1、 Rec. ITU-R RA.479-5 1 RECOMMENDATION ITU-R RA.479-5*Protection of frequencies for radioastronomical measurements in the shielded zone of the Moon (Question ITU-R 149/7) (1974-1978-1982-1990-1995-2003) The ITU Radiocommunication Assembly, considering a) that Resolution B16 of the 1994 XXIIth General
2、 Assembly of the International Astronomical Union (IAU) (see Annex 2) recommends that, once radio astronomy observations in the Shielded Zone of the Moon (SZM) commence, radiocommunication transmissions in the SZM be limited to the 2-3 GHz band, but that an alternate band at least 1 GHz wide be iden
3、tified for future operations on a time-coordinated basis between radio astronomy and lunar communication systems; b) that radio astronomical discoveries resulting from observations from spacecraft above the atmosphere of the Earth will reveal unexpected new astronomical phenomena; c) that, in additi
4、on to the establishment of line-of-sight communication links for scientific and other purposes between the Earth and spacecraft, it may be necessary to establish links between stations on the far side of the Moon and other stations on or visible from the Earth; d) that Article 22, Nos. 22.22 to 22.2
5、5 of the Radio Regulations (RR) recognizes the necessity of maintaining the SZM as an area of great potential for observations by the radio astronomy service and by passive space research and consequently as free as possible from transmissions; e) that earth satellites with high apogees, satellites
6、in the halo orbits near the Sun-Earth L2point, satellites in the Earth-trailing orbits, deep-space probes and transmitters located near, or on the Moon may each illuminate the shielded zone, where the Sun-Earth L2Lagrange point is detailed in Recommendation ITU-R RA.1417, recommends 1 that, in plann
7、ing the use of the radio spectrum, both nationally and internationally, account be taken of the need to provide for radio astronomy observations in the SZM; 2 that, in taking account of such a need, special attention should be given to those frequency bands in which observations are difficult or imp
8、ossible from the surface of the Earth; 3 that the frequency spectrum should be used in the SZM in keeping with the preliminary guidelines contained in Annex 1; *This Recommendation should be brought to the attention of Radiocommunication Study Groups 1 and 3. 2 Rec. ITU-R RA.479-5 4 that special att
9、ention be paid to emissions into the SZM from deep-space platforms, satellites in the halo orbits near the Sun-Earth L2point, satellites in the Earth-trailing orbits, or transmitters near or on the Moon; 5 that in the frequency bands which would be considered for joint use by active and passive spac
10、e stations in the SZM, radio astronomy observations should be protected from harmful interference. To this end appropriate discussions between concerned administrations may be conducted; 6 that in-situ radiocommunication equipment developed for the environment of Mars or other planets should not be
11、deployed in the SZM, but the choice of frequencies for the close proximity links in the SZM should follow the preliminary guidelines contained in Annex 1. Annex 1 The protection of radio astronomy observations in the SZM 1 Introduction The electromagnetic spectrum is now so heavily used on Earth tha
12、t much of its potential value for passive scientific research has already been seriously affected. Because of the general increase in radiocommunications, especially involving earth satellites, spacecraft, and deep-space probes, it is important that frequency allocations by the International Telecom
13、munication Union be coordinated to minimize interference with radio astronomy. In particular, since the far side of the Moon is the remaining accessible place where radio observations of the Universe are possible without interference over the whole radio spectrum, it is necessary to allocate frequen
14、cies for active use by deep-space probes, lunar satellites, scientific instrument packages and research stations on the lunar surface in such a way that interference with such passive observations is avoided. Part of the Moons surface is always protected from interfering signals generated on and nea
15、r the Earth because the Moon always presents nearly the same side towards the Earth. It has a period of rotation about its axis equal to its period of revolution around the Earth, but because its orbit is slightly elliptical and inclined, observers on Earth can see somewhat more than half the surfac
16、e of the Moon. If, in addition, the Moon is viewed from an earth satellite in an orbit of 100 000 km radius, another small fraction is seen. The remaining invisible portion of the Moons surface is that which lies more than 23.2 beyond the mean limb of the Moon as seen from the centre of the Earth. T
17、he SZM consists of the shielded area of the Moons surface together with an adjacent volume which is shielded from interference originating within a distance of 100 000 km from the centre of the Earth (Article 22, RR No. 22.22.1). Rec. ITU-R RA.479-5 3 2 General preliminary guidelines for the use of
