The collection documents the computer command subsystem of the Viking project. The originator of the documents varies. The Viking Orbiter was similar to the Mariner Mars 1971 spacecraft (Mariner 9), but used the Titan/Centaur boost vehicle. The major modification from Mariner Mars 1971 was the addition of a lander system which required a larger orbital propulsion system to accommodate trajectory corrections and orbit insertion about Mars, and also required a larger structure to support the additional mass of the lander. Another modification was the restructuring of the Viking Orbiter Computer Command Subsystem. On Mariner Mars 1969 and Mariner Mars 1971, maneuver relays were wired in with the Timing of Events relay in the Central Computer and Sequencer. The command systems aboard the earlier probes only knew what they were supposed to do, not what actually happened. The Viking Orbiter Computer Command Subsystem was more sophisticated than the earlier systems in that it was a fully redundant subsystem with the capability of knowing what did happen as well as what should have happened. The CCS was configured as a block-redundant computer. Each half of the subsystem was an independent special purpose computer containing a power supply, processor, memory, and output unit. All inputs were applied to both halves of the CCS, with either half being capable of providing all mission requirements. The two processors operated asynchronously and were capable of being programmed to perform different functions simultaneously. The utilization of a dual computer provided both redundancy and extended command capability. The function of the CCS was to command the spacecraft. Commands were issued in a sequence according to the programs stored in the CCS Memory. The CCS consisted of two processor units, two output units, two coded command buffer units, two discrete command buffer units, and two power supplies. The CCS Memory consisted of a wire memory stack with associated read/write electronics to store 4096 18-bit words. The construction and manufacture of the CCS was contracted out to General Electric, Aerospace Electronic Systems Department, Utica, New York. The construction and manufacture of the CCS Memory was contracted out to SCI Systems, Inc. (formerly Space Craft, Inc.) of Huntsville, Alabama. Spacecraft Operations Handbook (Boxes 1-2). The Viking '75 Project Spacecraft Operations Handbook served as the single source of technically authoritative information on the Viking flight hardware and software. It was created for specific use by the Viking Flight Team, both before and during Viking mission operations. Viking Design Books (Boxes 3-5). The Viking Design Books were an artificial creation, consisting of binders of reports, memoranda, parts specifications and notes regarding various subjects dealing with the Viking orbiter. The books are organized by subject into different volumes. The volume numbers have been retained in the folder listing. Volumes 3-5 are missing. It appears that the Viking Design Books were from the office of Gary Kunstmann, Section 361. Preliminary Design Review (Boxes 5-6). The Preliminary Design Review (PDR) was an early goal in the design of the Viking Orbiter. The formal review, held on October 19-20, 1971, came at the end of the conceptual phase for the design of the orbiter systems. The PDR gave all interested parties a look at the orbiter as JPL planned to build it. The working test models of each subsystem were evaluated with their own PDRs throughout 1972. The Computer Command Subsystem PDR occurred in November 1972. Critical Design Review (Boxes 6-7). After the PDR, the next important milestone was the Critical Design Review (CDR). A general CDR for the entire Viking Orbiter system certified the readiness of the orbiter staff to begin building the flight-ready orbiters. The general CDR was held at JPL on July 9-10, 1973. Other Reviews (Boxes 8-9). These reviews consist primarily of design and software reviews conducted from 1972-1975. These also came from different offices. The Flight Software Interface Review viewgraphs were originally from Ralph A. Proud and Gary Kunstmann. The Design Presentation Review material came from Wayne H. Kohl. Project Documents (Boxes 10-11). The Project Documents all deal with some aspect of the Viking Orbiter. They are arranged in the order they were found, by number. Action Items (Box 11). This small series of two files documents memoranda summarizing and reviewing action items, usually spawned from the Preliminary Design Review, Critical Design Review, or other design reviews. Included in the series are lists of items, the name of the person the item is assigned to, and the due date. Other lists summarize the items, and note if the item has been closed. Status Reports (Box 11). This is another small series of six folders, evenly divided into general Viking Orbiter status reports, and subsystem status reports. Included is a Viking status report, dated August 13, 1975, documenting a problem with the rotary switch on the Viking A orbiter that had the potential to delay the launch of Viking 1. Inspection Reports (Box 11). This is a series of four thick files, comprising the cognizant engineer's copy ("pink copy") of inspection reports of the computer command subsystem. Software Design Notes (Box 12). This small series of two folders was originally in a three-ring binder. The original tabs have been retained. The series consists of hand-written notes on standard lined paper, documenting the software design of the Computer Command Subsystem. Computer Command System Interface (Box 12). This series is one large file, divided into two folders, consisting of a grouping of memoranda and design notes documenting the various computer subroutines, showing what the purpose of the routine