Abstract A preliminary comparison is presented of the apex time computed during firing with the apex time presently available from post-firing trajectory evaluation. The apex was computed after burnout of Stage I on the basis of four different and independent measurements: a. Dovap measurements, b. S-Band radar, c. C-Band radar, and d. Acceleration with missile-borne accelerometer. The determined ignition signal time was 403.5 sec and the ignition time confirmed from telemetry was 403.7 sec....