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Iran’s aerospace program has been so active in the last few years it should be possible to say something about their development philosophy: the technological arc or trajectory they are following. For instance, why did they “jump” from SCUD-type missiles to the Shahab-3-type? Why didn’t they put a higher priority on clustering engines in order to achieve greater ranges before moving on to the Shahab-3? Many of my friends believe they should have. A large portion of their argument is centered on the fact that they believe Iran would have established a missile capable of hitting Israel much sooner if they had done that, perhaps as early as the mid-1990s. Of course, such arguments place an extraordinary amount of emphasis on such a military objective, especially when Iran’s nuclear program was much, much less advanced.

I’ve always thought, however, that Iran did make a strategic decision about the direction its missile development program was going in. But it was not a military-strategic decision but an industrial-strategic decision even if there were military advantages to be had further down the road. I believe Iran decided they needed to assimilate the technology for producing large engines indigenously and that this was a much higher priority for them than early production of a longer range missile. New images released at the same time as the “Kavoshgar-3” sounding rocket (with its animal passengers) was launched. Two amazingly important images were released:

A new, large, two-stage rocket with the Iranian space agency logos on it. The second stage appears to be the same stage (and nose fairing) as the Safir’s second stage.

Assuming that the smaller diameter second stage is the same as the Safir’s second stage (with a diameter of 1.25 meters), then the much larger first stage is consistent with a diameter of 1.95 meters. That is, of course, considerably smaller than twice the Shahab-3’s diameter of 2 times 1.25 (or 2.5) meters. So it is fair to ask “What can you put in there?” I think the answer is a cluster of four “Nodong engines.” And, voila, the Iranians show a new rocket power plant with a cluster of four Nodong engines at the same gathering where Pres. Ahmadinejad watched the Kavoshgar-3 launch:

An Iranian rocket scientist unveils the new cluster of four Nodong engines, known as the Phoenix (if Google translate is working properly). The yellow struts above the engines are for transmitting the thrust to the rocket’s airframe. Their presence implies that the first stage will use jet vanes for thrust vector control.

Phoenix, the name of the new power plant, is an interesting name. I’m not sure what the Iranian mythological implications are but as a Westerner, to me it means rebirth in fire. Perhaps they are implying the rebirth of this engine design in a new form. Of course, it is always dangerous to use one cultural point of view to analyze another culture’s literary allusions.

The yellow struts rising above the engine cluster (and their multiple turbopumps, perhaps four? one for each engine?) are for fastening the power plant to the rocket body and for transmitting the thrust they develop. They are angled slightly outward for increased structural strength. Pads at the top of the struts are the connections with corresponding strong points inside the first stage. But is the first stage wide enough to accommodate this cluster?

To answer that question, I have had to go through a chain of photo-interpretation; each of which undoubtedly contributes a certain amount of uncertainty or error to the final answer. First, I had to determine the diameter of the Nodong engine. (I know these are Shahab-3 engines, but I am so used to calling them Nodongs, it would be too painful to switch. Let it be known that I think these engines are indigenously produced in Iran, though Iran probably bought or licensed the production line for them from North Korea.) I get a diameter for the combustion chamber, just below the strong points for the struts, of 0.57 m.

Then, transfer this diameter to the image of the Phoenix power plant:

The top of the Phoenix power plant, showing the combustion chambers and the full diameter of the struts. Calculations by the author indicate that this cluster of four engines would certainly fit inside the large rocket body shown above.

Using this combustion chamber diameter as a reference point on length, I get a total separation between opposite pads at the top of the struts of 1.87 meters. Of course, a rather long chain of analyses was needed to estimate this length. And even the assumption that the farthest right strut pad and the farthest left strut pad represent the full diameter of the support system introduces a certain amount of uncertainty (though that is reduced by a cosine theta effect). Nevertheless, this is remarkably close to my estimate for the diameter of the new rocket’s first stage. Close enough to convince me that this is the new first stage’s power plant.

