Foreign Relations of the United States, 1958–1960, Volume III, Microfiche Supplement, National Security Policy; Arms Control and Disarmament

505. Letter From Gates to Dillon¹

Washington, October 28, 1959

Dear Douglas:

You will recall that in the letter of September 29, 1959, the Department of Defense recommended that the U.S. seek at Geneva a phased treaty providing in the initial phase for a ban only on nuclear weapon tests in the earth’s accesible atmosphere. In connection with high altitude nuclear explosions, it was noted that the detection system recommended by the experts at Geneva in July 1959 is based primarily on theory, and the Department of Defense is concerned that the United States may accede prematurely to a system which subsequent experimentation may prove to be inadequate for its purpose. It was considered that the uncertainties warrant further exploration before the United States undertakes an international commitment to ban tests in this environment.

On June 26, 1959, the Special Assistant to the Secretary of State (AE) requested the Director, Defense Research and Engineering, to conduct studies of a system for the detection and identification of high altitude explosions for the purpose of providing guidance to the U.S. Delegation in Geneva. Engineering studies are being conducted under the direction of the Advanced Research Projects Agency; a preliminary summary of their findings and conclusions to date is attached hereto. Of particular pertinence is the statement: “Theoretical estimates of detection capability are sufficiently promising to justify a comprehensive and time consuming research and development program. They are not sufficient to permit at this time any firm estimate of capabilities upon which to base national policy in the decision of whether or not nuclear tests in space can be reliably controlled.” The attached engineering study was based on the assumption that all facilities, costs and manpower required were in addition to any existing U.S. capabilities.

Consideration of the summary of these studies has reinforced the view of the Department of Defense that the United States should not, at this time, agree to a ban on very high altitude tests which would depend for its enforcement upon a detection system of uncertain capabilities. There is a further consideration that, before these capabilities could be proved out, an extensive and extremely costly program of experimentation would be required.

In view of the work now in progress in formulating the U.S. draft of a phased treaty, which will require a final determination as to what the United States should propose in such a treaty in the initial phase, it is recommended that the principals of the members of the Interdepartmental Working Group on Disarmament meet at an early date with a view to arriving at a decision with respect to this problem.

Representatives of the Department of Defense would be prepared to present a short oral briefing to the principals, setting forth the salient aspects of the studies which have been made.

Sincerely yours,

Thomas S. Gates
Deputy

Copies to:

Chairman, Atomic Energy Commission

Director, Central Intelligence Agency

Special Assistant to President for Science and Technology

Special Assistant to President for National Security Affairs

Assistant to SecDef (Atomic Energy)

Director, Defense Research & Engineering

Director, Advanced Research Projects Agency

Chairman, Joint Chiefs of Staff

Commander, AFTAC

Enclosure

Paper Prepared in the Department of Defense

Capabilities and Limitations of a System of Ground Stations and Satellite Based Detectors for the Detection and Identification of Nuclear Explosions at High Altitude and in Space

1. The Technical Working Group on the detection of high altitude nuclear explosions on 15 July 1959 reported its findings to the Conference on Discontinuance of Nuclear Weapon Tests in terms of an assessment of capabilities and limitations of possible techniques for the detection and identification of nuclear explosions at high altitudes above the earth and recommendation of techniques and instrumentation for consideration by the Conference for inclusion in the detection and identification system. Based on recommendations by Dr. Panofsky, head of the US representatives to the Technical Working Group, the Department of State requested the Department of Defense to conduct an engineering study of a system for the detection and identification of high altitude nuclear explosions for the purpose of providing guidance to the US Delegation upon its return to Geneva in October 1959.

2. The Advanced Research Projects Agency issued work orders to the Army Ballistics Missile Agency and to the Ballistic Missile Division of the AF and Space Technology Laboratory to conduct such studies.

3. On 15 October, ARPA invited the AFTAC to join with ARPA in listening to the reports of ABMA and BMD/STL and to jointly evaluate the capabilities and limitations of the proposed system for detecting and identifying high altitude nuclear explosions.

4. The problem of providing guidance to the State Department divides itself naturally into two major areas:

a. Determination of the engineering feasibility, costs, manpower and time factors involved in establishing a high altitude detection system including ground and satellite systems.

b. A scientific study of each of the detection techniques recommended at Geneva to evaluate their capability to detect nuclear explosions in various ranges of space as a function of distance, and yield of the explosion.

5. In the short time available to conduct this study, it was not considered possible to second guess the Experts’ theoretical estimates of range capabilities of the independent techniques. A final reliable determination of the potential detection ranges depends upon the sensitivity which might be achieved by the detectors, the character of radiation from nuclear explosions as a function of range, and the natural radiation background which may exist throughout the orbits contemplated for detection satellites. It is relatively straightforward theoretically to calculate the intensity of X-rays, neutrons and gammas from nuclear explosions as a function of distance from the explosion in space. It is not possible, however, to say what the background radiation will be without an extensive and time consuming research, nor is it possible to state at this time what types of detection instruments may be practical for use in satellites and exactly what their detection sensitivity will be since this is intimately associated with the level of background radiation in the space environment and in some cases with the detailed characteristics of the detectors themselves which will not be determined except through careful research and development.

6. The principal contribution of this preliminary study, therefore, has been in 4.a. above, namely, the engineering problems associated with establishing the satellite and ground platforms at which instruments for detection recommended by the technical group would be established.

7. This report, therefore, will present a summary of those engineering studies as well as an evaluation of system capability on the assumption that the ranges of the detection theoretically estimated or assumed by the Technical Working Group at Geneva are confirmed by subsequent comprehensive research programs.

8. Systems of satellites considered were those recommended by the Panofsky Working Group at Geneva. They include the Argus Satellite System of two satellites at an orbit radius of approximately 1,000 kilometers for detecting electrons trapped in the earth’s magnetic field. A near earth satellite system was considered to include 8 to 10 satellites in circular orbits of about 700 kilometers in radius. A far earth satellite system was considered with 6 satellites equally spaced around circular orbits of 50,000 kilometers or larger. Finally, a system of 4 solar satellites in orbits approximating that of the earth around the sun was considered.

9. Eight to ten satellites in near earth orbits will not provide complete coverage of the entire surface of the earth. The far earth satellite system can be made operational at almost the same time as a near earth system. The combination of poor coverage by the near earth system and evidence that a far earth system could be installed in about the same length of time prompts the decision that no effort should be wasted on establishing a system of near earth satellites.

10. The overall satellite system considered practical from an engineering standpoint only consists of the Argus Satellite System, the Far Earth Satellite System, and the Solar Satellite System. The engineering studies conducted at ABMA and STL indicate that the Argus system could be operational in the third year from “go ahead”; the far earth system could be operational at the end of the fourth year or beginning of the fifth year, and the solar satellite system could be operational about the middle of the fifth year from “go ahead”.

11. The total cost of the three satellite systems would be approximately $1,200,000,000. The annual operational cost was estimated to be $100 million dollars per year. Limitations and capability of the solar satellite system will be presented in following paragraphs. Because of those limitations, the following cost figures are presented for the Argus and far earth satellite systems only. For this limited system the total cost would be about $650,000,000 and the annual operating cost would be approximately $60,000,000 per year.

12. Manpower requirements for launching teams, tracking stations, and control and analysis of the satellite systems would be of the order of 1200 people.

13. The engineering study included estimates of cost, manpower, and time factors for detection equipment to be placed at the 170 control posts of the Geneva Experts’ system. The cost included two optical detectors, backscatter radar, and cosmic noise receivers, but excludes cost of building control posts. The total cost for the terrestrial system at control posts is estimated at about $120,000,000 with an annual operating cost of about $30,000,000. A total of over 2100 personnel would be required to operate the high altitude detection techniques at control posts.

