PDP-11 and the Space Shuttle

Reading a story about the development of the Shuttle’s thermal protective tiles, I was surprised to see a PDP-11 jump out. And then noticed that this was happening in 1969!

My job was to figure out a way to rapidly and accurately measure the heat transfer properties of these rigidized ceramic fiber tiles. We developed the lab equipment to measure those scattering and absorption coefficients from room temperature to 2400 deg F (1316 deg C), the maximum operating temperature for those tiles, using a specially designed vacuum furnace along with multi-channel lock-in amplifiers, a signal averager and a PDP11/40 minicomputer, state-of-the-art stuff in 1969. Traditional methods for doing these measurements took weeks and were very expensive and not particularly accurate for strange materials like these tiles. We could make these scattering and absorption coefficient measurements in 1 or 2 days. This was important because our material and processes engineers were developing dozens of variations of these tiles and they needed the heat transfer measurements done quickly to sort out the winners and the losers. All of this work would feed into our proposal to manufacture the Orbiter. The competition for this NASA contract was intense.