So I needed a new heavy tug

[Somtaaw]

So as I've been building my latest space station, I've been streamlining it and removing the "self-flight" capability from pretty much everything and started moving more and more heavily into using tugs. Now for small, 0.625m and 1.5m things, the spider tug I got here on the forums has been a great reliable ever since 0.23.5. But with 2.5m and larger, I just don't really have good movers, so I'm trying my hand out at designing a reliable workhorse.

Since it's supposed to be a tug, which basically means a space bulldozer, I slapped a great big engine with a good sized tank on it. 2.5m main docking port since that what I need it for with capability for drop tanks, but the placement of certain things like the SAS modules for stabilization and thrust burning has me a bit stumped. I dropped a bunch of radio's onto it because I really like RemoteTech, so I have a clipped/offset Communotron 16, a pair of DTS-M1's and a Communotron 88-88 for short/mid/long range comms so I can tug things all over Kerbol space.

 

Advice/Suggestions welcome on my tug, so I can tweak it.

Core Tug

Tug with drop tanks

 

Generic space station component, that my tug would be moving frequently.

[Sir_Robert]

Personally my tugs are RCS only, because they operate only near the stations. The launch stage delivers them to it.

So the Kerbodyne engine seems a little overkill to me, but that depends on what role you want it to fill. Either way, you should probably put up some way to slow down (unless you want to turn your tug + part around to use the main engines to slow down). So maybe 4 way RCS blocks, or rotated RCS blocks (it seems you are using the LF+OX RCS ports?)

 

Also: Does it have solar panels? Or some other way to generate power? It probably needs something

[Snark]

Really need some input about what the tug is used for.  Shuffling things around a station at a few meters per second?  Or providing heavy boost to move things between planets?

Unless you have some special need for really high acceleration and/or very massive loads, the Mammoth may not be the best choice for a tug.

For low-dV, cargo-handling capacity, I'll typically use something fairly lightweight, powered by a Poodle or a couple of Terriers.

If I need more dV capability, then my tugs are usually nuke powered, with the number of nukes being determined by how big a load the thing needs to move around.  I'm fairly patient, so I tend to prefer very low TWR tugs with few engines, so as to save on dV at the cost of needing longer burns.

My usual tug design is a central fuel tank, with a docking port on the front and another docking port on the back.  The engines are radially mounted on short booms, with small fuel tanks that have fuel lines leading from the central tank.  I generally give the tugs quite a bit of torque authority via reaction wheels.  I put the reaction wheels on the radial stacks, above the engines' tanks.

A design like that has a few advantages:

• Compact design means low moment of inertia, = fairly nimble to turn.
• Putting the engines radially means I don't have to put reaction wheels in-line with the central stack.  This really helps stiffness-- the central stack is basically just fuel tank, probe core, docking ports.
• Leaving both the front and the back open for docking ports makes it more flexible for mission options.  It means the tug can pull instead of push, if need be (useful for moving big floppy things).  It means I can leave it docked to a space station without using up one of the docking spots (since it has a docking spot of its own that's free.  It means that when I'm pushing (or pulling) a load, I can use the other docking port for some other purpose-- for example, if it's a high-dV interplanetary run, perhaps a fuel droptank.

[Somtaaw]

For power, there's a quad pack of PB-NUK's tucked away inside the Large SAS, along with the small omni-radio.

My super station is up in Kerbo-Synchronous Orbit, so this monster has to take something like my station fuel arm (fully laden with fuel) from LKO all the way up to KEO and within a 100m of the station; and/or it'll be pushing the components when I start going interplanetary. Which is why I gave this Titan tug the biggest set of engines I possibly could, since it's going to be fighting gravity alot.

 

LKO to KEO to possible Munar is the current primary role, future expansion of my stations will include possible regular flights to Duna, Eve, and possibly Moho and Dres, orbits permitting a mere Comm 88-88 letting my RemoteTech continue talking back to Mission Control.

 

I was thinking of dropping a second Large SAS ring on it, to give it even more torgue to help compensate for being a push-only model. I'm not quite comfortable yet designing pullers. My station is built entirely around arms more or less the length of a big orange tank plus the double ended 2.5m docking clamps.

