|
Post by Kerr on Nov 1, 2017 15:14:34 GMT
In my case, I have antimatter beam core (drive) vessels with fission reactors in the MW range; formed out of a culture that wanted to zip around fast and not much else - transports for the most part; with automated ion drive probes and lesser fission engine (though up to gas cores) for 'cargo', whatever that may be. So we have zip cans running around that for some reason are now armed and shooting at each other, but their reactor tech throws out anything but gunpowder weapons and missiles for the most part, right? If I understand correctly you want an reason Why you have AM Beam Core but use chem missiles and chemical guns?
|
|
|
Post by EshaNas on Nov 1, 2017 15:16:43 GMT
In my case, I have antimatter beam core (drive) vessels with fission reactors in the MW range; formed out of a culture that wanted to zip around fast and not much else - transports for the most part; with automated ion drive probes and lesser fission engine (though up to gas cores) for 'cargo', whatever that may be. So we have zip cans running around that for some reason are now armed and shooting at each other, but their reactor tech throws out anything but gunpowder weapons and missiles for the most part, right? If I understand correctly you want an reason Why you have AM Beam Core but use chem missiles and chemical guns? Not really, just what would work thereof. However, I am close enough to slapping a few Bushmasters or somesuch, much like BSG did, and calling it a day, compared to the problems and uncertainties that this great thread has crunched many times over.
|
|
|
Post by matterbeam on Nov 1, 2017 18:09:42 GMT
Hicks : The missile is a one-way spaceship. There are certain things you can do to a missile's drive to extract more performance because you only need to function for a short period of time - even if the design is a perfect copy of a spaceship drive. This might include running at an unsafe temperature, using corrosive propellants, removing radiation protection of emergency shutdown mechanisms and so on. SevenOfCarina : Bremsstrahlung is just light. It is massively easier to shield against light than it is to shield against penetrating neutrons. High frequency radiations such as X-rays can be blocked by thin layers of propellant. The amounts required are small enough that you can enclose the fusion fuels with these propellants/shields. When the propellant absorbs the X-rays, it heats up, explodes, and adds to your thrust. I made the same point about catching up to a target equipped with laser defenses when I said: "You want to minimize the time the missile spends floating in empty space. So, skewing the DVM/DVC balance towards DVM is recommended. Also, the spaceship might start accelerating in any number of directions away from the missile. This brings up the difference between AT and AM. Every m/s the target imparts in the same direction as the missile is removed from the DVM, so again we prefer having excess DVM. If your targets' AT is 50% of your missile's AM, then up to 50% of the DVM you carry onboard will be negated by the target." Accelerating just a bit faster than your opponent wastes a lot of deltaV and leaves the missile exposed to point-defense fire for longer than necessary. EshaNas : Watch out for how you scale the drive power! We already had nuclear thermal rockets with gigawatts of power output in the 70s (Project Timberwind, Rover). Making your advanced antimatter beam core engines less powerful than that would be quite weird. Kerr : I don't have that information, I am sorry. Very few if any modern laser manufacturers ever state the mass of their designs, and conceptual studies shy away from putting a 'kg' figure anywhere in their papers. I doubt however that efficiency is tied to specific power. Terawatt reactors are somewhat of a problem. Their main issue is the waste heat load. Imagine a modern rocket engine. Theoretically, you could point the ass of a Saturn V stage at the opening of a steam turbine and hope to extract 30GW of electrical power from a 60GW heat source. In practice, this isn't viable. Managing the heat load would require stupendously heavy equipment. The same goes for multi-terawatt rocket engines. Theoretically we can close the loop and have the exhaust point at an MHD. In practice, it would be a very inconvenient design.
|
|
|
Post by Kerr on Nov 1, 2017 19:12:16 GMT
matterbeamI just wanted your swag on the topic. I mean it terms of laser kind, something like an flash/arc pumped laser might have a far worse efficiency than say a FEL, but the Flash-pumped laser can operate at temperatures up to 900K, where the FEL requires cumbersome heat pumps so it doesn't need heat radiators that classify as a megastructure. Sure thing, it won't be efficient in any kind. Like for example exploding thermonuclear devices inside a gigantic pit of water to power steam turbines. But the point is, if you can get multi-terawatt high gain and efficiency fusion, you won't have to worry about energy requirements anymore. Filtering out a few tons of deuterium out of seawater in for example an saltwater treatment plant can support an such an superlaser for months of continuous firing. But some infos about the ITER Gyrotron suggest that performances of up to 10kW/kg for FEL's and Gyrotrons might be possible to achieve. Also thanks for the Gyrotrons infos, assuming an 80% efficient microwave gyrotron at 10kW/kg, and 75% efficient heat pumps at 1kW/kg. Resulting in 48t for an 252-62MW system. Plus an 21t 100m wide and 1mm thick aluminium mirror I get roughly 17.5mm/s at 10Mm, 68.8mm/s at 5Mm, 275mm/s at 2.5MM, 1.46m/s at 1Mm. I've assumed that an quality factor 5 might be reasonable, but I think it is a bit optimistic.
