I simulated an orbital insertion using Powered Explicit Guidance as used in the space shuttle.
The PEG algorithm works great. I hit all my targets: altitude, velocity, orbital inclination, longitude of ascending node.
But the algorithm does something I didn't expect: it causes the rocket to pitch down by >10 deg beginning maybe 30 seconds before orbital insertion (depending on altitude target, but generally a few tens of seconds).
Again, all my targets are hit. And if I try to stop the rocket from pitching down when it does, then I miss my targets. So the algorithm is clearly detecting that the rocket has to pitch down. It's doing its job, sort of.
But should the rocket be pitching down like this at orbital insertion? I thought it would be pointing at the horizon at the very end, but... no?
Just wondering if this is normal or (as I suspect) if I need to figure out what's wrong with the PEG algorithm (despite it working flawlessly otherwise, because it always always hits my targets, even when I change them mid-simulation).