Ch7-1

Computers in Spaceflight: The NASA Experience

- Chapter Seven -

The Evolution of Automated Launch Processing

[208] Rocket technology is both old and new. Since the Chinese first started shooting off fireworks a millennium ago, the sight of a rocket streaking ever faster skyward, a comet's tail of fire behind, has excited even those unimpressed with machines. Fireworks rockets, and, later, military bombardment rockets through the first three decades of this century, shared the same components: casing, fuel, and payload. Construction was complete when the gunpowder fuel was loaded in the casing, warhead affixed, and a fuse planted the base. Such rockets could be stored without maintenance and fired with little preparation, needing only to assure that the fuse was still attached. The difficulty came in the area of guidance. A set of fins or a balancing stick passively guided the early rockets. Frequently they would turn on the men who launched them or shoot horizontally over the heads of fireworks watchers. Thus, the old technology of preparing rockets for flight consisted of keeping them dry, aiming them carefully, and lighting the fuse.

In Germany during the late 1930s the new technology of rockets began to mature. Increased interest in rocketry developed in Europe and the United States after World War I. Rocket societies flourished in England, Germany, and the United States. Robert Goddard flew a liquid propellant rocket, the first of its kind, in Massachusetts in 1926. Liquid fuels, with their higher specific impulse and thrust potential, soon replaced solid fuels as the primary area of propulsion research. Shortly after Hitler came to power, the German army established a rocket development program that led to the liquid-propellant A-4 (popularly known as the V-2). A-4 rockets far exceeded the capabilities of previous ones, terrorizing the populations of London and Antwerp in the latter stages of World War II. Over 14 meters tall and weighing over 12,000 kilograms, an A-4 carried nearly 1,000 kilograms of explosive payload up to 400 kilometers. Its guidance system was a radio beam-rider type with an electronic analog computer controlling vanes in the exhaust and elevons on the fins. If wind deflection caused the rocket to veer horizontally off course, the analog computer would calculate corrections and activate the vanes. Complex plumbing and turbopumps were needed to feed the engine with fuel. Experience gained in nearly 2,000 expensive failures led German technicians working on the A-4 to develop techniques of testing the many components of the rocket during manufacture and before committing it to flight. For example, the guidance system was tested at the factory by an electronic analog computer that simulated the flight of the rocket so that the system's reactions could be observed¹. On the launching pad, engineers could test various moving parts of the vehicle by activating them using actual physical connections to the firing room.

German rocket scientists who came to the United States after World War II brought this new technology with them. Eventually based in Huntsville, Alabama, at the Army's Redstone Arsenal, they [209] conceived an increasingly sophisticated series of rockets: Redstone, Jupiter, Juno, and Saturn. Concurrently, the Air Force chartered the Atlas, Titan, and Thor ballistic missiles. During the 1950s, each of these vehicles was developed in programs marred by frequent flight failures. Actual numbers and the complexity of components grew by several factors over the A-4. The new devices and their failures led to more testing, both at the factory and before launch. The concept of a "countdown," during which each flight-critical component of the vehicle is systematically checked, reached a high level of efficiency.

As the 1960s began, most rockets and their payloads were still being checked out by discrete connections between the components and a test panel. When the countdown reached an advanced stage, particularly after fueling, the test engineers were cloistered in a block-house. Through cables from the rocket to the blockhouse, the engineers could monitor the status of various components and activate tests. An engineer would flip a switch, and something would happen, either on a dial or a strip chart, that he could actually see and interpret. When the first Saturn I rockets were launched and the Mercury spacecraft made their appearance, both in 1961, it became obvious that the level of complexity of both vehicles and payloads had reached the point where manual test methods were inadequate. Individual NASA engineers and managers on different programs began to evaluate the possibility of automating some of the checkout procedures using digital computers. Eventually, this led to the Shuttle's fully automated Launch Processing System.

The heart of the Shuttle is its computer system. Without it, no component of the spacecraft could be adequately tested or monitored. When a Shuttle is being refurbished after a flight in the Kennedy Space Center's orbiter Processing Facility, a large double hangar near the landing runway, the spacecraft's computers are connected to checkout and launch computers located in a firing room in the Launch Control Center. When moved to the Vehicle Assembly Building for mating with its fuel tank and solid propellant boosters, the Shuttle is reconnected to the firing room. After being transported to the pad, the final preparations are also controlled from the firing room. Finally, countdown and launch are executed from the same firing room. This scenario came after two decades of evolution, during which the role of computers became dominant both on board spacecraft and in launch processing. The integrated techniques exemplified in the Shuttle Launch Processing System developed from separate automated systems devised for vehicle checkout, spacecraft checkout, and telemetry monitoring. Important in the evolution is the part played by on-board computers. The journey toward full automation got great impetus from the Saturn and Apollo programs.

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FIGURE 7-1. Launch processing facilities at the Kennedy Space Center: the Shuttle Orbiter Processing Facility (left), the Vehicle Assembly Building (center), and the Launch Control Center (right). (NASA 116-KSC 377C-82/41)