The Hubble Space Telescope is one of the most powerful instruments ever deployed. Indeed, it has been cited in more scientific literature than any other piece of equipment. With it, we can almost see to the edge of the universe and the beginning of time. Dollar for dollar, no other NASA project has yielded so much useful data.
However, the Hubble days are over. With no space shuttle, there is no way to repair or service the unit. It will remain neglected, and eventually drop into our atmosphere and be incinerated. Nothing will stop that now.
As it stands, NASA does not have a successor. The James Webb Telescope is ridiculously powerful, but it is years behind schedule, only sees in the infrared, and is many billions over budget. James Webb has eaten up all the funding available for other space telescopes.
Through an incredible stroke of luck, two Hubble class telescopes have been discovered. The National Reconnaissance Agency, which manages spy satellites, had built the telescopes to view Earth, but decided they didn't need them. The units were found sitting in a warehouse in Rochester NY, still in the original packaging.
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This is incredible. Very seldom does one find exactly what one needs, lying around unused and available. To be sure, NASA will still have to adapt the telescopes for its own use, but that will be much cheaper than building new from scratch. The cost of adapting and and launching one of them might only be $1 billion, which for these types of things is an incredible bargain. One of the units will be adapted and launched in this fashion.
The other telescope will likely remain warehoused for the next decade, so that it can take advantage of better technology when it becomes available.