It's not really a successor to Hubble. There's some pretty large differences.
Firstly, Hubble looks mainly at the visible light spectrum and peaks a little into the infrared. JWT will be looking specifically in the infrared spectrum and not at visible light so any "pictures" it takes will actually be computer rendered and light shifted much more than the Hubble.
Secondly the Hubble is going to outlast the JWST. There's a couple of reasons for this. Although the Hubble is basically 1980s technology, it's also very sturdy and most importantly, it's relatively in our backyard. We just can pop up and fix it whenever we need to. The JWST as Summerbuzz points out is going to be at a special gravitational point in our Solar System called the L2 Lagrange Point (of Earth) and that is very very very far away. It's 5 times further away than the Moon and we can't just pop there whenever we fancy. If JWST gets to its position and fails to open then that is 25 years of development and tens of billions of dollars wasted. There is no chance of recovery, of fixing anything or of ever retrieving it, it will be the greatest failure in space science possibly ever and would spell political disaster for NASA. Even if it all goes well, it will last until around 2035 at best because it has a limited amount of fuel and eventually the tiny adjustments that it has to make to stay at the L2 point will burn through and, again, it's so far away that there is no way to refuel it with current or even proposed technology. The Hubble is estimated to last until about 2040 and I think any successor that is outlasted by the thing it is succeeding is probably a bad thing to call a successor.
So one might wonder why they are even bothering with this massively expensive 25 year project that has been cancelled at least twice and that has a high chance of being a total waste of money, spelling a massive political failure that will cut NASA's funding for a generation, which has to execute THREE absolutely perfect course corrections on its way and if it angles itself slightly wrong it will literally melt to pieces and can't even take pretty pictures? Good question. It's because it's one of the most important scientific machines ever developed by the human species and even with the massive risk, the short lifespan and the potential for humiliation, the information that it could reveal is as seductive as it gets in scientific terms.
Here's what JWST is scheduled to do, conservatively, within just the first few years:
- "Photograph" some of the first galaxies ever formed in the Universe, potentially changing our estimated age of the Universe
- Explore the innards of the Supermassive Black Hole in the centre of the Milky Way
- Determine the atmospheric composition of several Earth like candidates in other Solar Systems to see if there is water vapour in the air on those planets. It will also be able to determine the temperature.
- Watch new stars currently being formed in almost perfect clarity
- Look for signs of life in our Solar System in the Moons of Jupiter and other life potential objects.
- Examine the surface and composition of objects in the Kuiper Belt, called the "graveyard of the Solar System" where Pluto, Charon and many other dwarf planets reside.
There's a good chance that this stupid thing, which has 300 documented and realistic failure points for the record that would totally kill the whole project and had an original launch date of 2007,
could actually rewrite human knowledge of the Universe and the understanding of how stars and galaxies are formed while also finding signs of bacterial life on other planets and finishing with a side of discovering the first ever human liveable world outside of Earth. So it's worth a go.
Space missions are always a gamble, that's just the nature of visiting an extremely extreme environment. However our species has never attempted to launch something so finely engineered that will probably only last 10 years and with such huge failure risks before and the rewards had to be big for this even to be attempted. It's a marvel that we've even gotten this close in honesty, I can't see us doing something this ambitious for a long time. After the launch it will take months of travel to get to where it needs to be. Then it will need to sit completely still for three months doing nothing because it can't operate above -220 degrees Celsius and will need to cool down. But then, hopefully, possibly, it might turn on and if it does and it works then we have a good chance of answering some of the questions that humans have been asking for as long as humans have had language.
