Automating Launch Operations

A participant in the U.S. space program likened the Apollo-Saturn to the ancient Tower of Babel. The moon rocket might have duplicated the chaos that marked that earlier dream. In a manual checkout of the Apollo- Saturn's many systems, hundreds of technicians would have swarmed on and around the space vehicle. Their reports flowing into a central control room would have indeed been a babel. Automated checkout equipment avoided this confusion. The Saturn ground computer checkout system tested 2,700 Saturn functions and its computers monitored 150,000 signals per minute. Acceptance checkout equipment accomplished a similar task for the Apollo spacecraft. Wernher von Braun, after the first successful flight of an Apollo-Saturn V, credited success "to our automatic checkout procedure."! The story of Apollo is a study in automation.

Origins of Saturn Automated Checkout

Although automation has no precise meaning that is generally accepted in technical circles, there was considerable automation - however defined in the missile programs of the 1950s. Engineers employed pressure gauges, temperature gauges, frequency detectors, and other devices to passively sequence a series of events. Using relay logic, if event A occurred, then event B took place, and so on. Interlocking circuitry and relay logic allowed ground support equipment to control portions of a countdown [for the SA-1 countdown, see chapter 3-6]. In this chapter, the term automation will imply the use of digital computers and associated equipment.

In checking out the first Saturns, hundreds of control room switches sent signals over electrical lines to test points on the rocket. The launch vehicle responses, returning over the same wires or radio telemetry links, registered on strip charts and meters. The launch team then evaluated the test data. Automation began to change this procedure when, in 1960, Marshall engineers decided to design a test capability for Saturn's digital guidance computer (its maiden flight would come on SA-5). The first, tentative steps were to parallel, not replace, manual checkout. Quality Division representatives sought a flexible program that could be expanded to include other tests as automation proved itself.2

In early September Debus asked to have the Launch Operations Directorate participate in automated checkout discussions. Before the end of the year two computer systems were under study at Marshall. The Reliability Assurance Laboratory was testing a Packard Bell 250 for factory acceptance checkout while the Guidance and Control Division and the Quality Division investigated the use of an RCA 110 for launch tests. The RCA 110 was among the first priority-interrupt computers on the market. This feature provided for the division of the computer program into several sections, each one having an assigned priority level. The priority interrupt allowed an engineer to switch immediately from one test to another during operations. On the RCA 110 there were eight available levels and the computer could switch to a higher priority test in 100 microseconds. As the early use of the 110 indicated trouble-free operations, it became the workhorse of the Saturn checkout at the Cape.3

Marshall's first automation plan, published in September 1961, asked the question: "Why automation?" The advantages were speed and accuracy. The author, Ludie Richard, noted that man is a poor test conductor. He cannot run thousands of tests with uniform precision, and he frequently fails to observe the results. Machines ensure standardized testing and an accurate recording of the responses. Further, an automated operation required only a fraction of the time used in a manual procedure. The time savings would permit more testing, an important factor to operations personnel, particularly just prior to launch. With automation Marshall could duplicate the exact conditions under which a failure had occurred. Data would be available at the point of failure to aid in trouble-shooting and fault isolation. Richard also listed some disadvantages. Automated checkout procedures would complicate the Saturn, although the problem could be minimized by designing the automated test system into the vehicle. Another drawback was a lack of user confidence in the system. Richard attributed this to poor planning, either in training the users or in faulty machine language. A long-range problem involved the operators' possible loss of familiarity with the launch vehicle. Automation might work so well that its users would lose their "feel" of the rocket, with a corresponding drop in their ability to meet a crisis.4

Richard's automation plan proposed to phase the RCA 110 into Cape operations with the SA-5 launch from LC-37. The blockhouse computer would parallel the launch complex circuitry so that operations could proceed manually if necessary. At first the RCA 110 would check the digital flight computer and monitor other electrical systems. It was hoped that by SA-111 (the first Saturn I flight after the ten R&D launches) equipment reliability and user confidence would permit a fully automated launch.5

Planning for automation accelerated during the following months as Marshall moved from the C-2 to the C-5 version of the advanced Saturn. The Saturn V's size and LC-39's greater distance - 4.8 kilometers -from launch control center to pad precluded a manual checkout. On 1 October 1961, von Braun established an Automation Board at Marshall to automate the Saturn V checkout. Thereafter, design of a computer checkout system paralleled launch vehicle development.6

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Saturn I-IB Computer Complex

