Bill Phil

We actually know the abundance of elements in the lunar surface fairly well. Aluminum, titanium, magnesium, iron, and the like are fairly abundant on the surface. Copper might be less abundant than on Earth's surface, but not greatly so. There are likely deposits with higher concentrations, though as technology advances one trend is the increasing use of lower grade ores, both because of necessity but also because technology makes it practical. Even now something like 20% of copper production is done with bioleaching, using low grade ores or waste from mines because the high grade stuff is depleted. As for carbon - there isn't "no carbon", the abundance is tiny. There is carbon. In trace amounts. Probably not useful amounts. But if we're talking near term we can source carbon and other volatiles from Earth until a better source is developed. Asteroids could be used though Venus's atmosphere is filled to the brim with CO2. For other volatiles asteroids would be preferred though. The Moon actually did have volcanism in the past, possibly as recent as a few hundred million years ago. Lava flows were also common. Abundant iron, aluminum, titanium, magnesium, and oxygen will definitely be useful. Other elements can be sourced from other locations - Earth initially but over time a robust infrastructure for using asteroids and other planets can be developed. But there's not much reason to put the actual industry on or around Mars. I wouldn't call that convenient. Cycler orbits are still bound to the limitations of the synodic period. Shipping things from Mars to Earth could take years between production and consumption. If we were to go this route then nuclear or solar electric will likely be used. Not to go fast, but one interesting thing about low thrust trajectories is that they're less sensitive to transfer periods (a trajectory can be plotted for almost any time within a given delta-v constraint, might take longer though for sub-optimal trajectories). So you can pack a million tonne (or larger) cargo ship with cargo and send off on its merry way at virtually any time. Place it in a high orbit over Mars so that spiraling out doesn't take too long, or even give it a push using chemical engines. Then just spiral down to Earth's orbit and brake into a high orbit there. Rendezvous with a spaceport and offload cargo. Thing is that might be better suited for delivering raw materials, so there's not much need for industry on Mars beyond the needed amount to extract raw materials. Then similar vehicles could be used to deliver raw materials from all over the inner solar system (except Mercury because the vehicle may not be powerful enough to overcome the Sun's gravity there) and the asteroid belt. The Belt has infrastructure issues as well. But industry there is likely to be centered on the largest asteroids. And more advanced propulsion technology - such as any flavor of nuclear pulse propulsion - would enable less awkward transport. Though I suspect any industry in the Belt will be decentralized, with each small industrial center having its own source of the various elements needed and only needing small shipments for other elements, except for the cases where there are larger industrial sites. With abundant energy (solar is still usable in the Belt) low abundance for elements isn't that much of an issue. And even then, the largest industrial product will likely be the very habitats the people live in. I wonder if the disassembler part of a Santa Claus machine could be developed in the next few centuries. With abundant enough energy it may be possible to do without too much hassle. Then pretty much every naturally occurring element is available, in different amounts based on their local abundance. I see Mars as a source of raw material, but not as an industrial site. That would be better suited in orbit. And if industry in Earth orbit is more advanced and developed as it likely will be then it will likely be cheaper to just ship raw materials from Mars to Earth. Mars is there indeed. But why bother settling it? From a utilitarian point of view it would serve the species far better if we were to use it purely as a source of raw material. Earth has sentimental value, but Mars has less sentimental value. For a species looking to expand that has sufficient energy abundance, why not completely disassemble the planet? The energy required is significant but it may be available. If the project were to take a century it would require an average power of 1.542E21 joules - an enormous amount but that's only millionths of the output of the Sun. Since energy supply can increase exponentially the process could be shorter, though it may be more economical to make the process take longer to reduce the required power. If our future civilization has access to a black hole or Q-balls (if such a thing is even possible, which isn't really known) the process could even be bootstrapped in energy terms since the energy supply would grow as the amount of extracted mass grows. So it could even be self supporting in energy terms. But why disassemble Mars? Well, assuming 30 tonnes per square meter for a space habitat the mass of Mars would provide something like 20 trillion square kilometers of area. Less if the mass of Mars is used to power the process. And of course there are other things that the mass can be used for. That's a very long term prospect, but it is possible and likely preferable to settling Mars. And before that it would still serve better as a source of resources in a more conventional context: raw materials sent to the major industrial center of the Solar System. That's likely to be the Earth-Moon system. But it could be something else. The question isn't "why take advantage of Mars", it's "why live on Mars". There are superior alternatives in habitat terms and there are better uses for the planet itself.