|
|
|
Post by Hicks on Nov 1, 2017 19:15:10 GMT
Hicks : The missile is a one-way spaceship. There are certain things you can do to a missile's drive to extract more performance because you only need to function for a short period of time - even if the design is a perfect copy of a spaceship drive. This might include running at an unsafe temperature, using corrosive propellants, removing radiation protection of emergency shutdown mechanisms and so on. No? Missiles have 4 advantages over starships, they usually present a much smaller crossectional area and are therefore harder to accurately target at long range, their thrusters may accellerate faster than a crew could survive, they can use self destructive weapons without killing an onboard crew, and they can be launched from outside of a target's direct fire defence envelope. For these 4 concrete advantages they can suffer light speed lag if their controller is far enough away, and are more difficult to armor because they have a lower reaction mass to payload ratio for the same thickness of armor. But you're talking about fusion rockets, and I've yet to see a realistic design that is 100% efficient at rejecting all thruster waste heat with the rocket exaust. That means massive radiator wings for a fusion thruster, which favors the ship over the missile for the remass:payload dV ratio and balloons the targetable cross-sectional area of the missile. To mitigate that the missile would use a casaba nuclear lance to increase its effective destructive envelope. And then it's a question of engineering if the space ship defends itself with a big ass laser or goes back to the 60s and rapid fires a cloud of defensive casaba nuclear lances from conventional cannons or coil guns, either from the ship itself or more likely a defensive drone. As an aside, Casaba nuclear lances. Gosh, how great would it be for them to be in CoaDE? I'm pretty sure the meta would shift to drone blast launchers filled with ejectable nuclear lances.
|
|
|
Post by Kerr on Nov 1, 2017 19:29:25 GMT
Hicks : The missile is a one-way spaceship. There are certain things you can do to a missile's drive to extract more performance because you only need to function for a short period of time - even if the design is a perfect copy of a spaceship drive. This might include running at an unsafe temperature, using corrosive propellants, removing radiation protection of emergency shutdown mechanisms and so on. No? Missiles have 4 advantages over starships, they usually present a much smaller crossectional area and are therefore harder to accurately target at long range, their thrusters may accellerate faster than a crew could survive, they can use self destructive weapons without killing an onboard crew, and they can be launched from outside of a target's direct fire defence envelope. For these 4 concrete advantages they can suffer light speed lag if their controller is far enough away, and are more difficult to armor because they have a lower reaction mass to payload ratio for the same thickness of armor. But you're talking about fusion rockets, and I've yet to see a realistic design that is 100% efficient at rejecting all thruster waste heat with the rocket exaust. That means massive radiator wings for a fusion thruster, which favors the ship over the missile for the remass:payload dV ratio and balloons the targetable cross-sectional area of the missile. To mitigate that the missile would use a casaba nuclear lance to increase its effective destructive envelope. And then it's a question of engineering if the space ship defends itself with a big ass laser or goes back to the 60s and rapid fires a cloud of defensive casaba nuclear lances from conventional cannons or coil guns, either from the ship itself or more likely a defensive drone. As an aside, Casaba nuclear lances. Gosh, how great would it be for them to be in CoaDE? I'm pretty sure the meta would shift to drone blast launchers filled with ejectable nuclear lances. You don't have to eject 100% of all waste heat into the exhaust. For example D-HeΒ³, you have 75% protons and alpha particles, 20% X-rays and 5% Neutrons. 90% of Neutrons and x-ray will most likely just fly off into space, the remaining 10% will be absorbed by the blade shields which operate at 3000K and thanks to their 200:1 angle they reflect 99% of the x-rays, and because the blade shield is made out tungsten 99% of neutrons energy are scattered out of bladeshield. The remaining problem is magnetic nozzle efficiency, 85% is pretty much the practical maximum, which means you are left with 11% of the reactions waste heat, but you can have an magnetic field around your ship to protect it from the charged exhaust like it protects the ship from solar radiation storms. I dunno if it would be great, the details of the casaba howitzer indicate that they would annihilate anything from even 10Mm distances.
