Non-Nuclear Open Cycle Gas Core Beamrider

Gas core nuclear thermal rockets have long been attractive in paper
studies on the exploitation of space. Their high ISPs and high thrust
have the potential to open up the entire solar system. However, the
billions of dollars that engine development would cost, coupled with
the public opposition to the perceived risks of nuclear power, combine
to block exploration of this potential for the near-future.

I have been contemplating an alternative that would combine the
staggering performance of these designs with acceptable safety and
dense, storable propellants.

The core would be a vortex of ultra-hot sodium vapor/plasma.
Surrounding the core would be another vortex of ammonia and its
decomposition products. The core would be heated by a tightly focused
beam of high-frequency microwaves, which would be absorbed by the
sodium plasma. The exhaust would be a superheated mix of hydrogen,
nitrogen, and sodium. The mix would be weighted towards ammonia,
hopefully containing only 10% or less sodium by weight. The bulk
density of the propellants would therefore be slightly higher than
that of ammonia, somewhere around 0.7. The density could be increased
for flight vehicles by sub-cooling the ammonia, up to around 0.8.

The solid walls surrounding the concentric vortex cores of the would
be designed to reflect both microwaves and visible light, and would be
cooled transpirationally by ammonia. Even cooled, the temperature of
the core walls should be kept above the boiling point of sodium, to
avoid accumulation of sodium on the engine's internal surfaces.

The window into the core would have be transparent to microwaves, but
could be opaque or reflective to visible light. It would also require
substantial cooling.

Injection of liquid sodium into the vortex would be an important part
of the engineering. I don't know much about this, but I expect that
the injector design would be similar to that for Li/LF2/LH2 designs.

The critical factor in this design is the low cost of development,
when compared to nuclear, laser, or even modern cryogenic rockets.
The propellants are cheap, fairly safe to handle and store, and the
exhaust is virtually non-toxic. Microwave generators of the required
power are also fairly cheap and off-the-shelf. Power cutoff in the
event of an accident can be achieved within microseconds.

Transmitting microwaves to the rocket is the other critical part of
the design. Clusters of large hexagonal airships, operating above the
water vapor (15-20km), would relay power from ground stations of
moderate size to the accelerating rocket. Spacing of these airborne
relays would be on the order of every 300km along the launch path.
Distance from the relay to the rocket during powered flight would be
under 200km.

Getting microwave power from airships in the high atmosphere limits
the amount of final velocity you expect to deliver from this system.
15km/sec is about the best you can hope for. A large orbital system,
combining a solar concentrator/powerplant and a giant fishnet
microwave transmitter, placed in or near L4 or L5, could boost rockets
using this thruster up to perhaps 50km/sec, which would be around the
single stage maximum you could expect from a 2000sec ISP rocket.
50km/sec should be enough for fast trips even to Saturn. The return
trip would be tricky, though.

In conclusion, I believe a gas core microwave beamrider can deliver
high ISPs (2000?) combined with high thrust (1mN), without requiring
politically unacceptable nuclear power.

Charlie wrote:


The critical factor in this design is the low cost of development,
when compared to nuclear, laser, or even modern cryogenic rockets.
The propellants are cheap, fairly safe to handle and store, and the
exhaust is virtually non-toxic. Microwave generators of the required
power are also fairly cheap and off-the-shelf. Power cutoff in the
event of an accident can be achieved within microseconds.

Even if that's so, how much would the required amount of microwave
grnerators weigh? How much volume would they occupy? Same question of
their power source. And the waste heat radiators. And the support
structure for it all. This matters, if you intend to push a spaceship
with it.

Remember, we can also acheive fusion by directing beams of heavy
hydrogen nuclei at each other, but the energy released doesn't come
anywhere near that which the particle accelerators require, much lesa a
surplus. This sounds to me like that.


--

You know what to remove, to reply....

(Charlie) wrote in message . com...
Gas core nuclear thermal rockets have long been attractive in paper
studies on the exploitation of space. Their high ISPs and high thrust
have the potential to open up the entire solar system. However, the
billions of dollars that engine development would cost, coupled with
the public opposition to the perceived risks of nuclear power, combine
to block exploration of this potential for the near-future.
snip

The core would be a vortex of ultra-hot sodium vapor/plasma.
Shouldn't be needed. The ammonia should absorb microwaves well enough
once initially ionized. Perhaps an electric discharge.

Surrounding the core would be another vortex of ammonia and its
decomposition products. The core would be heated by a tightly focused
beam of high-frequency microwaves, which would be absorbed by the
sodium plasma. The exhaust would be a superheated mix of hydrogen,
nitrogen, and sodium. The mix would be weighted towards ammonia,
hopefully containing only 10% or less sodium by weight. The bulk
density of the propellants would therefore be slightly higher than
that of ammonia, somewhere around 0.7. The density could be increased
for flight vehicles by sub-cooling the ammonia, up to around 0.8.

sodium core dropped

The window into the core would have be transparent to microwaves, but
could be opaque or reflective to visible light. It would also require
substantial cooling.

