The original stimulus for the White Paper was a classic online “back o’ the envelope” response to an article, “ Going Backwards: Nuclear-Tipped Interceptors Studied [subhead] Rumsfeld Revives Rejected Missile Defense Concept”, which appeared in the Washington Post on Thursday, April 11, 2002, and which was reposted the next day to a private moderated listserver, Friends and Partners in Space, which is focused on Russian-American space history and affairs. The WP article criticized a recent Bush Administration initiative to reexamine an old ballistic missile defense concept which utilized exoatmospheric intercepts with neutron bombs (hence, ABMwERW). Before proceeding with my own point-by-point refutation of the article, and preliminary technical analysis of the ABM-ERW concept, I quote that re-post in full here:

>Fri Apr 12 09:19:16 2002
>Message: 5
>Date: Thu, 11 Apr 2002 14:47:18 -0500
>From: jgabryno
>Reply-To: jgabryno@olemiss.edu
>Organization: National Remote Sensing and Space Law Center
>Subject: [FPSPACE] Going Backwards Nuclear-Tipped Interceptors Studied
> Rumsfeld Revives Rejected Missile Defense Concept
>
>FYI
>
>Published on Thursday, April 11, 2002 in the Washington Post
>
>Going Backwards
>Nuclear-Tipped Interceptors Studied
>Rumsfeld Revives Rejected Missile Defense Concept
>
>by Bradley Graham
>
>Defense Secretary Donald H. Rumsfeld has opened the door to the possible
>use of nuclear-tipped interceptors in a national missile defense system,
>reviving an idea that U.S. authorities rejected nearly three decades ago
>as technically problematic and politically unacceptable.
>
>William Schneider Jr., chairman of the Defense Science Board, said yesterday
>that he had received encouragement from Rumsfeld to begin exploring the idea
>as part of an upcoming study of alternative approaches to intercepting enemy missiles.
>
>"We've talked about it as something that he's interested in looking at," Schneider said
>in an interview.
>
>The Pentagon experimented with nuclear-armed interceptors in the 1950s
>and 1960s and, for a short time in the mid-1970s, deployed an anti-missile
>system that relied on them. But the notion of nuclear explosions going
>off high overhead to block incoming missiles proved unsettling for many
>people.
>
>And the prospect that ionized clouds and electromagnetic shock waves
>associated with the explosions could end up blinding radar on the ground
>and scrambling electronic equipment eventually helped kill the plan.
>
>Since then, defense officials have focused on developing interceptors to
>destroy targets without the need for explosives, relying instead on the
>force of direct impact, a concept known as "hit to kill."
>
>Driving the new interest in arming interceptors with nuclear devices is
>the problem of dealing with decoys and other measures that an enemy might
>use to confuse an interceptor, Schneider said.
>
>The hit-to-kill approach depends on interceptors picking out the real
>enemy targets and homing in on them. By contrast, nuclear-armed interceptors
>need not distinguish actual targets from clusters of decoys but could rely on
>explosive power or radiation to wipe out everything in the vicinity.
>
>One other arguable advantage of nuclear interceptors, Schneider suggested,
>is their potential for ensuring destruction of missile-borne biological warfare agents
>such as anthrax.
>
>President Bush has made clear his interest in pursuing technological solutions
>to missile defense, removing long-standing constraints by deciding last December
>to withdraw the United States from the 1972 Anti-Ballistic Missile Treaty with Moscow.
>
>The Pentagon has embarked on experimental anti-missile programs,
>including land- and sea-based interceptors as well as airborne lasers and
>space-based weapons, with the hope of having at least a rudimentary capability
>in place by fall 2004. But until now, defense officials had shied away from
>the nuclear option.
>
>An extensive Pentagon review of missile defense alternatives undertaken
>in the first months of the Bush administration raised the possibility of
>nuclear-tipped interceptors, according to two officials familiar with
>the review. But the idea failed to make the list of programs worth funding.
>
>Its return comes in the context of other recent signs of the administration's
>general readiness to consider broader uses of nuclear weapons. A Pentagon review
>of U.S. nuclear policy, concluded late last year, put new emphasis on possible
>nuclear strikes against Third World adversaries and backed development of low-yield
>nuclear bombs to hit hardened or deeply buried targets.
>
>Russia, which built a missile defense system around Moscow in the 1960s
>that survives to this day, relied from the start on nuclear-armed interceptors.
>Although U.S. defense experts regard the Russian system as anachronistic,
>Russian military officials worry that the United States will eventually adopt
>the nuclear approach, according to Pavel Podvig, editor of an authoritative book
>about Russian strategic nuclear forces published last year by the Center for Arms
>Control Studies in Moscow.
>
>"They believe strongly that you cannot get an effective missile defense
>system using hit-to-kill," Podvig said.
>
>The Defense Science Board, set up in the 1950s, is a senior advisory body
>that reports to the secretary of defense on technological, operational and
>managerial matters. One of its task forces already is looking at some aspects of
>missile defense, including command and control systems, international
>cooperation and countermeasures such as decoys. Schneider said he plans to
>initiate the review of nuclear interceptors and other alternatives to hit-to-kill
>after the task force completes its study this summer.
>
>"The issue hasn't been looked at for about 30 years," said Schneider,
>a consultant and undersecretary of state for security assistance under
>President Ronald Reagan. "The last test involved a four-megaton device on a
>Spartan interceptor in 1971."
>
>Richard L. Garwin, a senior fellow at the Council on Foreign Relations and
>prominent missile defense skeptic, said nuclear interceptors still pose
>several significant technical problems.
>
>"When you actually look at the question, you find that it takes a very
>large warhead -- more than a megaton -- to destroy anthrax spores in bomblets
>that may be spread over a distance of five kilometers or more," he said.
>
>"Worse, there are hundreds of civilian satellites as well as many U.S. military
>satellites vital to our national security that would be imperiled by nuclear explosions.
>And there are electromagnetic pulse vulnerabilities in an advanced society such as
>ours that would occur to any point within line-of-sight of the nuclear explosions."
>
>© 2002 The Washington Post Company