Note that there are at least superficial differences between this rocket’s first stage and the DPRK’s U’nha-2’s first stage. If nothing else, Iran has designed the airframe itself. (I am being extra cautious about this, my own feeling is that Iran has designed the entire first stage itself. But that is such a key step in my understanding of Iran’s missile development trajectory, that I am hesitant to state it as a conclusion.)

So what do I think has happened? First, Iran purchased a production line for Nodong engines (and the other components of the Shahab-3 missile) from North Korea. However, though the years of producing them, flight testing Shahabs, and modifying them with the design and production of the Safir and other rockets, Iran has fully assimilated this technology and they are moving on to the next stage of development—clustering large engines (they obviously gained some highly important experience with the cluster of two engines on the Safir’s second stage)— and they are probably doing this largely on their own.

Note: a future post will estimate the range of this missile using the “hypothesis” developed here.

Comment [44]

As you undoubtedly noticed, Iran launched a rocket on February 2. And released pictures of a space launch vehicle. Which may not be the same thing.

As some of you may know, Geoff Forden is going through some personal stuff right now, which is why we are missing his usual detailed commentary on Iran’s space launch. (He has something coming, but I am inclined to be patient.)

So, in honor of Geoff, I am just going to create an open thread for the Iranian space launch. Here are images from IRNA, ISNA and Mehr to get you started.

Have at it.

Comment [9]

The Annual Threat Assessment of the U.S. Intelligence Community is out, and it’s official: cyber is the new black.

(The version presented to the Senate is linked above. Here’s the basically identical House version.)

Judging by the many threats ably described in this report, life is short, so let’s skip to the good stuff. Pages 13-15 summarize the IC’s view of missile and nuclear developments in rogue states the Axis of Evil Iran and North Korea. Today’s topic is Iran. Tomorrow — barring the Apocalypse or unforeseen delays — we’ll consider North Korea.

[Update | Feb. 7, 2010. After a Snowpocalypse-induced delay, we have a North Korea post.]

Two areas are especially worth a look: the analysis of the Qom enrichment facility, and the handling of the 2007 National Intelligence Estimate on Iran, a subject of fierce public debate, probably for years to come.

Qom — What is it Good For?

After summarizing what the IAEA reports say about Natanz, we get to Qom, a.k.a. Fordow, a.k.a. FFEP. Let’s focus on a few points of interest:

Second, Iran has been constructing—in secret until last September—a second uranium enrichment plant deep under a mountain near the city of Qom. It is unclear to us whether Iran’s motivations for building this facility go beyond its publicly claimed intent to preserve enrichment know-how if attacked, but the existence of the facility and some of its design features raise our concerns. The facility is too small to produce regular fuel reloads for civilian nuclear power plants, but is large enough for weapons purposes if Iran opts configure it for highly enriched uranium production. It is worth noting that the small size of the facility and the security afforded the site by its construction under a mountain fit nicely with a strategy of keeping the option open to build a nuclear weapon at some future date, if Tehran ever decides to do so.

Deep under a mountain. This echoes the characterization of the senior administration official who spoke to the press on September 25, 2009: “a very heavily protected, very heavily disguised facility.” But as Geoff Forden pointed out shortly thereafter, the available images show a cut-and-cover facility, neither deeply buried nor heavily protected by anything but its camouflage (“very heavily disguised”) and local air defenses. Is there some misunderstanding at work here?

To preserve enrichment know-how if attacked. This is almost what the head of the AEOI, Ali Akbar Salehi, told reporters at the time, but not quite:

“This site is at the base of a mountain and was selected on purpose in a place that would be protected against aerial attack. That’s why the site was chosen adjacent to a military site,” Salehi told a news conference. “It was intended to safeguard our nuclear facilities and reduce the cost of active defense system. If we had chosen another site, we would have had to set up another aerial defense system.”

The stated point, it appears, was to keep centrifuges spinning. The potential non-military application for uranium enrichment (in a hidden location, no less) after declared nuclear facilities have been destroyed is somewhat elusive. Bureaucratic inertia, as some have argued? A desire to prevent the West from imposing a “suspension by other means,” even if it has to be kept a deep secret? Or, as the IC testimony appears to suggest, to keep personnel trained up on centrifuge operations until large-scale operations could resume?

