Optimizing for Both Atmosphere and Space

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Postby Stark » 2007-01-08 11:03pm

Indeed, how does such forcefield control impact other areas, like defence, manufacturing, construction, etc? Throwing in stupid tech just to invent plausibility for a pet idea and not bothering to think about how it change the setting is the mark of crap fiction.

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Postby Sikon » 2007-01-08 11:04pm

The missions for which there would be hypothetical air/space fighters could instead be fulfilled in a hard sci-fi scenario by space warships plus landing craft. Space warships orbiting at hundreds to thousands of miles altitude could destroy fighters in the atmosphere underneath.

The following would be a good analogy to space warships firing upon air fighters far underneath:
Imagine a person standing above a pond while easily shooting ducks that were flightless or couldn't fly more than a foot above the pond surface.

If the air/space fighters are instead in space rather than in the atmosphere, then they still do poorly due to all of their design compromises, being defeated by space warships which could then proceed to blast planetary targets.

See an air base on the ground, an aircraft carrier on the ocean, or many other military targets, even individual tanks? Space warships can take them out with beam weapons, missiles, or even just cheap nuclear or conventional mass driver shells. Scan for targets with technologies like ground-penetrating radar, infrared, magnetic SQUIDs detecting from orbit masses of metal like submarines, and more. Hit appropriate regions of the planetary surface with EMP (microwave) pulses, nukes, lethal radiation beams, etc.

Then, after the planetary military seems to be wiped out except for what is left within cities, go to the next phase. Assuming cities are to be left mostly intact to limit collateral damage, send down reentry pods deploying hordes of unmanned recon drones, which would fly everywhere. When appropriate, ground recon robots can also be dropped off. If one of those finds survivors of the enemy military in a particular region or is fired upon, one of the orbiting warships can quickly incinerate that area with precise, powerful, fast-response beam weapons. For example, with foreseeable hard sci-fi technology, a very small recon drone couldn't carry gigawatt-class weapons itself, but it could have a link to a computerized fire control system such that one of the warship's powerful weapons could fire precisely in under a second on any location designated.

Only afterwards send in landing forces, such as occupation infantry and robotic armies to capture the cities. The enemy's planetary airforce is long gone before the first soldiers risk their lives on the ground.
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Postby Beowulf » 2007-01-08 11:18pm

I think people have the wrong idea for space fighters. You are all going for the interceptor idea, where the fighter dogfights it's way to victory. A much better idea is a missile carrier. It doesn't have to get down into the thick part of the atmosphere, it can stay high and fast, then boost it's way back into orbit with a nuclear thermal rocket or similar. It just lobs missiles at the attacking fighters, and runs when empty. Size and manuverability matter much less for this role.

For protection of the dropships closer in, you could stick a regular aerofighter in the dropship. You should be able to arrange it to only need a take-off roll of 1/8 of an inch (see the Zero Length Launch concept). Landing one would probably suck, though VSTOL technology would probably help.
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Postby darthbob88 » 2007-01-08 11:24pm

RedImperator wrote:
darthbob88 wrote:Snip stupid idea, already mentioned.

I already suggested this. I really don't see the fun in suggesting arbitrarily wanked technologies that serve no dramatic or speculative purpose. Why not skip the middleman and have an entire aircraft made entirely of force fields if you're going to go this route?
Mea culpa, then. I didn't read enough of the thread, obviously. I didn't want a plane completely made of shielding because a compromise would work better, I thought. If you need it to be there constantly, use metal, plastic, or ceramic; something nice and solid, which will be there until it gets blasted. If you need it to change on demand, then you use a forcefield, which can be altered at the speed of computing/light. Although, a plane made of forcefields might explain Wonder Woman's invisible jet. I agree though, this idea seems cool, but too wanked for serious use in fiction.
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Postby Batman » 2007-01-08 11:28pm

Beowulf wrote:I think people have the wrong idea for space fighters. You are all going for the interceptor idea, where the fighter dogfights it's way to victory. A much better idea is a missile carrier. It doesn't have to get down into the thick part of the atmosphere, it can stay high and fast, then boost it's way back into orbit with a nuclear thermal rocket or similar. It just lobs missiles at the attacking fighters, and runs when empty. Size and manuverability matter much less for this role.

That concept I believe is already known (in the real world to boot) as the missile cruiser. I seem to recall we were talking about fighters (for the moment disregarding the fact that space/starfighters apparently shouldnt work).
For protection of the dropships closer in, you could stick a regular aerofighter in the dropship. You should be able to arrange it to only need a take-off roll of 1/8 of an inch (see the Zero Length Launch concept). Landing one would probably suck, though VSTOL technology would probably help.

Does this make no sense whatsoever to anyone BESIDES me?
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Postby Beowulf » 2007-01-09 12:08am

Batman wrote:
Beowulf wrote:I think people have the wrong idea for space fighters. You are all going for the interceptor idea, where the fighter dogfights it's way to victory. A much better idea is a missile carrier. It doesn't have to get down into the thick part of the atmosphere, it can stay high and fast, then boost it's way back into orbit with a nuclear thermal rocket or similar. It just lobs missiles at the attacking fighters, and runs when empty. Size and manuverability matter much less for this role.

That concept I believe is already known (in the real world to boot) as the missile cruiser. I seem to recall we were talking about fighters (for the moment disregarding the fact that space/starfighters apparently shouldnt work).


So the Tomcat isn't a fighter (disregarding the fact that it's actually an acceptable dogfighter, it wasn't really designed as such)?

For protection of the dropships closer in, you could stick a regular aerofighter in the dropship. You should be able to arrange it to only need a take-off roll of 1/8 of an inch (see the Zero Length Launch concept). Landing one would probably suck, though VSTOL technology would probably help.

Does this make no sense whatsoever to anyone BESIDES me?


