has long-range plans to open the band to television broadcasting. Beyond this, it can be anticipated that plans for other satellite systems will be developed, and that as a result, an enormous equipment investment will be made in the 1980's and 1990's, both in the 1400 to 1727 MHz band and elsewhere in the spectrum, up to about 30 GHz. The effect of this huge prospective investment – perhaps tens of billions of dollars – will be to create great economic pressure against any attempt at a subsequent WARC to revise whatever allocations are devised in 1979. Certainly any protection given the 1400 to 1727 MHz band for SETI after 1979 will result in much greater economic dislocation.

On the other hand, much present use of the 1400 to 1727 MHz band is compatible with the operation of an ISS, or could be if properly engineered. In contrast to bands below 1400 MHz and above 1727 MHz, where one finds powerful aircraft acquisition radars with EIRP ranging from 107 to more than 109 W, terrestrial transmitters in this band are primarily low-power. Satellite users are still relatively few, and satellite equipment is still designed to be amortized generally in about five years, although construction for much longer lifetimes is planned for the 1980's and thereafter. The necessity of replacing equipment as it becomes obsolete provides an opportunity to engineer the new equipment to operate at a different frequency without incurring excessive costs. Then, too, a large fraction of present equipment can be cheaply modified for operation in a neighboring or other appropriate band. Since a large ISS would probably not be operational before 1985 at the earliest and large-scale preliminary searches will not be made before the early 1980's, satellite transmissions in the band can be tolerated until then, and perhaps longer if need be, to avoid economic hardships. Thus, if prompt action is taken, a plan that will protect the 1400 to 1727 MHz band with minimum economic impact can be developed and implemented. This plan would be in compliance with United States telecommunications law, which requires that, in the allocation of frequencies, public interest considerations, such as those that motivate a SETI program, prevail over economic ones; it should be based on the resolution of the Science Workshop (see Section I, Conclusion 2, p. 19, and Section III-9).

REFERENCES

1. Oliver, B. M.; and Billingham, J.: Project Cyclops, A Design Study of a System for Detecting Extraterrestrial Intelligent Life. NASA CR114445, 1972.

COMPLEMENTARY DOCUMENT 9

PROTECTION OF A PREFERRED RADIO FREQUENCY BAND

Prepared by:

Mark A. Stull

SETI Program Office
Ames Research Center

PROTECTION OF A PREFERRED RADIO FREQUENCY BAND

The Science Workshop, especially at its second, third, and fourth meetings, debated all considerations concerning whether the probability of finding signals from an extraterrestrial civilization is maximized in any particular frequency band. To the extent this problem requires knowledge of the motivation of such civilizations, it cannot be solved, but there are physical and philosophical arguments which imply that the frequency band between 1400 and 1727 MHz should have high priority for a search effort (see Section II-4). Because of the sensitivity of any interstellar search system (ISS), it is very important that the only telecommunications services which operate in this band be those that will not cause harmful interference to an ISS. In 1979 a general World Administrative Radio Conference (WARC) will be held; it will allocate world-wide use of the radio spectrum and allocations made then are likely to determine spectrum usage for the remainder of this century. The Science Workshop recognized the importance of obtaining protection of the 1400 to 1727 MHz band for SETI use at the 1979 WARC and, to emphasize this need, adopted the following resolution.

STATEMENT ON THE REQUIREMENTS FOR PROTECTION OF AN INTERSTELLAR SEARCH SYSTEM (ISS) FROM RADIO-FREQUENCY INTERFERENCE

In recognition of the rapidly advancing national preparation for the 1979 general World Administrative Radio Conference (WARC), the Science Workshop adopts the following final statement of policy:

1. There are important frequency bands for a search for radio signals from extraterrestrial intelligent civilizations. These are:

a. 1.400 to 1.427 GHz

b. 1.427 to 1.727 GHz

The 1.400 to 1.427-GHz band is of interest because interstellar transmissions may take place around the hydrogen line, while the 1.427 to 1.727-GHz band is located between the hydrogen and hydroxyl lines and lies near the minimum of the noise background. 1.400 to 1.427 GHz is currently allocated exclusively to the radio astronomy service and may be shared with it, while 1.427 to 1.727 GHz may be shared with services whose use will not cause harmful interference to the operation of an ISS.

2. Existing radio telescopes are already being used to search for radio signals from extraterrestrial civilizations, while the feasibility of constructing a very large ground-based ISS has been established. The performance of any ground-based instrument will, however, be seriously degraded by radio-frequency interference, primarily from line-of-sight transmitters. The only identified alternatives to an Earth-based ISS are:

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A space-based ISS, and

An ISS sited on the far side of the Moon

Both of these are possible in the future, but we do not know at what cost. Furthermore, a space-based ISS, unless shielded at additional expense, remains vulnerable to interference from satellite and ground-based transmitters; while an ISS on the far side of the Moon is vulnerable to all transmissions originating beyond the lunar orbit. Thus, there exists a need for RFI protection. We strongly recommend:

a. That the U.S. undertake immediate studies to determine detailed frequency protection requirements for an ISS, and submit the results of such studies to the 1977 Final Meeting of the International Radio Consultative Committee (CCIR) for inclusion in the supporting documents of the 1979 WARC, and

b. That the U.S. prepare and present to other administrations at the 1979 WARC a proposal which will include

an ISS.

i) Allocations for new satellite systems at frequencies outside the protected bands. ii) Appropriate frequency sharing criteria for uses compatible with the operation of

iii) Technical criteria for allowable spurious radiation from out-of-band uses.

iv) Phase-out of interfering uses now operating in the protected bands.

Subsequent to the Science Workshop deliberations and during the preparation of the final report, the SETI radio frequency protection need received its first international recognition. Reproduced below is Addendum No. 1 to Volume II, XIIIth Plenary Assembly of the CCIR, Geneva, 1974.

Note by the Director, C.C.I.R.

Subsequent to the publication of Volume II (Space Research and Radio Astronomy) of the documents of the XIIIth Plenary Assembly of the C.C.I.R., a new text relating to search for extraterrestrial life has been submitted for adoption by correspondence, in conformity with the provisions of No. 308 of the International Telecommunication Convention, Torremolinos, 1973.

It has received more than the twenty approvals necessary for its adoption by the Members of the I.T.U. and has therefore become an official Question of the C.C.I.R.

The text is as follows: