The DOD had two "better-than-Hubble" space telescopes just sitting around.
"Better-than-Hubble" is flat out wrong here, the only correct interpretation is "with larger apertures than Hubble", but there is so much more to a telescope, especially one in Hubble's class. A spysat is optimized for taking only exposures lasting a fraction of a second, for example, whereas Hubble is optimized for taking exposures that last many minutes at a time, with guidance that keeps Hubble pointed in the same direction to sub-pixel precision.<p>Let's take a moment to walk down the aisle with the label "Current Hubble Science Instruments". First, we come upon WFC 3, a 4k x 4k high quantum efficiency CCD imager with a wide field of view, spectral coverage from the near-UV through visible spectrum and with 63 different narrow and wide-band filters. Oh, and with a set of grisms and prisms for taking spectra, and with a separate 1k x 1k IR sensor with 17 of its own filters. Next up is NICMOS, an IR imager and spectrometer with a spectral range of 0.8 to 2.4 microns, this instrument alone places Hubble into the rankings as one of the top 3 or 4 most productive and capable Infrared telescopes in history all on its lonesome. Then there is STIS, a 3 CCD sensor with coverage from far-UV through near-IR wavelengths which is capable of taking high resolution spectra for 500 separate points simultaneously while also taking a full frame image, this instrument alone is responsible for much of all of the astronomical observations in the UV-range throughout all of history. And there are several other equally impressive instruments I have not mentioned.<p>The point is, none of these instruments or capabilities are going to be on a spysat. And they make up the vast majority of the value of a space based observatory. If a space telescope was nothing more than a big mirror, some guidance, and an imager then we could save billions of dollars, but they are so much more than that.