Visible light imaging of the heavens is limited on Earth primarily due to the atmosphere. I know the ISS is moving at 17000mph, but given the delays to the James Webb telescope, is there any merit in attaching a space-rugged visible light telescope to the outside of the ISS? Could it ever approach the visible light performance of Hubble?

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    $\begingroup$ Why attach it? That just adds vibration from the space station and pollution from gases and particles released by the station. If you could lift a telescope into orbit you may as well put it in its own orbit. $\endgroup$ Jul 4, 2019 at 14:09
  • $\begingroup$ It needs to be attached because it needs to be powered and controlled, and to send its image results somewhere. A self-sufficient orbiting telescope is basically Hubble mkII and would never get off the ground, literally and metaphorically! $\endgroup$
    – TopCat
    Jul 4, 2019 at 14:20
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    $\begingroup$ Power is a valid concern, but radio transmission for control and data is easy and cheap. $\endgroup$ Jul 4, 2019 at 16:17
  • $\begingroup$ Related: Is there a telescope on board the ISS? (Yes, inside.) $\endgroup$ Jul 5, 2019 at 10:43
  • $\begingroup$ The problem is that to be useful, the telescope needs a large mirror (or multiple mirrors). So you have to build it - and you want to build it to the highest precision possible - and launch it. Power and data transmission are solved problems. Attaching it to the ISS creates all sorts of pointing, light pollution, and debris problems. $\endgroup$
    – jamesqf
    Jul 5, 2019 at 16:48

3 Answers 3


A self-sufficient orbiting telescope is basically Hubble mkII and would never get off the ground, literally and metaphorically

Hubble was expensive because it was state-of-the-art, requiring development of many new systems. The systems it needed to function as a standalone satellite (compared to being attached to the ISS) were cheap by comparison (reaction control, power, communications) because they mostly didn't require new development.

So a Hubble successor attached to the ISS would not be much cheaper than a free-flying one.

Any telescope attached to the ISS has to deal with:

  • high vibration levels which degrade performance
  • outgassing which degrades performance
  • severe pointing constraints because it's surrounded by a large structure
  • bandwidth constraints because it has to share a transmitter with ISS operations
  • end of mission in 5 years when the station reaches the end of its life.

The advantages of attaching to the ISS:

  • easier servicing,
  • you get the option to store lots of data on the ISS and bring it down on a capsule. Downside is a latency of several months.

IMO you'd be better off building a standalone space telescope.

  • $\begingroup$ While the idea of having the lifespan tied to that of ISS remains the same, some quick research shows the projected lifespan of the station to be more than 5 years. $\endgroup$
    – Jasper
    Jul 5, 2019 at 11:08
  • $\begingroup$ I doubt that ISS would be simply let fall in 5 years. The political price would be many times higher that price of destruction of the Mir, and there would be no promised "it will be yet better" replacement. $\endgroup$
    – peterh
    Jul 5, 2019 at 22:18

Attach a visible light telescope to the outside of the ISS

This is a reasonable idea and it has been thought of before, but usually for other-than-visible light. Other answers do a good job of explaining why the disadvantages substantially outweigh the advantage. The cost to put something on the ISS large enough to outperform the top few dozen telescopes on Earth or approach the performance of the Hubble would be... Astronomical!

However, there is a moveable telescope mounted on the outside of the ISS right now but read further to see why.

Had the Apollo missions gone on longer there might have been an Apollo space telescope. See answers to How would the Apollo telescope have worked in the Apollo command module? Where would it be located and how would it be operated? and the YouTube video Missions we Lost When Apollo was Cancelled

The Skylab space station did have a space telescope!

See for example How did Skylab's electrographic camera work?. This telescope took advantage of being above Earth's atmosphere in order to photograph using ultraviolet light, something that you simply can not do on the Earth.

The Apollo astronauts also had an ultraviolet telescope on the Moon (see answers to How was the Moon's first telescope used? (Apollo 16))

The Chang'e-3 lander also has an ultraviolet telescope! (see also GBTimes' China’s telescope on the Moon is still working, and could do for 30 years)

The ISS also has a space telescope!

Finally, NASA has indeed attached a robotic, point-able telescope to the outside of the ISS. It is called NICER or Neutron Star Interior Composition Explorer and it is an X-ray telescope, also something that you can't see from he ground and need to put your telescope in space.

See this answer and links therein.

NICER X-ray telescope on the ISS GIF

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    $\begingroup$ The NICER looks remarkably like some sort of rocket launcher. $\endgroup$
    – Vikki
    Jul 5, 2019 at 3:24
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    $\begingroup$ @Sean ya I know just what you mean, perhaps to defend against alien invaders? ;-) $\endgroup$
    – uhoh
    Jul 5, 2019 at 6:38

I think there is nothing wrong with your idea in principle, there is already a modified Boeing jumbo jet specifically for the purpose of carrying a large telescope above the densest layers of the atmosphere in order to minimise atmospheric interference and absorption by atmospheric water vapor.

However, the telescope and the personnel who man it use up a considerable amount of space, though on the aircraft there are no competing activities going on beyond those necessary to fly the aircraft. On the ISS the main problems would be in finding the space to accommodate the telescope and its crew and making the necessary modifications to the fabric of the space station.

I don't think such a telescope could compete with Hubble, but that doesn't mean it couldn't do anything useful.

One advantage would be that if anything should go wrong,it could be somewhat easier to repair than it is with Hubble. Now that the Space Shuttle is no longer available, a crewed mission to Hubble would be extremely challenging and a robotic mission would require technology not yet available.

  • $\begingroup$ +1 and I am not sure why others have down voted. $\endgroup$
    – uhoh
    Jul 5, 2019 at 23:10

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