Here is the list of every space telescope launched by different space agencies - List of space telescopes. Most of the listed telescopes are placed in Lower Earth Orbit (about 95% of them). It's probably not an ideal location to place a telescope because of many obvious reasons like our earth radiates a huge amount of infrared radiation; as said by professor Michael Merrifield -"Its like doing astronomy with all the lights switched on" .

Now here is the list of all objects placed at Lagrange points - List of objects at Lagrangian points. There are hardly 10 objects at these points. The lifespan of these objects are quite low, but surely there are many upcoming missions in these orbits, the most famous one being the James Webb Space Telescope:

enter image description here.

The JWST will be placed on L2 Lagrange point. So clearly this will be the only orbit of choice for many future upcoming telescope missions. So finally concluding I have some questions-

Why are there so few Telescopes at the Lagrange Points despite having so many advantages? Is it a budget related issue, is it not feasible enough in a grand scale? There are/were some observatories at the Lagrange Points and we hardly heard about them - unlike the Hubble space telescope which is regarded as the most successful and most important man made creation by many. Will all future space telescopes be based at the Lagrange Points?

  • $\begingroup$ Alternately, is a lunar orbit feasible ? I mean it would of course be expensive to get it there, but would it last longer and perform better? $\endgroup$ Commented Jun 17, 2018 at 0:44
  • $\begingroup$ @KevinFegan its the opposite because there will be orbital decay,communication problems and the gravity varies that's why there are very less satellites on the lunar orbit $\endgroup$
    – Paran
    Commented Jun 17, 2018 at 14:09
  • $\begingroup$ Total layman here, but I imagine the moon and other planets might still mess up the equilibria. $\endgroup$
    – user541686
    Commented Jun 19, 2018 at 1:38
  • $\begingroup$ qwerty - My thought was that the stability of a lunar orbit wouldn't be that much harder/easier to maintain than a low-earth-orbit, and probably easier than maintaining an orbit at a Lagrange Point. And, being in orbit where there is no atmosphere has to be a benefit. @Mehrdad - "might still mess up the equilibria" what do you mean by equilibria? $\endgroup$ Commented Jun 20, 2018 at 6:15
  • $\begingroup$ @KevinFegan look up "Lunar Mascons" and it'll answer a lot more than we can in comments. $\endgroup$ Commented Aug 27, 2019 at 20:59

5 Answers 5


The reason there are so few spacecraft placed at Lagrange points is that it's much harder to get there. Launching sizeable payloads to Earth escape velocities requires a very large vehicle and is simply impractical/impossible for many missions.

For example, at the time of its launch, there was no launch vehicle in operation capable of lifting Hubble's 11000 kg mass even to Geostationary Transfer Orbit, let alone escape velocity.

Furthermore, halo orbits around the L1, L2 and points require ongoing stationkeeping since they are only pseudo-stable. For JWST this is expected to be some 2–4 m/s per year, giving it an estimated operational life of ~10 years.

Comparisons to other telescopes

As to why we hear about Hubble more than any Langrange-orbit telescope; we hear more about Hubble than virtually any other spacecraft. This is because Hubble operates at near-ultraviolet and visible wavelengths and therefore it produces a lot of PR-worthy material. Its well publicised teething problems probably also help Hubble's public image. As pointed out in the comments, had Hubble not been in LEO, the rescue mission to fix its optics wouldn't have been possible.

Compare this to other observatories:

The Chandra X-Ray Observatory (in a highly elliptical Earth orbit), another of NASA's Great Observatories which has an outstanding and lengthy history of discoveries that have provided invaluable data to the scientific community. Its only flaw? It operated (obviously) in X-ray wavelengths, making its observations often less photogenic.

The Herschel Space Observatory which operated at the Earth-Sun L2 for 4 years also provided vast amounts of invaluable data - producing 152 scientific articles in its first year first few months. However in 2013 its supply of helium coolant ran out and it was decommissioned.

The only telescope to challenge Hubble in fame in recent years may be Kepler, which is in a heliocentric orbit (but not at a Lagrange point). Its launch mass of ~1000 kg is less than a tenth of Hubble's which would have limited its capabilities.

The future

Will future observatories use Lagrange points? Possibly, but the launch constraints still exist today. JWST is definitely an exception rather than the norm. It is just within the capabilities of its Ariane 5 launcher and it has a budget beyond the dreams of most observatory programs.

