
Microwave Thermal Rockets - Ankaios
http://parkinresearch.com/microwave-thermal-rockets/
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ChuckMcM
Ah microwave beamed rockets. Such a wonderful sounding idea, and yet so
difficult to pull off. For those of you who know Keith Hensen his Solar Power
Satellites are best launched into orbit with laser powered (or more generally
ground powered) rockets. And the concept is mathematically sound, just the
notion of having a multi-gigawatt laser pointed up at things in orbit is so
destabilizing.

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.

~~~
beamatronic
Could you not hide a powerful ground-based laser anywhere you have a
significant existing infrastructure? If there was one at say, Area 51, would
we have any way to know?

~~~
VLM
Even with local power storage the grid demand would be noteworthy and you'd
notice some impressive power lines going into the desert just to keep up with
average demand.

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...

~~~
stcredzero
_I would imagine Somali style boarders would find the RF to be unpleasant. So
the emitter array will be dual purpose._

There are already truck mounted microwave systems that are tuned to cause
immense pain on your skin, for crowd control.

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trhway
a launch system with externally supplied energy is a massive infrastructure
project. If we muster a capability for large infrastructure project a huge
railgun launch would be much simpler.

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](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"

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krallja
Cold gas thrusters (DIY by inflating a balloon and then letting go) operate on
the same concept: the energy stored in the compressed gas is released through
the nozzle, providing thrust.

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.

~~~
geuis
Link to nuclear thermal rockets,
[https://en.wikipedia.org/wiki/Nuclear_thermal_rocket](https://en.wikipedia.org/wiki/Nuclear_thermal_rocket).
Thanks for mentioning that, its a really interesting read.

~~~
zardo
This website is meant as a tool for hard Sci-fi writers, but its a great read
on nuclear rockets.

[http://www.projectrho.com/public_html/rocket/enginelist.php](http://www.projectrho.com/public_html/rocket/enginelist.php)

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pingou
"If a bird flew just above the beam director during operation, the power
density it would experience is 1,000 times lower than at the rocket, which is
well above the altitudes of birds and planes"

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.

~~~
TeMPOraL
I assume it's because the bird will be flying very far below the focal point.

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.

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transfire
Could the microwave source be put in orbit? This might make it easier to track
the rocket as their relative speeds would become closer and closer as the
rocket reaches orbit. One could imagine standard jet propulsion for the first
stage, before the microwave rocket kicks in.

~~~
maho
To me, the better idea would be to place mirrors in orbit that focus solar
radiation on the rocket. A sort of ground-based-microwave/space-based-solar
hybrid rocket.

~~~
arijun
From the FAQ in the article:

>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.

