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How Risk Thinking Saved Apollo 13

Posted in on
March 30, 2021

Author: Ron Dembo

Astronauts live in a radically uncertain world. Yet they are trained risk thinkers. They, and their support teams at NASA, excel at figuring out risk factors and mapping scenarios as they evolve.

As Canadian astronaut Chris Hadfield writes, NASA teaches astronauts to look on the “dark side” – to imagine the very worst that could happen and ask, “Ok, what’s the next thing that will kill me?” 

They rocket up to space and face the totally unforeseeable, and, in some extreme cases such as the Challenger disaster in 1986 or Columbia in 2003, they do not survive. And yet, more often than not, they can navigate their way through each problem that comes at them.

Never has that been truer than in the case of Apollo 13.

The Explosion in Space

In 1970, Jim Lovell, Jack Swigert, and Fred Haise were halfway to the moon onboard Apollo 13 to conduct geological experiments. Suddenly, an unexpected explosion ripped through one of the service module’s two onboard liquid oxygen tanks and caused the other to fail. This crippled the electrical power generation and propulsion systems of the command module, Odyssey, leaving them without light or water and with a dwindling oxygen supply approximately 200,000 miles from Earth.

At this point, Swigert sent his now infamous message to ground control: “Houston, we’ve had a problem here.” And what had been a lunar landing mission would turn in minutes into a rescue one.

Thinking Through the Scenarios

In the face of radical uncertainty, risk thinking took over. The astronauts began considering scenarios. One benign possibility was an instrumentation problem – a faulty reading. But the thunderous crash from the explosion ruled that one out quickly.

What about a meteor collision? Despite the microscopically small chance of such an event, the downside impact was huge: the invisible punch would rip a gaping hole in the spacecraft and the life-preserving pressure pocket inside would be whisked out into the vacuum. Immediately they began mitigation. They moved to seal the hatch between the command module and the lunar module which, had it been hit, would now be rapidly depressurizing.

But it wasn’t a meteor.

The next candidate was a problem in the oxygen tank. Yet those were built with as few parts as possible, and the chances of a fault were extremely thin. Also, even if one failed, the other should have been more than capable of keeping the other components running. Except it wasn’t. They had failures in one tank, two fuel cells, and one bus – a statistical absurdity. To make matters more perplexing, the antennas on the ship had suddenly begun switching stations, and the ship itself started wobbling off its proper attitude as it hurtled towards the moon at 2,000 miles per hour.

Thoroughly perturbed, Lovell decided to perform one of the oldest pieces of analysis in the aeronautical books. He looked out the window.

What he saw was the beautiful and the damned. His spaceship was venting a ghostly gas that crystalized as it bled from the ship, stringing itself around them and out into space like a halo that went on for miles. It had been an explosion in the oxygen tank, then, and the second was emitting its liquid lifeblood rapidly.

Keep Calm and Strategize

Lovell, Swigert and Haise kept their cool. Already several contingency backups had come into play that had saved them, for it was just this type of scenario that had led NASA to install two oxygen tanks and multiple fuel cells in the first place. They had oxygen, though dwindling, and they had identified the cause of the spinning as the venting.

On the ground, the flight director, Gene Kranz, smoking heavily and pacing back and forth behind his console at Mission Control, executed some critical upside analysis, known, inversely in NASA-speak, as down-moding. What rewards, at what risk, were still available to them? If a moon landing was off the cards, perhaps an orbit was possible. If not an orbit, perhaps a loop around for some hasty sightings.

Each of these were exhausted as the situation worsened until Kranz was left with only one upside: return the crew alive.

In space, the astronauts transferred to the lunar module and converted it into a lifeboat for their journey home, rerouting power from the command module and using the lunar module’s oxygen supplies to stay alive.

Battling the unknown, the space crew overcame critically important obstacles: they recalculated their consumables, cutting their water intake to six ounces each per day, and they implemented a new way to strip dangerous carbon dioxide from the air using canisters, plastic bags, and cardboard.

Their biggest challenge, however, was adapting the command module’s navigational platform alignment for use in the lunar module whose only requirement until then had been to jump down to the surface of the moon and hop back up again. Now the crew had to undertake midflight navigational adjustments that returned them to Earth safely.

The Big Decision

At this point a decision had to be made. The craft was accelerating up to 5,000 miles per hour and closing in on the moon. The closer it got, the harder it would be to perform any midflight adjustments before entering the moon’s field of gravity and losing radio contact on the backside.

One option was a direct abort. This would use the service module’s main engine to return before ever getting to the moon. The upside was a speedy return; the downside was a catastrophic failure of the propulsion system, which the initial explosion could have damaged, and the death of the wavering fuel cells. This could leave them stranded or cause another explosion that obliterated the craft. It was also a maneuver that had to be calculated fast, and which also used up every last drop of fuel, so no adjustments could be made if they got it wrong.

Instead they decided to use the lunar module’s smaller engines, which had been designed primarily for descending to the moon’s surface, to adjust course for a free return trajectory – the famous slingshot around the moon. This hedge cost them some upside; the return journey would now take four days, but crucially it was safer and left fuel for another burn on the other side to correct their flight path and, importantly, speed the craft up.

Think Like an Astronaut

As details of the incident were communicated back to Earth, news reporters and analysts put the crew’s odds of survival at a meagre 10%. But astronauts don’t think like that. They don’t make single-figure forecasts. Each of their steps, the water conservation, the carbon dioxide syphoning, the navigational decisions, the multi-stage burns, played a part in the risk thinking methodology – a rolling reassessment of policy that accounts for evolving scenarios and enables the charting of the best course of action for the immediate future. 

That is, as Lovell himself said in interviews after the fact, “when you’re in a situation like this, you don’t think of the odds, you think of only how to improve the odds…as we got over one crisis after another…our percentage went up”. 

And they went up right until the crew splashed down into the Pacific, safe at last.

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