That is interesting, however the problem is that the thing has to be solved quick (this is for a novel, not the real world).

I'd thought using nukes might work, especially if they can be shaped so that they blow up in a torus, vaporizing junk but leaving Earth alone and not wasting its energy towards outer space. Although, for the areas that have the most debris, I think it might work.

Making a solar mirror might be a more permanent solution, but there is the issue of the effect such a thing would have. Image if the thing was aimed at a city.

First off I agree with almost everything Googlenaut said the posts since my last.  I also agree that nuclear bombs aren't the way to clear space junk.

But, on the question of other fusion reactions in nuclear bombs there might be some possiblities.  There is one test that I know of that used an entirely different fuel for the secondary.  That was the fist one...the Mike test in 1952.  The bomb used liquid deutrium as the secondary fuel and this is truely a high temperature reaction.  The big reason for Li-D is the secondary fuel is its storable for long periods.  Also all of the processes need neutrons.

As for as boosted primaries are concerned again I  agree but here the purpose is the generate a burst of neutrons at the middle of a fission bomb explosion to greatly increase burn of the fissionalbe material before it flys apart.  It isn't the energy produced by the fusion that counts but the neutrons so anything that degrades the neutron production is on desired.  My point is that one might consider a He3-D bomb just like Mike was a D-D device.  It would require cyrogenic cooling an so would be a very poor military design but it would explode and be a cleaner device.  Similarly why not a Boron-Hydrogen reaction?  A borane compond might a suitable material to burn in the secondary.  I don't know this would work but I can't see why not.  I just doubt if it had any military applications.

Yes, this wouldn't be perfectly clean but I think it could be made to work.  The point it why?  It doesn't have a lot of military applications.  I don't know if we have even stockpiled any bombs that use lead instead of U238 as a tamper for the secondary.  The military always liked the yield to wait advantage of the doubling of yield due to the fusion nuetron driven fission of U238.  The political types usual don't want to consider actually making bombs more usable hence the lack of interest.

I have no idea if there has ever been experiments on this type of device.  I think He3-D might be made to work but given scarcity of He3 why mess with it.  A cryogenic bomb is not practical.  The borane thing might actually be intesting at a high enough yield to produce a very clean device.

Short answer: No.

Longer answer--what you are talking about is laser induced inertial fusion. The main difficulty with laser induced inertial fusion is that the beam power (peak power here) must be on the order of a few hundred Terwatts. This is possible from a multi-kilowatt beam because the light is compressed into seperate 'discs' which are literally thinner than they are wide. Imagine the laser pulses existing as a moving stack of potatoe chips--only the chips would be spread out over quite distance--this is kind of how the pulse-train would look like.

You can't fuse lithium-deuteride with a multimegawatt laser unless you:
1) have a small enough target that you can get uniform laser illumination over the entire surface. This means the target must be a sphere. And the lasers must come at it from all directions. In otherwords, it must be in the center of a reaction chamber.
2) Have your laser pulses amplified and compressed so that all the energy is packed into just a few wavelengths but over a beam width no larger than the target.

3) The target usually consists of a tiny spherical glass bead or capsule, about 1-2 mm in diameter that contains a tiny bit of deuterium and tritum gas. When the laser hits the outside of the glass bead, it vaporizes or ablates. As the vaporized glass expands outward, it drives a compression wave inward. A shockwave forms which travels through the gas symmetrically toward the center of the sphere while the fuel gas continues to be sharply compressed behind it. Once the spherical shock reaches the center, fusion begins. Thermonuclear fusion burns for a few picoseconds and actually propogates back out before the cooling plasma quenches the fusion burn. Usually only about 10-20% of the available fuel is burned, the rest escapes in the expanding fireball. This is almost exactly what happens in miniature of a nuclear weapon explosion. This is why Lawrence Livermore National Laboratory originally built the NOVA laser system--not necessarily to study fusion energy per se, but to study nuclear weapons physics...


Your scenario would be almost impossible to cooridinate these laser systems enough to induce fusion--and then the explosion would be so small that it wouldn't be worth it. To induce fusion, the individual laser beams are actually all split from the same beam--the reason for this is so that the optics can be tuned so that the laser light all reaches the target's surface at the same instant. So you are talking about positioning optics smoothed to a fraction (about 1/16-lambda) of a wavelength of light to hit a target no more than 2 mm across in a target chamber about 2 m across. It is very, very hard to do this kind of thing.

For similar reasons, it would be very, very difficult to improvise a nuclear weapon: only specific, highly machined parts would do--and that's provided you have the materials on hand to do it.

