I think that puts that concept squarely into a box that excludes civilian/commercial applications
I don't think so. If the military can loft 12 000 pounds of satellites into orbit this way (see the screenshot I posted up thread), there is no reason the civilian market can't loft 12 000 pounds of... passengers later on.
I agree, let's the military pioneer the risks and we shall see.
just like aerial refueling is used nowadays by the military only, but by exactly none of any and all commercial airlines anywhere around the globe.
I disagree with that point of view. NOT about what you say - correct, no airline uses aerial refueling - but the rejection of aerial refueling as risky for the passengers.
Space travel is inherently risky. If we want to ferry tourists in orbit, risk will be superior to airline flight. Riding a Starship will be far riskier than taking a ride in an A380.
Then, I can't see why the risk of refueling would be more *unacceptable* than any of the other risk of classic rocketry or human space travel. Note that Ranulf mentions how the system abort modes are extremely begnin, as underlined by Jon goff here
The nice thing about such a setup is that if you do things right, most worst-case failures result in an aborted mission, not a loss of vehicle.
If one of the TSTO pairs doesn’t ignite when air-dropped, you abort (with the upper stage from that TSTO combo having enough propellant to make it home, and you only have to figure out what to do about the first stage).
If you can’t mate up in time, you abort.
If the QD doesn’t work, you abort.
If you can’t keep the vehicles together exoatmospherically, at worst the boom/hose fails, and you use hydraulic fuses to keep that from becoming a loss of vehicle event.
Now, there are many more things that can cause an abort in this scenario, but many of them are things that should get more reliable with practice.
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More on the military mission. What I have in mind for a twin keroxide Mk.1 rocketplane is very much something akin to
- Bantam (NASA)
- Rascal (USAF)
- Falcon (USAF)
- ALASA (Clapp was involved in this one, incidentally !)
- XS-1 (DARPA)
Or, reaching further in the past...
- TAV (Trans-Atmospheric Vehicle)
- ALSV (Air Launch Sortie Vehicle)
- ISINGLASS
- Aerospaceplane
Back in the 80's at Langley James A. Martin called it "orbit on demand". More recently it is called "responsive space".
What I mean is that the basic obsession of USAF with spaceplane is
- takeoff from any AFB
- go into orbit
- drop the satellite
- return to AFB
- refurbish, maintenance, 24 hours, rinse, repeat.
That's their absolute Holy Grail since 1959.
Well, then a turbofan+rocket spaceplane, with a suborbital refueling, is the one and only system that can achieve that dream, 100%. I mean, it checks every single box above.
Get the rocketplane out of the hangar with its payload. Fill it with kerosene, then with H2O2. Light the turbofans, climb to 50 000 ft, mach 0.95, raise the nose to 30 degree above the horizon, light the rocket, shut the jets, climb to 5 km/s and 50 miles.
There, throttle down, perform a brief oxidizer transfer via an identical "buddy" tanker.
Throttle-up again, ascent to orbit, drop the satellite.
Then re-enter the atmosphere, land on turbofan power at any airstrip under the trajectory. Once on the ground, take a load of kerosene, and fly subsonically back to the launch site.
Alternatively, you could load a C-5 or a C-17 with a large tank of H2O2 and send it at the landing site. There it meets with the rocketplane and pass it a load of oxidizer. This would allow for a new mission to proceed !
The CONOPS is simple. The only tricky part is the refueling. That's simplicity, is why I like this concept so much.
Suborbital refueling is not even necessary if you replace it (and the buddy tanker) with an expendable upper stage.
The twin flaws however, in this case are
a) the rocketplane don't go into orbit
b) the upper stage is expendable
Still an interesting solution to launch loads of cubesats. That's the exact shift Clapp and Zubrin made in 1996 when going from "Black Horse - speculative idea" to "Black Colt / Pathfinder." Unfortunately they were wrong.
"Suborbital refueling via a buddy tanker" is far more interesting than "subsonic refueling + expendable upper stage".
Yet Clapp and Zubrin picked the second solution in order to not scare commercial customers - after the Air Force abandonned the Black Horse concept.