- Nov 26, 2019
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I mentioned the computer on the SR-71 and you talked about memory. I don't remember the amount of memory there was on that onboard SEL computer, but it wasn't much compared to my cell phone.
Yet, when the pilot switched on the computer right after the first refuel (which happened as soon as they'd safely launched), the SEL controlled every aspect of the aircraft operation. And it was all running from a big magnetic tape in the airplane, each operation in sequence on the tape.
During the Carter Administration, we had to send each mission plan to the White House for approval prior to launch. For standard missions, we could plan them and send them a couple of weeks in advance. But sometimes we had emergency missions in which we had only a few days to plan and launch. But we still had to send the plan to the White House for approval. Frequently, the White House would want some parameter changed. Maybe fly a couple of miles further from that contested border. Maybe angle the approach so it didn't look so provocative. Maybe spend a bit less time in the "sensitive area."
After making a change to something in the mission plan program, we needed to check the entire program again because sometimes making a change introduced what we called a "spurious input." We'd change one thing but somehow something unintended got changed somewhere else in the program. That might be where an instruction to make a 90-degree right bank got unintendedly changed to a 270-degree right bank, or an altitude correction that was supposed to be 80,000 feet missed a zero. So, we had to go through the entire program tape again. Here is the catch: It took the same amount of time to review the program tape as the mission itself would take. So, if it was an eight-hour mission (the average...they'd range from six to twelve hours), it would take eight hours to review the tape for spurious inputs.
The Carter Administration sometimes delayed so long giving us a change order that we didn't have time to review the tape before launch. So, as the crew came out of their mandatory pre-mission crew rest, we'd have to brief them, "You remember that mission you studied before you went to sleep? Well, it changed while you were sleeping. And we also didn't have time to check the tape. So...while you're up there doing MACH 3, just be ready for the plane to do anything at any moment." Those were eye-bulging, white-knuckle flights.
Most often, the spurious input wasn't serious. Maybe it would just skip an airspeed check or fail to turn a camera on or off (which would be corrected by the subsequent camera command sequence). But if a spurious input was serious, the crew would have to turn off the computer and abort the mission. When the SEL went bad, turning off the computer meant going home.
I remember the first mission we flew after the Reagan Administration came into office. We sent them the mission plan as usual. The days ticked by until we started to get antsy, so I called my contact in DC to see if he could inquire about the delay. A few hours later, he called me back: "The White House said you can go ahead and fly the mission if you want to."
I said, "'If we want to?' What does that mean?"
Essentially, as far as Reagan was concerned, if the overall mission program already had White House approval, he didn't expect us to get his permission for each one. That instantly made my life easier.
Did you ever experience the dreaded “engine unstart” out of curiosity? I was saddened recently when Major Brian Schul of the Speed Check fame reposed, memory eternal.
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