Reply To: General thought on old coal mines.

[zapkitty]

As with my previous musings on spacecraft power generation and fusion-powered aircraft this will assume that the FF fusion power generator proves out and operates on aneutronic proton-Boron 11 fuel close to the currently hoped-for specs.

But unlike the propfan aircraft proposed earlier for cargo and passenger transport this time we want to see what what would be needed for jet-like engines to be implemented around an FF powerplant. Jet-like in order to enable supersonic flight as the first step to orbital flight.

It gets interesting as many of the assumptions that govern the design of current jet aircraft apply themselves very differently to a fusion-powered craft… or do not apply at all.

Also of interest is the fact that many of the standing assumptions about handling nuclear fission power plants in aircraft also turn out to have radically different implications when applied to aircraft powered by aneutronic fusion.

As a useful set of parameters to shoot for in this first cut I’m vaguely thinking of an aircraft that is between the SR-71 Blackbird and Reaction Engines’ Skylon spaceplane in size and capability.

If we can show that FF can get a few people and a few tons of cargo first supersonic and then into orbit that will be sufficient proof-of-concept for now. The single-stage-to-anywhere interplanetary cruisers can follow later 🙂

First up: safety.
Given the essentially unlimited power provided by FF I do not see any real advantage in trying to leave shielding off just to save a few tons in mass.

In fact design and implementation becomes much easier if one not only starts out with standard FF shielding but embraces it to the point where a flying FF unit is essentially as well-protected as a nuclear waste transportation container… only without being nearly so toxic and radioactive.

Then the FF craft can take off, fly amongst other aircraft, fly to orbit, dock with spacecraft and stations, undock, enter atmosphere, approach an airport, land, taxi, and enter a hangar… all without any concern at all as to where the engines are in relation to anyone else.

And not incidentally things are much cheaper that way 🙂

A standard jet engine:
In a standard jet engine a compressor stage pulls in air in front and feeds that air to a “burner” stage or “burner can” along with jet fuel. The fuel is ignited and the combustion and the combustion products heat the remaining air. All this heated material attempts to expand but finds it easier to escape to the rear of the engine. It becomes the jet exhaust. Along the way additional incoming air can be entrained with the exhaust, lowering the exhaust velocity but increasing the total thrust of the engine.

All this occurs at subsonic air velocities inside the engine. Even supersonic aircraft with ramjet engines must slow the incoming air to subsonic speeds at the engine intake before attempting to burn fuel in the airstream. This deceleration of air at engine intakes is a real drag (pun intended) and is a major source of unwanted heating in supersonic aircraft. And it is also why scramjets are seen as a way to true aerospacecraft. A scramjet (supersonic combustion ramjet) allows the engine to burn fuel in a supersonic airstream inside the engine. It’s not easy to do.

Another proposed solution to the engine airflow drag issue, and one that is very relevant to an FF-powered jet engine, is magnetohydrodynamics. MHD is hoped to enable conventional turbojets to reach hypersonic speeds… without needing supersonic combustion.

In these aircraft MHD generators are to be used to absorb the energy of incoming air, converting that energy to electrical power and slowing the air to speeds a conventional jet engine can handle. Once the air has been through the “burner” in the engine the MHD would take the electrical power it absorbed from the incoming air and accelerate the exhaust as it exits the engine. An energy transfer.

I believe that’s a recap of where we are starting from… might as well be as the forum chopped the rest of my post for length 🙂

… to be continued…