DARPA will launch a 20-meter membrane telescope into geostationary orbit
Modern military and commercial satellites engaged in photographing the Earth fly in orbits several hundred kilometers high. At the same time, their resolution reaches 50 cm per pixel. Placing in low orbits creates a lot of inconvenience - a satellite cannot continuously capture one point, moreover, no satellite can appear at all at the right time at the right time. The geostationary orbit is devoid of these shortcomings, but from an altitude of 35,786 km above sea level it is impossible to obtain images of acceptable resolution. The higher the resolution requirements, the larger the diameter of the lens or mirror of the telescope. So much more that it is not yet economically feasible to put such a bulky telescope into geostationary orbit.
DARPA MOIRE Project (Membrane Optical Imager for Real-Time Exploitation) is designed to solve this problem with the help of a fundamentally new design of the telescope. Instead of lenses or mirrors, it uses thin transparent membranes with microscopic grooves of a concentric shape, which focus the rays of light using diffraction. The effective diameter of such a diffractive lens is 20 meters. When folded, the telescope is compact enough to be lifted into orbit by an Atlas-5 class launch vehicle. The resolution of the membrane telescope will be 2.5 meters per pixel with a field of view of 10 per 10 km. The telescope will transmit a picture to the earth in real time at a frequency of 1 frame per second. It can be sent to almost any point of the Earth visible from orbit, that is, several such telescopes will almost completely cover the entire surface of the planet.
One of the prototype sections of the MOIRE telescope
Although the image quality of the membrane telescope is less than that of a refractor or reflector of the same size, this is compensated by its small mass. A traditionally designed telescope with similar characteristics would weigh about seven times as much. The MOIRE telescope will become the world's largest optical telescope. The Hubble telescope is 2.4 meters in diameter; the James Webb telescope , due to be launched in 2015, will have a mirror diameter of 6.5 meters. Even the largest ground-based telescopes have a smaller diameter. Only in 2020 is it planned to commission the Giant Magellanic Telescope with a mirror diameter of 24.5 meters.
Comparison of MOIRE sizes with the largest space and ground-based telescopes.
The main contractors for the MOIRE project are the United States Air Force Academy and Ball Aerospace & Technologies Corporation. To date, ground tests of a 5-meter prototype telescope have successfully passed. Although the main purpose of MOIRE is military intelligence, it is possible that the experience gained during its creation will be used to build telescopes for astronomical observations, because the Kepler and James Webb telescopes are also developed by Ball Aerospace & Technologies.