A question concerning those fumes, is it coming from the LH2 Back Up valve? If yes, is it normal to have it before normal MECO?
That's the FES exhaust plume. Which admittedly shouldn't be there very low in the atmosphere...
Unfortunately, I was a bit short by at least 50 Nm for this one, I follow the guidance, but no joy
This is somewhat embarassing...
I've just tried to redo this based on what I could see on your screenshots to see what happened.
* 1ST EO VI 5747 happens for me 2:47 into the flight (low inclination launch from KSC, empty Shuttle). That's well into the region where a TAL is available without payload (and outside the region where I've tested the RTLS, I think most of my tests were 1st stage engine failures)
* letting the AP fly the trajectory brings me to pitchdown at 7100 fps site-relative speed with 339 miles to site - the ideal MECO distance computed by guidance would be 288 miles
* now, there is a correction done to aim for the ideal distance modifying MECO target speed - which would suggest to go ~1000 fps higher
* however, out of qbar limit violation concerns, I have clamped that calculation to [-300, +300] around nominal MECO target velocity, so the correction is not fully applied
* and as a result you get short
* and since the cutoff is guidance-controlled whenever you're using RTLS guidance, you can't even fix this manually
-> However, my concern seemed to be baseless, since qbar at ETsep was at the lower end of the target range, thus I've increased the clamping window from 300 to 800 which should handle a late return trajectory more gracefully
-> Sadly I couldn't test this because some of my recent fiddlings (probably with NO Y JET) seem to have screwed something with the handover from powered to unpowered flight in the devel version (probably an uncaught integrator windup) so I need to track and fix this first.