Hey there
A week ago, I build a MK3 SSTO to do some mining & tourists contracts and everything worked quiet well. Just after the liftoff I pitched up ~10 degree, the SSTO accelerate pretty easy up to the "magical" 400m/s, the RAPIER engines got their boost to accelerate further and after reaching LKO I had ~3000m/s DeltaV left.
Today, I tried to start the same SSTO to do another contract but somehow it got pretty hard to accelerate up to 400m/s, instead im always stuck at ~340m/s o