Or even some kind of contraption that slowly releases gas from the balloon as it detects lower pressure in the atmosphere to help it maintain altitude and prevent the balloon from rupturing?
The very early comms sat experiments in the 50s were just aluminised passive balloons that reflected radio signals bounced off them while in orbit. [1]. However they were there because they were put there by a rocket. I'm not sure if your question is implying that you could float your way up to LEO altitude. I suspect you couldn't with anything that could be engineered.
> Or even some kind of contraption that slowly releases gas from the balloon as it detects lower pressure in the atmosphere to help it maintain altitude and prevent the balloon from rupturing?
This is done already in two ways. One passively does what you describe - a zero pressure balloon - by having a hole in the bottom so helium leaks out as it rises. Eventually enough leaks out that the net lift is zero and it just floats.
The other is a super-pressure balloon [2] which does what you described in your first paragraph - it's strong enough to not explode until the pressure (and so density) of the helium inside increases relative to the outside atmosphere until the lift becomes zero. But we're still a long way from an altitude that could sustain orbit. These operate at relatively low altitudes like 45km/150kft. The drag and heating there would be enormous at orbital velocities!
[1] http://en.wikipedia.org/wiki/Project_Echo [2] http://en.wikipedia.org/wiki/Superpressure_balloon
Even if you could make it, I doubt it would work for very long.
Such a balloon would presumably be quite massive and probably impossible to maneuver. As such it would be a nice target for things that were actually in orbit (moving quite fast relative to it). It would probably become swiss cheese in the matter of days/weeks. (probably not a problem for the balloon itself I suppose, but I can't imagine anything you would be hanging from it would be happy with that.)
No, because balloons don't orbit, they follow the wind patterns at a lower altitude than the lowest satellite orbits. And they're relatively short-lived at altitude -- from seconds to days.
> Or even some kind of contraption that slowly releases gas from the balloon as it detects lower pressure in the atmosphere to help it maintain altitude and prevent the balloon from rupturing?
No, not "releases gas" -- that would lose the gas irreversibly. Instead, consider a scheme that used solar power to drive a pump to put some of the gas under pressure as needed, and releases it later as needed to maintain altitude. Sort of how a submarine maintains its buoyancy by filling tanks with either water or gas, depending on the need, and that does this by putting the gas under pressure to change buoyancy (and avoid losing the gas).
But balloons don't have very long lifetimes at the moment. This might change in the future.
That doesn't sound plausible but I could be wrong.
To get something into a stable orbit you have to get it high enough to avoid significant atmospheric drag. In practice this requires an altitude of at least 200km [1] - although even at this altitude an orbit will decay fairly rapidly. The IIS orbits at 400km and most remote-sensing satellites are at 500km+.
Contrast this with Helium balloons, which usually top-out at an altitude of 35-50km with the record being 53km [2].
To stay in low-earth orbit you also need an orbital velocity of 7.8km/s. A balloon launched at the equator has about 0.5km/s horizontal component of velocity due to the earth's rotation and will not gain any as it lifts.
What you could do is use a balloon to carry a rocket up to its height ceiling before igniting [3]. This saves on fuel, but there are safety issues caused by the non-steerability of the balloon.
[1] http://en.wikipedia.org/wiki/Low_Earth_orbit
[2] http://en.wikipedia.org/wiki/Flight_altitude_record#Unmanned...
[3] http://en.wikipedia.org/wiki/Non-rocket_spacelaunch#Balloon
I was just curious if you could get the balloon to maintain an altitude within low earth orbit, without concern for where the balloon actually drifts.
I was imagining a way to get the balloon to behave as a buoy at sea (not anchored), floating above the thicker atmosphere the same way a rubber balloon or raft would drift at sea.
http://en.wikipedia.org/wiki/Orbital_airship looks like what I'm thinking of.