The twelfth Space Shuttle mission, STS-41-D, would endure three launch attempts before leaving earth successfully.
A bad backup General Purpose Computer (the Orbiter has five) scrubbed the first attempt on June 25, 1984. GPCs are the central computers of the spacecraft and control all critical aspects of flight.
The GPC was replaced, using one from Challenger, and a second attempt was made on the following day on June 26.
The countdown proceeded normally. When it reached 6 seconds, the three Space Shuttle Main Engines were commanded to ignite.
“We have main engine start…we have a cut-off!” said the NASA launch commentator.
The Launch Control Center’s controllers scrambled to safe the spacecraft. Aboard, Hartsfield and his pilot, Michael Coats, studied their consoles carefully. Two of the three engines showed a shutdown condition on their displays. Engine #1 did not show that same indicator.
In his book, Riding Rockets, Mullane recounted his tale of this dubious first of the Shuttle program: An RSLS abort. The redundant set launch sequence is automation that controls the final 31 seconds of a countdown. An RSLS abort at that stage meant that the computers detected a problem with one or more of the three SSME engines, which then aborted the rest of the launch sequence.
Pilot Michael Coats stabbed at the Engine 1 shutdown button but the indicator stayed dark. He and Hartsfield had no clear idea whether Engine 1 was truly shut down. Launch control teams were also initially unsure. Never in the early history of the Shuttle program had there been an engine-shutdown abort.
Mission Specialist Steve Hawley made a now-famous quip: “Gee, I thought we’d be a lot higher at MECO!” But Mullane, also seated with Hawley on the upper deck with the pilots, felt it was far from a laughing matter. Millions of pounds of liquid hydrogen and oxygen rested fully pressurized aside of them in the external tank, and the condition of Engine 1 was still up in the air.
Suddenly Mullane and others saw water drenching the forward windows of the Orbiter. Launch Control detected a fire.
Hartsfield called out for everyone to release their seat restraints just in case they needed to leave the spacecraft quickly. Judy Resnik had crawled to the side hatch, noticing that the crew access swing arm had returned to the side of Discovery. Not seeing any indication of fire, she called out to Hartsfield, asking whether to open the hatch.
Several tense moments passed before Hartsfield directed that the hatch stay shut and for the crew to wait things out.
As it turned out, Hartsfield made a very good decision.
Engine 1 was leaking hydrogen, which somehow had ignited. Fire suppression jets later sent water all over the vehicle, including the interior of the three main engines.
Hydrogen fires burn transparently to the human eye. The initial flames reached as high as the crew compartment, based on scorched paint found up the tower to the white room.
If Resnik and the others chose to leave, especially if they moved towards the slidewire baskets to escape the pad, they may have walked right into the invisible conflagration.
The crew waited patiently as the closeout crew rushed back up the Fixed Service Structure to assist the crew out of the spacecraft. Each astronaut became soaked to the bone from the suppression water as they exited, but were otherwise unscathed.
Discovery was later rolled back to the Vertical Assembly Building and Engine 1 pulled. The cause of the abort was traced to a problem in a hydraulic actuator that in turn caused a block in a hydrogen fuel valve.
STS-41-D was the first RSLS abort, but not the last in Shuttle history. Flights 51-F, 51, 55 and 68 would also suffer engine launch aborts.
After two months of repairs to replace the troubled Engine 1 (and with one additional launch scrub) Discovery would begin her career on August 30, 1984, on her way to become the Orbiter to make the most flights in the fleet.