[Sir_Robert]

If it's already in orbit, you aren't fighting gravity anymore

[Snark]

1 hour ago, Somtaaw said:

My super station is up in Kerbo-Synchronous Orbit, so this monster has to take something like my station fuel arm (fully laden with fuel) from LKO all the way up to KEO and within a 100m of the station; and/or it'll be pushing the components when I start going interplanetary. Which is why I gave this Titan tug the biggest set of engines I possibly could, since it's going to be fighting gravity alot.

LKO to KEO to possible Munar is the current primary role, future expansion of my stations will include possible regular flights to Duna, Eve, and possibly Moho and Dres, orbits permitting a mere Comm 88-88 letting my RemoteTech continue talking back to Mission Control.

I was thinking of dropping a second Large SAS ring on it, to give it even more torgue to help compensate for being a push-only model. I'm not quite comfortable yet designing pullers. My station is built entirely around arms more or less the length of a big orange tank plus the double ended 2.5m docking clamps.

If your payload is only on the order of a big-orange tank (i.e. under 50 tons), that Mammoth seems like massive overkill.  If your total ship mass (including tug) is under 100 tons, that means you'll be pulling better than four gees of acceleration with the Mammoth!  High TWR is generally not needed when you're in orbit, unless you've got some special reason for it.  And doing so without particularly high fuel efficiency-- the vac Isp of the Mammoth is only 315.

Just to put things in perspective:  Going from 80 km circular orbit to keosynchronous takes a total of about 1100 m/s of dV (first 670 m/s to eject from LKO, then 430 m/s to circularize at synchronous altitude).  If your total ship mass including tug is, say, 100 tons:  suppose instead of that Mammoth, you had a quartet of LV-N's.  That'll be a burn of about 4.5 minutes in LKO, easily doable, followed by another burn of 3 minutes to circularize in synchronous.  In return for which, it'll use less than 40% as much fuel to do so.  If you're too impatient for a 4.5-minute burn, you could use six nukes instead of four, bringing it down to a 3-minute burn.

(Of course, I'm assuming that you're playing career here, and therefore care about economy.  If you're playing sandbox and have infinite fuel, it means nothing to launch monster ships from Kerbin even if large amounts of fuel are wasted-- free is free.) 

 

[Somtaaw]

Hmm, maybe I'll switch around the engines then. How about the SAS placement, should I be aiming to have that closer or farther from my docking point to manipulate my payloads?

 

And my fuel tanks, should I be doing anything to those? They're doubling as extended drop tanks for fueling long-range burns outside of Kerbin SOI, and also extending where the Vernor's are from the CoM for turning.

[Snark]

59 minutes ago, Somtaaw said:

Hmm, maybe I'll switch around the engines then. How about the SAS placement, should I be aiming to have that closer or farther from my docking point to manipulate my payloads?

From the standpoint of torque authority, it doesn't matter where you put the SAS.  They will have exactly the same effect on rotating your ship, regardless of where on the ship they're located.

That said:  if you have wobble problems (big, flexible ships) then it can make a difference about where the wobble is.  And any time you have multiple short things in a stack (like batteries, SAS units, whatever), that adds a lot of joints that can bend which in turn greatly contributes to wobble.

It's why I really prefer to mount my tug engines radially.  It means I can put the reaction wheels on the radial stacks, which means that my central stack has very few parts in it and is therefore nice and stiff.  Also, the engines tend to be the heaviest parts of the tug, and by mounting them radially, they can be considerably farther forward than they would if they were mounted underneath.  This means that my tug has a much smaller moment of inertia around the forward docking port, which means it's less prone to wobble at the docking-port connection (docking ports aren't particularly stiff when connected).

The TT-70 radial decoupler makes a great "stand-off" mount for radial stacks.  Lightweight.  Available early in the tech tree.  Just click its "disable staging" button in the VAB when building, so you won't accidentally use it for the purpose for which it was intended.    Put a big LF-only tank in the middle (the Mk3 parts are useful for this), with a quartet of TT-70's sticking out the sides, and then on each one you put one of the little 1.25m LF tanks with an LV-N on the bottom and a reaction wheel or two on the top.  Attach a single strut to help keep it stiff.  Add fuel lines.  The top of the radial stack is a handy place to put a battery, and the sides of the radial stack are useful for mounting radiators to keep the nukes from overheating.

