Koos control: The man who made the Apollo 11 Moon landing possible

If it wasn’t for Dick Koos, it seems certain that the 20 July, 1969, Apollo 11 Moon landing would have been aborted just 10 minutes from completing the assignment announced by President John F. Kennedy eight years earlier. 

While Neil Armstrong and Buzz Aldrin – and, to a lesser extent, Michael Collins – dominate popular consciousness regarding the narrative of the 1969 Apollo 11 mission to land men on the Moon, it was a handwritten note from a Koos-inspired lunar landing simulation 15 days earlier that gave Mission Control the confidence to give the green light for the descent of the lunar module Eagle in the face of intense pressure to abort.

 It was 5 July, 1969, just 11 days before the launch of Apollo 11, and in the lunar landing simulator was the Apollo 12 backup crew of Dave Scott and Jim Irwin. Dick Koos was the simulation supervisor, and it was his job to introduce problems for the team to solve, so all contingencies would be covered before these problems could present themselves 384,000km from Earth. 

Koos was a NASA authority in space-flight simulations, and wanted to test the resolve and decision-making of Mission Control by introducing “Case Number 26”, a deliberately triggered restart scenario where the lunar module’s onboard computer throws up error alarms.   

Soon enough, when the crew were trying to land their simulated lunar module, the guidance computer crashed. The program controlling the lunar module’s descent had run out of memory, and rebooted. Its last words were “Program Error – 1201”. 

An error in the lunar module computer falls to GUIDO, the guidance officer in Mission Control. For the simulation on this day, the GUIDO was 26-year-old Steve Bales. 

Like just about everyone else, Bales had no idea what the 1201 error meant when it flashed up on the screen. It hadn’t happened in any previous simulation. 

To try to understand what had just happened, he turned to Jack Garman, a NASA Mission Control computer engineer who was in the GUIDO support team. It was their job to liaise with Massachusetts Institute of Technology, which had built and programmed the lunar module computer.

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After consulting the computer manual, it was determined that the lunar module computer – a single-processor computer – had overloaded and couldn’t execute all its programs simultaneously. Garman and Bales decided that with an unknown error on the computer in charge of the landing, the only safe response was to abort the landing. 

They made this recommendation to the flight director, Gene Kranz, and that was the end of the simulation. 

But Dick Koos wasn’t happy, and in the simulation debriefing he explained that the alarm wasn’t “mission-critical” and that the operating system had never failed to preserve the critical data. Everything else was working, and if this really happened just above the Moon’s surface, would aborting the mission be the right response? 

It was only as a result of Koos throwing a curveball into the simulation that Kranz, who fate would put in charge of almost every significant Apollo event, instructed Bales and Garman to go through every possible computer error and decide which really were aborts and which could be ignored. 

Garman then prepared a hand-written cheat-sheet that was stapled into the manual at the last minute, detailing the alarms and the correct response. 

Ring the alarm

Just 15 days after the simulation, almost unbelievably, as Apollo 11’s Eagle lunar module approached the Moon, Armstrong and Aldrin received a 1202 computer error that, like a 1201 error, meant that the computer was dropping low-priority, non-critical tasks – but neither Armstrong nor Aldrin knew that.

“Program alarm,” Armstrong says, his voice filled with tension.

Fate had arranged for Bales to be the GUIDO for Apollo 11, and had also placed Garman in the back room and Kranz as the flight director – the same team from the simulation. 

 “It's a 1202,” adds Armstrong. 

Bales, Garman and Kranz consulted their hand-written notes and realised that a 1202 error was very similar to a 1201. In the 1201 the computer was out of memory for calculations. In the 1202 it couldn’t start a new program, so they responded to Armstrong: 

“Roger. We got you … We're ‘Go’ on that alarm.” 

Over the next few minutes, Armstrong and Aldrin received repeated 1202 errors and some 1201s. Mission Control continued to instruct them to continue. 

The rest is, as they say, history, but if Koos hadn’t introduced the computer error into the simulation it’s almost certain that Apollo 11 would have aborted. There’s simply no substitute for training. 

Another hurdle

You may think that this was enough drama for the first manned landing on the Moon, but it wasn’t. 

When the lunar module separated from the command and service modules for the descent to the Moon’s surface, there was a small amount of air left in the tunnel between the two spacecraft. This pressure gave a slight extra kick so it separated from the command module just a little faster than intended. 

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This extra speed was minor, but as the lunar module descended closer to the Moon, it accelerated under the force of the Moon’s gravity, and the lunar module’s speed continued to increase.

Part of the landing procedure was to visually check landmarks on the Moon as the astronauts flew over them, to ensure they were on course. They also checked the computer’s estimates of their speed by calculating it from the time it took for the landmarks to pass. 

There’s no such thing as too many checks; not when you’re so far from home. These checks revealed that they were further down-range than intended, and also travelling faster than planned.

This isn’t necessarily a problem. But the Moon isn’t smooth. The Apollo 11 landing site had been carefully chosen to be relatively flat and clear of rubble. Now, they were going to fly past the site previously chosen and examined by Apollo 10 just months before.

At this point, Armstrong took manual control of the attitude of the spacecraft while the computer kept the vertical speed at a value that Armstrong chose with a switch in the lunar module. 

He immediately tipped the lunar module forward to get some extra horizontal speed so he could fly over a large boulder field that was exactly where the new trajectory would have them land. 

Avoiding the boulders was essential, of course, but it was using precious extra fuel. The lunar module only had a finite amount of fuel, and if they weren’t able to land by a certain time, they would have to abort the landing. 

In this case, they would return to Mike Collins and the command module, which was awaiting them in orbit. That return took fuel as well, of course, because the lunar module had to climb against the Moon’s gravity. 

So this amount of fuel had to be held in reserve, for an abort. Hence, there was a “bingo” fuel call, which meant “land in 20 second or abort”. This wasn’t negotiable. 

The tension builds

As Armstrong flew over the boulders, looking for a safe place to land, Aldrin was reading out critical flight data. Specifically, their height above the Moon, in feet, as well as their descent rate and forward speed, both in feet per second. 

The safe limits for landing were 10 feet per second down and only four feet per second forward. Exceeding the latter limit resulted in a significant risk that the lunar module would tip over. 

They were zipping across the moon at 50 feet per second and descending at 20 feet per second. At a height of only 300 feet, Buzz Aldrin calmly announces:

“You’re, uh, pegged on, uh, horizontal velocity.” 

This is Aldrin’s way of saying that the forward motion “speedometer” was showing its maximum value, and they were actually travelling even faster than that. 

To land, they needed to be below four feet per second. Armstrong immediately tipped the lunar module backwards to slow their speed, while still trying to avoid the boulders.

Meanwhile, Mission Control in Houston is counting down the seconds to the fuel bingo call. The situation is unbelievably tense. 

All the while, they also continually had those 1201 and 1202 computer errors. 

Can it, CAPCOM

The CAPCOM, or capsule communicator, is the only person allowed to communicate with the astronauts from Mission Control in Houston. 

This person is always an astronaut from the backup crew, so that he knows the mission as well as those in the spacecraft. 

For the Apollo 11 landing the CAPCOM was Charlie Duke, who would later fly to the Moon on Apollo 16. 

Duke was, in his words, “giving a running commentary” when Deke Slayton, the director of flight crew operations, punched him in the side and said: “Shut up Charlie, let them land!” 

At that time, the flight director, Gene Kranz, wisely said to all controllers: “From now on, the only callouts will be for fuel.”

Listening to the recordings, you can hear Houston calling out the time to the fuel bingo call: 

“... 60 seconds.”

“… 30 seconds.”

Finally, when the lunar module touched down, it had only 18 seconds of fuel left before it would have been forced to abort the mission. It was four miles (6.4km) down-range from its original point.

The Apollo 11 landing was a masterpiece of management, planning and, in the final analysis, gutsy flying from a team with nerves of steel.