Multiple Satellites/Craft in a Cargo Bay

[meyerweb]

I’m trying to build a launcher with a huge cargo bay that can carry and launch multiple satellites or other craft.  For example, I could load up three science probes to boost to Kerbin orbit, then detach/undock each one in turn and boost them out to their destinations.  (Or use the Burn Together mod to boost them as a fleet to one destination, whichever.)

The thing is, I cannot for the life of me figure out how to do this in the VAB.  I can build the probes, and I can build the Great Big Cargo Bay Launcher (GBCBL), but I can’t figure out how to attach the probes to the booster.  I’ve read various posts about multiprobe launchers, but none I’ve found have actually explained how it’s done, short of building a series of probes in serial and then building a booster underneath them.  I’m after something a little more modular, so I can design each probe separately and save (or subassembly) them, then add the ones I want to my GBCBL.  So far, nothing I do allows me to attach the probes to the GBCBL, whether I try to use stack separators or docking ports to make it happen, except that I can sometimes attach the probe core to a docking port—leaving everything on top of the probe core clipped into the GBCBL’s body, which I definitely don’t want.

So: is there a tutorial that goes through how to do this, step by step, with clear pictures and simple words?  Recent is preferred, but as long as whatever the tutorial describes works in 1.0.5, I’m fine with it.  Oh, and I’d greatly prefer the solution to be stock-compatible, but I’ll consider installing mods to make this work if there’s no other sane alternative.  Is the root tool somehow the answer, and if so, how?  I appreciate any help!

[Temstar]

7 minutes ago, meyerweb said:

except that I can sometimes attach the probe core to a docking port

You're already done then if you've figured out this part, now you just have to use the rotation gizmo to rotate your probe core 180 so the end with the body of the satellite is facing into the cargo bay rather than your carrier craft.

Remember you can hit F while the rotation gizmo has a part selected to switch between absolute and relative rotation angle.
 

[Snark]

9 minutes ago, meyerweb said:

I’m trying to build a launcher with a huge cargo bay that can carry and launch multiple satellites or other craft.  For example, I could load up three science probes to boost to Kerbin orbit, then detach/undock each one in turn and boost them out to their destinations.  (Or use the Burn Together mod to boost them as a fleet to one destination, whichever.)

The thing is, I cannot for the life of me figure out how to do this in the VAB.  I can build the probes, and I can build the Great Big Cargo Bay Launcher (GBCBL), but I can’t figure out how to attach the probes to the booster.  I’ve read various posts about multiprobe launchers, but none I’ve found have actually explained how it’s done, short of building a series of probes in serial and then building a booster underneath them.  I’m after something a little more modular, so I can design each probe separately and save (or subassembly) them, then add the ones I want to my GBCBL.  So far, nothing I do allows me to attach the probes to the GBCBL, whether I try to use stack separators or docking ports to make it happen, except that I can sometimes attach the probe core to a docking port—leaving everything on top of the probe core clipped into the GBCBL’s body, which I definitely don’t want.

So: is there a tutorial that goes through how to do this, step by step, with clear pictures and simple words?  Recent is preferred, but as long as whatever the tutorial describes works in 1.0.5, I’m fine with it.  Oh, and I’d greatly prefer the solution to be stock-compatible, but I’ll consider installing mods to make this work if there’s no other sane alternative.  Is the root tool somehow the answer, and if so, how?  I appreciate any help!

To be attachable, the attachment point needs to be the root part of the probe.

For example, let's say you want your probes to be attached on the bottom:  that is, the bottom-most probe has its engine on the bottom, and you want the engine's lower attachment node to connect to a decoupler on the GBCBL.  What you do is to use the root tool ("4" in the VAB/SPH) to make that engine (or a decoupler attached to it) the root node of the probe.  Then you can attach it.

Attach other probes on top of it the same way.

[FancyMouse]

My suggestion is not to use cargo bay if you're not doing spaceplane mission - just put 1.25m fuel tank, surface attach some cubic struts, then upside-down decoupler, then subassembly satellite under it. After that, fairing the whole thing (i.e. fairing as a one-time cargo bay - it's lighter anyway).

Doing a real cargo bay - you'll need to design satellites inside the cargo bay so that it can fit.

 

Also note: if you said you cannot attach your satellite - post a picture to clarify what have you done. This will help diagnose what happened 

[meyerweb]

4 minutes ago, Temstar said:

You're already done then if you've figured out this part, now you just have to use the rotation gizmo to rotate your probe core 180 so the end with the body of the satellite is facing into the cargo bay rather than your carrier craft.

In that case, wouldn’t the stuff underneath the probe core (like the batteries, fuel tank, and engine) clip into the GBCBL’s body, causing physics-engine problems when I decouple the docking port?  Like, explosion problems?

