The Four Inch Flight: The Comical Beginning to Project Mercury

Sep 17, 2020 0 comments

Like many firsts in spaceflight, Project Mercury began with a failure. The goal of the mission was to put a man in space and bring him safely back to earth, ideally before the Soviet Union did. The Soviets beat America by putting into orbit the first satellite, and now the race was on to put the first human.

Unfortunately, Project Mercury was having trouble getting off the ground. In July 1960, the very first attempt to launch a Mercury capsule (that would carry future astronauts) on top of an Atlas rocket failed when the rocket exploded mid-flight less than a minute after it was launched. As Project Mercury wore on without much to show in the name of progress, it began to face scathing criticism. Just two weeks after the Atlas rocket failure, a major journal in the aerospace industry, Missiles and Rockets, stated:

NASA's Mercury manned-satellite program appears to be plummeting the United States toward a new humiliating disaster in the East-West space race. This is the stark conclusion that looms in the minds of a growing number of eminent rocket scientists and engineers as the Mercury program continues to slip backward. The program today is more than one year behind its original schedule and is expected to slip to two. Therefore, it no longer offers any realistic hope of beating Russia in launching the first man into orbit around the earth - much less serve as an early stepping stone for reaching the moon.

The “Mercury Seven" astronauts

The “Mercury Seven" astronauts pose with an Atlas model on July 12, 1962. Photo: NASA

Project Mercury was a large and unproven part of NASA. Established just two years ago, this young organization didn’t even have a proper rocket capable of safely launching humans into space. They scavenged parts from the Redstone and Atlas family of rockets, that were originally built to launch missiles, and put them together for the Mercury program. When the Mercury-Atlas rocket exploded, the engineers went back to the drawing room and replaced the Atlas boosters with that of the Redstone. NASA chose the U.S. Army's Redstone missile because it was the oldest one in the US fleet, and had many successful test flights. A variation of the Redstone rocket was used to put the first US satellite, Explorer, in orbit. If there was a rocket that could place humans in space, NASA decided, it was the Redstone.

With fingers crossed, NASA wheeled a fully-loaded Mercury-Redstone 1 on to the launch platform at Cape Canaveral Air Force Station, Florida. The purpose of this flight was to qualify the Mercury spacecraft and the Mercury-Redstone launch vehicle for the sub-orbital Mercury mission. It would test the spacecraft's automated flight control and recovery systems, its automatic inflight abort sensing system, as well as the launch, tracking, and recovery operations on the ground, and millions of other things.

On November 21, 1960, the countdown began and progressed without any hiccups. At exactly 9:00 AM Eastern Standard Time, the engine of the Mercury-Redstone ignited and a great cloud of smoke billowed from under the rocket engulfing it. The TV camerman panned his camera towards the sky in anticipation of the launch, but there was nothing on the screen except blue sky and smoke. “I was surprised at how quickly the Redstone had accelerated and moved out of sight,” wrote NASA engineer Gene Kranz, who was at the console watching the launch.

The Mercury-Redstone 1 rocket getting prepared for launch

The Mercury-Redstone 1 rocket getting prepared for launch at Cape Canaveral's Launch Complex. Photo: NASA

However, moments later the embarrassing failure came into view. Although obscured by smoke, the vague outline of the Redstone was still there, standing on the launch pad.

It would be wrong to assume that the rocket didn’t fly, because it did, a whole four inches, before the engine shut down and the rocket fell back, miraculously landing upright on the launcher cradle. Immediately after, a strange sequence of events unfolded. First, the Mercury capsule's escape rocket jettisoned itself but without the capsule that remained attached to the Redstone booster. The escape rocket rose to an altitude of 4,000 feet (1,200 m) and landed about 1,200 feet (370 m) away. Three seconds after the escape rocket fired, the capsule, still attached to the rocket, deployed it parachutes. These fell limply to the side.

When everything fell silent, the incredulous engineers realized that they had a very big problem at hand. Here was a live rocket on the pad, full and pressurized with fuel, and because the umbilical control cables had disconnected at the time of liftoff, they had no control over the rocket. Besides, the booster’s self-destruct system was armed and there was no way to secure that system. Nobody had any idea what to do.

Gene Kranz wrote in his engaging book Failure is not an option:

We sat stunned, helpless in Mercury Control. We had no technical data on the spacecraft or the launch system beyond a simple manual, the equivalent of an owner’s manual for a new car. All of us were thinking in aircraft, not rocket, terms—and we were definitely behind the power curve. We had no data to work with because we weren’t smart enough to know what we really needed. We were dealing with a new control room, a new network, new procedures, and entirely new jobs, doing something that we had never done before, and something almost alien to our nature.

Re-connecting the umbilical cord was proposed and rejected because of the risk involved. Then somebody suggested shooting holes in the fuel and oxidizer tanks to relieve the pressure, and got an earful from the flight director Chris Kraft. Kraft would later establish the agency's Mission Control concept and develop its organization, operational procedures and culture.

Fortunately, the winds were calm that day and because there was no immediate risk of the rocket toppling over, one engineer suggested waiting until the batteries depleted. Then the rocket will be totally out of power, the destruct system will disarm, the oxidizer will boil off and the booster will depressurize, making the vehicle safe to approach. Kraft nodded, turned to his controllers and growled: “That is the first rule of flight control. If you don't know what to do, don't do anything.

Christopher C. Kraft Jr.

Christopher C. Kraft Jr. He was the primary inventor of the mission control concept, and implemented it during Project Mercury and after, including training a cadre of controllers and creating a worldwide tracking network. Photo: NASA

The cause of the failure was later tracked down to a faulty connection. The Redstone rocket was connected to the launch tower with multiple electrical cables that disconnected when the rocket lifted off and tugged at the plugs. One of these cables relayed various control signals, and another provided power and grounding. The control cable was supposed to separate first, followed by the power cable, a split-second later. However, for this launch, someone used the wrong control cable which was a tad longer than expected. When the rocket lifted off, it pulled at both cables, but the control cable being longer did not disconnect first. Instead the power went out before the control cable was severed.

When the power cable disconnected, the lack of electrical grounding caused a substantial current to flow through an electrical relay causing it to trigger an engine cut-off signal that it normally sends to the rocket at the end of powered flight. Once the engine shut down, the Mercury capsule’s computer acted as if it reached orbit and sent the command to jettison the escape tower which was no longer needed. The capsule, not sensing acceleration (because it was sitting on the ground), believed it was in freefall and thus deployed the parachute. The main parachute, not able to feel the weight of the capsule, acted as if it failed to open and so deployed the reserve parachute.

Mercury-Redstone 1 launching the escape rocket

Mercury-Redstone 1 launching the escape rocket during its infamous “Four Inch Flight”. Photo: NASA

Incredibly, the rocket suffered only minor damage from falling back on the pad. This was repaired. To prevent a failure like this from recurring, subsequent Mercury-Redstone rockets added a grounding strap about 12 inches long to electrically connect the rocket to the launch pad. This strap was designed to separate from the rocket well after all other electrical connections to the ground had been severed. The computer was also reprogrammed not to prematurely jettison the escape rocket, the only escape mechanism for the astronauts in case of emergency. Several other minor improvements were made to the capsule systems, so even though history books sarcastically refer to this embarrassing episode as “The Four Inch Flight”, it would be incorrect to write off the Mercury-Redstone 1 as a total failure.

# Gene Kranz, Failure is not an option,
# This New Ocean - Ch9-4,
# This New Ocean - Ch9-7,
# Wikipedia,


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