Ion Drives and Radiation Shields

[Aireal]

Could Ion Drive technology be the key to radiation shielding, while at the same time improving ion drive efficiency?

 

The standard ion drive has a stage of operation where it collects excess electrons and injects them into the ion beam to prevent the spacecraft from accumulating a large negative potential.

 

What if that stage could be eliminated, and the negative potential be used to help shield the crew and equipment. First we must look at the problems of radiation shielding for crews in outer space. The three main schools of thought on these are: Material Shielding, which has the drawback of mass. A major factor for a ship with ion drive. Magnetic Shielding, which is weak at some points, much like the Earth is. It also requires a strong magnetic field of about 20 teslas, which might have its own ill effects, we don't know yet. Electrostatic Shielding, by giving the hull a positive charge of 2 billion volts or so , you can repel cosmic-ray protons. But it creates a bombardment of electrons in the range of its field effect.

 

The key might be to combine the strengths of each of these, while reducing their drawbacks, with a unique hull concept.

 

Picture the hull as a giant capacitor, and the ion drive giving it a charge with the electrons that would normally be collected and ejected into the positive ion stream. Each charged layer of the hull would be separated by an insulator material that is also a good radiation shielding material. The most likely bet would be a plastic, or maybe a ceramic. The skin of the hull should have a neutral charge, where as one end of the ship would have a positive charge, and the other a negative, powered by the hull capacitor system. This will generate a magnetic shield around the ship. Now all three of the main shielding systems are in place, let's look at how they interact.

 

At this time a nuclear electric propulsion (N.E.P.) can deliver power levels of several hundred kilo watts to an ion drive, and may reach the megawatt category in the near future. This means an ion drive could generate a large charge in the hull to create a magnetic shield around the ship. I am not sure what the max. field strength would come to, but most likely not large enough to stop the radiation on its own. The good new is, it does not have to stop it, just redirect a few particles toward the poles of the ship, and slow down the rest.

 

Once the charged cosmic particles have been slowed down by the magnetic field, they will encounter the hull. Passing through the skin of the outer hull, they will next encounter the material which serves as insulator and shielding. This will slow the particles down even more. Then it will encounter the first charged layer of the hull capacitor system. These charged layers will act as electrostatic shielding within the hull. Then the cosmic particles must repeat the process of going through material and charged layers till it is hopefully stopped. Because our hull has both positive and negative layers in it, it will protect against a greater range of charged particles than the standard electrostatic field design. To a charged particle, this process will act as if the hull was a material shield with electrostatic shields within it, combining these two shielding concepts. As this setup is used to create the magnetic field, all three shielding concepts are now one system. So we now have all three of the main radiation shielding systems in place, all working together. So what are the advantages of this approach, let us look.

 

The first advantage is an overall reduction in mass needed to protect the crew. Every gram of weight saved in material shielding would be worth its weight in gold for an ion drive ship. With just material shielding alone, it would take about one kilogram of material per square centimeter to protect a crew, that's a lot of mass. Where as magnetic and electrostatic systems have huge energy requirements. By combining the magnetic and electrostatic systems into one, we have already cut the power needed by half. With the system using the potential difference created by the ion drive, the need for its own power supply is reduced or eliminated, another reduction in weight. Because the load of protecting the ship is split between three systems, we do not have to use as much power for magnetic and electrostatic systems as if the were run alone. So the overall energy requirements for the ship is reduced also. Yet every design has some drawbacks, so let's look at how these can be reduced in this system.