The development of the RCA 110 hardware for Saturn I tests proceeded at Huntsville under the direction of the Astrionics Laboratory with the collaboration of the electrical network group. Richard Jenke's automation team at KSC furnished operational requirements and participated in a number of design decisions. Some agreements between developer and future user came slowly. The two groups discussed the matter of control panel switches for months; the uncertainty centered on the desired status of the various test devices when the operations switched from a computer program to manual control. Eventually the two groups decided to treat each test device separately and modify the RCA 110 programs when experience dictated a change. About the same time the automation group approved a three-position switch for the Saturn IB control panel. During IB operations all signals, manual as well as automatic, would process through the computer. In the three-position switch, OFF manually terminated a function, such as opening a valve; ON manually initiated a function; and AUTO placed the computer in control for automatic testing. Experience with SA-5 demonstrated the need to prevent the computer from sending any command signals while it monitored the operation. The automation group added a discrete inhibit switch on SA-6 for the remaining Saturn I launches.7

The Cape played a larger role in the development of computer programs, called software. Marshall recognized the launch team's need to prepare its own tests and allowed KSC to manipulate "Boss," the 110's executive control program. Jenke's group, assisted by RCA, IBM, and Chrysler personnel, combined the 20 manual routines of the guidance computer checkout into four test sequences. While the performance of the RCA 110 on SA-5 left a few skeptics unconvinced, launch officials labeled the computer a success. On the following launch (SA-6) Jenke added a test sequence for automatic azimuth laying. The launch team added a cathode ray tube console (a television screen that displayed alpha-numeric characters received from the computer) for SA-7. The RCA 110 increased its monitoring role during the last three Saturn I launches, the Pegasus series.8

During the Saturn I program, automation moved forward at a slow, deliberate pace; at any time the launch team could have reverted to a manual operation. By the time of the first Saturn IB launch in February 1966, however, KSC was firmly committed to automated testing. While a completely automated checkout was still a long way off, the RCA 110A computer (a 110 with increased memory) was "on line" for the first IB operation. All test transmissions then went through the computer; if it failed, the entire checkout would stop. On-line status represented the decision to use the Saturn IB missions as a testbed for Saturn V automation.

COMPUTER SYSTEM SCHEMATIC

LC-34/37 computer system schematic. From B. E. Duran, "Saturn I/IB Launch Vehicle Operational Status and Experience," pamphlet 680739, Aeronautic and Space Engineering and Manufacturing Convention, Los Angeles, 7-11 October 1968. Courtesy of the Society of Automotive Engineers, Warrendale, PA.

Two RCA 110As - a "master" computer in the LC-34 blockhouse and a "slave" computer in the automatic ground control station-provided the brains for the Saturn checkout system. A high-speed data link, a coaxial cable running through the LC-34 cableway, connected the two computers. Engineers could initiate launch vehicle tests from display consoles or from programs stored within the master RCA 110A. In either case the computer in the launch control center digitized commands for transmission to the ground control station. The slave computer, housed beneath the umbilical tower, interfaced with the launch vehicle, issuing commands and receiving responses. Both computers were also tied into the spacecraft checkout system.9

In its design, the digital data acquisition system was typical of the digital systems employed at KSC. Sections, or modules, within each computer performed specific functions. The stage module had three distinct elements, each dedicated to one of the launch vehicle elements. Aboard the Saturn IB, three digital data transmitters (for the two stages and the instrument unit) multiplexed the pulse code modulated data, giving each signal a specific time slot on its channel. This data, reflecting the condition of the launch vehicle, was transmitted to ground receiving stations over coaxial cable or radio. The receiver decommutated, i.e., divided the data into its constituent parts, and then conditioned the signals for transmission. Another part of the digital data system, a high-speed memory core, stored the data for use by the 110A computers.10

A digital events evaluator determined whether or not a return signal indicated a change in the launch vehicle's status. After receiving data from the slave computer, the evaluator compared this signal with pre- programmed information in its memory or with a previous scan of the same function. The event was then time-tagged for identification and the results either printed for display or stored for retrieval by the master RCA 110A at a later date. The evaluator logged every event within approximately two milliseconds, providing real-time - virtually immediate - printouts of event changes. 11

Although the Saturn checkout complex was usually identified by the RCA 110A computers, the related electrical support equipment was the larger part of the system. Included was test equipment and a complex distribution system. The RCA 110As relied on input-output address lines to place test equipment in a receive or transmit condition, set sequence control relays, select analog or digital signal lines, drive digital-to-analog converters, and issue warnings. Input-output sense lines informed the computers of test equipment status. The computers employed input-output buffer registers to handle the heavy data flow with the Saturn guidance computer and telemetry system. Hardwire connections tied the 110As in with LC-34's timing system: the countdown clock, a Greenwich Mean Time clock, and interval timers.12

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