Friday, July 10, 2009

Sorry, folks!

I haven't been ignoring you, I've been off planet. No, I haven't been squirt boosting around the universe, I just took a slow (and safe, for me) shuttle to two local moons.

My company made a handful of very special machines whose sole purpose is the manufacture of one item. The cost was nearly thirty million bucks, and they will all only run once, if everything goes well.

The machines are to grind and figure a mirror. They were made under contract for a company making a deep space telescope for the rim.

When the Hubble was sent into space, and saw first light, a BUNCH of people were really pissed off.

See, some brain trust had decided that it made good sense to figure the mirror in atmosphere. The mirror that would be used in the vacuum of space.

Now, this would ordinarily not seem like a big deal; the index of refraction of vacuum is 1.0000000 (which is the baseline) but air is closer to 1.0003. Not much, right? On an 8' diameter mirror that's the difference between a sharp image and a crappy one. The wavelength of visible light falls between 400 and 800 nanometers, and a good mirror is supposed to be less than an eigth of a wavelength off at any point. Plus, it was figured and polished in earth gravity.Hubble might just as well have been a man's stainless shaving mirror. So they put 'Glasses" on it, which allow it to use about 3% of it's available surface area.

Anyway, my company made a machine that would be assembled in space where no discernable gravity but the mass of the machinery existed; this machinery cast the mirror in honeycomb segments and let them cool slowly by radiation, and when the entire mirror was cool it was stress relieved,and ground to shape.

The lapping was done by another machine, and both machines were dismantled and boosted away.

Then the final machine, the one I helped design, was brought into place. It's mass was infinitesimal, less than a hundred pounds. Pieces of it were actually made of bamboo, and we set the mirror spinning and used it's own mass to keep it going while it was polished.

We didn't have to build a chamber to coat it, we just set up the sputteror and deposited the aluminum right there in space. We did put sheets of plastic so molecular level molten aluminum wouldn't be roaming around the universe- I now keep a little piece of that aluminised plastic in my wallet.

A group of dignitaries boosted in from Earth to catch first light, but they ended up getting stuck farside for a couple days in quarantine- one had some nasty sinus shit and we didn't want to give it to the whole planet.

So I parked myself in the driver's seat, and slewed the big mirror around to Home.

it took a while for Earth to rotate into the right position, but I managed to catch a good view of Christmas Lake just before it rotated nightside. Nice scope.


  1. Cool story,but a bit of a quibble-the Hubble mirror was figured using a tester that was adjustable by using spacers. When it was done, someone in the shop suggested cross-checking using another test method, but the managemant apes Knew They Were Right so the idea was turned down. The cause of the misfigurement was later traced to the test rig having spacers that were, how to put this, THE WRONG SIZE.A much more mundane source of error, and one for which filtering methods exist. See also Challenger and Columbia.

  2. Ritchie: Were you there when the Hubble mirror was figured? I was. The "official" story is the one you know. Having ground and figured a few mirrors myself (my mom keeps asking when I'm going to move the barrel from her basement) I am pretty aware of the methods used to figure and test; and there is no "Spacer" that will compensate for the difference in refraction of light in air vs vacuum. It annoys me that this information is out there, but the assholes in command had to figure out a way to cover their ass while blaming the people who did the work. Go do a little research about how mirrors are figured.

  3. Been around the barrel a few times, but all my mirrors were small enough to lift by myself.

  4. There's probably a dozen versions of the story. I was working for Spindler and Hoyer, the German optics firm, when this all happened. Story we heard was similar - that the reference master they were using wasn't figured right. And that shop monkeys knew it, but the management ignored them