From Balloon to Orbit

Imagine with me a solution for getting a large payload into orbit.

Traditionally, we use multi-stage rockets that carry all their fuel from sea level to orbit and beyond. For going from ground to orbit, at least 90% of the weight of the rocket must be fuel. The remaining 10% can be structure. A smaller percentage of this can be payload. In the case of the Apollo missions, "payload" can be considered the weight of the astronauts, camera film, and a bag of moon rocks. Everything else- including the reentry vehicle, was technically disposable. To double the final payload would likely require doubling the initial size of the rocket.

A technically more elegant solution is to use a multi-stage, reusable system. The space shuttle, which only visits low earth orbit, has a much higher payload percentage.

SpaceShipOne, built by Burt Rutan to visit the lowest definition of "space" (about 60 miles) uses a combination of air-breathing jet engines and rockets. Different parts of the system land separately.

So, for the fun of it, I'm thinking about another way to do something similar. Only, in this case, we're going higher than the 53k feet that an air-breathing engine can handle.

Let's say that we need to get 250 miles high to achieve a reasonable, stable orbit. Let's say that we'll be getting there via rocket. Let's be generous and say that the mothership model (ie, WhiteKnight) gets you 10 miles high. That's 4% of the total distance. Aside from the advantage of not having to drill through the dense lower atmosphere while simultaneously gaining the necessary momentum to continue onward to escape velocity, this translates to only a marginal total advantage. The higher your target orbit, the less your advantage.

So, I propose that we get even higher. StratoLab V, a high altitude testbed from the early 1960s, still holds the world record for highest manned balloon ascent. Over 113k feet. Unmanned balloons have reached as high as 173,900 feet- more than half-way to the hard edge of space.

Imagine building a balloon that can lift a two-stage rocket powered shuttle glider as payload to about 80k feet. The shuttle would sit in a cradle, dangling beneath the balloon, and take off at an angle away from the balloon straight overhead. The balloon would achieve non-trivial speed using high altitude winds which would be added to the rocket's total lateral velocity. The balloon, which would likely be manned, would then be piloted to the ground by releasing billions of cubic feet of hydrogen.

In the event of an emergency, balloon crew would parachute to safety wearing pressurized suits. The shuttle would glide to safety. Crew would come down separately on parachutes and the shuttle would be flown remotely. If necessary, it would jettison its fuel and make a water landing. Otherwise, it would operate as designed, making a dead-stick landing at an airstrip. Its payload would be recovered and reused.

Alternately, instead of a shuttle, a two-stage, bare bones rocket would be used. Because of the high altitude, it would not even need to be particularly aerodynamic. The payload could be partially or even completely exposed to the open air.

After landing, the balloon would be deflated, disassembled, placed on trucks, and returned to base for refurbishment and reuse. Helium might be used as a buffer gas- for instance, providing a thin layer- held in place by ultra-thin polyethelene- to diminish the exposure of hydrogen to static charges on the balloon's surface. Because the helium would represent a small amount of the total gas volume, but would be enough to keep the gas envelope up (rather than raking against the ground during landing), this helium could be carried all the way back to earth and then be recovered, purified, and reused.

How big would this balloon be?

Let's imagine that we want to achieve 50k lbs of delivery to low earth orbit- similar to the Space Shuttle.

Let's estimate that the total advantage, over the traditional space shuttle, is about 40%. two-thirds of the advantage comes from being able to bypass the lower atmosphere's drag. The remaining one-third comes from a combination reduced distance, and the cumulative consequence of carrying additional fuel over said distance. A further 10% advantage comes from the reduction in total complexity and, therefore, weight due to being able to bypass the stresses of the lower atmosphere, as well as the 40% drop in total weight and the attendant complexity. Another 5% comes from improvements in rocket technology. That still leaves us with about 1,900,000 lbs (of which less than 3% is payload).

What kind of balloon can carry nearly two million pounds of payload? There's only one I know of.