<p><strong>More than 20</strong> if the Wikipedia's <a href="https://en.wikipedia.org/wiki/List_of_space_telescopes" rel="nofollow noreferrer">List of Space Telescopes</a> is accurate. I extracted the active ones, and removed duplicates (to the best of my knowledge):</p>
<ol>
<li><a href="https://en.wikipedia.org/wiki/Swift_Gamma_Ray_Burst_Explorer" rel="nofollow noreferrer">Swift Gamma Ray Burst Explorer</a></li>
<li><a href="https://en.wikipedia.org/wiki/AGILE_(spacecraft)" rel="nofollow noreferrer">AGILE</a></li>
<li><a href="https://en.wikipedia.org/wiki/Fermi_Gamma-ray_Space_Telescope" rel="nofollow noreferrer">FGST</a></li>
<li><a href="https://en.wikipedia.org/wiki/IKAROS" rel="nofollow noreferrer">IKAROS</a></li>
<li><a href="https://en.wikipedia.org/wiki/Nuclear_Spectroscopic_Telescope_Array" rel="nofollow noreferrer">NuSTAR</a></li>
<li><a href="https://en.wikipedia.org/wiki/Astrosat" rel="nofollow noreferrer">Astrosat</a></li>
<li><a href="https://en.wikipedia.org/wiki/HXMT" rel="nofollow noreferrer">Insight (Chinese: 慧眼)</a></li>
<li><a href="https://en.wikipedia.org/wiki/Spektr-RG" rel="nofollow noreferrer">Спектр-РГ</a> (Spektr-RG)</li>
<li>The famous Hubble Space Telescope, <a href="https://en.wikipedia.org/wiki/Hubble_Space_Telescope" rel="nofollow noreferrer">HST</a>, see <a href="/questions/tagged/hst" class="post-tag" title="show questions tagged &#39;hst&#39;" rel="tag">hst</a></li>
<li><a href="https://en.wikipedia.org/wiki/Korea_Advanced_Institute_of_Science_and_Technology_Satellite_4" rel="nofollow noreferrer">STSat-1</a></li>
<li><a href="https://en.wikipedia.org/wiki/Interface_Region_Imaging_Spectrograph" rel="nofollow noreferrer">IRIS</a></li>
<li><a href="https://en.wikipedia.org/wiki/Hisaki_(satellite)" rel="nofollow noreferrer">Hisaki</a></li>
<li><a href="https://en.wikipedia.org/wiki/Chang%27e_3#Lunar-based_ultraviolet_telescope_(LUT)" rel="nofollow noreferrer">Lunar-based ultraviolet telescope</a></li>
<li><a href="https://en.wikipedia.org/wiki/BRITE" rel="nofollow noreferrer">BRITE</a></li>
<li><a href="https://en.wikipedia.org/wiki/Near_Earth_Object_Surveillance_Satellite" rel="nofollow noreferrer">NEOSSat</a></li>
<li><a href="https://en.wikipedia.org/wiki/Transiting_Exoplanet_Survey_Satellite" rel="nofollow noreferrer">TESS</a>, see <a href="/questions/tagged/tess" class="post-tag" title="show questions tagged &#39;tess&#39;" rel="tag">tess</a></li>
<li><a href="https://en.wikipedia.org/wiki/CHEOPS" rel="nofollow noreferrer">CHEOPS</a>, see <a href="/questions/tagged/cheops" class="post-tag" title="show questions tagged &#39;cheops&#39;" rel="tag">cheops</a></li>
<li><a href="https://en.wikipedia.org/wiki/Odin_(satellite)" rel="nofollow noreferrer">Odin</a></li>
<li><a href="https://en.wikipedia.org/wiki/IBEX" rel="nofollow noreferrer">IBEX</a></li>
<li><a href="https://en.wikipedia.org/wiki/Alpha_Magnetic_Spectrometer" rel="nofollow noreferrer">AMS-02</a></li>
<li><a href="https://en.wikipedia.org/wiki/Dark_Matter_Particle_Explorer" rel="nofollow noreferrer">DMPE</a></li>
<li><a href="https://en.wikipedia.org/wiki/Chandra_X-ray_Observatory" rel="nofollow noreferrer">Chandra</a>, see <a href="/questions/tagged/chandra" class="post-tag" title="show questions tagged &#39;chandra&#39;" rel="tag">chandra</a></li>
<li><a href="https://en.wikipedia.org/wiki/XMM-Newton" rel="nofollow noreferrer">XMM Newton</a>, see <a href="/questions/tagged/xmm-newton" class="post-tag" title="show questions tagged &#39;xmm-newton&#39;" rel="tag">xmm-newton</a></li>
<li><a href="https://en.wikipedia.org/wiki/Neutron_Star_Interior_Composition_Explorer" rel="nofollow noreferrer">NICER</a> (Mounted on the ISS).</li>
</ol>
<p>Interestingly, the majority is satellite based, but there is e.g. also a moon-based one.</p>
<p>In addition to that, there are space crafts whose Instruments have been temporarily or permanently been repurposed to astronomy. For instance, you could look at the Moon with METEOSAT.</p>