 

Magnetic fields provides little shielding at the poles. As our magnetic field is created by the charged areas at each end of the ship, this problem will be increased from particle bombardment in these regions. The simplest way to solve this is to place the crew area in the center of the ship, away from the poles. Antenna or other extensions from the ship could move the poles even farther away from the crew, for an added measure of safety. As the crew would also need shielding from the reactor, the ship design may look something like this. A long cylinder with a antenna projecting from the front of it, the reactor and ion drive at the rear, with the crew area in the center. Of course other designs are possible with this concept. The standard electrostatic shielding concept has the drawback of causing particle bombardment due to its field radius in space around the ship. By locking these charged areas in the hull with a capacitive design, we limit the range that this field expands into space, thereby reducing the problem of particle bombardment. Next we must pick the shielding/insulator material. As it must fill two jobs, it may take some research to determine the best choices. Plastics like polyethylene might be a good starting point. If a lightweight material for the charged layers could be found, this would help in mass reduction, and make the charged layers better as material shielding. Work is already being done in this area. Adding carbon, graphite or nanotubes to plastics is one approach, polycarbonate might be a good chice for this, as it would add some impact protection also. Interpenetrating Polymer Network ( I.P.N.), and similar work by companies like the Eeonyx Corporation are promising also. Thus we can reduce the disadvantages of each of these systems while taking advantage of their strong points. The next question is, are there any other aspects we need to address with this design concept?

 

What if the capacitive charge in the hull started climbing too high for some reason? There would need to be a system in place to bleed off excess power and divert it to the ion drive or some other use. In the event of a solar storm, primary power could be diverted to increase the field strength. After the danger has passed, the extra power could be sent to the ion drive. This approach may allow for less than max. protection in the normal state, and protection increased when needed, resulting in an even lighter ship design. Perhaps a Faraday Cage (RF shielding) could be constructed around the crew area to help protect them from the magnetic field effects also. Another area for improvements would be the outer skin of the hull. Could it be made to generate usable power from the constant bombardment of particles. A recent discovery by researchers of the Material Sciences Division of Berkeley and partners show that alloys of indium, gallium, and nitrogen can convert virtually the full spectrum of sunlight, from the near infrared to the far ultraviolet, to electrical current. So even the outer hull of the ship may have more than one use in the future. The hull should be modular in construction and design. This will lessen the chance of system failure if a hull section gets damaged, allow repairs to be conducted in flight, and make construction quicker and more cost effective.

 

An increase in ion drive efficiency might be obtained by correctly locating the positive pole at the rear of the ship in relation to the ion drive. As the positive ion stream left the ion drive it would encounter the positively charged field at the rear of the ship. The ion stream would be repelled even faster away from the ship, while imparting a slight increase in thrust to the ship. While it may not be much of an increase, every little bit helps over long interstellar trips.

 

Hopefully this approach would reduce the weight and energy requirement of our spaceship by 2/3 over standard designs, while still protecting the crew and equipment. Let me know what you think of this concept, and any potential problems with it. I may have glossed over some points, as it is a long post to begin with, please forgive me if I have done so.

[GAHD]

Reading this i'm reminded of a discusion I had with a friend of mine, where he pinted out that if you uses a ferro-magnetic material to follow magnetic feild lines, it was akin to creating making that very material stronger via E=MC^2. The logic is there but Who could design and build one?

[Qfwfq]

That's a mighty loooooooooooooooooooooooooooooooooooooong post Aireal, I'm not sure how many are going to read it through.

 

What if that stage could be eliminated, and the negative potential be used to help shield the crew and equipment.

That would be the exact opposite of the positive carge on the hull that you mention, it would repel the electrons but attract the protons. It would also offset the thrust of the drive, especially if you really kept all the electrons.

[TheFaithfulStone]

My first thought was "Woe be to him who lands this spacecraft. What happens when you ground out two billion volts?" But then, I saw that you were basically building a huge capacitor and putting people inside it.

 

Theoretically, the people in the spacecraft should not be exposed to any of that voltage, right?

 

I don't know much about Ion drives, but it seems like you might be underestimating the amount of shielding needed to insulate this very large potential difference. If the potential for the ion drive area is +2billion volts, and the potential for the negatively charged portion of the hull is -2billion volts - To restrict the power flow across the difference to 2 milliamps (a fatal charge), your insulator would need to be 2 trillion ohms.

 

That's not utterly outside the realm of possibility, but 2 milliamps is quite a bit of current leakage. (Plus, you know, it kills people.)

