Surveyor Software and Flight Operations—John Gans

I joined the Surveyor Guidance and Trajectory Department, headed by Bill Grayer, as a Hughes fellowship rotator in 1963 and elected to continue in that organization upon completion of my two-year fellowship. I began working with John Ribarich and Len Davids on the MTGS program (Midcourse and Terminal Guidance Surveyor).  John was writing the equations for the error analysis portion and teamed with Len Davids on the terminal analysis portion.  I was directed to prepare the equations for the midcourse correction portion and set out to do that.  To back up a little, Mal Meredith had successfully obtained a copy of JPTRAJ, a huge program written by JPL that we then used as a subroutine of MTGS.  Much analysis was performed, the various equations of MTGS were coded by a software team in Culver City headed by Ray Gregory.  He and his six programmers coded everything up and the result was a program, written in Fortran II, Version 2 that consisted of 50,000 lines of source code supported by nine tapes which provided the ephemerides of the various planets and their moons which would affect the translunar trajectory.  About this time, Fortran II Version 2 was succeeded by Fortran II Version 4, but JPL, the prime contractor, directed that we use Version 2 which was more mature and would allow all of MTGS to be frozen for flight operations.

Prior to the Surveyor flight operations we conducted many runs of MTGS on an IBM 7090 in Culver City and it proved to be an excellent tool for analysis of the flight path and the needed corrections.  MTGS was then delivered to JPL and installed on their 7090 machine.

Next our Maneuver Analysis Team was organized with me as team leader and John Ribarich and Len Davids as participants.  We were to be part of the FPAC team (Flight Path Analysis and Command) with Mal Meredith as leader at the SFOF facility (Space Flight Operations Facility) at JPL in Pasadena.  Other parts of FPAC included the Trajectory Group and the Orbit Determination Group.  Together we then held numerous rehearsals, some in conjunction with the launch operations in Florida.

The sequence of events, following launch were:  Bill Whollenhaupt (a JPL employee) as leader of the Orbit Determination Group would determine the state vector of the Surveyor trajectory, Stan Dunn (a Hughes employee) of the Trajectory Group would determine the entire trajectory, I would then take the state vector, input it into MTGS with a selected time of midcourse correction and the desired landing site and compute the velocity increment required.  The result were the roll, pitch and yaw maneuvers required and a burn time to correct the trajectory and achieve the desired landing site specified in salenographic coordinates.  The resulting trajectory was used by John Ribarich and Len Davids to compute the maneuvers and a time delay following the 60-mille altitude mark, provided by the RADVS (Radar Altimeter and Doppler Velocity Sensor), to fire the solid rocket motor.  All of these commands were transmitted to SPAC (Spacecraft Analysis and Command Group) in the SFOF that were then forwarded to the Deep Space Net (Goldstone, California, Woomera, Australia and Johannesburg, South Africa) for transmission to the spacecraft.  This sequence was repeated a number of times for the seven Surveyor Spacecraft.  Surveyor 2 spun up at midcourse (one vernier engine failed to shut down) and then crashed on the moon and Surveyor 4 blew up upon retro motor ignition.  All other Surveyors with some anomalies managed to make safe landings.

Shel Shallon (Hughes Aircraft) would come by our Maneuver Analysis Team at many times during all of the Surveyor flights to obtain various parameters of the ongoing missions for dissemination to the public.  He played a vital role in describing ongoing operations.


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About Jack Fisher

Jack was a systems engineer at Hughes from 1961 to 1992. He contributed to various programs including Surveyor, Pioneer Venus, Galileo, Intelsat VI and innumerable proposals. He was the manager of of the Spacecraft Systems Engineering Lab until his retirement. Upon retirement Jack taught systems engineering at a number of national and international venues.