Now if you had a fission weapon already--it may be possible to create a fusion secondary--someone with the required knowledge if they had some high-Z (high atomic weight) materials (like Tungsten perhaps) and a small machine shop, could possibly do it. This is possible on a large space station provided that they had some lead time.

So I gather you're looking for an 'improvised weapon' defense for your station?

You might look at a multipath strategy: disperse a cloud of aluminum dust and and foil flakes mixed with a couple of paint cans full of ball bearings near your station: this will confuse enemy radar and optical targeting systems. It will scatter incoming high power laser fire. And it will positively beat the tar out of any missiles fired your way. Of course it will also make a mess of the space surrounding your station: but heh, war is hell! And all is fair in love and war, eh?

The first antisatellite weapons concieved of by the CIA and the Rand Corporation called for an attacker satellite to reaundezvous with a target and physically spray flat black paint on it. Simplicity itself--you let the sun cook the satellite to kill it. Another thing--dangerous, exciting, but very effective. Send over a boarding party that epoxies plugs over the enemy vessels reaction control thrusters. If they fire a thruster--it will be like a hand grenade going off--it would definately tear a big chunk out of their space craft. Likewise, stuffing something like a large umbrella into an OMS engine's chamber and throat would induce it to explode quite nicely. Spray painting the flight deck windows and some of the crew cab should make things uncomfortable for the attackers. Covering their communication array with aluminum foil sprayed with contact cement ought to do nicely to cut them off.

I would just add--do not discount the effectiveness of smalls arms fire in vacuum. A Kalishnikov AK-47 fireing semi-armor piercing rounds would be a very effective weapon out to a kilometer or so, more if a fire control computer directs the gun so the bullet's trajectory intersects the target. Even a .45 would be effective against the face shield of a space suit. All 'space war movies' which have lasers and 'blasters' aside, a single 20mm Vulcan, 25mm Bushmaster or a Russian 23mm autocannon would be a very formidable weapon in space. Your only defense is to so heavily armor your vessel as to virtually make it not spaceworthy, completely eliminate your enemy on first contact, or try not to get into a gunfight in space. Something as 'simple' as a twin 40mm Bofors antiaircraft gun--designed in WWII--simply firing large shot shells loaded with 5mm depleted uranium or even tungsten 'buckshot' would be the totally effective. No super high tech miniature proximty fused nuclear shells needed. Sometimes in war the simplest and most direct strategies will work the best. Think in terms of three dimensional space and use the physical properties of vacuum to your advantage. Even a couple of big shiny mirrors, maybe even you stations solar panels--could be redirected to reflect a couple of acres of sunlight onto the control section of the attacking spacecraft. The light and heat may be intense enough to force them to turn away from attack or even force the crew to abandon the control section. Surrender would be their only option then--and this would be just as effective as nuking it--better even because the spacecraft itself would be physical evidence of your country's hostile intent.

Anyways, some suggestions for you to mull over. Good luck with the writing and it sounds like a very exciting story!

Ty Moore

-- Edited by GoogleNaut at 14:15, 2007-05-20

-- Edited by GoogleNaut at 14:16, 2007-05-20

Yes, in retrospect using ICF to do a improvised nuke seem silly now.

Instead I will do another strategy: Lay trash around the station, as you suggested.

And aim a big blob of something towards the ship's sensors, maybe Jello (I'm not kidding, the military is looking into this) or something like that, possible in some mechanical thingamabob that will push the jello when it is expected near the ship, and the ship just sees it as harmless junk.

While it is blinded, three engineers (two of whom are conveniently the main characters of the story) use a small hauler to fly over the ship, plant some charges, clog up as much as possible (especially the thrusters) and leave. They will not attempt to fight in the ship itself, because the inner section of the ship is too well armoured, and the outer section isn't left for the monkeys to play on either.

The enemy ship will then attempt to fly blind, (as the enemies are alien) and fire the fusion thrusters to a diverging course in attempt not to fly into the space station. :)

From a dramatic point of view this standpoint is better.

They have no real weapons, as they are civilians. The lasers are actually there for clearing space junk, or in the case of the station, to fire upon stupid pilots. But they are not enough againts the enemy ship.

Sadly, no solar mirrors or arrays even. The station in question is too far away from the weak sun of its solar system to make solar panels useful. Instead aneutronic fusion is used. In fact, one of the main charecters is a nuclear engineer. But there isn't enough time nor materials to make an impromptu nuke.

Yes, I do know that standard gun-powder weapons work just fine in space. In the novel, they will occasionally use it (one of the characters have a modified 357 revolver), although lasers are preferred and civilians can't really can get their hands on military hardware. This sadly includes standard assault rifles and machine guns. Also, lasers are preferred for their greater accuracy.

