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One major reason to mine asteroids and the moon is to get water for rocket fuel in space, rather than having to lift it out of Earth's gravity well. Suppose that you've got to build a generic solar-powered water-fueled rocket for something like an unmanned space tug. You have to budget tankage, solar collector, engine, and associated structure/modules. Assuming that you have access to mined water in orbit at each possible destination, what makes more sense: building a solar-thermal water rocket, that simply uses giant mirrors to focus solar radiation, boil water, and eject it out the back of your rocket (low Isp but very simple), or solar panels that convert solar energy to electricity that is used for electrolysis to split water into hydrogen and oxygen to burn in a thruster?

We have been having a running discussion in this subforum for the last year or more concerning a type of energy that does not require an apparent mass to generate momentum. Although energy can be converted into light which has momentum it has very little momentum given the energy contained within, and so finding something that has a magnitude more momentum per input energy created alot of discussion. In the end here I hope to show that it really matters little. To start off this analysis lets imagine the settlers of the mid 19th century American west. To accomplish their journey they had wagons with supplies and draft animals to pull the supply, this carried them across an expanse that was devoid of trade goods to either feed themselves or their livestock. Along the way the live stock feed, and because high energy foods spoiled they would kill animals and butcher them for meat and fat. There was a thing called winter, at which point unless you had settled in, it would not be a good thing to be in space. Conceptually speaking all major exploratory journeys are like this, if we imagine the discovery ships, they had to have supplies to last them several weeks, they might stop at islands to pick up water and supplies, and they would not want to be caught in a hurricane. Therefore the concept of expanse, resource management and risk have been dealt with. So now lets consider the trip to or any planet. Our Mississippi river is the LOE, we first have to get our ship up across the problem of drag and its desire to fight orbits. During this phase of the journey we cannot rely on any space resource and so it is a given that the initial state provides the energy and mass to create momentum. Once we have a semi-stable orbit we then can examine the problem of space. Space is a name, it has a sort of implicit meaning that it has no stuff in it. Actually space has alot of stuff, at least our local space, relative to the vast expanses of emptiness between galaxies. The stuff in space however tends to get concentrated into inertially defined bodies. Between these bodies are gases and for a traveler these gases are always in motion and because the gases are almost always charged (that means gas is a mixture of plasma and gas), the gas is maintained in a rarefied state by momentum and electromagnetic energy from the sun, as a consequence it can at times be non-inertial. To be clear here, the density of gas, even in the atmosphere of the sun, is so dilute it is of little practical use. That is to say in the time frame of our journey their is neither the time or a relevant volume of space to collect this an use it. The material state of vacuum space is more than an annoyance if anything, in LOE it creates drag and in interplanetary space it carries ions that can damage equipment or injure travelers. The bodies in our space fall basically into three categories. The smallest of these are asteroids and comets. Asteroids are the left overs from planetary genesis, the gas from our sun slows down and hits things out in the outer system, cools, and gases and dust that did not form large bodies eventually coalesce into dirty ice balls that get tugged by our planets and burn up, eventually. The planets clear orbits and thus are clearly inertially defined in their motion, since they are no longer colliding. Finally you have the bodies in which atomic conversion is a major character of the bodies visible appearance, at high enough energy these also emit gases. To our traveler these are the resources of space, so lets define these as such 1. Asteroids and Comets. Resources - Mass (Carbon, Oxygen, Hydrogen, Nickle, Silica, Aluminum): sub resources (metal for building, water for drinking or fuel cells, carbon for food or electronics, all for momentum), trivial amount of inertia, and transitory or impermanent destination. 2. Planets and Moons. - Inertia (as in they warp space), destinations, and the resources of #1. 3. Stars - Electromagnetism, Inertia, trivial emission of Gas and Plasma (as such also a source of electric charge) 4. Not 1 to 3 above - Quantum space - Non-zero rest energy of fields that permeate our universe (which of yet we are not fully aware or know how to exploit). So basically above we can define space as a list of virtual items, in this we can then rank them to our Space traveler. My ranking may shock but . . . A. [Quantum] space - this is the most important resource of space because it permits long distance travel and because its fields make it possible to establish travel strategies. The physical distance between destinations is in the >109 meters, traveling in drag affords speeds of 100s of meter per second, therefore matter just slows down the process. Matter also creates lots of other problems like gravitational collapses and complex body problems. B. Destinations (virtual and