29
$\begingroup$

I was wondering if any planes had mounted telescopes with the intent to observe the stars. I understand that the atmosphere itself can warp and hinder incoming light and even completely obscure views on cloudy days. Would it be possible to have a telescope which could account for the speed of the airplane and remove motion blur? Would it even be worth it, seeing as the size of the lens would also be limited? Could we see anything interesting that a terrestrial scope of the same size would miss?

Hobbes has mentioned SOFIA as a great example of this being done. Does anyone have more information on the benefits of a plane mounted telescope over one on the ground for noninfrared observation?

Improve this question
$\endgroup$
10
  • 5
    $\begingroup$ As far as I remember there is a telescope on a plane. The speed of the plane is small when compared to the rotational speed of Earth at the equator anyway. Compensation of the rotation of Earth is state of the art for large telescopes to allow long exposures. $\endgroup$
    – Uwe
    Sep 12, 2018 at 14:32
  • $\begingroup$ @uwe nice point about the speeds. $\endgroup$
    – Magic Octopus Urn
    Sep 12, 2018 at 14:50
  • 1
    $\begingroup$ @Uwe "The speed of the plane is small when compared to the rotational speed of Earth" - I wouldn't second that. A regular jet plane will routinely travel at about 50% the speed of the earth at the equator. $\endgroup$
    – JimmyB
    Sep 13, 2018 at 12:46
  • 1
    $\begingroup$ Not sure if it counts as a "telescope", but it was used for astronomical observations - during the total eclipse in the UK in 1999, I remember seeing footage from a gyro-stabilised camera with an eclipse-viewing filter that was mounted on a Hercules aircraft to fly above the clouds so that people could see it whatever the weather. $\endgroup$
    – anaximander
    Sep 13, 2018 at 13:47
  • $\begingroup$ There were many spy planes in the 60s that had telescopes pointed towards the ground and they took pretty clear pictures. Is this really any different from pointing the telescope to the sky? Maybe less magnification? $\endgroup$
    – JPhi1618
    Sep 13, 2018 at 15:55

5 Answers 5

Reset to default
54
$\begingroup$

This has been done.

  1. SOFIA is an infrared observatory built into a Boeing 747 SP:

enter image description here

SOFIA takes advantage of the fact that some infrared bands are visible at atltitude, these are attenuated by water in the atmosphere so they're less visible on the ground.

There have been infrared observatories before SOFIA:

The first use of an aircraft for performing infrared observations was in 1965 when Gerard P. Kuiper used the NASA Convair 990 to study Venus. Three years later, Frank Low used the Ames Learjet for observations of Jupiter and nebulae.[20] In 1969, planning began for mounting a 910 mm (36 in) telescope on an airborne platform. The goal was to perform astronomy from the stratosphere, where there was a much lower optical depth from water-vapor-absorbed infrared radiation. This project, named the Kuiper Airborne Observatory, was dedicated on May 21, 1975. The telescope was instrumental in numerous scientific studies, including the discovery of the ring system around the planet Uranus.[21]

The proposal for a larger aircraft-mounted telescope was officially presented in 1984 and called for a Boeing 747 to carry a three-meter telescope. The preliminary system concept was published in 1987 in a Red Book. It was agreed that Germany would contribute 20% of the total cost and provide the telescope.

Other airborne astronomy is more incidental. Around solar eclipses, you'll often see some astronomy flights. Some of these are tourism, others perform science. These are usually passenger aircraft temporarily modified (scopes installed that look through the existing windows). These take advantage of the fact you can lengthen the eclipse by flying along its path, and you can reach eclipses in places otherwise inaccessible.