This is a long and fairly technical post, of interest only to rocket-heads.

>The Pentagon experimented with nuclear-armed interceptors in the 1950s
>and 1960s and, for a short time in the mid-1970s, deployed an anti-missile
>system that relied on them. But the notion of nuclear explosions going
>off high overhead to block incoming missiles proved unsettling for many
>people.
True, but incomplete, and worse, misleading (I think). From 1963 to 1975, the USAF ran a operational ASAT system out of Johnston Island in the Pacific Ocean using high-yield nuclear-tipped Thor IRBMs. [Chun2000] It was called Program 437. Because the exoatmospheric nuclear tests 1958-1962 such as the HARDTACK and FISHBOWL series were conducted using that same Thor launcher, which was basically identical to the configuration of the fielded ASAT, one could argue that the system had full-up tests, and was a going concern, in a sense, from at least 1962. The crews also conducted a number of launches with dummy warheads against real satellite targets in space as well as photographic interception missions in order to maintain their proficiency. Program 437 could work in co-orbital or direct ascent modes. I am sure that some FPSpacers were personally involved in this Program.

Another ASAT system, the US Army's modified Nike-Zeus, was tested 13 times out of Kwajalein Atoll, scoring a number of hits in space, but never deployed (kill radius of its ~250-kt warhead wasn't quite big enough, and the rapid response of the solid rocket wasn't required for the ASAT mission).

There were additional tests out of Vandenberg.

These ASAT systems were functionally equivalent to a limited ABM system. So, the author doesn't mention that the USA:
1. tested at least two other ABM-like systems;
2. deployed one of them for over a decade;
3. fired off actual rockets and hit actual targets in space on a regular basis; and
4. set off actual nuclear weapons in space.

If I didn't know these other facts already, I too would think from reading the article that the USA had just dabbled in the matter and discarded it as a bad idea. This is probably the interpretation which the writer intended, but it is still wrong. The fact is, there is ample technical and political precedent for the idea, much of it predating the 1963 Test Ban Treaty and 1967 Outer Space Treaty.