I have included some additional information from the very helpful comments

  • 18
    $\begingroup$ "much harder to get there" and also harder to stay there even after you get there. $\endgroup$
    – uhoh
    Commented Jun 16, 2018 at 22:07
  • 5
    $\begingroup$ As @uhoh says, it's indeed hard to stay there. For an L1 orbit, you typically need a few meters per second of delta V every other day. Compare that to the operation of a GEO spacecraft which can easily live with a station keeping burn once every two weeks. $\endgroup$
    – ChrisR
    Commented Jun 16, 2018 at 22:16
  • 5
    $\begingroup$ @uhoh, absolutely - JWST is expected to last ~10 years with its stationkeeping budget around L2, compared to (currently) 28 years for Hubble in LEO. $\endgroup$
    – Jack
    Commented Jun 16, 2018 at 22:19
  • 2
    $\begingroup$ Compton did good work and got even less pr (it was a gamma ray observatory). Then NASA dumped it into the atmosphere while it was still working because it got one failure way from loss of control. $\endgroup$ Commented Jun 17, 2018 at 1:18
  • 7
    $\begingroup$ And... if we did put Hubble at a Lagrange point we would have been screwed, because the telescope optics were bad and it required a manned mission to go up there to retrofit corrective elements. Sending a manned mission to LEO to repair Hubble was very expensive, but it was at least achievable. Sending a manned mission to L2 to repair a telescope, however, would be an unprecedented class of mission with a massive expense. $\endgroup$
    – J...
    Commented Jun 17, 2018 at 3:08

To add to the existing good answer about the practicalities of launching to Lagrange points, it's also worth considering why the missions which have gone that far are using the unstable Lagrange points, when L4 and L5 are stable.

It comes down to what happens if the satellite loses control. In unstable Lagrange points, if the satellite gets fried somehow then it'll drop out of the Lagrange point and eventually find its way to Earth or the Sun and burn up. And if it gets close to losing control, NASA (or whoever) can command that deliberately. Heading towards the Sun would be the choice, because we already have enough random crud around us.

If it's in a stable Lagrange point though, you'd need to give it escape velocity out of there. That requires the satellite to have a large amount of fuel kept just for this and to still be in full control. If not, you just end up with a random piece of junk stuck at that Lagrange point which you can never shift. In general, this is a bad idea.

If you're putting up a space station, of course, a stable Lagrange point is exactly what you want. In that case it's perfectly acceptable to have the space station (and nothing else) occupying that Lagrange point. But for a random satellite which may be joined later by more random satellites flying relatively close, ironically a stable orbit is not a good thing.

  • 5
    $\begingroup$ “find its way to Earth or the Sun” – the latter is unlikely. It's really tricky to find your way into the Sun, even deliberately: it requires getting rid of almost exactly all of your angular momentum. More likely is to get ejected from the inner solar system by a close pass at Venus and/or Earth, and thus end up in a comet-like orbit or captured by Jupiter (or else ejected further by a close pass to it). $\endgroup$ Commented Jun 19, 2018 at 12:58
  • 1
    $\begingroup$ As to your point about space junk: it seems not implausible that this is a reason why nobody has put anything into the L4 or L5 points yet, but it could use some references. $\endgroup$ Commented Jun 19, 2018 at 13:01

The other thing is you need more power to transmit large amounts from the Lagrangian points so that requires bigger solar panels hence more mass.

Another reason Hubble is in LOO is that the technology was essentially that of a spy satellite but pointing the other way! As they found out soon after Hubble was launched the satellite vibrated when the solar panels were heated and cooled – the US intelligence community were aware of this problem with the particular type of solar panels but did not inform NASA.


In addition to the other reasons: a Lagrange point has advantages for some telescope types, but less so for others.

Earth is bright in visible light, IR and some radio wavelengths, less so in gamma and X-ray wavelengths.


Each telescope has a mission or several. The selection process balances the expected scientific benefits with the cost. Although this balancing is far from perfect, the fact that it takes more delta v to get to the Lagrange points is against putting telescopes there. This can be presented as either a higher cost to get there or less mass that can get there with a given rocket. Many of the space based telescopes just want to be above the atmosphere to avoid the absorption of the wavelength band they operate in. The main reason to go to the Lagrange points is to avoid heating from the infrared emitted by the earth. That is important for infrared telescopes, where cooling is critical to avoid noise. For telescopes in shorter wavelength bands it is hard to justify the added cost of the Lagrange points. It is true that at the Lagrange points the earth represents a much smaller solid angle so you can see more of the sky, but from low earth orbit you can see any given point of the sky some of the time.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.