Basically this. There's no real benefit to settling Mars and there are not only viable but arguably superior alternatives. I don't know about using Mars as an industrial base for anything used on Earth. If it would be cheaper to do metallurgy and fabrication on Mars because of the law then it would be even cheaper still to do that metallurgy and fabrication either in orbit or on the Moon. The logistics of using Mars in that way is the main problem. So basically the setup would be exactly as you describe only on the Moon, plus some space manufacturing since there are some products that would benefit from free fall conditions. There's not much in metal terms that can't also be found on the Moon. The biggest issue with the Moon is the lack of volatiles. Perhaps the Martian moons or some other asteroids could serve as good sources for those. Maybe Venus's atmosphere could be used to source nitrogen and carbon, though that would suffer large logistical issues as well. Though if industry grows enough it may eventually run into a cooling problem, if the area available for radiators is limited to the surface of the Moon. Of course the Moon itself could serve as a heatsink, but that may not be desirable. It may be beneficial to place large industry in space for this reason. But that's a fairly long term problem.

From my understanding you should be able to treat it like a collision between two particles where the relative velocity between the two is the same after collision, but the velocities relative to their center of mass or another body will be different. Momentum is a conserved quantity so it shouldn’t be too hard to derive a reasonable approximation. That said it can get complex and eventually approximations break down.

Part of the concept of the NSWR is that the reaction occurs outside the engine. Whether or not this is possible or the mechanism by which it is achieved is not known. OP: The salt in Nuclear Salt Water is a uranium bromide salt, and I doubt Godzilla was able to acquire significant amounts.

Friend of mine let me have one of his old computers. Has a broken cpu, and possibly some other stuff. He stored the graphics card in a plastic bag, so it may be dead. But if not, then I could have a decent computer with just a little bit of work. Worst case I get a case and a power supply.

One can describe a black hole as the region of spacetime encompassed by the event horizon - thus saying "a black hole 2 miles across" works, provided you describe the region as spherical, at least approximately. Blackholes can have mass, but also angular momentum and charge. The event horizon can also have a temperature. The singularity of a rotating black hole is sometimes called a ringularity. Which is pretty cool if you ask me.

"I have been Roland, Beowulf, Achilles, Gilgamesh. I have been called a hundred names and will be called a thousand more before the world goes dim and cold. I am hero." -Marathon 2: Durandal What I love about this is that it could be referring to the main character. What's interesting about that is that Roland was the wielder of the sword Durandal. But in the game the AI Durandal is the "wielder" of the main character, who could be an incarnation of "Roland". It's kind of poetic in that way.

Marathon Get it here: https://alephone.lhowon.org/ I have a few major problems with it. The game itself isn't so bad. But I can't seem to get the mouse sensitivity right and the field of view is way too small. Now from my understanding that's by design, but still, it really hurts the gameplay. Still, pretty fun.

“It seems you’ve come across an alien spacecraft. Now things are beginning to make sense. More later.” -The Admiral, Maabus.

Remember Bussard Ramjets? Well, it turns out the corona is billions of times denser than the interstellar medium, especially the Local Bubble. A magnetic scoop could potentially collect significant amounts of hydrogen. Of course there are still issues with this. But considering that we want to just stay in orbit and the velocities are smaller, the drag issue may be possible to overcome. With a 1km collector diameter more than 5 tonnes per second of hydrogen could be possible. The main challenge will likely be keeping the superconductors cold. Might be possible however.

