For ESA's Herschel Mission, the End Is Near 40
Trapezium Artist writes "The European Space Agency's far-infrared space observatory, Herschel, will soon run out of its liquid helium coolant, ending observations after more than three years of highly successful scientific operations. Predictions by ESA engineers are that Herschel will run out of helium later in March, at which point its instruments will warm up,
rendering them effectively blind. Herschel was launched in 2009 along with ESA's Planck satellite to the Sun-Earth L2 point, roughly 1.5 million kilometers from Earth. At that location, the Sun and Earth remain along a more or less constant vector with respect to a spacecraft, meaning that it can cool to very low temperatures behind a sunshield. At such a large distance from Earth, however, there is no way of replenishing the coolant, and Herschel will be pushed off the L2 point to spend its retirement in a normal heliocentric orbit. With the largest monolithic mirror ever flown in space at 3.5 meters diameter and three powerful scientific instruments, Herschel has made exciting discoveries about the cool Universe, ranging from dusty starburst galaxies at high redshifts to star-forming regions spread throughout the Milky Way and proto-planetary disks of gas and dust swirling around nearby young stars. And with an archive full of data, much of it already public, Herschel is set to produce new results for years to come."
mmmmmm candy (Score:1)
"dusty starburst galaxies"
Did anyone else misread the headline as ESA Hershey Mission
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"dusty starburst galaxies"
Did anyone else misread the headline as ESA Hershey Mission
No, I read: extra Herschey mission
so.. (Score:1)
Re:so.. (Score:5, Interesting)
Herschel probably won't be able to gather new sights and data once blind, so any "new results" would come from further examination of what it has already seen.
Scientific instruments these days tend to generate more data than can be quickly processed, so there's probably a lot of images that still haven't been more than glanced at...and if scientists decide to take a second look at what they've already pored over, they can uncover some fun new objects with strange parallax or whatever.
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Nature tends to generate more data than can be quickly processed
FTFY. I would even amend that to "be quickly processed, or even stored". Think about a fluid dynamics simulation for instance. Say you want to store a velocity vector at each grid point on a 400x400x1000 grid at 500 time increments. How much harddisk space will you need? A quick calculation comes out at 1.8 terabytes of data! And that's just for the velocity field, you can easily triple that number in a realistic CFD case.
Re:so.. (Score:4, Funny)
You know your space program has a long way to go (Score:4, Insightful)
when you lose spacecraft because they run out of consumables. What could we have learned if we'd had continuous IR coverage since the launch of IRAS in 1983, instead of a couple of missions each 1-3 years long?
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Given the amount of effort it takes to put something up there, wouldn't it make more sense to replace aging equipment with new and improved equipment rather than go to the trouble of resupplying the old?
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Yes, of course! And that's why we do!
But.. if we were more advanced it might not take so much effort to put something up there. That would be a game changer. Rather than throw out spacecraft when their consumables run dry we would do it (or better yet recycle them) when they are technologically obsolete.
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It's no different than any other remote site science expedition. Great effort is made to ensure that Antarctic stations are supplied with consumables, oceanographic vessels come home when then they run low/out, etc... etc... Even fixed installations like LHC have ongoing logistics needs, like an on-site cryogenic plant to ensure a steady flow.
Logistics (and it's handmaiden, maintenance) are something all scientific equipment needs to deal with. Space isn't special.
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I seems to me that NASA has all the technology needed to create a spacecraft, manned or unmanned, to make accessing the local solar system (Earth, moon, etc.) a matter of routine. Perhaps if they had an appropriation that lasted for more than a year and they (Administration, Congress, NASA) stopped canceling things when they reach 75%-80% completion.
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Often when the projects are 75%-80% from completion, they are already 200%-500% over budget. Poster child -- JWST. Poster child #2 -- Constellation, though it didn't get close to 75% completion. How far do you let a rogue one go before you pull the plug as it eats up the funding for the other, possibly better managed, projects?
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So instead of fixing the project, you kill it, waste all that money and have nothing?
If I'm building a house and it's over budget, I do what I can to get it finished. At least then I have a house to live in.
Was the Constellation project really broke?
How much money do you flush down the toilet instead of seeing it through and having a product?
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In span of time between missions, there is usually incredible progress in a few key parameters, detector noise, spacial resolution, and frequency range. While you can argue that a "refueled" IRAS could beat down the noise by observing for years and years, changing out detectors and telescopes is effectively launching a new mission. Also, as our knowledge of astrophysics grows, we design missions to answer the unanswered questions. 10 years of IRAS is not necessarily as interesting as a couple of years of
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Space == no air.
