Microwave Thermal Rockets
parkinresearch.com
parkinresearch.com
The summary for this link and for ground powered rockets in general, is that the amount of energy you can get out of an Hydrogen/Oxygen reduction reaction is about about it as far as chemicals go, but you can combine a lot of energy sources into a single transmission beam and if you can transfer that energy to your propellent you can do much better in terms of rocket efficiency.
The diplomatic challenge is that you need to be able to create a large directed beam of energy that you can steer at orbital (or near orbital) velocities that can reach into space. And while it is great when you're pointing it at some heat exchanger which is converting heat to thrust, its rather unfortunate if the target is a satellite just going by overhead taking pictures perhaps.
So really, in the current political climate, it's a non-starter. Not from a physics point of view but from a stir up the rest of the world point of view.
Even if 99% of the transmitted signal were absorbed, the reflected signal would be staggering, strongest signal you'd detect on the ground, probably. The world has a couple radio fences at Graves and some NAVSPASUR sites which broadcast (well) under a megawatt continuous and are pretty trivial to detect when a satellite blows thru the fan shaped beam. Then again, who's listening on (obscure microwave ISM frequency) for 10 minutes at 2am one night. Possibly no one would notice. The existing fences are well within the ability of serious ham radio operators to use for meteor scatter predictions and stuff like that. Supposedly when the fences hit the moon its quite a bloop of signal, so I've heard.
As a side note its funny to try and estimate the total wattage of millimeter wave magnetrons and solid state power amps manufactured to date by humanity and compare to the plan, its depressing. Lets say someone with a three letter agency outright bought the entire production line at triquint... Even optimistically how many millenia would it take to produce the GW required? Hmm... In this way the idea is very manhattan project like in that the hard part isn't deciding to do it or even getting the cash, but building the infrastructure to build the infrastructure two maybe three layers down to finally build the actual device. You would notice if "they" did this at area 51 because of the world wide shortage in foundry capacity followed by a staggering production glut. The world wide famine of stuff you need to build the stuff you need to build the foundry to make the amplifiers would be noticed. OK so the entire world supply of machines to build positioners that are used in foundaries has disappeared from the market, interesting.
Something everyone is very careful not to discuss is a very small scale like a hypersonic anti-missile missile for a naval ship is "reasonable-ish" or less unreasonable anyway. Rather than talking about mach 25 orbits of tons, or building naval ships to carry dozens of mach 5 self propelled interceptor missiles, why not build naval ships that carry hundreds, even thousands, of microwave boosted mach 5 interceptors?
And speaking of death beams, strategic scale will be hard to build, but something that can near vaporize an incoming sea skimming cruise missile guidance electronics is much more scalable / reasonable. I would imagine Somali style boarders would find the RF to be unpleasant. So the emitter array will be dual purpose.
So I suspect there's something like this system installed and operating at a very small cheap scale at some naval research facility right now. Area 51 was all about the air force.
Now if I disappear after posting this, we'll know I was at least partially correct...
There are already truck mounted microwave systems that are tuned to cause immense pain on your skin, for crowd control.
Changing the orbit of another satellite is very noticeable too. Much like if you were in the desert and a car came over the horizon straight at you, you'd have a very long time to do something about it.
A heat beam is a little more concerning. It is a threat that presents itself in seconds, not minutes or days. If it happens at a point where you don't have your own IR optics watching space you could miss it and be very confused as to what occurred to your sat.
The bigger challenge is while microwave emitters are cheaper, the beam director becomes quite expensive as it has to be massive (thanks to diffraction). Even with lasers, your final optics need to be big, but still easy enough to move at orbital velocities (think something like what telescopes used to track regular rocket launches use).
What the article didn't mention, is you will need 2 ground power sites. The first one applies most of the energy needed to get into orbit, and the second site, located over the horizon from first, circularizes/finalizes the orbit. This makes site selection much harder as you need to find 2 places that are not too close, yet not too far, both with little weather to get in the way.
Disclaimer: I'm involved with a company that does laser power transmission/laser rocket research
With regard to incremental improvement upon what we already have - */LOX chemical launch, we have only scratched the cheapest and simplest way to boost specific impulse for the first stage - like 3 times - and thus to decrease the total launch mass 2+ times : http://www.astronautix.com/lvs/gnom.htm (much simpler than Skylon)
"The concept was evidently been proved on a subscale tactical missile, the PR-90, now on display at MAI's museum at Orevo, north of Moscow. The PR-90, with a launch mass of only 1500 kg, of which 550 kg was payload, could reach an altitude of 40 km and a range of 100 km. The booster unit used 200 kg of RAM-10 ballistite with a specific impulse of 180 seconds to get the missile up to ram-air ignition speed. Then the air-augmented unit, with a specific impulse of 550 seconds, cut in and used 300 kg of propellant to boost the vehicle to its 1 km/s cut-off speed. An equivalent liquid propellant missile (such as the American Lance) weighed over twice as much. A solid propellant equivalent (such as the French Pluton) would weigh three times more"
All other types of thermal rockets simply provide a way for this energy to be replenished, either by external (laser, solar, microwave) or internal (nuclear) sources.
The US built nuclear thermal rockets from 1955 through the 1970s. The Soviets experimented with a few for their manned moon missions. Nuclear thermal rockets heat their reaction mass with a nuclear reactor. No nuclear thermal rocket has flown, but NASA keeps tinkering with derivatives of the Rover/NERVA programs.
Can someone explains me that? It doesn't sound very intuitive to me..
I'm surprised the Army isn't throwing money at projects like this, it looks a lot like the High Energy Liquid Laser Area Defense System.
Edit: Nevermind, I forgot the beam would be shaped like a cone, sent from a very big transmitter.
Not that much people would care anyway; solar-thermal power plants routinely vaporize birds that happen to fly in the path of the beams that are being focused.
>Similar to laser or microwave beams, longer distances require larger dishes due to the effect of optical diffraction. However, sunlight is only partially coherent (unlike lasers and masers), so regardless of the actual size of the reflector used, it behaves as if it was coherent light emitted from a reflector that is only 70 microns in diameter. It is possible to show that at a distance of 350 km, as would be needed for launching rockets to orbit, such a beam spreads out to a spot size that is 6 km in diameter.
Although the distances might be smaller if the mirror was in space, I imagine they would still not be small enough.