Future aperture upper limits on balloon-borne telescopes are expected to be some 2.5-meters, about the size of the Hubble Space Telescope.

FORBES: Budgets Nudge NASA Toward Balloon-Based Planetary Science: First Target? Comet ISON

But the researchers who have been flying a balloon-borne telescope in Antarctica seem to have saved us from any mind-bending alternatives.

BBC: Pictures of the early Universe

To date, balloon-borne activities have centered around heliophysics and astrophysics that have not required precision-pointing, says Near-Earth Object (NEO) program officer Rob Landis at NASA headquarters.

FORBES: Budgets Nudge NASA Toward Balloon-Based Planetary Science: First Target? Comet ISON