Later, Mr. Graham writes:
>And the prospect that ionized clouds and electromagnetic shock waves
>associated with the explosions could end up blinding radar on the ground
>and scrambling electronic equipment eventually helped kill the plan.

The implication that EMP etc. was a showstopper is, as an academic would say, “not supported by the facts”. (Gotta love that LitCrit euphemism for "hogwash".) On 09Jul62, the 1.4 Mt STARFISH PRIME test @ z=400 km zapped 2 classified** birds (Transit IV and TRAAC) and Ariel, a joint US-UK science bird. The decisionmakers were fully aware of the potential for collateral damage to important friendly strategic assets and deployed the ASAT system anyway.
**(I'm guessing one of them was the Transit 4B navsat? with the SNAP-3 nuclear reactor, which quit transmitting right about then.)
The ASAT mission is like the ABM mission without as much of the time-critical element. If it looks like a duck, waddles like a duck, and quacks, it's a duck.

>The hit-to-kill approach depends on interceptors picking out the real
>enemy targets and homing in on them. By contrast, nuclear-armed interceptors
>need not distinguish actual targets from clusters of decoys but could rely on
>explosive power or radiation to wipe out everything in the vicinity.
>One other arguable advantage of nuclear interceptors, Schneider suggested,
>is their potential for ensuring destruction of missile-borne biological warfare agents
>such as anthrax.
[snip]
>Richard L. Garwin, a senior fellow at the Council on Foreign Relations and
>prominent missile defense skeptic, said nuclear interceptors still pose several
>significant technical problems.
>"When you actually look at the question, you find that it takes a very
>large warhead -- more than a megaton -- to destroy anthrax spores in bomblets
>that may be spread over a distance of five kilometers or more," he said.

These are interesting and legitimate technical issues. But I simply could not believe Garwin's number. So, naturally I whipped out my calculator, pencil, handy-dandy Nuclear Bomb Effects circular slide rule from [Glasstone, 1977], hopped online for awhile, and started figuring.

Commercial standards (e.g. ANSI/AAMI/ISO 11137) for killing pathogens specify 25 kGy [kilograys] of ionizing radiation delivered over a period of time. [Grecz&1987] That's 2.5 megarads - wow! - a lot of radiation. Microbes are a lot tougher than we are, obviously. "Killing" in this case means a six-log, or 99.9999%, or a million-to-one reduction in population. (One-third as much radiation kills 99.9%, or a thousand-to-one. The U.S. Post Office currently is using cobalt-60 sources to generate similar doses in order to kill anthrax in matter mail.) Because organisms can tolerate larger doses if they're spread over time, I imagine that a prompt impulse, where the total dose arrives in a microsecond, might be half as large to achieve the same sterilizing effect.

Now the weaponeers of Program 437 (the early U.S. ASAT program I discussed last week) were working to an interception range of 3 nautical miles, so they used an ordinary H-bomb in the megaton range (high yield by today's standards, but not those back then). I do think that a nuclear burst near a pattern of RVs mixed with decoys would effectively separate the wheat from the "chaff" (pun intended). Biological payloads might be sterilized and lightweight decoys may be disrupted enough to change their appearance. A better word than “interception” might be “interdiction”. A second layer of hit-to-kill interceptors could then concentrate on the relatively dense survivors since they are probably warheads. (I don't imagine that an attacker would waste throwweight on mass simulators - if they've got the throwweight, they'd fill it with warhead.)

However simply lighting off a big bomb, such as Garwin or Schneider quote, in low orbit is problematic due to EMP, poisoning LEO with trapped high-energy particles and weapon debris, collateral damage against strategic satellites, and possibly fratricide.

What's needed is a blast from the past - the neutron bomb.

Spraying a warhead with penetrating neutrons, even if it doesn't cause spallation or other mechanical failure (which is hard to achieve) may split and/or activate just enough nuclei inside the weapon so that when it arrives over target the Primary might go "fizz" not "bang", and the Secondary/Tertiary might not go off at all. Plutonium/tritium devices in particular are highly sensitive to isotopic impurities, and it doesn't take much to screw up the chain reaction or the energy budget downstream.

