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NYCAviation @NYCAviation
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There’s a lot going on in this #spacegif, and most of it is very wrong. So let’s talk about the story behind the failure of the Mercury-Redstone 1 launch. #AvGeek #Spacegeek
Mercury-Redstone 1 was intended as the first unmanned test flight to validate the Mercury capsule and the Mercury-Redstone launch vehicle that would eventually be used to launch Alan Shepard and Gus Grissom’s suborbital spaceflights.
There were 2 electrical cables connecting Mercury-Redstone 1 to the launchpad, 1 for power and grounding and the other for data. At liftoff, the data cable was supposed to disconnect first, followed by the power cable. Instead, the reverse happened.
With no electrical ground for a rocket that was still receiving control signals through the data cable, there was enough electricity to trigger the electrical relay that would normally command the rocket’s engine to shut down at the end of its burn.
Mercury-Redstone 1 flew about 4 inches and settled back onto its pad. It was upright and fully fueled, but it was no longer secured. Then, a rather odd sequence of events occurred.
With that engine shutdown relay now activated, several other spacecraft functions were now enabled. First, stage separation and the jettisoning of the (now normally unnecessary) launch escape system would be initiated immediately.
Now the stage separation system had an interlock to ensure that the rocket was accelerating at near zero Gs, thereby keeping the spent stage from colliding with the remainder of the spacecraft. Since acceleration was at 1 G on the ground, stage separation didn’t occur.
The launch escape system didn’t need such an interlock. Since it was rocket powered, there was no risk of a collision as the now unneeded tower rocketed away. So when the relay activated near the ground, the launch escape system jettisoned itself.
When the launch escape system was jettisoned, it also jettisoned the antenna fairing and enabled the parachute deployment system, which would automatically deploy the parachutes when at an altitude below 10,000 feet.
Current altitude of the Mercury capsule atop Mercury-Redstone 1: approximately 70 feet.
The drogue parachute was deployed, followed by the main parachute. When the Mercury capsule didn’t sense that the parachutes were supporting the weight of the capsule, it assumed that the parachutes had failed and deployed the backups.
Now there was a rocket sitting on the launchpad, fully loaded with propellant and oxidizer, with 2 sets of parachutes dangling from it just waiting for a gust of wind to pull the whole thing over into an almost certain fireball.
Launch Control was at a loss for what to do. Numerous suggestions were made, all of which were rejected by Launch Director Chris Kraft as unsafe. This would lead Kraft to declare, “That is the first rule of flight control. If you don't know what to do, don't do anything."
Finally, one launch controller suggested they just wait until the liquid oxygen had boiled off. Kraft agreed that this was the safest course of action given that light winds were forecast. The next morning, the rocket was no longer at risk of exploding and it was safely secured.
The Mercury-Redstone 1 launch vehicle only sustained minor damage. It was sent for refurbishment, but was never launched. The Mercury capsule was refurbished with parts from other capsules, and was launched as part of the replacement Mercury-Redstone 1A mission.
Many lessons were learned from the failed launch. A strap that would electrically ground the rocket until all other electrical connections had been severed was added, thereby preventing a reoccurrence of the Mercury-Redstone 1 failure sequence.
There were also concerns that if the launch escape system jettisoned while on the pad, it could leave an astronaut stranded atop a fully fueled and unstable rocket. So a timer was added to prevent jettisoning it until the rocket was close to normal engine shutdown.
That way, should a failure occur during a manned flight, even one that never left the pad, the launch escape system was guaranteed to be available. Thanks so much for following along!
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