The radial stacks arealso a handy place to put some floodlights for self-illuminating (useful when docking).

59 minutes ago, Somtaaw said:

And my fuel tanks, should I be doing anything to those? They're doubling as extended drop tanks for fueling long-range burns outside of Kerbin SOI, and also extending where the Vernor's are from the CoM for turning.

Not sure what you mean by "doing to" ... "put fuel in them" is about the most I have to offer. 

I like to use the biggest possible tanks.  It saves tedium by reducing the number of trips I have to make, and also saves lag by reducing part count.

For fuel transfers, I tend not to use a dedicated tug with a separate tank.  Instead, I make a "tanker" orbital ship which is a couple of really big fuel tanks with some radially attached LV-N's and a few docking ports.  Put one in low orbit around wherever I'm getting my fuel from, use dedicated fuel lifters to move the fuel from the surface to orbit, transfer the fuel, then move the tanker to wherever it needs to go.  I like to do this because orbital tankers and fuel lifters have different needs (in particular, the latter has to care about TWR a lot more than the former does).

By the way, if you're doing bulk transfer of stuff like fuel, you may like to check out the SpaceY Heavy Lifters mod.  Really excellent parts pack.  It includes really big tanks & engines (including 5-meter parts), plus lots of useful utility parts, such as 3.75m and 5m docking ports, and radially-attached high-torque reaction wheels for 3.75m and 5m stacks.

Also... just out of curiosity, any particular reason to choose keosync as the altitude for your big station, as opposed to LKO?  Misses out on a lot of Oberth benefit, and is expensive to come home from as well as to get to.  I find that (for me, anyway) LKO is a lot more useful and fuel efficient.  "What's the 'right' space station altitude" is one of those hot KSP topics with no one "correct" answer, it's just that I'm always curious about people's reasons when I read about a playstyle different from my own. 

Edited February 28, 2016 by Snark

[Nich]

All tugs should be made of nukes.

The Rhino isn't a bad option if you really need more TWR.  If I had a station that was 500t plus and already maxing my part count I would use the Rhino instead of nuke clusters

[Somtaaw]

20 hours ago, Nich said:

All tugs should be made of nukes.

The Rhino isn't a bad option if you really need more TWR.  If I had a station that was 500t plus and already maxing my part count I would use the Rhino instead of nuke clusters

By the time I start getting into the 400+ part range, is when I start using this Rhino pusher tug into start a long burn to another planet with the core of another station.

 

22 hours ago, Snark said:

Not sure what you mean by "doing to" ... "put fuel in them" is about the most I have to offer. 

Well I meant in my FL-T800 Fuel tank with a docking clamp on either end, and 4 Vernor's located on one end a 'good' extend range fuel tank design, or about as hideous as my pusher tug lol... I have only really done small tug work, LKO to Munar/Minmus orbits, and thats about it.

 

22 hours ago, Snark said:

Also... just out of curiosity, any particular reason to choose keosync as the altitude for your big station, as opposed to LKO?  Misses out on a lot of Oberth benefit, and is expensive to come home from as well as to get to.  I find that (for me, anyway) LKO is a lot more useful and fuel efficient.  "What's the 'right' space station altitude" is one of those hot KSP topics with no one "correct" answer, it's just that I'm always curious about people's reasons when I read about a playstyle different from my own. 

I chose a keosync orbit this time around because I always find myself with biiiig stations, and if you're trying to perform multiple rendezvous maneuvers, to gather the pieces for a stock ship to send off on a mission. Because I'm still not quite comfortable with truly big payloads, I've tried to keep things in the 50-100t range max, and then do multiple lofts. When you add a static station of 400+ parts to 6+ 100 part ship subcomponents, LKO starts getting pretty crowded and laggy.

