Why can't I attach this booster??

[Loren Pechtel]

This is driving me nuts trying to build this rocket.  Yeah, that's quite a bit of rocket but it's pushing a lander that's going to do multiple hops and I'm not the best pilot yet.  I can build this rocket with a 4x symmetry but if I do that I can't get the fuel lines hooked up asparagus style--putting a pipe on an outer rocket switches it to 4x and they all feed the central tank so it won't burn off two of them faster.

I then built the 2x design you see and attached another pair of decouplers front and back--and absolutely couldn't get the booster hooked to them.  I then tried side to side like you see--and again it absolutely won't attach to the decoupler, although I did manage to get it attached once slightly inside the other booster.

(And why don't we have an asparagus decoupler--one with a built-in fuel line.)

[Snark]

27 minutes ago, Loren Pechtel said:

I can build this rocket with a 4x symmetry but if I do that I can't get the fuel lines hooked up asparagus style--putting a pipe on an outer rocket switches it to 4x and they all feed the central tank so it won't burn off two of them faster.

Yes, that's a standard problem with asparagus designs.  The answer is to turn off symmetry when placing the fuel lines.  Just place every fuel line individually.  Yes, it's kinda tedious.  Yes, it means that the fuel lines won't be perfectly symmetrically placed, but in practice, as long as they're in approximately the right spot, it doesn't matter.

I might suggest attaching the decouplers to the top of the radial boosters rather than the bottom, so that the force of the decoupler will cause the booster to nose out from the ship rather than in.  This can help during launch, to prevent the ejected boosters from colliding with the central ship.

27 minutes ago, Loren Pechtel said:

I then built the 2x design you see and attached another pair of decouplers front and back--and absolutely couldn't get the booster hooked to them.  I then tried side to side like you see--and again it absolutely won't attach to the decoupler, although I did manage to get it attached once slightly inside the other booster.

How did you "create" that booster that you're trying to hook on?  Did you save it as a subassembly?  Or did you click-copy it from one of the existing boosters?

If you loaded it from a subassembly, that's likely your problem right there.  Every subassembly has a particular "root" part, and it won't attach to anything except by that root part. This somewhat limits the usefulness, or at least can require you to jump through hoops to get the root part to be where it needs to be for a particular application.  If you're dead-set on 2-way symmetry, the easy solution is to just click-copy the inner booster (from the decoupler) and apply that.

However, rather than doing that, I'd suggest just 4-way-symmetry the boosters and asparagus them.  It'll be structurally stronger.  Just means that you need to manually place the six fuel ducts.

Also, that 2.5m adapter on the top of your center stack is going to generate a lot of drag-- suggest replacing it with a conical 2.5m-to-1.25m adapter, and then putting a 1.25m decoupler on top.  More aerodynamic, and IIRC a bit lighter, too.

Also, I'd suggest connecting the fuel ducts from the top of the booster stack to the top of the central core. It'll help with CoM issues during ascent.  As you have it right now, the center engine will be draining the radial boosters from the top down, which is the exact opposite of what you want for aero stability.

Edited February 20, 2016 by Snark

[Plusck]

1 hour ago, Snark said:

Yes, that's a standard problem with asparagus designs.  The answer is to turn off symmetry when placing the fuel lines.  Just place every fuel line individually.  Yes, it's kinda tedious.  Yes, it means that the fuel lines won't be perfectly symmetrically placed, but in practice, as long as they're in approximately the right spot, it doesn't matter.

If you place one booster on the central stack without symmetry and attach a fuel line to the next booster, plus struts etc., you should be able to then lift it off, enable 2x symmetry and place it back on. All the fuel lines, struts etc. should copy perfectly.

Just be careful what you mouse over as you place it back on. If you mouse over something with 4x symmetry it'll switch to that instead.

[Loren Pechtel]

1 hour ago, Snark said:

Yes, that's a standard problem with asparagus designs.  The answer is to turn off symmetry when placing the fuel lines.  Just place every fuel line individually.  Yes, it's kinda tedious.  Yes, it means that the fuel lines won't be perfectly symmetrically placed, but in practice, as long as they're in approximately the right spot, it doesn't matter.

