(FAR) TWR planning for parallel stages

[S1gmoid]

Hey,

If a launch vehicle ignites a main engine and multiple boosters at the same time, with the boosters jettisoned before the main engine runs out of fuel, what's a good practice for setting thrust limiters? Generally, with discrete stages, I follow the rule of thumb of having a TWR of 1.3 at ignition, as suggested by several people, including Ferram, which works reasonably well.

That said, I'm really interested in optimizing launch parameters. As the mass of the rocket decreases with fuel consumption, and specific impulse increases with altitude*, TWR rises. I'm wondering if I should set the limiter for the main engine to provide a TWR of 1.3 at the time the boosters have been jettisoned, and increase the thrust of the SRBs in kind to set the launch TWR?

* of course in KSP this is only an issue with RealFuels.

[Geschosskopf]

Well, it depends on whether your boosters are SRBs or liquid. If liquid, then you don't need to limit thrust because you can just throttle back. Same for the central engine. With SRBs, you do need a limit.

Are you using MJ? If so, one trick you can do (even when flying manually) is to use some of the settings on the Ascent Guidance tab. Such as "limit acceleration". 15m/s^2 is a good number for FAR. Then even if you're doing the steering, MJ will keep you throttled back so you don't flip out.

[S1gmoid]

Well, it depends on whether your boosters are SRBs or liquid. If liquid, then you don't need to limit thrust because you can just throttle back. Same for the central engine. With SRBs, you do need a limit.

I prefer using limiters, not just for realism, but also because having to manage the throttle while overseeing the gravity turn would be slightly overwhelming.

Are you using MJ? If so, one trick you can do (even when flying manually) is to use some of the settings on the Ascent Guidance tab. Such as "limit acceleration". 15m/s^2 is a good number for FAR. Then even if you're doing the steering, MJ will keep you throttled back so you don't flip out.

Lol no, I'm a hardcore masochist. But thanks, the acceleration limit sounds like an interesting idea.