Four large factors work concurrently to favor tipping ABMs with 3rd-generation enhanced radiation warheads.
Factor #1. Recall that the tank-killing neutron bomb of the 1980s had a yield of 1-2 kt, tops. A neutron bomb is a tiny H-bomb optimized to produce lots of neutrons -- about 6X as many as a fission bomb of the same overall yield -- at the expense of blast, say -20%.
Factor #2. Furthermore, fast neutrons are weighted 10X as heavily as betas or gammas for relative biological effect because they're more massive, and they're far more penetrating than alpha, beta or most gamma radiation. Because neutrons don't have a charge, they don't interact with the electron shell. The effect of this property cannot be overstated.
Factor #3. Best of all, neutrons aren't absorbed in the vacuum of space, and the "rays" only fall off by roughly 1/r², instead of the 1/r³ law that usually applies when scaling weapons effects. "Shaping" or directing the neutron pulse might be possible with beryllium reflectors and such, but we'll assume a spherical distribution for now.
Factor #4. In general, a larger nuclear device is more efficient with respect to mass (more kilotons/kg) than a smaller one. In the U.S. arsenal, there is a three order-of-magnitude difference in efficiency across the yield range of six orders of magnitude.

Let's go with 120 kilorads of prompt neutrons delivered to a range of 5.5 km in all directions. How big would the warhead have to be? To work as an ABM, the 80s-era tank-killer would have to be scaled up, but not as much as I would have thought. (This /gedankenexperiment/ turned out to be full of surprises.)

Now, since neutrons are so strongly absorbed and gammas so attenuated in air, we can't simply scale from sea-level tests, which is what most of the graphs in [Glasstone, 1977] are based on. Instead, let's look at it from first principles [Craig&1986] :

Consider the third line. The radiation from an ordinary fission bomb is distributed 50/50 between gamma and thermalized neutrons. The extra radiation in the neutron bomb is almost entirely fast neutrons (hence the name), defined as >1 MeV (mega-electron-volt). A kiloton is defined as 1 trillion calories, or 4.18 E19 ergs, or 2.6 E31 eV. A "rad" is defined as 100 ergs being absorbed per gram of target (via gamma) or 10 ergs/g (via neutrons). The SI unit, Gray, = 100 rads. For the targeted biological or decoy materials, assume a density of 1 [g/cc]. The range is 5.5 km. Roughly 1/e, or 63%, of the neutron flux interacts with first approx. 10 cm (it's called the 'relaxation length') of target material no matter what it's made of - water, lead, or anything else. A typical RV is a cone 1.5 meters high with a half-meter base, therefore no point is more than 25 cm from the surface. The dose at the RV's centerline needs to be 120 kilorads to kill 99.9999% of the warbugs.

This is all the information we need to calculate exactly the required yield of the ABM-ERW. Using the methods described above and a lot of Kentucky windage, I get ...

(drum roll)

44 kilotons.

Surprised? Information theory tells us that the value of information is directly proportional to its degree of improbability. So technical surprise is useful and educational.

To get the same biological effect from an ordinary H-bomb requires 9 megatons, suicidal in LEO. By comparison, the W49 used in Project 437 was 1-Mt.

Factor #4 above implies a 3-fold improvement in mass efficiency across a 10-fold increase in yield. So, scaling from the existing W79-1 ERW (yield = 2 kt, mass = 98 kg) I expect the 3-gen-ABM-ERW to mass half a metric ton, +/- 50%. Other scaling efficiencies may well apply, since we're not trying to stuff a working warhead inside a tiny artillery tube, nor build it to resist 20,000 gees from being shot out of the same gun. Don't forget that once you've got a working Primary, the Teller-Ulam Principle says the Secondary can be arbitrarily large. The Secondary is what generates the fast neutrons.

