GB8SSD *Space Shuttle Discovery* Celebrating 33 years years since Launch

        

Space Shuttle Flight 12 (STS-41D)

Launch attempts

Attempt	Planned	Result	Turnaround	Reason	Decision point	Weather go (%)	Notes
1	25 Jun 1984, 12:00:00 am	scrubbed	---	Failure of Orbiter's back-up General Purpose Computer forced the scrub.[11]	(T-9:00 minutes and holding)
2	26 Jun 1984, 12:00:00 am	scrubbed	1 day, 0 hours, 0 minutes	Post-SSME start RSLS abort due to anomaly in number three main engine	(T-0:06)		Discovery returned to OPF for engine replacement; launch delayed over two months
3	29 Aug 1984, 12:00:00 am	scrubbed	64 days, 0 hours, 0 minutes	Discrepancy with master events controller relating to SRB fire commands
4	30 Aug 1984, 1:41:50 pm	successful	1 day, 13 hours, 42 minutes				delayed 6 minutes, 50 seconds when private aircraft strayed into KSC airspace

June 26: Abort flight:

June launch attempt

During the 26 June launch attempt, there was a launch abort at T-6 seconds, followed by a pad fire about ten minutes later.^[3][4]

Commentary: "We have a cut off."
"NTD we have a RSLS (Redundant Set Launch Sequencer) abort."
Commentary: "We have an abort by the onboard computers of the orbiter Discovery."
"Break break, break break, DLS shows engine one not shut down."
"OK, PLT?"
"CSME verify engine one."
"You want me to shut down engine one?"
"We do not show engine start on one."
"OTC I can verify shutdown on verify on engine one, we haven't start prepped engine one."
"All engines shut down I can verify that."
Commentary: "We can now verify all three engines have been shut down."
"We have red lights on engines two and three in the cockpit, not on one."
"All right, CSME verify engine one safe for APU shutdown."
"If I can verify that?"
"OTC GPC go for APU shutdown."^[5]

Mission Specialist Steve Hawley was reported as saying following the abort: "Gee, I thought we'd be a lot higher at MECO (Main Engine Cut-Off)!".^[6] About ten minutes later, the following was heard on live TV coverage:

"We have indication two of our fire detectors on the zero level; no response. They're side by side right next to the engine area. The engineer requested that we turn on the heat shield fire water which is what could be seen spraying up in the vicinity of the engine engine bells of Discovery's three main engines."

While evacuating the shuttle, the crew was doused with water from the pad deluge system, which was activated due to a hydrogen fire on the launch pad caused by the free hydrogen (fuel) that had collected around the engine nozzles following the shutdown and engine anomaly.^[7] Because the fire was invisible to humans, had the astronauts used the normal emergency escape procedure across the service arm to the slidewire escape baskets, they would have run into the fire.^[8]

Changes to procedures resulting from the abort included more practicing of "safeing" the orbiter following aborts at various points, the use of the fire suppression system in all pad aborts, and the testing of the slidewire escape system with a real person (Charles F. Bolden, Jr.). It emerged that launch controllers were reluctant to order the crew to evacuate during the STS-41-D abort, as the slidewire had not been ridden by a human.^[6]

Examination of telemetry data indicated that the engine malfunction had been caused by a stuck valve that prevented proper flow of LOX into the combustion chamber.

About the mission