Slashdot Mirror
For ESA's Herschel Mission, the End Is Near
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."
is it going to run out of coolant in march and be "rendered blind" or is it going to produce new results for years to come"
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?
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?
As far as I know, Space is not directly cold, it's a vacuum. So there is nothing that pipe could give the heat off to except via heat radiation...you might don't want to wait that long. To be perfectly honest, I'm very sure that was considered and was abandoned because of problems we (mortals) don't know about (and I'm to lazy to search for).
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.
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.
When Fascism comes to America, it will call itself Anti-Fascism, and tell you to give up your guns.
"dusty starburst galaxies"
Did anyone else misread the headline as ESA Hershey Mission
No, I read: extra Herschey mission
"If a boss demands loyalty, give him integrity. But if he demands integrity, give him loyalty." (John Boyd, 1927-1997)
Cooling systems have radiators. I work on very similar radio telescope receivers on Earth. We have a big compressor, like the one used in a home air conditioning system, to cool the gaseous helium to its condensation point of 4 Kelvin. The compressor has a large fan blowing air through it to remove heat from the helium.
Space == no air.
The determined Real Programmer can write Fortran programs in any language.
I understand if it can produce good science in a new orbit, but if it's being moved primarily to avoid cluttering up L2, I think that might be a mistake. Presumably it isn't moving very fast relative to L2, so another craft in L2 orbit should be able to capture it fairly easily. Sooner or later we'll have some kind of station at L2, and Herschel's parts will likely be useful somehow. Will it have sufficient power and good thrusters in 30 years if it's mothballed in place now? Why not wait and move it later if it's determined to be in the way?
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.
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 third stage rocket of the size that lifted it from LEO to L2 to get it back again - and you would have had to lift that booster to L2.
And to drop it into the sun would be even more expensive, because you have to loose all the velocity of the earth's orbit around the sun, which a quick calculation suggests is about 70,000 mph (against 25,000 mph for earth's escape velocity).
De-orbiting is really only possible from LEO. Even satellites in geosynchronous orbit are booted to graveyard orbits, not de-orbited.
Consciousness is an illusion caused by an excess of self consciousness.
I suspect that since it needs to be colder than what it's looking at, it needs to be below the temperature of interplanetary space, which I think is a few degrees K ("in the shade"). Liquid He dilution refrigeration (if Herschel uses that) can attain temperatures "in the milliKelvins", so that we can observe far IR emissions from dust in a distant nebula.
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 at L2, it's essentially at the same distance from the Sun as the Earth and thus, roughly speaking, it'll end up at the same temperature as the Earth.
The big difference, however, is that there's no atmosphere to transport heat by conduction or convection, so the side of the object that's facing the Sun will get hot and the other side, in the shade, will be colder. Of course, conduction by the object itself can transport heat from the hot side to the cold side, evening things out a bit. But if you can thermally isolate one side from the other, the side facing away from the Sun can get really, really cold, as it radiates any excess heat into the 3K "heat sink" of the Universe.
Which is exactly what spacecraft at L2 do. They have a hot side, facing the Sun and Earth, generating power to run the satellite and to communicate data back to Earth. Then they have a cold side, separated from the hot side by a sunshield and facing out into space, which can then get very, very cold, provided the two sides are thermally decoupled. You stick your telescope and instruments on that side and you can get nice and chilly.
(That said, you can only reach about 30–50K or so, which is fine for near-infrared observatories and their instruments, but the instruments used by far-infrared and sub-millimetre observatories need to be much colder, down around absolute zero, in order that their detectors don't blind themselves. That's why Herschel has liquid helium and why it will go blind when it runs out. Being at L2 is only half the story for Herschel.)
The beauty of L2 is that you keep the Sun, the Earth, and the Moon shining permanently on one side of the spacecraft, but never on the other side, if designed well. Spacecraft like Hubble in low-Earth orbit have to contend with half the sky being permanently filled with a big hot object called the Earth, and as you go around in orbit, the combined Earth and Sun illumination is constantly changing: not a good place to get a spacecraft really cold.
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.
http://blog.nexusuk.org
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 a significantly more advanced mission.
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?
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?
When Fascism comes to America, it will call itself Anti-Fascism, and tell you to give up your guns.
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).