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.
Balloon-borne telescopes have been in use since the 1950s. A 20–30 meter balloon telescope has been suggested.[41] The balloon would be transparent on one side, and have a circular reflecting mirror on the other side.[41] There are two main designs using this principle.[41]
Large Balloon Reflector (LBR) (sub-orbital version)
Waypoint-1 Space Telescope, visible light, UV and hyper-spectral imaging for astrophysical research and ground observation[48]
Whipple, proposed transit telescope for KBO and Oort objects
ZEBRA, Zodiacal dust, Extragalactic Background and Reionization Apparatus [49] A small infrared observatory sent out to 10 AU by NASA[50]
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.[51]
↑Realini, S. et al. (2018). "Concept design of the LiteBIRD satellite for CMB B-mode polarization". Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave. Proceedings of the SPIE. 10698. p. 68. doi:10.1117/12.2313432. ISBN978-1-5106-1949-4.
↑Reynolds, Christopher et al. (1 Nov 2023). "Overview of the advanced x-ray imaging satellite (AXIS)". UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XXIII. Proceedings of the SPIE. 12678. p. 49. doi:10.1117/12.2677468. ISBN978-1-5106-6570-5.
↑Wu, Yue-Liang et al. (24 February 2021). "China's first step towards probing the expanding universe and the nature of gravity using a space borne gravitational wave antenna". Communications Physics (Nature) 4 (1): 34. doi:10.1038/s42005-021-00529-z. Bibcode: 2021CmPhy...4...34T.
↑Carlesso, Franciele; Rodríguez Gómez, Jenny Marcela; Barbosa, Adriany Rodrigues; Antunes Vieira, Luis Eduardo; Dal Lago, Alisson (2022-06-24). "Solar Irradiance Variability Monitor for the Galileo Solar Space Telescope Mission: Concept and Challenges". Frontiers in Physics10. doi:10.3389/fphy.2022.869738. ISSN2296-424X. Bibcode: 2022FrP....10.9738C.
↑Apai, Dániel; Milster, Tom D.; Kim, Dae Wook; Bixel, Alex; Schneider, Glenn; Liang, Ronguang; Arenberg, Jonathan (29 July 2019). "A Thousand Earths: A Very Large Aperture, Ultralight Space Telescope Array for Atmospheric Biosignature Surveys". The Astronomical Journal158 (2): 83. doi:10.3847/1538-3881/ab2631. Bibcode: 2019AJ....158...83A.
↑Rabien, S.; Busoni, L.; Del Vecchio, C.; Ziegleder, J.; Esposito, S. (2024-08-23). "Membrane space telescope: Active surface control with radiative adaptive optics". Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave. Proceedings of the SPIE. 13092. pp. 148. doi:10.1117/12.3019682. ISBN978-1-5106-7507-0. Bibcode: 2024SPIE13092E..5OR.