There are tons of downsides and tradeoffs.

Top concers I would have is working lifetime, stability, and percision.

You don't want a dish that is continually changing shape. Gas and materials shrink and expand as temperature changes. The balloon will also leak.

> The ballon will also leak.

The US solved this problem in the early Cold War for passive balloon communications satellites by putting a chunk of solid volatile material inside the balloon, so sublimation kept a constant internal gas pressure. I suppose you'd stick a cheap servo on a door to control the sublimation rate if you need a precise mirror.

Besides, so long as you've already got the expensive sensors, navigation, propulsion etc. up there, why not just keep chucking up backpacks crammed full of new balloon modules for when your old one pops?

How many decades or years does that last?

I'm sure you could try to look it up— IIRC I think satellite lifespan in Project Echo was limited by drag on the balloon from a relatively low orbit, not depletion of sublimator.

But if you're just talking about the sublimator, why wouldn't it last however long you want it to, depending on how much sublimator you put in it? Plastic's pretty airtight even if it's not perfect, and it's not like you need a ton of pressure to hold shape in a zero-g vacuum.

These sound like manageable problems in space though.

Overall the temperature of the balloon will stay pretty constant if it stays on a fixed orbit around the sun.

The argument about precision I don't understand - the article talks about creating telescopes with this concept but NASA wants to use this for radio communication - the comparison with JWST doesn't apply, as it's mirrors had to be manufactured to a much higher tolerance.

> lifetime

I mean we had bigelow Aerospace with their module and it seems to be pretty durable. [0]

[0] https://de.wikipedia.org/wiki/Bigelow_Expandable_Activity_Mo...

>Overall the temperature of the balloon will stay pretty constant if it stays on a fixed orbit around the sun.

OK, so you just ruled out 99% of use cases. The world only has a handful of satellites in heliocentric orbits.

> You don't want a dish that is continually changing shape.

https://en.wikipedia.org/wiki/Adaptive_optics

Decent ground-based telecopes have to constantly change shape anyway. Perhaps it would in fact be easier to manage with a balloon.

JWST also unfolded from panels, so presumably has a way to calibrate itself.

Space is cold; I wonder if they could find a material that is inflatable at room temp but would quickly harden in space, so they would inflate it using warm gas, then wait for it to cool down.

Space is also hot.

NASA temperature conditions for flight hardware is as follows: LEO -65 ºC to +125 ºC, with 6,000 cycles/yr depending on orbit height. GEO is -196 ºC to +128 °C, with 90 cycles/yr.

That is some serious Thermal stress. Never mind the fact that it is also being blasted with UV radiation.

> Space is also hot.

Yes, of course. I was wondering if there are materials that once cooled down would harden but then remain as such also when temperature rises again. Assuming it's doable, it would likely suffer from dilation and contraction anyway.

> That is some serious Thermal stress. Never mind the fact that it is also being blasted with UV radiation.

This sounds like a problem that is easily solved by simply adding another, bigger balloon that sits between it and the sun.

One thing I am wondering about is SAT to SAT communication. I imagine the receiver / transmitter is facing "down", or is it maneuverable and does SAT to SAT support something like a BGP router network or something to ensure optimal comms.