Out of this world lessons from the Apollo Lunar landings–Part II
The first American spacecraft in the early 1960s was called Mercury. This “capsule” was so small that the astronauts joked that they didn’t get into the craft; they put it on!

Cutaway diagram of Mercury spacecraft (NASA)

It was cramped in the spacecraft. There was barely enough space for the astronaut to float, let alone share space with a 1960's era computer (these, believe it or not, were even larger than a 2019 flagship cellphone!). The Mercury spacecraft, therefore, had very primitive diagnostic tools.

Mission Control in Houston received a trickle of telemetry data with which it could interpret the status of the spacecraft.

Now, the most important responsibility of any spacecraft is keeping the astronaut inside alive and the heaviest part of Mercury was the massive heat-shield at the bottom. The heat-shield protected the spacecraft (and the astronaut inside) from the over 1,500 °C (3,000 °F) temperatures encountered during re-entry. As can be imagined, a heat-shield needs to be precisely aligned to dissipate the heat properly.

Near the end of the flight, Mission Control received a telemetry signal from the spacecraft to report that the heat shield had deployed prematurely. If true, this meant that the spacecraft might burn up during re-entry.

There was no supplementary information to the monitoring signal. It was a simple alarm light that blinked on.

Glenn had not reported hearing any knocks or feeling any of the vibrations in the spacecraft which were expected to occur should the heat-shield be deployed prematurely. Mission control only had one point of data to use and so they had to operate under the assumption that it was correct, even though they suspected that the monitoring sensor was faulty and did not reflect reality.

Mercury capsule being tested on the ground. (NASA)

In the image to the left you can see a Mercury capsule being tested on the ground. The base of the capsule is pointing to the left. The three braking rockets (the metal “pot” with three spouts) are connected to the spacecraft with very high tech straps.

The straps are connected to the heat-shield (the round base of the capsule).

There was little that could actually be done to solve the problem, and fortunately, it turned out to be a false alarm. There was no fault in the heat-shield, and Glenn returned to Earth without problems.
['Robert Barron']
['IBM', 'Apollo', 'NASA', 'Monitoring', 'Observability']