4 minutes ago, Snark said:

For example, let's say you want your probes to be attached on the bottom:  that is, the bottom-most probe has its engine on the bottom, and you want the engine's lower attachment node to connect to a decoupler on the GBCBL.  What you do is to use the root tool ("4" in the VAB/SPH) to make that engine (or a decoupler attached to it) the root node of the probe.  Then you can attach it.

Ahhhh, interesting.  If I root the engine, what happens when the probe is detached?  Does the engine stay the root node, or does it revert to the probe core?  If it stays with the engine, will that cause problems with flight control?  If I root a docking port, which stays with the main craft, what becomes the root of the probe?  Or does the concept of rooting not really apply in flight, but only in the VAB?

[Temstar]

1 minute ago, meyerweb said:

In that case, wouldn’t the stuff underneath the probe core (like the batteries, fuel tank, and engine) clip into the GBCBL’s body, causing physics-engine problems when I decouple the docking port?  Like, explosion problems?

I was assuming the way you worded that line that your satellite has the probe core as both the root part and the top most part with the rest of the satellite attached below it? After all when you save the satellite as a subassembly you have to drag it by a part (which becomes the subassembly root part) and that part has to either have a free node or be surface attachable.

If instead you want your probe core to be sort of sandwiched in the middle then do what @Snark said above and change the root part to something on either end of the satellite before saving your subassembly.

[meyerweb]

22 minutes ago, FancyMouse said:

My suggestion is not to use cargo bay if you're not doing spaceplane mission - just put 1.25m fuel tank, surface attach some cubic struts, then upside-down decoupler, then subassembly satellite under it. After that, fairing the whole thing (i.e. fairing as a one-time cargo bay - it's lighter anyway).

I had not considered that approach!  I’ll definitely have to play around with that idea.  However, I do want to use spaceplanes to launch one or more satellites as well, so understanding how to attach probes to cargo bays will still be useful to me.  It looks like part rooting makes the most sense for what I have in mind, but we’ll see.  Down the road, I might try to combine the approaches by creating a strutted framework holding several satellites as compactly as possible, then root that framework and attach it inside a cargo bay.  Or a fairing!

Edited January 4, 2016 by meyerweb

[Speeding Mullet]

3 hours ago, meyerweb said:

Down the road, I might try to combine the approaches by creating a strutted framework holding several satellites as compactly as possible, then root that framework and attach it inside a cargo bay.  Or a fairing!

You can certainly do that.  I've played around quite a bit with putting pretty tightly arranged constellations into fairing arrangements before, so possibly this may serve as inspiration.  Consider the following probes:

There's six of them, each of them is multi-staged, and also uses fairings (ignore the fact that used procedural fairings here as with the new fairings this is now possible).  How to compact this into a nice looking array and keep it within the confines of the stages width?  Like this:

 

Space plane or rocket, your best bet is to make use of sub-assemblies and root parts as others in the thread have suggested.

 

SM

[ForScience6686]

For small sub assemblies, I'll start building from my desired connection point so I don't have to mess with the root tool.  I would also agree with the fairing, less space restrictive and not necessary for a one use rocket.  Plus you can mount many more probes.  I used this method to haul 9 probes to eve.

[Snark]

12 hours ago, meyerweb said:

Ahhhh, interesting.  If I root the engine, what happens when the probe is detached?  Does the engine stay the root node, or does it revert to the probe core?  If it stays with the engine, will that cause problems with flight control?  If I root a docking port, which stays with the main craft, what becomes the root of the probe?  Or does the concept of rooting not really apply in flight, but only in the VAB?

I believe that root will stay with the engine, but it shouldn't matter.  Rooting doesn't matter (much) when you're in flight.  What matters is your control-from part, and my impression is that KSP has a set of logic for which part gets control-from priority, and that logic doesn't involve "which part is root".  So you should be good to go.

Note that if you take the approach of stacking things in a cargo bay like this, you'll likely need some struts connecting the most-distal probe with the inside of the bay, otherwise the whole stack will sway all over the place as the ship experiences g-force.

[meyerweb]

11 hours ago, Snark said:

Note that if you take the approach of stacking things in a cargo bay like this, you'll likely need some struts connecting the most-distal probe with the inside of the bay, otherwise the whole stack will sway all over the place as the ship experiences g-force.

Yep, I discovered that in my tests, in fact.  Thanks to all the help I got in this thread, I put together a five-probe scaffold on top of a rocket and got it into orbit!  And then realized I forgot to prevent fuel crossfeed, so all the probes were drained dry long before orbit.  Hooray for reverting to the VAB!

Now I just have to figure out how to lower the part count so I don’t keep crashing the game, and everything will be great.