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Space isn't really cold, not at least when you're close to a star like the Sun. After all, the Earth's isn't cold (well, relatively speaking), despite the fact that it sits in space. Sure, there's some internal heating from our molten core and some greenhouse effect from our atmosphere, but the underlying reason that the Earth is warm (again, relatively speaking) is because it's in thermal equilibrium with sunlight at a distance of 150 million kilometres from the Sun.
So if you stick something in space a
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Can any of the rocket surgeons here comment on what it would take to de-orbit such a device?
'Set the controls for the heart of the sun.' -- Pink Floyd
Energy. A lot of it. It is effectively outside the Earth's gravitational well, at the point where the Sun's gravity takes over. You have to decelerate it enough to intersect the atmosphere, at which point drag will bring it done for you. I am not sure of the exact figures, but I think it takes as much energy again to get something from LEO to escape velocity as it takes to get from Earth to LEO. Which is the same as the energy that it takes to get back again. Effectively, I think, You would need another thi
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OK, everyone knows space is big but doesn't this seem a bit cavalier, leaving old space junk in orbit?
It's orbit around the sun so there's lots more 'space' for junk to accumulate than say LEO but still. Seems like we're making the same short-sighted decisions over and over.
Can any of the rocket surgeons here comment on what it would take to de-orbit such a device?
'Set the controls for the heart of the sun.' -- Pink Floyd
Where are you going to deorbit it _to_? Bringing it back to earth is as big a job as sending it out there, deorbiting it into the sun is even harder. Even geostationary satellites don't get deorbitted when they reach the end of their life - they are boosted into a higher orbit to get them out of the way.
leave it at L2 (Score:2)
Re:leave it at L2 (Score:4, Informative)
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The whole point of moving it is that without liquid helium it cannot effectively do any science at all.
I really do not think it is ever likely to be possible to reuse parts of a satellite not designed to be reused.
I think it is a long time before we will want a station at L2. L4 and L5 are more useful for things other than exactly what this satellite was sent to do. The only thing we are likely to send is the James Webb telescope, effectively its successor, in a few years time, and we don't want any chance
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It would cost you more to build something to catch it at L2 and refill the dewar than to just build a new one-- it wasn't designed to have any sort of docking and refill capability. It will eventually fall out of L2 into a heliocentric orbit anyway, so they're probably just going to do it in a controlled way.
Re:leave it at L2 (Score:5, Informative)
It's not being moved because it will clutter up L2. Indeed, such satellites don't sit exactly at the L2 point, but travel around it in orbits which are hundreds of thousands of kilometres wide. There's effectively no danger of any satellites at L2 hitting future ones.
No, the reason is that L2 isn't a stable location: the gravitational potential there is saddle-shaped. Very crudely, along the line of the orbit around the Sun, the satellite sits at the bottom of a curve. Move forward a bit and the Earth's gravity pulls you back. Fall behind a little bit and the same happens. However, perpendicular to the orbital track, in the plane of the ecliptic (the plane containing the planets), it's more like the top of a gravitational hill. Fall a little away from the Earth and bingo, the Earth is no longer strong enough to pull you back and you fall off, outwards.
But if you fall inwards, towards the Earth, the Earth's gravity gets stronger and pulls you even closer. So much so, that you might end up hitting the Earth.
So that's the reason why Herschel and other satellites there (WMAP in the past, Planck today, Gaia and JWST in the future) are pushed off L2 while the satellites still have propellant and are functional (if not scientifically) into heliocentric orbits, to prevent the possibility of the falling onto the Earth in an uncontrolled manner later.
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Thanks, I'd forgotten that objects at L2 don't stay there forever. Which is good, if you don't want rocks eventually hitting your telescopes. Others misunderstood the point of saving it—not to reuse it (except possibly the mirror(s) ), but to reuse the materials in it, as expensive as it is to put mass into orbit. We've got to look forward more than a few dozen years. I also took exception to the notion that L2 isn't much good for anything in the future besides JWST.
By the same logic, instruments we s
Re:Seems Like a Waste of a Good Mirror (Score:4, Informative)
Problem is that Herschel's primary mirror was only polished to the level of surface roughness required for the telescope to be diffraction-limited (i.e. as good as it gets) at far-infrared wavelengths. It wasn't polished to the level necessary to form good images at optical wavelengths.
Just to put some numbers on that, Herschel's shortest operating wavelength is 70 microns (70 millionths of a metre), whereas the red end of the visible is around 0.7 microns, i.e. 100 times shorter.
Polishing the mirror to a factor of 100 lower surface roughness would have been far more expensive and perhaps even not possible using the underlying segmented silicon carbide technology. (SiC can be polished to optical tolerances, but I don't know if Herschel's substrate was made to the appropriate tolerances).