On the Sentinel Mission tour of Ball Aerospace. This telescope is just huge. By using lightweight diffractive optics etched onto the yellow film (25 micron thick), this primary mirror unfolds to 66 ft. wide, over 5x wider than Hubble (20m versus 2.4m).
Here’s a video of how it unfolds in space.
DARPA would use this giga-scope to spy on Earth from a geostationary orbit, so it could afford persistent video surveillance of any given region of Earth.
The scientists are excited to look outward; they could do exoplanet spectroscopy when planets around stars transit around the back and light up. Just as Kepler detects the shadow when those planets pass in front those distant suns, we could look at the increase in brightness when the planet transits from the back, and look for the spectral lines for oxygen, water and carbon dioxide to see if they are prospects for habitat worlds.
The Sentinel Mission tour in front of a couple segments at full scale, with Apollo 9’s Rusty Schweickart on the left and astronaut Ed Lu on the far right:
Checking out the wild rainbows cast by the diffraction gratings: 
Relative scale of the telescope mirrors: 
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