Vladika
SOC-14 1K
HG1 covered that very thing nicely. Additionally, practically EVERY piece of OTU artwork to date depicts a reaction mass thrust drive of SOME type.
A jump drive replacement for T5
- Thread starter Spaceresearcher
- Start date
HG1 covered that very thing nicely. Additionally, practically EVERY piece of OTU artwork to date depicts a reaction mass thrust drive of SOME type.
esampson
SOC-13
Oh! Yeah, that probably isn't much of an issue in a hard sci-fi setting, at least not in ship to ship combat. The distances between ships in space is so large that using your exhaust to attack someone is probably about as viable as a jet fighter using its wing turbulence against another plane.
Niven is correct that it is directly proportional, but HEPlaR drives are far less efficient that the fusion drives in Niven's universe and the main reason the fusion drives were usable as weapons in ToKS was because the Kzinti had forgotten about fusion drives (they were using gravity polarizers) and got suckered a couple of times. After that the humans had to switch to using their communication lasers as weaponry.
vladika said:
It's not so much their use in combat, which is what HG1 addressed, that's arguable although if you can shoot another ship with fusion guns or spinal mount particle accelerators, I really don't see why you can't shoot it with what is effectively a spinal mount fusion cannon. Anyway that's a side issue I'm prepared to concede.
The main problem is their use as a terror weapon, which is exactly what the planet killer problem is about as well. After all, if you can get close enough to dock with a space station, other ship, or even a ground based star port with a HELPAR drive, you are close enough to turn it into molten slag. The jet engine comparison just isn't apt. Do the sums on a high thrust HEPLAR drive for a decent sized ship and it's destructive power is pretty impressive.
Simon Hibbs
Various assumptions can be made... but HEPlaR has, apparently, an exhaust velocity in excesss of 1300km/s... in other worlds, about 0.5 PSL as the floor of HEPlaR exhaust speed. That should abraid away anything within a few hundred meters. (Keep in mind the abrasive effects of Helicopters, which move air only about a few hundred m/s.)
esampson
SOC-13
An fusion engine really isn't a spinal mounted fusion cannon. The whole reason I mentioned nuclear power plants and nuclear bombs was to illustrate the fact that even though they both have the same adjective they are really vastly different creatures (I realized later that we actually currently have some nuclear powered space vehicles that absolutely cannot do any kind of explosion on their own)
Consider this, and cannon is designed to minimize recoil and maximize how far it can deliver its payload. To be effective at space combat distances it has to have all sorts of equipment designed to take a relatively small package (in relation to what an engine has to output for thrust) and bundle it so it won't dissipate over distances of tens of thousands of miles. An engine on the other hand would be designed to do almost the exact opposite. It will be designed to have the absolute highest recoil possible. That will be a primary portion of its design since that's how it works.
I would also speculate that it will have secondary design concerns with trying to minimize the distance at which its exhaust is dangerous. This won't be an overwhelming design concern but in the same way that modern laws mandate such things as catalytic converters and mufflers which have a small negative impact on the overall performance of a car engine I think we can assume that the Imperium might have some laws that have small negative impact on engine output in order to reduce certain negative aspects of the engine (primary of which in this case is the dangerous exhaust). One solution might be some sort of mandatory diffuser in the design that expands the cone of escaping fusion (after it has cleared the nozzle) to around 5 degrees. This should still provide around 99% efficiency while expanding the exhaust by 8% of the distance travelled (and because the energy per meter is based on the area of the cone an 8% spread is an 18% reduction in energy per square meter).
Is it possible to design an mechanism that could be simultaneously used as both an engine and a weapon? Sure, but it would probably be very, very complicated to do so. You have aspects that I listed above that are mutually exclusive so you would need either some incredibly versatile equipment that would be capable of alternately confining smaller amounts of ejecta and packaging it or else directing larger amounts of ejecta for thrust or else you would need two complete sets of equipment (maybe some sort of magnetic bottling system before the magnetic nozzle and then another magnetic projecting system after it). If players (or terrorists) actually built their engines from scratch maybe some really talented ones could make a go of that but for the most part people just buy pre-built engines.
That is more of an issue, and it is one I've thought about as well. The idea of people using engines in that way does seem much more plausible than the idea of people using the thrust of their HEPlaR drives to cut up each other's ships in space combat. However I feel relatively sure that even that threat can be diminished more than you would think at first glance.
As I said earlier, those engines really have pretty short ranges. Sure, the particles are travelling at very high speeds but if we take your average 100 dton ship and we assume it weighs around 500 metric tons (just a very rough conversion based on size and weight of RL ships) that means a 6 G Heplar drive is putting out around 2.94 x 107 Newtons of force. At a distance of 2 km with a 5 degree cone it will have a cone just over 174 m across. This gives us a surface area of just under 23,863 m2 which means that the energy impacting the surface at that point is just under 1,232 N m2/s or 1,232 Watts per m2.
This is actually less than the amount of energy the Earth recieves from sunlight.
But what about as the ship gets even closer? Well, first off 2 Km is already incredibly close when you are talking about landing or docking. Go ahead and play a couple of Orbiter scenarios and you'll see what I'm talking about. When you are at those distances you are well, well into 'final approach' and when you get that close you don't use your main engines. You are using your Reaction Control System which are all the tiny little jet nozzles that sit all over your craft at the wingtips, nose, tail, etc. When you are in space your main engines are completely cold at this point. When you are landing in Orbiter you might be using them a little, but then Orbiter lacks gravitational lifters which you would be using.
Now the thing is that these engines are big. Really big. These aren't the kinds of things where you can stomp on the gas and in the space of a few seconds the engine suddenly goes from cold to running full bore like your car. It takes time to spin them up.
So what seems most likely to me is that any places such as space stations or reasonably equipped Starports (pretty much any place with an equivalent of Air Traffic Control) will have some kind of scanner monitoring the ships coming in. If you come too close (say 100 km) while performing landing (or docking) manuevers and your engines are reading as 'hot' they are going to wave you off. Keep coming in and 'appropriate measures' will probably be taken in the interests of self defense. Try and gun your engines at the last minute? Let's see, you're being tracked, you are basically at point blank range and you are travelling really slow. No, I don't think this is going to end well for you.
All of this, of course, is assuming that you aren't required to turn over control of your ship to the ground for safety reasons, a distinct possibility (we actually still do this in real life with ships entering harbors, although in that case it isn't done via remote but by a harbor pilot who comes on board, so don't just brush it off as 'people wouldn't put up with it'.)
Is that system fool proof? No, of course not, but it doesn't need to be. Like any safety system it only needs to reduce the 'threat' to a reasonable level. After all, even if the planets went absolutely berserk and did create some sort of unbeatable system for handling this sort of situation they would still face dangers such as people ramming their ships into the ground at high velocities, people dumping bowling balls and lawn darts out of the cargo bay while in orbit, or people packing nuclear devices on the ship and detonating them. All the security measures really need to do is reduce the threat to the point where something else becomes the more probable danger.
esampson
SOC-13
I should ammend something, this actually is a non-trivial amount of energy. You certainly would not want to be out on the tarmac being bombarded with this amount of energy without some form of protection. If you did it during the daytime it would be like being under a rather large magnifying glass (though not being at the focal point). Even at night the odds are that most of that is ionizing radiation as opposed to large amounts of EM that we are adapted to deal with. However, the energy output is low enough that it is almost a certainty that structures could be designed to handle it and protective gear for people required to be in what might constitute a danger zone should be quite possible.
I don't remember the engine type, but I read years ago the first encounter of a Human ship and a Kzin ship. The humans didn't have weapons. The Kzin was thinking of toying with them... then one of the human got the idea of spinning the ship around and using engine exhaust to heat the Kzin ship's atmosphere to super hot temperatures. The Kzin all died.
It's also only taking into account the kinetic energy and completely ignores the thermal energy of what is, if I might remind everyone, a fusion reactor core exhaust plume.
