Re: Back in the saddle
My control systems professor was a professionally irreverent fellow with whom I could never get along. He knew enough to give me a miserable grade, which I certainly earned. But I also kept my ears open for little things.
The computer center had acquired one of the first Altair computers with a little box monitor. Nearly the only software we had for it was a lunar lander game. Maybe one person in ten could get the lander down, one time in three, without it running out of fuel and crashing.
After my second failure, I remembered something that Professor C--- had said: often the optimums occur at extremes. I thought about how this might apply and realized that using the lander's rocket thrusters at anything less than full power was wasteful, because the thrust fraction that corresponded to hovering thrust was throwing fuel away.
I started again, and this time used the minimum possible fuel to slow the lander out of orbit and orient it rocket-down. I waited until I was about 60% of the way down, falling at a terrifying speed, and then used a full-power burn to slow the fall to near zero. I did it again with the lander only a couple hundred meters up, and had enough fuel to make a soft landing with just a little to spare.
I also had an audience. The person responsible for our Portable Slum (a story for another time) was watching, and he announced to the people in three rooms (full of noisy machinery) that I had succeeded. And then ... "I bet you can't do it again!"
I should have made him put money on it. He and a few others shouted "No! Use the rockets! You're going to crash!" as I repeated the performance, ending with almost 20% of fuel remaining.
I silenced them and spoiled the game by discovering what the NASA folks knew: that the only way it could work is if you used partial burn for only a few seconds while making the soft touchdown.