If Iran opts configure it for highly enriched uranium production. On the morning of September 25, President Obama stated flatly that “the size and configuration of this facility is inconsistent with a peaceful program.” It appears that the IC has now walked back the part about configuration, perhaps on the basis of findings from IAEA visits. Does this mean that the President was misinformed or misspoke, or did something change at the site, perhaps in the three weeks that passed before the IAEA’s initial visit? [Update: Peter Crail of ACA points out that the language on this point in the ATA is consistent with a Q&A released last September.]

Keeping the option open. This bit tracks with the September 25 background briefing: “our information is that the Iranians began this facility with the intent that it be secret, and therefore giving them an option of producing weapons-grade uranium without the international community knowing about it.”

Reaffirming the 2007 NIE, Sorta

The ATA states,

Iran’s technical advancement, particularly in uranium enrichment, strengthens our 2007 NIE assessment that Iran has the scientific, technical and industrial capacity to eventually produce nuclear weapons, making the central issue its political will to do so. These advancements lead us to reaffirm our judgment from the 2007 NIE that Iran is technically capable of producing enough HEU for a weapon in the next few years, if it chooses to do so.

But what about the other judgments? This passage does comment directly on the contentious questions of whether Iran A) suspended research on weaponization in late 2003, as the NIE had claimed, and B) later resumed the work, a possibility the NIE considered but did not embrace.

This question was stirred up again by the appearance of the celebrated or infamous uranium deuteride document in the Times of London last December. In early January, the New York Times reported that “top advisers” to the President had reached the conclusion that the NIE had been mistaken about the weaponization question, a view said to be shared in Britain, France, Germany, and Israel. The NYT did not mention the views of the U.S. IC, but a few days later, DIA Director Ronald Burgess told Voice of America something close to a reaffirmation of the contested point, but not quite:

“The bottom line assessments of the NIE still hold true,” he said. “We have not seen indication that the government has made the decision to move ahead with the program. But the fact still remains that we don’t know what we don’t know.”

Newsweek‘s sources claimed that the IC was settling on a view that Iran had resumed research, but not development of nuclear weapons. The Washington Times went further, stating that the IC was poised to walk back the claim that Iran had suspended work in the first place.

The closest that the new ATA comes to remarking on weaponization is this seemingly anodyne observation: “We continue to judge Iran’s nuclear decisionmaking is guided by a cost-benefit approach, which offers the international community opportunities to influence Tehran.” This language echoes the 2007 NIE Key Judgments: “Our assessment that Iran halted the program in 2003 primarily in response to international pressure indicates Tehran’s decisions are guided by a cost-benefit approach rather than a rush to a weapon irrespective of the political, economic, and military costs.”

Readers will have to decide what that really means. After the warm welcome received by the Iran NIE Key Judgments back in December of 2007, we should not expect to see a similar release anytime soon. For clarification, we’ll probably have to settle for the forthcoming Questions for the Record.

Comment [10]

Note: Two previously overlooked estimates have been added to the data table, and the “observations” section updated accordingly.

Last week, at an event sponsored by AAAS (depicted above*), I had the privilege of giving a presentation on “Expert Opinion on Iran’s IR-1 Centrifuge.” The session was off the record, but I can share with you, Dear Reader, a data table assembled for the occasion, along with a few observations.

This table is an amended version of the data previously assembled by the Federation of American Scientists (see Table 1 in this report). I’ve tinkered with this dataset before (see: Estimating SWU with Expert Opinion, December 6, 2009). The amended table covers every published estimate of the separative power of the IR-1 centrifuge that I could find, running from March 2003 to December 2009. Explicit repetitions of previous estimates [or estimates explictly derived from earlier estimates] are not included.

(N.B. “Actual” indicates the mean performance of actual devices. “Nominal” indicates the maximum power of the device on paper. Despite some ambiguities, it’s usually apparent from context which type of estimate is intended, when not stated directly. For example, I’ve tagged as “nominal” those estimates that relate to the machines believed by different experts at various points to be ancestors of the IR-1.)

