The James Webb Telescope

Dr. Matt Mountain explains the design of the James Webb Telescope and how infra-red will be used to study the very first galaxies that ever formed...
04 September 2011

Interview with 

Dr. Matt Mountain, Space Telescope Science Institute


Chris -   Now we have a very special extra guest who's with us this week and that's Dr. Matt Mountain.  He's the Director of the Space Telescope Science Institute and he's been overseeing some of the groundbreaking work that's been done with the Hubble Space Telescope, as well as working on its successor the James Webb Space Telescope. He's with us to answer some of my questions, but also, more importantly, some of your questions this week, and to tell us a bit about the project.  Hello, Matt.

Matt -   Hello there, Chris.

Chris -   First of all, can you tell us what is the James Webb Space James Webb Space TelescopeTelescope?  What will it do?

Matt -   Well the James Webb Space Telescope is designed to be the successor to the Hubble Space Telescope.  If you like, sort of Hubble 2.0.  It's designed to work not as the Hubble is, at optical wavelengths, but actually at infrared wavelengths and it's much bigger than the Hubble.  It's 6.5 metres across when the Hubble is only 2.4 metres across.  It is a very big telescope, which actually has to unfold on its way to orbit. It's orbit is roughly four times the distance between the moon to us away, roughly a million kilometres away. It's designed to look at the very first galaxies that ever formed in the Universe's history and, we hope, look at planets that are orbiting other stars and actually perhaps detect for the first time liquid water on those planets.

Chris -   How was it conceived and how is it being constructed and how far along are you?

Matt -   It was conceived by people at the Space Telescope Sciences and by the astronomical community in the US generally and now in Europe.  As the Hubble started work, we began to understand the limits of what we would be able to see with the Hubble.  For example, we began to understand there was actually a whole class of galaxies - very early galaxies - that the Hubble could only barely see. It could see the sort of peak of the iceberg and there's a whole sort of hidden Universe in the infrared which in fact we called the "Dark Ages."  It's the time from when the Big Bang and the background radiation, and the sort of irregularities in that radiation, turned into galaxies. Then galaxies appeared, and the galaxies that we see in the optical come from a certain point back in the Big Bang, roughly 13 billion years ago. But we know the Big Bang started 13.7 billion years ago, but that period in-between, these Dark Ages, was inaccessible.  We realised that there was a very rich Universe there and we needed a telescope that was much bigger than the Hubble that could operate in the infrared.  So, it's been under construction for over 5 to 6 years now and each of its mirrors are part of a hexagonal segment.  It's rather like a ground based Keck telescope, which is a very large telescope in Mauna Kea in Hawaii.  This telescope is made up of segmented mirrors that all have to operate as a single mirror. It's a very radical design and it will be flying far beyond the moon at a point called Lagrange point 2, which is a sort of stable point beyond the moon. There it will cool down to a ridiculously low temperature, roughly 40 degrees Kelvin, which, speaking from the US, is roughly minus 400 degrees Fahrenheit.  So it can be very, very cold and where we are right now is that all the mirrors have had been made.  In fact last week, they were completed.  We have had some problems with cost overruns and some technical problems.  We had to invent 10 new technologies to get this task going but we're hoping to get this thing launched by 2018.

Chris -   Yes, that's a bit of a sore point, wasn't it. Because if you look the history of the James Webb Space Telescope, it was conceived in, what - the mid-90s?  It was supposed to be flying by the mid "noughties" and it was supposed to have a price tag of half a billion.  That price tag is now nearly 9 billion.  So, how optimistic are you that you will be seeing this thing returning data to Earth by that date?

Matt -   Well it was never actually supposed to - yeah, I mean you're absolutely right.  There's a lot of controversy going on right now but it turns out that it was never supposed to be flown for half a billion Dollars.  That was an estimate that people thought you perhaps could actually get something like this going if you launched it by sort of the late '90s.  By the time people started studying this though, they realised that really something of this scale was going to cost between 3 to 4 billion Dollars if we could get it launched by sort of 2011.  But delays and some of the technology challenges really have pushed the whole launch date out and as you push the launch date out of this very, very complicated telescope, the cost goes up.  And on top of that, we then started actually realising we needed far more complicated instruments than had originally been put together. You stack all that up, and yes, you're looking at a price tag probably to get this thing launched of at least 8 billion Dollars, which of course is an enormous amount of money.  But the Hubble itself, to get it launched in today's Dollars, cost roughly 10 billion Dollars.  So for something of the order of the cost to get the Hubble launched, you're getting a telescope which is almost 4 times larger and incredibly more powerful and in a much more stable orbit than where the Hubble is.

Dave -   And, I mean, one of the first things you said was this thing has got to unfold - that immediately rings alarm bells for a telescope! You're trying to position your mirrors to within a wavelength of light - I guess, for a really good quality telescope - so that's got to be a serious challenge?

Matt -   Absolutely, and in fact when you first watch the movie (you can go to one of our websites and you can watch this thing unfolding) people do actually turn to you and say, "Are you kidding?".  What they've forgotten of course is, on the ground for example, the 10-metre Keck telescope on Mauna Kea. It has lots of segmented mirrors, and it holds its figure perfectly in wind at all conditions on Mauna Kea.  What we use is a thing called a wave front sensor where we actually measure a star from the mirrors and we measure the wave front and then correct, because each of these mirrors has an individual adjustment on it.  so we're constantly adjusting these mirrors to actually have them line up as a perfect single mirror. That technology was in fact mastered back in the '80s by the Keck telescope on the ground.


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