 

So I dropped my fuel hub station into keosync, to reduce part count in LKO. And when I'm having tankers coming in from Minmus to replenish fuel I can use a much lower part count transport from keosync to LKO, to deliver to the skeletal baby station, and then send off the extra-Kerbin missions. I'll put up an action shot of my keosync station after I get my tug up there with the latest fuel booms.

[juanml82]

21 minutes ago, Somtaaw said:

By the time I start getting into the 400+ part range, is when I start using this Rhino pusher tug into start a long burn to another planet with the core of another station.

 

Well I meant in my FL-T800 Fuel tank with a docking clamp on either end, and 4 Vernor's located on one end a 'good' extend range fuel tank design, or about as hideous as my pusher tug lol... I have only really done small tug work, LKO to Munar/Minmus orbits, and thats about it.

 

I chose a keosync orbit this time around because I always find myself with biiiig stations, and if you're trying to perform multiple rendezvous maneuvers, to gather the pieces for a stock ship to send off on a mission. Because I'm still not quite comfortable with truly big payloads, I've tried to keep things in the 50-100t range max, and then do multiple lofts. When you add a static station of 400+ parts to 6+ 100 part ship subcomponents, LKO starts getting pretty crowded and laggy.

 

So I dropped my fuel hub station into keosync, to reduce part count in LKO. And when I'm having tankers coming in from Minmus to replenish fuel I can use a much lower part count transport from keosync to LKO, to deliver to the skeletal baby station, and then send off the extra-Kerbin missions. I'll put up an action shot of my keosync station after I get my tug up there with the latest fuel booms.

The only part count that matters is the parts within a 2.5 km radius. And even if you have multiple ships in LKO, they are unlikely to randomly get so close to each other

[Nich]

Na I have debris pass by me when I am launching LKO all the time it is a nightmare.  Closest near miss was been 1.1 km It is only a mater of time

[Snark]

1 hour ago, Somtaaw said:

Well I meant in my FL-T800 Fuel tank with a docking clamp on either end, and 4 Vernor's located on one end a 'good' extend range fuel tank design, or about as hideous as my pusher tug lol... I have only really done small tug work, LKO to Munar/Minmus orbits, and thats about it.

Ah.  Well, personally, I wouldn't bother with FL-T800 as individually pilotable/dockable drop tanks-- they're just too small to be worth bothering with, too much time spent docking and too many parts-per-ton-of-fuel adding to your lag.  Furthermore, attaching them radially the way you do, you have to attach them in matched pairs, plus you have to worry about getting the alignment just right.

My suggestion:  Move to a fore-and-aft tug that has docking ports on both front and back.  That way, your drop tank can be a big cylinder (e.g. with docking ports fore and aft, you can use much larger tank sizes (big orange or larger).  Fewer trips, fewer parts, more fuel.

1 hour ago, Somtaaw said:

I chose a keosync orbit this time around because I always find myself with biiiig stations, and if you're trying to perform multiple rendezvous maneuvers, to gather the pieces for a stock ship to send off on a mission. Because I'm still not quite comfortable with truly big payloads, I've tried to keep things in the 50-100t range max, and then do multiple lofts. When you add a static station of 400+ parts to 6+ 100 part ship subcomponents, LKO starts getting pretty crowded and laggy.

LKO is quite manageable, if you're reasonably careful about it.  I like to use just-over-120km as my altitude, because that's just high enough to go to 100x timewarp.  From that altitude, you can get efficient Oberth ejections, and it's really really cheap to go home from the station (just a very tiny burn will dip your Pe into atmosphere).

If debris is a concern, the main thing is to make sure that your common repetitive operations don't eject debris while sharing orbit with the station.  It's not hard, just a little attention to design is all:  only the last stage goes to orbit.  For example, if you're sending up a fuel delivery:  Only the very final stage (the one that has the big fuel tank on it) should actually make it to orbit.  All the other stages won't be a problem, because they're ejected before you reach orbit and therefore will just fall back to Kerbin.  After your fuel tank docks with the station and you drain it and it becomes trash, that's easy to deal with.  Just undock it with a little smidgeon of fuel left in it.  Doesn't have to be much, just a tiny amount will do.  Use that smidgeon to burn retrograde, and the tank deorbits itself.  Problem solved.

You don't have to be religious about it, a little debris once in a while doesn't make any difference.  Just make sure you don't clutter up your station's orbit by having your repetitive tasks drop debris right there in the orbit.

1 hour ago, Somtaaw said:

And when I'm having tankers coming in from Minmus to replenish fuel I can use a much lower part count transport from keosync to LKO, to deliver to the skeletal baby station, and then send off the extra-Kerbin missions.

Why not just ship the fuel from Minmus straight down to LKO?  I don't see how the part count would vary-- a transport that can go from keosync to LKO can just as easily go from Minmus to LKO.

[Somtaaw]

On 2/28/2016 at 9:25 PM, Snark said:

It's why I really prefer to mount my tug engines radially.  It means I can put the reaction wheels on the radial stacks, which means that my central stack has very few parts in it and is therefore nice and stiff.  Also, the engines tend to be the heaviest parts of the tug, and by mounting them radially, they can be considerably farther forward than they would if they were mounted underneath.  This means that my tug has a much smaller moment of inertia around the forward docking port, which means it's less prone to wobble at the docking-port connection (docking ports aren't particularly stiff when connected).

The TT-70 radial decoupler makes a great "stand-off" mount for radial stacks.  Lightweight.  Available early in the tech tree.  Just click its "disable staging" button in the VAB when building, so you won't accidentally use it for the purpose for which it was intended.    Put a big LF-only tank in the middle (the Mk3 parts are useful for this), with a quartet of TT-70's sticking out the sides, and then on each one you put one of the little 1.25m LF tanks with an LV-N on the bottom and a reaction wheel or two on the top.  Attach a single strut to help keep it stiff.  Add fuel lines.  The top of the radial stack is a handy place to put a battery, and the sides of the radial stack are useful for mounting radiators to keep the nukes from overheating.

The radial stacks arealso a handy place to put some floodlights for self-illuminating (useful when docking).

 

 

So I've done up a radially mounted tug like you're suggesting, and it feels really wierd. Maybe it's because I decided I'm a lazy wanker, so I gave it the capability to push AND pull, regardless of which end actually connects to the payload. So I now present, the Titan-class v2 tug

 

If I tap 1, it'll activate the downward facing nukes, the lights looking down also activate (with a red tinge) to remind you which way the exhaust is going, and the opposite set of solar panels so if I'm pulling an asteroid there's less chance of the panels getting eclipsed.

4 is the opposite and uses the bottom solar panels, and top facing nukes & red lights. Staging activates the various radios, and the small cooling vanes (did a test, even on a maximum thrust burn, they max out @ 74.99% thermal bearing). And Abort turns off all 8 nukes, and extends a secondary set of cooling vanes while extending all solar panels; debating if I should add in detaching of whatever payload I might be connected to as part of the abort.

 

 

Thoughts and comments on the newly updated radially engined Titan class?

[Snark]

2 minutes ago, Somtaaw said:

Thoughts and comments on the newly updated radially engined Titan class?

Nicely done!  And looks like you really had fun putting it together.

It might be a bit more nimble with an extra set of reaction wheels (e.g. add four more of the 1.25m ones, stacked on top of the existing wheels).  The current design will work, it's just a question of how patient you are about waiting for it to turn 'round (especially if it's lugging a load).

The fore-and-aft nukes are a cute idea.    Personally, I'd probably drop 'em if it were my own tug (that's 12 tons of dead weight)... or, if I figured I had the 12 tons to spare, I'd flip 'em around and have all eight pointing the same way for more thrust.  It's quick to flip the tug around if I change my mind about what direction I want to go.

But that's just me, if this fits your style then go for it!

I see you've got two stacked fuel tanks.  I take it that one of those is LF-only and the other is LFO?