Keep in mind that oxygen is one of the most abundant elements on rocky planet surfaces. It also makes up 89% of the mass of water. So for a suitably energy rich civilization that has managed to run low on water you could take hydrogen from a gas giant and bond it with oxygen from a rocky planet. Indeed one plan for lunar resources was to extract oxygen from the surface and being hydrogen from Earth. Now for a twist on the Elite aspect - fuel scooping a star could be a way to get some hydrogen while the nearest planet could be a source of oxygen. Easy.

It's insane how huge chunks of both of those numbers are from the USA. More than half in the case of the space budget. I completely disagree. Space exploration is critical to our future in space. At least as an underlying foundation for future exploration. You're free to have your opinion of course. And that's ignoring potential benefits from the industrialization of space. Even just cislunar space would provide enormous benefits, on Earth. More GPS satellites could lead to higher GPS accuracy, for example. A space industry would allow larger satellites which could enable things we haven't even thought about yet. And we could also build solar power satellites which could be used to beam power to Earth, though that's somewhat far off. Not to mention that Earth science is a major part of space science. Data from orbiting satellites can provide information that assists agriculture, environmental conservation, and more. And if enough initial investment is made in space industry it could probably become fairly self reliant relatively quickly. The US spends more on its prison system than the entire globe spends on space exploration. The problem is that there just isn't that many resources we can save by not going to space. There are many other areas we can save on. Now for my unpopular opinion. Overpopulation isn't the problem. Our system of resource distribution, lack of effective environmental conservation efforts, use of fossil fuels, and more are the problems. But the biggest problem is that addressing those problems is virtually impossible because of how the world works. Population control looks like a solution but it isn't. It'll lead to further problems down the line and if any new problems crop up we may not have the population size necessary to deal with them. It is far easier to deal with our problems while having a growing work force than it is with a stagnant or shrinking work force. And to connect this with space, if we wish to maintain or improve standard of living we'll need to increase energy use per capita. This means we'll run into a heat limit on Earth that will force us off the planet or we'll risk massively increasing the temperature of the planet. Even if we don't "solve" any of our problems, we may still run into this issue rather soon. So a robust space infrastructure is a must in case we need to begin the process of taking civilization to space.

An antimatter initiated nuclear reaction would be a torchship with a large enough thrust power. If you took @MatterBeam‘s Epstein drive concept and initiated the reactions with antimatter you would basically have a high power torchship. A fission-fusion hybrid using Lithium-Deuteride as its main fuel could potentially work extremely well, using the neutrons from uranium or plutonium fission to fission the Lithium into Tritium and Helium and provide enough energy to kickstart the fusion reaction. Plus Lithium-Deuteride would be denser than D-T ice or gas and could be cheaper since Tritium production is difficult. However the drive would be highly radioactive because it would emit neutrons, though some of that energy could be absorbed by propellant.

They might exist, but they would be unstable.

Lagrange Points like in the Earth-Moon and the Sun-Jupiter systems are stable because of the enormous difference in mass between the primary and its satellite (specifically L4 and L5). If Rask and Rusk are within an order of magnitude in mass, there shouldn't be any stable Lagrange points.

Considering that KSP is already teaching elements of rocket science adding a scripting system would probably be useful, and relatively simple for players to use. Make it capable of hardcore stuff too - like launch and landing guidance scripts. But if you never want to touch it - you don’t have to.

Assuming a 4.5 km/s exhaust velocity and a 10 km/s delta-V target, you need a mass ratio of 9.23. Taking 1.8 km/s out reduces that requirement to 6.19. That said, 10 thousand gee is pretty huge.