I might suggest attaching the decouplers to the top of the radial boosters rather than the bottom, so that the force of the decoupler will cause the booster to nose out from the ship rather than in.  This can help during launch, to prevent the ejected boosters from colliding with the central ship.

How did you "create" that booster that you're trying to hook on?  Did you save it as a subassembly?  Or did you click-copy it from one of the existing boosters?

If you loaded it from a subassembly, that's likely your problem right there.  Every subassembly has a particular "root" part, and it won't attach to anything except by that root part. This somewhat limits the usefulness, or at least can require you to jump through hoops to get the root part to be where it needs to be for a particular application.  If you're dead-set on 2-way symmetry, the easy solution is to just click-copy the inner booster (from the decoupler) and apply that.

However, rather than doing that, I'd suggest just 4-way-symmetry the boosters and asparagus them.  It'll be structurally stronger.  Just means that you need to manually place the six fuel ducts.

Also, that 2.5m adapter on the top of your center stack is going to generate a lot of drag-- suggest replacing it with a conical 2.5m-to-1.25m adapter, and then putting a 1.25m decoupler on top.  More aerodynamic, and IIRC a bit lighter, too.

Also, I'd suggest connecting the fuel ducts from the top of the booster stack to the top of the central core. It'll help with CoM issues during ascent.  As you have it right now, the center engine will be draining the radial boosters from the top down, which is the exact opposite of what you want for aero stability.

 

Aha, that works!  When I tried to do it with 2x symmetry it was always switching to 4x the instant I touched a 4x part.  With symmetry off I was able to build it as 4 columns around the core and hook everything up correctly.

The rocket piece that I was trying to attach was not a subassembly--I can't get it to accept parts like that as subassemblies in the first place.  It was simply a part I had built but which was horribly misattached, I took it off and tried to put it in the right place.

The game really needs the ability to use the keyboard to move a part in x, y & z dimensions while building rockets.

I switched to the smaller decoupler but what's up on top is aerodynamic hell anyway--it's going to Minmus and not coming back.  I don't have a large enough fairing to cover it and I can't get the fairing builder to cover the stuff that I think it could cover.  At least I could use it to build jettisonable nosecones.

[Snark]

11 minutes ago, Loren Pechtel said:

Aha, that works!  When I tried to do it with 2x symmetry it was always switching to 4x the instant I touched a 4x part.  With symmetry off I was able to build it as 4 columns around the core and hook everything up correctly.

Excellent, glad it worked out!

If you run into flipping problems at launch, there's a high likelihood it could be CoM issues (tank stacks draining from the top down).  If that happens, you can address that via strategic placement of the fuel ducts.

I'd suggest replacing all those 8-ton tanks with the 16-ton tanks instead.  (They're unlocked on the same tech tree node, so if you have one, you have the other).  It'll keep your part count down, reduce wobble, and help a bit with CoM issues.  In general, any time you can avoid making tall stacks of little things, it's a win.

(Actually, ideally you'd replace 'em with the big orange tank and get rid of stacking altogether, but that's a higher tech node that you may not have unlocked yet.)

Edited February 20, 2016 by Snark

[Plusck]

20 minutes ago, Loren Pechtel said:

 

Aha, that works!  When I tried to do it with 2x symmetry it was always switching to 4x the instant I touched a 4x part.  With symmetry off I was able to build it as 4 columns around the core and hook everything up correctly.

You should also check out the various keyboard shortcuts. "X" increases the symmetry setting, "shift-X" decreases it. Very helpful to avoid mousing over things (though again, it can get stuck on a given symmetry setting and require dropping an object and picking it back up).

[Loren Pechtel]

12 minutes ago, Snark said:

Excellent, glad it worked out!

If you run into flipping problems at launch, there's a high likelihood it could be CoM issues (tank stacks draining from the top down).  If that happens, you can address that via strategic placement of the fuel ducts.