Another point is penetrative power. The recoil of a pistol into a shooter's hand is the same kinetic energy as that of the bullet hitting the target. It's all about velocity and impact area. The rocket exhaust will be a mix of subatomic particles and ionized atoms traveling at 5% of the speed of light. The impact energy per sq meter may not be that great that far out if you assume it's spread out evenly, but in reality the particle storm is going to tear through normal matter like a hail of bullets through a crowded street.
Finally, any mandated system for spreading out the exhaust plume is going to have to be based on using a magnetic field as a choke. To stop the choke from spreading the beam, all you have to do is switch it off or otherwise cut it's power feed. I'm not sure how you're going to ensure that any ship approaching isn't capable of doing that.
So ok, I suppose the point is in principle arguable either way given enough enthusiasm and tweaking of assumptions.
The problem for me is that the planet killer problem is generally a theoretical one. That actual situation doesn't come up much in play except as a hypothetical and the players would have to go out of their way to put it into practice with multiple opportunities to throw curve balls at them in the mean time. Whereas a setting with ships armed with fusion rocket thrusters comes up with the drives-as-weapons problem all the time directly in play. Any time a player decided he's going to toast some bad guys using this fusion engine built right into his ship, this argument is going to come up and you're going to have to talk it out. It's a practical question of what a player can or cannot do right there and then with the equipment the character has immediately to hand. That's a much harder issue to brush under the carpet, especially with creative players that can come up with ways to get round any arbitrary obstacles you put in their way, such as the exhaust spreader concept.
Simon Hibbs
esampson
SOC-13
Actually, it's about impact area and the speed of energy transfer. Velocity doesn't figure into very much other than A) as a method for carrying the kinetic energy (little objects travel faster than larger objects with the same kinetic energy) and B) ensuring at least a certain minimum in the rate of energy transfer. When you fire a pistol the exact same energy is pushed back into the firer. However it is both spread over a larger area and because of the mass and operation of the gun the energy is delivered over a longer period of time.
Below a certain threshold, however, the length of time doesn't matter. It doesn't matter if the energy was delivered in .001 seconds or .00001 seconds. Remember, you are getting hit with high speed charged particles all the time. Just not very many of them thanks to our magnetic field. When one of them interacts with you the velocity and moment of transfer are ridiculously high. It is just that the amount of energy carried on a single particle is very low.
The recoil of a pistol is a great example for why a fusion drive would not make a good weapon. Assuming you had to design some sort of handheld propulsion device for an astronaught in zero-g which would be a more efficient design, something that functions like a sub-machinegun or something that functions more like a fire extinquisher?
Make it part of the overall containment system? If someone cuts the power to it the entire magnetic bottle goes 'pop' and the fusion reaction fizzles out? Put failsafes in the engine that shut it down if they detect that the magnetic choke is not functioning?
Yes, people can get around those given enough time. Again, such a system doesn't have to be foolproof. It simply has to make it difficult enough to use an engine as a weapon that people would chose other solutions.
Also, let's not forget that eliminating the magnetic choke is only part of the problem. The bigger issue is that actually you probably can't fly that close to starports, space stations, or heavily populated areas with your fusion drive on without authorities making a fairly vigorous response.
Sorry. I don't see the idea that ships would have mandated safety equipment that would make it harder to use an engine as a weapon of mass destruction as 'arbitrary'. Yes, the core concept behind what is going on in a fusion drive is scary (this is not, incidentally, saying they are terribly effective as weapons. Lots of things are 'scary' without actually causing that much damage. Far more people are killed by bees every year than sharks yet I have never seen a government try to string up bee netting). Things that are scary cause people in power to take action to make them less scary. That's not arbitrary. That's reasonable behavior on the part of NPCs (for a given definition of 'reasonable'. i.e. it accepts that people might be reacting emotionally and focusing on things that may not actually be as dangerous as immediately percieved).
Don't ask yourself 'why can't players do this'? Ask yourself 'if it really is this easy then why isn't it being done a lot'? As I see it there are three possible answers to that question.
