zapkitty wrote:

i meant the THz laser beam

At what efficiency is the beam expected to operate?

To be determined. I don’t have detailed-enough spectral charts to assist with the task of optimizing it, and spectroscopy guys tell me to be prepared for the possibility that the data might not yet exist — so there’s science to do. The emitters would likely be a large array of nano-klystrons.

For comparison, quartz heaters are 85% efficient at heating objects *without* heating the air, but they operate as blackbody radiators, with bulge around 100 THz.

We’ll be looking for strong absorption lines for air, in the 1 to 6 THz spectrum, that remain strong over a range of temperatures from about 240 to 2000 kelvin.

Atmospheric pressure is ~0.01 bar at 35 km. We’ll want to know the path length for 100% absorption, here.

240 K is the inlet temperature at 35km altitude; and 2000 K is the upper bound to avoid production of NOx. Keeping this squeeky-clean on the environment sure would help to sell it.

2000 from 240 K is an 8:1 increase in pressure, as gas flows through the expansion tube. the scramjet design does not slow the gases. for low speeds, the air inlet shape might have to change to avoid back-pressure in the tube. there are several ways to accomplish this (including the plasma window).

Yes, this could go into a surface-to-orbit vehicle. Being an air-breathing engine while flying through atmosphere, it will really save on propellant. Mach-24 horizontal flight at high altitude is the magic threshold that will make it possible. We can expect, if this works at all, to see the classic shock diamonds characteristic of rocket thrusters and scramjets.