18、the electromagnetic spectrum in the SZM The SZM is expected to be free from terrestrial interference over the whole frequency spectrum. It is a unique site for scientific observations. As it is expected that radioastronomical and other scientific experiments will soon be carried out in this zone, it
19、 is essential to regulate the activities of the radio services whose facilities may illuminate it. Account must be taken of the requirements of earth satellites, deep-space probes and transmitters located in the SZM, on the understanding, however, that it is desirable to maintain the SZM as a zone f
20、ree from radio interference and hence of great value for passive observations. The use of the frequency spectrum by services with facilities which are located in the SZM or which illuminate it could be based on the following preliminary set of guidelines, which will need to be reviewed when addition
21、al information is received. The entire radio-frequency spectrum in the SZM is designated as available for passive users (the radio astronomy service and other passive users as defined in the RR), with the following exceptions: frequency bands currently available and allocated in the future to the sp
22、ace research service, and those frequency bands in the space operation service, the Earth exploration-satellite service and the radiodetermination-satellite service, that are required to support space research; frequency bands currently available or allocated in the future for radiocommunication and
23、 for space research transmissions within the lunar shielded zone. Except for these essential transmissions, it is intended to keep the SZM free from man-made transmissions. In the planning of such transmissions, it is desirable to avoid the areas of the spectrum of greatest astronomical importance a
24、nd to provide frequency flexibility in transmitting systems. The proposed guidelines do not impose any restriction on existing or future terrestrial radio services or on existing or future space radio services, the transmitters of which are switched on at a distance of less than 100 000 km from the
25、centre of the Earth. Under the proposed guidelines, existing or future space radio services for which transmitters are switched on at a distance of more than 100 000 km from the Earth and which operate in accordance with the RR should coordinate their activities with the radio astronomy service. It
26、is essential that provisions governing compatibility between the radio astronomy service and other services, based on the technical features of the services, be specified by a decision adopted by the ITU. 3 Protection of radioastronomical observations in the SZM For radioastronomical observations, t
27、he SZM presents unique advantages, which have been long recognized. In addition to offering the closest to an interference-free environment, advantages of the SZM for radio astronomy include the lack of a substantial atmosphere, which allows the study of regions of the electromagnetic spectrum which
28、 are inaccessible from the Earth. In particular, lack of a lunar ionosphere allows study of the spectra of celestial sources between about 50 kHz and 4 Rec. ITU-R RA.479-5 30 MHz. The absence of appreciable water vapour and oxygen in the lunar atmosphere allows observations of the microwave and subm
29、illimetre-wavelength region above about 50 GHz, which is either completely or partially absorbed by the atmosphere on Earth. Radio astronomers interest in the SZM has been recognized in RR Article 22 (RR Nos. 22.22 to 22.25). 3.1 Lunar radio astronomy in the 30 kHz to 30 MHz range Ionospheric limita
30、tions to ground-based radio astronomy below 30 MHz are described in Chapter 3 of the ITU Radioastronomy Handbook. Cosmic radio emission has been observed with ground-based radio telescopes at frequencies as low as 1.5 MHz, but observations below 30 MHz are possible only under exceptional circumstanc
31、es, at special locations, and for limited periods of time. Terrestrial radio interference, natural as well as man-made, seriously limits the possibility of carrying out sensitive radio astronomy observations in this frequency range from near-Earth space as well as on the Earth. Radio interference in
32、 the 1-30 MHz range results largely from communications transmissions and noise which is generated in comparable amounts by human activity (ignition and machinery noise) and natural sources (mostly lightning). Below about 500 kHz, the dominant source of noise is auroral kilometric radiation (AKR), r
33、adio noise produced high above the auroral region. The entire frequency range below 30 MHz is either totally inaccessible or is extremely difficult to observe from the ground. Important scientific targets in this range include the galactic non-thermal background, the spectra of extra galactic source
