# List of proposed space telescopes

This list contains proposals for space telescopes, space-based (situated in space) astronomical observatories. It is a list of past and present space observatory plans, concepts, and proposals. For observatories in orbit, see list of space telescopes. Unlike that list, this one includes concepts and proposals that are unlikely ever to be launched, as they may have been cancelled or were only proposals.

## Space observatories under development

| Name | Agency | Type | Proposed launch date | Status | Proposed location |
| TOLIMAN | NASA | visible | 2026 | under construction | Low Earth orbit |
| Xuntian | CNSA | ultraviolet, visible, infrared | 2026 | under construction | Low Earth orbit |
| PLATO | ESA | visible | 2026 | under construction | Sun-Earth L$_2$ Lagrange point |
| ULTRASAT | ISA | ultraviolet | 2026 | | Geosynchronous orbit |
| Nancy Grace Roman Space Telescope | NASA | infrared | October 2026-May 2027 | confirmed and named 2020 | Sun-Earth L$_2$ Lagrange point |
| Compton Spectrometer and Imager | NASA | gamma ray | 2027 | | Low Earth orbit |
| ARIEL | ESA | visible, infrared | 2029 | | Sun-Earth L$_2$ Lagrange point |
| Spektr-UV (WSO-UV) | Roscosmos | ultraviolet | 2030 | funded | Geosynchronous orbit |
| UVEX | NASA | ultraviolet | 2030 | | Highly elliptical orbit |
| LiteBIRD | JAXA | millimeter radio | 2032 | Approved for development | Sun-Earth L$_2$ Lagrange point |
| AXIS (Advanced X-Ray Imaging Satellite) | NASA | X-Ray | 2032 | early planning | Low Earth orbit |
| PRIMA (PRobe far-Infrared Mission for Astrophysics) | NASA | far-infrared | 2032 | early planning | Sun-Earth L$_2$ Lagrange point |
| Taiji | CNSA/CAS | gravitational waves | 2033 | phase 1 of 3-phase development completed | Heliocentric orbit |
| Advanced Telescope for High Energy Astrophysics | ESA | x-ray | 2035 | | Sun-Earth L$_2$ Lagrange point |
| Laser Interferometer Space Antenna (LISA) | ESA | gravitational waves | 2037 | Approved for development | Solar Earth-trailing orbit (approx. 1 AU) |
| Habitable Worlds Observatory | NASA | Ultraviolet, Visible, Infrared | 2041 | early planning 'Phase 1' | Sun-Earth L$_2$ Lagrange point |
| X-Ray Great Observatory | NASA | X-Ray | 2047 | early planning 'Phase 1' | possibly Sun-Earth L$_2$ Lagrange point |
| Far-Infrared Great Observatory | NASA | Far-Infrared | 2051 | early planning 'Phase 1' | possibly Sun-Earth L$_2$ Lagrange point |
| AstroSat-2 | ISRO | Near Ultraviolet, Far Ultraviolet, Visible | TBD | – | Low Earth orbit |
| ExoWorlds Mission | ISRO | | TBD | | |
| Indian spectroscopic and imaging space telescope (INSIST) | ISRO | | TBD | | |
| Galileo Solar Space Telescope | INPE | Visible and ultraviolet | TBD | Admission process at AEB | Low Earth orbit or Geostationary orbit |

## Merged, cancelled, or superseded space observatories

| Name | Agency | Type | Proposed launch date | Status | Proposed location | Ref(s) |
| X-Ray Evolving Universe Spectroscopy Mission (XEUS) | ESA | X-ray | Merged into IXO | Merged into IXO | – | |
| Constellation-X | NASA | X-ray | Merged into IXO | Merged into IXO | – | |
| International X-ray Observatory (IXO) | NASA & ESA & JAXA | X-ray | No funding 2011; rebooted as ATHENA | No funding 2011; rebooted as ATHENA | – | |
| Exoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) | NASA | ? | 2016 | – | Sun-synchronous Earth orbit, 2000 km | |
| SIM Lite Astrometric Observatory | NASA | ? | 2015 | No funding 2010 | – | |
| Darwin Mission | ESA | ? | – | – | Sun-Earth L$_2$ Lagrange point | |
| Terrestrial Planet Finder | NASA | ? | TBA | No funding 2011 | – | |
| Dark Universe Observatory | NASA | ? | Superseded by Roman/WFIRST | Superseded by Roman/WFIRST | Earth orbit (600 km) | |
| Joint Dark Energy Mission | NASA & DOE | ? | Superseded by Roman/WFIRST | Superseded by Roman/WFIRST | – | |
| Astromag Free-Flyer (Particles) | NASA | ? | 1 January 2005 | – | Earth orbit (500 km) | |
| VSOP-2 (Astro-G) (Radio) | JAXA | ? | 2012 | Cancelled 2011 | – | |
| SAFIR | NASA | far infrared | Superseded by Origins | Superseded by Origins | Sun-Earth L$_2$ Lagrange point | ref? |

## Additional examples and non-space telescopes

For launch in the 2030s, NASA is evaluating four possible designs: the Origins Space Telescope, Lynx X-ray Observatory, Habitable Exoplanets Observatory (HabEx), and Large UV Optical Infrared Surveyor (LUVOIR).
Balloon-borne telescopes have been in use since the 1950s. A 20–30 meter balloon telescope has been suggested. The balloon would be transparent on one side, and have a circular reflecting mirror on the other side. There are two main designs using this principle.
* Large Balloon Reflector (LBR) (sub-orbital version)
* Space-based Large Balloon Reflector (LBR)
** TeraHertz Space Telescope (TST)

## Additional examples

* Advanced Telescope for High Energy Astrophysics (ATHENA)
* Big Bang Observer
* Cosmological Advanced Survey Telescope for Optical and UV Research (CASTOR)
* Deci-hertz Interferometer Gravitational wave Observatory (DECIGO)
* EChO
* Fast Infrared Exoplanet Spectroscopy Survey Explorer (FINESSE)
* Gravity and Extreme Magnetism Small Explorer (GEMS)
* Habitable Exoplanets Observatory (HabEx), a large UV to NIR focused design, 4 meter mirror
* LOFT - Large Observatory For X-ray Timing
* Large Ultraviolet Optical Infrared Surveyor
* Large Interferometer For Exoplanets
* Nautilus Deep Space Observatory
* Near-Earth Object Surveillance Mission (formerly Near-Earth Object Camera (NEOcam))
* PEGASE
* Planetary Dynamics Explorer
* Space Infrared Telescope for Cosmology and Astrophysics (SPICA)
* Telescope for Habitable Exoplanets and Interstellar/Intergalactic Astronomy (THEIA)
* THESEUS
* Waypoint-1 Space Telescope, visible light, UV and hyper-spectral imaging for astrophysical research and ground observation
* Whipple, proposed transit telescope for KBO and Oort objects
* ZEBRA, Zodiacal dust, Extragalactic Background and Reionization Apparatus A small infrared observatory sent out to 10 AU by NASA
* Membrane Space Telescope: A concept of huge reflecting telescopes in space, where the primary mirror would be composed of very thin and lightweight membrane, that would be kept in the required accurate shape by thermal radiative pressure projected from behind. ~15nm RMS precision was achieved in prototype testing.