UPFG fails to converge with upper stages with a very low (initial) TWR. Haven't done any extensive testing on this but noticed the problem during an attempt to extend an otherwise perfectly well-working vehicle with an extra upper stage that would have about 0.12 TWR at ignition. Theoretically (in terms of $\Delta v$) the vehicle should be able to get to orbit after several hundred seconds of upper stage burn, but UPFG was unable to converge for that vehicle.
Investigating this would require looking back at the MATLAB prototype for some more simulations and I am not doing that (until I retire or something). Leaving this here as a known issue and a warning.
UPFG fails to converge with upper stages with a very low (initial) TWR. Haven't done any extensive testing on this but noticed the problem during an attempt to extend an otherwise perfectly well-working vehicle with an extra upper stage that would have about 0.12 TWR at ignition. Theoretically (in terms of$\Delta v$ ) the vehicle should be able to get to orbit after several hundred seconds of upper stage burn, but UPFG was unable to converge for that vehicle.
Investigating this would require looking back at the MATLAB prototype for some more simulations and I am not doing that (until I retire or something). Leaving this here as a known issue and a warning.