dalekduster

It seems to me that whatever could reduce drag would also reduce lift, and would also require more energy from somewhere. However, even if the final stage orbital ascender can achieve a true air speed that is a significant fraction of orbital velocity before it hits a "max q" barrier, it could be useful as a rocketoon solution. At 250,000 feet a true air speed of 3km/s or ~10000km/h would probably give you a heat stress < mach 4 at sea level, I think. That may be achievable, in which case the orbital ascender could be used as a sub-orbital rendezvous platform. A rocket powered craft can aerobrake down from orbit, pick up fuel and payload and accelerate back into orbit. Aerobrake will be relatively easy for a small light craft that only descends with at most the same payload it takes up, ie no fuel. In the case of a missed rendezvous, it could drop its payload and have enough shielding to fully deorbit for a surface landing. I think at 250,000ft and 3k/ms, delta v budget for orbit would be about 5km/s. In that case a 1 ton craft with fuel and almost 1 ton payload would weigh about 6 tons fully fueled. This assumes LH2/L0X rocket with Isp 450, which is maybe a bit ambitious, but BlueOrigin are already done serious and successful research into affordable multiple firing LH2/LOX rockets, which should give an Isp well over 400 at 250,000 feet and higher. Hence, it seems that the maths might just stack up if the logistics can be realistically made to pay. The thing is, that current research into flyback boosters and air launch rockets tends to suggest that it should be easier to make these systems work and be much cheaper than previous generation launch systems. That may be true but a viable space economy will require a lot of "dumb mass", much of which will be in the form of hydrogen, oxygen, nitrogen, carbon etc (probably at least 75%). Sending thousands of tons of that up to orbit from the surface, using rockets or even using skytrams or ram accelerators involves a certain amount of "violence" that tends to preclude 100% re-usability of these systems. Using airships to get to 250,000 ft and 3km/s doesn't seem like much of a gain for the logistical headache involved, but on reflection, I think it could be well worth it., and perhaps the only economically viable solution available any time soon. For a pipeline to space that can continually supply thousands of tons per year or more there is the possibility to harvest water and volatiles from the stratosphere and miss out the lower steps of the pipeline.