|
|
|
Post by matterbeam on Nov 2, 2017 1:12:12 GMT
@wtfitsomg: I kind of dislike that guesswork. Either I can get a rough estimate or I just make sure the numbers don't matter. Here's my take on a high power density laser weapon system based on today's technology: Gyrotron-pumped VECSEL. I found the laser to be 10kW/kg and has an efficiency of 50%. However, seeing the performance of frequency doublers, 60% would be a better figure. Personally, I would go for fibre optic lasers. Their lower efficiency (~50%) is largely compensated for by high resistance to heat and simple design. Heat pumps have an efficiency and a coefficient of performance. The former is debatable but values from 35% to 80% have been reported. The latter is defined by the ratio of the hot side temperature to the temperature gradient. So, for example, pumping heat from a 500K source to a 1500K radiator incurs a 1500/1000: 1.5x energy penalty. For each watt you move, you need to feed the heat pumps 1.5W. Then, the intrinsic efficiency comes into play. At 80% efficiency, the heat pump actually needs 1.875W per watt moved. The actual efficiency becomes 53%. If laser weapon webs are a thing in your setting, there is no point in ever having a single massive mirror. You have your laser generator and a 'first link' mirror. This first link connects to an interplanetary network of laser mirrors, or a tactical fleet of mirror drones. Placing a mirror halfway to your target dramatically reduces the total mirror area: the 'first link' mirror only needs to keep the beam spot size smaller than the 'second link' mirror, and the 'second link' mirror only needs to focus across half the distance. The 'first link' can therefore have a massive spot size at the halfway distance. The second link has 1/2^2: 1/4 times less area than a mirror that tries to focus across the entire distance. In total, a simple mirror at halfway might reduce the total mirror area to perhaps 26% of the single-mirror setup!
|
|
|
Post by ππππππππππ on Nov 2, 2017 4:00:10 GMT
Terawatt grade is a pretty high level of power. We are talking about reactors that if coupled with a laser, could easily snipe spaceships at millions of kilometers of distance! The missiles will have to be very effective to stay in the game. Neutron radiation is something you want to avoid if you want high specific power fusion propulsion. At low power, you can just use shielding and passive cooling. At terawatts of power, you could have hundreds of gigawatts escaping a D-T reactor. They do not contribute to the propulsion and require huge amounts of shielding on top of a thermal management system that can handle hundreds of gigawatts of waste heat. With aneutronic fusion, especially p-B11, your shielding and cooling requirements are much lower and simpler. Going by my extremely feeble understanding of high temperature particle physics, shouldn't p-B11 fusion still produce bremsstrahlung? If I'm interpreting this study correctly, at the 300keV plasma energies necessary for p-B11 fusion, 600 gigawatt of bremsstrahlung X-rays can be expected for every terawatt of fusion power. This compares to 200 gigawatt per terawatt for D-He3, which still produces neutron radiation equal to 5% of the fusion power. Is there something about bremsstrahlung that intrinsically makes 400GW of it easier to shield from than 50GW of neutron radiation? Or have I misunderstood something? One trick to obtaining better missile performance without changing increasing power requirements is sacrificing your Isp and increasing your thrust. This shortens the time it takes for a missile to catch up with its target, so it has to spend less deltaV overall. In my opinion, merely catching up to a warship with terawatts of thrust power is of no consequence when a missile swarm is going too slow to clear the killzone before being wiped out by point defence lasers. Even standoff warheads like casaba-howitzers become useless when lasers can shred non-maneuvering targets at ranges of millions of kilometres, unless a missile has a high relative velocity (>1000km/s) and high acceleration (>1m/s2). just remember that, even if the terawatt reactor only cost 1 gigacredit, in the game, its not practical in real life, and the actual amount of R&D required would make it so that only very advanced nations could use them. that means that if you are the side with terawatt reactors, you can probably use missiles because the enemy doesnt have good enough rech to laser snipe them from the other side of the solar system.
|
|
|
Post by bigbombr on Nov 2, 2017 5:36:14 GMT
@wtfitsomg: ... If laser weapon webs are a thing in your setting, there is no point in ever having a single massive mirror. You have your laser generator and a 'first link' mirror. This first link connects to an interplanetary network of laser mirrors, or a tactical fleet of mirror drones. Placing a mirror halfway to your target dramatically reduces the total mirror area: the 'first link' mirror only needs to keep the beam spot size smaller than the 'second link' mirror, and the 'second link' mirror only needs to focus across half the distance. The 'first link' can therefore have a massive spot size at the halfway distance. The second link has 1/2^2: 1/4 times less area than a mirror that tries to focus across the entire distance. In total, a simple mirror at halfway might reduce the total mirror area to perhaps 26% of the single-mirror setup! This assumes mirrors are 100% efficient.
