The fiery explosion of a Titan rocket at Vandenberg Air Force Base April 18, less than four months after the loss of the space shuttle Challenger, came as no surprise to many of the pioneers who helped give birth to the space program.
“It’s amazing it took so long to happen,” said one.
“People have forgotten the history of the space program,” said John W. Daily, associate professor of mechanical engineering at the University of California, Berkeley. “Right up to the start of the Mercury program, we had failure after failure. I mean all the time. These systems are really complex, and a lot of things can go wrong. We’ve really been riding a lucky streak, and it may be coming home to roost.”
The fact that disaster struck both the Titan and the shuttle is an interesting historical twist because they are similar vehicles, designed to make the most of what was available, hybrids called upon to do great things.
And both owe part of their origin to a fierce battle waged among some of the keenest minds in the world over which course to follow in the early development of the nation’s missile program.
The nuclear age was in its infancy, and a mushroom cloud over Japan had altered the course of human history. In laboratories throughout the land scientists and engineers fought among themselves about how best to proceed on a course that would carry the world into the age of the Intercontinental Ballistic Missile.
The struggle divided quickly into two camps over a most fundamental question: What kind of fuel should the rockets burn?
Wernher von Braun, the German genius who had such great success in the development of Germany’s V2 rocket, had emerged as the leader of the U.S. effort. History had convinced Von Braun that only liquid-fueled rockets like the V2 could be counted on to do the job.
But liquid rockets required constant attention and were far more complex than the emerging technology of solid-fueled rockets. The solids were like firecrackers, always ready to go.
All you had to do was “press the button, and it goes,” recalled Melvin Gerstein, professor of mechanical engineering at USC and one of the pioneer’s in America’s rocketry program.
The question then was simple. Should the nation go forward with the proven technology of liquid-fueled rockets, despite their problems, or should it proceed with the new concept of solids?
It turned out that the debate was so difficult to resolve that the decision was made to develop both technologies at the same time, Gerstein recalled. The Minuteman missile would see if the proponents of solids were right. And the Titan would prove if the advocates of liquids were correct.
The liquids won the first round, with the Titans giving the nation an awesome arsenal of long-range ballistic missiles. The solids won the second round as the Minuteman moved in to replace Titans in silos across the heartland of the nation.
But in the end, the two technologies came together to move the United States into the era of the mighty Titan 34-D, powerful enough to launch an object as heavy as a large truck. They also made the space shuttle possible.
The two vehicles are similar in that both use liquid-fueled motors as their primary propulsion units, and both use strapped-on solid-fuel rockets to help break the bonds of Earth in the first stage of ascent.
And now, both represent the shaken confidence of a nation that not so long ago thought it was knocking on the door of the universe.
Source of Failure
The bitter irony of the tragedy of the Challenger on Jan. 28 and the explosion of a Titan 34-D earlier this month is that they came back-to-back, both apparently caused by the failure of the part of each system that had been considered most reliable, a solid rocket.
The disasters are similar in many ways, as are the systems. Both systems combined the best of different technologies to move the United States more quickly--and more cheaply--into the space age than would have been possible if the nation had chosen to develop the best, rather than the most expeditious, technology, Gerstein said.
Both experienced a relatively long history of success before disaster taught them humility.
But to experts who were there in the beginning, the greatest irony is that it took so long to happen.
Men like Gerstein recall that the early days were punctuated frequently with failures. Most of the early rockets either did not fire at all, or got a little way up and, to the consternation of people on the ground, turned around and came right back down.
“We used to call them pad-to-pad missiles,” Gerstein quipped.
It is “phenomenal,” he said, that the nation has come so far so fast.
The development of solid rockets began so primitively that the propellent, which must meet exacting specifications, was prepared in standard mixers used to make bread. Sometimes the mixers blew up.
Bread mixers were fine in the early days, when the rockets were small, but as the program became more successful the rockets got bigger and bigger. And fuel fabrication became a real art.
“Structural integrity (of the propellent) is extremely important,” Gerstein said.
The exact cause of the explosion at Vandenberg is still under investigation, but sources familiar with the probe have told The Times that failure of the propellent in one of the solids is the leading suspect. If the propellent burned too rapidly, for whatever reason, the pressures within the rocket could have increased almost instantaneously, causing the explosion, according to one source who spoke on condition he not to be named.
The $65-million rocket was carrying a classified payload, believed to be some kind of spy satellite.
The solid rockets on the side of the Titan 34-D are more than 90 feet tall and 10 feet in diameter. In order to work, the propellent must burn at exactly the right rate and it must withstand the enormous pressures of liftoff, when the rockets generate 2.1 million pounds of thrust. The propellent burns through the center of the entire rocket simultaneously, generating gas that is forced through the nozzle to give the rocket its lift.
The rate of burn is determined by the texture of the propellent--which is about the same as a pencil eraser--its composition, and the shape and size of the hole through its core where the burning occurs.
The “reactive rate” of the aluminum and oxidizer propellent, meaning the gas that the burning generates, is determined by the nature of the propellent and the amount of surface within the rocket that is exposed to burning.
