HermannH wrote:

As I mentioned before, an F-16 (a small, single-engine, lightweight fighter) in full afterburner consumes the rough equivalent of 300 MW. The top speed of an F-16 in full afterburner is about Mach 2.0 at altitude. Believe me, you’re gonna need power in the GW scale to even think about a hypersonic high-altitude first stage or a hypersonic trans-continental aircraft. As a “fun fact” comparison, each of the 5 Saturn V first-stage engines consumed a heat-content equivalent of over 30GW. It’s hard to wrap your head around the shear power requirements needed for high-performance flight..but they are indeed quite steep.

This is the crux of the story. The F-16 can generate power at a rate of 300 MW, but only for about an hour or two. After that the tank is empty.
A FF reactor will probably never produce enough power to lift itself into low earth orbit. The power to weight ratio is way too small.
Once you are in orbit and want to travel to distant planets or solar systems the story is different: you can let the engine burn for days or months and keep picking up speed. 5 MW for a couple of months beats 300 MW for a couple of hours.

Actually, an F-16 can produce 300MW for about 11 minutes before the tanks go dry so it’s far worse than even that scenario. But it’s apples-to-oranges since a FF-powered craft would, for all practical purposes, never run out of fuel and thus could take a longer path to achieve a given speed and altitude as long as it could get off the ground in the first place. My main point (as you’ve mentioned) is that the power-to-weight and power-to-volume of FF would have to be DRASTICALLY improved from today’s concepts/prototypes to be suitable for flight due to the enormous amounts of power required. Not saying it can’t happen (never bet against the ingenuity of motivated engineers)…just that there are probably easier technical avenues for achieving orbit and subsequent space flight (eg space elevator + FF-powered ion engine).

And by the way, the basic premise of the FF-powered aircraft (as envisioned by belbear in this thread) is not new. Look up “project Pluto” for a “blast from the past” 😉