|ICBM Night Launch.
The flames surrounding the missile are normal.
There were many significant technological breakthroughs that had to occur to create today’s modern nuclear-tipped intercontinental ballistic missile (ICBM). The one I probably know the most about is the miniaturized on-board computer.
In order to place the nuclear bomb on target, an on-board computer must be present to perform the real time calculations. Once there, the computer can also provide some other important functions using the rest of its capacity. But the key reason it must ride along is to compute “on the fly”.
After WWII, it was clear that the Atlantic and Pacific Oceans were no longer barriers to other countries’ abilities to deliver bombs onto our homeland. A strong defense meant that we had to ensure we had that capability as well. Manned bombers were the focus of a lot of technological innovation. But when it became clear that nuclear weapons could be miniaturized to the point of being able to be placed on a rocket, development of intercontinental missiles were a priority above manned bombers.
These rockets were natural successors to the Nazi V-2s. In fact, the concept of a pendulous integrating gyroscopic accelerometer (PIGA) started with the V-2’s Mueller PIGA which was used only to cut off the fuel when sufficient velocity had been achieved.
About this time, Dr. Charles Stark Draper of MIT convinced the US government that he could improve the precision of the PIGA by several orders of magnitude (thousands or tens of thousands) and that gyroscopes could provide the precise information needed to guide the missile warhead (bomb) to its target halfway around the world. The original concept of a radio controlled ICBM was abandoned and a “spoof-proof” concept of ICBMs that carried their own precision instruments to provide internal inertial navigation was born.
This increased the pressure for a means of performing the required navigation calculations. An on-board computer could take the information provided by the on-board gyroscopes and figure out where the missile was in order to get it where it needed to be.
A few of the technological breakthroughs, therefore, were miniaturized nuclear bombs, very precise inertial instruments (gyroscopes), and a sufficiently small on-board computer.
My small involvement came many years later when I was hired by TRW in 1985 to help sustain ICBMs. My first assignment was to work on the project to create a training device for the sump pump located at the bottom of the missile silo. Really, how low can you start? I was literally at the bottom. But I must have done OK with that, and subsequent other assignments, because two years later I was asked to join the ICBM guidance team and become the TRW on-board computer computer expert.
|Old Minuteman ICBM guidance system with gyros at the top,
gyro controller electronics to the left,
the flight controls amplifier at the bottom,
and the on-board computer to the right.
I pulled together the drawings, logic, and wiring diagrams and eagerly started my studies. There were a few electronics cards containing analog components that performed the usual tasks such as power supply. But my attention was drawn to the almost 3 dozen electronics cards marked as “logic”. This must be where the computations occurred.
A word on modern computers. Nowadays, all the computing action occurs on a tiny electronic chip. These chips include some memory to make the computations fast. Early chips did little more than add and subtract, multiply and divide. And they did this in very small memories called registers. Additional memory resided outside the chip. This was pretty rudimentary, but it was enough to create powerful and fast mass-market computing machines. As an engineer and hobbyist, I had programmed my Radio Shack TRS-80 computer chip directly using machine and assembly language. So I knew how those chips worked.
But the Minuteman ICBM computer (at that time) was far more primitive. All those logic cards contained dozens and dozens of NAND gates. These were the first miniaturized integrated circuits, built by Texas Instruments, and nearly 100% purchased by the USAF.
|NAND Gate Logic|
The drawings and wiring diagrams showed me how all this hardware connected. And the logic diagrams gave me the formulas for the various calculations that this computer had to perform.
It was a grand puzzle to figure out.
But where was the memory? It was contained on a spinning disk on one end of the computer (at the bottom of the computer in the photo). The multiple and dedicated read and write heads were fixed in place and the computer used the track associated with each head for a particular purpose in the calculation.
This grand old marvel has since been replaced by a more modern version. But it was a real pinnacle of ingenuity. How marvelous was it? This was the same technology that the Apollo astronauts used to reach the moon.
|The early 1950s computer, Whirlwind, did not fit into a missile guidance system.|
Before leaving this subject, let’s mention a few more technological breakthroughs.
In 2010, I had the privilege to organize an engineers week panel at the ICBM building where I worked. We had retired engineers from Thiokol and the USAF come talk to us about how they created the Minuteman I Stage 1 capable of directing forces along the high tech nozzle and propel the missile out of a buried silo. It did all this without blowing up. See photo at the start of this post. This would be 3 more tech breakthroughs, raising the count in this post to 6.
In their 80’s now, these “kids” then in their mid-twenties, had been hired to create this hardware. When one of them asked: “How do we do this?” They were told: “That’s why we hired you!”
For more on the creation of the first on-board computers, see Beyond the Limits: Flight Enters the Computer Age Paul E. Peruzzi, 1989.