Airbreathing SSTO
Posted: Wed Feb 20, 2008 12:25 am
I've been reading an old paper about the QED engine spectrum, and apparently the spaceplane concept involved using conventional turbojets to get up to Mach 2 - 2.5, then QED rockets for the remainder of the flight. Total Isp was estimated to be similar to that of a turbojet (maybe up to 2500 s or so).
It seems to me that there might be benefit to using an airbreathing engine, despite the "copious ozone production". Take off with either electric QED turbojets (or conventional turbojets...) or an electromagnetic sled, and use a ram/scramjet-type QED engine to rapidly accelerate and climb to optimum thrust altitude. Once there, increase speed to very high Mach and go up and out, reaching orbital velocity or better by the time you run out of air. The only propellant required is for the circularization burn, yielding a ridiculously high Isp.
It may even be possible to design a combined-cycle engine that can go from ground start to ram/scram to rocket in one module, thus saving weight. This would be simplified by the EM-sled launch since a turbocompressor (and means of powering it) would not be required.
The disadvantage is that you'd have to design the airframe to fly at all speeds between Mach 0.8 and Mach 25. Probably not impossible even with current technology, but it sure sounds like fun.
However, I suspect Dr. Bussard's concept will need similar treatment, because lift is required to make up for the lack of thrust inherent in a high-Isp design, and thermal loads on the grid mean that reactors larger than maybe 6 GW (if we're really smart about cooling) start to scale marginally, so you can't just crank up the juice.
Besides, it doesn't have to cruise at that speed. It's like a re-entry, but in reverse.
Thoughts?
It seems to me that there might be benefit to using an airbreathing engine, despite the "copious ozone production". Take off with either electric QED turbojets (or conventional turbojets...) or an electromagnetic sled, and use a ram/scramjet-type QED engine to rapidly accelerate and climb to optimum thrust altitude. Once there, increase speed to very high Mach and go up and out, reaching orbital velocity or better by the time you run out of air. The only propellant required is for the circularization burn, yielding a ridiculously high Isp.
It may even be possible to design a combined-cycle engine that can go from ground start to ram/scram to rocket in one module, thus saving weight. This would be simplified by the EM-sled launch since a turbocompressor (and means of powering it) would not be required.
The disadvantage is that you'd have to design the airframe to fly at all speeds between Mach 0.8 and Mach 25. Probably not impossible even with current technology, but it sure sounds like fun.
However, I suspect Dr. Bussard's concept will need similar treatment, because lift is required to make up for the lack of thrust inherent in a high-Isp design, and thermal loads on the grid mean that reactors larger than maybe 6 GW (if we're really smart about cooling) start to scale marginally, so you can't just crank up the juice.
Besides, it doesn't have to cruise at that speed. It's like a re-entry, but in reverse.
Thoughts?