Jeffrey LewisIran & the Bomb 2: Iran's Missiles

This is second part in a three part series on Iran’s nuclear capabilities that I am writing at the urging of Noah Shachtman from DefenseTech. (Read Part 1).

Once upon a time, Persian scientists spent their considerable talents making the world a better place, inventing useful things like batteries and studying the heavens (left).

Lately … not so much. They’ve focused on less ethereal pursuits like developing the technology to rain death and destruction on their neighbors.

Which brings us to today’s question: How far could Iran launch a nuclear weapon on a ballistic missile?

The answer really depends on two things: The size of Iran’s missiles and the size of Iran’s warheads.

Iran’s missiles aren’t that big, and its warheads aren’t that small. Without more testing of both, I think Iran would be hard pressed to deliver a missile to Israel, let alone Europe or the United States.

That said, Iran—with low confidence—might be able to build a 500-1000 kg warhead could hit targets throughout the Middle East, including Israel if mated to its Shahab 3 IRBM (which, in a nod to Persia’s better days, means meteor or shooting star).

This is, I think, the very edge of Tehran’s capabilities and they would have very low confidence in either system without testing both, first.

Iran’s Nuclear Warheads

Iran’s nuclear weapons are the easy subject of speculation because they are, at this time, largely imaginary.

I tackled a similar question in a post entitled “Can North Korea Mate a “Simple Fission Weapon to the Taepo Dong 2?

Since we are talking about a crash program here—let’s assume that whatever Iran builds will not be tested except under what we might call “operational circumstances.”

Iran’s nuclear program is based around uranium, which can be made critical either by slamming a uranium pellet into a nearly critical mass of uranium (a gun-type device like we dropped on Hiroshima) or imploding sphere of uranium (like the Chinese did in the 1960s). The latter is the more likely route for a number of reasons, largely related to the size of the weapon. Since we are talking about a ballistic missile delivered weapon, let’s assume Iran goes the implosion route.

Harvard Professor John Holdren chaired the National Academies Committee on Technical Issues Related to Ratification of the Comprehensive Test Ban Treaty (2002). Holdren et al describe the limits to what new nuclear states might be able to build without nuclear testing:

Nagasaki was destroyed by an implosion weapon containing about 6 kg of plutonium. It weighed 9,000 pounds and had an explosive yield of about 20 kilotons. Fifty-five years later, and with all the information that has since been declassified, a state with the requisite technical skills in explosives, electronics, and metallurgy could with some confidence reproduce the Nagasaki device without the full-scale test the United States conducted in New Mexico on July 16, 1945. Many non-nuclear tests would be needed to demonstrate the mastery of the technology, and there would be some uncertainty in yield. A weapon weighing 1,000–2,000 pounds might similarly be built, with somewhat less confidence; this might resemble the U.S. Mark-7 bomb of 1951 that weighed 1,800 pounds.

The task of perfecting an implosion weapon is more difficult than the path leading to a U-235 gun-type weapon, but is essential if plutonium is to be used and also provides, as noted above, a path to a weapon using less U-235 than a gun design requires.

So, Holdren et al claim that the best a new state could do is a range of 450-1000 kg, with a much heavier design more likely.

That’s pretty consistent with what we see from new nuclear states. China’s first bomb—a uranium implosion device—weighed 1550 kg and had to be wheeled to the tower.

China tested its first missile delivered warhead with it’s fourth nuclear test, in October 1966 (see image at right).

The design for that device ended up in Pakistan, then Libya and (perhaps) Iran. David Wright and I estimated the warhead design was about 0.8-0.9 m in diameter and weighed about 500 kg—consistent with press reports about the size of the device. (See: More on Libya’s Bomb Design …, October 08, 2005).

As I said, Iran may have received a copy of this Chinese design, although it isn’t clear how helpful it would be. There is also the curious case of our friends at Langley, who may have thought it a clever idea to provide partially accurate implosion designs to Tehran in a misguided effort to confuse their scientists.

On the other hand, 500 kg is a damn small weapon for a new nuclear state. DIA, by comparison, estimates that the best North Korea could do is 650-750 kg warhead (using plutonium)—much too heavy for a Taepo Dong (and by extension, a Shahab 4, but more on that later).

