Once again, the inaccuracies of MECOTool has shown themselves. I was trying to get a accurate post-MECO trajectory for STS-107, based on the numbers in the STS-107 Mission Report. Using

these numbers into MECOTool yields a too low target altitude in Orbiter. I encountered the same problem when trialing the MECO parameters for STS-109, in the end I had tell it to aim for a target altitude 10 km above that of what I wanted. It seems that MECOTool is seriously lowballing the numbers.

Please, what inaccuracies does MECOTool have????

I'll say it once again, I've checked the math it and it's all correct.

As I know it, our "trajectory issues" are:

1) MECOTool doesn't take into account the -Z translation;

2) MECOTool doesn't take into account a possible post-MECO +X translation;

3) MECOTool doesn't take into account the MPS dump;

4) MECOTool doesn't take into account the MECO perigee altitude (I made a version where MECO Pe is a parameter, but I think I haven't committed it because MECOTool is so hated...);

5) MECOTool doesn't take into account atmospheric drag post-MECO;

6) for Standard Insertions, the "standard" MECO target probably changed during the program, and is probably different with the flight inclination... MECOTool has 1 MECO SI target, which will make the OMS-1/2 not match for flights with a different MECO SI target;

7) our AscentDAP is unstable in pitch prior to MECO, generating a FPA error;

8) our AscentDAP has generic SSME tailoff dV values, which will produce an underspeed for heavy vehicles, and overspeed for light ones.

IMO, #7 is by far the one with most blame. The c.g. moving in big steps, plus our algorithm only working in "constant thrust" mode, when late in the ascent we need a "constant acceleration" mode, should be to blame.

On the MECOTool, #4 is the big one and it affects only the OMS-2 MET and dV (not altitude) (and where the ET reenters). IMO the others are not large "error generators" but yes, they do affect OMS-2 time, altitude and dV, but it should be only pennies. So, IMO even with its short comings, MECOTool is very good.

There's also the unexplained "52NM MECO", which apparently means nothing as flights allegedly kept hitting MECO at 57NM. :shrug: If MECO really is at 52NM, and we are targeting 57, this would probably be second on the list behind issue #7.