14. In evaluating just how the various ground detectors and satellite based detectors would be integrated into an effective control system, we have applied one basic principal which has guided the United States throughout its experience with detection system design over the past eleven years. Briefly, this principal is that reliable detection and identification of nuclear explosions requires recordings from a minimum of two independent physical techniques and preferably three or more independent measurements. Reference to the chart of capabilities of high altitude detection techniques attached to this report makes possible the following conclusions concerning possible capability of the high altitude detection system assuming that present theoretical estimates of detection range are confirmed by research program estimated to take a minimum of three years to accomplish.

a. A system including the recommended techniques at 170 control posts plus the Argus and far earth satellite system may possibly provide a reliable detection capability for nuclear explosions of 1 megaton or larger at distances of 105 and possibly 106 kilometers from the earth.

b. For explosions as small as 1 kiloton, this system could provide reliable detection by several independent techniques to distances of only 104 kilometers from the earth.

c. At all distances beyond 105 to 106 kilometers (approximately the orbit of the moon), only a single technique possesses the theoretical range to detect nuclear explosions at these vast distances from the earth. This technique based on X-radiation from the device is highly vulnerable to shielding considered feasible by our scientists. Its maximum range is estimated as about 100,000,000 kilometers for a shielded 1 megaton nuclear device. The solar satellite system suggested by the Panofsky high altitude working group, therefore, could be instrumented only for X-ray detection. Since the radius of the orbit of the earth around the sun is about 150,000,000 kilometers, the X-ray technique, having a range of only 100,000,000 kilometers for shielded 1 megaton devices would not be able to detect explosions behind the sun or behind the moon even if one were willing to accept the result of a single pulse of X-rays unsupported by any additional measurement as an adequate detection capability. It can only be concluded at this time that a system of solar satellites does not serve the purpose of providing reliable detection of nuclear explosions which might be detonated in the earth’s orbit beyond the range of the near earth satellite system (approximately the distance of the moon).

15. Theoretical estimates of detection capability are sufficiently promising to justify a comprehensive and time consuming research and development program. They are not sufficient to permit at this time any firm estimate of capabilities upon which to base national policy in the decision of whether or not nuclear tests in space can be reliably controlled.

16. SUMMARY. It is not possible at this time to state with confidence the capabilities of a system for detecting nuclear explosions in space. It appears probable that given a minimum of three years of research and development that a reliable system for detecting shielded nuclear explosions in space out to about the moon may be possible in about five years at a cost of about three-quarters of a billion dollars for installation and about 90 million dollars a year for operation. If theoretical prediction that the short pulse of X-rays expected from nuclear explosions is unique to such a source and is not present as a result of natural causes, and if convincing evidence that pulses of X-rays from solar activity could not be used by a violator to detonate a nuclear device and thus screen the resulting short pulse of X-rays by the longer duration pulses of X-rays from natural sources, and if such evidence could be considered sufficient without independent confirmation by other techniques such as gamma rays or neutrons, it is possible that in about five years confidence might be established that a solar satellite system could be relied upon to detect nuclear explosions in space roughly circumscribed by the earth’s orbit around the sun.

17. CONCLUSIONS: The engineering studies indicate

a. At least three years of research are required to establish the feasibility of a system to detect nuclear explosions in space.

b. Adequate redundancy of recordings to insure reliability of detection can be obtained only for shielded explosions of 1 megaton out about as far as the moon.

c. A system to detect 1 megaton shielded nuclear explosions between the earth and the moon if proved feasible by a comprehensive research program can be installed in about five years at a cost of about three-quarters of a billion dollars.

d. Detection of nuclear explosions in space beyond the moon will depend upon whether or not research proves that a single short pulse of X-rays is unique to a nuclear explosion and cannot be concealed in some way by a violator.

e. If proved feasible a solar satellite system instrumented for measuring X-rays only for detecting unshielded explosions of 1 megaton in space roughly circumscribed by the earth’s orbit could be installed for about one half a billion dollars additional to the cost of the system described in 17.c.

1. Source: Question of a lack of effective system to detect high-altitude tests; includes summary of engineering studies. Secret. 8 pp. Eisenhower Library, White House Office Files, Additional Records of the Office of the Special Assistant for Science and Technology, Panel-Disarmament-NT-Policy 59.