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August 30, 2007

Fuel scooping variable Minimag Orion proposal

A recent paper "Use of Mini-Mag Orion and superconducting coils for near-term interstellar transportation" discusses using a massive laser beam to accelerate fuel pellets to catch up to and supply a minimag Orion with fuel. The 1000 ton minimag Orion could then accelerate to 10% of light speed. The laser array would need 2500 times the electrical power of the United States in 2007.

I am making proposals that would help to get rid of the need for a laser array that uses 2500 times the electrical power that is currently generated in the USA as a prerequisite to interstellar or solar travel. Needing a monster laser array and mass production of 250,000 nuclear power plants seemed to be something that would delay the arrival of interstellar travel a long time.

My proposal pre-deploys a bread crumb trail of nuclear fuel pellets which would be scooped up by the nuclear rocket. The giant laser would not be needed or could be greatly reduced in size and performance. Existing technology or very achieveable technology and infrastructure is enough. We can have ships slowly leave multiple trails of nuclear fuel pellets which would be gobbled up by the nuclear rockets similar to the old video game Pacman.


Pacman gobbling up dots

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minimag Orion

Good old fashioned project Orion rockets are designs from the 1960's that used nuclear pulsed propulsion You fire a series of small (100-1000 tons of TNT equivalent) bombs through a hole in a large metal disk. the bombs explode and push the large metal disk with your rocket attached to it. You can then accelerate massive space ships to high speed. 6000 to 100,000 ISP were possible for nuclear fission versions and 1,000,000 ISP for nuclear fusion.


Project Orion vehicle image

Minimag Orion uses sub-critical explosions (not quite full nuclear bombs) that are initiated using magnetic Z-pinches. The explosions are about 5 to 10 tons of TNT equivalent.

They were talking about the minimag as being something that could not be as easily weaponized as good old fashioned Orion's.

However, using ye old impact calculator, for something about 1000 tons

If that object was turned around, it would hit with 251 megatons of force going at 1% of lightspeed.

Going at 10% of lightspeed it would hit something with 25,000 megatons of force.

Also, the GW to TW to PW laser arrays would be pretty threatening too (especially relative to a few thousand measily 100-1000 ton explosions.)

If you are cruising around the solar system at high speed then you are powerful no matter what. In which case, we should crank this up to critical explosion levels and just figure out how to get the maximum performance out of it.

I think we could get a variable minimag Orion/full Orion where we configure it for rapid subcritical explosions to launch from the ground. And then crank it up to critical explosions once we clear the atmosphere.

Fusion powered version of Orion could get to 1 million ISP.

The more advanced levels of Gabriel (from a recent Nasa re-examination of Project Orion)
1. Mark I: Solid pusher plate and conventional shock absorbers (small size, possible with current technology)
2. Mark II: Electromagnetic coupling incorporated into the plate and shocks (medium size, Mark II and beyond require some research and development)
3. Mark III: Pusher plate extensions such as canopy, segments, cables (large size)
4. Mark IV: External pulse unit driver such as laser, antimatter, etc. (large size)

The Mark II starts getting the electromagnetic coupling that minimag Orion has.

I also had an idea that we could start firing sheath/pellets out in front of the minimag Orion before we launched the minimag. The minimag could scoop up slower moving pellets as they caught up to them on their flight path. We could then use a less powerful laser accelerator and/or let the minimag climb to higher speeds than we can accelerate the pellets. We would need to research on a way to get a pellet scooper created that would safely scoop up slower moving pellets. The pellet bread crumb stream could be laid out years in advance of the launch of the minimag. It would be an artificially created fuel stream similar to the principle of the Bussard ramscoop which was to scoop up interstellar hydrogen to power a fusion rocket.


This is a representation of the Bussard Interstellar Ramjet engine

Laying out pellet streams for our pacman minimag Orion or fullblown Orion would be a boost in performance to any one of the Orion concepts. The rocket would not need to carry most of the fuel.

So
1. Minimag subcritical ground launch. It would be wasteful in performance in a couple of ways. In order to switch to full Orion mode later we would not have the weight savings from the flimsy mesh for catching the subcritical plasma. However, simultaneously firing off 100 ten ton explosions would be about as good as one 1000 ton. It would be going back to bigger ships. However, detailed scaling and designs would be needed. Advanced materials (carbon nanotubes, nanograin metal) could still allow for a fairly light pusher plate relative to 1960's versions.

2. Variable and tuneable Z-pinches so that the system converts to higher performance full criticality explosions once it is passed the atmosphere and a certain distance from earth. Some more complexity in the design.

3. System for efficiently laying out a fuel pellet stream years in advance and creating a pellet catcher scoop for the variable minimag Orion. Might not need much of a sheath for the fuel pellets. We could use pellet droppers. We also would need supercomputers to calculate and account for any drift for the pellets from the time they are deployed until the time they are scooped.

Photonic laser propulsion with mirrors to reflect the light 1000-100,000 times could be used to propel the fuel pellet droppers The reason would be that the mirror reflections would let us use far smaller laser arrays say only a gigawatt. The multi-stage and planned aspect of fuel deployment for a nuclear rocket means that we can get a far bigger ship going to 10% of light speed than we could with the same size lasers and power sources.