Improve this answer
$\endgroup$
4
  • 1
    $\begingroup$ Cool! I had no idea about SOFIA, now I get to read about neat astronomy airplanes while I wait to board my next flight. Thanks Hobbes. $\endgroup$
    – Magic Octopus Urn
    Sep 12, 2018 at 14:36
  • 4
    $\begingroup$ There was a predecessor called the Kuiper Airborne Observatory (en.wikipedia.org/wiki/Kuiper_Airborne_Observatory) which used a smaller telescope in a C141 StarLifter. It was one of the first instruments to show that Pluto had a thin atmosphere through observing a stellar occultation. $\endgroup$
    – astrosnapper
    Sep 12, 2018 at 15:17
  • 2
    $\begingroup$ Indeed, the two 747s that used to ferry the space shuttle orbiter are now being used as spare parts for SOFIA. $\endgroup$
    – DrSheldon
    Sep 12, 2018 at 19:22
  • $\begingroup$ "Other airborne astronomy is more incidental" ... not if you count balloons : asd.gsfc.nasa.gov/balloon . They tend to be used for investigations that need a longer duration (and thus can't be done via sounding rocket). In some cases, they're testing designs for instruments that might get flown on a spacecraft. $\endgroup$
    – Joe
    Sep 14, 2018 at 17:51
11
$\begingroup$

As others have pointed out, SOFIA does exactly this. The USAF has done some work with airborne telescopes. I believe the US Navy has as well. I can only assume the Russians did during the years of the Soviet Union and perhaps continue to do so. Not sure about anyone else.

Why the military? For imaging satellites and the like.

For the most part, airborne telescopes aren't worth the cost or trouble. That's not to say they never are, but there's some big hurdles to overcome. You have to provide an ultra-stable platform that compensates for all motion and vibration (I'm guessing they use strong gyroscopes for this), and cut a hole in the roof of the plane for it to stick out of (because using a window will screw with your image quality). Then you have to have a plane that can fly high enough for long enough to make it worthwhile. And THEN, you only get a limited amount of use out of it. Add to the cost of building and maintaining the telescope the cost of modifying and maintaining a jet aircraft, costs which are non-trivial, and then take into account the fact you can't realistically carry all that large a telescope this way... it's just very impractical.

SOFIA does some amazing things, but it is also very limited and specialized for those things. Even then, it doesn't get anywhere near high enough to avoid all of the atmospheric filtering of IR energy.

For non-infrared observing, just dealing with the atmosphere, it's MUCH more cost-effective to construct a large telescope on top of a mountain where the air is much thinner and steadier, and then using active optics to enhance image quality. And then, because these kinds of telescopes are used for photographic observation as opposed to active visual, you can further make use of speckle interferometry to further enhance the detail captured.

So, yes, it's possible, just not effective, to mount telescopes in aircraft.

Improve this answer
$\endgroup$
11
  • $\begingroup$ Thanks for the great answer including why its not too effective of a solution. Whats the highest altitude stationary telescope versus how high SOFIA would fly? $\endgroup$
    – Magic Octopus Urn
    Sep 12, 2018 at 22:34
  • $\begingroup$ @MagicOctopusUrn ask a new question! "Whats the highest altitude stationary telescope versus how high SOFIA would fly?" is a perfect title. $\endgroup$
    – uhoh
    Sep 13, 2018 at 2:22
  • $\begingroup$ According to Wikipedia (en.wikipedia.org/wiki/…), the highestm is Cerro Chajnantor in Chile at 18,500 feet. SOFIA flies at around 45,000 feet (en.wikipedia.org/wiki/…). Still, as high as this is, there's still sufficient atmosphere to block a lot of infra-red energy. It can get a lot MORE than ground observatories, but it's still limited. This is one of the things the James Web Telescope will excel at. $\endgroup$
    – J.M. Haynes
    Sep 13, 2018 at 15:24
  • $\begingroup$ "ultra-stable platform that compensates for all motion and vibration" No. You can use digital image stabilization teqniques. $\endgroup$
    – Sam
    Sep 13, 2018 at 20:16
  • $\begingroup$ "strong gyroscopes for this" No. You use other telescopes to do this. look up "star tracker". "cut a hole in the roof of the plane for it to stick out of (because using a window will screw with your image quality)" No. there is optical quality glass you can use. "cost of modifying and maintaining a jet aircraft" are negligible compared to the costs of building, testing, and launching a telescope that you can't maintain (space based) $\endgroup$
    – Sam
    Sep 13, 2018 at 20:22
9
$\begingroup$

The other answers don't seem to stress one advantage of snakes telescopes on a plane; that of rapid movement and portability!

Here are examples of

  1. IR viewed by a telescope on a plane other than SOFIA, and
  2. observation using SOFIA's plane but not it's large IR telescope!

The questions Why the thermal imaging of Mercury's surface requires a telescope on a jet flying through an eclipse? as well as the linked NASA page Chasing the Total Solar Eclipse from NASA’s WB-57F Jets describes two telescope-equipped jets:

Amir Caspi of the Southwest Research Institute in Boulder, Colorado, and his team will use two of NASA’s WB-57F research jets to chase the darkness across America on Aug. 21. Taking observations from twin telescopes mounted on the noses of the planes, Caspi will ­­­­­capture the clearest images of the Sun’s outer atmosphere — the corona — to date and the first-ever thermal images of Mercury, revealing how temperature varies across the planet’s surface.

While IR is involved, the jets are necessary because of the speed at which the solar eclipse umbra moves relative to the surface of the Earth, or in this case, the speed relative to the atmosphere which due to friction mostly moves with the Earth's rotation.

So SOFIA is not the only telescope on a plane!

Watch the video NASA Jets Chase The Total Solar Eclipse! Here is a screenshot:

Screenshot from NASA Jets Chase The Total Solar Eclipse

The question Timing shadows from the Kuiper belt! Any news? Did it work? describes the use of the SOFIA observatory, but not it's primary infrared telescope to observe the occultation of a star:

update 24-Jun-2017: SOFIA Arrives in New Zealand to Observe Southern Skies There are plans to fly SOFIA through another predicted occultation path on July 17. SOFIA is a huge (2.5 meter dia.) infrared telescope (1 ~ 250 um) with various cryogenic focal plane arrays that is flown above most of the water in Earth's atmosphere (YouTube). It sound like they will just use the visible light guide camera (behind the Nasmyth mirror?), rather than the infrared capability, but the portability is certainly handy. This mission might be "An Airplane Hunting for Shadows from the Kuiper Belt".

So it seems that in this case they are using SOFIA for portability, but not necessarily it's infrared capability, and not even for the large telescope!

See the NASA page SOFIA Arrives in New Zealand to Observe Southern Skies

enter image description here

above: From AsteroidOccultations.com's News & Announcements for 2014 MU69

From this answer (this particular image sequence is from a ground telescope):

Update July 20

At least 5 telescopes have captured the occultation during the July 17 observation campaign (animated GIF):
blink

Improve this answer
$\endgroup$
8
$\begingroup$

SOFIA (as described in @Hobbes answer) is currently the only astronomical telescope mounted on a plane. It does overcome some problems with the Earth's atmosphere and circumvents the huge costs and extreme environmental conditions of a space telescope, but it comes with a whole host of other difficulties!

The plane can only take off and land in certain places, and it's better if it lands where it came from so the observations (which only come from one side of the plane) are looking at different places on the way out and the return. Coupled with the fact that the plane has a limited amount of fuel means you don't get very long integration times (how long the telescope is looking at one patch of sky) so you can't see a lot of detail or very faint objects.

The plane shakes, moves and changes temperature, and all of that affects the telescope and reduces the quality of your observations.

Also, while this might be cheaper than a space mission, and give more opportunity for upgrades and maintenance, it's not super cheap.

Basically, SOFIA is cool, but probably no one else is going to build one and I'm not sure how much longer SOFIA will be funded. It is a good alternative in some ways but not good enough to make it viable.

Improve this answer
$\endgroup$
1
  • $\begingroup$ "...is currently the only astronomical telescope mounted on a plane" is not exactly correct. $\endgroup$
    – uhoh
    Sep 13, 2018 at 2:52
6
$\begingroup$

In addition to the above examples, a telescope was once mounted in a Concorde for viewing a total eclipse. The speed of the aircraft allowed it to stay in the zone of totality for an extended period of time. The airplane's cruising altitude of around 60,000 ft. (half again as high as subsonic commercial jets) also reduced the absorption of light by the atmosphere.

https://aviation.stackexchange.com/questions/22083/how-were-astronomical-observations-performed-from-concorde

Improve this answer
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .