We now turn our heads to the past, with “This Week in Rocket History”, where every week we cover an important launch event that happened roughly around the same time in history, and this week we have a doozie!

On February 20, 1962, John Glenn was launched into space from Cape Canaveral in the Friendship 7Mercury capsule, sitting on top of an Atlas LV-3B launch vehicle.

The launch was initially delayed because of weather and various failures in the guidance and fueling systems, which were all eventually fixed, and the Mercury-Atlas vehicle launched successfully at 14:47 UTC.

The vehicle performed admirably, passing maximum dynamic pressure, or Max Q, at T+1:24, and at T+2:14 the booster engines cut off and were separated from the craft, followed by the escape tower twenty seconds later.

The Atlas then pitched over further and kept pushing the capsule until T+05:24 when the engines shut off, and John Glenn became the first American to achieve an orbital flight trajectory around the Earth. The Mercury-Atlas vehicle is notable for providing the quickest ascent-to-orbit of any crewed rocket. Glenn experienced nearly 8 Gs on the ascent.

Once on orbit, ground controllers informed Glenn that he would be able to complete at least seven orbits, while the computers at the Goddard Space Flight Center predicted that he was moving fast enough to complete a hundred orbits.

The capsule separated from the rocket using its posigrade rockets, but a five-second rate dampening operation which was supposed to be initiated at the same time started two and a half seconds too late, causing the capsule to begin its 180° turnaround maneuver with a substantial initial roll. The attitude systems managed to compensate for the error at the expense of a little more fuel than originally anticipated.

Initially, everything seemed to be going perfectly, with all systems “go” as Glenn flew over the Atlantic. As he passed over Nigeria, however, Glenn noticed that his instruments were indicating the capsule was in the wrong attitude, so he took manual control and adjusted the yaw so that he was more properly aligned with the desired orientation.

Glenn’s flight path took him and Friendship 7 over the city of Perth in Australia, where many people turned on their lights so that Glenn could see them as he flew over. Shortly thereafter, the sun began to rise on Friendship 7, and Glenn reported seeing “thousands of little specks, brilliant specks, floating around outside the capsule”. Those only appeared as the sun was starting to rise and completely disappeared when the sunlight was stronger. It was later determined that those were probably ice crystals venting from the spacecraft’s systems.

When he was nearing the end of his first orbit, Glenn once again noticed issues with his yaw flight controls. He observed a drift to the right of about a degree and a half per second, and once again switched to manual control in order to correct his yaw using fly-by-wire, a system which controlled the vehicle’s systems electronically rather than via mechanical linkages, which he had to keep using for the rest of the flight despite the automated system intermittently kicking in.

Interestingly, the same problem had occurred previously on the Mercury-Atlas 5, which was crewed by the chimp Enos was not trained to fly manually, so the flight had to be aborted early. Enos, for those worried, survived the harrowing experience.

It was in the second orbit, however, that things started getting really concerning. An engineer named William Saunders noticed that a sensor that provided data on the spacecraft’s landing system, called “Segment 51”, was reporting that the heat shield and landing bag were no longer in their default “locked” position, meaning they might be loose and could be damaged during re-entry or worse. The controllers did not inform Glenn right away but did instruct him to ensure the landing bag switch was set to “off”.

During his third orbit, Glenn was instructed to test the landing bag deploy switch again, at which point he realized they must have found a problem with it. The test was technically successful, as no warning lights lit up, but ground control was not satisfied. They decided to keep the retrorockets attached to the capsule during re-entry, as the rocket pack went over the heatshield and would help keep it in place. This would only be possible if all the retrorockets fired, otherwise any unspent fuel would be ignited upon re-entry. There was also a concern that the rocket pack would disintegrate due to the excess heat of reentry, but it was determined that by the time that happened the atmospheric pressure would be enough to push back against the heat shield and keep it attached.

As the capsule got close to the California coast, Glenn fired his retrorockets — which thankfully all fired — and then angled his spacecraft into a 14-degree nose-up pitch for re-entry. As the capsule started re-entering the atmosphere, Glenn reported he saw chunks of debris flying past his window, which he was afraid was the heatshield, but it ended up being parts of the retrorockets, as anticipated by the engineers on the ground. 

When the capsule reached maximum g, Glenn lost manual control and the capsule started oscillating violently. He used the auxiliary dampening systems to try and smooth the motion of the spacecraft in hopes to regain enough stability by the time he had to deploy his drogue chutes. It worked for a short while, but even the auxiliary systems ran out of fuel eventually, and 51 seconds before chute deployment, it started oscillating again. Glenn was going to deploy the chutes early to regain attitude control, but the automated systems of the capsule beat him to it, and the spacecraft started gaining stability and eventually splashed down safely in the North Atlantic.

Investigations after the fact have determined that both the landing bag and the heat shield were functioning properly, and “Segment 51” was simply having a sensor malfunction.

In the years to follow the stressful yet successful flight of Friendship 7, the capsule was taken on a tour around the world, known as “The Fourth Orbit of Friendship 7”. The Friendship 7 capsule now resides in the National Air and Space Museum in Washington DC, and John Glenn became a national hero, but the mission would not have gotten off the ground without the work of another, now-famous figure: Katherine Johnson.

According to an article from NPR, Johnson’s calculations were an indispensable part of Glenn’s preflight routine, apparently asking her personally to double-check the “new computer” calculations of Friendship 7’s planned flight. Mrs. Johnson recalled that “When he got ready to go, he said, ‘Call her. And if she says the computer is right, I’ll take it’.”

In the words of Margaret Lee Shetterly, author of the book Hidden Figures: the astronaut who became a hero, looked to this Black woman in the still-segregated South at the time as one of the key parts of making sure his mission would be a success.

On this, the one-year anniversary of her passing, we here at CosmoQuest salute her, and all the other heroes at NASA who made this moment in history possible, providing the foundation for the seemingly routine space flights of today. It doesn’t happen without people like Katherine Johnson.

More Information

NASA article

Katherine Johnson obituary (NPR)

Mercury-Atlas 6 article (NASA)

Western Australian Museum article 

The Mystery of John Glenn’s Fireflies Returns (Universe Today)

‘Hidden Figures’: How Black Women Did The Math That Put Men On The Moon (NPR)