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Telescopes from the Ground Up
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Compare space telescope mirror sizes
The size of a space telescope primary mirror is limited by the size of the vehicle carrying it into orbit, the expense and effort of launching it, and the difficulty of deploying it in orbit. It's much easier to build large primary mirrors into ground-based telescopes.
Graphic comparing telescope sizes.
Spitzer
Spitzer is currently NASA's largest infrared telescope in space. Its mirror was small enough to fit inside the rocket that launched it into orbit.
Hubble
Hubble has a large, single mirror that was the right size to fit inside the hold of the Space Shuttle.
Webb
Webb, the next infrared space telescope, has a mirror designed to fold up inside the rocket that will launch it. Once in space, it will unfurl into the biggest mirror of any telescope in orbit.
Ground-based telescopes
Telescopes on Earth, like the Keck telescopes in Hawaii, have fewer technological limitations and have much larger mirrors than space telescopes.

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