deorbiting a hydrogen balloon

[farmerben]

I wonder if a balloon is a good way to descend through the Earth's atmosphere.  Potentially it opens up whole new exploration missions on other planets including the giants.  

How would we go about figuring out the rentry heating profile?  I wonder if a titanium foil balloon of hydrogen would survive.  

[Spacescifi]

22 minutes ago, farmerben said:

I wonder if a balloon is a good way to descend through the Earth's atmosphere.  Potentially it opens up whole new exploration missions on other planets including the giants.  

How would we go about figuring out the rentry heating profile?  I wonder if a titanium foil balloon of hydrogen would survive.  

 

The answer depends on how steep the reentty dive is as well as how chilled the balloon is.

Why not use tungsten foil instead? Resists more heat.

[sevenperforce]

1 hour ago, Spacescifi said:

The answer depends on how steep the reentty dive is as well as how chilled the balloon is.

The temperature of the balloon will not have any impact. The entry angle will, though; I'll give you that.

[kerbiloid]

If take the spherical Vostok capsule and fill it with hydrogen, it will be technically a hydrogen balloon with thick envelope and heat protection.

So, yes, but depends on its skin thickness.

The inflatable ballons are too thin-skinned.
https://en.wikipedia.org/wiki/Project_Echo

[CFYL]

If it is possible to generate more lift with the same amount of drag, this might be possible IMHO. An unattende LEO sat may fall due to friction in a few orbits,  but with a balloon (I would prefer Helium for safety lower in the atmosphere) it can keep you afloat much longer, and lose speed gradually. For example, fly for a few days up there 70-90km high, gradually losing speed from 7.9km/s to some 3-4km/s, then dive a bit deeper to 50-70km to lower horizontal speed to below 1km/s (also trying to fly to the intended landing spot), finally going down to conventional hot air balloon speeds and just touch down softly. Or do it with more accuracy and just slow down and dive deeper at the same slow rate. Seems possible.

This is what we have for airplanes. 

Why not do it for sats/spacecrafts with inflatable balloons?

Just make sure the craft is afloat in the upper atmosphere when speed is still too high to enter the lower atmosphere. This can be done by fine tweaking the pressure/volume of the balloon, while also making sure nothing overheats. This descent may take days. 

I'm just thinking of the opposite way up. This is a video made by a Chinese vlogger with KSP. It exploits the fact that the heatshield generates a tremendous lift while a tiny drag, going to LEO from 340m/s in the lower atmosphere, with low TWR ion thrusters. He also made it to Venus surface and back using the same trick. This may be impossible IRL because, while a balloon do provides tremendous lift with a minimal mass, it also causes a tremendous drag.

And this is his craft.

 

Edited May 14, 2022 by AllenLi

[Gargamel]

8 hours ago, farmerben said:

Potentially it opens up whole new exploration missions on other planets including the giants.

The issue I see, as mentioned, is the survivability of a balloon in re-entry.  You'll probably need a heat shield of some sort, and when the vessel slows down enough, you can then inflate the balloon and drop the re-entry vehicle and gas storage tanks.   I have trouble believing any already inflated balloon capable of providing any meaningful lift would survive re-entry.

Also, the gas giant's atmospheres are mainly hydogren, with Neptune being the least amount of H2 at 80%.   This doesn't leave a lot of payload left for the balloon to lift.  Even if you descend to a level where the atmosphere dense enough to lift a balloon, I think the winds and turbulence would not be our friend.   Even if we do have an envelope capable of surviving in these conditions, get transmissions out might be be an issue, and possibly even power.   Although perhaps a wind generator would work. 

I think that leaves Venus as our only viable target, as Mars's atmosphere is too thin.   The topography of Mars even extends above the atmosphere, which would probably prove both exciting and disastrous.    Venus though, would require in flight, post entry, inflation, as we obviously can't land on the surface, and even if we could survive landing there, I don't think we'd carry enough stored gas to overcome the surface pressure.

Now.... all that said, the back of my mind is screaming that there are multiple projects on the board with this concept, so I'm not one to rely on.   But I don't think an inflated balloon could survive entry and provide usable lift.  I think you have to pick one. 

9 minutes ago, AllenLi said:

(I would prefer Helium for safety lower in the atmosphere)

I don't think Hydrogen on the gas giants presents the safety issue that it does on Earth, seeing as they are all at least 80% H2 already. 

[CFYL]

5 minutes ago, Gargamel said:

I don't think Hydrogen on the gas giants presents the safety issue that it does on Earth, seeing as they are all at least 80% H2 already. 

Yeah I was focusing on this sentence in the OP

8 hours ago, farmerben said:

I wonder if a balloon is a good way to descend through the Earth's atmosphere. 

and forgot about the the rest  My bad

Edited May 14, 2022 by AllenLi

[Gargamel]

14 minutes ago, AllenLi said:

and forgot about the the rest  My bad

And I forgot about that one

[JoeSchmuckatelli]

13 hours ago, farmerben said:

I wonder if a balloon is a good way to descend through the Earth's atmosphere.  Potentially it opens up whole new exploration missions on other planets including the giants.  

How would we go about figuring out the rentry heating profile?  I wonder if a titanium foil balloon of hydrogen would survive.  

If you have a craft in orbit it's already traveling at Ludicrous Speed compared to the atmosphere... So no matter what you are going to get friction and thus, heat. 

Balloons, to fly, need to be exceptionally thin and flexible and light and not porus -  anything that meets those criteria does not manage heat well enough to survive reentry. 

Plus other stuff mentioned above 

Edited May 14, 2022 by JoeSchmuckatelli

[farmerben]

Even if exploding due to heat is likely possibility, I think it worthy of an experiment.

[kerbiloid]

The experiment was mentioned above, Echo-1&2.

[farmerben]

On 5/14/2022 at 12:16 PM, kerbiloid said:

The experiment was mentioned above, Echo-1&2.

so what happened when they entered the atmosphere?

 

[kerbiloid]

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

Quote

It ended up surviving much longer than expected, and finally reentered Earth's atmosphere and burned up on 24 May 1968.

Quote

It reentered Earth's atmosphere and burned up on 7 June 1969.