The proposals that I am making would involve more planning, but the tolerances and requirements for the system are relaxed. We can use a far smaller laser and power sources that are 1% of our current electrical production instead of 250,000% of current electrical production. Costs come way down.

What is needed?
Still need a working minimag Orion.
Need a fuel pellet deployment system.
Need a fuel pellet scooping system, which is probably magnetically based.
Ideally and optionally design and create a variable minimag Orion that can transition to full Orion mode.

UPDATE: Improved fuel pellet deployment

Jim Moore in the comments mentions the inefficiency of scooping up stationary or slower pellets. However, we still would like to avoid laser arrays and power sources that are 2500 times the current electrical production of the United States.

My new solution is to develop Mason Peck's lorentz force propulsion capability

Peck wants to use natural forces to propel starships no bigger than the integrated-circuit chips in your computer. Specifically, he would harness the Lorentz forces that drive charged particles in magnetic fields, and which physicists use to whip bits of atoms to hellacious speeds in giant particle accelerators on Earth. Jupiter, with a rapidly rotating magnetic field 20,000 times stronger than Earth’s, packs a powerful Lorentz punch. Spacecraft like Voyager and Cassini routinely use gravity boosts from large planets to gain acceleration; why not use Lorentz forces as a means of propulsion too? Boosts from rotating magnetic fields could theoretically accelerate spacecraft to speeds of 1 to 10 percent of the speed of light, according to Peck’s early calculations. Because this free energy source works best on small objects, he suggests building a really tiny starship. Extrapolating from today’s state-of-the-art, he assumes we can solve the practical problems of nano-fabricating a spacecraft-on-a-chip, a single semiconductor crystal only a centimeter square and weighing less than a gram. One side would consist of solar cells for power. A rudimentary radio antenna and digital camera would be etched or deposited on the other. Attitude could be controlled by spinning the spacecraft and by torquing against the magnetic field, a technique already used for Earth-orbiting satellites.


Improved electrostatic charge density can be achieved using carbon nanotubes. The increased charge could allow us to scale up the object to move the 80 gram pellet at the correct speed.

While micron-thick wire can be used, the limiting configuration is a fiber consisting of carbon nanotubes. With a capacitance per length of perhaps 4×10-11 F/m values of q/m approaching 3×10**6 C/kg can be achieved for a single nanotube.



self-capacitance architectures

Mason Peck's paper on millimeter scale spacecraft for interstellar travel

So we combine the ability for tiny spacecraft to use propellantless means to achieve high speeds (1-10% of lightspeed) and use that as a means to have an accelerated stream of pellets without the monster laser array and power. The challenge becomes one of the nano-fabrication of the lorentz propelled pellet-ships.

I think the my proposal could be achieved with a few tens of billions of dollars and 15-20 years of dedicated development.


FURTHER READING
My recent article examining the new minimag Orion paper and concept

Earlier article on minimag Orion

Article on updated Project Orion concepts

Examination of Nuclear thermal rockets

Photonic laser propulsion

My early article on using laser array propulsion

Project Orion info online

6 comments:

jim moore said...

interesting post, but your pellet catcher will expend a lot of energy. You will need to accelerate the pellets from their current velocity to the velocity of the ship when they intercept one another. The faster you go the more energy the pellet catcher will need. Now i am not saying that the idea isn't a good one, but it may not be as efficient as one would like it to be.

bw said...

Updated my article with lorentz propulsion to accelerate tiny ships to 1-10% of lightspeed as a mean to get pellets up to speed.

Tom Craver said...

If I read what you intend correctly, you plan to "catch" the pellets?

Once you hit 1% of C (perhaps before), why not just let them slam into a target mass a bit behind the ship, and use the resulting explosion to propel the ship? The faster you're going, the less mass the target has to have.

Or is that actually what you had in mind?

Tom Craver said...

And if the target mass is designed so the collision triggers fusion, that would seem to get you an even bigger boost.

bw said...

Tom,

I had not worked out the catching of the pellets. Either the pellets are slower and the craft overtakes them and catches/scooops or they are faster. With potentially far faster pellets from lorentz propulsion, slamming into the pusher plate makes sense.

Frogwatch said...

Back when Andrews first published on MiniMag orion, I immediately did a calculation on the fuel pellet trail idea and then realized that it is easier to produce a neutral particle beam of fuel. We would arrange things so the beam velocity is always zero wrt the ship meaning we have to launch fuel beams waaay before we launch the ship. However, it is easier to collect such a beam than to collect pellets, you simply follow the beam.
Beam current would be very high, I cannot remember the numbers but it was Meg-amps or so and requires that the beam is then neutralized. The advantage of such is that such a beam can be aimed toward various destinations easier than a pellet launcher. Such a neutral beam device could also be used to support several missions at once by magnetically steering the beam and pulsing it.
The beam device would be built in solar orbit to support missions to outer planets and to inter-stellar missions. Thus it would be available for multiple missions.
The advantage of this is that although the actual energy expenditure may be higher than carrying the fuel, it means the ships engines can be smaller because it does not have to carry the fuel.
A similar calculation can be done for a Xenon based electric thruster getting to .1c where power is provided by a nuke reactor and we simply scale up the NASA Deep Space 1 thruster. We use a neutral Xe beam. It looked reasonable except for the large amount of expensive Xenon. However, i have just heard of a "helicon" thruster using nitrogen gas.............