There are 29 31 estimates, although some of the “nominal” estimates from ISIS appear to be repetitions. (More on this point in a few moments.) Here it is: the whole megillah.

Note: Thanks to Scott Kemp for the clarification on his 5/27/08 estimate, which was actually two estimates. Thanks also to Andreas Persbo for the similar observation about his estimate of 2/27/09. I’ve corrected the table to reflect both of these inputs. I’ve also corrected a few minor errors and inconsistencies.

Author(s)	Data source(s)	kg SWU/yr	Estimate of	Date
Hibbs	Official sources	7 to 15	Actual	3/13/03
Hibbs	IAEA sources	12 to 14	Actual	5/12/03
Hibbs	AEOI data	6 to 7	Actual	5/12/03
Albright & Hinderstein (ISIS)	Senior Western officials	2	Actual	9/1/03
Albright & Hinderstein (ISIS)	Senior IAEA officials (stated subsequently)	3	Nominal (based on 4M)	3/1/04
Gilinsky, Miller, & Hubbard	Unclassified sources (and educated guesses)	1 to 3	Actual	10/22/04
Hibbs	IAEA and Western governments	2	Nominal (based on SNOR & CNOR)	1/31/05
Glaser	(not stated)	2	Nominal (estimate of P-1)	6/14/05
Lewis	Rademaker (USDOS) statement	2 < and < 3, closer to 2	Actual	4/15/06
Lewis	Aghazadeh (AEOI) statement	2.3	Actual	4/18/06
“Feynman” via Lewis	Aghazadeh (AEOI) statement	1.46	Actual	5/12/06
“Feynman” via Lewis	Aghazadeh (AEOI) statement	2.3	Nominal	5/12/06
Albright (ISIS)	Aghazadeh (AEOI) statement	1.4 to 2.7	Actual	5/17/06
Albright (ISIS)	(not stated)	2.5 to 3	“the high end of the possible”	7/1/06
Albright & Shire (ISIS)	Level Pakistan is said to have achieved	2	Actual of P-1	11/1/07
Garwin	Aghazadeh (AEOI) statement	1.362	Actual	1/17/08
Glaser	(not stated)	2.5	Nominal (hypothetical max. of P-1)	4/16/08
Kemp via Lewis	Observed efficiency of 42%	1	Actual	5/27/08
Kemp via Lewis	(not stated)	2.5	Nominal	5/27/08
ISIS NuclearIran FAQ	(not stated)	1 to 2	Actual	~9/1/08 (n.d.)
ISIS NuclearIran FAQ	(not stated)	3	Nominal	~9/1/08 (n.d.)
Persbo	Cascades operating between 27 and 36% of total capacity	0.59 to 0.79	Actual	2/27/09
Persbo	(not stated)	2.2	Nominal (based on SNOR)	2/27/09
Salehi (AEOI)	(not stated)	2.1	Unclear; nominal?	9/22/09
Oelrich & Barzashka (FAS)	IAEA reports	0.5	Actual	9/25/09; see also 11/23/09
Wisconsin Project	IAEA reports	0.5	Actual	11/16/09
Albright & Brannan (ISIS)	IAEA reports	1.0 to 1.5	Actual	11/30/09
Albright & Brannan (ISIS)	(not stated)	3	Nominal	11/30/09
Oelrich & Barzashka (FAS)	IAEA reports	0.44 to 0.88 (0.88 is highly unlikely)	Actual	12/1/09
Kemp	IAEA reports	0.6 to 0.9	Actual	12/1/09
Wood via Kemp	Max. of P-1 based on validated hydrodynamic codes from the U.S. program	2.1 to 2.2	Nominal (max. of P-1)	12/1/09

Four Observations

First, as noted previously, the trend of the estimates declines with time. This effect only becomes more pronounced with the inclusion of the estimates reported by Mark Hibbs in NuclearFuel and Nucleonics Week in early 2003: now the trend of the decline is follows an exponential curve. These reports appeared when IAEA inspectors had just put eyes on the IR-1 (then called the P-1 in IAEA reports) for the first time. Their initial frame of reference presumably involved more up-to-date machines, rather than centrifuges whose design heritage extends back to the 1960s.