 

And, since your ship is a giant capacitor, that insulator could fail, resulting in a pretty spectacular explosion, when all of the current bridged across. Overvolt a capacitor someday and then multiply it by several billion, and you'll be scared. 3 uF will knock you flat. I didn't calculate the capacitance for the hull, but I suspect it's probably measured in some ludicrous unit like megafarads. :)

 

Also, if your hull had that kind of potential, while it might repel free electrons (it would actually ATTRACT free protons if it had a negative potential) any time you touched some solid object which had less negative potential, wouldn't you get a huge current drain? I mean, you might hit a micrometeorite and end up vaporizing half your hull?

 

I should mention that my knowledge of electronics is mostly practical (white wire neutral - black wire HOT) so everything I say should be taken with a grain of salt.

 

TFS

 

edit: so I looked it up - the higest resistance material I could find was about 5 tera-ohms - which gives a current of .0004 amps. That's not fatal - and probably not even noticable, but with a 2billion volt potential behind it gives a power output of 800,000 watts. That's a lot of juice to be losing.

[Aireal]

Gahd, What you said could prove to be very helpfull. It may increase field strength, allowing for reduced power. I will do some research on it. If it will help, I might have a way to apply it. Thanks, that will keep me busy for a while.:)

 

Qfwfq, Sorry, I know it's a long post. Really sorry. The bad part is that there is very little filler, and only the key points are included. The whole work is only part of a larger ship dsign, no way I could put all that in a post. The mass of the electron when compaired tho the mass of the positivly charged atom being expelled is very small. Ion drives do not even waste power to accelerate them as they do the Ions. So the thrust lost by not exhausting them into the ion stream is very small. If they are used for anything at all, it would make an improvement. Also it is unlikely I would need all of them or power levels could climb too high.

 

TheFaithfulStone, This is part of a larger project of mine for a ship built in space that would never land, the post was long enough allready. Plus I did allow for a way to discharge the capacitor system. Overloading that system would be far worse than a few rads.:hyper: Only the ends of the ship have a potential, but yes they would ATTRACT charged particals in those areas, thats part of the idea. You are also correct that they would cause a huge current drain, helping to keep the hull from overloading.

 

I am a retired stage hand with a lot of time on his hands. I have taken courses throughout my life, but only have a two year degree. Thus I am no expert, and there are gaps in knowledge do to my lazy pace of schooling. Thank you all for the interst in my post, after all, it was a looooong post.

[TheFaithfulStone]

If your reactor is 1 megawatt and you lose 800,000 megawatts to powerbleed, you're wasting 80% of your energy, though.

 

Now, here is where I show my cosmic ray ignorance. If cosmic rays consist of protons, why do you need the electric shield? I think that a spaceship coated in 5 teraohm insulator might repel those protons on it's own. Are there heavier ions that would be a problem? Or are the protons just moving so fast that they blast through the insulator?

 

Afterall, the positive field need to propel these protons consists of protons. A LOT of protons.

 

And don't you end up generating thrust from getting hit with all those little charged particles? Like a mag sail or like this

 

TFS

[UncleAl]

Magnetism does not spark. Like charges repel. Look up the training of linesmen who work on 69-750 kilovolt DC powerlines - and the Faraday suits they wear. 2 GV is 30,000 times larger than 69 KV.

 

If +2 GV repels cosmic ray protons, what of solar wind plasma electrons? Do you think 2 GV beta-rays constitute a more tractable problem?

[GAHD]

Magnetism doesn't spark, but a capacitor can short. The capacitance shorting could still be a problem. Without any real schematics to troubleshoot I can see your problem though.

[Kayra]

I suspect long term spacecraft will have to be built with protection of the craft more then the protection of the crew in mind.

 

I personally believe that in order to "Live" in space, humankind will either have to adapt (unlikely) or be adapted to space environments.

