If it is using a peripheral device, the calculating circuits are not used. In a batch process, if the computer is doing a calculation, the input and output devices are idle. This sort of processing, in which the entire program must be loaded into memory and data must be available in discrete form, is called "batch." Over time, computer systems were changed to make them more efficient than batch computing allowed. A typical ground computer of the early 1960s, when the first computers flew on manned spacecraft, would process programs one at a time, right after each other. On-board computers and ground-based computers store data and do their calculations in the same way, but they handle processes and input and output differently. As missions change and become more complex, using software to adjust for the changes is much cheaper and faster than changing the hardware. Increased versatility is the result of the power of software to change the abilities of the computer in which it resides and, by extension, the hardware that it controls. This transition has made it possible for current spacecraft to be more versatile. In fact, both carry many computers, not just one. Yet now, the manned Shuttle and the unmanned Galileo spacecraft simply could not function without computers. Fifteen years of unmanned earth orbital and deep space missions were carried out without general-purpose computers on board. However, Mercury, the first manned spacecraft, did not carry a computer. Today they are used for guidance and navigation functions such as rendezvous, re-entry, and mid-course corrections, as well as for system management functions, data formatting, and attitude control. Computers are an integral part of all current spacecraft. Thus, the impact of NASA on computing differs in extent as a result of the separate requirements for each field of computer use, which is one reason why the three fields are considered in separate parts of this volume. These three areas have quite different requirements, and the nature of the tasks assigned to them resulted in varying types of computers and software. NASA uses computers on the ground and in manned and unmanned spacecraft. Any ways in which NASA contributed to the development of computer techniques were side effects of specific requirements. Thus generalizations cannot be made, other than that there was no conscious attempt on the part of NASA in its flight programs to improve the technology of computing. This was especially true on unmanned spacecraft, because the absence of human pilots allowed greater chances to be taken. However, in other cases, some use of nearly leading edge technology existed, mostly for ground systems, but occasionally when no extensively proven equipment or techniques were adequate in a flight situation. Thus, the agency often found itself in the position of having to seek computer solutions that were behind the state of the art by flight time. In most cases, because of the need for reliability and safety, NASA deliberately sought to use proven equipment and techniques. Actually, the situation is not so straightforward. Since NASA is well known as an extensive user of computers- mainly because spaceflight would not be possible without them- there is a common sense that at least part of the reason for the rapid growth and innovation in the computer industry is that NASA has served as a main driver due to its requirements. ![]() Where once the only solution was the large, centralized computing center, distributed computers now share the load. Where there were no computers, such as on aircraft or in automobiles, computers now ride along. Where there were giant computers, small computers now do similar tasks. These remarkable changes mirror developments in the commercial arena. Within another 10 years the giant groundbased mainframe would be supplanted by clusters of medium-sized computers in spaceflight operations, and the single on-board computer would be replaced by multiple machines. ![]() Moreover, to the amazement of anyone who knew the computer field in 1958, NASA also flew computers in orbit, to the moon, and to Mars, the latter machines running unattended for months on end. Within a decade and a half, NASA had one of the world's largest collections of such monster computers, scattered in each of its centers. Expensive to purchase and operate, the giant computer needed a small army of technicians in constant attendance to keep it running. When the National Aeronautics and Space Administration came into existence in 1958, the stereotypical computer was the "UNIVAC," a collection of spinning tape drives, noisy printers, and featureless boxes, filling a house-sized room. ![]() Computers in Spaceflight: The NASAExperienceĬomputing and Spaceflight: AnIntroduction
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