[Update | 22:54. See Mark Hibbs’ account in the comments below.]

Second, the decline comes in bursts, coinciding with the availability of new information. This effect is loosely similar to the influence of news on stock prices, as documented in event studies. The effect tends to be prompt in finance; a bit less so here.

• From mid-2003 into 2005, which covers the first period of centrifuge operations at PFEP in Natanz, we see the gradual sorting-out of the design heritage of the IR-1.
• The next wave comes in mid-2006, right after AEOI chief Gholamreza Aghazadeh gave some detailed figures during an interview with Iranian TV. Here we start to see some divergence between “actual” and “nominal” estimates, with “actual” figures falling below 2 kg SWU/yr.
• Next come the estimates of late 2007 to early 2009 2008, after the commencement of enrichment work at the FEP in Natanz, whose results were periodically documented in IAEA reports.

• A final burst of estimates, explicitly derived from the ever-accumulating IAEA reports, takes place in late 2009. Here, “actual” estimates fall below 1 kg SWU/yr.

Third, in most cases, a “new entrant” tends to lead the way in pushing “actual” estimates down. That is, someone who wasn’t previously in the game seems to take hold of the new information and bring it to light, with the rest shortly catching up. In 2003 and 2004, it was David Albright and Corey Hinderstein of ISIS. In 2006, it was Jeffrey Lewis and a pseudonymous correspondent here at ACW. In 2009, it was Ivan Oelrich and Ivanka Barzashka of FAS.

[Update | 23:51. In hindsight, Andreas Persbo was the first to present an “actual” estimate below 1, using recent IAEA reports. This contribution may have been overlooked because it was couched as a range of percentages of a nominal figure.]

Fourth, there are lingering differences between experts in both “actual” and “nominal” figures. Much of the basis of the “actual” differences was laid bare in the FAS-ISIS debate of late 2009. The “nominal” differences seem to originate with early reports about the design heritage of the IR-1. In March 2004, ISIS related that the IR-1 was copied from URENCO’s 4M centrifuge; both designs have four aluminum tube rotor segments. In January 2005, Hibbs reported that the IR-1 was derived from URENCO’s SNOR and CNOR machines.

Both 4M and CNOR are said to have been capable of about 3 kg SWU/yr. The CNOR had six segments, each responsible for about 0.5 kg SWU/yr, according to Hibbs. Since the Pakistani P-1 and the Iranian IR-1 have four segments, their nominal output, if they are understood to be CNOR derivatives, is about 2 — or, according to some recent figures, 2.1 or 2.2. Most experts seem to agree with Hibbs, or wind up close to his figure. But Albright and colleagues persist in viewing 3 as the real ceiling.

Should you, Dear Reader, notice any other subtle patterns in the data, well, that’s what the comments feature is for!

*Actually, the picture at the top of this post does not show me giving a presentation.

Comment [10]

Quite a few of my friends have been urging me to write something about the “new” images of Iran’s space center that have shown up recently on Google Earth.

The trouble is, I hate rehashing stuff I wrote about almost two years ago when I “discovered” the facility—much like Columbus “discovered” America—and wrote about it in Jane’s Intelligence Review (see Geoffrey Forden, “Smoke and Mirrors: Analyzing the Iranian missile test”, JIR, April 2008, pp. 47-51; I have never understood how the editors pick titles for my papers).

Perhaps the most interesting part of the imagery now, given the connection between these two countries’ missile programs, is the similarity between a building at North Korea’s launch site and one at Iran’s. For those who would like to examine the site themselves, let me replicate the coordinates I published in the open literature for the first time nearly two years ago:

35.234440° N, 53.920798°E.

