Interplanetary transport of unwieldy items

[glen.mack]

Discussion: Planning for the unplanned, mother-ship transport.

Assumptions;

1. Mother-ships, once assembled always remain in orbit

2. Most mother-ships are designed around the specific craft they transport

3. In reality (and in the Ares missions in The Martian) you would want a ship that could do several round trips to maximise efficiency

4. The very front and the very back are bad ideas due to wobble, or perhaps bringing asymmetric items

5. You can't make a bigger cargo bay with tweakscale

How would you design a "mid-section" cargo area?

The main problem I see is this, in KSP you can go out radially, but you can't bring those radial constructions back to a center line. You can add a single item to one radial construction arm, as centered as you can figure, then strut the others to that single item as I have here;

I know in KSP you really should design for a specific mission, but the point of the mother-ship is re-usability. I have no idea what I might want to put in there once I get back from the first mission, but I'd like to have the option of something larger than a MK3 cargo bay.

Main questions:

How to maintain perfect center line to prevent wobble/thrust not being aligned with COM?

How would you balance the number/size of radial structures with actually maneuvering things into the cargo space?

Is there some other serious design consideration I'm missing?

[Wolfos31]

I like the idea of motherships, but every time I try to execute them they typically come out as less than impressive and often less efficient than other designs. I haven't tried since ISRU became a thing and I think that will go a long way toward making motherships viable. It helps to define what a mother ship is as well. Based on your description of multiple uses and different cargoes I think of interplanetary nuclear tugs instead of motherships. 

For me tugs are low part count high efficiency nuclear designs. Typically large or medium docking port, probe core, generous RCS supply for docking, powerful reaction wheel for directional control, a few solar panels (or 1-2 RTGs), and then as much liquid fuel as I can squeeze into the design all routed to 1, 2, or 4 nuclear engines depending on the weight rating of the tug. Once I build a tug it never comes back down unless I've unlocked significantly improved tech later along in the tech tree. 

Motherships to me mean crew quarters, a lab, comms, etc. Almost a space station that is mobile and compactly designed with enough DV to push along a significant load. And usually I decide that I could just as easily or more efficiently make the trip with 2 tugs. One for payload and the other for crew. 

[WuphonsReach]

A lot of my "first station into space" designs almost function as a mothership.  They typically have (1) regular docking port at the nose, (2) regular sized along the spine and (2) junior sized docking ports along the spine.  The main body is a fuel tank and crew quarters (usually welded). The bottom of the station typically contains the highest ISP engines that I have, enough to push at 0.50 TWR when fully loaded.

It goes up mostly empty of supplies and functions itself as the final stage of a multi-stage launch.  

After launch, I refuel using supply ships and bring up a crew.  Eventually other modules get added to the front of the ship.

For motherships, I generally assume that the parts that I'm ferrying to other worlds (via nuclear pull tugs) have docking ports on the front.  Or if I'm sending multiple of something, that they can dock to the "spine" of the mothership in a balanced fashion.

[Mikki]

I discovered than you can do almost everything in Stock-Game KSP.

(I confess, the only mod i use eversince is KJR, Kerbal Joint Reinforcement)

I have a "The Martian"-like ... "Mothership" currently in Duna orbit: (around 6500dV, Asteroid ISRU caps, go anywhere)



Minor offset of small Crew Taxis or RCS tugs have no influence to the ship at atll.

But to get that thing to orbit i had to build this one:



I play KSP like the way i live in RL. My daughters (2) are probably older than the average KSP player. I have 2500 hours+. I work about 50hours serious in RL, i sleep about 5 per night, if i have time to sleep at all.

Edited December 30, 2015 by Mikki

[problemecium]

On 1/16/2015 at 9:41 PM, Azimech said:

How to build gigantic, sci-fi worthy spacecraft using stock parts and without tweakscale, in a few minutes!

 

^ Try this idea from Azimech.

Edited December 30, 2015 by parameciumkid
I continue to despise this newfangled post editor.

[glen.mack]

20 minutes ago, parameciumkid said:

^ Try this idea from Azimech.

Two issues, I'm actually trying to construct a "realistic" mothership, this thing can't get to orbit on it's own, and what you'd have to build to give it another 2k delta V would have to be awe inspiring. The "module" I designed at the top is about 10t, as opposed to the 836t of this thing. Second, I believe this is more of an aesthetic thing, these kind of designs are to be hyperedited into space for cool screen shots, not used for missions.

[bewing]

2 hours ago, glen.mack said:

 

How to maintain perfect center line to prevent wobble/thrust not being aligned with COM?

 

 

Build the ship with a center line (made out of girders or anything you want) -- ie. don't put in that klaw initially. Use symmetry to build the radial stuff attached to the perfectly straight center line. Then trash the center of the center line. Then add your klaw.

[cantab]

In my view and experience I'd keep the docking arrangements simple and not worry overly about flex, provided you use senior ports and don't have too many connections it'll be fine. Consider that this mess flew without a hitch: https://flic.kr/p/nTmzTU

Engine clusters are your friend. If you have three or more engines you can lower the thrust limiters on some to compensate for off-axis centre of mass, for example if you have two different modules docked radially to your propulsion module.

"Control from here" is also your friend, put a probe core near the engines and main fuel tank and control from it, because that's what SAS will respond to the movements of. If you control from a nice stable point then it doesn't matter if the other end of the ship flexes around a bit.

[Vanamonde]

For some time now I've been taking this design 

and loading it up for missions to Eve, Duna, and Dres. 

And using this one 

for trips to Moho, Eeloo, and the moons of Jool. 

As you can see, they are generic tractor ships, not built for specific cargoes. The side cargo mounts may look awkward, but actually serve quite well since big ships like this operate at very low accelerations anyway. I agree that they aren't pretty.  My PC isn't particularly powerful, and I need to keep part counts to a minimum. 

[Pecan]

24 minutes ago, Vanamonde said:

I agree that they aren't pretty ...

I think they're pretty!  They're a lot bigger than the ones I use though.  I just never move so much stuff around in one go - I'm with Wolfos31

[Azimech]

6 hours ago, glen.mack said:

Two issues, I'm actually trying to construct a "realistic" mothership, this thing can't get to orbit on it's own, and what you'd have to build to give it another 2k delta V would have to be awe inspiring. The "module" I designed at the top is about 10t, as opposed to the 836t of this thing. Second, I believe this is more of an aesthetic thing, these kind of designs are to be hyperedited into space for cool screen shots, not used for missions.

 

This is almost a year ago. I've got a whole series in my signature. Would need a little reconstruction and maybe a heavier launcher to get to work in 1.0.5. The craft in the upper album was judged by an ex NASA employee working on rocket engines, got second prize. Just because it looks implausible, doesn't always means it is ;-)

Here's a link to the manual I created for the MMMagus: https://www.dropbox.com/s/453epbibnbq9v59/77Industries-MMMagus-InstructionManual.pdf?dl=0

Edited December 31, 2015 by Azimech

[Francois424]

I'm personally hoping that Unity5 + 64bits will speed things up and allow ppl to use 500-600 parts design like the earlier versions of KSP... if not more.  Wishful thinking it might be but to be honest, without mods, it's kinda required.
Otherwise Tweakable tanks/parts is strongly encouraged to reduce parts count.

That being said, to me the best mothership is the biggest fuel tanks you need for it's propulsion stacked togetter (ring-shaped or star-shaped + struts so not too long) , and you want a 5k d-V burn to take imho no more than 10min @100% Thrust.  If you eschew efficiency, you can go with mammoths  with big tanks.  otherwise you are stuck with 60 thrust nukes (lol) or 2 thrust ions (rotfl); meaning you need a lot of parts, which bogs down the game to a crawl.  

In stock KSP large motherships aren't very useful except for looks and kicks (Better send 10x small crafts rather than a 700+ parts big one).
Modded is an entire different ball game, and I can understand ppl for going to that for large interplanetary missions.  My 1.1 game will be modded I think, but only once I unlocked all science nodes.

@glen.mack If you want a middle section like this that can be enlarge easily as needed and lower on part counts, just remove all side girders and use struts instead. 
Center of mass is no problem if you build your interplanetary ship around your payload in symmetrical fashion. .. just make sure you strut both sides together, and to the payload
or just build your mothership to be High and wide, but slim, and attach your payload to the back.  No need for bracers and girders, just a large docking port or 3 (for stability) and struts if you have KAS.

There's many ways to do it, and it depends on taste more than anything else 

[Xavven]

I had this same problem when going for a Jool-5, and started out doing something similar to what the OP is doing: building a frame from girders and ibeams and then attaching engines around the chassis.
 However, as I started refining the design more and more, I realized that the girders, ibeams, and panels were just added mass. My final mothership design used the fuel tanks themselves to perform double-duty as both fuel storage and form the frame of the ship.

The best arrangement that worked for me was not building in symmetric radial fashion, but rather arranging the tanks in a flying V pattern (like how a flock of birds fly). This gave me more attachment points for the "cargo" with better clearance and balance, and the V shape is stronger from a structural standpoint than radial pancakes.

Lastly, if your "cargo" is perfectly balanced on the center line, you will need RCS or engine gimbals to stay on course during burns. Unfortunately, my last mothership designs were during the beta when the LV-N still had an engine gimbal. I'm not sure how I'd handle the problem now -- probably vernors?

 

[Francois424]

36 minutes ago, Xavven said:

I'm not sure how I'd handle the problem now -- probably vernors?

That's what I did, I added about 4 "small" LF/Oxidizer tank for 6000 unit of LF/Ox for that purpose.

[cantab]

9 hours ago, Francois424 said:

If you eschew efficiency, you can go with mammoths  with big tanks

The Rhino is significantly more efficient, and actually a great choice of vacuum engine if you have a large payload and don't want to use the LV-N.

[GoSlash27]

 Full disclosure: I haven't messed around with "mothership" designs where the payload is in the middle of the assembly. Like others here, I use space tugs with a docking port on the front. It's structurally simpler and easier to launch/ assemble.

 I'm looking forward to seeing how it works out for you!

Best,

-Slashy

[Beowolf]

I use Bobcat's old "MPSS Nautilus" parts for all my mothership needs. They're quite Ares-like, which makes sense considering both ships are based on different versions of the same NASA design.

Available here, but ignore the crappy pic he used. My ships using the Bobcat parts look 100x better than that! http://forum.kerbalspaceprogram.com/index.php?/topic/73884-release-bobcat-ind-spaceampplanet-products/

 

[Captain Sierra]

I ignore the restriction on end-placement, because using modded docking ports that are made out of unobtanium (ridiculously heavy but very stable) and KJR means that part wobble is nonexistent at docking connections when using 2.5m. It results in things like this (massive image warning):

Spoiler

For heavier payloads (20+ tons i.e. Eve ascent vehicle), I tack those onto the front of the propulsion stage, opting to push rather than pull (pendulum fallacy becomes slightly less of a fallacy when the no. 7 tensile truss is in use).

[richfiles]

50m Stanford Torus with four 8m biodomes. Yes, I'm aware it's "built wrong. This should be spinning in space, with the domes flipped glass inward. It has a small forest inside.

What makes this base significant, other than it's gravity defying silliness, is that I launched and landed it as a single vessel, from KSC to Minmus, in 0.90. The "rover" weighs 44 tons on Kerbin, in comparison to the massive base. I relied on an incredible asparagus staging configuration that spanned the width of the VAB, and exceeded the fuel line length limit. It used triple height stacks of the large LARGE tanks, with mammoths at the bottom of every stack. I forget the cost, but it's the only thing that ever brought my budget back into 6 digits after unlocking the full tech tree (yes, this was a career save).


You can see the means of landing here. 4 mammoth engines, with empty Kethane tanks (I've since quit using Kethane) ringed by landing legs. There are 8 of those landing leg stacks. there should be another one just off image to the right of the mammoth tanks. That's one "spoke" of the torus. There are four spokes, with 4 mammoth engine clusters total, one per spoke. There was a Kethane drilling rig at the center. The rings that the mammoths, the kethane storage tanks, and the extra SAS wheels attach to are the radial attachment point. I did use tweak scale to make those WAY bigger. Couplers would have been attached to the bottom of the two kethane ISRU tanks and the SAS wheels on each spoke, plus there was a central stack attached to the drilling rig. This made 13 stacks of the large Kerbodyne S3-14400 tanks, stacked 3 tall, with 12 mammoths at the bottom of those, and 4 on the vessel structure itself. the central tank was stacked one tank taller, and had decouplers all along, staged very late. This tank stack is important for landing. The outer most tanks had girders hanging between the tanks, reaching out for one another, with Oscar-B mini tanks at the end. This let me string 3 fuel lines (first stage to drop across a girder to an Oscar-B, the Oscar-B to another Oscar-B, and finally, the second Oscar-B to the next tank to be staged... The stacks really were that far apart on the stack! the next inner stacks only needed one girder with an Oscar-B to accommodate the distance. The inner ring of stacks could have fuel lines run normally. They all fed to the central tank, and from there, they in turn also feed to the landing motors.

I had my control from here screwed up, and had to fly the pancake by adjusting engine throttle, as cantab mentioned. Until i reached orbit, that was my sole control. didn't even bother with RCS or SAS. on a vessel that massive, it's slow anyway. Once in orbit, I found the RIGHT probe core to control from, and flew it to minmus. On the top side, by the biodomes, are a number of LF+O and mono tanks, for resource collection. The general idea was that I lower the entire vessel to the planet on the fuel from the large central stack, and when each tank segment depletes, I drop it, and pray that it blows up and leaves my landing site clear of debris. Once the last stage is depleted, I drop it to be destroyed on impact, and burn the fuel stored in the ISRU LF+O tanks. There was just enough fuel for a safe landing on the numerous landing legs.

Part of me wants to recreate this base, or one much like it in my current career. I know what mistakes I made last time, and what to do differently, but i also have no idea if the aerodynamics would ever let me launch this thing again. It IS mostly open space... Four spokes and a ring, but it's still massive. I really need a bigger VAB, as this was at the extreme limits of what I could do in the VAB already.

if using tweak scale, I find that the double, triple and quad stack adapter are nice for splitting stacks into multiple columns. It does take some struts, cause of the limits in how KSP likes (or rather doesn't like) cyclical stack connection paths. One joint invariably REFUSES to snap and bond. Struts are your friend. symmetrically applied radial attachment points are really wonderful for creating good patterns of symmetry if you want multiple stacks coming off a central one.

Much of the same can apply to mother ships. I have found that the Docking Port Sr is your friend in station/mothership design. Save the regular size and Jr. for probes, landers, and ferries. For any bulk transit, you need the structural strength of the large docking port.

Another tip for large vessels, particularly long ones with many assembled segments, is to use a puller engine configuration. You go from wet spaghetti to a space train. Bonus points if you make it actually look like a train!  It makes a WORLD of difference... as long as you put your engines far enough out at the ends of girders or radially mounted tanks to CLEAR the trailing ship. KSP will calculate the losses of occluded thrust, not to mention possibly overheat whatever you're burning against, so take diameter into consideration. If you use a design like that though, then you can have a singular rigid engine/control/SAS/RCS unit, and it will always orient correctly for a burn. even if the tail end is kinda floppy, it'll pull it into a straight line by virtue of everything being pulled by a centered force. A pusher configuration works very well in a grid body, but the disadvantages of pullers can overcome the impossibility of pushing a non rigid body. In theory, you could have a literal train  made of segments joined by unlocked, pivoting claws, and it'd still ultimately pull in the right direction.

**EDIT**
And as a number of people have mentioned... GET KJR. Kerbal Joint Reinforcment is your friend. They use it, I use it. My understanding is that the way it works is it "eases" the physics on by ramping from no physics to full physics effects gradually, over the course of a second or two. it also tweaks the joint rigidity and strength to try to balance it out. Something like that. Fewer randomly rapidly disassembling vessels when you come out of warp or load them, and far less wobble when being and orienting vessels.

Edited January 10, 2016 by richfiles

[Brainlord Mesomorph]

I play a stock game.

One thing I do with oddly shaped payloads (i.e. carrying spaceplanes or boats to Laythe or Eve):

JUST CARRY TWO OF THEM!

then you can mount them on the sides and you CoM is stable.  (no center payload bay required)

hth

 

EDIT also works on rockets hauling the stuff to orbit

Edited January 9, 2016 by Brainlord Mesomorph

[elpollodiablo]

On 30.12.2015 at 8:43 PM, glen.mack said:

How to maintain perfect center line to prevent wobble/thrust not being aligned with COM?

How would you balance the number/size of radial structures with actually maneuvering things into the cargo space?

As you are using InfernalRobotics, i'd highly recommend Quantum Struts (or KAS if you're not as lazy as i am) and the Welding Mod.

Welding helps tremendously with the stability of the Cargo Bay, and the cool thing is if you consider this cheating, you can actually build something that would be that sturdy without getting into trouble with part counts. And struts help with keeping things in place with the robotics, as they become very wobbly when things are attached to them. You can build pretty sophisticated things that actually work this way, and even have not much lag.
Its not a cargo bay, but without these mods, even if the disk would survive an atmosphere by a miracle, the "doors" would fall of in the first few seconds:

Spoiler

 

If you already use these mods, nvm

[SkyRender]

In KSP at least, cargo bays are mostly only for aesthetics once you're in space proper.  Better to build a severely docking-friendly design:

Edited January 9, 2016 by SkyRender

[StrandedonEarth]

On 12/30/2015 at 0:59 PM, parameciumkid said:

^ Try this idea from Azimech.

 

On 12/31/2015 at 7:23 PM, Azimech said:

 

This is almost a year ago. I've got a whole series in my signature. Would need a little reconstruction and maybe a heavier launcher to get to work in 1.0.5. The craft in the upper album was judged by an ex NASA employee working on rocket engines, got second prize. Just because it looks implausible, doesn't always means it is ;-)

Here's a link to the manual I created for the MMMagus: https://www.dropbox.com/s/453epbibnbq9v59/77Industries-MMMagus-InstructionManual.pdf?dl=0

OMG these are just mind-blowingly awesome! I've never seen anything like these. That cavernous docking bay is simply maaaaahvelous.

As to the OP:

On 12/30/2015 at 11:43 AM, glen.mack said:

How to maintain perfect center line to prevent wobble/thrust not being aligned with COM?

I highly recommend the Throttle Control Avionics mod. A great solution for asymmetric designs. I use designs similar to Vanamonde's, and use TCA when one of a pair undocks.

Another trick i learned somewhere on these forums deals with bringing branches back together for greater rigidity and other purposes. Simply place two docking ports facing each other at the branch ends, using the editor gizmos to place them as perfectly as possible. When physics loads, the ports will snap together. Great for making a large ship the core of the rocket on the pad. Having docking ports stage-able makes this even easier. Note: this is just a station, not a tug/mothership

  

Edited January 9, 2016 by StrandedonEarth

[richfiles]

11 hours ago, Brainlord Mesomorph said:

I play a stock game.
One thing I do with oddly shaped payloads (i.e. carrying spaceplanes or boats to Laythe or Eve):
JUST CARRY TWO OF THEM!
then you can mount them on the sides and you CoM is stable.  (no center payload bay required)
EDIT also works on rockets hauling the stuff to orbit

That was the thing I was missing! DUH!!! 

I launched "Gilly Vanilli" (the 44 ton rover) that way. sent one to Minmus, and the other to Gilly. Gilly Vanilli was launched in my 0.90 save, on a large launcher rocket, flew itself to a low gravity body on a rear mounted NERV, landed, roved, performed a vertical takeoff, and could then perform the transit back to Kerbin, and safely land on Kerbin using parachutes. it could hold a crew of 4, two scientists, a pilot, and an engineer, preferably. It used docking ports to create a springy rocker bogey suspension (with 32 wheels!), and had landing legs to both protect the wheels during landing, and to lift the vessel off the found for an engineer to be able to repair the wheels (the vehicle is heavy enough, that repairing wheels sometimes fails unless the vessel is off the ground. This is also HILARIOUS when activated on Gilly... Those lander legs can be used AS a VTO system there!  There were a bunch of the small stack decouplers attached to the rover's VTOL engines, with struts that then attached to the suspension, to keep it stable during launch. The two vessels were strutted to one another, and to the launch rocket.

