With Apollo anniversary celebrations still fresh in our minds, let’s salute those brave space pioneers by remembering the unique risks of travel beyond our planet. In 2002, while researching the upcoming 35th-anniversary Apollo book I was writing for a major publisher, I got some real surprises about how dangerous that project really was.
In the early ’60s, when engineers had asked Bob Gilruth, director of the Manned Spacecraft Center, and Walt Williams, the Project Mercury director, what kind of security and reliability should be engineered into the new Apollo program, they got two very different answers. Williams announced that he wanted to make the risk of astronaut death one in a million. Engineers present at that meeting kept straight faces out of politeness, but knew that such a level of redundancy and security simply could not be accomplished. Even airline passengers of the day did not enjoy that degree of safety. Merely to attempt such risk-aversion would delay the Moon program by years.
“How about three nines?” Gilruth suggested. And this was accepted: The success odds were to be 999 out of 1,000. Spacecraft systems, subsystems and rockets would be designed so that each astronaut faced only a one-in-a-thousand chance of not making it back alive.
That was the official engineering criterion. The “inside” truth, however, is that few at NASA really believed that this degree of safety had ever actually been achieved. (And unfortunately, in the fullness of time, they were proven right.) Nearly everyone expected an eventual fatal accident. There simply was too much that could go wrong.
It wasn’t merely Murphy’s Law. The Saturn rocket alone contained nearly a million parts, along with tons of flammable kerosene and explosive hydrogen. The Command Module had another half-million parts. Already the space program had seen its share of disconcerting mishaps, as when a cover had inadvertently been left on a piece of equipment, causing the 1965 Gemini 6 launch to shut down after the engines had already started to fire and the massive rocket was an inch off the ground. How could absolutely nobody, of the 420,000 people working on the program, screw up in some significant way? Was it even possible?
Very early on, engineers and planners identified which systems or subsystems simply could not be allowed to fail. For example, the single engine of the Service Module would have to function for the astronauts to leave lunar orbit. Unless they could increase their speed by at least 2,000 miles per hour at that time, they simply could not come home. The single engine of the Lunar Module ascent stage would also have to fire, or else the men would remain to die of suffocation on the lunar surface. The parachute system would also have to deploy, or else the astronauts would receive fatal g-forces when they hit the ocean at 350 miles an hour.
The engineering philosophy employed to ensure that critical systems would always work was to use the simplest possible technology and then build in redundancy wherever possible. For example, the truly critical engines would use a hypergolic fuel mixture of hydrazine and nitrogen tetraoxide. When these two liquids come in contact with each other, they ignite spontaneously. No ignition system is required, nor any spark, nor even an electricity source.
The next safety step is to store the two fuel components in tanks with nylon bladders. Helium gas, released from a special tank into the space between the fuel tank and its bladder, squeezes the fuel and drives it toward the combustion chamber. No fuel pump is required, just the release of inert gas. Ball-valves also driven by gas pressure open and close to release the two fuels. Duplicate valves can take over if any fail. Simple. And it worked every time. In fact, it was hard even to imagine how these engines could fail.
But NASA insiders, and the astronauts themselves, also knew of Apollo’s weak spots, some of which would produce fatalities and mission aborts throughout the decade. Such perils are sobering to remember for those who now push for manned missions to Mars.
Want to know more? To read Bob’s previous columns, click here. Check out Bob’s podcast, Astounding Universe, co-hosted by Pulse of the Planet’s Jim Metzner.