I don't want to spoil more. I'll promise to post the first chapter here, once its finished. :) Don't hold your breath though, I've been doing it for quite some time.

-- Edited by Andrew at 18:00, 2007-05-20

Not necessarily. There are two problems: heat and range.

Range: Lasers are not subject to inverse square law, but they are subject to diffraction. Only x-ray lasers are usable over 1 light second.

Heat: Lasers are not always very effective devices. If you have a several megawatt-sized lasers, you will have a few megawatts of waste heat that you need to get rid of quickly. You can use passive radiators, which will be a very big, very bright weak spot. Or you can use coolant material that will limit the number of shots you can do.

Here is a good site about lasers as weapons: http://panoptesv.com/SciFi/DeathRay.html

Questions:
What about alternative energy weapons? Are there any?

The idea of having magnetically held plates around your ship as shield, is a good one?

There was the mentioned "warp metric". Would it be possible to have the two: a, form a protecting bubble that isn't going nowhere and cannot harm whatever is in the bubble (but whatever is in the bubble cannot harm whatever is outside)? and b, make a black hole from a significant distance of the warp drive?

The problem with Promethean-style power generation, beyond that over 50-70% of the power generated is lost, is that they require massive radiators in space. And in space combat, those radiators will light up with a massive "shot me" sign easily observable from several AUs away.

If you face only a single opponent, you can turn the radiator's edge towards him (or her or it or whatever), but when faced with multiple opponents, that will not work.


You can create x-rays with FEL (Free Electrpn Lasers) fairly well. The main difficultly is focusing the x-rays. Early battleships will rather use ultra-violet.

The issue of efficiency is not only heat but power. If your laser is only 45% effective, then you'll get a heat generator that gives photon side effects, rather then the other way around.

Also, the less waste heat you have to deal with, the high the refire rate. The higher the refire rate, the more firepower the laser has. Thus I want to know the efficiency of these gas dynamic laser. FEL's have the maximum efficiency of 65%.

Curiously, if a battleship has multiple lasers, could spin-fire like a wheelbarrow, contentiously firing while allowing the lasers to cool.


I'm not interested in deflector shields. I'm pretty sure that Rosenberry actually took the name from E. E. Doc Smith's Skylark series (or one of E.E.'s work, the guy invented space opera).

What I was thinking, could be defined a bit more like this: such a bubble would separate you from the universe, allowing literally nothing, not even light, to leave or enter. I recall that the Aulbucre warp drive concept had the flaw that it may just sit stationary. What would be the effect of this?

I also have three question:

-What amount of energy does a gram of radioactive Plu-238 decay give in watts?

- Would something called "ultra-fission" work? The idea is not to separate the uranium into two smaller parts, but to split the uranium atom altogether making high-speed hydrogen atoms instead (with neutrons)?

- Do neutrons decay?

GoogleNaut wrote:

---

Neutrons do decay with a half-life of about 12.3 minutes. Neutrons decay by emission of an electron and an anti-neutrino to form a proton:

n = P(+) + e(-) + neutrino

---

Curiously, neutrons are quite happy NOT decaying at all, if they are in an environment such as the nucleus of a stable atom, or inside a neutron star.

Somebody once explained to me why that is so, but unfortunately I no longer remenber the details.

At the time, the context of my question was whether neutron stability was also possible in a so-called Bose-Einstein condensate (an extremely cold form of matter).
As I recall, the answer was "no."

When you start with 1 g of Pu-238, you start with 1 g of Pu-238. So this is at the very beginning of the half-life. In about 84 years you will have half-the amount of the isotope left--this is the definition of a half-life. There is no total life, because the amount of the original isotope will decrease exponentially with time--eventually after 10 half-lives (840 years) you will have about (1/2)^10=1/1024 or about 1 milligram of the original isotope left. After 100 half-lives (84,000 years) you will have about (1/2)^100 = 1/10^30 of the orginal amount left, so it would be unlikely that even a single atom would be left at that point.

When an isotope decays by alpha decay the atomic number decreases by two, and the atomic mass decreases by about 4 units.:

Pu-238 ---> U-234 + He-4


Using Pu-238 for a power source is O.K., but if you want to use it for something like a Life Support Power supply, then you must get rid of the heat. Also, Pu-238 emits gamma-rays. Not necessarily a significant energy source from the power generation point of view, but a definate hazard from the biological point of view. It is something that must be shielded, or isolated or both from an environmental point of view.

