ALTHOUGH ROCKETS BURNING BLACK POWDER HAD existed for centuries, only in 1926 did Robert H. Goddard, an American physicist and rocket developer, launch the first known liquid – propellant rocket. It then took the United States until the mid – 1950s to begin spending significant sums on rocket development. The country soon (January 1958) began launching satellites, and by the end of the cold war (1989-91), the United States had developed extraordinarily sophisticated and powerful missiles and launch vehicles. From the Atlas to the Space Shuttle, these boosters placed an enormous number of satellites and spacecraft into orbits or trajectories that enabled them to greatly expand our understanding of Earth and its universe and to carry voices and images from across the seas into the American living room almost instantaneously. What allowed the United States to proceed so quickly from the comparatively primitive rocket technology of 1955 to almost routine access to space in the 1980s?
This book provides answers to that question and explains the evolution of rocket technology from Goddard’s innovative but not fully successful rockets to the impressive but sometimes problematic technology of the Space Shuttle. Although propulsion technology has often challenged the skills and knowledge of its developers, by and large, its achievements have been astonishing.
This combination of complexity and sophistication caused some inventive soul to coin the term “rocket science." But often in the history of rocketry, so-called rocket scientists ran up against problems they could not fully understand. To solve such problems, they often had to resort to trial-and-error procedures. Even as understanding of many problems continually grew, so did the size and performance of rockets. Each increase in scale posed new problems. It turns out that rocketry is as much art as science. As such, it best fits the definitions of engineering (not science) that students of technology, including Edwin Layton, Walter Vincenti, and Eugene Ferguson, have provided. (Besides engineering as art, they have discussed the discipline’s emphasis on doing rather than just knowing, on artifact design instead of understanding, and on making decisions about such design in a context of imperfect knowledge.)1
In the light of their findings and the details of rocket development discussed in the present book, I will argue that designers and developers of missiles and space-launch vehicles were fundamentally engineers, not scientists, even though some of them were trained
as scientists. For instance, Ronald L. Simmons received a B. A. in chemistry from the University of Kansas in 1952 and worked for 33 years as a propulsion and explosive chemist at Hercules Powder 2 Company, a year with Rocketdyne, and 13 years for the U. S. Navy, Introduction contributing to upper stages for Polaris, Minuteman, and other missiles. He considered himself to be a chemist and as such, a scientist, but admitted that he had done “a lot of engineering." Unconsciously underlining points made about engineering by Vincenti and Layton, he added that it was “amazing how much we don’t know or understand, yet we launch large rockets routinely. . . and successfully." He believed that we understood enough “to be successful. . . yet may not understand why."2
This is not to suggest any lack of professional expertise on the part of rocket engineers. Rocketry remains perplexingly complex. In the early years, engineers’ knowledge of how various components and systems interacted in missiles and launch vehicles was necessarily limited. But quickly data, theory, and technical literature grew to provide them a huge repository of information to draw upon. Some processes nevertheless remained only partially understood. But when problems occur, as they still do, the fund of knowledge is great, permitting designers and developers to focus their efforts and bring their knowledge to bear on specific kinds of solutions.
Yet often there are no clear answers in the existing literature. Engineers must try out likely solutions until one proves to be effective, whether sooner or later. In the chapters that follow, I sometimes refer to this approach as cut-and-try (cutting metal and trying it out in a rocket) or trial-and-error. Neither term implies that practitioners were experimenting blindly. They brought their knowledge and available literature (including science) to bear on the problem, measured the results as far as possible, and made informed decisions. Limited funding and rigorous schedules often restricted this process. Given these circumstances, it is remarkable that they succeeded as often and well as they did. Not rocket science, this cut-and-try methodology was part of a highly effective engineering culture.
This book is about launch-vehicle technology. Because much of it originated in missile development, there is much discussion of missiles. These missiles launch in similar fashion to launch vehicles. But they follow a ballistic path to locations on Earth rather than somewhere in space. Their payloads are warheads rather than satellites or spacecraft. Especially in the discipline of propulsion, they have employed similar technology to that used in launch vehicles. Many launch vehicles, indeed, have been converted missiles or have used stages borrowed from missiles.
