There's probably an obvious answer but this is a "why don't they" question that's been bugging me for many years, every time i hear anything about rockets and space i can't help thinking that launching them from earths surface seem very inefficient, is it something like 70% of a rocket is just fuel to get it into orbit. Anyhow I've always wondered why we don't just stick a big Balloon on the top of a rocket to lift it some/most of the way and then get into space from there, i mean Felix Baumgartner used a balloon to get up to 24mi so why don't we launch from there?
Well, aside from the size of the balloon needing to be huge, you'd have to get it and the rocket through the jet stream and remain stable, then you'd still need enough fuel on board for the rocket to achieve escape velocity, which is the majority of the fuel used in the flight so the weight difference wouldn't be that big. Felix and his capsule didn't weight very much by comparison, even accounting for his massive brass balls.
Yes it would need to be a really big balloon but isn't that better than making something that's basically an over-sized fuel tank, and isn't the jet stream only in small bands? Also doesn't the needed escape velocity go down when you're further from the center of gravity though, the further from the ground the less speed you need, no? It's obvious there's a reason NASA hasn't done such a thing but it just seems so strange that we have balloons and planes that can reach the stratosphere but we still launch rockets from the surface.
Rockets = technologically simple (the tech is basically just 'souped up Nazi V2s) Launching from a flying platform = technologically complex (see Spaceship One/Virgin Galactic) as the platform is not 100% stable, and any perturbation at launch can have massive repercussions to its direction stability and lifespan...! Best place to launch from would be a mountain on the equator.
Lifting the vehicle with a balloon, or launching from a mountaintop, would make almost no difference to the fuel required to reach escape velocity. At the ceiling for a large balloon the reduction in the force of gravity is minuscule at most.
I don't think you realise quite how big the balloon would need to be. The rocket/shuttle/whatever would still need SRBs to achieve escape velocity and they are incredibly heavy. Granted, you wouldn't need the same ones used for a shuttle launch, but they weighed over 500 tonnes each (including fuel), never mind the weight of the vehicle or payload. Now, just think of the balloon required to lift Baumgartners 1.3 tonne capsule.
Relatively speaking yes, but relatively small is still up to six miles deep and wind speeds in it can reach 250mph. Firing a dense, aerodynamic rocket through that is relatively simple, lifting a balloon through that and keeping it facing in the correct direction and remaining stable would be much harder.
You say that and I'm not doubting it but i don't understand why, going on the wiki article about escape velocity it says on the surface of the Earth the escape velocity is about 11.2 km/s, while at 9,000 km altitude in "space", it is slightly less than 7.1 km/s, so why doesn't getting higher mean you need to carry less fuel and have light craft.
9,000 km gives a reduction of approx 30% in required fuel and Baumgartner managed an altitude of ~ 39 km and that other chap managed 41 km, giving us an idea of the ceiling for balloon flight. How much less fuel do you think you'd need? Not a lot, I'd wager.
I don't have a clue, that's why i made this post. Yes it may not save much but how many lbs of fuel is need to lift 1lbs payload, isn't it something like 9 lbs, if so wouldn't even a small saving in fuel weight mean you'd use even less fuel.
Remember that getting up there is only half the work anyway. Staying up there is another problem. Plus the earth's atmosphere is pretty thin anyway.
Beside trying to achieve orbit, a balloon delivery system fails due to cost. The shuttle had a maximum liftoff weight of 110t (tonne not ton) of which 25 t could be payload. The Stratos Jump used approximate 834,000m³ of helium to lift 1.3t. In order to lift the maximum payload, a balloon will require 19 times the volume of helium of 16,000,000m³. The main boaster of the shuttle held 103 t of liquid helium which is about 606,000m³ at sea level. Thus a balloon would use approximately 26 times more helium than hydrogen. I don't know what NASA pays for helium and hydrogen, but for me helium is about 3 times more expensive than hydrogen. The price difference for gas alone is about 80 times higher for a balloon. Disclaimers: I am using numbers from the internet so no guarantees. I assumed that the balloon was lifting 100% payload and there was no overhead weight. The shuttle is lifting payload and overhead weight. I have not considered other cost factors such as the solid fuel boasters or the cost of oxygen.
It's actually been done, albiet on a small scale. During the 1950's (I think, memory is fuzzy on this) They launched weather balloons with sounding rockets to research the upper atmosphere. I can't remember the program name, but I've seen drawings and photos of it. EDIT: Or I could just Google... https://en.wikipedia.org/wiki/Rockoon
