Stardate 20030430.2346

(Captain's log): Tracy and I have been exchanging mail today about the relationship between science and engineering, and the last letter I received said this:

I think that my opponents realise that scientists use engineers' creations, especially since some of them are scientists themselves who want the government to pay more money for big pieces of equipment for them, but the attitude is that scientists just go out and buy them off the shelf, like they buy food to keep living, there's no complicated linkages.

It depends enormously on which field of science you're in. But even when equipment is purchased "off the shelf", if it's moderately complicated it was probably custom designed for an industry, even if not for a specific customer. (Not a lot of call for DNA sequencers among the general public, for instance, and not too many of us own scanning electron microscopes.)

But there is a lot of science which depends on direct custom engineering. One of the best examples of that I know of is the European Southern Observatory. This is a massive project I've been following closely for several years now. The ESO is a joint project of several major European countries, who have built two large observation sites in the high deserts of Chile in the Andes. Not only is the southern hemisphere less well supported by big scopes, but the sites in question in Chile are among the best in the world for this purpose, being high and cold and getting almost no rain or even clouds. Both sites are a long way from any human settlements, so there's no light pollution. And the projects have been amply funded. This is all being done in cooperation with the nation of Chile and certain universities there, and one of the parts of the agreement was that Chilean astronomers would be entitled to a certain percentage of the observation time.

The original site was La Silla, and they put in a series of medium sized scopes there, the largest of which was 3.6 meters.

But they decided they wanted to do much better, and began plans for Paranal, where they have built the Very Large Telescope, the VLT. At that site they've got three 1.8 meter scopes, a 2.5 meter, plans eventually for a 4 meter scope, and they've now completed four scopes with 8 meter mirrors, known as Antu, Kueyen, Melipal and Yepun. (The names come from Inca mythology.)

I am stunned by the attention to detail and the sheer quality of the work which was done on these big scopes. One of the things they want to try to avoid at all costs is air turbulence, and the biggest source of air turbulence is local heat sources. So each day they have weather forecasters make a prediction of what the night-time temperatures will be, and the telescope enclosures are precooled to that same temperature. When they open, the temperature will be the same. Likewise, humans don't go into the enclosures during observations; a human body is much too warm and will cause all kinds of problems.

But they didn't stop there. All the main bearings on the scope mounts are water cooled so that heat from friction doesn't screw things up, and of course the motors that move it are too. A lot of the top-level engineering documentation is online; for someone like me it's fascinating to look at. (And maybe for some of you, too.)

All of the observation instruments were custom designed, too; systems like ISAAC and FORS set new standards.

By the way, a lot of the pictures you see in the viewport at the top of this page came from the VLT.

But the real star of the show is the interferometer, which is a mechanism which has the ability to take light from all four big mirrors and some of the secondaries and to merge them in real time so as to permit the entire observatory to be used as one great big mirror. It will have the resolution of a scope 200 meters across (though of course not the light gathering power). This is a non-trivial problem.

The only thing like it I know of is at the American Gemini Observatory in Hawaii, which merges the light from two mirrors. But the VLTI will merge light from 7 (I think it was) mirrors all at once, and that is extremely tough.

One does not buy this kind of thing "off the shelf". Some of the computers they're using there are standard make, but they're running a hell of a lot of custom software to operate all this stuff.

And a lot of the rest of the design approaches science fiction. For instance, the big mirrors are all on active mounts which dynamically control the amount of force applied at the support points as the mirrors change direction so that they maintain their shapes. And they're also using adaptive optics, which I don't even understand. (I know what it accomplishes, but I'll be damned if I know how they tune it in real time. What I do know is that it's a real bitch to do well.)

The designers are not content. They're in the initial planning stages now for something even bigger. It is currently known as OWL, the OverWhelmingly Large Telescope. And that, my friends, is not hyperbole.

If it gets bui