First-Hand:My Work on the Apollo Program


Submitted by Richard Coen

In the spring of 1962, I and my boss, Ken Mac Lean, were assigned the task to develop a communications system design for the proposal to develop the Lunar Excursion Module for the ongoing Apollo Program.

Ken was the head of the Communications systems at RCA’s Astro- Electronics Division (AED), located near Princeton, NJ. He was then 64 years old, and had spent his career entirely with RCA. He had transferred to the Astro division from RCA Laboratories, the corporate research laboratory in Princeton. (Later renamed the Sarnoff Laboratory). AED was a spinoff from RCA Labs, and all of its original employees had been with the lab.

Ken had extensive experience in communications equipment and systems design, and was an expert in modulation and multiplexing systems. He had designed the innovative FM modulation system used on the Tiros Weather Satellite, the program that got the AED started. The Tiros Satellites were the most complex satellites in space at the time.

I had joined AED from IT&T’s research lab in Nutley, NJ the previous year. I was 29 years old. I had 7 years of experience in the field, primarily in communications equipment design and systems design.

The Lunar Excursion module was an afterthought. The original intent of the Apollo design, headed by North American Rockwell, was to land the command and service modules on the moon’s surface. After completion of the operations on the lunar surface, the service module and its command module payload were to blast off the moon and return to a low Earth orbit, after which the command module would detach and return the astronauts and the lunar samples they had collected back to Earth.

We were told that a young NASA Engineer had determined that a separate lunar excursion module, unencumbered by the heavy heat shield needed on the command module to re -enter the Earth’s atmosphere, and the extra fuel in the Service Module needed to return he spacecraft to Earth Orbit, would allow more samples to be returned from the Moon than would be possible with the original design. I never learned who had done this work, or even whether he was actually a direct employee of NASA or was a contractor. Almost all design work on the Apollo program was actually done by contractors.

The Engineer’s work caused NASA to plan a separate contract to build the lunar excursion module. RCA teamed with Grumman Aircraft and an engine manufacturer to compete for the contract, with RCA being responsible for the LEM electronics suite.

Since this was to be a large contract, the RCA effort was assigned to the Major Systems Division (MSD) in Moorstown, NJ under the direction of F.J Gardiner as project manager.

ACCD, in Camden, was given primary responsibility for the communications system design, with AED in a support role. AED was to be responsible for communication design for the phase where the LEM was on the lunar surface, and for weight and modulation studies.

Ken and I began a preliminary communications system design, with Ken doing the critical weight and modulation studies, while I did the system block diagrams and path loss calculations.

ACCD was doing similar work, but our designs differed in detail, due to differing starting assumptions and other factors.

Applied Physics assigned 13 engineers and a project manager to the task. Astro assigned two engineers, Ken Mac Lean, the head of the Communications Group, and myself, to the same task.

Ken was an expert on the unusual reduced - bandwidth FM system used on the Tiros series of weather satellites to transmit pictures back to Earth. He proposed a similar modulation system, plus a reduced frame rate and lower resolution, to provide the least possible weight for the TV transmission system.

I incorporated the high power TV transmitter amplifiers to provide emergency voice communication in the event that the LEM lost attitude control, and had to switch to an omnidirectional antenna to communicate with Earth or Apollo. We generally used components for multiple purposes whenever possible to minimize weight and increase redundancy.

I designed the system of communication, command and control links and the radars that exchanged information between the LEM, the command module, and Earth in each phase of the mission, and I did the path loss calculations.

Ken designed the modulation methods, complete with minimum signal strength thresholds and noise improvement factors. He also acted as an effective sounding board in working out the overall link design, and provided much valuable insight into relative equipment weight and reliability, based on his vast design experience.

Ken’s design employed pre and post distortion methods to reduce the bandwidth required for FM transmission of the video information, an extension of a method used on Tiros. He also taught me a vector - based graphical method for analyzing distortion in FM systems, which I often found very useful.

The telemetry data rate requested by NASA was 30,000 bits/sec! Our initial estimate was much lower, and the 7000 bit/sec rate was a compromise.

The need to minimize the total mass of the spacecraft was extreme, so every effort was made to design the overall telemetry system to send only needed information in the most compact form possible, which required a lot of ingenuity. Our original minimalist design was deliberately very conservative, to ensure reliability if some design targets were not met.