34、s, pulsars, interstellar refraction and scattering phenomena, and radio emission of the quiet and active Sun as well as Jupiter. Information about many of these cannot be obtained by any other means. Thus, the entire range below 30 MHz should be reserved for radio astronomy. 3.2 The 30-300 MHz range
35、 This portion of the spectrum is heavily used by the active services on Earth to the point where it has become difficult to conduct radio astronomy observations. The region contains a number of weak, high-order radio recombination lines of carbon and nitrogen. Further, astronomers continue to search
36、 for the red shifted spectral line of neutral hydrogen (HI) in primordial galaxies, downwards in frequency to below 150 MHz. Continuum observations of pulsars, quasars, and steep spectrum sources are also of importance in this region of the spectrum. In the shielded zone, use of the range below 300
37、MHz by active services should be avoided entirely. 3.3 The 300 MHz to 3 GHz range Some of the most interesting and heavily studied spectral lines lie in this portion of the spectrum, which also faces the heaviest competition and most commercial pressures at present. Lines of great astrophysical inte
38、rest are: the 327.4 MHz hyperfine transition of the deuterium atom, an extremely weak line of great cosmological significance, detected in 1990 after many unsuccessful attempts; Rec. ITU-R RA.479-5 5 the 1 420.4 MHz neutral hydrogen (HI) line, discovered nearly four decades ago, and still the most i
39、ntensely studied line in the radio spectrum; the four OH radical lines at 1 612.2 MHz, 1 665.4 MHz, 1 667.4 MHz, and 1 720.5 MHz. Molecular radio astronomy began with the detection of the spectral lines of the OH radical in 1963. Several thousand spectral lines from more than 125 molecules have been
40、 discovered since then, and discovery of more lines continues to this day. The lines of greatest importance to radio astronomy are listed in Recommendation ITU-R RA.314. Nevertheless, important information has also been derived from many of those not listed as being of the greatest astrophysical sig
41、nificance. Portions of the spectrum containing these lines and their limited blue- and red-shifted extensions are allocated to radio astronomy on Earth. Although heavily used, these bands have serious problems for astronomical observations either because they are not adequately protected from space-
42、based in-band or out-of-band interference or because the band allocated to radio astronomy is far narrower than the red shift range of interest. For example, red shifted HI observations provide information on the formation of galaxies and the early Universe, topics that have been and continue to be
43、the subject of intense research efforts. An example is the discovery of the 1 420.4 MHz line, red shifted to 323 MHz. The existence of red shifted OH megamasers, observable at frequencies as low as 500 MHz and below, has also been predicted. Highly red-shifted objects emitting in the HI or OH lines
44、are expected to be of great interest to astronomers well into the next century. Since the Shielded Zone of the Moon is likely to be nearly interference free, interest in observations of these faint objects may increase greatly when a lunar observatory becomes available. Continuum observations in the
45、 300 MHz to 3 GHz range are carried out in the 1.4 GHz (1.400-1.427 GHz), 1.6 GHz (1.66-1.67 GHz), and 2.7 GHz (2.69-2.7 GHz) bands. The 2.29-2.3 GHz deep space band is also used to make very long baseline interferometry (VLBI) observations. In view of the great astrophysical importance of red shift
46、ed HI and OH observations, the 300 MHz to 2 GHz range should be reserved for radio astronomy observations. 3.4 The 3-20 GHz range This region of the spectrum is increasingly used by airborne or satellite services, and a number of astrophysically important lines have become difficult to observe. Some
47、 important lines were discovered only recently; e.g., the methanol line at 6.7 GHz, which is in the middle of bands allocated to satellite services. Astrophysically important lines, most of which are not adequately protected and which have been detected in this spectral region are: methyladyne (CH)
48、lines at 3 263.8 MHz; 3 335.5 MHz and 3 349.2 MHz, observed in our own, as well as in external galaxies; formaldehyde (H2CO) lines at 4 829.7 MHz and 14.49 GHz also observed in our galaxy and external galaxies; 6 Rec. ITU-R RA.479-5 methanol (CH3OH) lines at 6.7 GHz and 12.2 GHz. These strong maser
49、lines, discovered after 1987, have been observed in our Galaxy, as well as in the Magellanic Clouds, but have not been given recognition in the RR; cyclopropenylidene (C3H2) line at 18.3 GHz, observed in our Galaxy and in the Magellanic Clouds, but not recognized in the RR. Continuum observations are also conducted in a number of bands in this spectral range with ground-based radio telescopes. The continuum bands used by radio astronomers are in the neighbourhood of the following bands allocated to the passive services: 4.99-5.0 GHz, 10.68-10.7 GHz and 15.35-15.4 GHz. Ra
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