atomic_fungus (atomic_fungus) wrote,

#4291: Back to the flash flood warnings

The amount of rain we had in June could charitably be called "excessive" and it looks like we're getting more of it over the next few days. I had thought to perhaps cut the grass today, but since it rained last night--and enough to make the window well leak again--I really can't; the grass will be too wet.

Short of reengineering the back yard, there really isn't any way to improve the drainage, either. Probably the only thing that would really fix the window well leak problem would be to put drainage tile in the middle of the back yard and run it to the street, but since rainwater runoff can no longer be dumped directly into the sewer there is no longer any good way to accomplish that. The street is lower than the back yard, so in theory a competent installation would keep the back yard from becoming a swamp, and the tile could drain into the street without causing anyone any trouble, but even trying to imagine what installing such a thing would cost makes me despair. ("Do it yourself"? Digging a hundred feet of trench and laying tile by hand? I'm not John freakin' Henry, damn it.)

...and all that to remedy a problem which does not occur except under unusual circumstances--even if we've had them happen several times this year--would be of dubious economy.


* * *

So I found a web site which has--among other things--transcripts of the Apollo mission communications, including a transcript of the first couple hours of Apollo 13. The movie of Apollo 13 cleaned up the launch sequence to a considerable extent, because there was a lot more chatter around the failure of the central engine on the first stage than the movie showed.

Apollo Lunar Surface Journal is the page where you can find all that good stuff.

The transcripts give you an idea of how much work the astronauts had to do while en route. They weren't just hanging around and talking; they were constantly in motion, flipping switches, reading back displays, and so on. There are brief breaks in the transcript for a few minutes here and there, but nothing really calls attention to them, so when you read these things it seems as if those guys were perpetually occupied.

It's a nice look at the dead art of traveling to other worlds, though. *sigh*

I ended up there there after seeing a YouTube video posted on AoSHQ of a guy trying to reverse-engineer a component of the Apollo launch controller. Built using state-of-the-art components in the 1960s, the part under inspection consists of a couple dozen extremely simple logic ICs on a multilayer circuit board. It's diode-transistor logic (DTL), and each IC has perhaps one or two gates on it; modern logic chips are TTL (twin transistor logic) and ICs with six gates each are dirt cheap in bulk.

The circuit board is, in fact, perhaps twice as large as the entire computer would be if it were implemented using technology about twenty years old. (Rather than fifty.)

The original launch computer weighed some eighty pounds, all told, took up a sizable amount of space, and was thrown away after use. Yeah. Apparently no examples of its programming remain; that was some of the information which was thrown away by NASA when they wanted to eliminate competition for the Space Shuttle.

That's really only a shame from a historic perspective, though. If we were going to build a modern Saturn V, all that stuff would have to be recreated anyway since the computer hardware is approximately neolithic. All the computers used in the Moon trips used ferrite core memory--the Space Shuttle's computers used ferrite core memory!--and it takes a lot of tiny ferrite cores to store even a moderately complex program.

The launch computer had 32k "words" of memory, with each word being 26 bits long; it works out to about 104k using conventional 8-bit bytes. Early computers had some weird architectures and nothing was standardized, so they were typically built using whatever was most convenient for the task at hand, and frequently each "word" contained both opcode (instruction) and operand (data) as well as other information like parity (for error correction).

The launch computer was distinct from the actual guidance computer that lived in the command module, and which the astronauts did all the fiddling with. The launch computer only controlled the launch, and there was no external interface to the thing; it was a black box and once the ship was in orbit it was dead weight. Since it was part of the third stage, though, it didn't go to the Moon.

I figure that modern electronics would probably save about five hundred pounds from the weight of the Saturn V third stage...and that's being conservative. It's probably more than that, because in addition to having less mass, modern electronics run at lower voltages and consume less power, thus dissipating less waste heat, which means less cooling is needed (and we've gotten better at that, too).

And there are a hell of a lot of electronic gizmos and gewgaws in a complete Saturn V. How many tons would modern electronics save in the liftoff budget?

* * *

Apropos of nothing in particular, I noticed that SpaceX is hiring....

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