Comment [8]

Iran is justifiably proud of its satellite launch last February. After all, both North and South Korea failed in their satellite attempts in that same year. It appears from images that are starting to show up on the web—pointed out to me by the ever observant Wonk-Reader Tal Inbar—that they have taken the show given to President Ahmadinejad at the Iranian Space Center on the road. These images show new and revealing details of both the Safir/Omid system and some indication of the quality of workmanship that goes into it. The image above is another image of the back of the Safir’s second stage engine platform showing more about how the turbopump is enclosed. Compare it to the image shown here, which shows more of the turbopump. The very frail looking “flaps” are light-weight baffles to prevent the fuel from sloshing about particularly during staging. Other images show what appear to be drain holes to the fuel tanks, a new telemetry dish antenna, and several nice views of the first stage engine (and are those indigenously produced components laid out on little pedestals?) Any help translating the Farsi on any and all these images would be gratefully appreciated!

Comment [16]

click on the image for a larger version

This is the second in a series of preparatory posts leading up to a discussion on the Safir’s guidance system. The first discussed the orientation of the Safir at launch and showed, as closely as the errors associated with photo-interpretation would allow, that it’s first stage guidance and control system was a standard SCUD-type system: Fin I is oriented along the direction of flight of the missile and its pitch program operates in that plane.

This short blog post discusses the ground terminal trucks Iran used to communicate with the satellite. Iran, in accordance with the “rules of the road” organized by the International Telecommunications Union (ITU), had an uplink (401 MHz) and a downlink (465 MHz) frequency for the Omid satellite recorded in the ITU-R’s Master Registry. Various computer animations of the launch show mobile ground stations positioned around Iran for communicating with the satellite and it would be nice to confirm that images taken of ground station trucks are used for that purpose. It also turns out to be a very satisfying exercise in photo-interpretation. A future post will discuss communications for guidance purposes, as was implied in the secret missile memos.

As the image above—taken during a visit to the Iranian Space Center by President Ahmadinejad—shows, there are trucks with potentially suitable antennas. The dual antennas are of a Yagi-Uda design (often simply called a Yagi antenna) with 12 passive “directors,” a looped Balun-type element for radiating the signal and, at the very rear of the array, a somewhat larger “reflector.” The reflector is to ensure that there is a preferred direction to the antenna as opposed to being sensitive to signals from both directions along the boom. The Balun radiator matches the impedance from the simple coaxial cable to the array and the directors increase the “gain” or directionality of the antenna. Interestingly, there are both vertical and horizontal arrays on each boom with the horizontal array set back a quarter wavelength (see below), perfectly suited for detecting or radiating circularly polarized radio waves. That is needed because the Omid satellite tumbles as it orbits and its polarization—while not circular—is directed in an arbitrary, time varying manner. The bulky cable run up to the antenna hub is for controlling the direction of the antenna arrays and could, though there is no way to know from the photo, be capable of autonomous direction if it is set to maximize the strength of the signal.

Yagi antennas are nice from a photo-interpretation point of view because their dimensions are so easily related to their wavelength. For instance, an optimal 13 element (counting the radiator but not the reflector) Yagi for 401 MHz has a boom length of 2.7 meters. That’s from reflector to last director. It also has a reasonable antenna gain, which means that half the uplink beam is radiated into a cone with a half angle of about 16 degrees. The question then becomes: is the observed array consistent with these expectations?

The image to the left is taken from a more suitable perspective for photo-interpretation. The antenna arrays are nearly horizontal and close to being aligned with the rear of the truck. I have drawn two vertical lines continuing up the truck’s rear edges and a third, horizontal, line paralleling the antenna booms. Of course, there are a great number of approximations taken in this drawing. But then again, there are some approximations still to come. The most important of those is to assume that the truck’s rear cabin is approximately two meters in width. With that assumption, we can estimate the boom length to be approximately 2.9 meters long (from radiator to last director). This is consistent with the Omid satellite’s uplink frequency given all the approximations we have made. Either the far antenna in the image is shorter than this (if it is used for the downlink) or they are running the antennas nonoptimally for reception or there is a different receiver somewhere not on the truck.

What I find most interesting is the conclusion that if there are antennas on the Safir that have significantly different lengths than the Omid’s, then these trucks are not being used to communicate with them.