It is a simple process in theory, because if the propellent burns the way it is supposed to it will generate enough thrust to power the rocket, but not so much internal pressure that the rocket will explode.
But success depends on mixing huge quantities of propellent in exactly the right amounts, to exactly the right texture, and with absolutely no flaws.
“Let’s say there is a crack somewhere in the propellent,” Gerstein said. “Suddenly the surface area (exposed to the burn) changes, so you are creating a lot more gas. The thing blows up. It’s a pressure explosion from too fast of a reaction inside the rocket.”
The same thing would happen if the propellent had a bubble.
Bubbles can occur when the propellent is poured into any of the five sections that are bolted together to form the solids on the Titan 34-D. Cracks can occur even after the rocket has been assembled.
Twisting a pencil eraser back and forth between his fingers, Gerstein noted that the propellent “must be able to take tremendous acceleration pressures” during liftoff. “If it’s not exactly right, it can crack.”
David Altman, retired vice president of United Technologies Corp.'s Chemical Systems Division in Sunnyvale, which built the solids for the Titan, believes that the sheer size of the huge rockets mitigates against such problems, however. Altman believes the rocket is so big that a single bubble, for example, is unlikely to raise the internal pressures to the point of explosion.
One fundamental drawback of the solids is that there is no way to test them fully before the flight to see if they are going to work.
“You can’t scratch a little off the surface of the propellent and test it,” Gerstein said, because that would change the surface and the reactivity of the rocket, and it would not tell if the propellent is cracked or has bubbles.
“There is no way of non-destructively testing a solid rocket,” he added.
Solid rockets deteriorate with age, so every now and then the Air Force hauls a Minuteman out of its silo in the Midwest and trucks it to Vandenberg. The crew comes with it, and the rocket is placed in one of the silos at the sprawling base. The crew remains on alert until the order to fire is given. The result tests both the crew and the rocket.
After the firing, the Air Force can determine how well the missile performed. If it shows signs of deterioration, other missiles of the same vintage must be replaced.
Titan missiles are used sparingly now, having been all but replaced by the Minuteman--as nuclear weapons--and the space shuttle--for satellite delivery--but not before generating an illustrious history of delivering heavy payloads to space. Although the first of the Titans were liquid-fueled only, the system became a grab-bag of components from which various parts could be assembled to meet different needs. It became the Volkswagen van of the space age.
By the mid-1960s, Titans were in missile silos across the United States, constituting the first true intercontinental delivery system, although fortunately no one had to prove whether they would work as planned.
They did work, however, on a number of scientific missions.
Titans were used for the Gemini launches, and on March 23, 1965, a Titan II blasted astronauts Virgil Grissom and John Young into space for the first mission of the Gemini spacecraft, a milestone in the U.S. space program.
That was purely a liquid-fueled Titan, but another generation, called Titan III, was already on the way. Since the most inefficient period of spaceflight, from the standpoint of energy, occurs at liftoff, scientists wanted to develop a way of launching the Titan and then turning on its powerful liquid engines after it was far above the Earth. To do that, they worked out a means of literally bolting on two solid rockets that could blast the craft off the pad.
That meant that about two minutes into the flight, when the craft had reached an altitude of about 29 miles, the liquid engines could take over and the solids could be blown free with explosive charges.
That also marked a major turning point for the space program.
The huge solid rockets gave the old workhorse Titan a new life. Titan IIIs were used to launch unmanned Viking spacecraft to Mars as well as the intrepid Voyagers. It also proved that the combination of solid- and liquid-fueled rockets could be used for the space shuttle.
While engineers consider the record of the Titan remarkably good, there have been some notable failures. Four Titans have been lost in 136 launches, ironically in two sets of back-to-back failures, two in 1959 and two since last August. Another blew up in an Arkansas silo in 1980, killing one Air Force crewman and injuring 21 others. Congress later determined that there had been 125 less serious incidents at 54 Titan sites over a four-year period.
Many people who lived near the Arkansas silo complained bitterly about toxic fumes from the blast, and the issue became a source of strong resentment from many residents. But with the exception of the Arkansas tragedy, most incidents involving Titans have attracted little attention.
A Titan 34-D believed to be carrying a sophisticated photographic spy satellite had to be destroyed last August when one of its liquid engines shut down when the missile was well over the Pacific. Although that failure has been blamed on a fuel pump, it is still not clear exactly what caused the pump to fail.
“They have three different possible causes,” said one source who spoke only on the condition that his name not be used. “They don’t know what caused it.”
The incident attracted little notice, however, partly because it happened when the rocket was miles from shore, and partly because it preceded the explosion of the Challenger.
The most recent failure made headlines around the world because it illustrated the plight of the U.S. space program and brought the Titan program to a standstill.
But space experts believe that no matter how successful the program eventually becomes, it will always be accompanied by occasional failures.
That is because the program will always be somewhat experimental.
“When you have no misfires, you build the next generation,” Gerstein said.
Lee Dye reported from Los Angeles and Mark A. Stein from Sunnyvale.