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Author Topic: Orbits Question
extrinsic
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Aerospace enthusiasts know about O'Neill habitats and Lagrange points as proposed locations and the orbital dynamics thereof. Recent proposals have added two-to-one resonance orbits to considerations.

Three two-to-one resonance orbit types are possible for the Earth-Moon system; one, Earth orbited, Earth perigee, and apogee inside the Moon's orbit; two, Moon orbited, Moon perilune, and apolune inside Earth's orbit; three, Earth and Moon orbited, third body orbits outside both bodies' orbits. Each of the orbit types is highly elliptical and many variable apogee/-lune and perigee/-lune altitudes are possible. The primary function of the three is close matter transfer proximity to the Earth and Moon at phases of the orbits.

Option one, the third body, a space platform orbits Earth, approaches the Earth in close proximity every orbit, at perigee, roughly a 14-day orbit, and the Moon once every other orbit, at apogee, or roughly every twenty-eight days. That's the two-to-one resonance and comparatively stable, therefore, low energy station keeping.

Option two orbits and places the Moon in close proximity every orbit, at perilune, and the Earth close every other orbit, at apolune, roughly an orbit time each of likewise fourteen days for close approaches. Likewise somewhat stable and low energy orbit.

Option three orbits outside both Earth and Moon's orbits about each other, and options vary widely, up to several weeks and longer than options one and two. Because the system's barycenter is a quarter the distance below Earth's surface, the orbit elliptical, each orbit passes close to Earth once and close to the Moon twice, again, a two-to-one resonance. Likewise somewhat stable and low energy orbit.

Each option has advantages and disadvantages, missions and functions. The question I'm exploring is which most suits a next stage to permanent near-space settlement? The ISS is at a LEO orbit, a stage, so to speak, to a next High, High Earth altitude platform. Satellites crowd geostationary and lower and higher geocentered and geosynchronous orbits. L4 and L5 are roughly equidistant from Earth and Moon and somewhat fixed relative to both bodies, about a sixth of the Moon's orbital path away from both bodies, kind of far away from their resources and less than ideal for next stage benefits of both resources.

I'm inclined toward option one though don't know what I might be missing. Any suggestions?

[ December 17, 2015, 06:47 PM: Message edited by: extrinsic ]

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Grumpy old guy
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Pardon me, perhaps I'm slow, but I'm not sure what you're asking for. Are you concerned about re-supply?

Phil

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extrinsic
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Supply, resupply, construction, personnel and goods and services throughput, mining, ore concentration, manufacturing, energy, etc., self-contained platform colonies where people work and live and make others richer while they attempt to enrich themselves and a transfer stage to further and farther frontiers.
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Grumpy old guy
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The biggest cost in spaceflight is overcoming the gravity well. This makes Earth a costly supplier compared to the moon .

Phil

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extrinsic
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Assume Earth to orbit costs dropped to around $500 per kilogram, down from about $25,000 or so presently.
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Grumpy old guy
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quote:
Assume Earth to orbit costs dropped to around $500 per kilogram, down from about $25,000 or so presently.
Then getting freight into lunar orbit would cost $100 per kilo--still cheaper. But it isn't just cost per kilo. From the moon you get more payload per launch vehicle for the same cost. Or, more importantly, launching from the on you can give the spacecraft a launch velocity at least twice that from Earth, perhaps even as much as three time. this gives higher orbital speeds if you were servicing mining colonies in the asteroid belt--a favourite of sci-fi writers.

Phil.

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rstegman
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One idea would be to enter solar orbit in line with the earth. One could, almost without minor adjustments, stay a given distance from the earth.

Beyond that, I see is that we will be going to the asteroids and mining them, rather than going to the planets. There is something about colonizing planets but the gravity wells make it very expensive to operate to and from there.

Once you are in space, out of the gravity well, it does not take much fuel to get to another point. Likely, lower orbit will be loaded up with supplies and then go from there to the asteroids.

Put processing equipment and very soon, the asteroids should be able to provide raw materials so one need not have to send supplies from Earth.

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extrinsic
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A stage to outward bound settlement, the next space station is likely to be one where many accesses are intended: Moon, near-Earth asteroids, L's, and solar L's, Mars, asteroid belt, and beyond.

The Interplanetary Transportation Network, indeed, is a low energy, long mission duration access method, using gravity slings and drags, atmospheric drags, and planetary and solar transfer libration stages to anywhere in the Solar System. Long duration missions that are reasonable for uncrewed missions though dubious for crewed missions.

Humans might not be needed for numerous missions: tele control, remote control, drone, autonomous intelligence, etc., profiles suit a number of missions, including asteroid mining. However, the indomitable human spirit and a human presence require human deployment. That's a, if not the, pivot for space settlement and a feature for fiction if not prose generally about humans in space -- by, for, and about humans and their conflicts and complications.

At first, humans will come and go from Earth and transport costs need to be lower than they are currently. They will get there, though which of many proposed methods will prove most safe and economical remains to be seen.

Several Earth-based transfer proposals are pie-eyed pipe dreams, practical in a pure peace, though too vulnerable to warfare, sabotage, and terrorism. A factor that must be considered, I believe. Several are environmental catastrophes waiting to happen. Several are practical and possible though the technology isn't quite there. A best advised method is stages, from the ground to a high altitude platform, to LEO, to a HEO, and to beyond.

The Moon is an ideal source location for a number of bulk resources, building materials, some propellant resources from regolith trapped gas molecules and ice volatiles. A solar powered lunar mass driver launch to a space platform is ideal for the near term, though vulnerable to conflict -- conflict is inevitable at some knowable future time.

The Earth is ideal for near-term strategic resources, and people.

Near Earth asteroid resources likely contain stony materials and metals, perhaps some water volatiles, though they have mostly evaporated. Asteroid belt asteroids are more likely sources of water volatiles. Hydrocarbons -- nowhere close by outside of Earth -- the gas giants and their moons, Jupiter's Titan in particular. Hydrocarbons for plant and therefore animal food and CO2 supply are essential. Their transport could be economical from, say, Titan, if remote controlled tankers carry the freight. Earth's abundant CO2 and nitrogen will serve in the interim. Then there's the comet cloud out beyond the planetary orbits, what resources it might contain.

The milieu I'm most interested in is after all processes are in place and the particular station is a relic of the start, wanted for salvage, wanted to be replaced though crowded with retirees and malingerers who no longer can or will contribute and unwilling to relocate and considered a drag on the "master plans." Some work to keep the station fit for human habitation and some work on drone management -- in- and outbound drones, some work manufacturies, and some are administration, some are young delinquents, most are retired laborers who don't want to return to Earth or down any gravity well.

The Earth centered cislunar Moon orbit is, to me, the logical choice, due to lower radiation shielding needs and hazards. However, the Moon centered HEO Earth orbit strikes me as an alternative due to every other orbit apolune swings out as far away from the far lunar side as it does toward Earth for the other orbit. More radiation concerns though a wiser choice for inbound material capture from asteroids and beyond -- less chance of missed capture and possible Earth impact.

The Earth-Moon system outer orbit also has more radiation concerns and wiser access to material capture and transfer launch and is a more costly option at first.

Not to mention, stations at this time populate the habitable planets, planets' orbits, their moons, planetary libration points, solar libration points, and strategic asteroidal and cometary zones out to the edge of and just beyond the Solar system and looking to leap farther.

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