guest post by Dr. Jeffrey Lewis of armscontrolwonk.com.
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 it’s 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 thoughout 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 it’s first missile delivered warhead with it’s fourth nucleat 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.
guest post by Dr. Jeffrey Lewis of armscontrolwonk.com.
The 'Vindhyagiri' (F42), a Leander class frigate, and helicopters from the Naval Air Station, Kunjali were involved in pursuit of the merchant vessel. The MV Alpha, a Vietnamese registered vessel in route to Panama, was intercepted, boarded and searched. The crew were questioned and the ship's papers checked and the vessel released.
My fellow citizens, at this hour American and coalition forces are in the early stages of military operations to disarm Iraq, to free its people and to defend the world from grave danger.
�Such people [Islamists] must be shot in the forehead! If necessary, I�ll shoot them myself.