Back in the 1960's, the US military experimented with how to get fighters off the ground in a post nuclear environment, where there weren't likely to be be any usable runways. Their solution, which was tested on an F-100, amongst other planes, was to strap a massive rocket engine onto a fighter, the axis of thrust going through the center of gravity. The plane had a takeoff roll of about 1/8 of an inch. So, at low altitudes, where the missile cruisers aren't so effective, you chuck a air fighter out, with a freaking powerful rocket engine to get it up to speed. Since you probably don't have a runway to use, you equip it for vertical landing. It doesn't really have much to do with space fighters.
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Postby darthbob88 » 2007-01-09 12:37am

Beowulf wrote:Back in the 1960's, the US military experimented with how to get fighters off the ground in a post nuclear environment, where there weren't likely to be be any usable runways. Their solution, which was tested on an F-100, amongst other planes, was to strap a massive rocket engine onto a fighter, the axis of thrust going through the center of gravity. The plane had a takeoff roll of about 1/8 of an inch. So, at low altitudes, where the missile cruisers aren't so effective, you chuck an air fighter out, with a freaking powerful rocket engine to get it up to speed. Since you probably don't have a runway to use, you equip it for vertical landing. It doesn't really have much to do with space fighters.
Not that I doubt your veracity, but do you have any other sources? I seem to be misunderstanding what you say.

Along those lines, when the Americans were experimenting with long-range, high-speed strategic bombing, they came up against problems in developing an effective fighter escort that was capable of both sufficient range and speed to keep up with the Russia-bound bombers. One solution they considered was actually attaching fighters to the bombers, piggyback style. Parasite fighters.
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Postby Beowulf » 2007-01-09 01:33am

darthbob88 wrote:
Beowulf wrote:Back in the 1960's, the US military experimented with how to get fighters off the ground in a post nuclear environment, where there weren't likely to be be any usable runways. Their solution, which was tested on an F-100, amongst other planes, was to strap a massive rocket engine onto a fighter, the axis of thrust going through the center of gravity. The plane had a takeoff roll of about 1/8 of an inch. So, at low altitudes, where the missile cruisers aren't so effective, you chuck an air fighter out, with a freaking powerful rocket engine to get it up to speed. Since you probably don't have a runway to use, you equip it for vertical landing. It doesn't really have much to do with space fighters.
Not that I doubt your veracity, but do you have any other sources? I seem to be misunderstanding what you say.

Along those lines, when the Americans were experimenting with long-range, high-speed strategic bombing, they came up against problems in developing an effective fighter escort that was capable of both sufficient range and speed to keep up with the Russia-bound bombers. One solution they considered was actually attaching fighters to the bombers, piggyback style. Parasite fighters.


http://www.vectorsite.net/avzel.html gives a decent explanation of Zero Length Launch.

The parasite fighters were abandoned because they had problems connecting back up with the mothership, and they were able to get fighters able to have the range necessary to escort the bombers.
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Postby SirNitram » 2007-01-09 01:50am

Honestly, if you're anywhere near Hard(And by that I mean 'Up to and including SG-1'), you're better off optimizing for atmosphere and giving them a good rocket engine and attitude rockets to let them function sorta-kinda in short space runs. More a fighter that can get transatmospheric than a true starfighter, but starfighters are probably a silly idea anyway.
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Postby Batman » 2007-01-09 11:16am

Beowulf wrote:
Batman wrote:
Beowulf wrote:I think people have the wrong idea for space fighters. You are all going for the interceptor idea, where the fighter dogfights it's way to victory. A much better idea is a missile carrier. It doesn't have to get down into the thick part of the atmosphere, it can stay high and fast, then boost it's way back into orbit with a nuclear thermal rocket or similar. It just lobs missiles at the attacking fighters, and runs when empty. Size and manuverability matter much less for this role.

That concept I believe is already known (in the real world to boot) as the missile cruiser. I seem to recall we were talking about fighters (for the moment disregarding the fact that space/starfighters apparently shouldnt work).

So the Tomcat isn't a fighter (disregarding the fact that it's actually an acceptable dogfighter, it wasn't really designed as such)?

Not YOUR idea of a fighter, no (which incidentally ISN'T an interceptor, but a air/space superiority fighter, the function of an interceptor being to intercept (sic) bombers. Dogfighring is the province of the superiority fighter.) It's primary mission was, indeed, to lob missiles at enemy aircraft (bombers, mainly) at long range.
For protection of the dropships closer in, you could stick a regular aerofighter in the dropship. You should be able to arrange it to only need a take-off roll of 1/8 of an inch (see the Zero Length Launch concept). Landing one would probably suck, though VSTOL technology would probably help.

Does this make no sense whatsoever to anyone BESIDES me?

Back in the 1960's, the US military experimented with how to get fighters off the ground in a post nuclear environment, where there weren't likely to be be any usable runways. Their solution, which was tested on an F-100, amongst other planes, was to strap a massive rocket engine onto a fighter, the axis of thrust going through the center of gravity. The plane had a takeoff roll of about 1/8 of an inch. So, at low altitudes, where the missile cruisers aren't so effective, you chuck a air fighter out, with a freaking powerful rocket engine to get it up to speed. Since you probably don't have a runway to use, you equip it for vertical landing. It doesn't really have much to do with space fighters.

That would have been lot clearer if whoever came up with the stupid 1/8th inch terminology just called it what it is-rocked-assisted VTO. And if you're launching from a dropship why bother? Just shove the fighter out the airlock and let gravity do the initial acceleration.
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Postby LaserRifleofDoom » 2007-01-09 06:45pm

Batman wrote:That would have been lot clearer if whoever came up with the stupid 1/8th inch terminology just called it what it is-rocked-assisted VTO. And if you're launching from a dropship why bother? Just shove the fighter out the airlock and let gravity do the initial acceleration.


Because you would be falling at the same speed as the dropship?

I came to the same conclusion several months ago about space fighters only being really useful for supporting ground operations. I decided that any fighter carrier might as well be a support/bombardment platform for an entire ground operation, and that a fighter would probably only be in space during less than 10% of combat. This was operating under the assumption that entering orbit would be easy enough for fighters to go back and forth.
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Postby Batman » 2007-01-09 07:09pm

LaserRifleofDoom wrote:
Batman wrote:That would have been lot clearer if whoever came up with the stupid 1/8th inch terminology just called it what it is-rocked-assisted VTO. And if you're launching from a dropship why bother? Just shove the fighter out the airlock and let gravity do the initial acceleration.