Both types of rockets use a variety of technologies, but this book focuses on propulsion as arguably more fundamental than such other fields as structures and guidance/control. The book starts with Goddard and his Romanian-German rival Hermann Oberth. It follows the development of technology used on U. S. launch vehicles through the end of the cold war. Because the German V-2 influenced American technology and was a (not the) starting place for the Saturn launch vehicles in particular, there is a section on the German World War II missile and its developers, many of whom, under Wernher von Braun’s leadership, came to this country and worked on the Saturns.
Chapters 1 and 2 provide an overview of missile and rocket development to furnish a context for the technical chapters that follow. Chapters 3 through 7 then cover the four principal types of chemical propulsion used in the missiles and launch vehicles covered in chapters 1 and 2. Chapter 8 offers some general conclusions about the process of rocket engineering as well as an epilogue pointing to major developments that occurred after the book ends at the conclusion of the cold war. (There is no discussion of attempts at harnessing nuclear [and other nonchemical types of] propulsion— sometimes used in spacecraft—because funding restraints and technical risks precluded their use in production missiles and launch vehicles.)3
The book stops about 1991 because after the cold war ended, development of launch vehicles entered a new era. Funding became much more restricted, and technology began to be borrowed from the Russians, who had followed a separate path to launch-vehicle development during the Soviet era.
Most readers of this book presumably have watched launches of the Space Shuttle and other space-launch vehicles on television, but maybe a discussion of the fundamentals of rocketry will be useful to some. Missiles and launch vehicles lift off through the thrust produced by burning propellants (fuel and oxidizer). The combustion produces expanding, mostly gaseous exhaust products that a nozzle with a narrow throat and exit cone cause to accelerate, adding to the thrust. Nozzles do not work ideally at all altitudes because of changing atmospheric pressure. Thus, exit cones require different angles at low and higher altitudes for optimum performance. For this reason, rockets typically use more than one stage both to allow exit cones to be designed for different altitudes and to reduce the amount of weight each succeeding stage must accelerate to the required speed for the mission in question. As one stage uses up its propellants, it drops away and succeeding stages ignite and assume
the propulsion task, each having less weight to accelerate while taking advantage of the velocity already achieved.
Most propellants use an ignition device to start combustion, but so-called hypergolic propellants ignite on contact and do not need an igniter. Such propellants usually have less propulsive power than such nonhypergolic fuels and oxidizers as the extremely cold (cryogenic) liquid hydrogen and liquid oxygen. But they also require less special handling than cryogenics, which will boil off if not loaded shortly before launch. Hypergolics can be stored for comparatively long periods in propellant tanks and launched almost instantly. This provided a great advantage for missiles and for launches that had only narrow periods of time in which to be launched to line up with an object in space that was moving in relation to Earth.
Solid-propellant motors also allowed rapid launches. They were simpler than and usually not as heavy as liquid-propellant engines. Solids did not need tanks to hold the propellants, high pressure or pumps to deliver the propellant to the combustion chamber, or extravagant plumbing to convey the liquids. Normally, rocket firms loaded the solid propellant in a case made of thin metal or composite material. Insulation between the propellant and the case plus an internal cavity in the middle of the propellant protected the case from the heat of combustion, the propellant burning from the cavity outward so that the propellant lay between the burning surface and the insulation. The design of the internal cavity provided optimal thrust for each mission, with the extent of the surface facing the cavity determining the amount of thrust. Different designs provided varying thrust-time curves. Solid propellants did pose the problem that they could not easily accommodate stopping and restarting of combustion, as liquids could do by using valves. Consequently, solids usually served in initial stages (called stage zero) to provide large increments of thrust for earth-escape, or in upper stages. For most of the period of this book, the Scout launch vehicle was unique in being a fully solid-propellant vehicle.
Liquid propellants typically propelled the core stages of launch vehicles, as in the Atlas, Titan, Delta, and Space Shuttle. Upper stages needing to be stopped and restarted in orbit (so they could insert satellites and spacecraft into specific orbits or trajectories after coasting) also used liquid propellants, as did stages needing high performance. But in liquid-propellant engines, the injection of fuels and oxidizers into combustion chambers remained problematic in almost every new design or upscaling of an old design. Mixing the two types of propellants in optimal proportions often produced instabilities that could damage or destroy a combustion chamber.