Our design used analog technology. At that time, it was lighter and more reliable than digital systems with comparable performance. Our design also incorporated very extensive redundancy. It used an automatic logic system that would reconfigure the system components to preserve the most important functions in the event of a partial failure.

This automatic system used hard - wired logic and sensors, rather than a computer based system, both to save weight and power and to increase reliability. I still have my original design notes on this project, which was not classified. Hard wired logic systems have the advantage that unlike software based systems, they can be completely tested, and require fewer components, but are rarely used today because they are more difficult to design.

The Applied Physics design was largely digital, but offered fewer features, higher power consumption, and greater weight.

I had also designed a unique space - suit radio system that provided true full - duplex communication between either one or both astronauts on the moon’s surface, and automatically relayed their conversations and biomedical data to the Command module from the LEM, or back to Earth directly, via the LEM. This permitted full time biometric data from the astronauts during all phases of the mission, which was originally a requirement.

No other proposals incorporated this feature, and NASA eventually dropped the requirement for it. I was told that the reason that they did so was that they had already contracted for the Space Suit Radios, and the existing design could not support my design requirements. They were unwilling to modify or replace their contract.

As it turned out, they could have modified the radios to incorporate my design without impacting the schedule, and with little or no impact on costs. This kind of mistake is often made by government engineers and contracting officials.

My design also incorporated another feature, that was not originally requested by NASA. I was able to show that video of the upper stage of the LEM lifting off the surface of the Moon could be incorporated with very little increase in payload mass.

The camera and the high power (20 Watt) transmitter amplifier were to be left on the Moon to maximize the mass of the samples that could be brought back to Earth, so by adding a lightweight directional antenna on a tripod and pointed toward Earth, the system could provide a short, but dramatic view of the liftoff.

I was told that NASA had wanted to do this, but had not included the requirement because they could not afford the extra weight of the servo for another parabola mounted on the Descent Stage of the LEM. I had to point out that , since the same side of the Moon is always facing Earth, a servo to keep the antenna pointed earthward was not required.

In the early days of the space program, even technically trained people often did not seem to realize how different operations in space or on the moon were quite different than those encountered in (say) high altitude flight.

A large meeting was convened at Grumman, in Bethpage, Long Island, to decide which of the two RCA designs they would choose. Ken and I went to represent the Astro design, and all 14 of the Applied Physics team went to present their design.

A Grumman vice president opened the meeting by describing their design of the spacecraft itself, which incorporated two adjustable thrust rocket motors and a cleverly designed landing gear system.

They brought out a model of the LEM, which looked much like the finished product, except for one large difference. One side of the LEM was a large “Greenhouse” - like the bubble cockpit of a helicopter.

Ken and I stared in startled disbelief!

“Ken” I said, “If NASA sees a picture of that model, they will toss the proposal in the trash without bothering to read it! Sun shining into that bubble will cook the Astronauts. You need to tell them.” “Yes”, agreed Ken. “ It won’t work. You tell them.”

“OK” I said, “you’re the boss”, and raised my hand.

The Speaker called on me, and I pointed out that the sun shining into the large greenhouse would increase the internal temperature to where it would be fatal to the crew.

The Speaker was an expert on aircraft, but not aware of the problems facing spacecraft. He looked puzzled, and said “We will air condition the Cockpit.”

I pointed out that to do so they would need to reject the heat coming through the bubble, by radiating it back into space, with a radiator placed on the “dark side” of the spacecraft - that is the side away from the Sun. No such radiator was provided.

“Oh”, said the Speaker, “ Then we will just run the Mission at Night”

“There is no night” I replied.

“What do you mean, there is no night” he asked. By this time some of the engineers in the audience were trying to suppress laughter.

I quickly arranged coffee cups on the conference table to represent the sun, earth, and the moon with a glass representing the Apollo Spacecraft, and pointed out that once the Apollo passed out of the Earth’s shadow it remained in full sunlight for the entire journey to and from the Moon. “Why do you need the large helicopter bubble on the side of the spacecraft anyway?” I asked.

He explained that it was required so that the pilot could see past the rocket exhaust and the dust cloud that it was expected to throw up as the LEM descended to the Moon’s surface.

