Mega Mun space station: assemble there or in LKO?

[Maybeso83]

I'm designing a ridiculously large mun orbital station*. Since the modules are mostly the same size/mass, I'm planning on using the same lifter to get them all into LKO. And then another lifter to send them to mun orbit. Are there any advantages to putting it together in LKO and then sloooowly moving it to the mun? Other than some epic visuals perhaps? - I am already joining pairs in LKO to verify alignments, clearances, etc. and I want to avoid mun rendezvous if they're harder than Kerbin.

Maybeso83

*It's a test of a sky hook. I suspect with a 1 km arm I can't spin it fast enough to get the tip stationary near the surface. Assuming I can solve the persistent rotation thing. Plan B is minmus, or a spinning secondary arm ...

[steuben]

given the floppiness of docking ports you're better off hauling two or three modules at a run to the mun.

[Gargamel]

Check out the Konstruction mod.  It has docking ports that can be 'welded' together in flight.  They are removed from the vessel, reattaching the two main parts together.  This really helps keep the part count down, removing two parts from every docking. 

I'd go up in pieces.  Munar orbit isn't that hard to reach with a small tug craft.  Build yourself a reusable "space taxi".  Just a drone core with engines, rcs and a generic docking port on the front.  Build it so it's capable of putting say 30 tons into Munar orbit.  Then you can just load the taxi, and build each new section on top of that, or drop a subassembly on to it.   You can build one, launch, do your munar transfer burn, then flip back and build and launch the next.   You'll end up with a stream of taxis on the way to the Mun, and the next one will get there just as you're done docking the previous one. 

If you're playing career, make the taxi recoverable, just drop it into a 30km peri orbit around kerbin from the mun.

If you were going to another planet, then I'd say build in LKO and go from there.  But since the Mun has transfer windows that happen every LKO orbit, the logistics of multiple launches is much easier than building in LKO, and then trying to make an engine big enough to get it there.   And from what you describe, I'm guessing the axis of thrust won't be close to the COM, so you'll have navigation issues too. (Maybe not, depends on how you build it)

But a working sky hook would be cool to see.

[Cadet_BNSF]

Holy cow, a skyhook? is that even possible?

[ajburges]

Assemble LKO and use a low TWR tug to transfer.

Since the Mun is in Kerbin SoI Pe boosts can get you there easily. A low TWR avoids most structural issues. Assembly over Kerbin means less RCS fuel to take there.

[Maybeso83]

Thanks for all the great answers. I'll send the first sandbox test in pieces. Then for the real thing I'll assemble in LKO only if I suck at orbital rendezvous. I'll try to put together progress pics or a vid for the space station thread - I figure it will succeed or fail spectacularly so ...

Maybeso83

FYI: A 4.86 km equatorial orbit around the mun is too low ...

[Tyko]

11 hours ago, Maybeso83 said:

Thanks for all the great answers. I'll send the first sandbox test in pieces. Then for the real thing I'll assemble in LKO only if I suck at orbital rendezvous. I'll try to put together progress pics or a vid for the space station thread - I figure it will succeed or fail spectacularly so ...

Maybeso83

FYI: A 4.86 km equatorial orbit around the mun is too low ...

The middle ground is to do partial assembly in LKO - let's say you have 9 pieces. Assemble them into blocks of 3 and then move those three blocks to Munar orbit. That's how I've been doing things and it seems to work well - it's mostly because I got tired of doing a bunch of identical runs to the Mun 

[RizzoTheRat]

How many launches are we talking about? 

Obviously separate transfers mean more miles covered/time taken, but presumably the freshly launched modules are nicely balanced and will be a lot easier to move around than groups of modules that might not be well balanced.  I use a twin nuke powered tug to haul stuff around, with large docking ports front at back, so something like that would let you haul at least a couple of modules at a time, but bear in mind you need multiple docking ports, on each part (or a claw on the tug) to allow you to move stuff between launch vehicle, tug, and station.

You say it depends on how easy you find the rendezvous, but lets face it, if you're putting up loads of modules you'll be doing a lot of rendezvous so will get good at it

[Maybeso83]

The key factor so far is that my modules are 50 m pillars, so my lifter is attached radially in 3 or 4 pieces (based on symmetry) to put CoM just above 25 m for arrow-stability. Version 1 was 3-way and easy to tweak stages but I still ended up with enough dV to get to the mun. Version 2 was 4-way, tough to tweak but my excess was much lower.

I'd like to continue this somewhere with pictures ... the "show us your stations" thread or where?

Maybeso83

[Spricigo]

8 hours ago, Maybeso83 said:

...I'd like to continue this somewhere with pictures ... the "show us your stations" thread or where?

If you have pictures,  post in this thread. Is where we are discussing how to deploy yor station

[Maybeso83]

My original plan was for 100 m segments, which don't fit in the VAB so I used "flying girders" to duplicate 3 outer connections when the center is connected. Reduced that to 50 m; here's two segments connected in orbit, with around 2k extra fuel in that final lifter stage (and waaay too much rcs).  Two 3-symmetry segments

Next version has 5 connection points. Another two segments in orbit, again with over 1.5k fuel left over. I'll get it eventually.  Two 4-symmetry segments

Third version - turns out the structural fuselage is the same mass as two struts. Here's a 50 m segment plus lifter on the pad. I extended the arms because of the diameter. I'm thinking about connecting two or three, transferring last stage fuel to the upper one and using that to get to the mun ...

One 4-symmetry segment plus Lifter

-Maybeso83

Edited February 21, 2018 by Maybeso83
In-line images inside spoilers didn't work.