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Post by bigbombr on Jun 6, 2017 20:47:38 GMT
Yes, I said (max) to state that this value is the highest possible efficiency for AM-Production. But even at 1% (9PJ/gram) efficiency Antimatter wins the day. For 90TJ you could produce 10mg of antimatter (5t payload to 2300km/s) or accelerate a 5kg spacecraft with 1-2kg payload to 120km/s. "Current particle accelerators are horribly inefficient at generating antimatter, but Dr. Forward says this is because they were designed by physicists, not industrial engineers. He is of the opinion that a dedicated antimatter factory built with current technology could approach 0.01% efficiency" www.projectrho.com/public_html/rocket/spacegunexotic.phpWhich is no longer hugely dominating over a laser sail. I prefer laser thermal propulsion over photon pressure. Where onboard propellant is heated by offboard (or possibly onboard, with tech advances) laser light and sent out a nozzle. Thrust is low but reasonable, and exhaust velocity is nice if you concentrate the light for extreme heat. A magnetic nozzle would probably be mandatory at high power. I always viewed laser thermal and lasersail as two very compatible technologies: you use laser thermal to get into orbit (if no Lofstromloop available), and lasersail for interplanetary and interstellar travel.
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Post by Kerr on Jun 6, 2017 20:51:58 GMT
Yes, I said (max) to state that this value is the highest possible efficiency for AM-Production. But even at 1% (9PJ/gram) efficiency Antimatter wins the day. For 90TJ you could produce 10mg of antimatter (5t payload to 2300km/s) or accelerate a 5kg spacecraft with 1-2kg payload to 120km/s. "Current particle accelerators are horribly inefficient at generating antimatter, but Dr. Forward says this is because they were designed by physicists, not industrial engineers. He is of the opinion that a dedicated antimatter factory built with current technology could approach 0.01% efficiency" www.projectrho.com/public_html/rocket/spacegunexotic.phpWhich is no longer hugely dominating over a laser sail. I prefer laser thermal propulsion over photon pressure. Where onboard propellant is heated by offboard (or possibly onboard, with tech advances) laser light and sent out a nozzle. Thrust is low but reasonable, and exhaust velocity is nice if you concentrate the light for extreme heat. A magnetic nozzle would probably be mandatory at high power. You don't have to produce all the antimatter yourself, "lots" of antimatter are trapped inside the magnetic of the earth, placing some magnetic trap satellites inside these rings might produce Antimatter. A 7t collector with a small 200 KW reactor generates 25ng per day. If you place several million of them around the solar system you can generate nearly a gram per day. Still let's take the numbers. Thanks for correcting my 1%. For 9PJ you can create 10mg of Amat, 2300km/s 5t payload. Or launching a Lightsail weighing 5kg to several to 12Mm/s. Or 12km/s for 5t payload (with a weightless sail). You mean laser ablative? Laser thermal has too low of a specific impulse to be considered even for interstellar travel. 90% Laser Ablative drive: Dv: 2080km/s Wet mass: 1800kg Dry mass: 900kg Burn time: 15min (900s) Still quite a bit worse than AM Fusion, and the 2300km/s is only for a 20% efficient D-T reaction. You can also use laser pulses to ignite fusion pellet. But this would increase the complexity to extreme amounts. Microsecond pulses, perfect focusing, infrastructure, and star system limited range. Laser is the answer for trade routes. AM fusion is the answer for military and exploration [1]. [1] Finding new places for colonies, ressources (He3, AM (if bigger than our sun)). and to place refocusing mirror lines, ike roadway being build.
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Post by Enderminion on Jun 6, 2017 21:49:23 GMT
jupider has a lot of Amat in its fields
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Post by The Astronomer on Jun 7, 2017 10:07:23 GMT
Actually I'm surprised that proton + Boron-11 fusion got so much votes. If I am correct, other than being fully aneutronic it is useless, being harder to start and releasing much less power than other reactions. Am I wrong about this?
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Post by Kerr on Jun 7, 2017 11:28:01 GMT
Actually I'm surprised that proton + Boron-11 fusion got so much votes. If I am correct, other than being fully aneutronic it is useless, being harder to start and releasing much less power than other reactions. Am I wrong about this? It's reactants can be made out of sea water. And it is even more aneutronic than D+He³. D+He³: 75% Helium-4, 5% Neutrons, 20% "Radiation". p+B11: 100% Helium-4. Other than that is pretty useless, maybe good for civil use in a Type I-II civilization.
