SUMMARY

The SDI leadership and those who worked on the studies which defined the SDI are aware that the technical challenges which must be met on the path to achieving the President's dream are considerable. The view expressed in the report that the problems are nearly insurmountable is not supported by the technical data, nor by the technical experts most familiar with the technologies involved. The SDI has been expressly formulated to address the many very real issues. To succeed, the SDI needs the full support and involvement of the scientific and technical community. Together, we may be able to turn the President's dream of hope for a safer future into a reality.

OTA'S RESPONSE TO GENERAL ABRAHAMSON'S COMMENTS ON BACKGROUND PAPER ENTITLED "DIRECTED ENERGY MISSILE DEFENSE IN SPACE," MAY 17, 1984

On May 8, 1984, Lieutenant General James A. Abrahamson, Jr. commented to the press on OTA's Background Paper entitled "Directed Energy Missile Defense in Space" (see "Department of Defense Comments on Directed Energy Missile Defense in Space"). General Abrahamson addressed several technical areas where his information seemed to differ from OTA's. This note reaffirms the correctness of the technical information in OTA's Background Paper on which General Abrahamson commented, explaining each point.

This note first treats the specific comments raised by General Abrahamson and then turns to some general comments on interpretations of the Paper made by various parties.

SPECIFIC COMMENTS

Booster Characteristics

1. Fast-burn boost requires nothing like a 70-90 percent reduction in ICBM payload. It is not necessary to turn to single-warhead missiles in order to have fast booster burn. Both highly MIRVed (MX-scale) and single warhead (Midgetman-scale) fast burn boosters were designed in Defense Department studies. These missiles are only slightly larger than their slower-burning counterparts, MX and Midgetman, yet they carry the same payload. Note that the hypothetical defensive system architecture described in section 7 of the Background Paper was designed to counter a future Soviet booster similar to the MX Peacekeeper, not a fast burn MIRVed booster (the MX burns faster than the Soviet SS-18 but much slower than the hypothetical fast burn boosters envisaged as countermeasures).

2. Fast burn does not require sacrificing precise warhead accuracy. Precision deployment is possible above 90 kilometers. Fast-burn missiles can be silo killers.

Note also that to destroy U.S. cities, as opposed to U.S. silos, Soviet missiles need not have precision accuracy.

3. Fast-burn boosters can carry decoys and other penetration aids for evading midcourse and terminal defense layers. However, the short deployment time and atmospheric drag at low altitudes might make deployment of penetration aids from fastburn boosters more difficult than from today's missiles. This possibility is a legitimate point in favor of boost phase defense and was noted on page 56 of the Background Paper and repeated on page 59.

Boost Phase Technologies

1. We recognize that there is some variation among workers in this field in their estimates of how many satellites carrying weapons of a given kind (20 MW chemical lasers with 10 m mirrors, in the first example in the Background Paper) would be required on orbit to achieve a given level of defensive capability. These variations in constellation size and absentee ratio can be as much as a factor of two or three, but not five to ten as General Abrahamson seems to imply elsewhere. These variations are not large enough to affect conclusions, especially since many other uncertainties in these calculations are at least as large. Our estimates lie between the Fletcher Panel's estimates and those of the Union of Concerned Scientists, though much closer to those of the Fletcher Panel, and we consider them to be reasonable estimates.

Factors affecting constellation size estimates include: (1) geography of offensive missile deployment; (2) the fact that required weapon dwell time varies depending upon the position of the satellite with respect to its target; (3) the coverage of the constellation fluctuates in time, so that the protection afforded by a given number of defensive satellites varies around some average, dipping periodically to a "worst

case" where satellites involved in the engagement are on average farther from their target. (Of course, the Soviets could calculate, for any deployment, when this worst case would recur.)

2. The Background Paper does not mention that power levels for impulse kill are smaller than for thermal kill because it is pulse energy and pulse repetition frequency, not average power, that is the measure of merit relevant for impulse kill. 3. We have reviewed our estimates of parameters for a thermal kill ground-based laser system and have found no error; General Abrahamson does not explain where his estimates differ.