Because you would be falling at the same speed as the dropship?

And? The dropship is either a) high or b)slow enough (likely both) for that not to be a problem. Because if it is chances are the dropship is about to crash anyway and you might as well not bother launching the fighter.
Anyway if the fighter crashing after launch is a problem, the time by which launching the fighter might have gained you something worthwhile is long past.
Either the dropship made it to a safe landing without the fighter's assistance, or it didn't in which case chances are, again, it's about to crash.
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'Hey, we both have a Martian's phone number on our speed dial. I think I deserve the benefit of the doubt.'
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Postby Beowulf » 2007-01-09 07:37pm

How about: with out positive ejection, the plane might not be able to actually leave the dropship. Or: if you just open the airlock, the plane might end up in a spin/stall immediately after egress.
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Postby Batman » 2007-01-09 07:56pm

Beowulf wrote:How about: with out positive ejection, the plane might not be able to actually leave the dropship. Or: if you just open the airlock, the plane might end up in a spin/stall immediately after egress.

Let me rephrase:You absolutely need to get the airfighter clear of the dropship to prevent it crashing into said ship if nothing else.
What it does NOT need (but would certainly benefit from) is a massive speed boost.
1. Spin. So what? Even if we're talking about a flat spin (and how, exactly, would that happen?) if you're close enough to the ground for this to be a problem the time to release the airfighter is long past. Not that I see how a RATO would avoid those.
2. Stall. Same deal. Gravity itself will take care of that. Put the fighter nosedown and wait until your airspeed builds up. IF you don't have the altitude for that, why is the fighter still hangared?
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'Hey, we both have a Martian's phone number on our speed dial. I think I deserve the benefit of the doubt.'
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Postby LadyTevar » 2007-01-10 04:19pm

Second silly question/example: Battlestar Galatica's Vipers.
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Postby Teleros » 2007-01-10 04:51pm

LaserRifleofDoom wrote:I came to the same conclusion several months ago about space fighters only being really useful for supporting ground operations.

Same. Although they might also be useful in patrols, as electronic warfare / missile platforms etc - a squadron of fighters with decent sensors might not be as efficient as simple recon drones but there'd probably be some advantages to having a human on the scene.

Moving back on topic, could something akin to a Langston field be used to replace say the radiators required for space travel? If our fighter could say adsorb and store the waste heat (perhaps convert it to electrical energy?) you could certainly reduce the need for radiators, perhaps to the extent that they could be more easily fitted onto the aerodynamic shape needed for atmospheric flight. Of course this means a less efficient and heavier fighter, but it might be one way of at least easing this problem.

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Postby RedImperator » 2007-01-10 05:00pm

Teleros wrote:
LaserRifleofDoom wrote:I came to the same conclusion several months ago about space fighters only being really useful for supporting ground operations.

Same. Although they might also be useful in patrols, as electronic warfare / missile platforms etc - a squadron of fighters with decent sensors might not be as efficient as simple recon drones but there'd probably be some advantages to having a human on the scene.


No. No there wouldn't. The Raptors can be justified, but not the Vipers. For the cost of a single Viper, they could build dozens of missiles; for the cost of a Viper and a pilot, they could build thousands. A human in the loop adds nothing that cannot be compensated for, and carries significant penalties. Most critically, all other things being equal (and they're not), a missile has twice the range of a fighter because it doesn't have to come home.

Moving back on topic, could something akin to a Langston field be used to replace say the radiators required for space travel? If our fighter could say adsorb and store the waste heat (perhaps convert it to electrical energy?) you could certainly reduce the need for radiators, perhaps to the extent that they could be more easily fitted onto the aerodynamic shape needed for atmospheric flight. Of course this means a less efficient and heavier fighter, but it might be one way of at least easing this problem.


This would improve the situation, though even if the Langston field was 100% efficient and you didn't need radiators at all, there would be other design compromises needed that would make the vehicle a sub-optimal atmospheric fighter and a sub-optimal spacecraft at the same time.
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Postby Admiral Valdemar » 2007-01-10 05:18pm

LadyTevar wrote:Second silly question/example: Battlestar Galatica's Vipers.


...Are hopelessly unrealistic. Anyone who can make robots that are fully autonomous can make missile buses that can perform far better than any organic piloted craft. They are there because the original BSG, like SW, was created via those who witnessed the great dogfights of the wars they saw on TV when growing up. There is no practical reason for any manned fighter in space, or, for that matter, in atmosphere when an AI can control a missile interceptor craft with far greater agility and acceleration.

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Postby RedImperator » 2007-01-10 05:41pm

Destructionator XIII wrote:I am not convinced of the need for recon in space. In space, no one can hear you scream, but everyone can see you burn, from great distances.


In nBSG and any other universe with FTL, scouting is probably necessary. In the real world, you're right. Unless something is hidden under the surface of a planet, it's cheaper, faster, and safer to turn a bigger telescope in the enemy's direction than send a scout. And if a scout is needed, as you said, a disposable robot is a much better idea.

Actually, isn't it even more? Consider a simple case. The missile only needs one big burn: it gets to the target and smashes into it at high speed.

The fighter burns to get there, then burns to stop, then burns again to get back, then burns one last time to stop and dock / land with the mothership. All those would have equal delta-v (ignoring the relative accelerations of the target and mothership), making its range 4x less than the missile.


Actually, yes, you're right. Assuming no time at all spent on station and a stationary mothership, you'd need to accelerate, decelerate, accelerate, and decelerate again. You could get around this if the mothership burned to intercept you at some other point, but if your mothership is capable of doing that, why did you bother sending a fighter?
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Postby Sikon » 2007-01-11 12:45am

Destructionator XIII wrote:Sikon, you'll have to forgive me for scraping your brain here...

Sikon wrote: Space warships orbiting at hundreds to thousands of miles altitude could destroy fighters in the atmosphere underneath.

What kind of energy would be needed for this? I ask because I know there have been problems with the atmosphere absorbing too much of the energy from a laser to make it economical to use as a ground to space energy transfer system for modern day spacecraft. If a significant amount is lost to the atmosphere, then the laser would need to be higher power on the ship, which also means more waste heat, and obviously, more power generation is required, which may be the limiting factor for these tactics.

