twr and max acceleration

[ForScience6686]

Thanks for all the help guys, I have successfully launched my manned lander can and separate rover to duna. Not my first, but I at least have confidence in them making the journey. I will have to go to my ships already enroute and check if they have the delta-v.

I do have one final question. How would calculation the lifter go? Lets make it somewhat easy and say we have a center stack with main sail. And then 8 onion staged srbs. Would I just calculate the dv of the boosters and the engine or does the fuel loss during srb ignition have to be accounted for?

[Red Iron Crown]

That's a two stage design, you would have to do two calculations. How it is done depends on the staging, either "burn SRBs first then ignite core stage" (easy) or "ignite everything and stage away boosters when they burn out" (harder).

The former case should be easy enough, the latter one involves calculating how much LFO the liquid core stage burns while the SRBs are still attached, then treating it and the SRBs as a single stage with a net Isp calculated as shown on the previous page.

[ForScience6686]

That's what I figured. I am guessing the easiest method would be to test how much fuel is remaining after the srb burns, then do the math.

[Red Iron Crown]

You don't need to test, the propellant consumption rates (in tonnes/sec) are given in the part descriptions and the Wiki, you can use those to calculate how much LFO is used during the SRB burn.

The only thing that might throw off the calcs is any time between SRB burnout and jettisoning them, that will be using the fuel from the next "stage" inefficiently.

[ForScience6686]

Oh that's helpful info. What about thrust limiting, that would change all the numbers, so lets say is set to 75, would I use .75 to figure thrust and fuel consumption? Then from there I should be able to calculate time.

[Red Iron Crown]

Yes, that works. The throttle/thrust limiter is perfectly linear, so a 75% setting delivers 75% of the thrust at 75% the fuel consumption.

[ForScience6686]

Perfect. Red, you are a great teacher. Thanks for all the help.