So 500-1000 kg—in keeping with Holdren et al—forms a useful range for the mass of a nuclear weapon the Iranians could build (albeit one in which they would have low confidence without testing) if they were involved in a crash program to build a warhead for a ballistic missile.

This really, really heavy—as we’ll see, probably too heavy for any of Iran’s ballistic missiles. This is why folks like Sandy Spector have spent years writing articles like “Foreign-Supplied Combat Aircraft: Will They Drop the Third World Bomb?” (Leonard S. Spector, Journal of International Affairs 40:1, 1986)

Iran’s Missiles

The most useful information about Tehran’s ballistic missile program was laid out in Congressional testimony by National Intelligence Officer Bob Walpole entitled, The Iranian Ballistic Missile and WMD Threat to the United States Through 2015. Additional detail is available from Proliferation: Threat and Response and Ballistic and Cruise Missile Threat.

Tehran has a large number of short range ballistic missiles (100-500 km range) like the CSS-8, Scud B and Scud C. These can carry heavy payloads and reach targets very close to Iran—although they are famously inaccurate even for nuclear weapons.

What most of us want to know concerns Iran’s long range missiles—the ones that can hit us and our friends (and no, “allies” who forbid women from driving cars don’t count). Iran is developing the Shahab 3, which is basically an extended-range (1,300) North Korean No Dong (don’t snicker). Iran may also be developing an even longer range (2,000) km version. Bill Gertz relays the assessment of some Pentagon officials:

The two Iranian missiles are believed by the officials to be derivatives of the 620-mile-range Nodong and are dubbed the Shahab-3 and the Shahab-4. According to the Pentagon officials, the Shahab-3 will have a range of between 800 and 930 miles and will be capable of carrying a 1,650-pound warhead; the Shahab-4 will include improved guidance components and can travel up to 1,240 miles with a warhead weighing up to 2,200 pounds.

At 1,300 km (the official IC estimate for the Shahab 3), Iran would be able to target most of the Middle East, including Israel.

David Wright and Timur Kadyshev provided a technical analysis of the No Dong, including a notional payload-range curve, that helps explain the relationship between the size of Iran’s warheads and the range of the Shahab 3.

A 500-1000 kg warhead is probably the heaviest warhead the Shahab-3 could accomodate, particularly depending on the mass of Iran’s re-entry vehicle for the physics package. (DIA claims re-entry vehicles can consume about half the payload of longer range missiles and, even if you’re an anti-semitic jerk-off, you still don’t want your precious bomb breaking up on re-entry.)

I should also note that the Wright and Kadyshev estimate the circuclar error probable (CEP) for the No Dong on the order of 3-4 km—that means that half of the No Dongs would fall outside a 3-4 kilometer radius from the aim point. This is a significant inaccuracy, even for a nuclear warhead, that would limit Iran to targeting civilian populations instead of military targets. This is, of course, little comfort to folks living in the target of an attack, particularly its surburbs.

Iran is also working a longer range version of the Shahab that could extend Iran’s range into the Balkans, India and Egypt.

Iran’s chances of building an ICBM that can reach the United States arer pretty low for the near term—Iran would have to build a missile with a range of 9,000 or 10,000 km. Delivering a warhead with an ICBM also requires a shielded re-entry vehicle to protect the warhead that impose a substantial weight penalty.

Still, the US IC—as of 2005—judged that “Iran will have the technical capability to develop an ICBM by 2015” although “it is not clear whether Iran has decided to field such a missile.”

Putting It All Together

All and all, Iran might be able to deliver a nuclear weapon by ballistic missile against Israel, although Iran would have low confidence in the warhead and the accuracy of the missile.

That’s not much comfort if you live in Tel Aviv, but it wouldn’t give the Iranians, at least early on, much of a threat.

Iran could, of course, figure this all out eventually. It isn’t clear to me, however, that Iranian scientists have been thinking seriously about this problem—despite what you might have read in the New York Times.

