Peeking Into the Unknown

Planned Mexican telescope could give scientists a keyhole to the past

ON the outskirts of this tiny Mexican village, past the horse-drawn carts struggling over a pot-holed road, past the veterinarian's office, you'll find Alfonso Serrano Perez-Grovas extolling the potential virtues of the world's largest, most advanced radio telescope.

``This is not just a big toy for astronomers,'' says Dr. Serrano, director of Mexico's National Institute of Astrophysics, Optics, and Electronics. ``This is the most ambitious and costly scientific project ever attempted in Mexico. This will have a significant impact on Mexican industry and academic institutions.''

Four years in planning, and with much of the financing lined up, the $52 million joint United States-Mexican project could get under way within a few months.

By virtue of its size, the ``Gran Telescopio Milimetrico'' (GTM) or Large Millimeter Telescope would enable scientists to catch more radiated energy and therefore see fainter celestial objects in finer detail.

``It will be much more sensitive than any other radio telescope,'' says William Irvine, director of the Five College Radio Astronomy Observatory at the University of Massachusetts, Amherst.

Dr. Irvine is co-director of the GTM project. He says the scope will enable astronomers to ``look further out into the universe and therefore further back in time. It will help us to understand how galaxies and stars form.''

If scientists can peer further back in time, they could see at what stage in the early universe there were enough carbon, nitrogen, and other elements considered essential for life, Irvine says. The GTM can also be used within our own solar system to examine the atmosphere of planets or analyze the chemical composition of comets, which may provide clues to planetary formation.

The GTM will be designed to monitor high-frequency radio waves, near the shortwave and infrared band. This range is particularly useful for studying the molecular makeup of interstellar objects. Chemical compounds and elements radiate at different frequencies. Radio telescopes enable astronomers to take a fingerprint of the chemistry of the radiating material.

In short, the GTM will give astronomers a chance to venture into the unknown. But it's not built yet. And the huge 50-meter parabolic antenna to monitor the radio waves presents an unprecedented engineering challenge.

Traditionally, optical and radio telescopes are structures built with hefty amounts of steel to ensure the integrity of the parabolic shape. Small movements or aberrations in the dish surface can cause distortions.

``To observe at the 1 millimeter wavelength, we need a surface that's perfectly smooth to within 1/10 of a millimeter,'' Serrano says. ``When a telescope tracks an object across the sky, the parabolic surface changes slightly due to the weight of the telescope. Temperature changes can also distort the surface. If it changes more than 1/10th of a millimeter, the image blurs.''

O build an accurate radio telescope of this size using a solid-steel supporting structure would require an investment of several hundred million dollars, Serrano says. But there's a more elegant engineering solution: substituting silicon for steel.

The GTM will not be made of a single surface but of 126 hexagonal, precision-made sections. Each hexagon will have a set of sensors and actuators to move it. Making 10 calculations per second, computers will monitor and continually adjust the shape of the parabolic dish.

To help prevent warping of the hexagons due to temperature differentials, the telescope will be enclosed in a dome designed to maintain a constant temperature.

This type of design has never been attempted before on a radio telescope. But a 10-meter optical scope, the Keck Telescope, is now being built in Hawaii by the University of California and the California Institute of Technology, using similar principles.

The GTM team is talking with the Keck engineers to learn what they can before beginning construction of their larger scope.

The five-year engineering project provides Mexico with a unique opportunity to develop world-class expertise in several fields, Serrano says. ``There's the potential for joint ventures between US and Mexican engineering and construction firms.

``The telescope will create a need for 50 to 100 students with specialties in mechanical engineering, temperature control, high-frequency electronics, and radio astronomy. Those numbers may seem small, but those are very significant numbers in the Mexican scientific community,'' he says.

The Mexican government, and some private donors, have already agreed to foot $26 million, or half the construction cost.

``Our government is committed to Mexico's technological de-velopment. And this kind of project is a catalyst for scientific and technological progress,'' says Miguel Jose Yacaman, assistant director of scientific research for the government's National Science and Technology Council.

If the US isn't able to come up with the other half of the cost, Mexico will push ahead with the project anyway, Dr. Yacaman says.

The US team is likely to spearhead the research and development of the specially designed radio-telescope receivers. It has experience in this field, having built the receivers used in a smaller radio telescope at the Five College Radio Astronomy Observatory in Massachusetts.

So far, the exact site for the GTM hasn't been settled on. Serrano's institute is testing several sites in central Mexico and Baja California. This month the US team will be in Mexico to investigate some of the potential locations.

Irvine says building the GTM in Mexico makes sense from a research standpoint. ``The southern sky is relatively less explored than the Northern Hemisphere where most of the industrialized nations are doing research.''

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