Orbital Fuel Depot

[MisterKerman]

I recently decided to decommission some rather flamboyant and impractical assets and go for a soulless, modular, rather minimalistic design for the new orbital fuel depot.

My original station destabilized from it's 120k circular orbit. This new station will be set up as a train of modular segments.

I'll use Clamp-O-Tron Sr connections between modules and a very simple/cylindrical shape with an efficient booster on the aft end. Would a tug be better than a booster?

Aside from usual considerations like communication, power, fuel, docking space, and control, which other things should I be considering in regards to setting my station up in a funtional manner?

[Tonka Crash]

If you aren't averse to mods, you might consider weldable Konstruction ports instead of Clamp-O-Tron's between modules. Dock the modules, click a button and poof your parts are mated to each other with no docking ports between them. I've found this to be more stable than using docking ports in the long run. 

Do you need to move the station under it's own power?  Then you need to worry about balancing the CoM around the thrust line as you add modules. Do you plan to do EVA assembly with KIS/KAS? Then I'd think about lights around the station. Do you plan to have a science lab or several, then your power requirements on the dark side just sky rocketed. I assemble stations in the VAB and then figure out where to cut it into modules for shipping to orbit. Concentrate reaction wheels around the CoM. If they are spread out it seems to lead to more wobbliness in the final assembly.

This is the most recent station I built as a fuel depot around Minmus. It was assembled over a dozen or so launches in Kerbin orbit and moved under it's own power out to Minmus. It arrived with at about 5% of it's total LFO capacity and I've spent the last two weeks shipping ore up to it between other missions to only get the tanks up to 45%. It uses a Near Future Nuke power plant, so no solar panels. The CoM is offset just a hair from the thrust line, but I've got enough reaction wheels to keep it pointed in the right direction. After assembly all the RCS thrusters were stripped off during EVA (about 80) and recovered back to Kerbin to keep the parts count down.

Same save, this is an older station around the Mun launched quite early in the game mainly as a transfer point for Mun surface missions and to service landers. I know the solar panels were all replaced with Gigantors when they became available and again RCS thrusters get stripped eventually. The biggest problem now is it doesn't really have nearly enough fuel capacity to keep up with all the Mun landing missions I've done, so I have a ship go retrieve debris with fuel to keep topping off the tanks. I added a science lab parts pack mid way through this game so expansion was pretty haphazard. It needs all the panels to keep the science experiments running in daylight. I added a second engine late to adjust the thrust line for the station expansion below it's original thrust line. These engines are needed for periodic orbital adjustments.

[Zhetaan]

@MisterKerman:

I prefer docking/assembly tugs to boosters because the depot itself shouldn't need to move; if I want it to move, then I build a tanker, which is a somewhat different design paradigm.  Also, tugs that are designed well will give much finer control than main engines.

You may want a probe core with the ability to hold normal/antinormal (I believe that requires an OKTO2 or higher) to ease docking because the normal vector doesn't precess as the prograde and radial vectors do.

I'd suggest to stay away from ore processing; it's usually cheaper to process ore on the ground and only deliver fuel to orbit if you intend to eventually include this depot as part of an in situ refuelling plan.

Also mind that you don't add too much control.  Clamp-O-Tron Sr. ports are strong but they can still wobble, and long stations, in my experience, invite issues if the reaction wheels are too assertive.

Edited August 31, 2018 by Zhetaan

[MisterKerman]

25 minutes ago, Zhetaan said:

@MisterKerman:

I prefer docking/assembly tugs to boosters because the depot itself shouldn't need to move; if I want it to move, then I build a tanker, which is a somewhat different design paradigm.  Also, tugs that are designed well will give much finer control than main engines.

You may want a probe core with the ability to hold normal/antinormal (I believe that requires an OKTO2 or higher) to ease docking because the normal vector doesn't precess as the prograde and radial vectors do.

I'd suggest to stay away from ore processing; it's usually cheaper to process ore on the ground and only deliver fuel to orbit if you intend to eventually include this depot as part of an in situ refuelling plan.

Also mind that you don't add too much control.  Clamp-O-Tron Sr. ports are strong but they can still wobble, and long stations, in my experience, invite issues if the reaction wheels are too assertive.

This is a very brutally simple example of what I'm going for. Mostly a terminal for Moon-bound passengers with multiple leg journeys, and a few docking ports for parking and refueling. Small stuff.

I made the CM act as a tug at the very front, though it has no ability to store fuel when undocked, which is fine with me.

What is auto-strutting precisely? It would be good for a station like this, no?

Edited August 31, 2018 by MisterKerman

[MisterKerman]

Is there a point to putting Reaction Wheels anywhere but the CoM? I sort of put them at the CoM of each module but I think collectively once assembled it would be best to focus on having the RCS seated at the assembled station's CoM and ideally nowhere else.

