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Suppose you have a manned orbital shipyard. It obviously has no manufacturing capability, but instead it serves as an anchor and assembly point for modules launched from earth. It might have remote manipulator arms for mating the modules together, and the crew would preform EVAs for more delicate assembly tasks.

What, if any, advantages would this confer over the rendevous-and-docking style assembly planned for missions like Mars Direct or Constellation?

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It depends a lot on what capabilities this shipyard brings. One of the primary advantages could be in tremendous volume savings - by having a dedicated spot to do the majority of the spacecraft assembly, one could send up raw (read: dense) materials to feed into the assemblers on this station/array. The array could then process these into the required components through refining and sub-assembly. This doesn't result in any weight savings, however. This could also be useful for processing any asteroid materials, but that presents another suite of problems and issues.

Another method, and one that is close to being tested, is sending up the raw material required for the largest structures on a spacecraft while sending up the assembled spacecraft bus. An assembly drone could then use the raw material to build the extra structure on top of the pre-built satellite bus (this being what contains the most complicated elements). This would be highly advantageous for building large orbital telescopes, reflectors, or antennae as there is no great way to pack large structures like this into launch fairings (look at the complexity involved in the JWST deployment for example). A few companies have received SBIR grants for concepts related to this (the company I work for being one of them - I'm too leery of saying what our tech is though).

So, in summary - the capabilities of the array matter. Assembly alone at the array would provide for some advantages. Assembly and some degree of fabrication extends these capabilities and the worth of such an array, and inclusion of refining allows for usage of materials acquired in space. Further capabilities in manufacturing electronics, silicates, organics, plastics, and so on would advance its worth to be tremendous (and I may have misidentified things here, my apologies).

Some interesting links:

https://www.nasa.gov/spacetech/niac/2013phaseII_hoyt.html#.V5pxeLgrKUk

https://ti.arc.nasa.gov/news/IRG-Dragonfly-robot-UI/ - currently underway, attempt to build a large antenna in orbit using robotic methods

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    $\begingroup$ Add to this a good, inexpensive 'per ton' (but with big up-front cost) way of sending raw materials into orbit - the 'space gun'; a ground/underground structure that launches slugs of material equipped only with bare-bones minimal propulsion (e.g. a small primed SRB) for the circularization burn. That way orbital manufacturing becomes quite economically viable. Without orbital manufacturing, a simple 'assembly from modules' as OP describes, while nice to have, would be doubtful to be worth the cost. A small swarm of assembly drones would be both cheaper and more useful. $\endgroup$ – SF. Jul 28 '16 at 21:24
  • $\begingroup$ Thats the direction the NASA SBIR efforts and contracts are heading - including a couple from DARPA. Specialized drones, no bigger than 6U, built to do simple construction. Spiderfab is the one that comes to mind for that. It just makes simple structures, rather than a whole spacecraft or other elements. The orbital gun is neat, but if I recall correctly, we currently don't have any materials that could be used to make the body of the slug/missile with, since they'd effectively just vaporize due to their immense velocity. It would be a tremendously useful cost-saving device though. $\endgroup$ – fuchstraumer Jul 28 '16 at 21:39
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    $\begingroup$ The materials for the space gun aren't that much of a problem - it's merely a matter of how much ablator we'd be forced to pack (and that would be a lot!), plus a high-altitude location (mountains) would help a lot. Its main problem is the acceleration, which will obliterate anything save for most robust, durable and as result, simple internal structures. Most weaker materials are liquefied at these accelerations. It's viable for delivering materials though, there's just no market for sending big slugs of steel or aluminum into space currently. $\endgroup$ – SF. Jul 28 '16 at 22:25
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    $\begingroup$ @SF Mark Adler suggested in his answer to this question that the projectiles would need to be fired SRB end first. $\endgroup$ – Jerard Puckett Jul 29 '16 at 12:58
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    $\begingroup$ @JerardPuckett: as for the disposable nosecone from the comments in that question... that would be the ablative heatshield. With it detached at apoapsis before the circularization burn, it would reenter the atmosphere - no space junk. Tricky task: calculate it such that it survives the ascent (barely) but burns up on reentry. $\endgroup$ – SF. Jul 29 '16 at 19:41
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There are several proposed spaceship designs (or rather elements of spaceship design) that require quite large distances:

  • A Shadow shield works best far, far away from the crew module
  • Spin gravity works better when the RPMs are lower (due to the Coriolis effect)
  • Photovoltaic power tends to require rather large structures

All these aspects are practically not feasible when you want to launch your spaceship with one single rocket. So a space-yard is necessary for ships with nuclear-thermal propulsion, photovoltaic power support or artificial gravity.

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  • $\begingroup$ Makes me think, if you were building an nuclear reactor powered or NTR equipped ship, you could pack the faring of your rocket with structural beams to assemble into the backbone of a ship. That way you're not spending money to launch empty space in a rocket. That, and you can build arbitrarily large structures with just a few launches. $\endgroup$ – UIDAlexD Jul 29 '16 at 0:30
  • $\begingroup$ Yes, exactly! That is the biggest premise from my comment. Pack things tightly so we can build big! You could build large heatsinks (that would be necessary for nuclear/NTR vessels), solar panels, comm arrays, etc and could do so robotically (either autonomously or leveraging VR for a better interface). Empty space is bad, and launching rockets is all about being as efficient as possible :) $\endgroup$ – fuchstraumer Jul 29 '16 at 17:43
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I don't know why they haven't expanded ISS with a large room. Imagine a tuna can shaped room (as large as can be launched). Roll up the top and bottom and the side, launch them, assemble them, seal them, stack many of them and fill them with air. You could have an airlock to go out and fix whatever you needed to fix.

Also, as for going to the Moon and beyond, you don't need to ride in the same ship you launched in. You could have a room the size of a starbase (OK, start with a three floor building) and push it to the Moon. You go up to the 'starbase' and hang out while they build your 'train' of cargo cars.

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