One minor suggestion for usability/convenience:  you could add some radially-mounted 1.25m docking ports so that you could use the tug as a convenient refueling tank for smaller ships.  One option would be to rotate the placement of your radial nukes by 45 degrees, so you could put a foursome of 1.25m ports on the four "sides" of the central tanks.  However, that's not optimally convenient, since anything docking there would have to thread its way between the nukes.  A more convenient option might be to do something like this:

• instead of mounting the reaction wheels directly to the radial decouplers, put a 2-ton LF tank on each radial decoupler
• then mount the reaction wheels and nukes above/below that LF tank
• Move the radiators that are currently sticking out of the reaction wheels so that they're attached to the big central tank, in between the nukes
• This gives a nice, large, blank place on the outer surface of the little 2-ton LF tanks-- perfect for putting a docking port on, nicely accessible.
• It also moves the radiators where they're less likely to get snapped off by another ship passing nearby.

Might be worth giving the tug a couple of little radially-attached monopropellant tanks (even if it doesn't need monoprop and you leave the tanks empty).  Adds operational flexiblity-- you can use it to deliver monoprop if needed.

One option to consider (not necessary, just a thought):  you could use the rotate tool to angle the nukes very slightly outward.  This would give you a slight amount of extra flexibility in designing the craft that your tug can pull:  by angling the exhaust outward, you give a smidgeon more clearance, so the tug can pull a slightly wider load.  Of course, that means you'll lose a little bit of fuel efficiency, but it ought to be fine as long as you keep the angle small.  For example, if you go just one "click" of the rotate tool while holding the shift key down, that's a 5 degree rotation, which would cost you less than half of 1% of your fuel efficiency in cosine losses.

[Nich]

Yes it is much simpler to have 2 sr docking ports so the tug can connect to a back of a front :/

[Vahal]

I'm quite curious. Why making a generic tug when a dedicaced one would fit better? From my experience, tugs need arms with RCS/verniers thrusters at the end to be sure to have better control of the assembly. And due to space station modules, the shape of the arms has to be tweaked, adapted almost everytime. So a subassembly for the core, but the arms need to be built around the payload since the arms can't be too short or too long too narrow, too wide... So I just made disposable tugs launched with the payload and deorbited after they docked it, so It reduce parts count (all RCS and redundant SAS/fuel tanks/probe core/batteries/solar array/RTG are dumped with the tug) so my space stations aren't crippled by computer performance, and I can use them without playing Kerbal 1 frame per second Program  (Parts count is an obsession  )

[Snark]

10 hours ago, Vahal said:

I'm quite curious. Why making a generic tug when a dedicaced one would fit better?

The converse question would be "why make a dedicated tug when a general-purpose one is more useful and flexible?"

The fact is, no one design approach is "best".  There are a lot of ways to design tugs (or anything) in KSP, and which one is "best" depends completely on the player's style, preferred design approach, and other factors.

For example, I myself never use custom one-off tugs.  I use either a general-purpose tug (that is designed specifically to be useful in general fashion), or else I abandon tugs entirely and use ships that "are their own tugs" (e.g. a dedicated fuel hauler between LKO and Mun/Minmus).

10 hours ago, Vahal said:

From my experience, tugs need arms with RCS/verniers thrusters at the end to be sure to have better control of the assembly. And due to space station modules, the shape of the arms has to be tweaked, adapted almost everytime.

That hasn't been my experience.  I never put "arms" on my tugs or other ships, don't need 'em, don't want 'em.  They're a perfectly legitimate design choice; it just happens to be that I don't like them and prefer to make designs that don't require arms sticking out.

 

10 hours ago, Vahal said:

And due to space station modules, the shape of the arms has to be tweaked, adapted almost everytime. So <description of design approach to tugs>

Sure, and if that design works for you, great!    But there are other approaches, too, and from the OP's posts thus far, it appears that he prefers a more general-purpose design and is looking for how to accomplish that.

[Somtaaw]

14 hours ago, Snark said:

I see you've got two stacked fuel tanks.  I take it that one of those is LF-only and the other is LFO?

