Let's Make Robots!

Unmanned Hot Air Balloon Near Space?

After researching various DIY weather balloon setups, I was less than satisfied with the short flight time due to the balloon always exploding. I then had an idea: Why not use a hot air balloon that runs on electricity and recharges through solar panels/mini "windmills"? After all, electrically heating a balloon through something like a hairdrying coil is a lot more effecient and can go a lot higher than propeller powered uav's. It also could have an indifinite flight time (in theory)! Has anyone done something like this before? Could a prop be added for manual control, or would the wind be too fast for that? If so, how could the balloon be controlled for going to different "waypoints", or is that even possible?

This will most likely be my summer "project"!

Here are the laws I found regarding these near space balloons (subsection D): http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&sid=ea968eea871ed9ab2380f6d979eaa7a6&rgn=div5&view=text&node=14:

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I wonder if you could use nuclear fission to heat the air in a balloon enough to lift the Uranium rods.  That would be safe wouldn't it?  I can't imagine anything going wrong with that scenario.

Is there any issue with just making a robot-brain, autonomous hot air balloon? I mean, close to the ground, "normal" altitude and with "normal" heating (petroleum fuel). That would be cool as hell.

They had one of these configured as a blimp-fish floating around an art gallery I saw a while back.  A simple fan with a rudder provided slow enough movement through the air that it could use ultrasonics and an Arduino to not hit the walls overhead. It looked to be around a meter long by a half meter in diameter at the center and the body was mylar.  The lift was from helium I assume.

It won't work because the higher you go the thinner the air gets. This means you need to keep increasing your heat. Your hot air balloon would need to handle extremely high temperatures.

As it also gets colder as you go higher up it means that the air needs to be heated even more thus requiring more power. Forget soloar power, you need a "Mr. Fusion" like they had in "Back to the Future II".

Current nuclear power designs are a little bit too big and heavy for anything as flimsy as a hot air balloon.

plastic solar panels. They have lower efficiency than the standard home based panels, but, they are much lower mass.

You are right back to the issue of energy density. The number of calories (or watts or BTU's or whatever measurement you want to use) in a bottle of propane is thousands of times greater than what you could get from solar panels. 

You are just not going to get the wattage you need from the panels. At the point you do, the panels will be so extensive that the thing will never get off the ground.

The math is just not there, dude.


Looks like I need a new summer project!

If there is a hole in the bottom (like a regular hot air ballon), all the air will come out when you start going from sea level pressure to the close-to-zero pressure of the high atmosphere. If you seal the balloon to prevent this, well, you are back to the popping ballon. 

For the record, the popping of the ballon is usually the way you get your electronics back.