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This aspect has been extricated from the necrophobic STS discussion and the like. Makes no sense to go on shooting a dead horse, but obviously some people get alot of pleasure out of it. So let them continue to live in the past, antiquated policies and luditic ambitions. This is a thread for the forward looking. In a past life we had the flexible although somewhat limited STS system which took part in repair of satellites, assembly of ISS and finally its no more, for better and worse. The ISS has a robotic arm and has involved itself in assembly . . . . . but it sterically hindered and its function and inertia limits its use in other occupations. So the question is whether NASA has a viable plan for a space factory or assembly station. I think that before you can build a station of that type you need to decide where its going to be. But we here in KSP are not limited by what any space agency thinks, since the powers-that-be (rattling the moderators cage ) endowed each of us with a brain, its best we put it to our own use and create. And as creators and artist we will tolerate the failings of each other but accept the critiques as a means of communicative growth. But the argument does have to be constrained by what is currently feasible. So for example we could could say build a launch pad in say Boca-Chica for that 50 kT rocket (toasting everything within a kilometer), but we currently cannot launch a fusion powered rocket, so that we cannot argue, place factory in polar orbit because i have a 'god'-mode drive. Lets premise the discussion with a global 'god' commandment that we all can agree on. That progress in space exploration is the target, manned when its appropriate or of benefit, and unmanned at other times. So that neither are we going to restrict one for the other or vice versa. Part 1. Physical Basis I want to use a kind of use a quantum perspective on Earth, we have to argue from a spatial point of view that Earth is a particle with an infinite number of dimensions which define its state, the same argument can be made about the moon. And we need to perform operations on both. If we are to compare it to an atom, the mass being the nucleus and we are electrons or photons that are being effected by its various parameters, depending on the operation. Within the dimensions are qualities (e.g. mu, axial tilt, atmosphere, . . . . .) all defined by dimensions. The reason I want to describe the earth this way is because its not a simple planet rotating on a axis perpendicular to its orbit about the sun so that depending the operation we can select a vector in that space and operate on it to see what happens (so for instance you can use a rotational reference frame, cartesian, change of basis, hamiltonian, etc). The structure is important but details are not until you want to use one then you fabricate the dimensions you want and create vectors). So for instance to assemble a certain set of functions are going to describe how you get information (mass, energy, operations .. . . people) from the Earth to the assembly point and the second how you get mass from the assembly point to an escape. In doing this we can define the energy required to create a particle and then to expel a particle along a desired vector (and all that the expulsion requires). Because of its extended dimensionality and because of this we are sometimes using complex spatial vectors in multiple reference frames. But the desire ulitimately to cross all these frames out and have an orbit to Mars, the Asteroid belt, Jupiter within the common inertial plane of the solar system (we don't have to worry about the galaxy). The math is very complex and I am not going to bore the abstract discussion with that, but just to say there is no perfect plane to go everywhere at everytime. I think everyone already knows this, but its not simply planar problem it is a 4 dimensional problem with other parallels(momentum, acceleration, dM/dt, etc). The broad definition allows us to compute on all operations define local outcomes create a change vector and move to a different system fluidly. Again details are not needed just the framework of testing various models. So the summary here is this. The Earth is a base of information, energy is required to project that into space. In our handwaving dimensional system there are three points. 1. a complex dimensional point denoted QSP-basis, its on the earth, 2. Mission basis, its a facility in space, this is the place were individual missions begin after all components are assembled 3. destination-basis a variable by which you want to go. There are two aspects of this model that are subject to change. 3 does not change, for example the variable Mars is always were mars will be. Once you designate Mars as the destination you, the global operator, cannot change where Mars is. We can dicker over a landing site on Mars, but that is something of submission specific details and for the sake our argument it outside of this thread and in another thread 'Exosystemic Space Stations'. So the concept here is that we have some control over (1) we can manipulate in real time (where we launch from, how much mass, and when within launch window) and likewise we can move (2) anywhere we want but it must be in our planetary system. And so the complexity of the potentials is immediately apparent. Part 2. Logical basis To frame the problem I will create the Query Space Agency .. .QSA, which is of course on Earth, where it is on Earth doesn't matter, but its not at a pole it could be in Russia, Ecuador or Argentina. QSA then has mission objectives. Mars is the default, Moon is a strong second, Asteroid belt is a third, NE-Asteroids are a collective, Venus is an option and Mercury tails the list. Each of these on the list have an ideal dV, which can only be defined in context. To get a feel how part one is essential. For instance lets argue the amount of dV required to get any where in the Solar system is X and that is the minimum required. From that point of view the potential is always realized from the lowest LEO possible and in some case LEO may not be achieved (point 2 is expeditiously removed on your trip to pluto). That is to say, while you are still have notable positive radial velocity remant from your lauch you burn most of the dV required to reach your destination. Ultimately this can be done from the lowest LEO and extracts the most energy from the fuel that the craft gains. Note that we switch to a rotational coordinate system to define radial velocity diagram for the rocket and this allowed us to maximize the Hamiltonian (Hl, lets call it the energy swap thingy KE---> PE KE-PE = SPE). The point we define as the basis is what . . . . . .it evolved during the burn becoming the basis at the end of the burn which the Hl could be predicted for the trip to the LEO, then change of basis and out of the solar system. We could then theoretically just point any rocket at any target in space, fire to lowest dV and we would have the lowest. Actually no, this violates the premise of the argument . . .we do not have a god-mode drive, or a god-mode drag ablation system, god-mode thrust, god-mode visceral fortitude for manned missions. Consequently the time spent in total vertical motion accelerating and fighting drag would consume more dV than making a tangential turn and burning along the tangent outward. This is trivial right? Not exactly, the two statement justify the commencement of missions distal to (1) at some location (2) where drag is not an issue (if you have a craft that is very bulky) and where the burn initiates always along the tangent. The counter argument is why we don't launch all mission from this 'sweetspot' in space, and the answer is most current missionswill have lower specific energy requirement than the sweet spot and can manage within the bulk maximum of primary. Thus (2) by definition is a secondary mission initiation site. In the same way returning an astronaut from the ISS can be seen as part of a different mission than his launch to ISS. So by the logic we can suggest there is a point in space (2) whereby for some manmade objects that are assembled from multiple launches of 1 (cost/risk) is a lower cost/risk than the most efficient launch from earth. The absurd argument is this, we have a function called an 'massive Aerogel' (mass as in huge manifold) in which we are going to use the Aerogel to land something on Mars. But the manifold needs to be formed, so we have a facility in orbit that, say forms the Aerogel and places it on the martian ship, the martian ship takes off and it bounces around on the surface of Mars (what it does on Mars we dont care, like SpaceX launching the fully formed vessel is our mission complete). Anti-god-mode restrictions tell us that we cannot form the Aerogel at Mars and you cant launch the Aerogel rom terra. Part 3. Decision basis. So then we list out all the possible (2) points that can be used for all potential missions inside of our (1->2) basis (contains all missions that are too high for direct, bulky to go direct, or massive to be launched from earth) The minimum dV requiement of each of these is defined along with fuel requirement of crew rotations, station assembly requirements .. . . . .and we get a spatial manifold around Earth at any given time that has one or more minimum. This means we could at some medium future point have several points. Part 4. Evolving (U) exceptional basis (4). The exceptional basis gives us new parameters (4) that we can use for change functions. Lets take an absurd argument. Today every amount of fuel but not power must come from Earth (excepting solar wind, photon push, cannae drives and oberth effects), at somepoint say J2040 we now have power that comes from an asteroid with a comet inside that has undergone system capture (although we care where it is in our system, we don't need to know exactly where it is to create a infinite dimensional state vector for it that can be operated upon, the details can be applied at convenience). This then includes the capture. So for instance the body crosses into the planetary system and then there are operations to capture it and exploit it. Then there are operations to associate its state with other states by association vectors. In associating the exceptional state with all the other (2) states we then begin to reoptimize (2) and indirectly (1) to take advantage of (4), so that (4) and (2) can change (3s never changes since its a target not a waypoint, in this since they are always changing but we never change them). So this is the framework for future technology in space, we work in space for a time and a benefit of this is that the total required-power metric decreases and operations evolve in response to this. The counter argument to this it that exception basis evolves and is not current. This is important to the creative argument, what it means is that any fabrication that assumes that the exception basis is current and not dU4/dt is just like god-mode thrust; its a violation of the constraints. This is not Star Trek you cannot create a transgalactic warp-drive by using Wesley Crusher's best friend experimenting in an engineering lab overnight to suddenly escape the borg. dU4/dt also means that there is a cost involved in the change of state that needs to be applied to other associated systems and that the faster dU4/dt evolves the higher the cost in resources to other aspects. That means that developing an exceptional basis creates a necessary trade off of resources. Here is an example, suppose you are using Space X to supply the transfer and load requirements to an interplanetary shuttle that drops stuff at mars then heads back and reloads. Although you can for instance extract argon from comets its not very efficient and most of the fuel goes to Earth, suddenly now there is a comet in orbit in which a huge amount of hydrogen and oxygen can be produced, so now what you are doing is hauling empty hydrogen tanks back from Mars, but still you need argon gas to route. You can convert to magnesium but theres a cost. In addition to initiate the new system there has to be tanks shipped from Earth, and your argon supply drops off, so the hydrolox tanks build up in Mars orbit. Secondarily manned resources on your station are shifted to the comet and equipment coming from earth is also shifted to the comet. So for a time, as a space tug, your operations slow down as with all operations on your basis (2x). In addition that asteroid or comet is a (3) that is converted to (4) and that conversion has a resource cost before it even reaches the system. This means that missions (2->3x) need to be cancelled and diverted to 2->33->4. The thread is long enough so I will just add a few statements. Although I am still working on the details of how best to use ION drives from Earth orbit, I foresee a best set of circumstances from LEO/MEO. By this I don't mean crazy low LEO, it has to be far enough up where the Sun covers most of the angular displacement * time of a craft in orbit over time. Particular with Solar +prograde exit vectors the burn optimum is beyond termination the Earth this means to expose the craft while burning the craft has to be significantly high or have lightweight and efficient batteries. The mass efficiency comes from the differential between chemical Ve (4700) and ION drive Ve (>30000) that, in essence you do not want to use chemical reaction energy propellants to push an ION drive with bulky solar panels. The point however I want to make that it is possible to use ION thrusters during most of the orbit without loosing dV as long as certain parameters are preserved (IOW not a continous spiral) and also it might be faster to do this than a spiral. So that even a weakly powered ION drive has some modifyers that can get it out of Earth orbit faster (for example using highest ISP thrust for some operations and lowest ISP thrust for others, such as at the rmin in an orbit or when making the final kick. The direction of thrust can be varied to keep the rmin optimal and even reversed at highest possible ISP (or even a photon drive). OTOH the orbitally-static stations are attractive in the sense that we can always have them in a state that is optimal for most outgoing vectors. The problem that I don't like about these is they generally are 4000dV vectors at Ve of 5000 or lower. I cannot see ION drives doing this thing since their best benefit is in the kick from the LEO/MEO Earth to its destination, and in actuality tolerates super-Hohmann transfers that markedly shorten time. But there are time constraints on some missions so crawling out of L/MEO to L2 may be the best means of doing this, and certainly saves alot of dV on ION-IP shuttles. The problem is that for an ION drive once you are at L2, you are no longer required, and if PL need to use L2 to use your thrust is really not of a benefit in the PL to L2 transfer. It could be of some benefit, perhaps a smaller number of kicks where solar (minimal) and ion contribute to the kick over say 2 days. The simple problem is that ION drives would be really really useful if they had more thrust and of course that requires a power supply that we don't have. If we keep in mind that energy maximization is all about dV @ V this means that if orbital minimum is a 6531 m its V = 7812 m/s and 5523 m/s at 13063 km. For each amount of fuel burnt at gives a change of energy of 7812/dV at 7812 and 5523/dV at 5523. This goes to 12000E/dv at and somewhat less than 11500E/dv for the starting 5523. Again so there is basically a loss of 1500E/dv by doubling the radius. Thats a heavy tax to pay in addition to circularization costs. But it increase the burn span by almost 80 degrees. Of course as the orbit expands you issues with timing of optimal burns that cannot be circumvented so it might be wise to thrust up the Drives by changing the grid voltage and increasing amps. The final comment involves the shuttle and its potential application to the problem that has been de-optioned. Most of the gateways are programs and are fixed in nature, therefore if program flaws occur there is essentially little change options. With a shuttle based assembly the assembly states can change, since the initial state X is only in a place where shuttle can reach, if the X assembly point then spawns other Xs the shuttle is no longer required, however inefficient it might be its functionality could be leveraged into other states, and those states would make the shuttle obsolete, which is desired.