Sunday, January 04, 2009

Doing the impossible

Yesterday's post on the Crab Nebula was inspired by this recent APOD (Astronomy Picture of the Day) showing the ghostly wisps of X-ray radiation surrounding the nebula. The image was made by the Chandra X-Ray Observatory, in orbit around the Earth.

The story of Chandra is told in a book I reviewed several years ago for the Wilson Quarterly: Revealing the Universe: The Making of the Chandra X-Ray Observatory, by Wallace Tucker and Karen Tucker (Harvard University Press). The book might more appropriately have been called Revealing NASA. There is not much in it of the universe; the narrative ends as the first images are coming in from the $2 billion Chandra, named for the great astrophysicist Subrahmanyan Chandrasekhar, and launched into Earth orbit by the Space Shuttle Columbia in 1999. These images, in which invisible X-rays are rendered in false color, are rather less dramatic than the pictures we are used to seeing from the Hubble Space Telescope. They may be packed with valuable information for astronomers, but the average reader can be forgiven for thinking, "Ho, hum."

Which is not to say that the book is a "ho, hum" read. At the beginning, I was put off by an alphabet soup of acronyms (even Chandra started life as AXAF, "Advanced X-ray Astrophysics Facility"). But as the pace picked up, I was sucked into a thrilling revelation of how NASA works, technically and politically, and how an instrument like Chandra gets built and deployed.

Wallace Tucker and Karen Tucker are ideal guides to Chandra's story, science spokesman and science writer, respectively, for the Smithsonian Astrophysical Observatory, parent institution for Chandra science. They saw much of it happen, and they had access to the key players.

The universe reveals itself in every part of the electromagnetic spectrum, from low-energy radio waves to high-energy X-rays and gamma rays. X-rays are produced by the most violent objects in the universe -- black holes, colliding galaxies, exploding stars -- but they are absorbed by Earth's atmosphere, so much of the fun stuff can only be seen if we heave our instruments hundreds or thousands of miles into the sky.

The short wavelengths of X-rays place extraordinary tolerances on the optics used to focus them. At the time I reviewed the book, Chandra's mirrors were the most perfectly shaped and polished ever produced; perhaps they still are. The fragile mirrors and detectors had to be aligned to within the thickness of a few atoms, placed atop a hugely powerful rocket and blasted it into space. Perhaps never in the history of engineering has there been such an incompatible conjunction of delicacy and power.

In fact, as you read the Tuckers' book, you wonder why the astronomers and NASA managers and technicians ever bothered to try. The number of things that could go wrong was so great that the odds against success seem overwhelming. And that does not include the political gauntlet that any project like Chandra must run to even get to the launch pad.

As I finished the book, I had an even more profound respect for the scientists who conceived the great space observatories and made them happen, and for the amazing technical skills that hide behind the alphabet soup of NASA acronyms. Lots of taxpayer dollars were riding on Chandra's success; lots of careers too were in the balance. Nearly 30 years passed between the first proposal for a large X-ray telescope and final deployment. That's a huge chunk of one's life to devote to a chunk of machinery that may never fly -- and may not work if it does fly.

By the time I got to the "Launch" and "First Light" chapters at the end of the book, I was sitting on the edge of my seat.

(This post is a reshaping of the Wilson Quarterly review.)

Discuss this essay and more over on the Science Musings Blog.