4. With respect to the X-ray laser, General Abrahamson seems to be referring to certain ideas (still classified) for making a somewhat new type of X-ray laser. The author is fully aware of these ideas, but they remain only untested concepts, and they are different from the much-publicized Excalibur device under investigation at the Lawrence Livermore Laboratory. The Background Paper's discussion of Excalibur is correct.

5. The Background Paper correctly cites the beam divergence associated with gas cell stripping to form a neutral particle beam. It is true, as General Abrahamson points out, that other methods of removing the extra electrons from negative ions might ultimately reduce the beam divergence introduced by stripping.

6. The Background Paper's estimates of the altitude to which the neutral particle beam can penetrate are based on calculations of the interaction of the beam with the air and on realistic engagement geometry. It is possible that in his own estimate, General Abrahamson calculated the depth to which the beam would penetrate if fired straight down. However, in order for each weapons satellite to have a reasonable radius of coverage, the line of fire must be on average far from vertical, meaning the beam must pass through more air to reach a given altitude.

7. "New and innovative" applications of charged particle beams are treated explicitly on page 31 of the Background Paper. The author is fully aware of related efforts at the national laboratories.

8. The Background Paper shows clearly that a guided projectile weighing less than 15 kilograms had better be a "research and technical objective of the SDI," since otherwise the on-orbit weight of a rocket-propelled system would be too large, as General Abrahamson states. We chose 15 kilograms advisedly, taking into account the fact that the guided projectile must have sizable terminal divert motors in addition to sensors and electronics. Interceptor weight is roughly proportional to projectile weight for constant velocity gained.

9. The Background Paper does not assert that electromagnetic guns will not work, but it does point out that the projectile energies are substantial. This energy must be supplied from on-orbit sources.

Other Element of Boost Phase Defense

No comment.

Countermeasures

1. Battle stations deployed in low earth orbit would be impractical to conceal over long periods from future sensors. The author believes that no one familiar with space surveillance (from space and from earth) will contradict this statement.

2. Battle stations are impractical to proliferate unless they are at least several times cheaper than the means to destroy them. This is true because the offense must only "cut a hole"-containing of order a tenth of the satellites-in the defense constellation.

3. General Abrahamson's analogy between battle station hardening and booster hardening is superficial: one must compare not only the shields surrounding these objects, but the circumstances under which they would be used and the economics of their respective missions. There are three major differences:

Timing-The offense/ASAT attacker can afford tens of seconds-maybe minutes of dwell time, and repeated attack, to burn through satellite shielding. If a booster shield only succeeds in prolonging lethal dwell times to several seconds, by contrast, it forces the defense to large increases in battle station number in order to handle all the boosters in the few hundred seconds of booster burn time. In addition, defensive satellites must be shielded at all times, yet ready to sense, communicate, and shoot at a moment's notice.

Geography and Geometry.—The entire defensive satellite must be hardened to attack from all directions: from space or from the ground. Only the upper stages of boosters must be hardened against directed energy weapons that do not penetrate the atmosphere. Most crucially, defensive satellites can be attacked from the Soviet

Union. How, for example, will satellite shields hold up against repeated large impulse-killing pulses from the ground-based excimer and free-electron lasers General Abrahamson mentions?

Economics.-If the offense hardens just some of its boosters, but does not reveal just which ones are hardened in which way, the defense faces a choice: either it can assume all are hardened and beef up the defense accordingly (e.g., adding more battle stations, since dwell times must be longer to penetrate shielding; or doubling the number of X-ray lasers, so a first burst of X-rays destroys the shield and a second destroys the booster); or it can leave the defense as is, allowing the shielded boosters to penetrate unharmed. Just the opposite cost-exchange picture holds for satellite shielding. The offense need only threaten those satellites over its silo fields at the moment of attack; the defense needs to harden the entire constellation of defense satellites.

4. Decoy boosters do not need warheads, guidance systems, or upper stages (most of the cost of the booster). Moreover, they do not need protective silos, since they can be defended (by a less-than-perfect defense) against first strike. Or they can be used in a first strike.

Hypothetical System Achitecture

1. To meet midcourse interceptor size and cost goals, and to avoid basing the defense outside the continental United States, at least two midcourse launch sites would be needed to cover all ICBM approaches. Still more sites would be needed to cover all SLBM approaches.

