Inflatable hydrogen balloon for booster recovery

[sevenperforce]

This might be a stupid idea, but...

Consider a basic hydrolox strap-on booster. At the end of its burn, it will still have some residual hydrogen in its tanks. If the booster had three really large cylindrical balloons collapsed and packed along its outer skin, could it use that residual hydrogen to rapidly inflate them, both stabilizing the booster and allowing it to float? A high-altitude drone could be used to recover and tow it to the launch facility, where it could land softly using the balloons as airbags. 

[AngelLestat]

You need really big balloons with a cuestionable amount of h2, depending the wind you can have a hard landing or a soft landing (and you can not control where you will land).

This idea only works in Venus, where you can float your stage at low altitude where is super easy to float, and you dont have a ground to crash and more easy for recovery.

PD: you need to reduce your speed before inflate your balloons.

Edited February 17, 2016 by AngelLestat

[Hannu2]

First problem is that hydrolox engines have relatively low thrust. Therefore they are useless as strap-on boosters. They must have very high thrust at cost of ISP.

I think that gas balloon is too weak to be useful in this purpose. Parachutes are stronger but not enough in booster recovery.

[sevenperforce]

You could go for a tripropellant kero-hydrolox booster. Yes, you'd need large balloons and a good deal of residual hydrogen. Recovery isn't a problem if you have an autonomous solar-powered high-altitude drone to tow it in.

[DerekL1963]

43 minutes ago, sevenperforce said:

Consider a basic hydrolox strap-on booster. At the end of its burn, it will still have some residual hydrogen in its tanks. If the booster had three really large cylindrical balloons collapsed and packed along its outer skin, could it use that residual hydrogen to rapidly inflate them, both stabilizing the booster and allowing it to float? A high-altitude drone could be used to recover and tow it to the launch facility, where it could land softly using the balloons as airbags. 

That's difficult in two respects - first, you'd need some truly huge balloons as hydrogen only lifts about 60lbs/1000ft^3 (.22kg/m^3) at STP.   The second is that the gaseous hydrogen is going to be cold - nearly cryogenic, giving it even less lifting force.   (And finding a balloon material that is a) light enough, b) strong enough to withstand deployment forces, and c) not going to crumble at near cryogenic temperatures... is going to be really, really interesting.)

And how exactly are balloons that are above the booster going to act as airbags, which need to be below it?

[sevenperforce]

Yes, the balloons would be huge.

An appropriate design would probably do some kind of preheat cycle in order to warm up the hydrogen.

The balloons would be cylindrical rather than spherical and would deploy along the outer skin of the booster, from top to bottom. I suggested three, but you could have a whole cocoon thing going on.

[AngelLestat]

16 minutes ago, sevenperforce said:

You could go for a tripropellant kero-hydrolox booster. Yes, you'd need large balloons and a good deal of residual hydrogen. Recovery isn't a problem if you have an autonomous solar-powered high-altitude drone to tow it in.

If you have winds higher than 30kmh (something super common at high altitudes) you can not bring it back.
Why you don't do the math, how much volume you need with the balloon and how much kg of h2.

[DerekL1963]

42 minutes ago, sevenperforce said:

Yes, the balloons would be huge.

An appropriate design would probably do some kind of preheat cycle in order to warm up the hydrogen.

The balloons would be cylindrical rather than spherical and would deploy along the outer skin of the booster, from top to bottom. I suggested three, but you could have a whole cocoon thing going on.

When you have to keep making things more and more complicated in order to make your scheme work...  that's generally a sign that you're haring off down the wrong path.

[sevenperforce]

42 minutes ago, DerekL1963 said:

When you have to keep making things more and more complicated in order to make your scheme work...  that's generally a sign that you're haring off down the wrong path.

Point taken, but then again, that WAS part of the original specification. And a reheat cycle is not particularly complicated; there would have to be some sort of pump or channel for controlled venting anyway.

[DerekL1963]

10 minutes ago, sevenperforce said:

And a reheat cycle is not particularly complicated

It's not that a reheat cycle is complicated, but that adding one adds complication to the overall system.   (And a not inconsiderable amount of weight, because it's going to take quite a bit of energy.)

One simple thing is simple, two simple things in series is less simple, etc... etc...  The engineering version of Conway's Game Of Life - where complex behaviors arise from very simple rules.