Design a modular spacecraft w docking ports

[Clear Air Turbulence]

Hi there

Noob, sandbox mode.

I want to design a modular spacecraft a la our own moon landing. A transfer vehicle that can take me places, and a dockable lander that can land and come back up.

How strong are docking ports as structural components? I don't want to fly to some far off planet and find my spacecraft breaks in half in the middle because the port could not stand the strain.

Edited October 22, 2015 by Clear Air Turbulence

[mdkendall]

They are plenty strong enough, and your craft will not break in half under normal conditions.

They can be a bit wobbly, especially if you use an undersized one (e.g. the "standard" 1.25m one in the middle of a 2.5m stack). You can strut across the joint for extra strength, e.g. to survive launch, and the struts will disappear the first time you undock.

If you are making Apollo-style craft you won't have any problems. If you are assembling giant vessels in orbit, with powerful engines up one end and lots of mass up the other, separated by a long thin structure with a docking port in the middle, you may have some difficulty.

I suggest avoiding the "junior" one except on small craft, at least at first. Not only is it more wobbly than the larger ones, but its small size means greater accuracy is required when docking, which makes it harder to use.

[Vanamonde]

The result of an aerobraking attempt that went badly. Anyway, nothing on that ship broke until it hit the water.

[zolotiyeruki]

http://i.imgur.com/oCGhctH.png

The result of an aerobraking attempt that went badly. Anyway, nothing on that ship broke until it hit the water.

Holy cow, man, that's about the most Kerbal thing I've ever seen. The part count on that must have been brutal!

[magnemoe]

For something like an 2 man Mun lander the standard docking ports works well. It you want to dock larger modules use the 2.5 meter docking ports.

And yes modular stuff makes a lot of sense. Going to Duna or other places you do want an ship and a lander.

One well known tricks is to dock an tug and have the tug help you push the ship up to 900 m/s before it transfer most of its fuel to ship and return to LKO where you refuel it and wait for next mission.

[Pax Kerbana]

Oh yes, it can be done. I'm doing it now in a LV-N free game. Trick is to use the regular clamp-o-trons along the length of the ship. This is the best way to deal with the issue of engine thrust shaking or breaking the ship. For example, 2 sets of 4, one at the top of a resusable core and the other at the bottom, will allow four radial "boosters" that can be detached in pairs.

Trying to build a modular ship axially is a recipe for spagetti and ship compaction...

[Snark]

Yes, you'll do fine with standard docking ports, as long as you're not doing super-huge accelerations or you have two craft that are both really massive. If one of them's a little munar lander, you'll be fine.

When you graduate to bigger ships, you can use the jumbo-size docking ports, which are stiffer.

If you start building really big ships and the wobble really becomes an issue, one mod that's really handy is Kerbal Attachment System. I don't use most of its features, but there's one I really like: Deployable struts. It has a part which is basically a "strut socket". They work like this:

1. In the VAB, put a few of those around your docking port on ship A, and a few around the docking port on ship B.

2. Dock the ships as usual.

3. Take a kerbal on EVA. Go up to one of the sockets, right-click and choose "Link". Drift over to a socket on the other ship, and click "Link" there.

4. Presto, there's a strut connecting the two sockets! (You can unlink them later when you're ready to undock).

This allows setting up struts between docked vessels, which can make building huge multi-section ships more practical.

I only mention it for future reference, though-- for your little munar lander it would be massive overkill. You'll do fine with the basic docking port.

[Alshain]

Generally speaking, the link between two docking ports will not break before the link between the docking port and the part it is attached to. Bigger sized docking ports are used to reduce and prevent wobbly effects, like Vanamonde's image, not to give them a stronger hold.

[Norcalplanner]

SpaceY has 3.75m and 5m docking ports that are even stronger.

[DancesWithSquirrels]

I've also used multiple docking ports in the past, although the build techniques have to adapt to the tree structure describing the craft. Here's a mission using tricouplers:

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In that case (IIRC) I was running career (no, science), and wanted to go to Duna before unlocking the Clamp-O-Tron Sr. - with a reasonably rigid ship that could maneuver without smacking the CM with the trailing fuel tanks on turns.

The trick to creating those multiple dockers is to fill the first tricoupler with single ports (no symmetry), add a single matching port and the bottom tricoupler rotated out, add the last two, and rotate the tricoupler back in to align (E/Q in the VAB). The unconnected ports will (should) dock on the launch pad right after loading.

The craft part tree then looks like this, with no loops:

   ...
    |
  Tank
    |
  Tricoupler
   |   |  |
port port port
             |
            port port port
               |   |  |
              Tricoupler
                 |
               Tank
                 |
                ...

If you use symmetry or attach all three ports before the tricoupler, the tricoupler will only be hooked through a single port, and (ahem) there will be dangles.

[eddiew]

As long as you use the right size port for the craft, should be fine. On the other hand, if you have to do an emergency docking and fly a station and a ship home as one unit... expect wobbles. This monster was hard to steer and only survived re-entry by detaching the supplies capsule and separating the ships a few seconds before deploying the chutes xD

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