The Biggest Eyes in the Sky

NASA's "Great Observatories": Hubble, Chandra, Spitzer and Compton, cost on average $1-2 billion each to build, launch and operate, in a program that has well taken over twenty years to develop. By way of comparison, NASA spends approximately $1.3 billion per year on astrophysics (excluding Solar and Solar system related research), or about $5 billion per year on science in total, out of a total budget of $18 billion per year. This useful PDF describes the Great Observatories program, its aims, and NASA's budget.

Together they covered much of electromagnetic spectrum inaccessible to ground based observatories due to atmospheric absorption: Hubble probed ultraviolet as well as optical wavelengths, Spitzer probed lower energy infra-red radiation, while Chandra and Compton were sensitive to X-ray and Gamma ray radiation respectively. In many ways they are the most advanced telescopes ever created by mankind, for those specific wavelengths.

However, for the optical, near-IR and radio wavebands there is no doubt that much better telescopes have been launched into space, and built at greater cost to the public. The difference is that they're not pointed outward but instead inwards, down at the Earth. They are, of course, spy satellites. Quite apart from the vital intelligence-gathering work they do, they're fascinating and impressive technical accomplishments.

The NYT has a fascinating article by Philip Taubman about spy satellites, more specifically about the financial woes affecting latest generation of US spy satellites. Well worth a read when you're having a break from work.

[Edited at Mon Nov 12 11:09 to fix formatting and note article is mainly about the financial aspects of the spy satellite program]