Ceramic construction, preheat propellant in regenerative cooling.

sodium dropped

The critical factor in this design is the low cost of development,
when compared to nuclear, laser, or even modern cryogenic rockets.
The propellants are cheap, fairly safe to handle and store, and the
exhaust is virtually non-toxic. Microwave generators of the required
power are also fairly cheap and off-the-shelf. Power cutoff in the
event of an accident can be achieved within microseconds.

Transmitting microwaves to the rocket is the other critical part of
the design. Clusters of large hexagonal airships, operating above the
water vapor (15-20km), would relay power from ground stations of
moderate size to the accelerating rocket. Spacing of these airborne
relays would be on the order of every 300km along the launch path.
Distance from the relay to the rocket during powered flight would be
under 200km.

Getting microwave power from airships in the high atmosphere limits
the amount of final velocity you expect to deliver from this system.
15km/sec is about the best you can hope for. A large orbital system,
combining a solar concentrator/powerplant and a giant fishnet
microwave transmitter, placed in or near L4 or L5, could boost rockets
using this thruster up to perhaps 50km/sec, which would be around the
single stage maximum you could expect from a 2000sec ISP rocket.
50km/sec should be enough for fast trips even to Saturn. The return
trip would be tricky, though.

In conclusion, I believe a gas core microwave beamrider can deliver
high ISPs (2000?) combined with high thrust (1mN), without requiring
politically unacceptable nuclear power.

Joann Evans wrote:
Charlie wrote:


The critical factor in this design is the low cost of development,
when compared to nuclear, laser, or even modern cryogenic rockets.
The propellants are cheap, fairly safe to handle and store, and the
exhaust is virtually non-toxic. Microwave generators of the required
power are also fairly cheap and off-the-shelf. Power cutoff in the
event of an accident can be achieved within microseconds.

Even if that's so, how much would the required amount of microwave
grnerators weigh? How much volume would they occupy? Same question of
their power source. And the waste heat radiators. And the support
structure for it all. This matters, if you intend to push a spaceship
with it.

The idea is I think that the microwave generators are not on the
ship, just antennas to focus and transmit it to the chamber from
a source on the ground/atmosphere.
This is a smaller, though not tiny problem.

Joann Evans wrote in message ...
Charlie wrote:
Even if that's so, how much would the required amount of microwave
grnerators weigh? How much volume would they occupy? Same question of
their power source. And the waste heat radiators. And the support
structure for it all. This matters, if you intend to push a spaceship
with it.

The mass of the microwave transmitters and the power source is
irrelevant to the performance of the rocket, because they are not part
of the rocket. The microwave transmitters would be integrated into
the upper surface of hexagonal airships. The power source would be
the terrestrial power grid.

Separate waste heat radiators might be required, as they are in most
4000+ ISP nuclear gas-core designs where regenerative cooling is
insufficient. They would decrease the T/W ratio of the engine, but it
can only be determined experimentally how much.

(Peter) wrote in message . com...
(Charlie) wrote in message . com...
The core would be a vortex of ultra-hot sodium vapor/plasma.
Shouldn't be needed. The ammonia should absorb microwaves well enough
once initially ionized. Perhaps an electric discharge.
...
Ceramic construction, preheat propellant in regenerative cooling.

Yes, ionized ammonia should be capable of absorbing microwave energy.
However, I am not convinced that a beamrider using a simplified
ammonia-only thrust chamber would be able to achieve gas-core
performance levels.

One of the major pluses of this concept is that it would develop
valuable experience in gas-core engine building that would eventually
be useful in fission-powered GCNTR applications.

There is no question that it is possible to heat your ammonia
propellant directly with microwaves. Small engines using that
methodology have already been built and tested. I do not believe that
they have generated a measured ISP higher than 700sec, though.

Note, there is little reason to develop high ISP microwave rocket
motors unless they get MUCH higher T/W than existing ion/Hall/MPD
systems.

Substantial paper-study design work has been done on gas-core engines.
This is a suggestion to leverage much of that completed work to
enable high ISP, high thrust rockets to complete their development and
begin flight testing as quickly as possible.

--

Some rocket scientists would assert that ISP's in excess of 1200
seconds or so are overkill for LEO/GTO/Translunar work. I would
disagree. In addition to allowing airlaunched small (100) ton
rockets to deliver very substantial payloads, very high ISP's would
also permit rocket engineers to consider the concept of killing most
of your orbital velocity under power before beginning reentry.

In article ,
Charlie wrote:
...In addition to allowing airlaunched small (100) ton
rockets to deliver very substantial payloads, very high ISP's would
also permit rocket engineers to consider the concept of killing most
of your orbital velocity under power before beginning reentry.

Bear in mind that you have to be able to do a reentry without this, to
cover abort cases. That considerably reduces the benefit.

Note also that we know how to build lightweight, reliable heatshields with
large safety margins, provided they don't have to be reusable. And the
technology is *nearly* in hand to do the same for reusable systems...
provided you don't insist on them having wings.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |