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It is a known concept that if ships were to be constructed in space, it would save a lot of fuel and allow for larger ships. My question is, what would be the best location for an orbital "dockyard" for lack of a better word. I am looking for an answer such as x distance from earth's surface orbiting over (city, country, area, etc.) or coordinates and although it is not nessesary I would be interested in knowing a feasible method for transport to the dockyard other than rockets launched from earth's surface. The technological capability used is just slightly more advanced than ours. What must be contained within the facility is as follows

  1. Crew quarters for short stays
  2. Storage for materials, food/water, fuel, and tools
  3. Long extensions capable of holding a large ship
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    $\begingroup$ What's your technology level? What's easy, what's difficult? What's cheap? What's not really affordable yet? $\endgroup$ – Mołot Feb 13 '17 at 23:16
  • $\begingroup$ @Mołot Current technology level, ignoring politics, unlimited supplies\money $\endgroup$ – Cameron Leary Feb 13 '17 at 23:18
  • $\begingroup$ Currently we don't have tech or need to build orbital shipyards at all. In your world, you must have a reason. Most probable one is asteroid mining, but first recon missions are planned to be built dirt side. $\endgroup$ – Mołot Feb 13 '17 at 23:23
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    $\begingroup$ Can you elaborate on tech level, supplies, requirements for whats on board, etc, in the question via an edit? You may also want to ask about alternative transport to the dockyard in a separate question, as that somewhat broadens this one. $\endgroup$ – Zxyrra Feb 14 '17 at 0:43
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    $\begingroup$ I want to suggest playing Kerbal Space Program. You'll get a pretty good feel for orbital mechanics and, if you have the patience, you can build a space station around Kerbal (fake Earth), the Mun, a tiny moon, or also around captured asteroids. And the stock game has fuel mining mechanics, so you can also get an idea of what it takes to refuel from a moon base. $\endgroup$ – csiz Feb 14 '17 at 11:20
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In orbit of the moon. The heaviest part of a space ship is usually the fuel, so you'll want to be close to the fuel source. There's water on the moon which can be made into fuel, and the Moon's gravity well is a lot less deep than Earth's, so it's a good idea to get your fuel from the moon instead. The advantages increase if you build some sort of moon base where you can gather additional raw materials.

Another option is Ceres, but that's quite a bit further away, probably better as refuelling station.

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There probably is no such place as the best for the task. It is a matter of preferences accordingly to chosen technologies for the building and other, maybe even not related to technologies, factors. I mean, it depends; the place comes with the how and maybe why you do the building of ships, how much of ships you plan to build, etc.

I would go with L1 or L2 Sun-Earth, Lagrangian point and I prefer L1 over L2, because even when L2 is beyond umbra, but it is still in the penumbra (it might be a good thing actually; needs to be calculated, maybe not that big of a deal). New words I have learned today and can't wait to give you the joy to learn them today too. With Halo orbit in mind, it can really depend on future plans.

As the source of materials for the L1,2-dock, I would go with the Moon.

The reasons for the case, are the same as for any large scale construction we might wish to build in space and for the particular reason in the particular situation, there might already be a construction which helps in the ship building process.

Advantages of L1

Distance

Distance is one of the advantages of L1. Particularly its constant relative distance from the Earth and the distance is relatively close to the Earth and is about 1.5 million km or about 5 light seconds.

If we compare the solution with asteroid based locations, the problem of asteroid belt based locations - it is beyond the mars orbit and varies from 2 to 3.5 a.u. orbits and the relative distance from the Earth change from l to 4.5 a.u. over the Earth year. As a result the connection delay is 500-2'000 seconds in the best case scenario. The delay may or may not be disadvantageous, but for sure it moves the solution into more automation or more people field of implications.

Energy

At the L1-location, energy flow from the Sun is unobstructed and it is about the same as on earth orbit 1360 W/m2, but without orbital motion problems (some time in the shadow of the earth).

Compared to asteroid solutions, the density of energy is 4-12 times more than at 2-3.5 a.u. orbits and thus we spend 4-12 times less effort to get the same amount of energy compared to asteroid belt solutions. I have to note it might or might not be a problem - it depends.

