Heat exchanger laser launch

Anyone know the status of research on heat exchanger laser launch
technology? By that I mean a vehicle that carries a propellant (maybe
ammonia) that runs through a heat exchanger in the skin of the vehicle,
is heated by a ground-based laser, and is exhausted through a nozzle,
thus propelling the vehicle spaceward.

Googling brings up mention of various papers and symposia on beamed
propulsion but is anyone actually _building_ anything? I was under the
impression that small bench-top trials could be done without lasers,
using other, cheaper heat sources.

There is nothing that says it can't be done. Its just that a laser big
enough, narrow enough and at the right frequency hasn't been built yet.
Glass lasers show some promise for such things and are in use at NIF.
So it is possible, I just don't think anyone has deceded to put the
money into it yet. It basically boils down to a materials problem.
Though you could probably use multiple lasers to focus on the ships.
You would do so at an decrease in efficentcy.

:

Anyone know the status of research on heat exchanger laser launch
technology? By that I mean a vehicle that carries a propellant (maybe
ammonia) that runs through a heat exchanger in the skin of the vehicle,
is heated by a ground-based laser, and is exhausted through a nozzle,
thus propelling the vehicle spaceward.

Googling brings up mention of various papers and symposia on beamed
propulsion but is anyone actually _building_ anything? I was under the
impression that small bench-top trials could be done without lasers,
using other, cheaper heat sources.

I don't either, but please post links if you see anything. I believe
microwaves can be used the same way too, and a microwave emitter should be
cheaper than a laser setup, I think.

Earl Colby Pottinger


--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

Earl Colby Pottinger wrote:
:

Anyone know the status of research on heat exchanger laser launch
technology? By that I mean a vehicle that carries a propellant (maybe
ammonia) that runs through a heat exchanger in the skin of the vehicle,
is heated by a ground-based laser, and is exhausted through a nozzle,
thus propelling the vehicle spaceward.

Googling brings up mention of various papers and symposia on beamed
propulsion but is anyone actually _building_ anything? I was under the
impression that small bench-top trials could be done without lasers,
using other, cheaper heat sources.

I don't either, but please post links if you see anything. I believe
microwaves can be used the same way too, and a microwave emitter should be
cheaper than a laser setup, I think.

I saw a paper on this...
Aha.
http://monolith.caltech.edu/Papers/ParkinLauncher.pdf

140-240Ghz microwaves impact on (IIRC) a 2m diameter carbon fiber heat
exchanger, for an ISP of around 1000, for a largely hydrogen propellant
vehicle.

Jordin Kare did a presentation on this at Space Access. His work
implies that it could be done at this point, but not very effectively.
Basically, the rocket design is simple (though he has some interesting
techniques on optimizing the heat transfer), testing the design is
simple (any heat source will do), the design is reasonably effifcient,
it get good Isp (700s), BUT - the lasers are a problem.

Current technology is good enough, but very expensive and very large.
The problem is that a single coherent source is not available, so you
have to use non-coherent laser clusters (As in point a bunch of lasers
in the same direction). The problem being that noncoherent energy
scales with the square root of the number of sources - so to take the
inexpensive 1KW lasers that are available up to 1MW of delivered power
(orbit is about 1MW/kg according to Jordin) would require 1 million
lasers. Under a billion dollars possibly, but a logistical nightmare!

However, at the conference he mentioned that three new methods for
coherently combining lasers have come out - so he is hopefull that this
will soon be a viable option.

I wonder if the size of the vehicle was chosen because of limits on how
small the beam can be? It seems they chose up to 19g acceleration
because of the need to do all the accelerating while the ship is in
sight of the microwave array. Would it be that big a deal to build a
series of smaller microwave arrays, spaced out over 1000 km, and
passing the vehicle from one array to the next? Obviously the cost is
higher but then acceleration can be kept lower, allowing human flight.

If tabletop testing can be done with any heat source, the rocket design
is simple, and the Isp is high, a proof-of-concept demo would seem to
be a project crying out for a NASA grant. I wonder what the
requirements would be for a tiny, sub-orbital,
launch-straight-up-to-100km demo?

The real disadvantage to using microwaves is the spot size on the
spacecraft. Jordin Kare's analysis showed that once the spacecraft was
most of the way to orbit, an optical system would only be delivering
about half of the energy output onto the vehicle. With microwaves,
that would be much worse.

There are probably ways around this though. Perhaps using some
material with a negative permeability could focus more tightly. Those
materials exist for microwaves, but are challenging for optical
wavelengths.

wrote:
I wonder if the size of the vehicle was chosen because of limits on how
small the beam can be? It seems they chose up to 19g acceleration
because of the need to do all the accelerating while the ship is in
sight of the microwave array. Would it be that big a deal to build a
series of smaller microwave arrays, spaced out over 1000 km, and
passing the vehicle from one array to the next? Obviously the cost is
higher but then acceleration can be kept lower, allowing human flight.

Human testing has proved that taking 19G for 1 minute is quite possible.
Which takes you to most of orbital velocity.
Bloody unpleasant, but possible, at least for selected humans.

The arrays would have to end up nearly the same size - otherwise they
wouldn't have the focus I suspect.

In article .com,
"David Summers" wrote:

The real disadvantage to using microwaves is the spot size on the
spacecraft. Jordin Kare's analysis showed that once the spacecraft was
most of the way to orbit, an optical system would only be delivering
about half of the energy output onto the vehicle. With microwaves,
that would be much worse.

There are probably ways around this though. Perhaps using some
material with a negative permeability could focus more tightly. Those
materials exist for microwaves, but are challenging for optical
wavelengths.

Another possible approach would be to hand off powering of the craft to
an orbital source. This could probably be located in LEO, so it
wouldn't need to have an enormous antenna. But it would itself need a
pretty massive power source -- either a huge solar array and well-timed
launches, or a smaller array with a large power storage system (perhaps
ultracapacitors). Certainly not cheap infrastructure, but if it's the
sort of thing that enables low-cost, high-rate launches, maybe it'd be
worth it.

- Joe

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'