 

The damage from radiation is really negligible (we get damaged all the time) except where

A) It damages cell directly. Cell repairs itself or self destructs. Small chance that the DNA is damaged and not repaired which primes chance of cancer.

 

:hihi: A massive does of radiation overwhelms the body's ability to repair itself. It generates considerable levels of free radicals which affect not only cells struck by the ionizing radiation, but many of the bystanders as well. Fast dividing cells most affected. (intestines) Odd side effect is chances of getting cancer lowered.

 

We have some ability to deal with type A, which is by far the more common issue. This ability can either be enhanced (small doses of radiation seem to prime the repair system), or replaced with a better system entirely. (Like the system used by bacteria found to be living in the HOT reactor cores).

 

Even if we can not change our repair system easily, within 10-25 years the threat of cancer will be negligible. We are already learning how to prime our body to kill these cells long before they become a threat.

 

The body already have several mechanisms for detecting and dealing with egg and sperm cells that have been damaged. For long term lifestyles in space though, removal, storage, and protection of these cells will probably be required. (something already being done for cancer treatment patients)

 

 

Type B would only occur from accidental exposure to an active nuclear core, exposure to material that generates ionizing radiation, or getting caught in a solar flare. The latter would be the largest concern for a person living in the inner rings of the solar system.

 

The bottom line is that we continuously repair ourselves and are figuring out how to accomplish this better all the time.

 

I would be more concerned about long term effects on the spacecraft.

[TheFaithfulStone]

Prepare yourself.

 

Because if Al comes back you're going to get it. :hihi:

 

That said, I did see that interstellar radiation consists mostly of protons (87%) but the solar wind is 95% ionized hydrogen.

 

I doubt that being in interplantery space is instantly fatal - but I also doubt that it's very good for you. See - now I'm going to get it too.

 

TFS

[Kayra]

Me understanding Al is like a frenchman trying to understand a Scott.

 

He says many things that I am certain in my heart are insightful and meaningful. It is unfortunate I understand so little :)

 

I guess my point is, while interplanetary space is hard on us, we can be adapted to not only survive it, but thrive in it. Just imagine if we had this little fella's capabilities.

 

http://www.wistar.upenn.edu/research_facilities/heberkatz/research.htm

http://www.biochemsoctrans.org/bst/033/0413/0330413.pdf

 

 

All we have to do is borry a few interesting parts from some of earths other creatures, or figure out how to get ours working better.

[Aireal]

Hi FaithfulStone.

 

Nearly all of the 800,000 megawatt powerbleed is not really a waste, it is the amount of cosmic radiation absorbed, or deflected.

 

Cosmic radiation consists of protons, electrons, beta gamma ect. rays, and any charged particle you can think of, from almost any source. Most are moving at or near the speed of light. This is what makes shielding crews and equipment from it such a complex issue. Also I do believe I answered UncleAl post on another forum, I will have to ask if it was him. The mag sail you mentioned is a cool concept, but I would have to learn a lot more to grasp how best to use it.

 

Kayra mentioned that damage from radiation is really negligible. She is correct, most of the time. However we have recorded levels which would render an unpotected human, unable to function in 10 min. with death coming within hours. But this is rare. The random levels of cosmic radiation is also a big problem. The longer you are in space, the higher the chance of hitting periods of high radiation.

 

Kayra may be glad to know that advances are being made protect from lower levels of damage. Some vitamins and minerals aid the body in this, as does anything that helps it to heal. Genitic modification may also soon be an option. This is of no help to the equipment onboard a ship as she pointed out. Equipment may still need protection for a long time to come.

[Kayra]

Magnetism does not spark. Like charges repel. Look up the training of linesmen who work on 69-750 kilovolt DC powerlines - and the Faraday suits they wear. 2 GV is 30,000 times larger than 69 KV.

 

If +2 GV repels cosmic ray protons, what of solar wind plasma electrons? Do you think 2 GV beta-rays constitute a more tractable problem?

 

Dang.. it took me a while to get this :Tupac:

You were right Buffy, all I had to do was keep reading it over and over...