physical) - travelers will eventually need resources or a travel interest. C. Electromagnetic radiation - discussed below. Essentially EM is the purest source of energy, that is not to say it is the sole source of energy, but rest mass as an energy source has an investiment cost (in space this translates into mass). D. Inertially derived warping of space time - for the occasional Oberth effect. E. Mass - E = mc^2, p = m * v These are the resources what are their costs. A. Space - Not suitable for biota, no push-off mass, all* momentum must be derived within (*the status of the rf resonance cavity thruster goes undefined), energy required to reach space and return, energy taken by contamination within vacuum space. B. Destinations represent almost always a non-inertial logic, a dV required to reach them, we talk about space-time, we also have to consider dT. Destinations may have other problems like too much or too little of some other resource (Namely light). C. EM - heat dissipation with too much, energy conversion for use in propulsion and systems. D. Oberth masses - Friction or obstructions, space-time (see B). E. Mass - collection, landing, mining, conversion (not to mention cooling equipment) So basically we have a list of issues for our traveler. Breaking this down much of traveler concerns are non-inertial movements in space-time which require energy and for the most part momentum derived from mass ejection. The above is not the intent of the article, it simply breaking things down into abstractions that the next part can deal with. So what is the problem of traveling (not the traveler). If you are not going to something that cross the same space-time (in some relevant timescale) point dV needs to be applied somewhere. We derive dV Light - almost never used, but requires no mass (we have to assume at this point that the rf resonance cavity thruster is not this type of drive) Chemical - the fuel becomes the ejection mass - limited to bond breaking partial bond formation energy of the fuel. Basically at high temperature unfavorable bonds break the most stable reform as the cool. There is a finite limit on how much energy can be obtained from a chemical bond, it is defined in calories per mole and typically is in the form of O-O, H-H, N-O, N=O, C-C, C-H, C-N, C=C, C=N. Electrodynamic - the mass becomes energized by the input of energy and accelerates. (Ion, plasma, VASIMR, Hall effect, rf resonance*) Atomic - a source of heat is used to rarefy gas or liquid which then expands like chemical energy drive. We can see we need energy to produce light, we need to carry mass to produce chemical energy, we need to carry a nuclear reactor or we need to accelerate ions. Unless you want to carry all the energy with the craft there is a limitation of space, right now its solar power, (given the high mass issues with nuclear and cooling issues) Space gives effectively about 1N of thrust for every 233kg of solar panels (C). This gives a maximum 4.2 mm/s2 of acceleration (0.0004g), with that one needs about 233 meters of space. You can assume that a manned spacecraft this will be 10% of the mass so you are effectively limited to about 0.04g. I have created new ion drives and panels in the game to reflect this (HiPep design thrusters). The major problem is orbiting, this designed requires another source of accelation and is not suitable around low hv objects. Nuclear is worse, the reactors cost as much as the panels in terms of weight but much more in terms of cooling. if we argue that solar is kg per sqm then any means of reducing this improves the portability of the system. Modern age silicon lens are light weight and can focus light on a panel of much lower size and weight. This type of system works great in interplanetary flight, however only at a tangent to orbit, so inefficient transfers are not optimal unless the lens are placed on tracks that can move their positions. They also do not work well in non-inertial manuevers close to inertial bodies, this is because the incident angle shift with prograde motion. The mass of the ion drive is trivial (the most efficient drives of a few kilograms will easily consume all the energy we can currently produce), at 9000 dV the mass of the fuel becomes trivial (because you cant produce enough energy to eject it), the mass of energy production facility is just about everything. Find a way to lower the mass of energy production and Manned missions to (but not landing on) are possible.

I have a proposal for a (really really)endgame engine that is a nuclear powered R.A.P.I.E.R in it`s open cycle it utilizes the nuclear reactor to heat and expand the atmosferic air to provide thrust,when clear from the atmosphere you would change to the closed cycle that uses the internal propelent like the Nerv engine. Well: It would be much overpowered? Yes. Even for a endgame engine? I guess not,it would be the game`s last engine. Why would you make such a engine? To make more dinamic SSTOs that can make a bit longer trips not using mk3 parts. So, what you guys think of this in the stock game? And if there`s a mod that have a engine like that let me know please.

So, photons exert a tiny force when they reflect off of something. I was thinking about the EMDrive yesterday, and how it supposedly uses radiation pressure for thrust. Then I had this ridiculously funny and impractical idea of how the EMDrive is supposed to work, according to the physics we know. It would best be explained by a picture: It would use mirrors as fuel, and would leave a stream of mirrors in it's wake as it slowly gets pushed along. It's completely impractical, but would work. I thought it was a funny idea...