Take the issue of “new” reentry vehicle that Iran tested for the Shahab in 2004. A former Israeli official told Jane’s Defence Weekly that the nose cone had been made extra roomy for a nuclear warhead:

The missile has a modified nose section allowing it to hold a larger warhead and thus provide additional room for a nuclear device. Israeli officials have said the larger nose section is capable of separation and visually appears similar to that used on the Russian SS-9 intercontinental ballistic missile. “It is not a copy of a known missile but the new Shahab has a major-league design. It’s clear that it is the work of seasoned missile engineers, probably Russian, rather than an experimental beginners,” version, added [Uzi Rubin, former director of Israel’s Ballistic Missile Defence Organisation].

Such extra room is vital as Iranian nuclear engineers would face major technical challenges in making the country’s first nuclear weapon light enough and small enough to fit on its existing missiles, particularly without benefit of having conducted full-scale nuclear weapons tests. The weapon is believed by US officials to be an indigenous design although knowledge gained from blueprints of a working, but too large nuclear weapon, provided by the Pakistani nuclear scientist AQ Khan would be helpful to the effort.

Using the the same photo analysis technique of publicly available photographs from the test (similar to the one pictured at right) that I described earlier in this post, David Albright calculated the diamater of the notional nuclear weapon could not exceed .6 M—much smaller and lighter (200 kg or so) than anything the Iranians could hope to build.

Extra roomy? Maybe. Roomy enough? I doubt it.

The bottom line: Iran might, might, be able to deliver a nuclear weapon against an Israeli city, but that would be at the extreme edge of their capabilities.

Much more worrisome, I would think, would be the weapon delivered by terrorists, perhaps on a ship.

Part 1 discussed how close Iran was to building a bomb; Part 3 will discuss prospects for a strike against Iran’s nuclear facilities.

Comments

  1. dan (History)

    you mention ship-borne (and bomber-borne) weapons without much discussion. I take it your claim is that Iran’s goals in developing a nuclear arsenal is essentially defensive, i.e. they want a deterrant rather than an offensive weapon. You’ve demonstrated that pretty persuasively over the years re: the Chinese; is there similar evidence re: what the Iranians are thinking?

    To put it differently, I’d be more sanguine about a nuclear Iran if I wasn’t worried about their nukes getting into the hands of terrorists.

  2. John Field (History)

    Obviously, this is a hard thing to estimate. Yet, I always come out that they could do pretty well – that is if they got their act together – which is a big if.

    Consider, at least, the following observations :

    -spacex falcon i claims 570 kg to low earth orbit

    -carbon-carbon materials should greatly reduce the rv weight. Presumably, with great effort, an indigenous industry could be built to support that in Iran

    -there is no point in building a 99% reliable bomb with a 90% reliable missile. Significant weight reductions could be expected here.

    -related to that is the use of uranium not plutonium. Highly purified HEU should greatly reduce the risk. And, maybe even more importantly, it seems like they are going to be awash in HEU down the road.

    -linear implosion seems much more accessible today, and therefore the narrow missile should be no consolation. A 2d hydrocode will run on any laptop computer. If you have lenses, you have oblique shock at interfaces anyway and therefore your codes need to be able to handle it. Furthermore, such codes don’t need radiative and neutron transport, to study the assembly event. So, many uncertainties are removed. Computational load is greatly reduced, and correspondingly resolution is much higher.

    -anyone now can go buy a gigahertz oscilloscope on ebay. See for example ebay item # 7582282128. Total overkill. 25 grand; I can have it on my bench in a week.

    -fast high voltage electronics. See for example IXYS DE375-102N10A mosfet. Nanosecond switching, 1000 V breakdown voltage, 60 A(repetitive) peak current. I seriously doubt that you need krytrons any more. Vacuum spark gaps triggered by these monster transistors should provide low jitter, that is IF you don’t have laser triggered gaps.

    I wouldn’t even know where to stop because the list just goes on and on.

    The world is awash in technical talent. It is everywhere. Yet, it remains an unsolved problem to design effective organizations. Estimates of Iranian technical capability will always be ‘fat-tailed’ for this reason – we are measuring the wrong figure of merit. Yet, in America, the land of high infant mortality and also highest MRI machines per capita, it is a mistake we are very prone to make.

    We need to focus our efforts on preventing them from fielding an effective organization. That is the key. And injecting confusion and disorder is the path. This is why despots fail.

  3. Arnold Evans (History)

    The idea that once upon a time Iranian scientists worked on improving the world but now not so much doesn’t seem fair.

    Does Iran devote a greater proportion of its scientific research to weapons than the US or Israel?

