If Hubble were to descend in a completely uncontrolled re-entry, parts of the main mirror and its support structure would probably survive, leaving the potential for damage or even human fatalities.
While the telescopes' 8-foot-wide (2.4 meters) main mirrors are comparable to that of Hubble, the NRO instruments are designed to have a much wider field of view, NASA officials have said.
I saw Athens as the main mirror reflecting the political and economic situation in the country.
Located in the Davis Mountains 450 miles west of Austin, the observatory today uses a reflecting telescope whose main mirror is 30 inches wide and a laser that sends out short bursts of up to one billion watts of power.
First to deploy will be solar arrays and antennas to provide power and communications with Earth; then the sunshield will unfurl to begin cooling the telescope and instruments; finally, the secondary mirror will swing into position and the main mirror wings will snap into place.
Future generations of ground-based telescopes, such as the proposed European Extremely Large Telescope (with a 30m main mirror), could be operational by 2030, and would be powerful enough to image the atmospheres of faraway planets, looking for chemical signatures that could indicate life.
Light sources on the ceiling will create an artificial universe, allowing NASA engineers to run light all the way through the system from main mirror to detectors for the first and only time in spacelike conditions.
"Once the telescope points at the star we want to observe, the light [from this star] first reflects off the main mirror, which then concentrates it towards the secondary mirror, and then sends it to one of the three instruments of the telescope," says Mr Guisard.
Its main mirror, which will gather light from distant stars and galaxies, will be 39 metres in diameter, made of 798 segments.
The main mirror of the Hale Telescope measures 5 metres (200 inches) across and weighs 14.5 tons.
