gimbel's in the their start positions. at t minus two minutes and 55 seconds, external tank liquid pressure began. it t minus two minutes 50 seconds, retraction of the gaseous oxygen venter began. crown launcher -- sequence verified its full retraction at t -37 seconds. water wasression started at t -16 seconds. at t minus eight seconds, hydrogen igniters were turned on to burn off any free hydrogen. before launch, challenger's liquid fueled main engines were ignited in sequence and run up to full thrust. thrust from the main engines spec.he shuttle when it returned to vertical the solid rocket boosters ignited. at t zero, the holdout bolts were explosively released. after the initial prerelease twang ocean, structural force is dissipated at a rate of three cycles per second. >> it has cleared the tower. initiated ater was 7.724 seconds. the maneuver was completed at 21.124 seconds. >> normal throttle for most of the flight, 104%. the main engines were throttled after 65% for about 16 seconds in order to alleviate maximum

the gimbel sequence ends with the engines in their start decisions. at t minus three minutes 55 seconds, external liquid pressurization began and main engine purging was completed. retraction of the gaseous oxygen vent hood again. the ground launch sequencer verified its full retraction at t -37 seconds. sound suppression water was started at t minus 16 seconds. at t minus eight seconds, hydrogen make nighters were turned on to burn off any free hydrogen. 6.6 seconds before launch, challengers liquid fuel main engines were ignited in sequence and run up to full thrust. thrust from the main engines bounced the shuttle stack. when it returned to vertical the solid rocket boosters ignited. then the holddown bolts were exclusively -- explosively released. after the initial motion, structural forces dissipated through vibration at a rate of three cycles per second during the first few seconds of flight. roll maneuver was initiated at seven 724 seconds. at maneuver was completed 21.124 seconds. >> 104%. throttling in. >> the main engines were throttled back