  4. Anonymous

    Just to be nitpicky: you used “it’s” incorrectly at least twice (in both cases “its” would have been correct):

    “Iran’s missiles aren’t that big, and it’s warheads…” or “China tested it’s first missile delivered…”

    [Fixed it, thanks. JGL]

  5. Muskrat (History)

    I’d like to address the “what if Iran gave their nuke to terrorists” question. Since the downside of doing so is very large (if traced back, either pre-or post-detonation, it would probably mean the end of the regime), let’s assume that a nuke would be the last thing Iran or anyone else would give to terrorists.

    Next, let’s look at what they have given terrorists so far. Money, support, convetional weapons of various sorts – I’m no expert. But the key question isn’t “What have they given to terrorists before?” but “What haven’t they given?”

    there must be things they could have given to terrorists but didn’t (I’m thinking advanced comunications, entire aircraft or drones, high-end weapons like field artillery, or especially CW).

    Why not? Presumably some kind of rational calculus of self interest versus the political benefits they get from supporting terror attacks.

    If that calculus kept them from giving CW to terrorists, why would they give them a nuke?

  6. john (History)

    But where would they get the plutonium or uranium without years of work on centrifuges to purify what they can mine? Why is assumed they are trying to make a bomb, and what risks would there be to anyone, with both Israel and the US having enough to destroy them if they tried anything?

  7. Papa Ray (History)

    Iran’s intentions and history are what the President of the United States has to deal with along with their capability.

    Given many unknows..ie- Russian assistance, NK assistance, even Pak assistance in the design and manufacture of missiles and warheads, not yet seen anywhere, but in vast underground manufacturing facilities, and only by trusted select personel, the President of the United States has to err, on the side of stopping them from accomplishing their intentions.

    Not on what they might have or what they might build or what they might have bought or stolen.

    Boil it down to this. A bad guy has lived in your neighborhood for 30 years, has been convicted for many crimes, has a lot of money and some very powerful friends and has developed a hatred of everyone and seems a little crazy.

    He says he is going to destroy your neighborhood. How, you are not sure, but you believe him.

    What do you and your neighbors do.

    So, this discussion is really not all that important..at all.

    Papa Ray
    West Texas
    USA

  8. Arrigo (History)

    “Much more worrisome, I would think, would be the weapon delivered by terrorists, perhaps on a ship.”

    Jeffrey, this is a complete “non sequitur” with respect to the rest of the discussion!

    Why, pray, would Iran want to pass on a nuke to terrorists when they know full well that technology is there which would allow the target nation to rapidly and easily figure out who enriched the fissile material?

    Without listing vast quantities of references on the subject it should suffice to mention your very own blog and the investigations on the Lybian nuclear programme material seized by the USA.

    If I hadn’t been reading you longer I’d say this was a wink towards the various hawks and the partisans of the “all states which are not the USA are terrorists”.

    I think it would be very timely for you to write an article on the issues of dirty bombs based on discarded radioactive material around the world. You could start from the trivial “pick up the discarded X-ray machines at 3rd world hospitals” to the more sinister “ecomafia”, i.e. that section of the Mafia which devotes itself to the illegal dumping of high-risk material from 1st world countries into 3rd world countries.

    It would take a terrorist group far far less resources to make a dirty bomb than to smuggle in a nuke on an iranian freighter… indeed, they would probably find the material directly on their victims very own soil.

  9. MVS (History)

    Three words—
    Scuds on Ships!

  10. hiphink (History)

    Arrigo, I assume what Mr Lewis was referring to was a commissioned op.

    Iran has warfare by proxy down to an art, it’s their MO. If the pasdaran Qods organisation in some hypothetical scenario was tasked with a retributive nuclear mission, chances are they would invoke proxies.

  11. Thomas the Wraith (History)

    Couldn’t Iran put warheads on fighter planes and have suicide pilots fly below radar all the way to Tel Aviv? Or even inside a commercial aircraft and detonate on landing approach over London?

    Once they have the device, it seems like there are a variety of delivery methods besides ballistic missiles, especially for a regime with a robust culture of suicide martrydom.

