Posted by: Kash Farooq | July 21, 2011

The James Webb Space Telescope

Edit: Some possible good news!

A couple of weeks ago the US Congress released its Appropriations Bill, which covers science funding and in particular, decides how much funding NASA gets. Despite President Obama being a supporter of NASA, Congress clearly isn’t. The Bill announces massive cuts and includes the following statement that shocked the astrophysics community:

“The bill terminates funding for the James Webb Space Telescope, which is billions of dollars over budget and plagued by poor management.”

So, it appears that Congress wants to just write off the billions of dollars spent so far. It should also be noted that the European Space Agency has contributed $300 million to the project.

So, what it is it and why is it so special?

 Illustration of the James Webb Space Telescope, current as of September 2009

Illustration of the James Webb Space Telescope, current as of September 2009

The James Webb Space Telescope is the planned replacement for two current space telescopes: Hubble and Spitzer. Hubble is well past its sell-by date. It launched in 1990 and has had frequent upgrades and repairs performed by Space Shuttle astronauts. Indeed, soon after launch a focusing problem was discovered; Space Shuttle astronauts were dispatched to, essentially, fit Hubble with a contact lens. Now that the Space Shuttle programme has come to an end, repairs cannot happen anymore.

Spitzer’s main instruments operate in infrared light and require cooling; the liquid helium used to do this run out in 2009 so most of the primary mission instruments don’t work anymore. It is still doing science, but not infrared science.

So we are left with one practically dead telescope and one that surely won’t last much longer.

The James Webb Space Telescope is a hugely ambitious project. The light collecting area is 25 m2; this is over 5 times bigger than Hubble. The mirror is so big that it cannot fit into a rocket in one piece. It has been designed as 18 hexagonal segments that will unfold into position once the telescope is in space.

James Webb Space Telescope Mirrors

Cryogenic testing of the mirrors - they will be subjected to temperatures dipping to -250 degrees Celsius. There will be 18 mirrors in total.

It is hundreds of times more sensitive to anything else we have, and will provide a far higher resolution. We will be able to see fine details that have never been seen before. It will allow us to look much deeper into space and hence further back in time. It is expected to be able to see the Universe as it was 300 million years after the Big Bang. It will be able to image any exoplanets that lie within 25 light years of Earth. That’s potentially a lot of planets.

The size of the mirror, and the fact that it needs to unfold itself, becomes even more ambitious when you consider where the telescope is expected to operate. Unlike Hubble, the James Webb has been designed to have a heliocentric orbit, rather than a geocentric one – basically it will be an artificial satellite of the Sun, not of the Earth.

Orbit of James Webb Space Telescope, at L2 – the second Lagrangian point.

Orbit of James Webb Space Telescope, at L2 – the second Lagrangian point.

The selected location is called the Second Lagrangian point. This point is 1.5 million kilometres from Earth – that’s 4 times further away than the Moon. It’s an ideal location for space observatories – think of it as a gravitational sweet spot with the added bonus that the Earth can be used to help shield the telescope from the Sun – an important consideration for instruments sensitive to heat.

This does mean, however, if it doesn’t work once it gets to the Second Lagrangian point there is no way to go and fix it.

The story isn’t over yet. Many prominent astronomers are writing to Senators and Representatives, and encouraging their Twitter followers to do the same. Several have already replied and stated that they will fight this decision.

As they say – watch this space.

Pun intended.

Finally, I highly recommend you watch this video. I think we should stick this guy in front of the funding decision makers.


I recorded a version of the above for episode 93 of the Pod Delusion – a podcast about interesting things.

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