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TMT - Thirty-meter telescope -

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TMT - thirty-metre telescope

Ed Stone outlines the plans for a thirty-metre telescope. It will be made from 492 hexagonal
segments all controlled by a computer. The site for the telescope hasn't been selected yet. New
adaptive optics techniques allow removal of the effects of the atmosphere. This gives the same
resolution as the Hubble telescope has in space. Ed Stone cites dark matter as the area of
astronomical physics that he'd be most pleased to have resolved!


This transcript was typed from a recording of the program. The ABC cannot guarantee its complete
accuracy because of the possibility of mishearing and occasional difficulty in identifying

Ed Stone: We are developing a new telescope called the Thirty-Meter Telescope, or TMT for short,
which means the mirror itself is 30 metres across. It will be modelled after the Keck telescopes in
Hawaii. We have two Keck telescopes which are ten metres each. Two key innovations make a large
telescope possible. Number one innovation is making a mirror out of segments rather than a single
piece of glass; hexagonal tiles, if you like. We have 36 such segments in the Keck mirrors each,
and for this one, because it's much larger, we have 492 hexagonal segments, all shaped so when
they're put together and controlled by a computer they form a perfect optical surface just as
though it was made from a single piece of glass.

Robyn Williams: So it is glass?

Ed Stone: It's a special kind of glass ceramic which has a very low temperature coefficient so that
it doesn't change shape when the temperature changes.

Robyn Williams: Where's it going to be?

Ed Stone: We're looking at five sites. We're looking at a site in Hawaii near the Keck telescopes,
we're looking at three sites in Chile, also very good high sites, and a site in Baja California,

Robyn Williams: When will you choose actually which site will get the blessing?

Ed Stone: We're in a process where we will probably pick two sites, a north site and a south site,
this May, and then a year later pick the site for the telescope, either Chile or Hawaii.

Robyn Williams: Chile or Hawaii, both a fairly long way away from where you sit. I suppose in Chile
you've got the height, as well as presumably the Kecks are pretty high up. I remember driving to
the top of what was virtually a volcano, and it's so high in Hawaii that you actually get sunburn
within minutes if you're not careful. So both of them would be very high up, would they?

Ed Stone: Yes, they would be. At Mauna Kea we're at an altitude of 14,000 feet where the atmosphere
is 60% of what it is at the earth, so you do notice that you're at an altitude.

Robyn Williams: I got burned for days, it was quite amazing. Where are the mirrors being made at
the moment?

Ed Stone: We haven't actually started construction. We have been in what's called a design
development phase and we started that in April of 2004. We will finish that phase in April of 2009
and be ready for construction. So we're currently having glass poured for that purpose and we're
testing out different sources of glass and different polishers. So we have not decided yet where we
will buy the glass and who will do the polishing, but we're doing some prototyping so that we'll be
ready to go in about a year.

Robyn Williams: And transporting it to those distant places, that must be a challenge.

Ed Stone: It certainly will, yes, but fortunately the segments themselves are only about five feet
across, so that even when properly boxed they're easily transportable. So that's another advantage
of a segmented mirror.

Robyn Williams: Such a gigantic instrument...when you look at, for instance, not just the Hubble
which has got an extended life now but its replacement, what are the advantages of having a
30-metre telescope here on Earth that nonetheless has got to look through some atmosphere?

Ed Stone: Ah! The second innovation. The second innovation is adaptive optics. With the Keck
telescope now we have a system which allows us to remove the effects of the atmosphere, and we now
with the Keck ten-metre telescopes have the same spatial resolution as Hubble has in space, and
that's achieved by essentially having a separate small flexible mirror which is deformed 1,000
times a second to exactly or almost exactly compensate for the turbulence in the atmosphere,
creating a near perfect image. That's a working system and we will be doing an elaboration of that
system for the 30-metre telescope so that it will have even higher resolution, it will have three
times better resolution that the Kecks because it's three times the diameter.

Robyn Williams: In the 50th anniversary of the formation of NASA, will the arguments be used by
some people that now you don't need to go into space and have another Hubble?

Ed Stone: Space is still important because even at the top of the highest mountain that we will be
at there are just narrow windows that we can look through in the atmosphere in the infrared because
the water vapour there will absorb some of the infrared light. So if you want to see the complete
infrared spectrum, you still need to go into space. If you want to see the ultraviolet spectrum you
need to go into space, because even at 14,000 feet the radiation doesn't get down to the

Robyn Williams: When it's up, this 30-metre giant, will that really be as big as you get for a

Ed Stone: There is talk of an even larger telescope. The Europeans are talking about a 42-metre
telescope, just twice the area of the 30-metre telescope. So that's what they're currently planning
and designing.

Robyn Williams: I find that extraordinary.

Ed Stone: Yes, that will be even larger.

Robyn Williams: You started in astronomy way, way back. You've just celebrated your 70th birthday.
When you look back from where you began, did you expect to reach these kinds of zeniths of
achievement or is it slightly less than you expected?

Ed Stone: It's much more than I could have imagined actually because when I was interested in
science in high school it was before the space age began, so there was really no way to imagine
that in fact all these incredible things would have been happening. Fortunately when I was in
graduate school the space age began with the launch of Sputnik in 1957 and so I was right there at
the beginning of the space age. It was very fortunate, the timing was just perfect.

Robyn Williams: Well, 50 years of space travel, 50 years of NASA, and how long...ten years at JPL?

Ed Stone: Yes I was the director at JPL. Of course I started working at JPL in 1972 as the chief
scientist for Voyager. I'm still the chief scientist for Voyager, so I've been doing that now for
over 35 years. But then in 1991 I went fulltime as the director of JPL until 2001, then I came back
here to Caltech to resume my position as a professor.

Robyn Williams: Some of the achievements that you can look forward to...lots of people of course
are still counting the planets. Many people, on the other hand, are being bemused by those dark
energies and dark matters that seem immensely confusing, and even more mysterious things like those
gravity waves we keep searching for. What's the thing that you would be most pleased to have out of
all of those as the major discovery, to cap it all for you in your career?

Ed Stone: I think that certainly a very important issue is what is the dark matter. It is really
unknown what it is. It's clear it's there, we see its gravitational effects on orbiting objects and
galaxies and so on, but we don't know what it is. So that's going to be a very important discovery.
Dark energy is even more of a mystery. What is it? Why is the universe actually accelerating in its
expansion rate? This is really a very new result and I think it again could be a very fundamental
result, but that's something that I think will take some years to resolve.

Robyn Williams: Stick to Voyager.

Ed Stone: I will stick to Voyager, yes.

Robyn Williams: And we'll hear from Ed Stone about that incredible Voyager mission with which he's
been linked for over 30 years in a forthcoming Science Show.