I don't have a picture of the double Gilly Vanilli launcher, only the individual vessels, but I have another launcher that uses the symmetrical double payload technique: My "Eve'n'Gilly" and "Ike'n'Duna" launchers:


Both launchers are identical, save for their destination. I do use Tweakscale in these launchers to produce the nifty little science payload stacks. Rather than try to fit these inline, with the ISRU scanners in place, I decided to mount them side by side. Note the use of the 2-1 stack adapters and the center fuel tank adapter. I forget the actual part names. It gave me an efficiently compact 2 engine rocket for doing my orbital capture burn. Once I have that, I can decouple each of the two payloads, extend the additional solar panels, and use the ion engines to direct them to their final destinations. 


These payloads feature a combination of reusable science modules, and a redundant supply of reusable modules. Struts are your friend. KSP does NOT like to have loops in it's stack, but you can strut things. Interestingly, you can create parallel stacks with docking ports, but it can be tricky, as the alignment has to be perfect if you want all the docking ports to actually connect. Struts will keep things rigid, even when there is no connection in a stack. These probes are designed to spam science at their destination. each probe can perform 9 Mystery Goo and 9 Science Jr experiments. The reusable experiments are all included. My goal is to get these into a polar orbit, so I can cover as much of the planet's/moon's biomes as possible. If I have any modules leftover, I may try to get some atmospheric science in, hopefully before they reach the ground. The gilly probe actually has legs added... The Ion engines should be enough to biome hop on Gilly's low gravity. This pic would be of the "Ike'n'Duna" probe.

Regarding playing a stock game, I can certainly get that some people prefer stock play. If you ever consider moving beyond stock play, KSP is really a game that can be heavily improved upon with mods, and not every mod will bring your computer to a grinding halt. I would make just a few honorable mentions... Tweakscale, GPOSpeedPump, Kerbal Alarm Clock, and KER/MechJeb.

Tweakscale REALLY is a beautiful mod. It really fills in the missing parts that the game doesn't really provide. Masses, volumes, and values scale accordingly. Another great mod that really compliments an OTHERWISE near stock game is GPOSpeedFuelPump (formerly Goodspeed Fuel Pump). It just adds some very nice integral fuel pumping and balancing options to the game. I can design a station, lander and refueling tankers that automatically pump fuel in the right direction, without ever having to right click a single tank. Really great for complex little landers that use a dozen tiny tanks situated around the vessel to keep the CoG low. Traditionally, you'd have to right click every one of those to refill. Not with this mod though. Kerbal Alarm Clock is a wonderful, simple tool to keep track of multiple simultaneous missions. It's exactly what it says... a fancy alarm clock, and well worth it. I have two Eve/Gilly and two Duna/Ike missions, along with a lively amount of activity around Kerbin. KAC lets you easily focus on what you want to do int he here and now, and not have to worry about being distracted and forgetting to do a capture burn 76 days from now.

The last two, Kerbal Engineer Redux (KER) and MechJeb, are very powerful tools in KSP. It IS true that MechJeb features powerful autopilot functionality, but I understand that can actually be disabled, if you prefer. What's important, are all the fancy spacey numbers that both mods give you. I can tell you this... for a while, i used to have MechJeb launch my ships, and dock them, and rendezvous... truth is, I just don't bother with the auto pilots anymore. the only "auto" tools I use these days are the maneuver planner, the execute maneuver node button, and Smart A.S.S. (a better version of the SAS buttons to the left of the navball). I know how to do all the things. I just let MechJeb point the ship and stop the engines. I get a nice landing projection when i land (which I also still do manually). The thing i don't think I could live without though, are the stat windows. Vessel stats, Orbital stats, Surface stats... I feel the game is not complete without giving me the option to see those "rocket sciency" numbers. If you have that much of an aversion to the temptation of auto piloting, stick with KER. It's just the stat windows. I just happen to see no reason to install both, as I'm already accustomed to the MechJeb interface.

Edited January 10, 2016 by richfiles

[DoctorDavinci]

On 2015-12-31 at 11:27 PM, Francois424 said:

In stock KSP large motherships aren't very useful except for looks and kicks (Better send 10x small crafts rather than a 700+ parts big one).

I disagree with this statement ... Why? ... well because of this: Dres Love Missions