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.

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