CC BY-SA 4.0
2021-03-30T14:28:13.027Z
Alas, Spektr-R the radiotelescope mission is over. I didn't know about Spectr-RG until just now!
uhoh
CC BY-SA 4.0
2021-04-04T16:15:59.593Z
SOHO with EIT and Lassco?
Dr Chuck
CC BY-SA 4.0
2021-03-30T13:59:54.587Z
2021-04-03T09:54:01.653Z
2021-04-03T09:54:01.653Z
B--rian
<p>Hubble, Chandra, XMM-Newton, Kepler,... I can name a few off of the top of my head, but how many space telescopes are there in all?</p>
<h3>Related</h3>
<ul>
<li><a href="https://astronomy.stackexchange.com/questions/884/what-are-the-next-planned-space-telescopes">What are the next planned space telescopes?</a></li>
</ul>

CC BY-SA 4.0
2021-03-30T15:31:11.570Z
Kepler is already out of service, isn't it?
B--rian
CC BY-SA 4.0
2021-03-31T00:02:08.157Z
It's an ambiguous question, because there is no clear distinction between space telescopes and narrow-angle cameras on deep space probes. For example, the LORRI imager on the New Horizons spacecraft is now being used to observe distant bodies - does it make it a space telescope?
cuckoo
CC BY-SA 4.0
2021-03-31T06:44:32.000Z
@cuckoo If you follow the Wikipedia page I linked in my answer, "space-telescope" looks pretty well-defined as "dedicated astronomy space-missions", (my definition). I agree that strictly speaking, the term "space telescope" probably refers to all non-terrestrial observing equipment.
B--rian
CC BY-SA 4.0
2021-03-31T10:51:52.693Z
But you listed the Lunar-based ultraviolet telescope (which is not a dedicated telescope mission), and any telescope mounted on the ISS isn't a dedicated mission either.
cuckoo
CC BY-SA 4.0
2021-03-31T11:12:37.953Z
I answered following my own, wider definition "all extraterrestrial telescopes (I am aware of)". I am happy to add the telescopes you mentioned.
B--rian
<space-telescope>
How many space telescopes are currently active?
usernumber
# How many space telescopes are currently active?

(Asked by: username_0 on 2021-03-30)

Hubble, Chandra, XMM-Newton, Kepler,... I can name a few off of the top of my head, but how many space telescopes are there in all?

### Related

* [What are the next planned space telescopes?](https://astronomy.stackexchange.com/questions/884/what-are-the-next-planned-space-telescopes)

**Tags:** space-telescope

> **Comments:**
> **username_1**: Kepler is already out of service, isn't it?  
> **username_2**: It's an ambiguous question, because there is no clear distinction between space telescopes and narrow-angle cameras on deep space probes. For example, the LORRI imager on the New Horizons spacecraft is now being used to observe distant bodies - does it make it a space telescope?  
> **username_1**: @username_2 If you follow the Wikipedia page I linked in my answer, "space-telescope" looks pretty well-defined as "dedicated astronomy space-missions", (my definition). I agree that strictly speaking, the term "space telescope" probably refers to all non-terrestrial observing equipment.  
> **username_2**: But you listed the Lunar-based ultraviolet telescope (which is not a dedicated telescope mission), and any telescope mounted on the ISS isn't a dedicated mission either.  
> **username_1**: I answered following my own, wider definition "all extraterrestrial telescopes (I am aware of)". I am happy to add the telescopes you mentioned.  