Instability of L1

Instability of L1 can be considered as an advantage because any not managed debris will fly off the location (eventually), which is not the case at orbits around Moon, Earth, or at asteroid locations. (Or some debris can be dumped with use of little or zero energy in the way that it will fly to the Earth or Moon and be utilized by atmospheric braking or lithobraking.)

It might be considered as a disadvantage, as eventually, the debris can hit the Earth or the Moon, but until the debris is small enough it can be considered as an advantage. (The only problem is satellites in earth's orbit, so better to loose things in a way they hit the Moon after some period of time. Not sure if it is so easy, but needs more detailed investigation to answer the question.)

Matter/material source

One of the problems with L1, as it is an unstable location, thus there is basically nothing in terms of construction materials and such.

But having the Moon as the material source is a nice thing, because it is big enough and because same way as L1 it has a pretty constant relative distance to the Earth and is close enough to the L1 location.

Second choice for the material (including humans) source is Earth for sure.

The asteroid belt source

For asteroid location, in the asteroid belt (2-3.5 a.u. orbits) and delivering materials from there to earth orbits (not around the planet, but to 1 a.u. orbit around the Sun), if you crunch numbers for Hoffman transfer delta-v requirements (can be seen in this answer). You will get surprisingly significant numbers for moving from 2 a.u. orbit to 1 a.u. orbit 3'860 m/s first maneuver and 4'600 m/s second (you can play with the numbers here, Instacalc, Hoffman (R6 has to be 1.32692605*10^20 (G*Msun), planet radius 0), or 5300 m/s and 7352 m/s for 3.5 a.u to 1 a.u. respectively.

So, delta-v requirements for the transfer from the asteroid belt to orbits close to earth are about the same as launching stuff from earth into earth orbit. (Asteroids still preferable than doing the same from earth, but for reasons other than delta-v requirements - because of microgravity environment near asteroids, but there are higher probabilities of meteorites hitting, especially for larger constructions, as orbits near our planet are cleaned from most of debris by definition of the planet.)

The Moon as a source

As the source of construction materials and ores the Moon is preferable both to earth and to the asteroid at initial phases of the construction processes (when there is not a lot of capabilities to solve different difficulties).

The Moon is relatively good as matter sources, because everything you expect to find in asteroid belts (except water and gases, carbon) will be on the surface of the Moon, because those asteroids had bombarded the Moon since the forming of the Moon, hires moon picture here.
Some gases and carbon, water can be potentially found in some places and they are in ppm, ppb concentrations in lunar regolith. Fe, Al, Ca, Mg, Ti - are in percentage concentrations on the surface of the Moon, in form of lunar regolith (fine dust, rocks).

One of the advantages for the Moon as a material source: it is big, compared to most of the asteroids. Its big size means that you are able to build large (long) constructions on the surface in gravity fields in more or less old fashion, as we do them usually.

Escape velocity for the Moon is 2380 m/s - but potentially we can build Maglev style mass drivers to launch payloads from the Moon surface. Compared to a big enough asteroid such activity will have lesser effects on its orbital characteristics (none basically), which are important for permanent construction, which might be 1000's km long.

Another nice thing with the Moon and mass driver is its ability to deliver construction material with 0 fuel expenses into L1 location, because we can launch payloads clockwise and counterclockwise around the earth and catch those payloads sky hook style (or by other means) and keep zero average momentum of our L1 construction.

Energy wise expenses of launching materials from the Moon (about 3MJ per kg) are not that big, especially if we launch mostly raw ores and compare the energy to the energy we need to extract materials, reduce elements to their base stat. And to energies we need to produce useful products from the materials. (Energy will be a few percents in the total energy expenses for the materials.)

Bonus for L1 position

As I said before there might be other constructions, which might help in building ships. By that I meant infrastructure, energy.

The L1 location is the only point suitable to reduce the amount of sunlight which the Earth gets and thus there can be a structure which regulates the amount of light and by thus regulates the climate on the Earth. But at the same time the structure can generate a lot of energy in useful (at that place) form - electricity, heat and light. And building the construction, as useful for 7 billion people on Earth, can justify building mass drivers' on the Moon and perfecting the launching of materials and constructions from the Moon to L1.