One minor suggestion for usability/convenience:  you could add some radially-mounted 1.25m docking ports so that you could use the tug as a convenient refueling tank for smaller ships.  One option would be to rotate the placement of your radial nukes by 45 degrees, so you could put a foursome of 1.25m ports on the four "sides" of the central tanks.  However, that's not optimally convenient, since anything docking there would have to thread its way between the nukes.  A more convenient option might be to do something like this:

• instead of mounting the reaction wheels directly to the radial decouplers, put a 2-ton LF tank on each radial decoupler
• then mount the reaction wheels and nukes above/below that LF tank
• Move the radiators that are currently sticking out of the reaction wheels so that they're attached to the big central tank, in between the nukes
• This gives a nice, large, blank place on the outer surface of the little 2-ton LF tanks-- perfect for putting a docking port on, nicely accessible.
• It also moves the radiators where they're less likely to get snapped off by another ship passing nearby.

Might be worth giving the tug a couple of little radially-attached monopropellant tanks (even if it doesn't need monoprop and you leave the tanks empty).  Adds operational flexiblity-- you can use it to deliver monoprop if needed.

One option to consider (not necessary, just a thought):  you could use the rotate tool to angle the nukes very slightly outward.  This would give you a slight amount of extra flexibility in designing the craft that your tug can pull:  by angling the exhaust outward, you give a smidgeon more clearance, so the tug can pull a slightly wider load.  Of course, that means you'll lose a little bit of fuel efficiency, but it ought to be fine as long as you keep the angle small.  For example, if you go just one "click" of the rotate tool while holding the shift key down, that's a 5 degree rotation, which would cost you less than half of 1% of your fuel efficiency in cosine losses.

 

Actuallly that's a single MK.3 fuselage (long) of purely LF for the core hull of the Titan II [changed the naming scheme slightly now for better iteration tracking]. I didn't really see a need to mix LF+O when the nukes operate on pure LF. On each radial decoupler is a tiny FL-T100 tank, with an offset Z-1K battery and an Advanced Inline Stabilizer clipped inside the T100 tank. The LV-N's themselves are also partially clipped inside the tank to reduce their vertical clearances, and I carefully placed the decouplers as close to CoM as possible so docking orientation doesn't matter.

 

I'll take your advice for moving the radiators to the main hull, I thought they had to be attached near the thermal points for best effect. Might upsize them to mediums while I'm at it. And moving the engine nacelles off to the 45 degree points to leave the flat sides for docking ports. And I'll probably rotate the engines by 10 degrees; with how big my fuel tank is I can afford a bit more waste.

 

Edit: Titan III now has 10 degree angled nukes, 2 each of both 0.625 and 1.5m docking clamps, and I reduced the part count from 87 to 67. I'm not entirely sure there's much left to do, except post a snapshot of the new Titan III and the core station it's going to be taking on a trip out to Duna for me.

Edited February 29, 2016 by Somtaaw

[Snark]

53 minutes ago, Somtaaw said:

Actuallly that's a single MK.3 fuselage (long) of purely LF for the core hull

Ah, okay, that makes sense-- was hard to tell from the screenshot.  I couldn't see where the Vernors were getting their oxidizer from.

53 minutes ago, Somtaaw said:

I'll take your advice for moving the radiators to the main hull, I thought they had to be attached near the thermal points for best effect.

It doesn't matter.

In terms of realism, it should matter where they're placed:   in real life, you need radiators placed where they can "see" the environment, so they're radiating to empty space and not to other parts of the ship), so they need to be mounted as far "externally" as possible.

However, KSP doesn't model that at all.  It only models radiation between the ship and the environment-- it doesn't model radiation between different parts on the same ship.

Therefore, for game purposes, it doesn't matter where you put the radiators.  The only reason to put them in a sticky-out location would be for "role-playing" purposes (i.e. "I know the game doesn't care but I think it's unrealistic so I'm gonna do it this way").

Also:  the active radiators pull heat from whatever parts on the ship are the hottest, regardless of how far away they are.  So from that standpoint, it also doesn't matter where the radiators go.  (Supposedly the static, non-folding panels are supposed to have a limit that they can't be more than 2 parts away from the thing they're cooling, but I've observed that they work fine for the whole ship, so maybe that's a bug.  And in any case, you're using the folding panels, so that's not an issue for you anyway.)