I'd suggest replacing all those 8-ton tanks with the 16-ton tanks instead.  (They're unlocked on the same tech tree node, so if you have one, you have the other).  It'll keep your part count down, reduce wobble, and help a bit with CoM issues.  In general, any time you can avoid making tall stacks of little things, it's a win.

(Actually, ideally you'd replace 'em with the big orange tank and get rid of stacking altogether, but that's a higher tech node that you may not have unlocked yet.)

Is this mission ever going to get off the ground?

It seems like every time I think I'm ready to fly it I find something to improve it.  I do have the orange tank.  The part lists really should say how big the parts are without careful inspection!

[Snark]

13 minutes ago, Loren Pechtel said:

Is this mission ever going to get off the ground?

It seems like every time I think I'm ready to fly it I find something to improve it.

lol, welcome to KSP! 

13 minutes ago, Loren Pechtel said:

I do have the orange tank.

Excellent, that's a great workhorse of a tank! Use that and your CoM issues are solved.  Plus, your ship will be a lot more rigid.

I suspect you're going to have some TWR issues unless you boost your engine power.  Right now, each of your radial boosters is packing around 38 tons (32 tons of fuel, 4 tons of tank, a ton or two for engine & etc.), which needs 550ish kN of thrust if it's to maintain a reasonable launchpad TWR of 1.5.  With those Swivels on the radial booster and a Skipper on the main stack, you're going to struggle to get off the pad.

A decent compromise would be to go to Skippers under the radial boosters, and (depending on what payload you have on top of the pictured assembly) either a Skipper or Mainsail  on the center stack.

If you find that you're still strapped for dV, you can put a quartet of Kickbacks around the center stack (in between the radial liquid-fuel boosters), or alternatively, you could go from 4 radial boosters to 6.

Edited February 20, 2016 by Snark

[Loren Pechtel]

13 minutes ago, Snark said:

lol, welcome to KSP! 

Excellent, that's a great workhorse of a tank! Use that and your CoM issues are solved.  Plus, your ship will be a lot more rigid.

I suspect you're going to have some TWR issues unless you boost your engine power.  Right now, each of your radial boosters is packing around 38 tons (32 tons of fuel, 4 tons of tank, a ton or two for engine & etc.), which needs 550ish kN of thrust if it's to maintain a reasonable launchpad TWR of 1.5.  With those Swivels on the radial booster and a Skipper on the main stack, you're going to struggle to get off the pad.

A decent compromise would be to go to Skippers under the radial boosters, and (depending on what payload you have on top of the pictured assembly) either a Skipper or Mainsail  on the center stack.

If you find that you're still strapped for dV, you can put a quartet of Kickbacks around the center stack (in between the radial liquid-fuel boosters), or alternatively, you could go from 4 radial boosters to 6.

Yeah, after rebuilding the rocket I saw the TWR was too low and swapped out some engines.  I also used two tanks in the center, now even with my bad piloting it should have plenty.  Lots of science to be had but it's not coming home, I'll have to pull the crew off with another rocket--my first try at docking.  It doesn't have enough delta-v for the whole moon (nor have I unlocked the scansat that will show me the biomes which means I can't hit the small ones), I'll probably go back at some point with fuel and finish the job.

[Snark]

This is for Minmus, right?

Biome hopping on Minmus is super cheap, if the thing doing the hopping is small.  Here's a suggestion:  Design your Minmus lander to be small and light.  Put a docking port on it.  Leave your big fuel tank (the one you use for getting from LKO to Minmus orbit) in orbit around Minmus, and make sure it has a compatible docking port on it, too.

So you just move the whole shebang to Minmus orbit, then separate the lander and it goes down to hop biomes.  When it gets low on fuel, it goes up, docks & refuels from the orbiting tank, and repeats.

Note that your lander only needs to seat one kerbal, if you're doing repeated trips.  If you have multiple kerbals on the crew, you could send them down one at a time in the lander (swapping them out for each trip), so they all get the landed-on-Minmus experience.

However, if you're going for simplicity over optimum fuel efficiency:  just put all your kerbals in the lander, which is designed not only to hop around on Minmus but also to go home.  The orbiting fuel tank can be unmanned; its purpose is just to be a fuel supply with a docking port, nothing more.  It can stay in orbit around Minmus when the lander goes home.

[Loren Pechtel]

9 minutes ago, Snark said:

This is for Minmus, right?

Biome hopping on Minmus is super cheap, if the thing doing the hopping is small.  Here's a suggestion:  Design your Minmus lander to be small and light.  Put a docking port on it.  Leave your big fuel tank (the one you use for getting from LKO to Minmus orbit) in orbit around Minmus, and make sure it has a compatible docking port on it, too.

So you just move the whole shebang to Minmus orbit, then separate the lander and it goes down to hop biomes.  When it gets low on fuel, it goes up, docks & refuels from the orbiting tank, and repeats.

Note that your lander only needs to seat one kerbal, if you're doing repeated trips.  If you have multiple kerbals on the crew, you could send them down one at a time in the lander (swapping them out for each trip), so they all get the landed-on-Minmus experience.

However, if you're going for simplicity over optimum fuel efficiency:  just put all your kerbals in the lander, which is designed not only to hop around on Minmus but also to go home.  The orbiting fuel tank can be unmanned; its purpose is just to be a fuel supply with a docking port, nothing more.  It can stay in orbit around Minmus when the lander goes home.

Yeah, the cheap cost of hopping is why I picked Minmus as my first landing target.  I'm bringing two Kerbels--a pilot and a scientist to reset the experiments.  I'm sure I could have done it the way you suggest but I'm also using the fuel tanks to give me a nice wide base for my landing legs.  For my first try I'm making it as easy as possible.  The big one is going to be about empty at that point anyway.  Next mission to Minmus I just push a big tank with a docking port and use the old lander.

[Snark]

1 minute ago, Loren Pechtel said:

Yeah, the cheap cost of hopping is why I picked Minmus as my first landing target.  I'm bringing two Kerbels--a pilot and a scientist to reset the experiments.  I'm sure I could have done it the way you suggest but I'm also using the fuel tanks to give me a nice wide base for my landing legs.  For my first try I'm making it as easy as possible.  The big one is going to be about empty at that point anyway.  Next mission to Minmus I just push a big tank with a docking port and use the old lander.

Fair 'nuff.  If you want to keep your ship smaller/lighter, and if you have at least the OKTO probe core unlocked (or even better, the HECS, though the OKTO's doable), you can skip the pilot.  Just send a scientist, and let the probe core handle the SAS for you.

That cuts the necessary mass of the lander nearly in half, and since that's at the pointy end of the rocket, it cuts the overall size of your entire mission nearly in half.

(That's assuming that all you want out of this is the science. If you have some other reason for wanting to send the pilot along for the ride, such as giving experience points, never mind.)

[Loren Pechtel]

3 hours ago, Snark said:

Fair 'nuff.  If you want to keep your ship smaller/lighter, and if you have at least the OKTO probe core unlocked (or even better, the HECS, though the OKTO's doable), you can skip the pilot.  Just send a scientist, and let the probe core handle the SAS for you.

That cuts the necessary mass of the lander nearly in half, and since that's at the pointy end of the rocket, it cuts the overall size of your entire mission nearly in half.

(That's assuming that all you want out of this is the science. If you have some other reason for wanting to send the pilot along for the ride, such as giving experience points, never mind.)

Yeah, the point is science. 

I hope to get enough science from this mission to unlock that good probe core and quit worrying about pilots.  I can't see it cutting the lander mass in half, though.

[Snark]

16 minutes ago, Loren Pechtel said:

I can't see it cutting the lander mass in half, though.

Depends on the lander.  If you're going for a very lightweight lander, the biggest single component of the mass is the crew compartment.  The rest of the ship is basically just a delivery mechanism for the crew compartment.