Also, if the warships can shoot down, could a ground based system shoot back up (assuming, of course, any ground weapons survive the first wave of bombardment), or would that be too inefficient to be feasible on the ground (I know lasers generate a lot of waste heat, and on the ground that could be an environmental disaster)?

With a projectile or missile, how much mass would be required for it to not burn up before hitting the target? Also, how hard would it be for them to hit a moving target from that range?

I have no doubts that hitting a stationary thing on the ground with a kinetic kill mass would be easy, but fighters I always assumed would be much harder to hit.


It is an interesting topic. I was going to write some thoughts on this anyway, and this post will also be relevant to your questions.

Megajoule weapons could be enough, but attainable firepower in the gigajoule to terajoule range is likely.

Space warship power generation, waste heat, etc.

Usually the power generation and storage system is considered a major limiting factor for electrically-powered beam weapons. Future ultracapacitors could have an energy density higher than 60 Wh/kg along with a power density greater than 100 kW/kg. Such is from a MIT study on ultracapacitors for future cars: implied here. That would be up to 0.2+ TJ of energy storage per 1000 metric-tons of ultracapacitors, able to be discharged at a rate of 0.1+ TW. For example, a hundred thousand ton warship with just five percent of its mass being ultracapacitor banks could store a terajoule, then discharge it at a rate of half a terawatt. Technology of the distant future is unknown, perhaps far superior, but the preceding is a reasonable expectation for a probable lower limit. For a large ship, let's figure the maximum output energy of each beam-weapon or mass-driver shot is most likely in the 0.01 TJ to 1 TJ range, depending upon assumptions like the size of the space warship, power handling per unit mass, inefficiencies, etc.

Another question is the recharge rate, depending on warship power generation. One nuclear-electric concept with a MHD generator was estimated to obtain 0.37 kg/kWe, which would be 2.7 MW/metric-ton. For perspective, car engines of today are sometimes hundreds of kW of mechanical power per ton (i.e. 200 hp engine = 150 kW), with aircraft engines up to much higher power density. Even with need for electricity rather than mechanical power alone, the many thousands of tons involved in a space warship would allow it to have power generation at least in the gigawatt range or higher, likely terawatts for large ships. Even hard sci-fi technology could be well beyond today's concepts. Either fission or fusion reactors would work. There would also be inefficiencies.

What about waste heat? Deploying large radiator panels while firing weapons wouldn't be desirable. Internal phase-change-material (PCM) heat sink possibilities could include using ice/water to absorb some terajoules of energy. Actually, if the space warship has structure, armor, and individual weapons massing thousands of tons, such would be able to temporarily absorb some waste heat. But such could not sustain a high rate of fire for long without needing a "cooling off" period, so a different system would be needed, at least as a supplement. Interesting options include liquid droplet radiators, charged (solid) particle radiators, etc.

Radiator mass for the weapons is going to depend much upon their acceptable operating temperature. If most parts of the weapons can operate at moderately high temperature, transferring away heat fast enough becomes plausible without excessively large radiator area and mass being needed even when a lot of power is involved. That is particularly plausible at the high technological level implied in this sci-fi scenario. One study of what is obtainable for heat rejection in space with merely today's technology indicates that 30 MW of heat could be dealt with by a 45 metric-ton Curie point radiator (CPR) or by a 29 metric-ton liquid droplet radiator, for an average temperature of 380 degrees Celsius or 650 K. The space warship would operate at least in the gigawatt range, with at least around a couple orders of magnitude greater heat rejection from its weapons, but it could afford to have orders of magnitude greater radiator system mass. And it would be much more advanced technology. The preferred radiator design for an armored warship would tend to be a droplet radiator or a particle radiator, not large flimsy panels.

Let's add an intuitive illustration of the overall picture. Consider 10% of the mass of a 100,000-ton warship being a beam weapon, with the maximum energy of each shot it could fire being somewhere between 0.01 TJ and 1 TJ. That proportionally corresponds to as much firepower per unit mass as a half-kilogram energy pistol firing shots between 500 J and 50 kJ of energy. Such is equivalent to the energy pistol being able to vaporize a volume of ice between 0.72-cm and 3.3-centimeters in diameter per shot. While the whole range is conservative by sci-fi standards, one could take the low end of the range if concerned about the reliability of it being plausible. The comparison is proportional since the sample space warship's weapon masses 20,000,000 times more than the energy pistol.

Yet the warship's shots each correspond to the equivalent of approximately between a 2500-kg bomb and a 0.25-kiloton tactical nuke in the energy delivered. Beam weapons of such energy can have "unlimited ammunition," powered by the discharge of the capacitors, which are recharged by the warship's nuclear reactors to fire thousands of shots in a period of a few hours. Or smaller shots could be used for an even higher firing rate.

For perspective, a 100-kJ vehicle-mounted laser concept is considered by the Department of Defense to be lethal against common rockets, aircraft, and light ground vehicles. Yet, at the technological level implied by sci-fi interplanetary or interstellar space war, set in the distant future, average firepower of large space warships could be astronomically higher, either in the energy per shot, the number of shots fired per minute, or a combination of both. Every 0.01-TW of average weapons power corresponds to 100,000 times the energy per second: 400 million times it per hour.

Propulsion system power would likely be even much greater. For example, the MS Word document from researchers here describes a magnetic compression pulsed fission concept with a magnetic nozzle, in which a vehicle of 1310 metric tons initial mass and 100 tons final mass could have 263 GW jet power. That is between 0.2 GW/ton and 2.6 GW/ton, with relatively straightforward technology. For this sci-fi scenario with advanced technology, the preceding is just a probable lower limit. A much larger 100,000-ton space warship could be more than 1 GW/ton, corresponding to an exhaust jet power above 100 TW. But one conservatively treats weapons power as orders of magnitude less than what is sure to be possible for propulsion, not counting on more than the 0.01-TW previously implied.