The speaker was not giving up. He suggested putting a cover over the greenhouse, and blowing it off just before touchdown. “We can land at night. There is night on the moon, isn’t there?” he asked.

I confirmed that there was, and that it was two Earth weeks long, but asked how the pilot would see the surface at night. “We’ll drop flares” he quickly replied. “On parachutes, Right?” I interjected. By this time I was half expecting to be fired for antagonizing a customer, but I continued.

I suggested that they could replace the greenhouse with a periscope, sticking out the side, to provide a view past the dust cloud.

“You can’t fly a plane with a periscope!” the speaker shouted.

I took a deep breath. Titters were growing louder.

“It is not a plane, it does not fly, and you can too.” I replied.

“I have seen the actual “Spirit of Saint Louis” plane that Lindbergh flew across the Atlantic, in the Smithsonian. It has no windshield. There is a gas tank there instead. Lindbergh took off, flew, and landed it by looking out a side window to a mirror on the wing strut. In effect, he used a periscope.

Lindbergh is a NASA consultant, so we can ask him how he did it. Does anyone know the area code for Hawaii?”

Someone quickly took the telephone from me. Grumman’s executive agreed that they would come up with a replacement for the bubble and would do a preliminary thermal analysis as part of the proposal.

They actually came up with a good solution. They provided the two small triangular windows used for landing that are on the finished spacecraft, and added a thin hollow tube, 8 feet long, descending from the bottom of one of the landing foot pads. A microswitch at the end of the tube would operate when the craft was still 8 feet above the surface. The switch illuminated a large red light in the cockpit. This would signal the pilot to shut down the descent engine at the right altitude, even if dust prevented him from seeing the surface.

Grumman chose our Astro Electronics version of the RCA electronics package, and the Grumman - RCA proposal proposal won the NASA LEM contract.

The Command Module Simulator

After I left RCA and joined Link, then a division of Singer, one of my first assignments was the completion of the design of the large cathode - ray tube displays that formed the views that the astronauts could see through the windows of the Apollo Command Module Simulator. These used large CRTs with hemispherical faceplates that were attached to an “infinity” optical system that incorporated the windows themselves as part of the lens system. The tubes operated at 50,000 volt second anode voltage, and the original design had reliability problems. My redesign proved successful.

One of the main functions of the simulator was to train the astronauts to dock and undock the command module with the LEM, a critical operation.

I had expected that the Apollo “Stack” would be modified to place the LEM above the command module, to avoid the need to disconnect the command and service modules from the stack during midcourse, rotate them 180 degrees, dock the command module to the LEM, then separate the LEM, Command Module and Service Module from the Saturn upper stage before transferring the descent team to the LEM.

However, North American Rockwell claimed that their design was too far along to make such a change.

Instead, the LEM was placed between the service module and the Saturn. Rockwell’s claim did have some merit, in my opinion, as the design of the emergency escape system would have been made much more difficult.

The Command Module Simulator was quite elaborate. The images on the CRTs driving the infinity optical system were produced by high resolution cameras and flying spot scanners .

The star field was produces by a large black celestial sphere studded with ball bearings of varying size, to simulate stars of varying magnitude. The sphere was rotated to simulate changes in the spatial orientation of the command module.

The image of the LEM was produced by a scale model of the LEM mounted on a servo, viewed by a track - mounted camera that simulated separation and approach of the LEM with a combination of physical motion and a zoom lens.

Although we could not simulate free fall , the simulator proved to be a valuable training device.

When I first joined RCA AED, I had considered applying to the Astronaut program myself, as I met the original requirements set by NASA, which were: fairly small size, a technical degree, good vision and experience in the Arctic or in submarines (to select applicants not affected too much by isolation from other people).

However, when Eisenhower secretly militarized the space program, the requirement for 1000 hours of jet pilot instructor service was added, to insure that only military pilots could be selected. (This requirement was relaxed later in the program).

Aerodynamic piloting skills were not actually useful in controlling the spacecrafts, of course, although most non - technical people did not realize this. However, the requirement helped in finding applicants with fast reaction times and good vision.

Further Reading

MacLean and Coen Preliminary Communications System Design for the Apollo Lunar Excursion Module, June 9, 1962

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