If you browse the internet, it's easy to find an image of the International Space Station taken by an amateur astronomer that looks as if it was taken only a mile away. DARPA wants to go several magnitudes better with a telescopic system that can take detailed images of satellites in geosynchronous orbit. The research agency is seeking ideas on how to achieve this from an unorthodox mix of small businesses, academic and research institutions, and first-time government contractors.
If there's one thing the US government is keen on, its keeping tabs on objects in space. In recent decades, there have been remarkable advances in optics that create telescopes to take images at distances of up to 1,200 mi (2,000 km) with resolutions of one pixel per ten cm, allowing remarkably detailed images of objects like the ISS to be taken from the ground. The problem is that many satellites orbit the Earth at much higher altitudes. For geosynchronous satellites 22,000 mi (36,000 km) up, the best pictures are mere blurs of one pixel per two meters
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This matter is more than amateur photography. Modern civilization is heavily dependent on civilian and military satellites, so being able to properly identify, assess, and track spacecraft is a vital US interest, which is where DARPA comes in.
DARPA's goal is to develop the capacity to closely inspect geosynchronous satellites with the same precision as those in low-Earth orbit. This isn't simply a matter of building larger telescopes with larger mirrors. According to DARPA, the telescope needed would have to be 200 m (656 ft) wide and weigh far too much to move without breaking. Even if such an instrument could be built, the atmospheric turbulence that makes stars twinkle would hopelessly distort any image captured.
To find a way around this DARPA is seeking ideas in a number of areas as part of a Request for Information (RFI). The basic approach is that instead of making one gigantic telescope, a number of smaller ones would work in concert to form a huge interferometer, where images taken from the different telescopes are combined to form an interference pattern that can then be used to build up a high-resolution image.
DARPA's RFI seeks proposals for tackling one or more of the major areas of the project. One of these is to look for a way to assess local atmospheric distortions that is simple and effective. Another is to find a way to reliably make a large number of 0.5 m to 5 m (1.6 to 16 ft) scopes in a short time while compensating for any optical defects. Then there is the development of algorithms and post-processing methods to produce a high-resolution image from a number of lower resolution ones. And finally, there is a request for ways to economically build test beds to help develop the technology.
Lindsay Millard, DARPA program manager, says that such an instrument would more powerful than anything previously like it and would be able to see such details as improperly deployed antennas or partially unfurled solar panels.
"The image resolution this RFI envisions — down to a milli-arcsecond, or approximately one-3.6-millionth of a degree — would be up to 100 times more powerful than the current state of the art," says Millard. "Beyond helping us achieve our immediate needs on orbit, that improvement could significantly advance astronomy research, helping us learn about black holes and galaxy dynamics, as well as characterizing nearby exoplanets and detecting more-distant ones."
DARPA is seeking proposals until July 3.