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Post by The Astronomer on Jun 7, 2017 11:43:18 GMT
Actually I'm surprised that proton + Boron-11 fusion got so much votes. If I am correct, other than being fully aneutronic it is useless, being harder to start and releasing much less power than other reactions. Am I wrong about this? It's reactants can be made out of sea water. And it is even more aneutronic than D+He³. D+He³: 75% Helium-4, 5% Neutrons, 20% "Radiation". p+B11: 100% Helium-4. Other than that is pretty useless, maybe good for civil use in a Type I-II civilization. Still surprised, though. Proton + boron-11 is much harder to catalyze than deuterium + helium-3, and the output is also lower. Don't think even civilians would like to use it.
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Post by Kerr on Jun 7, 2017 12:02:22 GMT
It's reactants can be made out of sea water. And it is even more aneutronic than D+He³. D+He³: 75% Helium-4, 5% Neutrons, 20% "Radiation". p+B11: 100% Helium-4. Other than that is pretty useless, maybe good for civil use in a Type I-II civilization. Still surprised, though. Proton + boron-11 is much harder to catalyze than deuterium + helium-3, and the output is also lower. Don't think even civilians would like to use it. You Can divide the LC by 10x if you use a laser-generated proton beams. Again, it's cheap, cheap as dirt. Helium-3 is very rare, so it will be most likely be reserved for military applications where efficient and powerful fusion fuel will be needed. Other than that I have no idea why to choose it, same with D-T fusion. It has it's advantages, but also it's disadvantages. Overall D+He³ seems to be the best fuel performance wise, and D-T economically wise. Also 500x LC doesn't mean it needs 500x the energy, D-D has a criterion of 30x (13 KeV) but only needs 5x more energy than D-T (2,6 KeV). Other topic: I have calculated some numbers on how much AM you might need. For D-T, I couldn't find the "activation" energy for D+He³. For every TJ Fusion energy you need 2,057µg AM, example: An DT engine with 3Mm/s exhaust velocity and 100g mass flow needs 0,926µg of AM per second. For 10t D-T you need 92,6 mg Amat. Some documents mentioned that only 1µg Amat is enough to catalyze a fusion reaction any size but these numbers are for solid Fusion fuel balls which will also be compressed through explosive lenses. Important: This numbers only used the 3x 250 MeV Pions and none of Neutral Pions nor gamma rays. The Amat requirement might be actually a bit lower.
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Post by apophys on Jun 7, 2017 13:49:50 GMT
You mean laser ablative? Laser thermal has too low of a specific impulse to be considered even for interstellar travel. [...] You can also use laser pulses to ignite fusion pellet. But this would increase the complexity to extreme amounts. Microsecond pulses, perfect focusing, infrastructure, and star system limited range. Laser is the answer for trade routes. AM fusion is the answer for military and exploration [1]. [1] Finding new places for colonies, ressources (He3, AM (if bigger than our sun)). and to place refocusing mirror lines, ike roadway being build. No, I do mean laser thermal (I haven't actually seen laser ablative, and I'm not sure why there would be a difference). The reason for this is that, afaik, a laser can be focused onto an arbitrarily small space, heating up propellant to terrific temperatures. At high enough temperatures, the exhaust velocity becomes comparable to fusion power. Let me illustrate with a simulated example in CoaDE. Here's a diborane rocket. It takes less than 65 GW of heat to produce this kind of performance, which could be supplied by an external 100 GW laser at 65% efficiency. The craft itself would reach 1% lightspeed, and be able to decelerate from that on its own with an onboard 10 GW laser (albeit 10 times slower than the acceleration provided by an offboard 100 GW laser). Burn time for deceleration would thus be 100 months. Do note that 1.8 billion Kelvin is sufficient temperature to ignite proton-boron fusion (according to Wikipedia), which should significantly improve performance. But this isn't actually required for the craft to be useful. I am ignoring the mass and power of a magnetic nozzle, the mass of the main mirror, as well as the mass of onboard laser components and radiator (but these should all be negligible, I think, with a liquid droplet radiator on a 65% efficient laser). There may be some limits I am not aware of that would prevent this from being a good simulation of a laser thermal craft. Also, yay, god status.
