Check out this magnificent picture of the 68-million-light-year distant spiral galaxy NGC 3892 taken by Hubble:
OOooo, pretty! Click to engalactinate (or go here to grab a monstrous 2500x2600 pixel shot).
I've written about images like this before: why there are spiral arms, how the red light denotes hydrogen gas, the location of active star birth; the reddish-yellow glow of the core indicating old stars.
But what amazed me most about this picture -- besides its sheer beauty -- is that it's composed of images from three separate generations of Hubble cameras! The Wide Field/Planetary Camera 2 was installed on Hubble in 1993, the Advanced Camera for Surveys went up in 2002, and the Wide Field Camera 3 last year in 2009. All three took images that were used to make this lovely portrait of the spiral galaxy; images that span nearly a decade of time between them.
One of Hubble's strengths is that it can be periodically upgraded as technology improves. But this comes at a cost, literally: it's expensive. NASA has a finite budget, and finite manpower. Money spent to upgrade Hubble and keep using it is money that cannot be used for other missions. That's why, after 20 years, no more servicing missions are planned. What we have with Hubble right now is pretty much what we'll get... unless private space companies take over, or NASA gets a massive infusion of cash. Neither seems likely to me.
But don't despair. The James Webb Space Telescope launches in a few years, and promises to deliver more epic images and science. And there will be other observatories as well. Hubble may be the first space telescope most people heard about, but it won't be the last.