The researchers behind Mini-Mag Orion proposed Z-Pinch of around 40 grams of fissile material. Curium-245 was chosen but other fissile isotopes were possible. This implies that it is possible to compress masses of tens of grams to critical mass density. If 40 grams of Plutonium-239 is the target, then it would have a volume of 0.002 cubic centimeters (assuming a density of 19.86 kg/cm^3, though different allotropes have different densities, and a hollow space would be required for the DT - which acts as a neutron source and potentially a fusion boost). Less compression would be required to reach criticality than would be required for DT targets to reach fusion conditions. Larger target masses would require even less compression. There is likely an optimal mass that would be possible with current drivers, considering that the fissile target will be much less compressible than the fusion target. However new facilities would likely be required, but no advances in driver power may be required. This setup, if possible, would still have advantages over IC fusion systems: Since the target masses are much larger more energy will be released per shot, and fairly large burnup rates can be possible if boosting is used. The yield per shot would likely be in the hundreds of gigajoules - the reactor must be able to survive large numbers of consecutive shots. The rate at which the reactor operates will determine the power output - at 100 GJ per shot a 1 GWth reactor would only need a shot every 100 seconds, assuming all or the vast majority of the energy ends up as thermal energy. However a shot every 100 seconds is likely easier to accomplish than 10 shots per second, as IC fusion might require - assuming 100 MJ per fusion shot. Of course larger fusion targets are possible as well but those would require much more powerful drivers, as I understand it. An IC fission reactor may not need drivers that are much more powerful than already existing drivers. I'm not sure about the numbers though. It would also have advantages over conventional fission reactors, which I outlined in the OP. One disadvantage would be that using nearly pure fissile material as the fuel could make nuclear proliferation a much larger issue. However, surrounding the fissile material with other dense materials which could act as a "pusher", or just a shell of decent mass, can reduce this risk. This shell can be a dense material with a higher melting point than the Plutonium, so that melting fuel pellets - if some party were to obtain them - would give said party an impure mixture of molten material. So the fuel pellets can be engineered so that they are not easy sources of fissile material. There are technical challenges, but they appear surmountable. From what I can find Plutonium is more compressible than Aluminum, and much more compressible than steel. Obviously that varies with its conditions and allotropes, but I think it's compressible enough that a 40 gram target could be made to undergo fission, though I'm not sure about the amount of energy necessary. 40 grams of Plutonium-239 would actually release around 800 GJ at a 25% burnup rate. So to get 1 GWth a reactor would only need to fire a shot every 800 seconds. Only 108 in a day. That's around 4.32 kilograms. To keep a reactor fueled for a period of six months each reactor would need 777.6 kg of fissile material. However this would be stored in discrete pellets with other elements in their makeup. They could also be stored in extremely secure storage containers, each one containing perhaps around a day's worth of fuel. Storage in a highly secure area with automated delivery to the reactor so that as few people as possible are involved in fuel handling would be preferred. So I believe it is possible, and perhaps more achievable than IC fusion. Or perhaps a Z-Pinch could be used to compress the fuel? As in Mini-Mag Orion. It may be possible to capture the waste and separate out the fission products - some percentage of the remaining mass could be usable fuel. Perhaps as much as half or even more. This could be directly sorted on-site using a mass spectrometer, where the actual waste could then be dealt with. Though if such a system is too energy intensive or too difficult to create on the desired scale a dedicated facility could be preferred. Breeding Pu-239 from natural Uranium may be possible (and perhaps more effectively than in a breeder reactor) using neutron spallation from particle accelerators - if the neutron economy in the IC fission concept can't be made to reliably reproduce its fuel supply.

I'm aware of accelerator driven reactors. Cool stuff. I think it's worth developing. For Z-Pinch Curium-245 isn't necessary - that was proposed for Mini-Mag Orion for reasons that seem to be unrelated to physics. Any fissile isotope should do.

