World's Largest Airborne Telescope Delivered

Thurog writes "SOFIA, the Stratospheric Observatory for Infrared Astronomy, has received the telescope built in Germany by the German Space Agency, DLR. SOFIA consists of a Boeing 747SP aircraft modified by L-3 Communications Integrated Systems to accommodate a 2.5 meter reflecting telescope. When on a mission, it will soar through the higher levels of the atmosphere, thereby overcoming the fact that atmospherical humidity filters most of incoming infrared radiation. It's not the first airborne telescope, but so far the most powerful."

Why not use a balloon?

[HorsePunchKid]

I was surprised to see that the platform for the telescope is a 747. I was under the impression that most stratospheric observation was done with balloons [nsf.gov]. This is what BOOMERANG [ucsb.edu] used to map the cosmic microwave background, which (along with COBE) was pretty groundbreaking. So is there something about infrared astronomy that makes a jet a more suitable platform? I would assume that a jet's flight would cause a lot of small-scale vibration in the telescope that would seriously degrade the quality. Is there some way around that? Adaptive optics or something?

Also, slightly OT, but a new ground-based gamma ray telescope has just been put into action [nasa.gov]. Interesting, because it detects the rays indirectly by observing the Cherenkov radiation.

This is a BIG telescope

[roberto0]

My best guess is that Balloons just won't get high enough.
Or maybe they can pilot a 747 to go exactly where they want it to go without getting blown off course as easily as a balloon.
Or maybe the cost of jet fuel is much less than the cost of filling a balloon with helium

That last one is supposed to be a joke.

Maybe the Lens is just too big for any existing Balloon?

Re:This is a BIG telescope

[dunedan]

I'm pretty sure balloons can get at least as high as airplanes

I think the world record or at least a world record was held by a nasa balloon at over 100,000ft.

Last I checked 747's don't get that high

Re:This is a BIG telescope

[littlerubberfeet]

try twice that actually. Steve Fosset of presious baloon fame is trying to make it to 100,000 in a glider. Gliders can handle small pieces of equipment. Anyone know of scientific applications for that platform?

Scientific Applications for Gliders

[Mark of THE CITY]

NASA's ER-1 (U-2 variant) is used for in-situ high altitude atmospheric analysis. A 100,000-foot glider could do similar work, trading off mission duration for higher altitude.

Re:Scientific Applications for Gliders

[littlerubberfeet]

hmmm......but I would ponder the fact that Ray Linsky and other glider pilots have done 8 hour flights, and given that Wave soaring is not daytime/nighttime tempature change depandant, mission durations of a day could be possible with 2 pilots and an O2 tank.

Atmospheric research would be neat in a glider

Re:This is a BIG telescope

[lommer]

What would be the point of using a glider?

Specifically, what advantages does it offer over traditional airplanes? Especially considering that gliding off of mountain waves is actually quite risky, would you trust your brand new telescope to that rather than a proven airplane?

Gliders are to Airplanes as sailboats are to powered freighters. Ask anyone who sails and they will tell you that there is a certain "aura" around sailing that is not achievable in powered craft, but when you get down to economics and practicality, there really is no contest.

Re:This is a BIG telescope

[littlerubberfeet]

Interesting. Not mountain waves. That is ridge lift. WAVE soaring is using high altitude (20000 feet) lift and sink that forms from ocean phenomina. And gliders are proven airplanes. A Shweitzer 2-33 is a common glider that has worked for 45 years (I learned in one). And gliding is far less risky then driving every day. Ridge, wave, and thermal soaring are all quite safe.

As for the glider advantage:
1) They do not vibrate
2)They do not use fuel, so 14+ hour flights are possible
3) Maintenence is lower (no engine)
4) They are cool.

Re:Why not use a balloon?

[foolish]

Err, It's really heavy that's why. Suspesion, primary mirror and secondary mirror assemblies all weigh about 31,500 lbs. Which means you need about 492187.5 ft^3 of helium.

And to date, there are not highly sterrable, controllable ballons in operation that can oeprate at those heights (41,000 ft). Those companies pitching the 'new' blimp concepts just aren't there yet.

--foolishone

Re:Why not use a balloon?

[Jackazz]

Also what about the fact that infrared rays probably won't penetrate the baloon and make it to the mirrors?

I bet it is extremely difficult to build the heavy platform on top of a balloon so that the balloon does not obstruct the view. A little wind to unbalance the load, and the thing does a catastrophic flip, dumping your telescope on the ground.

I am surprised they don't use a satellite though, I would think it is damn expensive to run a 747 as opposed to just the one time launch fee and then relatively low maintenance cost for a satellite.

just my two cents,
J

Re:Why not use a balloon?

[HorsePunchKid]

I don't think that obstruction of view would be too big of a factor. The high-alititude balloons that I've seen photos of seem to generally be very large (need room for gas to expand into), but also extremely tall. The only constraint would be that you couldn't point your telescope within, say, 15 degrees or so of straight overhead. But foolish's point about it being very heavy is probably the main factor. BOOMERANG was relatively small. Check out this picture [ucsb.edu] of the gondola with the telescope inside. The whole thing can't be more than 6m or 7m tall, and the main mirror only weighed about 12kg [lbl.gov].

Re:Why not use a balloon?

[Thurog]

The main advantage of an aircraft mounted telescope is that, well, it comes back to earth in one piece. Repairs and upgrades can be made between missions, something which is REALLY expensive with a satellite telescope. See Hubble.

Someone care to give numbers comparing the actual cost of plane vs. satellite telescopes? I'm lost there.

Re:Why not use a balloon?

[lommer]

Is that "492187.5 ft^3" at sea level or at 41,000 ft?

Just curious as to whether you factored that into your calcualtions.