 

So Al's concern as that the "Shield" will actually act as a particle accelerator to negatively charged particles. Worse, it is aimed right at the heart of the ship. Does that sound about right? Normally, your skin can stop Beta radiation.. I wonder if that would be true after a kick in the pants from the shield.

 

Since we can withstand pretty severe radiation for very short periods of time, it might be more worthwhile to construct a reversible shield system that is turned on only when the radiation is at dangerous levels. (perhaps even shutting down propulsion to power it if required). Otherwise, business as usual.

[GAHD]

ASssuming the design of said ship makes the feilds produced funnel any particles to where the ship itself might capture and use them, while keeping humans out of harms way, such a problem could become a nifty asset.

[Aireal]

Sorry it has been a while since my last post, my daughter has been on spring break from school and I have not been able to get to the computer.

 

Kayra and Gahd Yes it does cause particle bombardment, however as Gahd pointed out, I am useing that to my advantage. As Uncle Al pointed out, there are a number of free electrons that will be attracted to the positivly charged end of the ship. As I placed it near the positive ion stream, they will help to neutralize the ion plume. The positive particles attracted to the other end of the ship wil help to neutralize the negative potential of the ship. What makes this system complex is the interactions amoung the different fields and systems present, as they are interconnected, a change in one affects all of them. Thus the system responds to varying levels of radiation, to a degree. The whole system can be shut down when not needed, but would still provide some protection even then. When the need arises, power can be diverted to incress the protection.

 

In space, even a free electron could be considered a resource. I am just trying to make the most of what resources a ship would have in space to my advantage.

 

Now I do not have a degree in this field, I am a retired stage hand with lots of extra time on his hands. I am mostly self taught and only have a two year degree, but I have taken many college classes during my life. I have been working on this project about 5 or 6 years now. I wish to thank all of you for responding. If I ever get to give this to those who can use it, you all have shown me where I must put more detail into a proposal, and other things I must address. Thank you all very much.

[CraigD]

This means an ion drive could generate a large charge in the hull to create a magnetic shield around the ship.

Nowhere in this thread do I find mention of an important principle of electromagnetism: a static charge doesn’t create a magnetic field. For a magnetic field to be generated, the charge carriers – the electrons – have to move. So the usual way to generate a magnetic field is to have an electric current. If the induced field changes the momentum of a lot of charged particles, as is desired to protect a spacecraft from dangerous particles in the solar wind (95% protons, 4% helium nuclei, 1% heavier ions, an insignificant number of free electrons), it must have power at least equal to the change in momentum / time that the field strongly effects the particles.

 

I can see no advantage to having a lot of extra electrons. What’s needed is energy to power the electric circuits necessary to create the magnetic field. The electrons in the neutrally charged conductor are enough for this. I think the usual plan for ion rocket engines to discard the ionized electrons along with their more massive and useful nuclei is a correct one.

 

There’s been some mention in the popular press about this lately, in connection with both the ISS and a possible manned Mars mission. Whether such a system would offer any advantage over a physical shield of some kind (water and 3789 are popular choices at present), is debatable.

 

:Exclamati I think most of the issues involving both propulsion and shielding of near-future spacecraft is that most of them are a consequence of assuming that energy will be available in amounts only slightly greater than existing spacecraft. I suspect this assumption is incorrect, and that for manned interplanetary spaceflight to be practical, systems with thousands of times more energy will be required. I optimistically hope that such systems are less far off in time than many people may expect.

[GAHD]

Hmm, what does that Ron Quigley guy that designed those super-desks say about protection...something about adding layers of defence. If we go to such lenths to protect ourselvs from each other wee may as well do it for such a touchy place as space. I'd go so far as to say buld each room as a lifepod with X days rations and and spare EVA suits tucked somewhere. Room by room sheilding so thet people could retreat to the 'dark side' during bad storms. The problem with that is the extra mass it requires :/

Craig, what makes you think energy supplys will open up so vastly on a kilogram per kilovolt basis?