This severe problem remained only partly understood, and although engineers usually could find a solution, doing so often took much trial and error in new or scaled-up configurations. Solid propellants were by no means immune to combustion instability, although the problems they faced were somewhat different from those occurring in liquid-propellant engines. And often, by the time solid-propellant instabilities were discovered, design was so far along that it became prohibitively expensive to fix the problem unless it was especially severe.
Besides propulsion, missiles and launch vehicles required structures strong enough to withstand high dynamic pressures during launch yet light enough to be lifted into space efficiently; aerodynamically effective shapes (minimizing drag and aerodynamic heating); materials that could tolerate aerothermodynamic loads and heating from combustion; and guidance/control systems that provide steering through a variety of mechanisms ranging from vanes, canards, movable fins, vernier (auxiliary) and attitude-control rockets, and fluids injected into the exhaust stream, to gimballed engines or nozzles.4
With these basic issues to deal with, how did the United States get involved in developing missiles and rockets on a large scale? What sorts of problems did developers need to overcome to permit a rapid advance in missile and launch-vehicle technology? The chapters that follow answer these and other questions, but maybe a brief summary of how the process worked will guide the reader through a rather technical series of projects and developments.
Launch-vehicle technology emerged from the development and production of missiles to counter a perceived threat by the Soviet Union. In this environment, heavy cold-war expenditures to develop the missiles essentially fueled progress. In addition, many other factors (not always obvious to contemporaries) helped further the process. No short list of references documents the complex development discussed in this book, but one element of the effort was an innovative and flexible engineering culture that brought together a variety of talents and disciplines in a large number of organizations spanning the nation. People from different disciplines joined together in cross-organizational teams to solve both unanticipated and expected problems.
Likewise, supporting problem solving and innovation was a gradually developing network that shared data among projects. Although military services, agencies, and firms often competed for roles and missions or contracts, the movement of people among the competing entities, actual cooperation, professional organizations, partner-
ing, federal intellectual-property arrangements, and umbrella organizations such as the Chemical Propulsion Information Agency promoted technology transfers of importance to rocketry. At the 6 same time, the competition spurred development through the urge Introduction to outperform rivals.
A further factor helping to integrate development and keep it on schedule (more or less) consisted of numerous key managers and management systems. In some instances, managers served as heterogeneous engineers, managing the social as well as the technical aspects of missile and launch-vehicle development, stimulating support for rocketry in general from Congress, the administration, and the Department of Defense. By creating this support, they practiced what some scholars have defined as social construction of the technologies in question. At times, managers engaged in both technical direction and heterogeneous engineering, while in other cases technical managers and heterogeneous engineers were separate individuals.5
Although rocket technology is complex, I have tried to present it in a way that will be comprehensible to the general reader. The primary audience for this book will tend to be scholars interested in the history of technology or propulsion engineers seeking an overview of the history of their discipline. I have included many examples of problems encountered in the development of missiles and launch vehicles and explained, as far as I could determine, the way they were resolved. Even though I have not written in the technically rigorous language of engineering (or in some cases because of that), I hope my discussion of the evolution of propulsion technology will engage the interest of everyone from rocket enthusiasts to technical sophisticates.
SPACE-LAUNCH – VEHICLE TECHNOLOGY
evolved from the development of early rockets and missiles. The earliest of these rockets that led to work on launch vehicles themselves was Robert Goddard’s in 1926, generally regarded as the first
liquid-propellant rocket to fly. But it was not until the mid-1950s that significant progress on large missiles occurred in the United States, greatly stimulated by the cold war between the United States and the Soviet Union. (Of course, the Germans had already developed the A-4 [V-2] in the 1940s, and the United States launched a series of reconstructed German V-2s in the New Mexico desert from 1946 to 1952.) Missile development was especially important in furthering the development of launch vehicles because many missiles became, with adaptations, actual stages for launch vehicles. In other cases, engines or other components for missiles became the bases for those on launch vehicles. By 1966 large, powerful, and comparatively sophisticated launch vehicles had already evolved from work on early missiles and rockets.