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For ESA's Herschel Mission, the End Is Near

Soulskill posted about a year ago | from the winding-down-after-good-service dept.

Space 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."

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40 comments

mmmmmm candy (0)

rossdee (243626) | about a year ago | (#43089729)

"dusty starburst galaxies"

Did anyone else misread the headline as ESA Hershey Mission

Re:mmmmmm candy (-1)

Anonymous Coward | about a year ago | (#43091505)

nope were not fatties like you !

Re:mmmmmm candy (1)

gadget junkie (618542) | about a year ago | (#43092693)

"dusty starburst galaxies"

Did anyone else misread the headline as ESA Hershey Mission

No, I read: extra Herschey mission

so.. (1)

illestov (945762) | about a year ago | (#43089991)

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"

Re:so.. (5, Interesting)

game kid (805301) | about a year ago | (#43090023)

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.

Re:so.. (1)

BTWR (540147) | about a year ago | (#43090105)

Exactly. New discoveries from Voyager were made well into the 80s and 90s by looking at the reams of data that had been sent back earlier.

Re:so.. (2)

semi-extrinsic (1997002) | about a year ago | (#43090139)

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.. (0)

Anonymous Coward | about a year ago | (#43090373)

Well, for CFD, you're talking about a computer generating data, not so much nature. So that's not so impressive.

Also 1.8 TB isn't so much, as it still fits on one hard drive. Nice sized grid you have there, but certainly not the biggest these days:

http://torroja.dmt.upm.es/events/madrid03/presentations/kaneda.pdf

You know your space program has a long way to go (3, Insightful)

hackertourist (2202674) | about a year ago | (#43090725)

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?

Re:You know your space program has a long way to g (0)

Anonymous Coward | about a year ago | (#43091107)

You know you're primitive when you find that it's (much) cheaper to replace said spacecraft than to resupply them. When we find that it's economical to send out a tanker full of cryogens, then we will truly be an interplanetary species. Not holding my breath. (Bear in mind that Herschel is out at L2, not in Earth orbit.)

Re:You know your space program has a long way to g (1)

Anonymous Coward | about a year ago | (#43091239)

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?

Re:You know your space program has a long way to g (1)

morgauxo (974071) | about a year ago | (#43093147)

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.

Re:You know your space program has a long way to g (0)

Anonymous Coward | about a year ago | (#43094907)

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.

Emphasis mine. I doubt it will ever be economically sound - no matter how cheap spaceflight is - to recycle satellites, unless we start making them out of gold. Refueling only makes sense when the total mission cost is less than that of launching a new one. I appreciate your point about the dropping cost of spaceflight but there's a very long way to go; the cost of the actual satellite isn't as large a fraction of the mission cost as one might think.

Re:You know your space program has a long way to g (2)

DerekLyons (302214) | about a year ago | (#43091421)

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.

Re:You know your space program has a long way to g (2)

sycodon (149926) | about a year ago | (#43092619)

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.

Re:You know your space program has a long way to g (1)

thrich81 (1357561) | about a year ago | (#43096083)

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?

Re:You know your space program has a long way to g (1)

sycodon (149926) | about a year ago | (#43096457)

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?

Re:You know your space program has a long way to g (1)

drunkenkatori (85423) | about a year ago | (#43095699)

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.

Why is it so difficult to cool (0)

Anonymous Coward | about a year ago | (#43091123)

Sorry, maybe a stupid question but why is it difficult to cool something in space which has a temperature of near absolut zero? couldn't you just run something through a pipe in the shade of yourself?

Re:Why is it so difficult to cool (0)

Anonymous Coward | about a year ago | (#43091275)

Basically, radiative cooling in space takes either a. a very, very hot thing that needs cooling or a very, very large radiator. Radiative heat loss is miniscule at low temperatures, so sometimes it makes more sense to just dump the warm refrigerant overboard, so to speak.

Re:Why is it so difficult to cool (1)

Robert Zenz (1680268) | about a year ago | (#43091345)

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).

Re:Why is it so difficult to cool (1)

NixieBunny (859050) | about a year ago | (#43092727)

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.

Re:Why is it so difficult to cool (1)

DriveDog (822962) | about a year ago | (#43093421)

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.

Re:Why is it so difficult to cool (1)

Trapezium Artist (919330) | about a year ago | (#43094963)

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.

The beginning of the end. (0)

Anonymous Coward | about a year ago | (#43091321)

They already predicted that we will run out of helium, Herschel is just the beginning.

No balloon for you!

but but but (0)

Anonymous Coward | about a year ago | (#43091899)

space is cold?

Space Junk (0)

Anonymous Coward | about a year ago | (#43092665)

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

Re:Space Junk (1)

AlecC (512609) | about a year ago | (#43093191)

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.

Re:Space Junk (1)

FireFury03 (653718) | about a year ago | (#43095019)

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 (1)

DriveDog (822962) | about a year ago | (#43092827)

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?

Re:leave it at L2 (3, Informative)

NixieBunny (859050) | about a year ago | (#43093169)

Hopefully, the scientific instruments will have improved substantially in 30 years, so its guts will be obsolete and therefore useless. As a worker in terrestrial radio astronomy, I can assure you that we don't use any receivers more than 15 years old, and those are about 5x less sensitive than current instruments. Any system designed for space will use the latest proven technology, given the cost to get it up there.

What about the mirror, which is relatively large? (0)

Anonymous Coward | about a year ago | (#43099807)

What about the mirror, which is relatively large?

Re:leave it at L2 (1)

AlecC (512609) | about a year ago | (#43093259)

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 of the two bumping.

Re:leave it at L2 (1)

bitingduck (810730) | about a year ago | (#43093971)

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 (4, Informative)

Trapezium Artist (919330) | about a year ago | (#43094769)

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.

Re:leave it at L2 (1)

DriveDog (822962) | about a year ago | (#43098447)

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 send to L4 or L5 are probably going to be there forever, not having the means to break free of the wells. But wells are probably highly populated with junk trapped over the last couple of billion years. So that might or might not be good for an L5 space colony.

Seems Like a Waste of a Good Mirror (0)

Anonymous Coward | about a year ago | (#43095781)

I have no technical knowledge of the Herschel telescope, but it seems a mirror like that should be useful, for example, at visible wavelengths without the cooling the helium provided. I guess it would require different detectors or some other technical modification that can't be performed remotely, so... Oh well.

Re:Seems Like a Waste of a Good Mirror (3, Informative)

Trapezium Artist (919330) | about a year ago | (#43097555)

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).

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