217
talk with Guido and asked him to sound out the experts and gather opinions
on a 10-m segmented mirror.
The United States had successfully built a large telescope with a 10-m segmented mirror. Until then, the largest telescope mirrors had been of a single
piece (monolithic) and care had to be taken to avoid deformations due to
changes of temperature and flexion caused by the inclination of the telescope.
But the technical and operational difficulties in managing the immense mass
of monolithic mirrors rendered it impossible to make them wider than
8 metres. Note that, while an 8-m monolithic mirror weighs some 23 tonnes,
a 10.4-m segmented mirror weighs a mere 16.5 tonnes in comparison.
We began to see many future advantages in this new type of telescope. We
did not want our 8 metre to be the last of the monolithic telescopes, an instrument of the past, even though it would be more manageable and easier to
build. When the telescope experts met at the IAC, we presented them, as an
alternative to the 8 metre, a 10-m segmented-mirror telescope project. The
finest were gathered there: Jerry Nelson, Director of the American 10-m Keck
and pioneer in the building of segmented-mirror telescopes; Masanori Iye,
Director the Japanese 8-m Subaru; Massimo Tarenghi, Director of ESO’s four
8-m Very Large Telescope; and Matt Mountain, Director of the 8-m Gemini.
A very interesting discussion ensued, and the experts finally advised us to opt
for the segmented design. That meeting showed the door to large monolithic
mirrors.
We started afresh with a new conceptual design and its corresponding feasibility study. It soon became clear that the cost of a 10-m segmented-mirror
telescope would be of the same order as a telescope with an 8-m monolithic
primary; in other words, for the same price we could achieve a 50 per cent
bigger light-collecting surface and, therefore, much better angular resolution.
A team of three astronomers and four engineers from the IAC spent some
time in California, where the segmented-mirror Keck Telescope, now in operation, had been built. They then went on to Hawaii to talk to the astronomers
and technicians using it. They went over every minute aspect of the fabrication, fine tuning, and operation of the segmented mirror. They saw the Keck
Telescope in action and could verify its high observing performance. At last,
after an exhaustive study of the pros and cons of the segmented versus the
monolithic model, the decision was taken to opt for a segmented-mirror telescope, optically equivalent to a 10.4-m monolithic-mirror telescope, that
would be optimized to observe in the visible and infrared.
Of course, in order to continue with the conceptual design of the telescope
and carry out the feasibility study we had to obtain the approval of the
Governing Council of the IAC, which it granted in February 1996. The
21 The Biggest, Most Advanced Telescope in the World (1989–Present)
talk with Guido and asked him to sound out the experts and gather opinions
on a 10-m segmented mirror.
The United States had successfully built a large telescope with a 10-m segmented mirror. Until then, the largest telescope mirrors had been of a single
piece (monolithic) and care had to be taken to avoid deformations due to
changes of temperature and flexion caused by the inclination of the telescope.
But the technical and operational difficulties in managing the immense mass
of monolithic mirrors rendered it impossible to make them wider than
8 metres. Note that, while an 8-m monolithic mirror weighs some 23 tonnes,
a 10.4-m segmented mirror weighs a mere 16.5 tonnes in comparison.
We began to see many future advantages in this new type of telescope. We
did not want our 8 metre to be the last of the monolithic telescopes, an instrument of the past, even though it would be more manageable and easier to
build. When the telescope experts met at the IAC, we presented them, as an
alternative to the 8 metre, a 10-m segmented-mirror telescope project. The
finest were gathered there: Jerry Nelson, Director of the American 10-m Keck
and pioneer in the building of segmented-mirror telescopes; Masanori Iye,
Director the Japanese 8-m Subaru; Massimo Tarenghi, Director of ESO’s four
8-m Very Large Telescope; and Matt Mountain, Director of the 8-m Gemini.
A very interesting discussion ensued, and the experts finally advised us to opt
for the segmented design. That meeting showed the door to large monolithic
mirrors.
We started afresh with a new conceptual design and its corresponding feasibility study. It soon became clear that the cost of a 10-m segmented-mirror
telescope would be of the same order as a telescope with an 8-m monolithic
primary; in other words, for the same price we could achieve a 50 per cent
bigger light-collecting surface and, therefore, much better angular resolution.
A team of three astronomers and four engineers from the IAC spent some
time in California, where the segmented-mirror Keck Telescope, now in operation, had been built. They then went on to Hawaii to talk to the astronomers
and technicians using it. They went over every minute aspect of the fabrication, fine tuning, and operation of the segmented mirror. They saw the Keck
Telescope in action and could verify its high observing performance. At last,
after an exhaustive study of the pros and cons of the segmented versus the
monolithic model, the decision was taken to opt for a segmented-mirror telescope, optically equivalent to a 10.4-m monolithic-mirror telescope, that
would be optimized to observe in the visible and infrared.
Of course, in order to continue with the conceptual design of the telescope
and carry out the feasibility study we had to obtain the approval of the
Governing Council of the IAC, which it granted in February 1996. The
21 The Biggest, Most Advanced Telescope in the World (1989–Present)