Observatory Satellite A Major Step In 1969

Press, Volume CX, Issue 32194, 13 January 1970, Page 14

Observatory Satellite A Major Step In 1969

For the Americans 1969 was a year of fulfilment in space activities. The first footsteps on the moon overshadowed all other events in space. Most astronomers were more interested in the achievements of the first successful Orbiting Astronomical Observatory satellite, 0.A.02, hailed as a major step forward in space technology.

This unmanned space observatory, with its 11 telescopes, has now spent more than a year examining the ultra-violet light from almost 20,000 stars and other celestial objects. For comparison, in the 15 years prior to 2 only three hours of ultra-violet data from a mere 150 stars was gleaned at the expense of 40 sounding roeket flights. The use of satellite or rocketborne instrumentation is essential for detecting ultraviolet radiation which is blotted out by the earth’s absorbing atmosphere. It is just as well for life on earth that we have a protective atmosphere, otherwise ultraviolet rays, x-rays and gamma rays from our own sun would have destroyed the first molecules of life just as soon as they surfaced in the earth’s primordial seas. But the earth could not have, seas without an atmosphere, anyway. The astronomical world is rejoicing at the exceptional performance of 0.A.0. 2 because it has opened a completely new window on the universe. Already some astronomers have been impressed enough to rate O.AO. 2 as being a leap forward for astronomy as great as that of the invention of the telescope four centuries ago. This attitude rather contrasts with the somewhat bitter views expressed by many - astronomers a couple of years ago when OAO. 1 suffered an electrical failure after less than a day in orbit A famous astronomer then lamented that the s7om loss of OA.O. 1 could have financed three more Palomartype 200 in telescopes. Progress is rarely won cheaply and no astronomer would now deny the need for telescopes in orbit

Startling News During its first year in space 0.A.0. 2 has made several major contributions to astronomical knowledge, the most important being evidence that the’ universe is probably much larger than hitherto believed. This rather startling news is the only reasonable conclusion to be drawn from the fact that 0.A.0. 2 has recorded a far greater intensity of ultraviolet radiation from many galaxies than astronomers had expected. This must mean that very distant galaxies, whose ultra-violet light is shifted into the visible region of the spectrum by the expansion velocity of the universe, are intrinsically brighter and hence further away than their apparent brightness indicated. Since the distant galaxies appear so faint to us they must be at greater distances than had been assumed x and therefore the observable universe is several times larger than we imagined. Cosmologists those scientists who study’ the origin and evolution of the universe are understandably excited by this discovery because it will help decide the validity of various conflicting theories. In this regard they are also interested in some of 0.A.0. 2’s other discoveries, particularly the observation that any undetected matter in the rn verse does not radiate in the ultra-violet region of the

spectrum. This makes it much less likely that such matter exists, a finding that may set an upper limit on the total amount of unobserved material in the universe and thereby demolish the notion that the universe is a closed system as demanded by one form of Einstein’s General Relativity theory. Hot Stars Another major contribution by OA.O. 2 is the establishment of a more-accurate temperature scale for stars. The space observatory has proved that blue stars are hotter and red stars are cooler than ground-based observations had indicated. Also the extremely hot stars are found to be losing mass so rapidly that their lifetimes must be shorter than had been assumed. The experts on stellar evolution now have to adjust their theories of energy production in large hot stars. Furthermore, the lost mass affects the birth process of nearby small stars by altering their composition. And so it goes on, in a chain of cause and effect which may even shed light on the formative stage of planetary systems such as our own.

Four of the 11 telescopes carried by O.AO. 2 have been devoted to the first colour survey of the ultra-violet light from more than 17,000 stars. One of the four telescopes has revealed that in its particular range of colour sensitivity all but the very brightest stars are obscured by a brilliant foreground glow which has been traced to the presence of hydrogen gas. This hydrogen constitutes the extreme outer atmosphere, or geocorona, of the earth as it is found only at heights equal to or above the 480-mile orbit of OA.O. 2. Thus, unexpectedly, O.AO. 2 is providing a unique survey of the extent and richness of hydrogen in the outer fringes of our atmosphere. Another geophysical bonus has been provided by the other seven telescopes on 0.A.0. 2 which, in addition to their astronomical tasks, were employed to measure the air-glow emission from various levels in the atmosphere—the first time this has been done directly with high precision in a wide range of wavelengths. Deteriorated The designers of future astronomical observatories in space will benefit immeasurably from the lessons taught by 0.A.0. 2. After one year in space the detection devices in the O.AO. 2 telescopes have have deteriorated by factors of as much as 40, oartly as a result of their high exposure to particle radiation from the sun and the earth’s radiation belts and partly because of their long hours of operation. The telescope camera tubes, for example, have lasted eight times longer than similar tubes in standard TV broadcast cameras, so they have really performed very well indeed.

Another OA.O. is due to be sent into space soon for further studies of the starlight invisible from groundlevel. The next development will be the Apollo Telescope Mount, AT.M. based on a modified lunar module. It will be sent into orbit to permit manned operation of a medium-size space telescope. Beyond the A.T.M. is the Large Space Telescope, L.S.T.

For more than three years a select committee of the Space Science Board of the United States National Academy of Sciences has been engaged in a detailed study of the feasibility and usefulness of a 120 in telescope in space or on the moon. The committee chairman (Professor Lyman Spitzer, director of the Princeton University Observatory) claims that such an instrument i would be uniquely important • for solving problems in ■ astronomy. In their report the L.S.T. committee calculates that a 120 in telescope in space would be able to detect stars as faint ias the 29th magnitude. . whereas the night-time airglow’from our own atmosphere limits observation to stars of about magnitude 23 or 24 by any terrestrial telescope, no matter how large. ’ The improvement wrought by > the space-based telescope is therefore about as great as the difference in brilliance between the brightest and i faintest stars visible to the naked eye. •

Questions Already the list of astronomical questions which could be answered or at least partly solved by the L.S.T. is quite staggering and, to quote Professor Spitzer, “experience indicates that some of the most exciting results obtained in a space programme are likely to be those which had not been foreseen.” Even so, some fascinating possibilities have already been suggested. One of these is the direct observation of the curvature of the universe, provided, of course, 'the curvature proves to be real. The spacecurvature would be revealed by the apparent diameters of objects at great distances being observed to increase with increasing distance. The possibility of an observer using the L.S.T. to peer into the depths of space in order to see the back of his own head will, however, remain a fiction. It will be many years before space telescopes render their ground-based counterparts ■ obsolete, if ever. The much lower capital cost of ground-based telescopes will ensure that they will continue to act in a supporting role.

The observing time of space telescopes is too precious to ■ waste on studies that can be i made from the ground. Space telescopes have : before them an almost limit- • less task in unveiling the i secrets of the cosmos. It is ; not overmuch to expect that ’ they may reveal the existence , of planetary systems belong- ■ ing to other stars. They may : even be the means of making : the first contact with other 1 sentient beings on distant ; worlds. It would not be sur- •' prising if space telescopes ' might even hold the key to ; man’s ultimate survival. Sales ' talk? Maybe. But just as Galileo, with the limited i power of his first telescope, could not even glimpse distant galaxies and quasars 1 neither can we hope to guess what future space telescopes may reveal.