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Symmetry & Emptiness

Real Life Hard SF

Yesterday, I came across a really charming anecdote that reads like hard SF, but is in fact non-fiction. It is from the question and answer session following astronaut Michael Foale's keynote address at the 10th Anniversary Mathematica Conference, Friday, June 19, 1998, published in The Mathematica Journal in 1999. Foale took has own laptop with Mathematica on it with him to the Mir:

I had Mathematica with me; I owned it personally. It wasn't even a copy that NASA had bought for me. And I had intended to work on tensor calculus in all that free time that I was going to have. And I had it along with my music CDs in my CD pack that NASA nicely made for me, in the Spektr module. I also had it on the hard drive, installed on a laptop in the Spektr module.

But there was an accident. An experiment in which the crew was to try to dock a Progress convoy vehicle to the station didn't work out and caused severe damage to the Mir.

A simple TV image was used to measure the rate at which we were closing in. That's "black ground rush" to a parachutist. As you come in closer, the image gets bigger, and you can try to use that to calculate what the speed is while at the same time deriving a closing rate. Then you figure out the docking, using a little joystick to fire the thrusters.

As you know from the media, this was a terrible mistake. It left the station not mortally, but severely, wounded. The Progress basically impacted, we think now, on this part of the solar array on the Spektr module, and then it bounced and slowly floated away along the base block.

The Progress weighs seven tons. We think it collided at about three meters a second. I was in the base block; I didn't see it at all. Sasha Lazutkin saw it; he told me, in all haste, to go straight to the Soyuz escape craft, and as I was passing into the node region of the Mir, I heard a big thump. . . .

It had hit the Spektr module. If we'd been strapped in, we'd have all been shaken around. This is just the opposite of being on Earth, where you're in a car and you're always supposed to strap in. Bash the space station, and nothing happens to you because you're not in contact with the station -- an interesting backwards twist.

Like any good hard SF protagonist, Foale set out to do a bunch of calculations aimed at solving the problems encountered by the crew of the crippled space station. (For those who want to know all about the calculations, the keynote speech discusses them in detail.) He whipped out his trusty slide rule. Well, no, it was a little more complicated than that.

First, the problem he was trying to solve:

The task was this: when you lose attitude control on the station, what happens? The station, low-powered, starts to tumble; then the solar arrays are no longer pointed toward the sun; and then slowly the batteries of the station start to deplete, because the solar arrays aren't charging the batteries. And then in about two or three hours you have no power on the station.

Gyrodynes, the momentum wheels, are always acting, spinning at different rates to change the orientation of the station very slightly. Once the station's lost all its power, or the guidance and control system has failed, the gyrodynes start to spin down, and that momentum gets transferred back into the station. It spins in the opposite direction to the gyrodynes.

Lo and behold, because you have twelve gyrodynes all spinning and working really well to do a nice job at holding the station in attitude, as the space station loses control of those gyrodynes and the gyrodynes spin down, then the space station picks up all of the angular momentum that was in the gyrodynes and starts to spin in the opposite way -- and in an unpredictable way.

So my whole task was to basically try to figure out what the rotation was, null it, establish an orientation, and then spin. But the problem with the station is that it has unequal moments of inertia.

So, hard SF readers. You're in a damaged space station and you need to do some calculations on your computer. But the power keeps going out. Your install disks for the crucial program flew out will the escaping air when the station was damaged. People on the ground are trying their darnedest  to help. What else can possibly go wrong. Read it and find out! Actually solving the equtions seems to have been the least of the problems.

(Did you know that the IBM Thinkpad warranty does not cover exposing your laptop to hard vacuum?)

PS: Further to the subject of math, check out the amusing flame war in the reader review section of the Amazon page on Stephen Wolfram's A New Kind of Science; the book, published 3 years ago, has 318 reader reviews so far.

 

 

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