Half the crew compartment means you need half as much ship.

It's not strictly true (the science instruments do have a little mass, and halving the crew won't cut that in half)... but it's mostly true.  A decent Minmus hopper based around the Mk1 lander can, with all science instruments, is buildable at around 3 tons.  Is your lander much more than that?

[numerobis]

One trick for CoM management when you have multi-tank asparagus boosters: put the fuel line at the *top*. That way, your engines will draw fuel from both ends of the fuel tank stack, so your CoM doesn't move back as much.

Here's two ways to set up your rocket: you've got the payload on top, the decoupler (I mark it with an = sign), then a center stack with engine 2 at the bottom; and side stacks for engines 1 and 3 with fuel tanks A and B on top, C and D on the bottom.

  X     |     X
  =     |     =
A-X-B   |   A X B
X X X   |   X X X
X X X   |   X X X
C X D   |   C-X-D
^ ^ ^   |   ^ ^ ^
1 2 3   |   1 2 3

On the right is what you have, on the left is my proposal.

On both designs, engine 1 looks up the stack for its fuel, and stops at tank A. It burns fully out of tank A.

On your design (on the right), engine 2 looks up one tank, then follows the fuel lines at C and D, and then keeps looking up the stack. It ends up finding tanks A and B. So A is feeding 1.5 engines (namely engine 1 and half of engine 2) and empties out pretty fast. The center of mass moves down the rocket.

On my proposed design, engine 2 looks up all the way up, follows the fuel lines at A and B, then keeps looking to the end of those stacks. It ends up finding tanks C and D. So tank A is feeding one engine (engine 1), while tank C is feeding half an engine (engine 2, shared with tank D). That means the center of mass moves down more slowly, which means your gimbals, and drag, have a longer lever arm to straighten you out.

I'm assuming you want to fly prograde, not retrograde, of course. But most rockets do.

[swjr-swis]

5 hours ago, Loren Pechtel said:

Is this mission ever going to get off the ground?

It seems like every time I think I'm ready to fly it I find something to improve it.

Welcome to the curse of KSP.

[Loren Pechtel]

56 minutes ago, Snark said:

Depends on the lander.  If you're going for a very lightweight lander, the biggest single component of the mass is the crew compartment.  The rest of the ship is basically just a delivery mechanism for the crew compartment.

Half the crew compartment means you need half as much ship.

It's not strictly true (the science instruments do have a little mass, and halving the crew won't cut that in half)... but it's mostly true.  A decent Minmus hopper based around the Mk1 lander can, with all science instruments, is buildable at around 3 tons.  Is your lander much more than that?

I didn't weigh it.  Remember, though, it needs battery power to operate in the dark, a radio, solar cells, landing legs, RCS fuel etc.

[Snark]

5 hours ago, Loren Pechtel said:

I didn't weigh it.  Remember, though, it needs battery power to operate in the dark, a radio, solar cells, landing legs, RCS fuel etc.

Yes, but those are pretty minor considerations.  Even the 1000-charge battery (which is far more than you need) is only 50 kg.  Four or so OX-STAT panels are plenty (5 kg apiece).  Four micro landing legs, total 60 kg.  RCS fuel:  zero, unless you're planning on docking.  If you do need docking, it's not very much, just 50 kg or so of monopropellant and another 160 kg for RCS thrusters.

Yes, it adds up.  But all of that pales in comparison to the minimum 600 kg for a Mk1 lander can, or 800 kg for a Mk1 pod.  Dropping 600-800 kg from a lightweight science lander makes a huge difference to the total weight of the craft.

But anyway, the beauty of KSP is that you can build whatever you want ... and each player finds their own style and technique.  So build what suits you best!  I'm just pointing out that "smaller" is an option, if you are so inclined.

