balloon-borne telescope
[bəˈlun bɔrn ˈtɛlɪˌskop]
A balloon-borne telescope is a sub-orbital astronomical telescope that is suspended below one or more stratospheric balloons, allowing it to be lifted above the lower, dense part of the Earth's atmosphere. This has the advantage of improving the resolution limit of the telescope at a much lower cost than for a space telescope.