Imaginary Elephant in the room: instability of L1

Halo orbits are pretty inexpensive to maintain and with access to the material from the Moon (with the supply of the materials) not that big of a problem to maintain (with reactive propulsion, or with possible impulses from catching materials, or might be with solar sails). Considering the excess of Oxygen from reducing metals from their oxides, which is not needed in such quantities, there is always a cheap reactive mass available for the purposes of corrections.

Another solution is to build tether like structures with counterweights to correct and dynamically stabilize the position by retracting or releasing those tethers. They have to be long, which is not a problem in those conditions, as gravity there (the difference) is less than 100μm/s2. Thus no problems to have 100 thousand's of kilometers long cables made out of ordinary materials (iron, aluminium) and it takes months do destabilize the position. The length of the cables you might need is around 10'000 km. They might have to be longer, but the required length is less than 100'000 km for sure (less than the typical halo orbit size). A slightly rotating system of those cables (,which can be used to catch the payloads,) should work well (when you orchestrate it well).

Conclusion

All that being said, go with L1 if you would like to have 100's m or km's sizes ships/constructions, habitats for the crew.

If they are smaller than that - the Moon can be a pretty ok place too.

As for radiation protection, which people are concerned about a lot most of the time: with access to prices of 2.8MJ/kg of materials, you can build the shelter as thick as it is - enough to protect the humans from the radiation.

Small constructions -> bigger constructions preferable places in that order are - orbit around the Earth, Moon, orbit around Moon, L1, Mercury.

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Most orbits are not over a certain spot on Earth. Objects circle around the planet.

  • A low orbit reduces the fuel requirement to bring things up from the surface of Earth.
  • One of the Lagrange points, probably L-4 or L-5, is good for long-term stationkeeping in space.
  • A geostationary orbit is possible, which would stay over any one spot on the equator. Going that high might have the drawbacks of both LEO and Lagrange and few benefits.
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Why orbital? The obvious place to put a dockyard would be in the asteroid belt. Plenty of materials and minimal gravity. Use solar panels to power a magnetic catapult to toss the ships towards the Earth or wherever you want the ships.

If you're stuck in the Earth area, put it on the moon. Low gravity, plenty of materials, easy access to solar energy if located near the poles. Again, solar panels to power a magnetic catapult to launch the ship into orbit.

If you want a place to put people on ships and are willing to go near future, build a space elevator and make the counterweight a dock. The counterweight would be in the area of 36,000 km or 22,000 miles from the surface. I.e. above geostationary orbit. Where to anchor? See this question.

The reason to prefer the asteroid belt to the Moon or Earth is that there is no gravity well from which materials need to be pulled. Given sufficient transit time, even a relatively small push can send material from the asteroid belt to Earth orbit. By contrast, even the Moon requires a big initial push just to achieve escape velocity.

There is diffuse but constant solar light to provide power in the asteroid belt. The Moon has more intermittent power even in a polar location. The Earth only has power half the time and has an atmosphere in the way. The Earth's poles are horrid places to put solar panels, as there's too much atmosphere between the panels and the Sun. Not to mention precipitation and cloud problems.

The small size of most asteroids is helpful. Instead of digging a gigantic hole that can collapse, just take apart the entire asteroid.

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    $\begingroup$ Contrary to popular depictions, the asteroid belt is mostly empty; with a mass that is 4% of the moon, its inner radius is twice that of the Earth orbit, and the outer radius more than 3 times the Earth orbit (so, its surface covered would be like 16 times the surface defined by the Earth orbit). Going from asteroid to asteroid would probably be comparable to going from Earth to Mars moons, and for a considerable yes material supply than in the Moon. en.wikipedia.org/wiki/Asteroid_belt#Characteristics $\endgroup$ – SJuan76 Feb 13 '17 at 23:53
  • $\begingroup$ Although @SJuan76 is correct, and the largest asteroid is roughly 1% of the mass of the moon, that is still a LOT of material. $\endgroup$ – BobTheAverage Feb 14 '17 at 1:06
  • $\begingroup$ @SJuan76 in terms of placing the thing near one asteroid (it is enough) the answer is ok. Ther in the list List of Solar System objects by size 260 belt asteroids greater than 1km radius. If OP will correct the answer accordingly it will be nice. However, changing orbit need delta-v, and pushing stuff to earth is changing orbit. $\endgroup$ – MolbOrg Feb 14 '17 at 5:04

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