Beam weapons against atmospheric fighters and other planetary targets

Before considering other weapons types, let's first illustrate with a space warship firing a lethal radiation beam against planetary targets including aircraft. Against humans, on the order of 10 kJ per square meter of some types of radiation would be enough to cause enough exposure for relatively quick mortality, much above the level for slow death. The end result is a little like the effect of the radiation of a neutron bomb, for which 8000 rads or 0.08 kJ/kg-tissue are enough to immediately incapacitate enemy soldiers like tank crewmen according to an U.S. military estimate, a couple orders of magnitude above the dosage usually lethal over a longer period of time (1% as many neutrons = 80 rads = 800-1600 rem in long-term). But the radiation would be like penetrating cosmic rays, not neutrons.

Since natural cosmic radiation experiences an attenuation factor of 600 going through earth's atmosphere from space to ground at sea level, assume the wide-beam radiation should have an intensity on the order of 6 MJ/m^2 before entering the atmosphere. (Penetrating natural cosmic rays = 16 rem/yr for interplanetary space --> 0.027 rem/yr sea level). The situation could be better with more optimal choice of particles and when firing against aircraft above sea level, but, to be conservative, don't assume better.

The result is that each shot of 0.01 TJ to 1 TJ energy can deliver a pulse of quickly lethal radiation to an area around 46 meters to 460 meters in diameter. If a given intensity level is insufficient, such as firing against a relatively hardened unmanned target, dropping the beam diameter by an order of magnitude would increase the intensity by a factor of 100, and so on. But wide beams can kill ordinary tanks, aircraft, infantry, etc. The beam is unaffected by weather and sufficiently penetrates the 10000 kg/m^2 mass shielding of the atmosphere. Unlike even neutron bombs, the beam would have no blast effect when set to sufficiently wide-beam mode, leaving structures unharmed aside from disruption to electronics, yet killing the occupants.

Some kinds of beam weapons could be more limited in propagation through the atmosphere. For example, as implied by what happens to sunlight, visible light from space doesn't always reach the ground well on cloudy days. So visible light lasers might be an unreliable weapon against low-altitude enemy aircraft, unless the basic principle of this could be applied with ultra-intense pulses.

But microwaves can go through clouds. Against non-hardened targets, as little as a few joules per square meter or less can be enough, allowing gigantic "EMP pulse" microwave beams hitting up to multiple square kilometers per shot. Against ordinary civilian targets, such might be about the opposite of lethal radiation beams: At the wide-beam setting, such could devastate infrastructure without killing any people, aside from a few indirect deaths like crashing aircraft.

If necessary against hardened targets, the microwaves could be more focused, for physical overheating and destruction of targets, e.g. MASERs. At the 0.01 TJ to 1 TJ energies, a beam a few meters in diameter could be many megajoules per square meter, possibly gigajoules per square meter.

Nuclear projectiles and missiles

For another potential weapons system, consider space warships firing nuclear projectiles or missiles. For example, a cheap "brute force" method of dealing with atmospheric fighters trying to avoid shells or missiles might be to have them explode with sub-kiloton to single-kiloton yield. The equivalent isn't done by terrestrial militaries for reasons like political issues, but those don't necessarily apply so much in a sci-fi planetary assault scenario. Even in the real-world today, nukes don't have to cost more than merely hundreds of thousands of dollars each or less in mass-production, compared to fighters costing orders of magnitude more: tens to hundreds of millions of dollars each.

Fallout from such nukes would tend to be harmful to the planetary defenders and localized regions without making the planet unusable by the invaders. Localized radiation levels shortly after a detonation can be lethal, but such drops over time, since the radioisotopes emitting the most initial radiation are those which decay most quickly. (The rate of radiation emission per unit time from a radioisotope is inversely proportional to half-life, to a degree such that stable elements can be thought of simply as those with infinitely long half-lives). Compared to residual radiation one hour after the detonation, radiation levels are 1% as much after 2 days and 0.1% as much after 2 weeks. As implied, most is gone after the short-term timeframe. The fallout of a nuclear weapon detonation of low or moderate yield can much elevate radiation levels over a limited number of square kilometers, but it can do very little overall over the half-billion square kilometer total area of a planet like earth.

Historical above-ground nuclear weapon tests in the 20th century amounted to 440 megatons cumulatively, with 189 megatons fission yield ... 189000 kilotons (large PDF file). Total collective dosage to the world's population from such past tests corresponds to 7E6 man-Sv, for the UNSCEAR estimate for total exposure in the past plus the result of currently remaining radioisotopes projected up through the year 2200. The preceding total over the decades and centuries is less than what is received every year from natural sources of radiation, which is in turn orders of magnitude less than what would make an eventual death from cancer probable. Of course, from a real-world civilian perspective, any potential increased risk of cancer is undesirable, but, from the perspective of the hypothetical space invaders, the bulk of the planetary surface is not harmed enough for them to necessarily be concerned.

For example, even with fission devices, if the orbiting warships are firing quarter-kiloton-yield nuclear shells or missiles against targets like enemy aircraft, it would take on the order of 800,000 warheads even just to exceed the limited radiological contamination from the 189-MT fission component of the preceding nuclear tests. Only some invaders would care about that level of fallout. And the preceding is for fission devices. A hard sci-fi scenario could alternatively have pure-fusion devices, which would be cleaner.

Non-nuclear projectiles and missiles

Yet another potential weapons system for space warships is firing non-nuclear mass driver projectiles and missiles to hit air, sea, and ground targets on the planet below, impacting at hypersonic velocities.

A 1977 NASA Ames study referenced here determined that an earth-launched mass driver projectile going up vertically could pass through earth's atmosphere from ground level to space with a few percent of its mass being an ablative carbon shield, losing only 3% of its total mass in the transit. Such is for a telephone-pole-shaped projectile of a metric ton mass. That means the reverse is also possible for projectiles with the right mass, dimensions, ablative shield, and trajectory. For example, consider a similar projectile or missile fired from space, reaching the upper atmosphere at 12 km/s velocity and going nearly straight down. It could hit a ground target at about 11 km/s, a kinetic energy equivalent to about 15 tons of TNT explosive.