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Post by Kerr on Jun 7, 2017 14:11:26 GMT
You mean laser ablative? Laser thermal has too low of a specific impulse to be considered even for interstellar travel. [...] You can also use laser pulses to ignite fusion pellet. But this would increase the complexity to extreme amounts. Microsecond pulses, perfect focusing, infrastructure, and star system limited range. Laser is the answer for trade routes. AM fusion is the answer for military and exploration [1]. [1] Finding new places for colonies, ressources (He3, AM (if bigger than our sun)). and to place refocusing mirror lines, ike roadway being build. No, I do mean laser thermal (I haven't actually seen laser ablative, and I'm not sure why there would be a difference). The reason for this is that, afaik, a laser can be focused onto an arbitrarily small space, heating up propellant to terrific temperatures. At high enough temperatures, the exhaust velocity becomes comparable to fusion power. Let me illustrate with a simulated example in CoaDE. Here's a diborane rocket. It takes less than 65 GW of heat to produce this kind of performance, which could be supplied by an external 100 GW laser at 65% efficiency. The craft itself would reach 1% lightspeed, and be able to decelerate from that on its own with an onboard 10 GW laser (albeit 10 times slower than the acceleration provided by an offboard 100 GW laser). Burn time for deceleration would be 10 months. Do note that 1.8 billion Kelvin is sufficient temperature to ignite proton-boron fusion (according to Wikipedia), which should significantly improve performance. But this isn't actually required for the craft to be useful. I am ignoring the mass and power of a magnetic nozzle, the mass of the main mirror, as well as the mass of onboard laser components and radiator (but these should all be negligible, I think, with a liquid droplet radiator on a 65% efficient laser). There may be some limits I am not aware of that would prevent this from being a good simulation of a laser thermal craft. Also, yay, god status. Congratulations for god status. That isn't a laser thermal rocket anymore in the traditional sense, it's a laser plasma ablative. With that acceleration, this missile has to accelerate months until it reaches it's final velocity. And a few years to decelerate. How do you want to shoot a 65 GW Beam throughout the solar system?
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Post by bigbombr on Jun 7, 2017 15:31:38 GMT
No, I do mean laser thermal (I haven't actually seen laser ablative, and I'm not sure why there would be a difference). The reason for this is that, afaik, a laser can be focused onto an arbitrarily small space, heating up propellant to terrific temperatures. At high enough temperatures, the exhaust velocity becomes comparable to fusion power. Let me illustrate with a simulated example in CoaDE. Here's a diborane rocket. It takes less than 65 GW of heat to produce this kind of performance, which could be supplied by an external 100 GW laser at 65% efficiency. The craft itself would reach 1% lightspeed, and be able to decelerate from that on its own with an onboard 10 GW laser (albeit 10 times slower than the acceleration provided by an offboard 100 GW laser). Burn time for deceleration would be 10 months. Do note that 1.8 billion Kelvin is sufficient temperature to ignite proton-boron fusion (according to Wikipedia), which should significantly improve performance. But this isn't actually required for the craft to be useful. I am ignoring the mass and power of a magnetic nozzle, the mass of the main mirror, as well as the mass of onboard laser components and radiator (but these should all be negligible, I think, with a liquid droplet radiator on a 65% efficient laser). There may be some limits I am not aware of that would prevent this from being a good simulation of a laser thermal craft. Also, yay, god status. Congratulations for god status. That isn't a laser thermal rocket anymore in the traditional sense, it's a laser plasma ablative. With that acceleration, this missile has to accelerate months until it reaches it's final velocity. And a few years to decelerate. How do you want to shoot a 65 GW Beam throughout the solar system? Interplanetary lasernet?
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Post by apophys on Jun 7, 2017 15:43:41 GMT
Congratulations for god status. That isn't a laser thermal rocket anymore in the traditional sense, it's a laser plasma ablative. With that acceleration, this missile has to accelerate months until it reaches it's final velocity. And a few years to decelerate. How do you want to shoot a 65 GW Beam throughout the solar system? Acceleration is dependent on the power of the incoming laser. A 1 TW laser would bring it to the same 1% lightspeed in 1 month. A 10 TW laser in 3 days. The onboard 10 GW laser would accelerate it to 1% lightspeed in 100 months, which is long, but interstellar travels are inherently long anyway, so that is still fine; it doesn't strictly require boosting. As I've shown in the terawatt laserstars thread, a 1 TW laser with under 4% efficiency can hit 10 Gm range (7 solar diameters).
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Post by Kerr on Jun 7, 2017 15:54:24 GMT
Congratulations for god status. That isn't a laser thermal rocket anymore in the traditional sense, it's a laser plasma ablative. With that acceleration, this missile has to accelerate months until it reaches it's final velocity. And a few years to decelerate. How do you want to shoot a 65 GW Beam throughout the solar system? Interplanetary lasernet? The planets are never in a perfect line, you might have luck when you have 2 planets in a line for laser propulsion. A 77nm laser with a 1km Mirror has a spot size of 6cm (dia) at 300Mm, you need 15000x mirror in a straight line to propel your ship, and what if you want to go to alpha centauri but the laser net isn't facing the exact direction? You have to cluster the whole solar with mirrors. Mercury to Neptune, 15000x in every direction. You end up with millions of mirrors in your system. Again, your ship accelerates months until it reaches its velocity. At 0.1m/s (roughly your acceleration) you need 8 months to reach 2160 km/s, considering that your ship losses mass as it acceleration I say it reaches 1% of C . After this time a 100GW AM factory produced 2,3g of Antihydrogen.