Incidentally... when you arrive at Minmus, that's a great time to practice your vacuum landing technique.  Doing a vac landing efficiently takes a certain amount of finesse-- it's easy to waste scads of fuel on an inefficient approach.  Minmus' gravity is so low that the efficiency of your technique doesn't actually matter much (Minmus is very forgiving)... but that's exactly why it makes a nice "kiddie pool" to practice in before you go somewhere that technique does matter, like the Mun.

So, Minmus is a good place to practice your suicide burns.

Edited February 21, 2016 by Snark

[Loren Pechtel]

This is getting annoying--once again I can't attach to the decouplers.

I flew this and found my decouplers weren't in the right place and the tail of the rocket blew up when I staged.  Now I can't fix it.  I took apart everything from the heat shield on down and it doesn't help, the tanks insist on connecting directly rather than to the decoupler.

What's the trick to actually getting it to work??

[Snark]

28 minutes ago, Loren Pechtel said:

This is getting annoying--once again I can't attach to the decouplers.

I flew this and found my decouplers weren't in the right place and the tail of the rocket blew up when I staged.  Now I can't fix it.  I took apart everything from the heat shield on down and it doesn't help, the tanks insist on connecting directly rather than to the decoupler.

What's the trick to actually getting it to work??

 

One thing to be aware of:  for this sort of radial attachment to work, the midpoint of the tank has to be on the decoupler.  For example, you can't attach the decoupler to the very top end or bottom end of the tank.

You do have a little bit of leeway, since the decoupler's "face" has some size to it-- you can move the tank a meter or so up or down.

My guess would be that you're vertically off.  Here's what I usually do (since I generally want to attach radial tanks as low on the decoupler as I can:

1. Rotate the camera and adjust my vertical position so that I'm looking straight at the end of the decoupler (i.e. the decoupler is pointing straight at the camera).
2. Move my tank so that the tank's center is right where the center of the decoupler is.  I can tell that it's attaching to the decoupler rather than to the center stack because the center stack isn't highlighted green (which it would be if I were attaching there).
3. Slowly slide the tank downwards.
4. When it gets to the bottom limit (where the center of the tank is no longer on the decoupler, I can see that happen in two ways:  first, the center tank suddenly highlights; second, the tank I'm moving suddenly "snaps" away from the camera (since it's now attaching to the tank surface, which is farther from the camera than the decoupler surface.
5. As soon as I see that happen, I slide it a smidgeon back up again until I see that it's on the decoupler.
6. Release mouse button.

[Loren Pechtel]

35 minutes ago, Snark said:

 

One thing to be aware of:  for this sort of radial attachment to work, the midpoint of the tank has to be on the decoupler.  For example, you can't attach the decoupler to the very top end or bottom end of the tank.

You do have a little bit of leeway, since the decoupler's "face" has some size to it-- you can move the tank a meter or so up or down.

My guess would be that you're vertically off.  Here's what I usually do (since I generally want to attach radial tanks as low on the decoupler as I can:

1. Rotate the camera and adjust my vertical position so that I'm looking straight at the end of the decoupler (i.e. the decoupler is pointing straight at the camera).
2. Move my tank so that the tank's center is right where the center of the decoupler is.  I can tell that it's attaching to the decoupler rather than to the center stack because the center stack isn't highlighted green (which it would be if I were attaching there).
3. Slowly slide the tank downwards.
4. When it gets to the bottom limit (where the center of the tank is no longer on the decoupler, I can see that happen in two ways:  first, the center tank suddenly highlights; second, the tank I'm moving suddenly "snaps" away from the camera (since it's now attaching to the tank surface, which is farther from the camera than the decoupler surface.
5. As soon as I see that happen, I slide it a smidgeon back up again until I see that it's on the decoupler.
6. Release mouse button.

Aha, I'm sure that's it.

Edit:  It was.  Datrice, Sigke, Agaxy and Newgel say thanks for their orbital trip.

Edited February 21, 2016 by Loren Pechtel

[FullMetalMachinist]

7 minutes ago, Snark said:

-Lots of good stuff-

Step 7.  Use the offset gizmo to put the radial tank where you really want it, not just where it'll let you place it.