Balancing CoT with a variable CG

[DChurchill]

So, I'm building this truck, see. It's eventual destination is Gilly to mine and process ore. What I want is for this truck to be able to go from surface to orbit and back to refuel ships. Here's the problem: it's a truck, as I said, so imagine this truck with engines and rcs thrusters on all four corners. Problem is, the CG is going to change, longitudinally, based on the state of fullness of the tanks. It's easy enough in the VAB to change the thrust of either the back or front set of engines/thrusters to balance to the CG. Not so after it's in service.

What are my options? Any mods that will self balance it? Anything that will show me CoT and CG outside the VAB?

Thanks.

[Boris-Barboris]

 

[Oafman]

Can you balance the tanks to keep the CoM in position? Tac Fuel Balancer can do it automatically for you.

Otherwise, maybe just plenty of SAS and low thrust? The control authority can make up for the misaligned CoT. And this being Gilly, you don't need much thrust.  

[mk1980]

since you said it's for gilly, you can probably circumvent the problem altogether. just slap an engine at the back of the tank and use RCS thrusters or vernor engines (i guess even reaction wheels would be enough) to push the front of the truck upwards and then fire the main engine to ascend. likewise, you can just descent retrograde until you are almost down to the ground, then use reaction wheels / RCS to rotate the craft into a horizontal position.

[steuben]

So to understand your flight profile.
-  The truck starts in Gilly orbit with enough fuel to land (plus margin).
-  fill the tanks on the surface
- fly back to Gilly orbit and rendezvous

We can assume four cog states.
- orbit, with landing fuel
- surface, with almost dry tanks
- surface, with full tanks and cargo
- orbit with landing fuel and cargo

My suggestion is as follows, and requires KER, as it shows the data needed:
- for each of the four states remove fuel
- record the torque reported
- add sufficient reaction wheel torque to balance to the maximum

 

 

[DChurchill]

1 hour ago, Oafman said:

Can you balance the tanks to keep the CoM in position? Tac Fuel Balancer can do it automatically for you.

Otherwise, maybe just plenty of SAS and low thrust? The control authority can make up for the misaligned CoT. And this being Gilly, you don't need much thrust.  

I have TAC fuel balancer. The problem is fact that there will be a point on the low end that it won't be able to balance. I'll play around with all the options here.

It's for Gilly, but if I can work out the thrust, I can use it on other low grav bodies with no atmosphere. I'm thinking I could do it with RCS and SAS alone on Gilly.

Or I could just do it vertically on landing legs, but that's no fun.

1 hour ago, steuben said:

So to understand your flight profile.
-  The truck starts in Gilly orbit with enough fuel to land (plus margin).
-  fill the tanks on the surface
- fly back to Gilly orbit and rendezvous

That's it exactly.