EDIT: I think it would be a good idea to have emergency power solutions on important modules but have a Central Power-Plant/RCS-Center close to the CoM for supplying evenly distributed torque and power throughout.

DOUBLE EDIT: This is what I've got so far. Resisting the urge to add utilities to the crew quarters and docking ports because if I ever need to rearrange things I know it will be a pain in the butt. I think it's fine for now. Thoughts?

Edited August 31, 2018 by MisterKerman

[bewing]

1 hour ago, MisterKerman said:

What is auto-strutting precisely? It would be good for a station like this, no?

The Unity game engine has a bug that causes joints between parts to be too bendy. Autostruts are a "temporary" gift kludge from the devs that give you a way to rigidify your vessels in flight. You get them at the same time as you get regular struts on the tech tree, as long as you have "advanced tweakables" enabled in the settings. However, certain kinds of autostruts can be dangerous if misused -- especially if you use a lot of them. An autostrut is just a massless, dragless, zero cost regular strut that you can add in flight. From a selected part they can extend to one of several selectable endpoints. Grandparent autostruts are safest. Root and "heaviest" autostruts can change their endpoints automatically if the vessel's stats change -- like during a docking. Having an autostrut change its endpoint suddenly can be a violent process. Having many dozen autostruts do it simultaneously can easily destroy your ship. So it's best to keep the number of autostruts low, and sometimes it can be a good idea to disable them before doing a docking.

1 hour ago, MisterKerman said:

Also is there a point to putting Reaction Wheels anywhere but the CoM?

If you do the physics calculation and assume a perfectly rigid vessel -- then it turns out that the answer is that you can put them anywhere and the results are the same. In general in the game that's true enough. But because physics is calculated sequentially and the SAS system can do some funny games with reaction wheels -- it's best to have the active reaction wheels near to each other, and to deactivate all the distant ones. Otherwise you can get harmonic vibrations that can destroy your ship.

 

 

[Gargamel]

Looks like that size of station can be done in one launch, but if you are planning on doing orbital construction, use a Tug to do all the docking and such.  That way you can keep the part counts on the station itself to a minimum.   Remove the RCS, engines, etc from the station, and keep them on the disposable tug.  The station is supposed to be parked in an orbit and left there, no reason for it to have anything to make it move.    Unless you want it to move.    And even then you can just use a tug to move it around. 

 

 

[MisterKerman]

44 minutes ago, Gargamel said:

Looks like that size of station can be done in one launch, but if you are planning on doing orbital construction, use a Tug to do all the docking and such.  That way you can keep the part counts on the station itself to a minimum.   Remove the RCS, engines, etc from the station, and keep them on the disposable tug.  The station is supposed to be parked in an orbit and left there, no reason for it to have anything to make it move.    Unless you want it to move.    And even then you can just use a tug to move it around. 

 

 

I'll launch it in one piece, but I'd like the option to add to it later so I'll keep the modular design.

As for the tug, I just think it looks cool, mostly. But it has lots of RCS if I ever do need to rearrange the station, and features those tiny radial Cub engines to boost it's orbit when that inevitably becomes an issue.

The aft-end Senior docking port will be left exposed so I can latch RockoMax fuel-resupply tanks to the bottom on deliveries until de-orbiting the used up tank. Hopefully I will have envisioned a Rockomax-sized-payload-capable-SSTO by then.

The radial docking ports will be used for craft parking. I should only need a standard and a junior sized port for what I have planned, which leaves a second standard and junior ready for use when all is stowed, which is good. Hopefully parking doesn't get too squishy if I ever do need to use all 4 at once.

 

Does this seem like a reasonable and practical station for refueling commercial boosters/landers and launching moon tourism missions from LKO? What orbit should I try to keep it in; 125Km I suppose? I'll see if I can launch a Jumbo64 and a liquid O2 tank but I might go strictly LFO in the near future. I was underwhelmed by LV-N's performance prior to this and sticking with one fuel type and delivery method seems like the most straightforward and likely way for me to succeed, at least short term.

Edited August 31, 2018 by MisterKerman

[Tonka Crash]

I only use standard size clamp-o-trons for docking other ships when building a station. If I need a Jr. port I use a 3 part adapter (standard port/cone/jr port) that can move around as needed. As I advance up the tech tree I usually start with ships using the Jr. port and migrate to the standard size almost exclusively later on.

[MisterKerman]

I went with this design. There's still essentially a full Rockomax 64 with a poodle attached that I'll send to it's doom at some point. For now it can stay because it's still so juicy.

Thanks for your guys' input. I took it all into consideration when building this and I feel like it's probably close enough to being complete for me to close this topic. I'll still take any suggestions you feel are worth mentioning. I plan to put a science module on there eventually but for now I need desperately to add affordable moon tourism to my space program's money-making-repertoire.

Edited September 1, 2018 by MisterKerman