James Webb Telescope
The real problem is that all four of the NASA space telescopes are old and will be subject to failures. The next generation of space telescope is the James Webb Space Telescope. This project is grossly over budget, perpetually delayed and currently keeps failing test. Some of this is down to incompetence but a lot is all about waving the flag about how clever NASA are.
The costs of the JWST are just astronomical:
1996 $1 billion, 2007 launch
2018 £9.7 billion 2021 launch
If this does get launched there are just so many things to go wrong it will really be a miracle if everything works.
What is even more scary is that there is another NASA telescope, WFIRST is also over budget and delayed. To be fair, Hubble was also overran with an initial budget of $200 million but ended up at $1.2 billion plus the cost of fixing the mirrors. The thing is that there was always as good change of success. The new platforms are just so complicated and experimental that they risk being obsolete by the time they are commissioned. Improvements in ground-based telescopes and the significantly lower costs are eating into the space telescope's viability every year.