  12. Yale Simkin (History)

    jeffrey wrote:
    ——-/ Quote /——
    … might be able to build a 500-1000 kg warhead.
    … gun-type device… or imploding sphere of uranium… The latter is the more likely route for a number of reasons, largely related to the size of the weapon.

    …Holdren et al claim that the best a new state could do is a range of 450-1000 kg, with a much heavier design more likely.

    … 500 kg is a damn small weapon for a new nuclear state.

    So 500-1000 kg… for the mass of a nuclear weapon the Iranians could build…a warhead for a ballistic missile.
    —-/ END QUOTE /—-

    Could an early bomb state do better? Instead of sophisticated 3D implosion systems, what opportunities do uranium guns present?

    Little Boy at 9000 pounds and overpacked with 80% HEU does not do justice to actual production gun-assembly warheads.

    The South African uranium gun was much smaller and lighter even tho ultra-conservative and w..a..y overbuilt. (This was deliberate)

    Atomic artillery shells are much better examples of what a breakout nuclear state could accomplish.

    The US fielded a number of nuclear shells, first as uranium guns, then as extremely high-tech linear implosion plutonium bombs (which we can ignore).

    ===
    W-9 Artillery Shell (HEU gun-assembly) – Diameter: 0.28 meters – Length: 1.4 meters – Weight: 375 Kg – Yield: 15 kiloton

    Produced 1952-53 (80 units), retired 1957

    Notice how compact this >Hiroshima-yield warhead is. It is even 125 kg lighter than the 500 kg standard.
    This is a robust ruggedized artillery shell designed for 10,000 gees and rapid rotation. An Atomic Demolition Munition (the T-4) was built from retired W-9’s and was just a fraction of the weight.

    Here is a video of a firing of a W-9, the Grable shot. The range was 7 miles. Notice how small the shell is.

    http://www.nv.doe.gov/library/films/media/mpg/0800015.MPG

    ===

    W-19 Artillery Shell (HEU gun-assembly) – Diameter: 0.28 meters – Length: 1.4 meters – Weight: 275 Kg – Yield: 15 – 20 Kiloton

    Production started 1955, retired 1963

    ====

    W-33 Artillery Shell (HEU gun-assembly)

    Here’s an image of the W-33:

    http://solar-photon.com/images/mk33.jpg
    ————- – Diameter: 0.20 meters – Length: 0.94 meters – Weight: 110 Kg – Yield: 5 – 10 Kiloton (a boosted mod was 40 kilotons)

    Produced 1957 – 1965, retired 1992
    ~2,000 produced

    =====

    The W-33 used titanium to cut weight with high strength. It was a double gun which save weight by about a factor of 8 over a single gun.

    In the Holdren source that jeffery quoted from above is this:

    “For any nation with a modest technical competence, laboratory measurements would suffice for such a uranium-235 gun design, together with firing the gun with a dummy projectile. Knowledge… of the fact that the United States once possessed large numbers of artillery-fired gun-type nuclear shells might lead a proliferant country to a system much lighter and smaller than the Hiroshima weapon.”

    yale

  13. Jeffrey Lewis (History)

    The first South African devices (in the late 1970s) were extremely large and not deliverable by missiles.

    David Albright explains:

    The first “qualified” gun-type device was not completed until August 1987. This model could be delivered by a modified Buccaneer bomber. …

    The total mass of a completed device was about one metric ton. It had a diameter of nearly 65 centimeters and was about 1.8 meters long. Each device contained an estimated 55 kilograms of HEU. The cores of the second through seventh contained weapon-grade uranium. The reflector was made of tungsten. The calculated yield of each device was about 10 to 18 kilotons when the core had weapon-grade uranium. Using 80 percent enriched material halved the expected yield.

    So, no size reduction and not relevant to the question: “How far can Iran launch a warhead on a missile?”

  14. Yale Simkin (History)

    Jeffery wrote:———————————————The first South African devices (in the late 1970s) were extremely large and not deliverable by missiles.
    …..
    So, no size reduction and not relevant to the question: “How far can Iran launch a warhead on a missile?”
    ————————————-

    I fear I have been betrayed by my feeble failings as a writer. With my typical incoherence I seem to have obscured my main point. I was trying to point out that NEITHER Little Boy NOR the S.A. devices are valid examples of what a breakout nuke nation could do creating a lightweight uranium gun.