Be aware that the radiators use electricity while active.  It's not a huge amount, and you're not using a lot of radiators, and you have quite a few solar panels on your tug, so it's probably not an issue for you.  (Also, the time when you're using the panels will generally be when you're running the nukes, and the nukes themselves generate electricity while operating, which should be plenty to power the radiators.)

 

53 minutes ago, Somtaaw said:

And I'll probably rotate the engines by 10 degrees; with how big my fuel tank is I can afford a bit more waste.

Fair 'nuff.  To find out how much waste you'll have just take the cosine of the deflection angle to get your efficiency.  5-degree rotation is 99.6% efficient, meaning you waste 0.4% of fuel.  10-degree rotation is 98.5% efficient, so you waste 1.5%, which isn't too bad.

Probably don't want to rotate any more than 10 degrees, the losses start piling up in a hurry after that.

53 minutes ago, Somtaaw said:

And I'm thinking of upsizing the base radially mounted fuel tanks from the FL-T100's to the 200's for the extra oxide that the Vernor's need, or else switching to standard RCS and slashing the existing 16 Vernor's to 8 standard RCS.

These are both good plans.  It's good to have a bit of overcapacity for various resources on your tug, so it can serve as a "mini tanker" for topping off other ships, or taking on board their spare resources if they don't need them anymore.

I myself tend not to use Vernors, mainly because I use RCS very sparingly in my own designs and need only tiny nudges, so monopropellant is fine for me.  Another thing to bear in mind is that when the tug is doing its thing, it's going to be connected to another ship (which will likely be more massive than the tug itself), which means that when you're maneuvering the combination of the two, they'll be using all the RCS thrusters (mono or Vernor) together, and sharing fuel for all of them.  So, for example, if you decide to go with monopropellant-only and ditch the Vernors, it would be good to have a bit of overcapacity for your monopropellant, so that you can use the tug's mono supply to power the "payload" ship's RCS thrusters.

It's also a really good idea to make sure that your "payload" ships or containers have some RCS thrusters of their own, even if they don't have a probe core or a monopropellant supply, because then those thrusters will become available to the tug when it's docked.  It will make maneuvering much easier, because you really don't want a situation where you have a long, skinny, massive object (tug + payload) that has all its RCS thrusters way out on one end (i.e. on the tug, with nothing on the payload)-- it'll make for extremely wasteful docking.

The "right" way will depend on what sort of cargo you have in mind for your tug (e.g. complete ships, or simple dumb cargo tanks, or whatever).  For example, suppose it's shuffling simple dumb tanks around.  In that case a typical payload might be:  a fuel tank with a docking port at one or both ends, and a simple ring of four one-directional RCS thrusters around the tank's "equator".  That's a useful setup even if the payload has zero monopropellant storage of its own, because when you dock the tug to it, the tug can make use of the RCS thrusters on the tank.

 

Edited February 29, 2016 by Snark

[nli2work]

Give this a shot if you run part mods. Your builds actually give me idea for another part or two.:D

Edited March 1, 2016 by nli2work

[Somtaaw]

50 minutes ago, nli2work said:

Give this a shot if you run part mods. Your builds actually give me idea for another part or two.:D

 

That's a nifty little OUV. The reversible thrust especially, as I really hate having to undock to rotate just to start applying counter-thrust. And ultra-low part count sort of ties in with the part casting suggestion that we've all wanted for ages. Big enough to see and click things, yet small enough to maneuver easily around crowded stations. Radios so it ties in with RemoteTech users. I'm assuming that I will be able to fly it unmanned, so if it were somewhat expanded for crewing it can double from a space bulldozer to moving crews around.

 

For another idea, since it's your modded craft, how about adding wing 'deflection' to the engine pods so it can also benefit from angling the pods? Then I'd be all over that little OUV like flies over some fresh manure

[nli2work]

A RemoTech widget is great idea! 

wing "deflection" as in Control Surface? I think control surfaces are disabled in space? I'll have to test gimbal on the engine, not sure how it'll work with reverse thrust transform. I could integrate some RCS into a larger version of the radial NVs... someone else suggested a end cap/service bay shaped similar to the command pod, I think it would work as well as endcap/servicebay/dronecore