There are similarities to Mini-Mag Orion (which I am familiar with), but that uses Z-Pinch. Inertial confinement is a different concept. The target didn't go critical, but I can't find anything on the actual yield of the target. Perhaps similar technology could be made to break even... Another concept would be to make the fuel pellets similar to the secondary in a thermonuclear bomb - essentially surrounding the fuel pellet with a tamper of fissionable material. From my understanding the fissionable material (uranium or thorium) would also act as a pusher. I might be entirely wrong about this, but such a setup could bring about more efficient compression of the fusion fuel and perhaps better confinement as well. And fusion releases neutrons which can cause fission in U-238. The question then becomes how many fission events can we get per pulse. A high enough fusion burn rate may allow for very large fission burn rates. Basically, it may be possible to use the fusion of D-T fuel as a source of fast neutrons for the fast fission of U-238 or Th-232 fuel. It is well known that D-T fusion releases a large amount of neutrons which themselves have large amounts of energy. Could work. We need a quantitative analysis though.

There are other mechanisms that can be used besides direct compression. According to this: https://physics.aps.org/story/v5/st3 Fission was accomplished with lasers in 2000, 20 years ago. "Before each high-power laser shot, the Livermore team hit their solid gold target, mounted on a copper sample holder containing uranium, with a lower-energy pulse to briefly create a plasma of electrons at the target’s surface. They then used the world’s first petawatt (10^15 W) laser to blast the gold with a 0.5 ps,260 J pulse of infrared light–packing more than [10^20] W/cm2–which accelerated plasma electrons to energies of tens of MeV. The “quivering” of these electrons created gamma rays known as Bremsstrahlung radiation that liberated high-energy neutrons from gold and copper nuclei. These neutrons split uranium-238 nuclei and caused other nuclear reactions. With two strategically placed detectors, Cowan and his colleagues monitored the energies of electrons escaping the plasma during the laser pulse." Another team used tantalum instead of gold. And the laser pulse seemed to be very low energy at that - though I don't know how much energy the fission actually released. If the fission yield could be made considerable then it could be doable. And another option is to use uranium-238 as a kind of tamper-pusher. Essentially we put a shell of U-238 around the fusion fuel. Then the tamper compresses the fusion fuel after its bombarded by lasers and the fusion releases fast neutrons which then cause fission in the U-238. So a thermonuclear micro-explosion reactor. Might be better to use cylindrical pellets.

Inertial confinement uses lasers or particle beams to highly compress a pellet of fuel. Magnetic fields can be completely ignored - except maybe for an MHD system to convert the thermal energy to electricity. Fuel rods don't require confinement - but they do need to be kept at criticality over long periods of time. There are a few ways to get some neutrons in to kickstart the reaction - a proton beam of sufficient energy and with enough protons could generate neutrons through spallation. No, I'm proposing lasers as in ICF or particle beams. I'm not fully familiar with the physics involved. But from my understanding the critical mass of a fissile material (like U-235) depends on its density, so if you do massively increase the density then the critical mass is massively reduced, so an ICF would work with fissile material just as is, provided the pellet mass is large enough (though if shockwaves travel through the material the density could be even larger near the center of the pellet, so current driver systems could potentially do it with minimal changes). With non-fissile material that is still fissionable (like U-238), you have to use fast neutrons. One way to do this is to use a proton beam and generate neutrons via spallation in the pellet - of course you might need high energy proton beams. The question is whether or not that can be maintained for long enough. Perhaps we can treat it as a fusion boosted fission system, using an amount of fusion fuel in the pellet to increase the neutron flux even further. Or perhaps use even more proton particle beams at the right moment. Or alternately we can configure the system to act as a breeder reactor though such a system would be difficult. It seems to be a more workable concept than fusion, at least in the near term.

The use of a magnetic nozzle for a pulse vehicle is desired, though physical contact is possible. The mass of the magnets depends on various design decisions. Such a vehicle would need another system to put it into orbit, or it would need to be built in orbit. Now, another possible propulsion scheme could be a nuclear thermal rocket. A LANTR with an inertial confinement fission reactor and high enough mass flow could actually allow SSTO rockets. If the actual reactor can be made small enough then the shielding requirements could be reasonable.

