The James Webb Space Telescope (JWT) is the successor to the Hubble telescope. It took 30 years to develop at a cost of around $10bn. It is the largest and most powerful space telescope ever launched. While it could stay operational for up to 10 years, it was designed to be operational for around 5 and half years. The main mission will be to take images of stars and galaxies that existed around a quarter of a billion years ago.

Source: one, two, three