|
|
|
Post by Kerr on Nov 2, 2017 5:42:10 GMT
@wtfitsomg: ... If laser weapon webs are a thing in your setting, there is no point in ever having a single massive mirror. You have your laser generator and a 'first link' mirror. This first link connects to an interplanetary network of laser mirrors, or a tactical fleet of mirror drones. Placing a mirror halfway to your target dramatically reduces the total mirror area: the 'first link' mirror only needs to keep the beam spot size smaller than the 'second link' mirror, and the 'second link' mirror only needs to focus across half the distance. The 'first link' can therefore have a massive spot size at the halfway distance. The second link has 1/2^2: 1/4 times less area than a mirror that tries to focus across the entire distance. In total, a simple mirror at halfway might reduce the total mirror area to perhaps 26% of the single-mirror setup! This assumes mirrors are 100% efficient. You can usually get pretty close to 100% efficiency, if you use frequencies higher than 200nm.
|
|
|
Post by Kerr on Nov 2, 2017 5:51:34 GMT
@wtfitsomg: I kind of dislike that guesswork. Either I can get a rough estimate or I just make sure the numbers don't matter. Here's my take on a high power density laser weapon system based on today's technology: Gyrotron-pumped VECSEL. I found the laser to be 10kW/kg and has an efficiency of 50%. However, seeing the performance of frequency doublers, 60% would be a better figure. Personally, I would go for fibre optic lasers. Their lower efficiency (~50%) is largely compensated for by high resistance to heat and simple design. Heat pumps have an efficiency and a coefficient of performance. The former is debatable but values from 35% to 80% have been reported. The latter is defined by the ratio of the hot side temperature to the temperature gradient. So, for example, pumping heat from a 500K source to a 1500K radiator incurs a 1500/1000: 1.5x energy penalty. For each watt you move, you need to feed the heat pumps 1.5W. Then, the intrinsic efficiency comes into play. At 80% efficiency, the heat pump actually needs 1.875W per watt moved. The actual efficiency becomes 53%. If laser weapon webs are a thing in your setting, there is no point in ever having a single massive mirror. You have your laser generator and a 'first link' mirror. This first link connects to an interplanetary network of laser mirrors, or a tactical fleet of mirror drones. Placing a mirror halfway to your target dramatically reduces the total mirror area: the 'first link' mirror only needs to keep the beam spot size smaller than the 'second link' mirror, and the 'second link' mirror only needs to focus across half the distance. The 'first link' can therefore have a massive spot size at the halfway distance. The second link has 1/2^2: 1/4 times less area than a mirror that tries to focus across the entire distance. In total, a simple mirror at halfway might reduce the total mirror area to perhaps 26% of the single-mirror setup! Well, that is exactly what I wanted to know from you, thank you. I thought the calculation for heat radiators was T,hot/T,cold/Ξ·. So 1500/500/0.75=4 watts per removed watt of heat. I've also included the frequency doublers inefficiencies combined with heat pumps. The big r=50m mirror was an example for an laser in a "setting" where laser webs aren't widespread, mirror drones would make sense as they can highly increase lethality at high ranges.
|
|
|
Post by EshaNas on Nov 2, 2017 8:06:58 GMT
. EshaNas : Watch out for how you scale the drive power! We already had nuclear thermal rockets with gigawatts of power output in the 70s (Project Timberwind, Rover). Making your advanced antimatter beam core engines less powerful than that would be quite weird. As in using some of the antimatter beam core itself tie into power production? I had, admittedly, barely touched that.
|
|
|
Post by Kerr on Nov 2, 2017 15:30:35 GMT
. EshaNas : Watch out for how you scale the drive power! We already had nuclear thermal rockets with gigawatts of power output in the 70s (Project Timberwind, Rover). Making your advanced antimatter beam core engines less powerful than that would be quite weird. As in using some of the antimatter beam core itself tie into power production? I had, admittedly, barely touched that. You use beam core designs, which focuses charged particles out of the nozzle, those particles could be converted into electricity at efficiencies of 90% using Direct Conversion.
|
|
|
Post by matterbeam on Nov 2, 2017 16:02:25 GMT
@wtfitsomg: ... If laser weapon webs are a thing in your setting, there is no point in ever having a single massive mirror. You have your laser generator and a 'first link' mirror. This first link connects to an interplanetary network of laser mirrors, or a tactical fleet of mirror drones. Placing a mirror halfway to your target dramatically reduces the total mirror area: the 'first link' mirror only needs to keep the beam spot size smaller than the 'second link' mirror, and the 'second link' mirror only needs to focus across half the distance. The 'first link' can therefore have a massive spot size at the halfway distance. The second link has 1/2^2: 1/4 times less area than a mirror that tries to focus across the entire distance. In total, a simple mirror at halfway might reduce the total mirror area to perhaps 26% of the single-mirror setup! This assumes mirrors are 100% efficient. 98% reflectivity down to 1nm wavelength: www.newport.com/g/optical-mirror-selection-guide
|
|
|
Post by Kerr on Nov 2, 2017 16:15:16 GMT
I though only grazing incidence mirrors are possible at these wavelengths?
|
|