APPROACHES TO MAKING TELESCOPES
The principal problems in building very large telescopes on the earth's surface today are costs and construction time. A new 5-meter Hale telescope would now cost about 25 million dollars and take 10 years to build, while a 10-meter telescope would cost 200 million dollars and take 20 years to build, and a 25-meter telescope would require about 3 billion dollars and 50 years to construct. Clearly some dramatic changes in design are needed to lower cost and construction time.
A new telescope design, called the Multiple Mirror Telescope (MMT), which is well suited for infrared observations, has been installed on Mount Hopkins in Arizona. It uses a mosaic of independent mirrors of small size to collect and focus light in order to simulate the collecting ability of a largeaperture single mirror. The MMT consists of a circular array of six identical 1.8-meter mirrors on an altazimuth mounting; the array has light-gathering power equivalent to that of a 4.5-meter single mirror.
The six mirrors are not thick solid ones but are of a new lightweight design. They are partially hollow, which requires a smaller mechanical structure to move them; thus they save money and construction time. The six images from the six mirrors may be either superimposed to form a single image or aligned along a spectrographic slit, one on top of the other, to take full advantage of slit geometry. The pointing directions of the six mirrors are locked together by laser beams. This instrument has been successful in demonstrating the practicality of the multiple-mirror concept, and it may be the forerunner of telescopes that are equivalent to a 25-meter (82-foot) telescope. Under consideration is an MMT consisting of eight 5-meter lightweight mirrors, having the light-gathering power of a 14-meter telescope, the angular resolution of a 22-meter telescope, and (it is hoped) the cost of a 4-meter telescope.
The MMT is not the only new design which shows an artist conception of these new designs for future large telescopes, but it is not now certain whether any of them will ever be built. The success of the Space Telescope, a 2.4-meter conventional reflector that is to be put into orbit in early 1985, will not lessen the need for a mammoth new telescope on the ground but will probably increase it. Since Space Telescope does not have to contend with light losses produced by the atmosphere, a very large telescope will be required on the ground to observe in visible wavelengths what Space Telescope is able to observe at shorter wavelengths, where it will primarily operate.
The principal problems in building very large telescopes on the earth's surface today are costs and construction time. A new 5-meter Hale telescope would now cost about 25 million dollars and take 10 years to build, while a 10-meter telescope would cost 200 million dollars and take 20 years to build, and a 25-meter telescope would require about 3 billion dollars and 50 years to construct. Clearly some dramatic changes in design are needed to lower cost and construction time.
A new telescope design, called the Multiple Mirror Telescope (MMT), which is well suited for infrared observations, has been installed on Mount Hopkins in Arizona. It uses a mosaic of independent mirrors of small size to collect and focus light in order to simulate the collecting ability of a largeaperture single mirror. The MMT consists of a circular array of six identical 1.8-meter mirrors on an altazimuth mounting; the array has light-gathering power equivalent to that of a 4.5-meter single mirror.
The six mirrors are not thick solid ones but are of a new lightweight design. They are partially hollow, which requires a smaller mechanical structure to move them; thus they save money and construction time. The six images from the six mirrors may be either superimposed to form a single image or aligned along a spectrographic slit, one on top of the other, to take full advantage of slit geometry. The pointing directions of the six mirrors are locked together by laser beams. This instrument has been successful in demonstrating the practicality of the multiple-mirror concept, and it may be the forerunner of telescopes that are equivalent to a 25-meter (82-foot) telescope. Under consideration is an MMT consisting of eight 5-meter lightweight mirrors, having the light-gathering power of a 14-meter telescope, the angular resolution of a 22-meter telescope, and (it is hoped) the cost of a 4-meter telescope.
The MMT is not the only new design which shows an artist conception of these new designs for future large telescopes, but it is not now certain whether any of them will ever be built. The success of the Space Telescope, a 2.4-meter conventional reflector that is to be put into orbit in early 1985, will not lessen the need for a mammoth new telescope on the ground but will probably increase it. Since Space Telescope does not have to contend with light losses produced by the atmosphere, a very large telescope will be required on the ground to observe in visible wavelengths what Space Telescope is able to observe at shorter wavelengths, where it will primarily operate.