Projectiles and missiles fancier than the cheapest unguided shells could use small thrusters to adjust trajectory to home in on a target. Even with a proximity fuse for a large shrapnel pattern, hitting an enemy atmospheric fighter could be more complicated than with the nuclear missiles or wide-beam lightspeed weapons described earlier. However, advanced robotic missiles tracking by the right combination of infrared, visible, radar, and/or other sensors could help make the space-to-air missiles much harder to evade than today's air-to-air missiles.

Sci-fi technology might also mean other possible ordnance, such as biological weapons genetically engineered to have a non-lethal temporary incapacitating effect or infectious nanobots. Different attackers might use different techniques depending upon their psychology, ethics, objectives, etc. But the earlier parts of this post imply the general trend of space warships having vast firepower by the time of a sci-fi war like this.

Space warships versus planetary anti-space weapons

What about space warships fighting planetary anti-space weapons?

Fighters and missiles launched from a planet may tend to be smaller and more limited than space warships. For example, a mass driver sending even just 10 tons per hour to orbit could over a decade put almost a million tons up, enough to be potentially the seed of a society processing eventually billions of tons of extraterrestrial material into habitats and ships. But, in that scenario, billions of tons of spaceships might exist without the planet necessarily being able to launch more than a proportionally miniscule amount in a day. There is likely shipment offplanet of some valuable goods and also passenger traffic, but X million people per decade going offplanet only corresponds to just 20 * X * Y tons per day needed, where Y is the ratio of total launch mass to body mass.

A planet with some atmospheric fighters launching anti-space missiles would typically fail when fighting space warships. Warships can have point defenses. For example, a 100-kJ projectile can destroy an ordinary missile. (For perspective, 100-kJ is like the kinetic energy of a 200-gram projectile going 1 km/s, though the analogy shouldn't be taken too far since the momentum is different for a much higher velocity but smaller projectile). A 0.01 TJ to 1 TJ mass driver firing pellets like a shotgun could deliver on average a 100-kJ pellet per square meter within a 360-meter to 3.6-kilometer diameter pattern per shot, making it typically rather easy to hit an incoming missile from the planet.

Launch a missile from a planet with a regular rocket, and more than 90% of its mass is involved just getting off the planet. In principle, a planet could do better by instead launching nuke-pulse missiles, nuke-saltwater rockets, or other advanced propulsion concepts. But having such launched from a planet during a battle would make them relatively easy targets during their boost phase. The planet could do better by having missiles and warships in space long before the start of the battle, but such wouldn't be air/space craft or planetary weapons. The case of planetary assault presumes the attackers have already won the space battle.

What about planetary anti-space weapons other than launching missiles? While a planet could have gigawatt to terawatt range beam weapons (i.e. water-cooled, especially if by the ocean), the effective range of such against space warships would tend to be less than the effective range of space warships against planets. In a duel at up to light-minutes or greater range with lightspeed weapons, a properly utilized space warship fleet will win against an immobile planet.

A lot of examples earlier in this post have implied how enough firepower could make relatively wide beams effective against a lot of planetary targets, such as the lethal radiation beams killing any people not deep underground. That allows the ability to engage an immobile target like a planet initially at extreme distances if desired.

For example, if technology allows under 0.1-meter dispersion of a particular beam weapon at 100,000-km distance, the same weapons technology would tend to allow under 100-meters dispersion at 100-million kilometers distance. If thousands of GJ to TJ-level shots can be fired per hour with electricity from the nuclear reactors while only one has to hit, an immobile planetary target can be hit by a warship with under a hour of firing from several billion kilometers away. That corresponds to a few light-hours distance, giving the mobile warship plenty of time to evade any lightspeed weapons fire from the planet. Such would arrive hours later, long after the warship has moved to another location in the vastness of space.

Most likely, if a planet had anti-space beam weapons, warships would destroy those from long-range, then move closer to provide closer targeting, like initially engaging at millions of miles but then going into low orbit for the final fire support.

More on close fire support from warships and the use of recon drones

To clarify more on my last post, with good enough targeting information transmitted from recon drones through a computerized system, space warships could help kill even individual vehicles or even individual enemy soldiers from orbit when possible. Such wouldn't be their primary mission, and initially the warships would attack more valuable targets. But afterwards, a warship would still have practically unlimited ammo for its electrically-powered beam weapons running off nuclear reactors. Using a hundred-thousand-ton warship to kill a couple enemy soldiers riding around in a truck might superficially seem wasteful, but there is next to no marginal cost in the preceding scenario.

Consider a warship orbiting at a couple hundred kilometers low-orbit altitude for final fire support. A little like a terrestrial sniper can shoot an enemy from a half-kilometer away, some beam weapons on the warship could be designed to hit precise locations on the ground below, with potential accuracy of within a meter. If there was a single person or handful of people on the warship manually trying to search for targets, aim, and fire the weapons, it would be a slow process. Yet, if there were a large number of robotic recon drones searching for enemy vehicles and soldiers, transmitting their precise coordinates, a computerized fire control system on the warship could shoot thousands of designated targets per hour, continuing for hours or days if necessary.

Space warships would initially destroy all targets they could see from space, but, for foreseeable technology, one wouldn't expect orbital surveillance to find every last target. Robotic recon drones deployed on air and on the ground could help give further targeting information. For example, if a golfball-sized robotic drone with a miniature jet engine flies up to the window of a building and sees enemy soldiers inside, it can transmit a signal causing the warship's computers to fry the area within a 50-meter radius with a lethal radiation beam a fraction of a second later ... potentially very effective yet still with less collateral damage than just nuking the whole city.

Given the level of firepower and capabilities possible on one space warship, imagine what a fleet of thousands of such warships (or more) could do against a planet.

The preceding could be done before sending in regular armies or occupation forces in order to drastically reduce ground combat casualties, although use of non-sapient robots and/or telepresence whenever possible might make casualties beyond expendable robots be low anyway.

The unpredictability of future technology

Even in a hard sci-fi scenario, predicting the capabilities of technology that may be centuries or millennia beyond the 21st-century is highly uncertain. A little like a person from centuries ago couldn't very well predict the capabilities of modern combat, the preceding is mainly just a lower limit on what hard sci-fi technology could accomplish with the high technological level implied by a interstellar war scenario like this.