A while back, I had quoted a "magic number" of 5 km/sec as that which distinguishes an ABM from an ordinary SAM. Let's use that figure, plus an extra km/sec for varying target azumiths and maneuvering capability. Given:
m(payload) = 500 kg,
empty structure = payload,
solid fuel with I(sp) = 290 seconds,
delta vee = 6 km/sec,
g(0) = 9.8 m/s²,
and just a single stage.
I get an initial booster mass of 9 tonnes. Hell, you could practically base this thing in your backyard. It's half the size of a dinky Pegasus. Plus there would be no problem with orbital debris (so long as the booster is jettisoned at burnout to reenter) because the ERW vaporizes itself, neutrons kill the target but don't disintegrate it. Nor would there be a problem with poisoning LEO, since the yield of each warhead is on the order of the late-50s ARGUS tests which did not cause a problem. Also, there would be less fission products overall to be trapped in the Van Allen Belts. The neutrons would either rapidly thermalize by elastic scattering in the upper atmosphere, or escape towards interstellar space, since their speed would exceed solar escape velocity. Some of them would transmute nitrogen-14 in the air to carbon-14. In either case, the neutrons themselves would quickly (10-20 minute half-life) decay via beta emission into protons plus electrons, that is, innocuous hydrogen atoms, long before posing a threat to any people. (Otherwise, neutrons would eventually fall to the center of the earth like the balls in a giant Pachinko machine, and accumulate there as a ball of neutronium, whose gravitational gradient would eventually cause a real problem.)

Continuing with the /Post/ article:
>"The issue hasn't been looked at for about 30 years," said Schneider,
>a consultant and undersecretary of state for security assistance under
>President Ronald Reagan. "The last test involved a four-megaton device on a
. ^^^^^^^^^^^^^^^^^^^
>Spartan interceptor in 1971."
Holy cow.
(a) This is way more than actually needed. I think the writer dropped in the reference (to an actual underground test CANNIKIN in the Aleutian Islands in 1971) just to ridicule the whole idea. Another axe-grinder.
(b) Other than the first shots by China (1964), India (1974), the unpopular French South Pacific series, and South Africa (1979?) there haven't been many atmospheric tests since the Test Ban Treaty was signed in 1962. So what's this guy talking about?

My math may be off by a factor of 3, but not a factor of 100.

Ideally, we would like to get to a warhead of no greater yield than the 2 kiloton tests of Project ARGUS, which were widely acknowledged to have no discernable effects on the near-Earth space environment (by 1950s standards). Hardening the warhead to serve as an RV would be a waste of the interceptor's scarce throwweight. Therefore, a properly designed ABM-ERW could not easily be diverted to use as a ballistic missile.
To enhance the prompt nuclear radiation component of the partition and reduce the thermal/blast and delayed radiation components as much as possible, the Primary should be as small as possible. Fortunately, techniques for miniaturizing fission devices and working with very subcritical amounts of fissile material were worked out decades ago, for programs like SADM and the Davy Crockett. Therefore, this is one area lacking technical risk (good).

A 3-log kill may have sufficient military utility assuming robust civil defense and requires only 1/3 the rads, hence 1/3 the yield.
No cell repair OTOH means no benefit from prompt delivery, a factor-of-2 hit (or factor of 1.5 for humans).
Using modern navigation and electronics may reliably get the ERW within 1 nautical mile, not 3, which, given the 1/r² dependency, is a factor of 9 reduction in required yield. So long as the enemy RVs are intercepted early, this seems reasonable. (However, bioweapons are by nature area weapons, so the enemy may choose to scatter RV submunitions early in the trajectory to increase the difficulty of interception. OTOH, smaller RVs are easier to sterilize, and also carry less toxins or warbugs 1/L³).
So, instead of 44 kilotons, we now have something on the order of 3 kilotons.

Ideally, the total package should be compatible with the form factor of a Standard Missile, or fit in a Vertical Launch cell. Deployment on major surface combatants would achieve operational flexibility, permit rapid concentration of resources while complicating things for the attacker and increasing his operational risk. Security considerations would be no more burdensome than what the US Navy already deals with.

>"Worse, there are hundreds of civilian satellites as well as many U.S. military
>satellites vital to our national security that would be imperiled by nuclear explosions.
>And there are electromagnetic pulse vulnerabilities in an advanced society such as
>ours that would occur to any point within line-of-sight of the nuclear explosions."

