Sunrise, Sunset


So one morning almost three months ago, Rebecca and I are standing on Cocoa Beach. It’s her first time ever visiting an ocean, and I’ve arranged it that the first time she sees the Atlantic, she’s watching the sun rise over the horizon. It is, all in all, a neat experience.

Flash-forward to two weeks ago. I’m on a business trip to NASA’s Jet Propulsion Laboratory. It’s my fourth trip to California in less than a year, and so I decide that this time I’m going to finally get around to doing something I’ve put off on previous trips — I’m going to watch the sun set on the Pacific. And so I do.

I’m currently helping one of the Space Launch System executives work on an upcoming TEDx talk, using the transcontinental railroad as analogy for the future of human space exploration, playing with themes like public-private partnerships and the fact that, historically, there are almost no new transportation capabilities that do not improve everyday life.

I thought about that as I was standing on the beach in Los Angeles. I, a fairly normal person, had watched the sunrise over one ocean and set over the other two months apart. Just 150 years ago, before the completion of the transcontinental railroad, that was impossible in the United States. Today, if you really wanted to, you could see them both in the same day. On the International Space Station, you see sixteen sunrises and sunsets a day.

We live in a time of miracles and wonders. It’s good to be reminded to wonder at it.

Mars Rocket Yadda Yadda Horses’ Butts


08pd0640-s

According to an old story that’s circulated the internet for years, the dimensions of the space shuttle’s solid rocket boosters were prescribed by the width of a horse’s rear end.

The story goes from Roman chariots that were made wide enough to accommodate the back end of two war horses to British roads that were built for those chariots and ended up with ruts where their wheels were to Engish wagons that were built wide enough to fit those ruts to trains that were built from the jigs and toolings for those wagon and thus U.S. railroads were all built to the width of a Roman chariot and thus based on the width of two horse’s butts. And then it takes it a step farther to the fact that the shuttle solid rocket boosters were designed to be transported via rail and thus had to fit through a railway tunnel determined by the width of a  train and thus, yadda yadda, horses.

The particulars of the story get some stuff wrong. U.S. railways didn’t originally have a standard gauge, and were built to a variety of widths before being standardized, so there was no particular magic number that they had to be. On the other hand, it’s also worth noting that the original railroad cars were horse-drawn, so there was a more direct connection between the widths of train tracks and horses, so there is some basic truth to the story, even if the particulars aren’t exactly right.

I was thinking about this story again recently because of interesting fact I learned about the Space Launch System rocket I’m honored to support.

The core stage of SLS is 27.6 feet in diameter, because it’s designed to have the same diameter as the space shuttle’s external tank in order to more effectively take advantage of existing manufacturing and launch facilities. We were talking about that at work, and the question came up as to why the shuttle’s external tank had that diameter. We suspected at first it, in turn, had something to do with the facilities left over from the Saturn days, but weren’t able to find the answer anyway.

So I called someone I know who worked on the external tank, and asked him. And the answer has to do with the fact that the shuttle’s solid rocket boosters were to be mounted to the side of the external tank. Given the volatility of the fuels inside the tank, you wanted the attach points to be somewhere on the structure off of the fuel tanks inside it. The length of the solid rocket booster had already been established, and that determined what the length of the external tank would need to be to properly accommodate the attach points. The engineers knew what the volume of the tank had to be in order to hold enough fuel for launch, so once the length was established, the diameter was just a question of division.

Which means that the next time astronauts fly around the moon, they’ll be launched on a vehicle with a diameter determined loosely by the width of horses’ butts.