For example, perhaps technology would allow a million tons of raw materials to be quickly and cheaply converted to its mass-equivalence: a billion one-kilogram missiles to be dispersed at low altitude. Or there could be other weird military technologies.

But overall the advantage tends to be on the space side, not the planetary defenders. If technology is different like allowing even more warship firepower, such would probably make atmospheric fighters be even more outmatched by space fleets.
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Postby Broomstick » 2007-01-12 10:40am

I feel compelled to correct some facts here...

Batman wrote:
Destructionator XIII wrote:Also, in air, a plane turns by rotating along its long axis (the wings bank - it rolls). In space, that would do nothing.

As a matter of fact that does nothing to change the direction of an aircraft, either. It is I believe called a barrel roll. To actually turn, you COMBINE pitching (which the roll turns into a horizontal as opposed to vertical turn) with yawing (which would produce minimal course changes on its own thanks to inertia and aerodynamic drag).

Actually, Destructionator XIII had it correctly - it's the roll that turns the airplane, not the pitch or the yaw. Which is not to say pitch and yaw aren't important, or aren't used, but they are not the main thing here. (The reason pitch and yaw come into play is that aircraft do not work in a vacuum. Literally. The medium through which they travel does have an effect upon them)

To turn an aircraft you bank - that is, you roll about the longitudinal axis. The lift generated by the wing, which up until that point was maintaining your straight and level flight, then acts along a different vector which results in a change of course. The yaw involved is actually adverse yaw the "adverse" meaning "unwanted" - the nose actually pulls opposite the direction of turn, which reduces efficiency while increasing drag. The pilot uses the rudder to correct this. Early aircraft had LOTS of adverse yaw, since then we've learned to design the airframe to minimize this effect to the point that in turns with small banks - let's say under 30 degrees - it may be possible to make an acceptable turn without needing to touch the rudder. The pitch involved is used solely to counteract the drag and g-forces generated by making the turn, which otherwise might result in a reduction of altitude. Even then, it's only in high bank/high g turns that you really need to increase the pitch significantly.

You turn the aircraft with the ailerons, not the stuff on the tail. The exception being looping manuvers, which are turns but are turns generated and controlled by the elevator (or equivalent, as not all airplanes use identical control surfaces). The only time I can think of the rudder being properly used to make a turn would be a manuver such as a hammerhead, where pretty much the tail is your only working control surface anyhow. At that point you're getting into aerobatics which is not an area of aviation I have much knowledge of.

Of course, you can have manuvers such as climbing/descending turns and even more complex manuvers where you combine control inputs to, essentially, perform multiple simultaneous changes.

Depending on which way you want to turn, it's either. Pitch would be vertical, yaw would be horizontal (in a spacecraft those would presumably be relative to your direction of travel).

Nope - pitch, yaw, and roll are relative to the vehicle, not the direction of travel.

Pitch is movement about the lateral axis, yaw is movement around the vertical axis, and roll is movements about the longitudinal (or long) axis. Just light starboard, port, stern, and bow all are defined relative to the ship, not the direction of travel or an outsider's viewpoint.
Last edited by Broomstick on 2007-01-12 11:45am, edited 1 time in total.
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Postby Broomstick » 2007-01-12 10:58am

Destructionator XIII wrote:Like has been said, having work well in space and air is pure wank. Even if you ignore the technical difficulties mentioned, aircraft and spacecraft are also controlled very differently.

And I think that is a key point to remember.

Spacecraft fire thrusters to start and stop spinning, then the aft engine for a short burn to change their velocity. Aircraft use their engine to maintain their speed and use air resistance to change direction.

Very concise, I like that.

Also, in air, a plane turns by rotating along its long axis (the wings bank - it rolls). In space, that would do nothing. To change direction, you must rotate on another axis (if you look at it from above, you see it spinning in those two directions. I'm sure there is an aviation term for this, pitch or yaw I think, but I'm not sure). Whatever it is called, it is a very different move.

Or, to look at it a different way, an aircraft changes direction by pushing againt the air, much like a runner might rebound off an obstacle or grab a pole and then swing around it. In space, the ship is more like a runner on a featureless plain with no obstacles to utilize - all course changes are produced through internal power as it were. A very imprecise analogy, so don't expect it to map exactly, but it may help some folks visualize one of the differences between air travel and space travel.

The pilot would have to be aware of this and fly the craft differently in different environments. Even with a computer automatically detecting the change and switching the controls over so it simulates uniformity, the pilot would still have to know what is going on, and it would not be easy to get used to or train for.

I'm not so sure it's the inherent difficulty so much as having to thoroughly learn two different systems to equal proficiency. Then it becomes a matter of time and experience. As an illustration, it's quite common for new commercial pilots to be in their mid to late 20's. First time space shuttle pilots are typically in their early 40's. Does anyone have info on the ages of the Mecury and Apollo guys? I'm guessing late 30's to early 40's when they went up. And those were military pilots, which tend to be younger than their civilian counterparts in equivalent jobs. Rutan's first civilian spacepilot was over 60, the second somewhere late 40's to his 50's.

Presumably, more time, advancing technology, and a general rise in knowledge will push these first-time spacepilot ages downward somewhat, but you're still looking at extensive training to turn out a compentent aerospace pilot.

That brings me to another problem: the pilot would have to physically get used to the difference of being in freefall or fighting gravity. When astronauts get into orbit, many of them feel 'space sickness' which lasts a few days. They become disoriented and many even vomit. Their sinuses also get clogged. Then when returning to Earth, they readjust to gravity pretty quickly, but in the mean time, have some trouble in getting used to it: they would be in no condition to pilot a fighter airplane, or fight at all.

Although with more experience the spacesickness/gravity issues become less severe, this is an important human limitation to remember. Even the rather modent changes in g-forces experienced by airpilots take some getting used to, and on the upper end acclimitization is easily lost - aerobatic pilots who haven't flown manuvers for several months are advised to re-acclimitate on the same schedule as a first-time aerobat, starting with no more than 30 minutes at a time and gradually working their way back up to tolerance. Evolution did not really adapt us to these sorts of environments.

