For more than a decade the Hubble Space Telescope (HST) has served to re-imagine the optical Universe, allowing us to peer into the deepest regions of space and create startling images that continue to steal our imagination.
However, as impressive as this instrument is, it is getting long in the tooth, and will soon be reaching the end of its serviceable life. No more shuttle missions, no more spare parts. If we are to continue searching the visible heavens a replacement is needed.
The James Webb Space Telescope
NASA is probably known to most for its role in the space shuttle program and the Apollo moon program. In the 1960s the United States sought to establish its technological superiority over the Russians by being the first to send a manned mission to the Moon.
The administrator credited with bringing this vision to reality is James Webb. His contribution to the Apollo program is being honored by having his name adorn the next great technological achievement of this storied agency.
This new observatory will feature a primary mirror area that is roughly five times the size of Hubble's. This is important because the collection area of the primary mirror is the main indicator of how powerful the telescope is; that is how long observations need to be carried out to image deep space objects.
And despite being hailed as an optical instrument, like Hubble, it is skewed toward the infrared. This is because high red-shift galaxies have their spectra shifted toward this end of the electromagnetic spectrum.
Orbiting Far, Far Away
When we think of space based telescopes we often imagine them orbiting Earth, much like the Moon. However, the James Webb will actually not orbit the Earth at all, but will rather reside at the Sun/Earth system's Lagrange 2 point.
Normally, the farther away from the Sun you get, the longer the orbital period. However, if you are along the line connecting the Sun and Earth, for instance you will not only have the gravitational pull of the Sun providing the force necessary to initiate centripetal motion, but also the addition of Earth's gravity.
The Lagrange 2 point is the orbital radius from the Sun where the combination of the Sun's and Earth's gravitational forces are enough to keep an object in motion around the Sun with the same orbital period as the Earth.
In other words, despite the fact that the telescope will be at a nearly constant distance of about 1 million miles from the Earth (about 4 times the distance from the Earth to the Moon) in the direction away from the Sun, it will still orbit the Sun once every Earth year.
The advantage to having a telescope at this position is that it is free from interference from Earth, while the planet can still provide some shielding from solar radiation. In essence it is always in Earth's shadow.
This also keeps it (relatively) close to Earth, so that we can always be in communication with it and have easy access to data.
There is a downside to placing an instrument, such as the James Webb, out at the Lagrange 2 point. It is so far away that maintenance is nearly impossible; there would be no way to send a manned crew to repair it, at least given current technology.
This may not sound like a big deal, but recall the handful of missions that had to be launched over the years to make repair after repair to the Hubble Space Telescope.
For that reason, extra care is being given to this instrument, to make sure that it can stand the test of time and not need any repairs during its designed operational lifetime. Doing this, however, has led to significant delays and enormous cost overruns.
When Will it be Launched?
As early as 1996 a successor to Hubble was being planned, but little specifics were implemented until 2002. A launch date of 2014 was intended at this time, but that date has been pushed back until at least 2018.
In 2002 it was estimated that the project would cost about 2.5 billion dollars, but is now expected to approach the 9 billion dollar mark.
This sounds like a lot, and it is, but to put that in perspective this is almost exactly what was spent on the Hubble observatory (in 2006 dollars) once all the costs to maintain and repair the instrument are accounted for.