2. The Fletcher study did not conclude that "effective discrimination of decoys from warheads could be accomplished in mid course." Nor could it. The Fletcher study did examine some interesting (though not decisive) ideas for improving the prospects for midcourse discrimination. These ideas are discussed in section 6 of the Background Paper. In consideration of these ideas, the Background Paper permitted only ten midcourse decoys per RV, rather than many more, to fool the midcourse

sensors.

3. The Background Paper's estimates of terminal interceptor numbers are proper, though the author recognizes that, since the terminal system is not yet completely defined, differences among analysts of a factor of two (factor 1.5 in coverage radius), though not more, are possible.

GENERAL COMMENTS

OTA and the author realize that the circumstances of release of the Background Paper precluded the SDI program staff from reviewing the Background Paper before responding to Congressional inquires. We therefore greet General Abrahamson's comments in the spirit of open technological discussion which the SDI should welcome.

OTA and the author reaffirm the technical correctness of the Background Paper, including issues raised by General Abrahamson. We also note favorable reviews the Background Paper has received from Government laboratories and contractors, to which General Abrahamson referred.

The Background Paper stresses a fundamental distinction between useful but lessthan-perfect defenses, on the one hand, and defenses so good that the Soviet Union simply could not destroy our society with nuclear weapons, on the other. Insofar as the SDI aims at a perfect defense, the Background Paper casts doubt upon how realistic the program is. With respect to less-than-perfect defense, and with respect to ballistic missile defense in general, the Background Paper makes no judgments; it is at that point intended to be a technical primer on boost phase intercept technologies. The Background Paper does not say that boost phase defense will not work at all, nor that less-than-perfect defenses are undesirable.

The Background Paper does not address the SDI as a research program. Virtually everyone agrees that some R&D is desirable, but the Background Paper does not address the scale, structure, or management of the R&D program, nor whether all of its sub-elements compete favorably with other defense R&D needs.

APPENDIX

Senator LARRY PRESSLER,

WASHINGTON, D.C., April 25, 1984.

Chairman, Subcommittee on Arms Control, Oceans, International Operations and Environment, Senate Foreign Relations Committee, U.S. Senate, Washington,

D.C.

DEAR SENATOR PRESSLER: Enclosed is a statement of the results of the symposium held at the Peace Palace, The Hague, The Netherlands on

CONDITIONS ESSENTIAL FOR MAINTAINING OUTER SPACE FOR PEACEFUL USES

The symposium was sponsored by the United Nations University and the International Institute of Space Law and was really a workshop of some 30 international experts giving legal attention to all potential harmful influences that could damage or destroy the space environment, including but not confined to the military role in space.

Ambassador Buchheim, who testified at your hearing on "Arms Control and the Militarization of Space" was one of the participants. The Soviet Union sent a representative at the decisionmaking level, one who had participated in the Vienna antisatellite negotiations.

I anticipated that we would be able to conclude only optional proposals based on different assumptions concerning the role of the military in outer space, but finally we were successful in agreeing on a consensus statement. This was ready in time for presentation at the session in Geneva of the Legal Subcommittee of the UN Committee on the Peaceful Uses of Outer Space. And it is hoped that we can also be helpful to those who are negotiating in Geneva at the Conference on Disarmament. A future meeting is planned with a smaller number of participants.

One of the Judges of the International Court of Justice presided over the symposium, The Honorable Manfred Lachs.

Sincerely yours,

EILENE GALLOWAY.

CONDITIONS ESSENTIAL For MaintainING OUTER SPACE FOR PEACEFUL USES Symposium organized by the International Institute of Space Law and the United Nations University in cooperation with the Palace and The Hague Carnegie Foundation.

THE HAGUE, MARCH 12-15, 1984

The participants in the Symposium agreed to the following summary of their work; it was understood that the United Nations University will publish the written contributions and an account of the discussions where the details of the analysis and proposals made by participants will be found. The list of participants is attached.

I. General conclusions

The basic common view shared by participants was a sense of risk and danger: the danger of an extension of the arms race into outer space and the risk of armed conflict in outer space; the direction of armament development might jeopardize existing international agreements designed to limit and control the military uses of

outer space.

The symposium recalled the expressions of concern over current developments in international fora such as Unispace 82 and the United Nations General Assembly as well as by groups of concerned citizens in different parts of the world.