And different planets would have different atmospheres and masses, so the instruments on the aircraft would have to be readjusted to be accurate in this new environment as well (and most these instruments would be completely worthless in space, cluttering the cockpit). Even more things for the pilot to worry about.

You know, I think we may have touched on that in an old nBSG thread....

I looked at the objective of attacking a place and rescuing prisoners, and getting them back to the ship safely. The reason I chose this as a goal was that is was the only one I could think of that seemed feasible and somewhat plausible.

Or other snatch-and-run of any small, portable valuable.

Also, through a good portion of the reentry, the dropship would be blind: the plasma building up under it would block its radio transmissions and reception. It would also be easily visible to the defender - sneaking up on them is not possible.

Well, "sneak" is sort of a relative term - you may come in blazing like a meteor, but if you can get down fast enough the enemy won't have time to effectively block you.
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Now I did a job. I got nothing but trouble since I did it, not to mention more than a few unkind words as regard to my character so let me make this abundantly clear. I do the job. And then I get paid.- Malcolm Reynolds, Captain of Serenity, which sums up my feelings regarding the lawsuit discussed here.

If a free society cannot help the many who are poor, it cannot save the few who are rich. - John F. Kennedy

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Postby Broomstick » 2007-01-12 11:09am

Destructionator XIII wrote:And one last thing: I said it must have thrusters to adjust during reentry, which is true of the space shuttle, but I am not sure if that is true on all craft entering the atmosphere. Apollo's capsules I think just fell entirely unpowered, and finally parachuted into the water where the astronauts were picked up by waiting naval ships. So it might be possible to get by without the little thrusters (again, I am not sure), but of course, the other problems still stand, which are enough on their own.

In theory you could just launch something on a calculated vector and have it land precisely where you want it to. In practice, I don't think we can do that yet, and maybe never. We do pretty good - after all, we launch space probes to the outer solar system, have them loop around various planets, and most of the time they get to where we want them to go - but inevitably there are some sort of thrusters for course correction. Why? Because you might hit enough micro-bits to throw you off course. Because the atmosphere of a planet is dynamic, expanding and contracting and subject to currents of various sorts.

The shuttle lands precisely because it is an atmospheric craft as well as a space-going one. The Mecury and Apollow capsules re-entered on carefully calculated tragectories, had corrective thrusters, and still had massively large landing zones (one reason for landing them in the ocean was fewer hard lumps to hit). The Soviets, likewise, landed their spaceships in Siberia - relatively featureless landscape with fewer valuable things to collide with. For both space programs in the '60's, exact landing spots could not be determined in advance and a search was required to locate the returning capsules.

Increase computer power, knowledge, technology, and experience have enabled us to refine our landing abilities, but we still need real-time course monitoring and correction.
A life is like a garden. Perfect moments can be had, but not preserved, except in memory. Leonard Nimoy.

Now I did a job. I got nothing but trouble since I did it, not to mention more than a few unkind words as regard to my character so let me make this abundantly clear. I do the job. And then I get paid.- Malcolm Reynolds, Captain of Serenity, which sums up my feelings regarding the lawsuit discussed here.

If a free society cannot help the many who are poor, it cannot save the few who are rich. - John F. Kennedy

Sam Vimes Theory of Economic Injustice

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Postby Broomstick » 2007-01-12 11:23am

Destructionator XIII wrote:
darthbob88 wrote: produce near instantaneous braking or changes in direction.

*splat*

That was the sound of the pilot being turned to chunky salsa by the acceleration.

Other alternative sound effects include >squish< and POP!, depending on the forces involved. :twisted:

You also need to remember if there are people involved, they are often going to be the limiting factor. When talking about accelerations, there is only so much a body can take before breaking (bones can take only so much force) or causing the pilot to black out (blood not getting to the brain means no oxygen means no function).

I'm not sure of the g-force limits of bones, and for our purposes it doesn't matter so much as other g-limits because the bones can take more than a lot of other essential body parts can.

As a general rule - remember, people vary, being individuals - human beings start passing out at 5-6 postive g's due to blood being pulled out of the brain. There are tricks to increase the upper number, including certain breathing techniques, tensing lower body muscles, and g-suits, but they have limits. Generally, those limits are around 9 g's for a fully g-suited, trained, and acclimatized individual.

Some people have, through various sorts of training, managed to remain concious up to brief loads of 15-20 g's, but these are brief, even momentary g-loads and the individuals were expecting them to occur and so were able to maximally prepare for them. Part of the reason conciousness wasn't lost in these instances was because the length of time of the g-load was less than the time needed to drain blood out of the brain.

The aorta - a very major blood vessel one simply cannot live without - tends to rip out of its attachment to the heart starting around 20 g's. Smaller individuals will tend to have a slightly higher tolerance because, being physically smaller, the total weight imposed on the structure will be less which is one area where the short and female have an edge over the tall and male. This difference, however, isn't likely to be significant in most scenarios.

In other words, 20 g's and above tends to be fatal not due to broken bones but rather destruction of the cardiovascular system. 10-20 g's for more than a few minutes tends to be fatal due to brain not being sufficiently oxygenated. You can get strange scenarios of people surviving extreme g-loads but they're flukey/freaky and in any case the g-load doesn't last very long.

For a great many tasks, actually having someone there is a liability. If you do want to have a human in the loop, you have to remember all his limitations, both mental and physical.

So why have humans at all?

Because we handle the unexpected better than computers do. That's the one advantage human brains have - we improvise, create, and handle novelty much, much better. For the routine you want the machine, for the new you want the human.
A life is like a garden. Perfect moments can be had, but not preserved, except in memory. Leonard Nimoy.

Now I did a job. I got nothing but trouble since I did it, not to mention more than a few unkind words as regard to my character so let me make this abundantly clear. I do the job. And then I get paid.- Malcolm Reynolds, Captain of Serenity, which sums up my feelings regarding the lawsuit discussed here.

If a free society cannot help the many who are poor, it cannot save the few who are rich. - John F. Kennedy

Sam Vimes Theory of Economic Injustice


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