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View Full Version : It's a drive system! It's a particle weapon! It's both!



Professor Tanhauser
2008-Sep-27, 11:05 PM
I looked over the forums for a minute to decide where this topic would fit in best, and honestly decided this was the place, so if I'm wrong please don't think I didn't at least try to get this in the right place.

Now I have a question that I can imagine some people here just rubbing their hands together in glee as they prepare to type a lengthy answer, so I hope that people here enjoy answering it as much as I hopefully will enjoy having it answered.

The question is this: Could an ion engine serve as a particle beam weapon?

Seriously, it occurs to me that an ion engine essentially emits a hail of highly charged particles as high velocity. Hmm, charged particles and high velocity, don't they call that "hard radiation" in some cases? :eek:

One proposal for a space based particle beam weapon called for the weapon to project a stream of hydrogen atoms with high charges, producing a neutral particle beam that would remain coherent in space.

Well, isn't that somewhat like what an ion engine does, tho usually with bigger atoms, like mercury and cesium?

I basically wonder if a large ion engine could be used as a particle beam weapon, or it it might cause damage or disruption, possibly radiation damage, to nearby things even if not used as a weapon. I mean, if I were on a near future spacecraft I don't think I'd like the exhaust from an ion engine hitting my radar array.

I know that in space solar radiation will be a major factor and things will need to be shielded against that, so maybe an unfocused ion engine exhaust wouldn't be that dangerous, but, ah, but, would it be possible to focus the exhaust of an ion engine, perhaps making it coherent and therefore much more concentrated and powerful?

In his known space and man/kzin wars series, larry niven proposed that a fusion drive would make a potent weapon and that "crude" fusion engines devastated invading kzinti fleets equipped wth advanced gravity polarizer drives. I wonder if an ion engine, perhaps with a few mods or custom buil;t for the purpose, might also serve as a less spectacular but possibly useful weapon. Anyone here have any ideas on this?

dgavin
2008-Sep-27, 11:50 PM
Ok, i may be a bit dated here, as I'm basing my statement on the DS-1 Ion Drive which is the one I have some understanding of.

To sum it up the answer is no. Ion drives work by Ionizing a gas inside a negatively charged chamber, where the exit is opposite the gas injection area, and is a positively charged mesh like screen.

The charged Ion's accelerate away from the chamber (this is part of the thrust) towards the exit screen. As the gas passes through the positively charged screen, it loses some of it's extra electrons. And continues to lose these extra electrons until it's electrically neutral again.

This loss of electrons is what caused the faint blueish glow of the gas as it comes out of the engines.

As it quickly loses it's charge, and has almost no heat production, I suspect that this design would make a very poor weapon.

cjameshuff
2008-Sep-28, 02:11 AM
The question is this: Could an ion engine serve as a particle beam weapon?

A device could be made that serves as both. The exhaust of an ion drive built as an ion drive is not likely to be very dangerous...the individual particles are rather low energy, and not particularly penetrating. It's generally some tens of kilowatts of power for current drives, electrically neutral (electrons are discharged into the exhaust to keep the vehicle itself reasonably neutral), and not in a tightly focused beam, so while prolonged exposure at close range would probably cause overheating, it wouldn't make a very good weapon. I suspect the overall effect would be pretty much that of a hot spotlight.

A beam with much higher energy particles would affect electronics and passengers, as any other kind of ionizing radiation would. It seems unlikely for any near-future device to be able to be focused to the point of inflicting much physical damage, but if it kills the electronics and crew, that's not necessary. However, focusing a beam of high energy charged particles at the kind of distances needed for a weapon would be extremely difficult...if it's not fully neutralized, it will repel itself, spreading the beam. And an ion engine with an exhaust velocity high enough to serve as lethal ionizing radiation, while very fuel efficient, would require enormous amounts of power to produce enough thrust to be useful to any vehicle that would also use it as a weapon. Recall that momentum is m*v, while kinetic energy is 0.5*m*v^2...doubling the velocity lets you get the same momentum change from half the fuel, but requires four times the energy.

It might still work efficiently at much lower velocities and much higher beam currents, giving high thrust for reasonable power consumption, but I don't know if it would be feasible to make a system with that kind of flexibility.

mugaliens
2008-Sep-28, 03:25 AM
I think David stood a better chance with his sling...

tlbs101
2008-Sep-30, 04:30 PM
I...
The question is this: Could an ion engine serve as a particle beam weapon?

Seriously, it occurs to me that an ion engine essentially emits a hail of highly charged particles as high velocity. Hmm, charged particles and high velocity, don't they call that "hard radiation" in some cases? :eek:
...
Anyone here have any ideas on this?

In order to be considered (ionizing) radiation the energy level of the heavy ions like Xenon, Cesium, Mercury, etc. must be on the order of 0.5 MeV and higher. As a comparison, hard X-rays start slightly below 0.05 MeV. Anything less than 0.5 MeV and the ions will not cause damage to electronic equipment nor very little damage to bulkhead materials. To be considered "hard radiation" heavy ions must have energies far above 1 MeV. This is the case with cosmic background ions. These cosmic ions are difficult, if not impossible, to shield against.

The energy of the DS-1 Xenon ions are on the order 500 eV, so they would have to jack up the acceleration of DS-1 by at least 3 orders of magnitude just to be considered a low-end weapon. The current design of DS-1, its predecessors, and similar flight ion engines does not lend itself to even 1 more order of magnitude of energy level -- perhaps double or triple, but not 10 times.


But, this brings up an interesting thought for the future. When true ion beam weapons are actually developed and implemented, at the particle-energy and power levels necessary to be a true weapon; those designers will have to take into account the movement the weapon will cause in the spacecraft. That movement will have to be compensated for, in both position of the spacecraft and aiming of the weapon.

Noclevername
2008-Oct-07, 01:04 PM
It would be a very limited weapon, if so. You'd have to practically have your foe crawling into your tailpipe to take any signifigant damage over and above the usual cosmic rays and background radiation of space. And a simple magnetic field could act as a "deflector shield".

cjameshuff
2008-Oct-07, 02:42 PM
It would be a very limited weapon, if so. You'd have to practically have your foe crawling into your tailpipe to take any signifigant damage over and above the usual cosmic rays and background radiation of space. And a simple magnetic field could act as a "deflector shield".

Possibly. It's easier to get a strong magnetic field in the small volume within an accelerator than it is to surround a ship with such a field. On the other hand, you don't need (or even want) a high flux density field to work as a shield, and a superconductive loop around the ship could produce an enormous field.

tlbs101
2008-Oct-07, 06:32 PM
It would be a very limited weapon, if so. You'd have to practically have your foe crawling into your tailpipe to take any signifigant damage over and above the usual cosmic rays and background radiation of space. And a simple magnetic field could act as a "deflector shield".

That's why the US experimented with *neutral* particle beams in the late 1980s. They even flew and operated a prototype neutral beam accelerator (very low-power, very low-energy) in space (sub-orbit). Google: "Beam Experiment Aboard Rocket" for more info.

publiusr
2009-Jan-13, 12:43 AM
A laser used to accelerated any solar sail type craft to a high velocity would have weapon-order power if it is quite large.