5 ms·

Regardless, the Earth didn't substantially speed up between Ariane 4 and 5, so although the horizontal velocity figure might not be zero, it would at least be a

• InclinedPlane 14y ago
  The point I was making is that it is necessary to calibrate an inertial guidance system to the ground, you can't just pretend that the launchpad is stationary. More so, because a launch vehicle's guidance will become entirely internal (dependent only on the on board systems and commands sent from mission control) well before launch it's not so easy to have some software routines running on the rocket which don't run during an actual launch. I imagine it was far easier to simply use a timer to allow the routine in question to run up through T+40s than to attempt to programatically trigger deactivating the routine in the event the vehicle actually left the pad. More so given that running the routine through part of an actual launch, on an Ariane 4 at least, had never been problematic before. The problem was that nobody had formally detailed all of the assumptions and risks for every part of the code, so when the conditions changed and those assumptions became faulty nobody was the wiser because nobody was aware they were actually making such an assumption about the speed of the rocket.