a comet just like they land a probe the size of the Moon or Mars
Which is factually incorrect. Saw a documentary about this project yesterday and they were fully aware of the difference hence the harpoon and screws to try to keep the lander intact.
They even described the "what if" scenario if the harpoons would fail, but it doesn't help if the lander rest in a place where there isn't enough sunlight. That is just plain unfortunate.