    But first a couple of points about the S.A. weapon: While Little Boy was 4 metric tons, the SA physics package – as overbuilt and as overloaded as it was, weighed only 750 kilograms. The 1 ton normally used to describe the weapon includes the massive bomb casing. Here are images of those humongus overweight casings:

    Side:
    http://solar-photon.com/images/SA-GA-Side.jpg

    Rear:
    http://solar-photon.com/images/SA-GA-Rear.jpg

    The weapon – without the casings – was sized to be carried by the RSA missile under development:

    RSA Missile:
    http://solar-photon.com/images/RSA-Front.jpg
    ————————————
    As interesting as the SA device is, my posting was about atomic artillery shells being the better example.

    In your article you quoted Holdren, et al from “Technical Issues Related to Ratification of the Comprehensive Test Ban Treaty.

    My comments amplified this statement from that document:
    ——————————-

    “Knowledge…of the fact that the United States once possessed large numbers of artillery-fired gun-type nuclear shells might lead a proliferant country to a system much lighter and smaller than the Hiroshima weapon.”
    ——————————-

    Here is what I said (emphasis added):
    ———————————
    “Could an early bomb state do better? Instead of sophisticated 3D implosion systems, what opportunities do uranium guns present?
    Little Boy at 9000 pounds and over-packed with 80% HEU does not do justice to actual production gun-assembly warheads.
    The South African uranium gun was much smaller and lighter even tho ultra-conservative and w..a..y overbuilt. (This was deliberate)

    ATOMIC ARTILLERY SHELLS ARE MUCH BETTER EXAMPLES OF WHAT A BREAKOUT NUCLEAR STATE COULD ACCOMPLISH.”
    ———————————
    These gun-assembly uranium weapons are very straightforward and vastly less complex than a 3d implosion design and well within a new nuclear state’s ability.

    As I pointed out, the 15 kt W-9 from 1952 was 0.28 meters in diameter, 1.4 meters in length and weighed only 375 Kg (INCLUDING the 10,000 gee ballistic casing)

    Here is a video of a firing of a W-9, the Grable shot. The range was 7 miles. Notice how small the shell is.

    http://www.nv.doe.gov/library/films/media/mpg/0800015.MPG

    The 1955 W-19 (HEU gun-assembly) was also 0.28m x 1.4m but weighed only 275 Kg with a yield of 15–20 kt

    The 1957 W-33 gun-assembly shell was only 0.20m x 0.94 meters with a weight of only 110 Kg

    Here’s an image of the W-33:

    http://solar-photon.com/images/mk33.jpg

    About 2,000 were produced.————————————————
    Here is a quick-and-dirty “design” for a lightweight uranium gun that is extremely simple and well within the 500 kg limit.

    A 24 kg, 16cm sphere of HEU with a hole cored thru the center is nested within a 10cm thick beryllium shell with matching holes.

    Screwed into the poles of the sphere are two Chinese PLA Type-79 100mm mortar barrels, shortened to 67cm each.

    Inside each tube is boron-lined sabot carrying an 8 kg HEU cylinder with a 10cm Be backplate and propellent.
    Using a pair of electronically-triggered, matched off-the-shelf high-speed detonators the mortars are simultaneously detonated and the 2 projectiles penetrate the core at a combined 400 m/s (Little Boy was 300 m/s).

    This will assemble 2.5 critical masses and go SERIOUSLY High-Order (multi-kiloton).

    What does this weapon weigh? 40 kg for HEU, 40 kg for the 2 mortar tubes, and 40 kg for the beryllium reflector and say, 5 kg for fuzing mechanism.

    125 kilograms.

    A strong canister of corrugated .063 aluminum with a rigid foam filler (or with metal or plastic bracing) to rigidly support and protect and insulate the device will add 10 kg.

    The whole warhead is 0.4m x 1.5m with a weight of 135 kilograms and can be mounted within a bomb casing or missile RV.

    Although functional, this design should also include some type of mechanical safing, which adds weight. This would easily be offset by optimizing other aspects (titanium barrels instead of steel, shorter tubes, etc.)

    This design is easy to machine and simple to test with DU instead of HEU. Any nation which can build centrifuges would have no problem making a small lightweight powerful uranium gun.

    yale

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