Reply To: EmDrive + Focus Fusion = Space Access for all?

[Aeronaut]

texaslabrat wrote:

If the power density of the fusion power sources were sufficiently high (in terms of MW/m^3 and/or MW/kg) , that’s definitely feasible from at least a basic conceptual point of view (ignoring the complexities of the actual aircraft and propulsion system design). A lot of optimization and miniturization of the fusion source will be necessary to make this kind of system do-able for atmospheric flight propulsion.

One of the “advantages” of conventionally fueled craft is that they get lighter as they travel. With a FF powerplant instead, all the weight is constant. I presume there is some crossover point where a specific fixed weight fusion generator is more efficient than than a powerplant running on conventional fuel that gets lighter over time. But it is not immediately obvious that such crossover point can be easily reached — my guess is the fusion plant in such instance would have to be very light relative to its on-the-ground, fixed instantiation.

And I’m still not convinced that there would be any major advantage to such a system. As I noted earlier, the real problem with most launch systems isn’t lack of power per se (at least not power on the scale that an FF device would generate).

I’m not convinced it would be feasible in the near-term by any stretch…fitting probably a GW of power production into a space-worthy airframe (never mind the issues of power distribution within the craft) meant to take off from a runway presents issues that are non-trivial to say the least.

And while you say that an “advantage” of a conventional plane is that it gets lighter as it travels…I’ll counter by saying that a sufficiently miniaturized power source STARTS light so therefore has a huge advantage. Not having to carry the structural weight of a changing fuel load greatly simplifies the airframe design as well as makes the balance points and other dynamic issues easier to predict and control. That was the point I was trying to get across…that you would need to make the power source VERY small and VERY light to be advantageous over a conventially fueled craft…but if you could do so…it would revolutionize air (in addition to space) travel as you could then have non-range-limited aircraft in addition to the spacecraft previously discussed. All for a bit of boron…not too shabby. Very much “pie in the sky”…but an interesting thought experiment for sure.

In the mean time, I’ll still be putting my money on the space elevator tho 😉

The rocket equation taxes the living daylights out of any mass, weather it’s needed or not. Imagine ditching not only the boosters, but redesigning the payload structure so that it has no aerodynamic or re-entry heat loads to deal with. Now the remaining questions should be

1. How much is NASA going to blow on the mars program?
2. Why not use those monies to build an elevator on both planets?