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Share Your Story • Leonard Larks • October 28, 2013

My Memories of Professor Bruce Murray

Memories of Professor Bruce Murray My first memories of Dr. Murray were in regards to the Mariner to Venus and Mercury (Mariner 10) mission. Dr. Murray was the principle investigator of the science team for the visual imaging subsystem. I was an untried , unbuilt lens designer assigned to the visual imaging subsystem design team for Mariner 10 at JPL. The science team set the requirements for the performance of the visual imaging (television) subsystem, and it was up to the design team to meet the requirements. The lenses and telescopes designed for previous Mariner missions had been a commercial Zeiss 50 mm Biotar wide angle lens remounted for space flight, and a narrow angle telescope based on the Schmidt Cassegrain design. This design used aspheric surfaces on the Schmidt correcting plate and the primary–secondary mirror system. The elements were a matched set that required extensive hand figuring for optimization.

My assignment was to design a telescope that could be made with interchangeable elements that could be mounted with somewhat less exacting alignment. I proposed an all spherical Catadiotric Cassegrain design using spherical lens elements to replace the Schmidt plate for correction of the aberrations of the spherical primary and secondary mirror. Dr. Murray took great interest in the project and attended a number of design team meetings to follow the developing design.

Using modern lens design and analysis computer programs, a design that met or exceeded the requirements came into existence, and the expert mechanical design by Lloyd Adams, also came into existence to hold and align the elements. At a final design team meeting, Dr. Murray asked me if I had an alternate lens design that I would like to tell him about, and I did. While the telescope that I presented met or exceeded the mission requirements and was in fact diffraction limited, there was a design that used an extra element that was in fact, geometrically perfect as well. While both telescope designs met the science team requirements, the second one was a little heavier and, as both telescopes were limited only by the diffraction effects of the aperture, and as the second heavier design could provide no improvement in system performance, we agreed that the first design would go forward. Still, I appreciated Dr. Murray giving me to opportunity to present the “perfect” design.

Because I was an unproven lens designer, and as Mariner 10 was to be a national resource, Lloyd Adams and I were “invited” to present the proposed design of the Mariner 10 telescopes to a meeting of lens and telescope designers and astronomers at a meeting at the optical institute at the University of Arizona during the holiday season. We provided a complete design and analysis package for all of the attendees so that they could do their own analysis using their own computer programs. There was an extensive discussion at the meeting, including one comment by a well known telescope designer that this was the dumbest design that he had ever seen. Dr. Murray then commented that there were many ways to skin a cat, but that it appeared that this design would work, and that this design would now be on the Mariner 10 spacecraft and the design was now cast in concrete.

After the meeting, Lloyd Adams and I were invited to a Christmas party. I really do not remember much of that party. I believe that Dr. Murray was there along with other members of the Science Team. I remember some talk about the desirability of a wide angle view of Venus when we went by that planet, but the design was now fixed as two narrow angle telescopes, and the only thing left for development was the contents of the optical filter wheel… The next morning at breakfast, Lloyd and I tried to reconstruct from a stack of damp cocktail napkins what we had promised the night before, something we called a “Wide Angle Filter”. The original concept was to mount our old trusty Zeiss wide angle lens on the front of the telescope, carry the image to the plane of the filter wheel with a long high resolution fiber optic, and using a periscope arrangement of mirrors, get the image to the focal plane. A proof of concept model was built using a foot long commercial fiber optic and nicknamed the “deep space cystoscope”. When we tried to scale it up to meet our requirements for the mission, we quickly discovered that high resolution long fiber optics were not suitable for launch to spaceflight. We mounted the Zeiss lens at the filter wheel end of the telescope.

Dr. Murray continued to demonstrate great interest in the development of the Visual Imaging Subsystem through the hardware fabrication and testing phase, and onto the spacecraft itself. Mariner 10 to Venus and Mercury was now ready for launch. There was no reason for me to be at Cape Canaveral for the launch, but it was my first mission, and I found a JPL reason to be on the East Coast at launch time, and JPL got me a pass to get me to the launch site for that night. The launch was beautiful and spectacular. I went to the post launch party, and by the time I got back to my motel room, feeling no pain, I observed a red light flashing on my room telephone. I called the desk to find three messages: 1) from JPL, do not get on the plane in the morning, 2) from mission control at the cape, get back over here, and 3) from Dr. Murray, come with me. I got redressed, joined Dr. Murray, and he drove us back to the control center at the cape. Unfortunately, when we got there, Dr. Murray’s pass got him past the guard shack, mine good only for the launch, did not. The guard ordered me out of the car.

Dr. Murray told me to go with the guard, not to worry, he would fix the problem. I accompanied the guard to the shack, the guard looking at me suspiciously all the while and sat there for about a half hour. The blue telephone rang, and I remember the guard saying, “ yes sir he’s right here sir, oh yes sir I’ll see to it right now sir, immediately sir”. And with that, I became an honored guest of the Air Force Eastern Test Range, and was escorted to the Mariner 10 control center where waiting for me was Dr. Murray and other scientists and engineers of the mission around a large conference table. I was later told that Dr. Murray had called NASA in Washington, NASA called the White House, The White House called the Air Force at the Pentagon, and they called the command at the Cape, who called the guard shack. It seemed that the telescope heaters had failed, and the assembled group wished to know if the telescope could still perform. How cold were the telescopes? We don’t exactly know, but we want to know if this 93 million dollar mission to photograph Venus and Mercury will be a failure. The temperatures were below the design and test specifications, but the optics proved to be self compensating, and the mechanical design by Lloyd Adams kept them in focus.

At the end of the mission, Dr. Murray sent a very kind and complimentary letter to the subsystem design team in which he personally thanked the team, Lloyd, and me specifically. The Mariner 10 mission to Venus and Mercury and my interactions with Dr. Murray are among my fondest memories of my time at JPL.

Leonard Larks, O. D. Lens Designer / Optical Engineer Jet Propulsion Laboratory 1969-1980

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