Of a Fire on the Moon (9780553390629) (29 page)

In the course of this act, at an instant when the spaceship was not yet three-quarters of an inch off the ground, specific switches on the hold-down arms tripped loose a pneumatic system which gave power to surges of compressed gas which ran in pipes up the great height of the launching tower: the gas tripped the couplings of the five service bridges still connected to the rocket. Their umbilicals now detached, these arms pulled away as the ship began to rise. Six inches up, and loose from the pins, the stages of Apollo-Saturn climbed up the stories of the Mobile Launcher, climbed up on its self-created base of flame, up past the flying withdrawal of its bridges and its umbilicals. To clear the tower, to be free of any sudden gust of wind which might lash it sideways, a yaw maneuver, programmed into the rocket, was initiated one second after lift-off, and turned the nose a few degrees from the vertical further away from the tower. For the onlookers three and one-half miles away, the rocket appeared to waver, then stagger. In fact, it did. There was wind blowing, and the rocket had been designed not to fight wind (it was not stressed for that) but to give way to wind, to relinquish the trajectory it was on, and compute a new trajectory from the slightly different position where the gust had just left it. So separate commands kept issuing from the Instrument Unit at the top of Saturn, sometimes every half-second, and the motors kept responding with little spurts and sags of speed. The result was a series of lurches and bumps in the first few seconds. “Very rough,” said Collins afterward, “very busy.… It was steering like crazy. It was like a woman driving her car down a very narrow alleyway … She keeps jerking the wheel back and forth … a nervous, very nervous lady … I was glad when they called Tower Clear because it was nice to know there was no structure around when the thing was going through its little hiccups and jerks.” That was after eight seconds. At close to twelve seconds, the four outboard engines were swiveled through a few degrees, a pitch maneuver was initiated, and a roll. The roll would end in twenty seconds, the shift in pitch would continue for two minutes and twenty-five seconds, by which time the rocket would be climbing
no longer straight up, but rather at a reasonable angle close to twenty-five degrees from the horizontal, and would have already passed through the severest structural strains of its trip. The astronauts, lying on their backs, unable to see out the Command Module for the first few minutes with the heat shield covering their windows like a blanket, would feel this dynamic pressure at a minute and twenty seconds after lift-off, fifteen seconds after breaking through the sound barrier. Acceleration would continue, and as in a centrifuge or a mechanical whip, their bodyweight would go up to 2 G’s, 3 G’s, to close to four times their own weight, their eyes would feel a mean pressure, but 4 G’s was not intolerable for an astronaut—they were familiar with high-speed dives in test planes and gravity simulators. Besides they were lying on their backs—the blood would not drain from their heads. All this while, the noise of the rocket motors, if sounding like a prelude of apocalypse to the spectators on the ground, was no more than a quiet rumble in the sealed conical volume of the Command Module. If not for the five numbered Launch Vehicle Engine Lights on a dial before them, they could not know if a single motor went out; the volume of sound in the cabin was not high enough to distinguish the difference.

Indeed there was not that much in those moments for the astronauts to do. The first eleven and a half minutes would be spent in reaching up into an earth orbit. The firing of the motors, their cutoff, the guiding commands and the separation of the stages would take place as part of a sequence which had already been programmed into the Instrument Unit of the launch vehicle. The astronauts were effectively in automatic flight. They would have no need to touch a flight control unless something went wrong. Indeed their work in these early minutes was to watch the dials and so be on the alert for the first hint of any malfunction in a system or subsystem vital to this portion of the trip. Listen to how little is said by them through the first three minutes of flight. Of course they are flying on their backs and the weight of their intense acceleration lies like lead on their tongue.

In these three minutes from lift-off the rocket ship had accelerated from a rate of travel of a few inches a second to almost ten thousand feet a second, it was now forty-three miles high and seventy miles away and traveling at about one hundred miles a minute or six thousand miles an hour. It had burned half a million gallons of fuel weighing almost five million pounds and had already dispensed with its first stage, an object 138 feet long, and 63 feet wide at its fins, a short-lived stage which was more than three-quarters of its weight and half of its volume. Now, it was about to fire the ullage rocket or opening gun of the second stage. What speed, what acceleration, what onrush! Perhaps we must quit the rapidity of the process in order to discover how the speed is achieved.

Just as the Greeks could be confident they had discovered the secret of beauty because the aesthetic of their sculptors permitted no blemish to the skin, because their sculptors said in fact that the surface of marble was equal to the surface of skin, so classical physics remained simple because it did not try to deal with anything less than ideal form. Later, Western aesthetics was sufficiently ambitious to wish to discover the laws of beauty in skins with blemish and bodies with twisted limbs (and indeed would never quite succeed), just indeed as engineering could never prove simple and comprehensible to amateurs. At its best engineering was a judicious
mixture of physics and a man’s life-experience with machines: one insignificant dial on one bank of instruments was often the product of the acquired wisdom of a good engineer who had put in years of work reducing the deviations of an imperfect instrument of measure.

Any attempt to explain the mechanics of the flight of Apollo 11 in engineering terms is then near to impossible for one would be obliged to rewrite a set of extracts from technical manuals, and each manual would finally prove nothing but an extract from other more detailed manuals, which in turn would be summaries of the verbally transmittable and therefore less instinctive experience of veteran engineers. Yet, the pure physics of the flight was still simple, so simple and pleased with itself as a Greek statue.

The rocket rose because the forces which were pushing it up were larger than the forces which held it down. The thrust of its motors was greater than the heft of its bulk. So it rose upward, even as we can jump in the air for a moment because for just a moment the push in our legs up against our body is greater than our weight. Speak of potency!—the force of our legs immediately ceases; almost immediately we descend. While the rocket had no legs to propel it upward, it had rather a burning gas expelled from its rear, and this force did not cease. So the rocket continued to rise. In the beginning it did not rise very quickly. Seven million seven hundred thousand pounds pushed upward against six million five hundred thousand pounds of weight which pressed downward. The difference was therefore to be calculated at one million two hundred thousand. That was the same as saying that if the rocket had been mounted on wheels in order to travel down a level road (and so did not have to be lifted), one million two hundred thousand pounds would be pushing the same six million five hundred thousand pounds of rocket. It can be remarked in anticipation that as this force continued to push, the rocket would begin to go faster. Its velocity would increase at an even rate if the push remained the same and the weight remained the same. If at the end of a second, its measured speed was about what it should be—five
feet a second—it would reach fifty feet a second after ten seconds, and one hundred feet a second after twenty. The reason was not complex. The push did not diminish. Therefore the rocket would go five feet faster every second than the second just before. After two seconds it would be going at ten feet a second because five feet a second would have been added in that second interval of measure to the first five feet a second. After three seconds, fifteen feet a second would be its speed. The velocity would increase five feet a second, every second, so long as the push remained steady on that rocket rolling on wheels down that level road. At the end of seventeen and a half minutes the rocket we have used for an imaginary model would be moving at an imaginary speed of a mile every second.

Yet that hypothetical rocket is still traveling at a much slower rate than Apollo-Saturn. When Apollo-Saturn went into orbit one hundred miles up and fifteen hundred miles out, not twelve minutes were gone, yet it was traveling at five miles a second or eighteen thousand miles an hour.

The explanation is agreeable to a liberal mentality, for it suggests that expenditure is power. The greatest weight in the rocket is fuel, and the fuel is being consumed. The rocket loses weight at a rate as immense as thirty-five hundred gallons of fuel each second. Somewhere about thirty-five thousand pounds of weight vanish in the same interval, which comes out by calculation as close to two million pounds a minute. At the end of a minute, seven million seven hundred thousand pounds are pushing not six and a half million pounds but four and a half million. Thus, the ship is accelerating more rapidly each instant. Its speed of increase now would be not five feet a second but more than twenty. Since the engines, however, also increase their effectiveness as the rocket takes on high altitude and the near-vacuum of the thinning atmosphere offers less resistance to the fires of the exhaust, so at the end of two minutes and fifteen seconds of flight the thrust has actually reached over nine million pounds and is then pushing only a little more than two and a half million pounds. Now the rocket is being
propelled by a force almost four times as great as itself: so its acceleration would be not five feet a second as at lift-off nor twenty feet a second at the end of a minute, but more like ninety feet a second.

Apollo-Saturn however does not travel that fast for long. It takes two minutes and fifteen seconds to reach such acceleration, and then the center motor is shut down. The thrust reduces to seven million two hundred thousand pounds from the four continuing engines. Twenty-five seconds later the outboard motors are cut off. A few more seconds, and the first stage is released. The rocket begins to travel on the motors of the second stage, and these next five engines are not nearly so powerful. Never again will Apollo-Saturn pick up speed so quickly.

It hardly matters. The more modest acceleration of the second stage is added onto the high velocities already attained by the first stage. Apollo-Saturn will increase its speed to four and a half miles a second, and will be altogether out of sight when the second stage is discarded after nine minutes and twelve seconds of flight. Stripped of its first stage and its second stage, powered now by but a single motor which develops hardly one part in forty of the force the first engines developed to get off the ground, the ship now weighs only four hundred thousand pounds, or a sixteenth of its original weight. Drastically reduced, it is still in need of a little more speed, and the third stage will give it that, the third stage will take it up to something near five miles a second, or eighteen thousand miles an hour. To reach the moon it will yet have to go faster, it will have to reach twenty-five thousand miles an hour to escape the force of the earth’s gravity. But that is a subsequent step. Now the ship is wheeling through the near-heavens. A little bit more than one hundred miles overhead, it proceeds to circumnavigate the earth every hour and twenty-eight minutes. Its weight, fuel of the third stage partially consumed, is now down to three hundred thousand pounds and it is in that magical condition of defiance to gravity which is known as orbit.

But what exactly is this condition? What is orbit? How can a rocket continue to circle around the earth if its motors have been shut down? Why indeed is earth orbit even required? Why don’t the astronauts head directly to the moon?

If the last question is the first to be answered, that is probably because the answer is at hand. The excitement of the first twelve minutes of flight has been so great, so much has happened, so many parts of the ship have fallen off, and so many conditions have altered so rapidly that the astronauts, much like the men at Mission Control, need an hour or more to collect themselves, say farewell to earth, check over the conditions of their ship of space after these violent, hurtling, and most abrupt changes, and give us time to learn about the nature of orbit and what in fact is the very appearance of the ship.

So, despite all honors given to physics, the line of explanation may be obliged to pass again through engineering long enough to offer one last description of Apollo-Saturn as she sat on the pad. Already not twelve minutes in the air, she is of different appearance, and soon will be unrecognizable. So it is appropriate to offer a final opportunity to the reader to begin to glimpse the structure of that remarkable mechanical white whale which rose into the air at Cape Kennedy and soon disappeared.