During the second test flight of Saturn Five last April, several of these tubes, which carry fuel for the second and third stage engines, fractured so that these engines would not be triggered. There were no comparable failures during ground testing and brilliant engineering work was needed to track the problem.
It appears that the tubes were broken by vibration during flight, a contingency that ground tests proved to have been strangely excluded. During these tests, before air was pumped out of the test chamber (to simulate the vacuum of space), some of the contained moisture froze in the tubes. The amount of ice was tiny, but it was enough to affect the way the tubes responded to the vibration and thus prevent them from breaking.
An equally small defect in this Christmas can mean total disaster.
Of course, spaceflight is risky. In the words of General Samuel C. Phillips, director of the Apollo program, "You will not be able to board a large rocket for several years without any risk involved." But in several vital aspects the next flight involves risks of an order entirely new, totally different in scale from all previous manned flights.
The first risk is the absolute dependence of astronauts – with no possibility of support or rescue – on the spacecraft's engine that they will fire when they approach the Moon to orbit and 10 orbits later to orbit. Of course back to Earth.
Another totally new danger is the time it will take to bring the crew back to Earth in an emergency. In orbit of Earth, the astronauts are one or two hours of security, orbiting the Moon, they are between two and three days away.
A small defect in the oxygen supply of the cabin, or problems with temperature control that would lead to no more than an early landing of all previous flights could be fatal.
Finally, re-entry into Earth's atmosphere has to be achieved at a speed as fast as the return of Earth's orbit. Apollo Eight will have to reach a corridor of about 30 kilometers deep at 25,000 mph if it is to land safely. If it comes too strong, it will burn; if it comes not very strong, it will leave the atmosphere; and as the crew will have discarded all their oxygen reserves, they will die long before they can recover.
When raising her hair when this maneuver sounds, NASA officials do not consider it particularly dangerous. The long journey back from the Moon will leave plenty of time to compute the spacecraft's course and make the necessary adjustments. However, the margin of error is effectively zero.
Are all these entirely new risks justified at this stage? According to General Phillips, the next flight is a "normal progression" of the previous Apollo flight. But the fact that a completely different mission – testing the lunar landing module on Earth's soil – was originally scheduled, along with recent Russian success with unmanned aerial flights around the Moon, makes it look like a very desperate attempt to stop Russians another first.
In fact, the rearrangement of the program makes a lot of sense. The lunar module that should have been tested is not ready and have hoped that everything would be back for several months. The risks of a flight around the Moon had to be accepted at some stage and another Earth orbiting flight would have made little difference to them.
There has never been any question of testing in flight the Apollo spacecraft and the Saturn Five as comprehensively as a civilian aircraft is tested. That would probably involve hundreds of layoffs that, hundreds of millions of dollars at a time, are out of the question. Instead, NASA is relying on projects with large safety margins, very detailed soil tests, and planned missions so they can be shut down prematurely if necessary.
The spacecraft's vital engine, for example, has only three parts that are not duplicated; the fuel injector, the combustion chamber and the nozzle. If part fails, there is another to take. Some very important valves are quadrupled. The craft has also undergone one of the most elaborate test programs ever created by man. This included firing 157 explosive charges into the combustion chamber while the engine was running to see if the combustion process could be unstable.
The mission itself is planned with a series of "compromise points," where there is time to decide whether or not to continue with the next flight. But once compromised with a lunar orbit, the risks really begin to increase.
As careful as planning, testing, and ingenious design, accidents like broken tubes on the Saturn Five are about to happen. In Saturn Fine there are more than 5½ million pieces. Even though each one is so reliable that it fails only once in a million flights, there are so many of them that several failures are certain every time the rocket is used.
There are some accidents that no amount of testing or planning can avoid and the more complicated the equipment, the more likely they are. The odds of something going wrong can be called and certainly been called in Houston. My guess is no more than a guess is that there is a three-in-four chance that the mission will not go according to plan, and perhaps one in 10 that astronauts will not return to Earth alive.