is, how to use it, corrections and updates, and how to reset the subroutine in case of error. CCS Command Memos (Box 12). This is another two-folder series. The series consists of interoffice memoranda discussing various command formats for the Viking Orbiter. Problem/Failure Reports (Boxes 13-14). This series is filed chronologically, with selected files placed in their own folders at the end of the series. Included in the reports is a wire plated memory failure report from VO-1 that was detected while the mission was in Mars orbit after Earth occultation. Any corrective action was impossible, and it was recommended that the processor be put back online and that the five bad memory circuits be bypassed. In another instance, after exiting Earth occultation at day 285, the Data Storage Subsystem (DSS) could not lock up to the Viking 1 Orbiter downlink. Lock was established 20 minutes later, but the VO had switched to the low-gain antenna, and the orbiter could not find Canopus. It was found that the CCS-A operation was nominal while CCS-B was faulty. Design Requirements (Box 15). This series documents the design requirements of the hardware and software of the Computer Command Subsystem aboard the Viking Orbiters. The documents are all in rough draft format, some with numerous annotations. Hardware Review Items (Box 15). This series contains interoffice memoranda documenting various hardware reviews of various components prior to delivery to the Spacecraft Assembly Facility. Drawings/Diagrams/Blueprints (Boxes 15-16). This series documents diagrams, blueprints and drawings of various aspects of the Computer Command Subsystem. Also included are drawings regarding the electronic packaging of the Viking Orbiter. The inside of the binder had the label, "Issued to F. W. Brocksieper, Oct. 1963." The drawings date from 1973-1974. Orbiter Performance Analysis Group Memoranda (Box 16). The Orbiter Performance Analysis Group (OPAG, sometimes referred to as the Orbital Performance Analysis Group or Team) analyzed Orbiter engineering and science housekeeping data, including documenting and investigating incidents and surprises, problem/failure reports, and recommended Orbiter maintenance. While the Problem/Failure Reports are documented elsewhere in the collection, this series documents the memoranda and reports that the group generated. Also included is a seven-page memo, written by Brian Larman, Orbiter Data System Unit Lead, to Ronald A. Ploszaj, OPAG Chief, entitled "Some Reflections on Viking OPAG Operations" that summarized OPAG operations with the Viking Project. Failure Mode Analysis Reports (Boxes 17-18). These reports analyzed the various failure modes that would possibly occur, and the effects, remarks and consequences of any such failures. A few of the reports were prepared by the Reliability Section of SCI Systems, Inc., the contractor for the Computer Command Subsystem Memory. Meeting Minutes (Box 18). Included in this series are meeting minutes from the Telecommunications Working Group, the Engineering Steering Group, the Data Storage Subsystem Constraints Committee, the ad hoc Power Switching Review Committee, and other miscellaneous committees. They are by no means exhaustive, with some committees represented with minutes of only one meeting. Flight Software Memoranda (Box 18). This series includes memoranda and a set of viewgraph originals documenting various aspects of flight software. Software change request procedures and forms are also represented. The viewgraphs were from Ralph Proud, Section 361. Computer Command Subsystem Contract Information (Box 19). The construction and manufacturing of the CCS was contracted out to General Electric, and the construction and manufacturing of the CCS Memory was contracted out to SCI Systems, Inc. This series includes schedules, reports, agreements, summaries and memoranda regarding these contracts. Miscellaneous Reports (Box 19). This series is a small one, consisting of three reports that do not fit elsewhere. The most significant of these reports is the Viking Orbiter System Primary Mission Performance Report, dated June 15, 1977. This report describes the performance of each system and subsystem of the Viking Orbiter, and notes any anomalies detected. Viking Residual Parts Memoranda (Box 20). This small series consists of memoranda and lists of redundant and residual parts left over from the three Viking Orbiters, including the third orbiter itself, VO-3. Many of the parts were transferred to the Mariner Jupiter/Saturn Project, later renamed Voyager. General Electric Shipping Forms (Box 20). This small series consists primarily of the pink (originator) copies of Shipping-Receiving Memoranda. They document parts that were shipped to General Electric, the contractor for the Computer Command Subsystem. Miscellaneous Subject Files (Boxes 20-22). These files were ones that were originally filed chronologically. They were grouped together due to the similarities of subject. The files are organized chronologically. Included is a short report comparing Viking with other missions such as the Lunar Orbiter, Mariner, Biosatellite and Nimbus missions. Also documented is a power anomaly aboard VO-2 during August 1975. Memoranda discussing personnel issues such as car pooling and vacation times before, during and after the Viking landing on Mars, as well as a file on press and visitor activities at JPL during the encounter are represented. Two memos regarding the extended mission of Viking after completion of the primary mission are also represented. Miscellaneous Chronological Files (Boxes 22-23). These files were originally filed in no apparent order apart from chronological. No obvious link has been found to group them together by subject, so the chronological order has been retained.
