Why JWST will be better?
1- With a sunshield 22 metres (72 feet) in length, the size of a tennis court, and a mirror 6.5 metres (21 feet) wide the JWST, which is due to launch in October 2018, is over twice the size of the Hubble Space Telescope, making it the largest space telescope ever launched.
2- The JWST will take about a month to reach a position 1.5 million kilometres (930,000 miles) from Earth known as Lagrange point 2, or L2. Here the telescope’s observations will be unhindered by Earth and the Moon although, if it malfunctions (as happened with Hubble), we currently have no way to go and fix it.
It could find water on exoplanets
One of the JWST’s most notable abilities is that it will be able to detect planets around nearby stars by measuring infrared radiation, and it will even be able to measure the atmospheres of exoplanets by studying the starlight that passes through. By doing this it will be able to determine if an exoplanet has liquid water on its surface.
It’s seven times more powerful than the Hubble Space Telescope
The giant mirror of the JWST is made of 18 individual hexagonal segments composed of lightweight beryllium. It is almost three times the size of Hubble’s mirror, boasting a light-collecting area seven times greater, but both mirrors weigh almost the same owing to the lighter materials used on the JWST’s mirror.
5- One of the goals of the JWST is to observe the first stars and galaxies that formed just a few hundred million years after the Big Bang, an era of the universe that is not fully understood. The telescope will be sensitive to infrared light, which will enable it to do this.
6- The official mission lifespan for the JWST is between five and ten years. The telescope is limited by the amount of fuel it has on board used to maintain its position, which will be enough for a ten-year lifetime. Of course, other factors like budget cuts or malfunctions could end the mission earlier.
7-The side of the JWST that will always face the Sun, the bottom of the sunshield, will reach temperatures of 85°C (185 °F). The other side, which houses the mirrors and science instruments, will operate at a much nippier -233°C (-388 °F).