In Their Own Words: Cline Frasier on why NASA went digital for Apollo
Cline Frasier, NASA Project Manager during Apollo, explains Why NASA took the risk and switched to digital flight control for the Apollo missions:
"In early 1964, the guidance and control system designs for both the Command Module and the Lunar Module were fairly conventional. The designs had redundant analog control systems, a single digital computer and inertial system for navigation and guidance calculations. Each spacecraft also had a simpler 'get me home' capability in the event the guidance computer failed.
The MIT Instrumentation Laboratory had the design responsibility for the primary digital guidance and navigation system for both the Command Module and the Lunar Module. The spacecraft contractors (North American Aviation and Grumman) were responsible for their analog control and “get me home” systems.
Joe Shea had recently taken over the Command Service Module (CSM) and Lunar Module (LM) project. Shea recruited Robert C. Duncan to run the NASA Guidance and Control Division in Houston.
In the spring of 1964, I was part of guidance and control review team that visited MIT/IL and all the other contractors. In one of the meetings, a North American Aviation (NAA) person announced that they could not fit all the guidance and control equipment into the spacecraft – and they had no solution. In the meeting, the idea popped in my head that putting the primary control system into the digital navigation and control computer, along with a few other changes might let everything fit. This was a radical and heretical idea – no pilot had ever flown a digital flight control system. I was not yet 30 and I could envision the reaction I’d get – and knew what happens to heretics. I said nothing and went home to do a little homework.
A month or so later, NAA made a presentation at the Manned Spacecraft Center senior management and repeated they had no solution to the space and weight problems of the overall guidance, navigation and control systems. At a break in the meeting, with some trepidation, I talked with Duncan and outlined how the space and weight problems might be solved with digital flight control as the centerpiece. To my surprise, he said “meet in my office and tell me more.”
Basically, I proposed:
Eliminating one of the two MIT/IL navigation and guidance computers.
Moving the primary autopilot from the analog system into the MIT/IL guidance and navigation system.
Eliminating the redundancy in the analog systems.
Changing the primary responsibility for navigation from the MIT/IL system to the Manned Spacecraft Network (MSFN).
With the results:
Much to my surprise, Duncan and Shea saw this approach as way out of the “unsolvable problem” presented by NAA. It didn’t take long for Shea to decide that this was the way he wanted to go. He gave NAA the “bad news.” around mid 1964. Then I was told to go to MIT/IL, explain the situation to them and tell them what we needed them to do.
When I walked into the meeting, 5 or 6 of the most senior MIT/IL people were in the room. As I started to explain the changes, and the rationale behind them, I was hit with a barrage of questions and arguments. I was just 30 and they were all at least 10 years older and giants in the guidance and navigation field. I can still remember feeling I was shrinking under the barrage. They were not happy about losing the “primary navigation source” designation and the extra work involved in adding digital flight control to their system. To their everlasting credit, they listened to the NASA reasons for the changes. Then, Dave Hoag said “we can do it.” I flew home to recover.
I was right, there were going to be many unhappy people. In addition to some at MIT/IL, the astronauts didn’t like the idea. They didn’t trust any electronics, especially digital ones. Their view was that, once successfully launched, they would turn off the computer and take care of the rest of flight on their own. NAA didn’t much like the idea, but would accept the decision. Grumman didn’t like the idea, was sure it wouldn’t work for the Lunar Module, and unsuccessfully fought the decision.
All the manned flights were with digital autopilots in both CM and LM. The astronaut who initially told me he would not fly with the digital system went on to praise the system and use it to land on the moon.
Thus ended my direct involvement with digital flight control. I went on, as NASA Project Manager, to working on production and reliability with the contractors building the Primary Guidance, Navigation and Control hardware."