The quest for fusion power has been a long one. Sadly it seems that fusion is doomed to be decades away for quite some time. However, fission reactors are a well understood technology. Indeed, fission reactions are much easier to initiate than fusion reactions - fission requires interactions between heavy nuclei and neutrons whereas fusion requires light nuclei to overcome the electrostatic barrier between them. So fission is easier to initiate. However current conventional fission reactors - while efficient and better suited for baseload power than other low emission concepts - are quite expensive. They also produce waste and don't burn much of their fuel sources. Not to mention they require processed fuel that requires larger concentrations of U-235 than natural uranium. So I started thinking. What if we took Inertial Confinement Fusion drivers and used fission fuels instead? Assuming we also used a suitable neutron source, it's likely possible to use natural uranium or even natural thorium by employing fast neutrons. This could lead to more economical fuels than conventional fission reactors. It should be possible to get fairly large burnup rates for the fuel as well, so less waste could be produced per unit of energy than conventional nuclear reactors and less fuel would be required. Such reactors would also be safer than conventional nuclear reactors - meltdowns are completely impossible since a very small amount of fuel is reacting at any instant and the reactions only occur if the driver is operating. It could also be possible to have higher power densities than conventional reactors, so smaller facilities would be required and less shielding mass would be needed. Of course this depends on the size of the facility for the driver but the actual reactor itself could be much smaller. Such reactors could also be more thermodynamically efficient by combining conventional heat engine technology with MHD technology. And compared to fusion inertial confinement fission seems to be more achievable. So it could be more economical, safer, more efficient, lower waste production, and smaller than conventional reactors for a given power output. And compared to fusion such reactors could be possible much earlier. And it could lead to the development of more efficient drivers that could make inertial confinement fusion more practical. Or hybrid systems that use fission to initiate a fusion reaction could be possible. Now for some applications. The first one is obvious - baseload electricity. If such technology is more economical than current reactors it could be competitive with other energy sources as well. If developed as a small modular reactor it could be deployed quite rapidly. The second one may be less obvious but still important, though less likely: propulsion for cargo and container ships. Ocean shipping is responsible for quite a large percentage of pollutants and a decent percentage of GHG emissions, and those emissions are expected to grow substantially over time. And of course the one we're all probably more interested in: space propulsion. This can be done using nuclear pulse propulsion or nuclear electric propulsion. If the power density can be made high enough then nuclear-electric systems may be capable of interplanetary missions with reasonable mass ratios. And of course nuclear pulse propulsion could do the same. Such a system would probably be similar to Mini-Mag Orion but without the Z-Pinch system and without the need for other components that limit the performance of the Mini-Mag Orion system (such as the conductive elements needed for the Z-Pinch). So fast transfers to the outer planets would be possible with manned missions. I can't find much literature on this concept - mostly because the words "inertial confinement" are associated with fusion. But it could work with fission. And it seems that it could have some serious advantages over conventional nuclear reactors. Thoughts?

Fusion is the process of bringing atomic nuclei together. However, atomic nuclei have positive charges, and thus to get any two nuclei close enough to induce fusion a certain energy threshold must be met. Generally this threshold is quite large but after passing it the nuclear forces overcome the electric forces and fusion occurs. There are a variety of methods to reach this threshold. In magnetic confinement the goal is to create a high temperature plasma. This is necessary to get the nuclei past the energy threshold so fusion can occur. High temperatures correspond to high average velocities, and thus high average energies. Hopefully fusion occurs. Cold plasma is simply not going to do it on the desired scale. Sure some random events may happen, but not in the numbers needed for energy production. The idea is that the fusion reactions could release enough energy to maintain the high temperatures in at least some portion of the plasma. But plasma likes to induce its own magnetic field, and the whole thing falls apart. It may be possible, but it'll be tough. Personally I think we should be looking into more advanced fission reactors more-so than fusion (but fusion is certainly worth developing). Accelerator driven reactors could be deployed to burn off nuclear waste and get energy from it; turning the waste into easier to handle elements and isotopes. If such a technology proves effective it could be worthwhile in general since it can be kept sub-critical, runaway reactions with such a reactor are simply impossible.