The polar balloon

JPL presents, the stratospheric telescope.

Over the poles of a windy planet, the Vortex shouldn't shift the balloon much and you always know where it is. They're floating this at 40 km. Here the gravity is 9.71; air-pressure is calculated 34.5 hPa. That's an h: the same units of mbar, so yes 0.034 atm. It's not yet space (100 km) so the wind will carry this thing around the pole every ten days or so. They're proposing a 150 m (1.5 hm) wide helium-filled balloon to do it.

Payload, beside the balloon itself: gondola, solar-panels, a cryo-cooler, and the satellite dish itself to detect infrared. Okay. Er. Earth has seasons. If you're flying this in a polar winter, why do you need solar-panels. If not, the sun is swamping the infrared.

Since this is polar, the sun hits from the side. Given solar power, a spherical / oblate shape makes sense for the balloon. I trust the cable is a long one for midsummer noon.