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Post by Kerr on Jun 7, 2017 16:10:19 GMT
Congratulations for god status. That isn't a laser thermal rocket anymore in the traditional sense, it's a laser plasma ablative. With that acceleration, this missile has to accelerate months until it reaches it's final velocity. And a few years to decelerate. How do you want to shoot a 65 GW Beam throughout the solar system? Acceleration is dependent on the power of the incoming laser. A 1 TW laser would bring it to the same 1% lightspeed in 1 month. A 10 TW laser in 3 days. The onboard 10 GW laser would accelerate it to 1% lightspeed in 100 months, which is long, but interstellar travels are inherently long anyway, so that is still fine; it doesn't strictly require boosting. As I've shown in the terawatt laserstars thread, a 1 TW laser with under 4% efficiency can hit 10 Gm range (7 solar diameters). You can use the reactors which power these multi terawatt lasers for Antimatter production, Your 10TW reactor could produce 1g Antimatter per day, which can propel a spacecraft even outside the solar system. Great, but that wasn't what I meant, What's the spot size of your TW laser at a 300Mm? The design posted here has a mass flow of 15g per second, can your laser hit a 5cm³ pellet at several hundred thousand kilometers?
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Post by apophys on Jun 7, 2017 17:41:01 GMT
You can use the reactors which power these multi terawatt lasers for Antimatter production, Your 10TW reactor could produce 1g Antimatter per day, which can propel a spacecraft even outside the solar system. Great, but that wasn't what I meant, What's the spot size of your TW laser at a 300Mm? The design posted here has a mass flow of 15g per second, can your laser hit a 5cm³ pellet at several hundred thousand kilometers? Antimatter has a few other issues, not just production cost. It decays with bombardment by cosmic rays, it requires constant uninterrupted power for containment, and storage facilities may explode with containment breaches. So it's less likely to be used soon, compared to simpler technologies. The real draw of antimatter would be if we have antimatter factories in low sun orbit running off solar panels. My craft would be able to propel itself outside the solar system (slowly). It would be much easier to refuel if it's supposed to do something meaningful for long times over there (Really needs only fissile and propellant, and it can use almost anything salvaged as propellant to scoot around its target system). IIRC, the spot size was something like 40 meters radius at 10 Gm (with ~39 GW beam power). Which would work fine, if the craft has a mirror of that size on its rear end, focusing the big spot down into its thruster into a centimeter or so (which was my intention). There's no need to ignite a pellet directly from 300 Mm. The craft has over 80 tons of mass tied up in the crew module (for 30 people, which is clearly overkill; it may even be unmanned if we get good enough AI). Some of that mass would be repurposed for things like the back mirror, and spare fuel rods for the reactor.
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Post by Kerr on Jun 7, 2017 18:07:29 GMT
You can use the reactors which power these multi terawatt lasers for Antimatter production, Your 10TW reactor could produce 1g Antimatter per day, which can propel a spacecraft even outside the solar system. Great, but that wasn't what I meant, What's the spot size of your TW laser at a 300Mm? The design posted here has a mass flow of 15g per second, can your laser hit a 5cm³ pellet at several hundred thousand kilometers? Antimatter has a few other issues, not just production cost. It decays with bombardment by cosmic rays, it requires constant uninterrupted power for containment, and storage facilities may explode with containment breaches. So it's less likely to be used soon, compared to simpler technologies. The real draw of antimatter would be if we have antimatter factories in low sun orbit running off solar panels. My craft would be able to propel itself outside the solar system (slowly). It would be much easier to refuel if it's supposed to do something meaningful for long times over there (Really needs only fissile and propellant, and it can use almost anything salvaged as propellant to scoot around its target system). IIRC, the spot size was something like 40 meters radius at 10 Gm (with ~39 GW beam power). Which would work fine, if the craft has a mirror of that size on its rear end, focusing the big spot down into its thruster into a centimeter or so (which was my intention). There's no need to ignite a pellet directly from 300 Mm. The craft has over 80 tons of mass tied up in the crew module (for 30 people, which is clearly overkill; it may even be unmanned if we get good enough AI). Some of that mass would be repurposed for things like the back mirror, and spare fuel rods for the reactor. 1g of Antimatter will get hit by an average of 11,5 eV cosmic radiation per second, this means it will get hit every 100 days with a low energy cosmic ray (100 MeV). Yup, low sun orbit are a good thing. One hectare at mercury's distance can generate 2,4µg per day. 2,4g need 10 thousand square kilometers of solar panels, With a efficiency of 27%. 80 tons don't sounds overkill, if you consider that these people have to eat food and drink water everyday. Other than that, your design sounds solid, the immense infrastructure requirements might the very expensive but might pay out in the long run. Laser thermal for civil and trade and Antimatter Fusion for military purposes?
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