This list contains proposals for space telescopes, space-based (situated in space) astronomical observatories. The list of proposed space observatories 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.
"Active" in this list means it is still under consideration for development, not that it is in orbit
- Merged, Cancelled, Superseded
|LiteBIRD||JAXA||2020s||Approved for development||Sun-Earth L2 Lagrange point|||
|X-Ray Evolving Universe Spectroscopy Mission (XEUS)||ESA||Merged into IXO||–|||
|International X-ray Observatory (IXO)||NASA & ESA & JAXA||No funding 2011; rebooted as ATHENA||–|||
|SIM Lite Astrometric Observatory||NASA||2015||No funding 2010||–|||
|Darwin Mission||ESA||–||–||Sun-Earth L2 Lagrange point|||
|Terrestrial Planet Finder||NASA||TBA||No funding 2011||–|||
|Dark Universe Observatory||Superseded by WFIRST||Earth orbit (600 km)|||
|Dark Energy Space Telescope||NASA & DOE||–|||
|Wide Field Infrared Survey Telescope (WFIRST) (IR)||NASA & DOE||mid-2020s||–||Sun-Earth L2 Lagrange point|||
|AstroSat-2||ISRO||2020||–||Low Earth orbit|||
|Astromag Free-Flyer (Particles)||NASA||1 January 2005||–||Earth orbit (500 km)|||
|VSOP-2 (Astro-G) (Radio)||JAXA||2012||Cancelled 2011||–|||
|Exoplanetary Circumstellar Environments and Disk Explorer (EXCEDE)||NASA||2016||–||Sun-synchronous Earth orbit, 2000 km|||
|Laser Interferometer Space Antenna (LISA)||ESA/NASA||~2030s||Solar orbit (approx. 1 AU; trailing Earth)|||
|World Space Observatory (WSO-UV)||ROSCOSMOS||2025||funded|||
|Xuntian Space Telescope||CNSA||2024||–||Low Earth orbit|||
|Origin Space Yang Wang-1||private||2021||–|||
Four NASA Design studies from 2018:
Various proposals or concepts for high-energy light observatories (circa 2010s):
For launch in the 2030s, NASA is evaluating four possible designs: the Origins Space Telescope, Lynx X-ray Surveyor, Habitable Exoplanet Imaging Mission (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.