” by carrying a launch vehicle 30,000 feet in the air slung under the mammoth plane, then igniting the rocket motors. “
Why ONLY 30,000ft when a lot of jets can climb a fair bit higher???
More wing/speed needed to carry payload into higher/thinner air. There are tradeoff. Getting the rocket to 70,000 feet would be fantastic. You would need a plane with wings one mile in span to get it up there.
I assume lifting a rocket big enough to orbit big stuff requires the planes engines powerful enough to get it off the ground. There probably is a weight to lift ratio that requires sufficient oxygen in the planes jet engines and that limits altitude
Probably has to do with carrying a heavy load and air density. For the tonnage they want, that may be as high as they can feasibly carry it.
You are already above 70% of the atmosphere at that height. To go higher require a bigger launch vehicle with larger engines. They are looking for the economic sweet spot. If this works and it will, I would predict bigger vehicles and higher launch altitudes in the future.
I am sure there is an efficiency quotient there where the cost of lifting it further doesn’t result in a more effective launch.
What they said. :’) Getting a payload that large to that altitude requires composites and engineering that has rarely been done before. The C5 iterations came from Lockheed (which was in its heyday) and it’s difficult to find the real spec on that (for obvious reasons) but its max is said to be 35,000 (with the improved engines, that envelope may have changed a little), so having an operating altitude of 30K isn’t that farfetched. It’s probably the sweet spot between trying to maintain the airspeed needed to keep it out of stall and not burning so much fuel that it can’t make range (however, it uses in-air refueling regardless; in 1973 the C5’s then in use lifted the lion’s share of the wartime supplies to Israel, with one stop in the Azores each way).
During the X-Prize competition years ago, a Canadian entry was going to attempt balloon launching their vehicle, starting from a very high altitude to obviate the need for any main launch booster.
Burt Rutan finished first — SpaceShipOne.
Rutan’s involved in this project.
Still, a balloon launch is not a bad idea, at all. The crew vehicle has to land safely anyway, making recycling the system much simpler.