Why don't we send another space telescope up into space?

Why don't we(NASA) send another space telescope into space? I mean, send one way out into the solar system so that we could see even farther, but still be able to send commands to it? I know that the problem might be that it is too expensive or that it would be unrepairable, but I would like your expert knowledge.

One possible placement of NGST puts it at the L2 point, which is a position of relative gravitational stability just outside the Earth's orbit from the Sun. The 'scope itself will have a large shield that will keep the Sun's light off the mirror. The mirror itself is huge: NASA wants at least a 4 meter mirror (compare that to Hubble's 2.4 meter mirror)!

Lots more info can be found at NASA's NGST web page

Other telescopes have also been launched:

1. Hipparcos is a European telescope designed to measure the distances to nearby stars with unprecedented accuracy.

2. The Ultraviolet Imaging Telescope (UIT) has flown twice on the Space Shuttle, and returned lovely images in the ultraviolet of all sorts of objects.

3. SOHO was launched to look at the Sun, and recently found that the Sun has "rivers" of gas flowing in it.

There are also many more! Granted, these are all in Earth orbit, but that is mostly because getting to orbit is much easier than sending something far away. Most of these missions are not repairable if something goes wrong, or if the hardware can be updated like Hubble's. But it is usually simpler and cheaper to design a one-shot deal than something like Hubble which can be serviced. However, this will shorten the lifetime of the telescope, typically. Not many telescopes have Hubble's 15 year (at least) lifetime! One notable exception is the International Ultraviolet Explorer, which lasted for 18 years, although the design specs called for a 3-5 year lifetime!