Sky & Telescope February 1988 [antikvár]

focal pointA Refuge for Radio AstronomyThe march s, 1987, issue of Nature reported the detection of unexpectedly intense radio emission from methanol (methyl alcohol) molecules in star-forming interstellar clouds. Once astronomers calculate the conditions that must exist to give rise to such strong emission they will be one step closer to understanding the environment around newly forming stars.Unfortunately, the recently discovered emission occurs in a wavelength band reserved for commercial satellite transmissions. A ring of transmitters around Earth now beams television programs to all parts of the globe. Radio wavelength allocations and satellite positions in geosynchronous orbit are both filling up fast. Soon, listening to the tale methanol has to tell of star birth will be like trying to hear the song of a meadowlark during an outdoor rock concert.Every few years, World Administrative Radio Conferences (WARC's) are held in Geneva, Switzerland, to allocate the radio spectrum. However, the delegates to these assemblies cannot anticipate what frequencies will later prove to be important for astronomy. Therefore, to study the physics and chemistry of interstellar clouds we often have to sift through the noise of ground-to-air location services, point-to-point microwave communications, military radars, radar altimeters, and other services. Not surprisingly, some parts of the electromagnetic spectrum are already effectively useless for celestial observations. Our only hope is to have a refuge where most, if not all, of the spectrum can be reserved for astronomy.Not that an allocation means all that much. In 1977 astronomers at the Dominion Radio Astrophysical Observatory in Canada wrote an angry letter to Science reporting that the sacrosanct band reserved for studies of interstellar hydrogen had been invaded by powerful, unidentified interference. A number of times my colleagues and 1, working at NASA's Goldstone Deep Space Communication Complex, have noticed transient signals in the bands supposedly reserved for deep-space probes. The problem is serious enough that JPL engineers have installed equipment to characterize the radio-fre-quency spectrum at Goldstone. The data from these instruments support their negotiations with other spectrum users to protect the deep-space frequency allocations.Some violations are not so circumspect.however. When the Soviet Union designed its mission to float and track balloons in the atmosphere of Venus, it chose a frequency in the band reserved for studies of the hydroxyl ion. The rationale was ironically compelling the radio telescopes needed to track the payloads already had receivers for this frequency.Because radio astronomy will be increasingly difficult to do from Earth, the WARC for space telecommunications in 1971 recommended that the International Radio Consultative Committee (CCIR) develop a plan for choosing and protecting frequencies on the shielded back side of the Moon. The CCIR prepared both a report and recommendation for the 1979 WARC.The basic guideline proposed for future planning is that "the entire radio frequency spectrum in the shielded zone of the Moon is designated as available for passive users." Excepted are those bands allocated now or in the future for various services associated with space research. ACCIR recommendation has a powerful influence on spectrum users, though it isn't binding.On the surface the situation looks rather good. Astronomers can expect the electromagnetic spectrum on the back side of the Moon to be treated like a national forest. Some parts may be exploited, but only to the extent that the primary goal of conservation is met. But can astronomers be complacent? The constant struggle to protect forests should be a warning.Exploitation of the Moon may not be all that far in the future. NASA and the Strategic Defense Initiative Organization are now jointly funding research at the University of Wisconsin into extracting helium-3 from our satellite. A Space Shuttle load of this isotope in liquid form could provide enough thermonuclear fusion fuel to supply all of the United States' electricity needs for a year. More compelling, a small tank of helium-3 could fuel lasers putting out several hundred megawatts of power for the entire duration of a space war, about half an hour.The NASA administrator has asked study teams examining U. S. space goals to assess a staffed lunar base as a key option. Also, a NASA committee chaired by astronaut-astrophysicist Sally Ride recommends a lunar base as a "short-term goal." Once a base is established, how long will the back side of the Moon remain an electromagnetic quiet zone?It is safe to say that astronomers will not be the first to establish a presence on the far side of the Moon. Until travel to our satellite has become routine for other reasons, science budgets will not be able to support the transportation and deployment of telescopes there. There must, therefore, be vigilant and zealous lobbying of national governments by the world's scientific bodies and their friends to give substance to the CCIR recommendation. The spectrum on the back side of the Moon belongs to astronomy. Let's notTOM KUIPERKuiper studies molecular clouds at Caltech's Jet Propulsion Laboratory and is "Friend of the Telescope" for the NASA Goldstone Deep Space Communication Complex.