verses the cost of a replacement.*

The James Webb Space Telescope (formerly the Next Generation Space Telescope) is scheduled to be launched in 2010. Assuming no major slips and no premature failure of the HST, the maintenance money for Hubble could be better applied to make sure the JWST goes up on time.

While the Hubble has provided extremely impressive scientific returns for the past 11 years, it has been an expensive and maintenance intensive instrument since the beginning. It was years late being launched - partly due to the Challenger disaster but only partly - and grossly over budget. It had bad optics that required an expensive maintenance mission. It also had problems with bad solar panels and prematurely failing momentum wheels.

As sad as it'll be when the HST burns in, there comes time when an old system must be replaced. Sentiment isn't a valid reason to keep pouring money into a system. By 2010, the HST will have been in orbit for 20 years.

*On an infinitely more mundane level, I'm facing exactly the same decision about my wife's minivan. It's almost 10 years old but has low mileage. However, things are starting to break. We just replaced the waterpump last weekend only to find out that the transmission is leaking. I may be looking for a new car for her as soon as this afternoon, depending on how bad that transmission leak turns out to be. It's in a place that would cost over $600 to repair.