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NASA'S GIANT TELESCOPES

Almost everyone has heard of Hubble. The awe-inspiring, aesthetically-pleasing images which the giant telescope has been capturing in the unfathomable depths of outer space and transmitting back to Earth for 10 years probably leave no one unmoved: seldom before in the modern era has it become so clear to us that we are only insignificant tiny beings and that our fragile, beautiful blue planet is only a speck of dust in the vast expanse of the universe.

Chandra

An incredible wealth of shapes and colours assails our senses as we gaze at the large-format photographic images. Of course astronomers know better: in fact the universe is quite boring to look at, much of it is pitch-black, in places it is a little bit grey, but most of it is just dust and haze. The colours which Hubble appears to present are only illusions of the senses, artificially painted in by highly complex technical devices for the purpose of illuminating the confusing structures of the massive celestial apparitions. And yet these images transport all the experts in our world into raptures because they push back the visible frontiers of the universe, and hence the frontiers of our knowledge, by an order of magnitude towards infinity.

But what the average citizen here in Europe probably does not know is that Hubble is not NASA's only astronomical outpost to be floating in space. It may be the best or the one we know best, but actually it is only one of four cosmic brothers, primus inter pares among NASA's "Great Observatories" which are studying the entire bandwidth of the electromagnetic spectrum.

The names they were given at the planning stage were terse and technical. Thus GRO (Gamma Ray Observatory) was to be tasked with recording gamma rays, AXAF (Advanced X-ray Astrophysics Facility) with x-rays, LST (Large Space Telescope) with visible light and SIRTF (Space Infrared Telescope Facility) with infra-red light. But because only a few people can remember these tongue-twisting code-names and because NASA runs an exemplary educational programme for the general public, someone there came up with the bright idea of naming the satellites once launched after past astronomers or astrophysicists, just as HEAO-3 came to be known as the "Einstein Observatory". Suddenly Compton, Hubble and Chandra were on everyone's tongues, achieving a quite unanticipated degree of familiarity even amongst amateur astronomers.

Only SIRTF remains to be given a name as it will not begin its work for another 18 months. On the other hand Compton has already completed its allotted tasks to NASA's complete satisfaction, and in June 2000 it was steered into re-entry of the Earth's atmosphere, breaking up over the Pacific Ocean. The gaps between launches are not due to financial constraints alone, as the development, launch and operation of the giant telescopes has always cost billions and therefore had to be spread over several years.

But smaller and cheaper satellites are no longer on the agenda. Since cameras on board high-altitude research rockets first started delivering somewhat random images of the starry sky above the interference of the aerosphere in the late 1940s, astronomers of this world have been fired by a veritable race for new discoveries. It was not long after spacecraft launches had become a regular event that specialised astronomical satellites began being launched into ever higher trajectories, and since then their numbers have become legion.

Virtually every space nation has become involved to a greater or lesser extent, sending its own observatories out to collect new data. The German Rosat, ESA's Exosat and ISO, the Japanese Astro family and the Russian Astro and Granat are just a few examples. Naturally American scientists have contributed to the meteoric growth in our knowledge through a whole series of astronomical satellites, but by the end of the 1970s at the latest scientists were up against a barrier imposed by the then level of technology.

A new generation of large telescopes therefore had to be planned and built if we were to be able to look deeper into space. Thus, incorporating the latest optic and electronic materials and production methods, the Great Observatories took shape.

Meanwhile the approach adopted with the first three satellites, that the enormous cost was nevertheless worthwhile, has been superseded. "Faster, better and cheaper" is NASA's new catchword and, and thanks to new advances in technology, it should now be possible to achieve the mission objectives originally planned for SIRTF with a significantly smaller and lower-cost satellite.

But why is it that astronomers all around the world seek ever to gaze deeper into the universe? Because they do not measure distances in kilometres but in years, or rather in light-years, to be precise. Thus, they are not gazing into the distance but into the past, and in fact by the time the radiation given off by celestial bodies billions of light-years away reaches us it is perfectly possible that they do not actually exist any more. And if perhaps in the meantime they have exploded as supernovae, we may never find out, as these gigantic flashes of light in turn take billions of years to reach our corner of the universe. So does our sun system still exist?

This somewhat philosophical question does not concern astronomers. They are less interested in the death of distant suns than in their birth. It is not the explosion which interests them but the first flash of light, the beginning of the universe. Their goal is - quite presumptuously - to see the very first stars of all which were created shortly after the Big Bang, not to forget of course the planets which encircle them and possibly even alien forms of life.

This is why there are already ambitious plans for the era after the Great Observatories. Although it will take a number of years yet for scientists to prepare their data, programme development and project definition are already under way. Because the answers which the satellites are giving to questions asked long ago in turn raise new questions.

"Origins" is the name NASA has given to its astronomical research programme for the next few decades. The question of where we come from and whether we are alone in space is not only of interest to astronomers. It will take decades if not centuries to answer it. But it is worth all the investment and all the resources that will be needed, as curiosity has always been a critical driving force behind man's evolution.

From page 50 of FLUG REVUE 9/2000