An advanced society is also vulnerable to nuclear explosions on the ground, in rather more direct ways.

Nuclear-tipped ABMs for exoatmospheric interdicts are feasible, if the warheads are scaled up neutron bombs. Cost: $10-30 million/shot in quantity, comprising $3-10 million for the booster depending on slant range, $5 million for the bus, $2-15 million for the ERW tip, which includes some factor for white-collar welfare.

• Higher levels of neutron production may be possible. One important thing to learn is to what degree diverting neutron flux ruins the energy budget of a fusion bomb. The very thing that makes an ERW such an efficient producer of neutrons makes it more sensitive than other weapons to neutron flux in turn. Therefore, fratricide will be an important consideration.
  

• Compare the level of pulsed neutron radiation from the SNS with the flux from a scaled up neutron bomb. The damage to electronics will be on a solid state level.
  

• Get actual figures, not CYA standards, for 1-log through 6-log kills of sporulated warbugs. Develop estimates for secondary radiation.

• According to [Hillis et al] large ERWs are better candidates for the asteroid defense mission, since neutrons couple more deeply with the bulk of the bolide/target. Then again, freed of military constraints, and assuming that the throw weight exists or will be developed, a huge three stage weapon with a dead-simple gun-type Primary, and a Secondary based on stable deuterium rather than tritium may be best, given a long voyage thru the Inner system to intercept. Notice that the voyage times are roughly comparable with the intercept/yield curve, which places a huge premium on advance notice.
  

• Historical question: The USSR conducted quite a few FOBS tests, presumably with dummy warheads. Did they ever run a full-up test of the Galosh ABM? How many exoatmospheric bombs did they light off? How many of these were high-yield?
  

• Calculate rads/cm at centerline
  

• Calculate the fate of weapon debris, fission products, neutrons; those which impinge on the atmosphere, or are captured by the Van Allen Belts, or escape into interplanetary space and decay into hydrogen.
  

• Craig & Jungerman cite 1-kiloton for Spartan/Sprint endoatmospheric ERW
  

• Analyze whether spherical burst really is more forgiving of interception error compared to anisotropic or directed bursts; confirm that neutron "gas" probably homogenizes emission.
  

• The way Aegis works, the big SPY radar (up to 7 megawatts, 0.5 degree beamwidth, range=500 miles) gives you a rough location for your target interception, so you can loft your SAMs into a box. That's why Aegis missiles get such great range. They go out on autopilot and only do actual maneuvering for that last few seconds. SPG radar does final illumination. ICBM target goes Mach 11, 25K fps, 17K mph, 7.6 km/sec. RV is sturdy, not tissue paper like boosters. RVs now covered with material like space shuttle tile. The SM-2-ER Block 4 (in fiction) has booster stage to kick itself out of VLS cell faster and harder. SM is point defense not area defense with little cross-range, kill zone of HE warhead ~8m (3-10). Interception range of ER mod is ~200 miles

Robert Kennedy is president of the Ultimax Group Inc., a corporation distributed across 11 time zones from Moscow to L.A. He speaks enough languages to start bar fights in all of them. Robotics engineer, amateur historian, and jack of all trades, he spent 1994 working for the House Science Committee's Subcommittee on Space as ASME's Congressional Fellow. On the Sputnik anniversary in October 1997, he managed to make the Russian evening news. Robert telecommutes from Oak Ridge, Tennessee, where he resides with his wife, numerous cats, the occasional horse, and a yard full of trees and Detroit iron.

I thank all the people who assisted in the development of this concept, known and unknown. All mistakes are my responsibility.

[Chun2000] Chun, LTC C.K.S. Shooting Down a "Star": Program 437 the US Nuclear ASAT System and Present Day Copycat Killers, (Air Def.Univ., 2000)

[Grecz&1987] Grecz N, Brannon RB, Killgore G., “Radiation sterilization of surgical instruments with a consideration of metal shielding on sterilization efficiency”, American Journal of Infectious Control 1987 Jun;15(3):101-6

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