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Software Software was an integral part in the Space Shuttle hardware systems and it played a vital role in the design and operations of the shuttle. The longevity of the program demanded the on-orbit performance Introduction of the vehicle to be flexible under new and challenging environments. Gail Chapline Because of the flexibility required, quick-turnaround training, Steven Sullivan simulations, and virtual reality tools were invaluable to the crew Primary Software Aldo Bordano for new operational concepts. In addition, ground operations Geminesse Dorsey also benefited from software innovations that improved vehicle James Loveall processing and flight-readiness testing. The innovations in software Personal Computer Ground occurred throughout the life of the program. The topics in this Operations Aerospace Language Offered Engineers a “View” chapter include specific areas where engineering innovations in Avis Upton software enabled solutions to problems and improved overall The Ground Launch Sequencer vehicle and process performance, and have carried over to the next Orchestrated Launch Success generation of space programs. Al Folensbee Integrated Extravehicular Activity/Robotics Virtual Reality Simulation David Homan Bradley Bell Jeffrey Hoblit Evelyn Miralles Integrated Solutions for Space Shuttle Management…and Future Endeavors Samantha Manning Charles Hallett Dena Richmond Joseph Schuh Three-Dimensional Graphics Provide Extraordinary Vantage Points David Homan Bradley Bell Jeffrey Hoblit Evelyn Miralles 256 Engineering Innovations Primary Software use. This prompted NASA to continue NASA had begun developing a its search for a viable solution. high-order software language— HAL/S—for the shuttle. This software NASA faced notable challenges in NASA soon concluded that core would ultimately become the standard the development of computer software memory was the only reasonable for Orbiter operations during the Space for the Space Shuttle in the early choice for Orbiter computers, with the Shuttle Program. 1970s. Only two avionics computers caveat that memory size was subject were regarded as having the potential to power and weight limitations as to perform the complex tasks that well as heat constraints. The space Software Capability Beyond would be required of them. Even agency still faced additional obstacles: Technology Limits though two options existed, these data bus technology for real-time candidates would require substantial avionics systems was not yet fully NASA contemplated the number of modification. To further compound operational; the use of tape units for necessary computer configurations the problem, the 1970s also suffered software program mass storage in during the early stages of Space Shuttle a noticeable absence of off-the-shelf a dynamic environment was limited development . It took into consideration microcomputers. Large-scale, and unsubstantiated; and a high-order the segregation of flight control from integrated-circuit technology had language tailored specifically for guidance and navigation, as well as the not yet reached the level of aerospace applications was nonexistent. relegation of mechanized aerodynamic sophistication necessary for Orbiter Even at this early juncture, however, ascent/re-entry and spaceflight functions to different machines. These considerations led to a tightly coupled, synchronized fail- Personal Computer Ground operational/fail-safe computation Operations Aerospace Language requirement for flight control and sequencing functions that drove the Offered Engineers a “View” system toward a four-machine computer complex. In addition, the difficulties Personal Computer Ground Operations Aerospace Language (PCGOAL) was a custom, NASA faced in attempting to PC-based, certified advisory system that provided engineers with real-time data display interconnect and operate multiple and plotting. The enhanced situational awareness aided engineers with the decision- complexes of machines led to the making process and troubleshooting during test, launch, and landing operations. development of a single complex with central integrated computation. When shuttle landings first began at Dryden Flight Research Center (DFRC), California, Kennedy Space Center (KSC) engineers had limited data-visualization capability. The NASA added a fifth machine for off-loading nonessential mission original disk operating system (DOS)-based PCGOAL first supported KSC engineers applications, payload, and during the STS-34 (1989) landing at DFRC. Data were sent from KSC via telephone system-management tasks from the modem and engineers had visibility to the Orbiter data on site at DFRC. Firing room other four machines. Although this console-like displays provided engineers with a familiar look of the command and fifth computer was also positioned to control displays used for shuttle processing and launch countdown, and the application handle the additional computation offered the first high-resolution, real-time plotting capability. requirements that might be placed on the system, it eventually hosted the PCGOAL evolved with additional capabilities. After design certification review in backup system flight software. 1995, the application was considered acceptable for decision making in conjunction with the command and control applications in the firing rooms and DFRC. In 2004, The space agency had to determine the application was given a new platform to run on a Windows 2000 operating system. the size of the Orbiter computer memory to be baselined and do so As the Windows-based version of PCGOAL was being deployed, work had already begun within the constraints of computer to add visualization capabilities. The upgraded application and upgraded editor were design and vehicle structure. Memory deployed in December 2005 at KSC first and later at DFRC and Marshall Space Flight limitations posed a formidable Center/ Huntsville Operations Support Center. Engineering Innovations 257 challenge for NASA early in the Operating Software for The substructure within operational development phase; however, with the Avionics System sequences was a choreographed technological advancements that soon network consisting of major modes, followed came the ability to increase The Orbiter avionics system operation specialist functions, and display the amount of memory. required two independent software functions. Major modes were systems with a distinct hierarchy and substructured into blocks that NASA faced much skepticism from clear delegation of responsibilities. segmented the processes into steps or within its organization, regarding the The Primary Avionics Software System sequences. These blocks were linked viability of using a high-order language. was the workhorse of the two systems. to cathode ray tube display pages so Assembly language could be used to It consisted of several memory loads the crew could monitor and control the produce compact, efficient, and fast and performed mission and system function. The crew could initiate software code, but it was very similar in functions. The Backup Flight System sequencing through keyboard entry. complexity to the computer’s machine software was just that: a backup. In certain instances, sequencing could language and therefore required the Yet, it played a critical role in the safety be initiated automatically by the programmer to understand the and function of the Orbiter. The Backup software. Blocks within the specialist intricacies of the computer hardware and Flight System software was composed functions, initiated by keyboard entry, instruction set. For example, assembly of one memory load and worked only were linked to cathode ray tube pages. language addressed the machine’s during critical mission phases to provide These blocks established and presented registers directly and operations on the an alternate means of orbital insertion or valid keyboard entry options available data in the registers directly. return to Earth in the event of a Primary to the crew for controlling the While it might not result in as fast and Avionics Software System failure. operation or monitoring the process. efficient a code, using a high-order Major modes accomplished the programming language would provide Primary Avionics Software System primary functions within a sequence, abstraction from the details of the The Primary Avionics Software System and specialist functions were used for computer hardware, be less cryptic and performed three major functions: secondary or background functions. closer to natural language, and therefore guidance, navigation, and control of The display functions, also initiated by be easier to develop and maintain. As the vehicle during flight; the systems keyboard input, contained processing the space agency contracted for the management involved in monitoring necessary to produce the display and development of HAL/S, program and controlling vehicle subsystems; were used only for monitoring data participants questioned the software’s and payload—later changed to processing results. ability to produce code with the size, vehicle utility—involving preflight efficiency, and speed comparable to checkout functions. Backup Flight System those of an assembly language program. The Backup Flight System remained All participants, however, supported a The depth and complexity of Orbiter poised to take over primary control in top-down structured approach to requirements demanded more the event of Primary Avionics Software software design. memory capacity than was available

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