---

## 1 answers

### Answer by username_1 on 2021-03-30. Score: 8 | Accepted answer

**More than 20** if the Wikipedia's [List of Space Telescopes](https://en.wikipedia.org/wiki/List_of_space_telescopes) is accurate. I extracted the active ones, and removed duplicates (to the best of my knowledge):

1. [Swift Gamma Ray Burst Explorer](https://en.wikipedia.org/wiki/Swift_Gamma_Ray_Burst_Explorer)
2. [AGILE](https://en.wikipedia.org/wiki/AGILE_(spacecraft))
3. [FGST](https://en.wikipedia.org/wiki/Fermi_Gamma-ray_Space_Telescope)
4. [IKAROS](https://en.wikipedia.org/wiki/IKAROS)
5. [NuSTAR](https://en.wikipedia.org/wiki/Nuclear_Spectroscopic_Telescope_Array)
6. [Astrosat](https://en.wikipedia.org/wiki/Astrosat)
7. [Insight (Chinese: 慧眼)](https://en.wikipedia.org/wiki/HXMT)
8. [Спектр-РГ](https://en.wikipedia.org/wiki/Spektr-RG) (Spektr-RG)
9. The famous Hubble Space Telescope, [HST](https://en.wikipedia.org/wiki/Hubble_Space_Telescope), see [hst](/questions/tagged/hst "show questions tagged 'hst'")
10. [STSat-1](https://en.wikipedia.org/wiki/Korea_Advanced_Institute_of_Science_and_Technology_Satellite_4)
11. [IRIS](https://en.wikipedia.org/wiki/Interface_Region_Imaging_Spectrograph)
12. [Hisaki](https://en.wikipedia.org/wiki/Hisaki_(satellite))
13. [Lunar-based ultraviolet telescope](https://en.wikipedia.org/wiki/Chang%27e_3#Lunar-based_ultraviolet_telescope_(LUT))
14. [BRITE](https://en.wikipedia.org/wiki/BRITE)
15. [NEOSSat](https://en.wikipedia.org/wiki/Near_Earth_Object_Surveillance_Satellite)
16. [TESS](https://en.wikipedia.org/wiki/Transiting_Exoplanet_Survey_Satellite), see [tess](/questions/tagged/tess "show questions tagged 'tess'")
17. [CHEOPS](https://en.wikipedia.org/wiki/CHEOPS), see [cheops](/questions/tagged/cheops "show questions tagged 'cheops'")
18. [Odin](https://en.wikipedia.org/wiki/Odin_(satellite))
19. [IBEX](https://en.wikipedia.org/wiki/IBEX)
20. [AMS-02](https://en.wikipedia.org/wiki/Alpha_Magnetic_Spectrometer)
21. [DMPE](https://en.wikipedia.org/wiki/Dark_Matter_Particle_Explorer)
22. [Chandra](https://en.wikipedia.org/wiki/Chandra_X-ray_Observatory), see [chandra](/questions/tagged/chandra "show questions tagged 'chandra'")
23. [XMM Newton](https://en.wikipedia.org/wiki/XMM-Newton), see [xmm-newton](/questions/tagged/xmm-newton "show questions tagged 'xmm-newton'")
24. [NICER](https://en.wikipedia.org/wiki/Neutron_Star_Interior_Composition_Explorer) (Mounted on the ISS).

Interestingly, the majority is satellite based, but there is e.g. also a moon-based one.

In addition to that, there are space crafts whose Instruments have been temporarily or permanently been repurposed to astronomy. For instance, you could look at the Moon with METEOSAT.

> **Comments:**
> **username_3**: Alas, Spektr-R the radiotelescope mission is over. I didn't know about Spectr-RG until just now!  
> **username_4**: SOHO with EIT and Lassco?  

---

