How to land a base

[Duck McFuddle]

So I really want to land a mining base on Minmus but when I try to land the ship spins out of control because the engines are not placed right. I use the center of mass tool to see where they should go, but the engines are never spaced right. It's getting pretty frustrating. I started to make my bases smaller and smaller until it's basically just a drill and a tank, plus all the electrical stuff and radiators. Any tips?

Edited December 9, 2018 by Duck McFuddle
Forgot a question mark at the end

[Plusck]

38 minutes ago, Duck McFuddle said:

Any tips?

I've only ever used KER, which does a fine job of telling you exactly how off-axis your thrust is. There are other options, but I haven't used them.

I'm assuming that your base will land horizontally (otherwise you wouldn't be having these problems). This probably also means building the lander/base in the SPH.

1) The first tip to make sure your base/lander/whatever is balanced and stays balanced is to use a fuel tank as your core. Then you hang your engine(s) to the core using symmetry with snap ON, and then offset them (with snap still on). They will snap to the exact centre of your tank.
To hang the engines, you can radially attach smaller fuel tanks and rotate them down, or use the cubic struts (I tend to go for tanks, or octagonal struts).

Then you start attaching everything else to your lander/base and try to balance it as best you can. If you enable the CoM and CoT indicators, you can guesstimate the balance fairly well. Just don't ever move the engines off that central snapped line.

Once you"ve got everything more-or-less sorted, you can easily test it on the runway at Kerbin. Simply swap out the engines for more powerful Kerbin-atmosphere-capable versions, turn off gimbal and try to see if you can fly it around. If it works like that, it'll work elsewhere with the less powerful engines (and gimbal, if you have it).

2) Next up, you need to balance it for going up to orbit.

If you're using KER or similar tools, simply attach a fake earlier stage to the back, and check the thrust offset numbers.
If you're not, then you need to repeat the balancing process in the VAB. Attach an atmo-capable engine and fuel, and then using the CoT and CoM indicators, move things around carefully.
The easiest thing to move here is your engines (+symmetrical radial fuel tanks). This time, turn snap off and don't ever touch the slider that might move the engines off that centre line.

I've made quite a few belly-landing craft like that. I even did quite a few before installing KER, so it definitely works to get a reasonable system just using the built-in CoT and CoM indicators.

 

(edit: just remembered another couple of things...:)

3) Knowing which items can shift the mass around and which will simply add mass to the part they attach to is also a help.

For example, all of the surface mounted batteries and most science instruments (but NOT the goo and NOT the ore analyzer) add mass only to the parent part. Move them from part to part to alter balance, by all means, but on any given part their location is irrelevant.

4) If you have an external command seat, you need to balance it somehow. The mass of your Kerbal will be taken into account when using the seat. The solution I use is to add an Oscar fuel tank on the opposite side to the seat, and fill it to about 1/2 with locked-off fuel when there is a Kerbal on board, and empty it when there isn't. A very scientific process...

5) Belly-mounted Vernor engines can save you if you're imbalanced. If I use them, I assign two action groups to (1) toggling monoprop RCS thrusters on/off and (2) toggling the Vernors on/off. The monoprop thrusters are for docking, the Vernors for landing/surface movement.
 

Edited December 9, 2018 by Plusck

[ARS]

Build your completed base in VAB/SPH with this format:

- a central core (preferrably the one that acts as control point), that must contain the following: ISRU, fuel tank and engines with enough total Dv for going from LKO to land on minmus (calculation must be done on "complete mass" base configuration, not just central core)

- put docking ports in radial symmetry around this central core (preferrably in even numbers), this will be the module "hardpoint")

- make a module that'll be connected to the central core. Since it's radial symmetry, make so that each of these contains the remaining parts necessary to make a mining base, that is solar panels, drills, radiators, ore tanks (smallest is enough, it's better to convert ore directly, instead of storing it). In short, makes so that by itself, one symmetry module is inefficient at doing it's job, but with other symmetry modules, it's efficient. Since they are placed in radial symmetry, they'll be balanced. You can add more engines too

- if you want to add anything else, add a docking port on top the central core for anything else, such as habitation, antenna, etc. Don't forget to add landing gears on all symmetry modules and central core and make their height fits

-launch in this order: central core to LKO, all modules (do it one by one) docking with central core in LKO, then anything else you want to add on top the central core. Do this until the base is complete

-now all you need is just burn to minmus and land on it! The used fuel tank in central core now functions as fuel storage from mining

 

Edited December 9, 2018 by ARS

[Duck McFuddle]

Thanks! I will try that out and see if it works. (Not that I have any doubt - you both seem smart )

[Pecan]

2 hours ago, Duck McFuddle said:

So I really want to land a mining base on Minmus but when I try to land the ship spins out of control because the engines are not placed right. I use the center of mass tool to see where they should go, but the engines are never spaced right. It's getting pretty frustrating. I started to make my bases smaller and smaller until it's basically just a drill and a tank, plus all the electrical stuff and radiators. Any tips?

The gravity on Minmus is so low there's no need to make special landing arrangements.  Just land tail-first then, once you're comfortably down, tip the ship forward so it falls onto the axis you want.  Of course, you might want some legs for that bit but that's simple.  Unless your whole thing is huge and ungainly it shouldn't be necessary but if you need it SAS or a touch of RCS should be able to make the fall as gentle as you wish.

Of course, it's all just a lot simpler if you can orient things in tail-sitter position anyway but that may be harder for you.