A Pu-238 source is a compact, very powerful heat source. But you have to remember, the source of energy is heat. Pellets of Pu-238 will glow red with heat. The heat would need to be converted to another source of energy to be useful for anything else--so a 4 oz chunk of Pu-238 will be generate enough heat power to run a small Stirling Cycle engine that would generate (at about 30 percent efficiency) about 10-12 W of electricity--enough for a decent array of white LED lights. 3/4 of pound of Pu-238 would be needed to power a small (50W) incandescent spotlight.

If you need a kilowatt of heat power, you'll need a little more than 2kg of Pu-238. If you want a kilowatt of electricity with a Stirling engine with 30% efficiency, you'll need 3.3 KW of heat power, and that will require about 8 kg of Pu-238.

Incidently, the power will only drop by 25% in the first 42 years of operation, so it seems doubtful that a Stirling engine could last through even a single half-life of Pu-238! An Pu-238 isotope source will last a very long time for equipment purposes. This is one reason why the US Navy used them to power our SOSUS arrays on the ocean floors!

I suppose you can use just about any isotope for alphavoltaic generation (any isotope the emits alphas that is!) I haven't read up too much on it, but it does sound interesting. It is an alpha source analog of photovoltaic cells, and it probably uses something like a magnetic field to slow and stop alpha particles perhaps...

I can't imagine an alphavoltaic cell generating all that much current, as the alpha particles are zipping out very fast but the total flux is fairly low even for vigorous source like Pu-238 or Po-210.

Since alpha particles don't penetrate all that much, this implies to me that alphavoltaics are a surface phenomena--so the bulk of the Pu-238 must be rolled into a foil. A thin foil of Pu-238 won't get all that hot, but will emit as much alpha particles as the surface of a sphere. So in a sense what you do is greatly increase the surface area of your chunk of Pu-238. After that, I'm not really sure how it works...

A sheet of paper stops alphas, but it does nothing for the gammas. Pu-238 also produces gamma rays, it is just fairly low level. But for prolonged exposure to crew, you need to shield for that.
For short transient exposures (such as technicians checking RTG voltage and casing temperatures) exposures of a few minutes are probably fine. But I'd be willing to bet that they still carry dosimeter film badges just to meausure their cumulative dose...

Low current applications--why not just use an RTG? It has no moving parts, it has been proven to have years of operational performance--and is almost perfectly suited to providing a battery-like power supply for semiconductor devices...

Here's a nice picture of a cardiac pacemaker powered by Pu-238 (as stated on the inscription).
These pacemakers kept many heart patients alive for many years.....

The power produced is quite minuscule -- a few milliwatts at most, just enough to give the heart muscle the signal to beat at the right time (ie. its NOT for powering an artificial heart!).

Each pacemaker contains about 250milligrams of plutonium-238, which equates to approximately 4.27 curies.

There is a low level of gamma radiation, because it accompanies the alpha-induced reaction N14(a, p)O17, and also from impurities in the Pu238.

Surface radiation levels were approximately 2 mrem/hr for gamma emissions and 1 mrem/hr for neutron emissions.

Although the dose equivalent to tissue in contact with the implanted pacemaker ranged from 5 to 15mrem/hr (90 rem/yr average), the whole body radiation dose rate was less than 0.5 rem per year.

Heat dissipation is simply by surrounding blood flow and body cooling....

-- Edited by 10kBq Jaro at 23:09, 2007-05-28

High performance Stirling Cycle engines running with Helium gas pressurized in the case to about 200 bar (about 3000 psi) operating on a hermetically sealed linear alternator can achieve nearly 50% overall efficiency--that is nearly 50% of the heat input is converted in electricity. Less exotic Stirling engines running on helium pressurized to 100 psi can achieve 40-45% efficiency, and those running on air at atmospheric pressure are much less efficient. The efficiency in part is dependent upon the case pressure, the molecular weight and specific heat of the working fluid. Helium is an excellent choice because it has low molecular weight, high specific heat, and can be run at high pressure. Hydrogen would work better, but hydrogen empbrittlement of various parts can lead to high wear later on.

Gamma ray component of Pu238 according to my CRC handbook of Chemistry and Physics 2005 edition, section 11 page 150, is right about 0.45%, which means that about 4.5 milliwatts per thermal watt will be gamma rays. I am not sure how this relates to exposure, atleast in human terms, but this is not a trivial amount. Also, most of the gammas actually come from alpha interactions with nitrogen in the air. Removing air from around the Pu-238 may thus eliminate most of these pesky gammas. Also a couple feet of water ought to attenuate most of the rest because these are relatively low energy gammas anyway. A Radiation Dosimicist (usually a medical professional specializing in computing and minimizing radiation exposure in humans) will know much better than I.