The first is that it is being done a lot. People fly around in ships and use fusion exhaust to burn people out who sleep with their wives, fire them from a job, cut them off in traffic, etc. I think most of us can agree that isn't a good answer.
The second possible answer is that it isn't as easy as you think. You have to get much closer than you would think at first to use the engine as a weapon, especially since as soon as you turn it on you are going to be accelerating away very rapidly, so it isn't like holding a blowtorch on a target. You have to brake before performing the manuever because if you zip by at high speed you're more likely to cut a wide swath of superficial damage (not to mention the fact that if your trying this in an atmosphere you probably won't be able to point your main drive any more than 10 degrees off your line of flight).
The third possible answer is that in theory it is as easy as you think but because of that people make it hard. This is no more 'arbitrary' than the fact that it is really, really hard in the real world to buy fissile material. It is recognized that people could do bad things with it without too much difficulty and so steps are taken to prevent that.
The real answer probably lies somewhere between two and three. A 'pure two' world is one in which HEPlaR drives are completely safe. No one could use one as a weapon and so there is no need for authorities to step in. A 'pure three' would mean that they are absolutely as dangerous as you think and can burn out targets from dozens if not hundreds of miles away in the blink of an eye.
If that really were the case thenyou better believe that they authorities would be stepping in to prevent that. Maybe it is rules that force people to turn off their fusion drives when they are thousands of miles away. Maybe starships have to be on remote pilot within certain airspace. It doesn't really matter what the solution is because what is absolutely certain is that if you are living in anything but a universe where the drives are perfectly safe or else people just don't care then something is certainly being done.
Vladika
SOC-14 1K
Velocity has pretty much everything to do with the imparting of kinetic energy.
Kinetic energy of an object is directly proportional to the square of its speed. That means that for a twofold increase in speed, the kinetic energy will increase by a factor of four. For a threefold increase in speed, the kinetic energy will increase by a factor of nine. And for a fourfold increase in speed, the kinetic energy will increase by a factor of sixteen.
Given conservation of mass and energy:
(0.5 • m • v^2)ship = (0.5 • m • v^2)fission exhaust
I'd suggest trying not to stand behind it.
esampson
SOC-13
You cut out an important portion of that quote.
This was in response to a claim that the reason a bullet hurts the person who was shot while the same amount of kinetic energy being delivered to the shooter has a negligible effect was because the bullet was travelling faster.
Yes, a faster moving object has a greater amount of energy than a slower moving object of the same mass. It does not, however, become signigicantly more damaging than a slower moving object of a greater mass merely because it is travelling faster. If the slower moving object has greater kinetic energy then unless there are other extenuating circumstances that inhibit the transfer of energy the slower moving object will tend to inflict more damage (there's some wiggle room in there because a bigger object will have a larger cross section, but the core principal remains).
In this case we are dealing with objects with the same energy. When that happens you don't just get to wave your hand and say 'well yes, but since source A is faster it is automatically much more damaging'.
After all, you'll never get hit with anything travelling faster than a photon but the last I checked your average AA minimag-lite flashlight isn't going to suddenly start boring holes in anyone
Yes, photons are massless particles and the earlier particles we were discussing had mass, but it none the less illustrates that velocity isn't the sole factor. After all, given enough photons in a tight enough area delivered rapidly you can do some significant damage. That's because the Joules per second per m2 is very high. When that amount drops way down (as it did in my landing example earlier) it becomes very easy to resist that amount of energy.
And I'm not trying to claim you can simply stand behind the engine with no problem. Yes, it will fry you to a crisp in a matter of seconds. What I am saying is that it does not have some enormous 'lance of death' that allows you to use it on people who are miles and miles away. To use the engine as a weapon you have to get very, very close to your target. So close that it might make the manuevering very tricky since the thrust is trying to push you away from your target.
Is it impossible to do so? Not at all. Of course someone could do it. I've been agreeing with that all along. However the difficult involved is probably significant enough that it might be easier to just shoot the target with your shipboard weaponry.
...unless they were about to board you...
Similar threads