Comment [2]

You have no doubt seen the Times of London story, in which Catherine Philp claims to have obtained a 2007 “technical document” from from Iran that “describes the use of a neutron source, uranium deuteride, which independent experts confirm has no possible civilian or military use other than in a nuclear weapon.” (The Times published a more detailed discussion of UD3 in a separate article).

I have no idea whether the document is authentic, but I do want to confirm that Pakistan appears to have used uranium deuteride (UD3) as a neutron initiator.

The Times story doesn’t adequately convey that this is a relatively novel source of neutrons for a bomb design. Technically inclined readers may recall that earlier accusations against Iran focused on more traditional route of polonium-beryllium (Po-Be). Several colleagues have emailed me, expressing surprise that Pakistan is alleged to have used UD3 instead of the Po-Be.

But yes, it appears that both China and Pakistan explored the use of UD3 as a neutron source. There are two data points of which I am aware.

The first, and most colorful, is a well-known picture (above) of AQ Khan from the cover of his book, modestly titled Dr. A. Q. Khan on Science and Education.

AQ Khan graces the cover, holding a soccer ball (which is basically the size and configuration of the shell of high explosives in a nuclear weapon), standing in front of a blackboard showing a nuclear weapon diagram. The most shocking detail is the notation “Uran Deuteride Initiator.”

(A funny side note, the book Deception (2007) by Adrian Levy and Cathy Scott-Clark reproduces the image, with a portion of the blackboard redacted. Unfortunately, they redacted the wrong portion!)

Now, you may be thinking “How does that work?”

Four scientists from the Southwest Institute of Fluid Mechanics in Sichuan (which is the part of China’s nuclear weapons complex responsible for hydrodynamic research) published a detailed explanation in a 1989 paper entitled “Fusion Produced by Implosion of Spherical Explosive.” The paper is included in the proceedings of an American Physical Society meeting published as Shock Compression of Condensed Matter, (S. C. Schmidt, James N. Johnson, Lee W. Davison, editors, North-Holland, 1990.)

I had previously sort of steered clear of mentioning this on the blog, but between AQ Khan’s entrepreneurial activities and the Times of London, there’s not much point in denying it.

I won’t put the paper on line, but you can readily purchase your own copy.

Update | 3:09 pm ISIS has placed Farsi and English versions of the document online, along with a short analysis that basically describes the process outlined in the Dong et al paper.

Late Update | 6:12 pm Danny Stillman and Tom Reed mentioned the picture and the Dong et al paper in Nuclear Express on pp 250-251:

In 1997, a publishing house in Lahore, Pakistan, relaesed a collection of mid-1980s to mid-1990s lectures by A. Q. Khan entitled Dr. A.Q. Khan on Science and Eduction. This book discloses some of Dr. Khan’s early knowledge about nuclear weapons, including a sophisticated neutron initiation scheme. Initiators are the devices needed to assure an adequate supply of neutrons to the weapon core at the moment of maximum supercriticality. During World War II, the United States achieved this result by mixing beryllium and polonium at the center of an implosion. In later years the United States and most other nuclear weapons states turned to pulsed neutron tubes, essentially mini-accelerators, to produce a surge of neutrons when needed. But in 1989, at an American Physical Society conference in Albuquerque, the Chinese explained their very different approach to neutron generators. That Chinese initiation scheme appears with Dr. Khan’s book, and thus the origins of Pakistan’s A-bomb are unambiguously confirmed.

I should say that the first place I heard about all this was a talk we organized at Harvard for Danny. I didn’t link it to Danny since the talk was under the Chatham House-rule, but since he was able to put it in a book …

Comment [77]

So what is the separative power of the IR-1 centrifuge, really? We’ve touched on this question before, sometimes in connection with Natanz breakout scenarios. Lately, it’s come up in connection with the Qom facility, a.k.a. Fordow (see: Iran: Compliance in Defiance?, December 1, 2009). But simple answers are not forthcoming.

If you follow this blog, you’re probably already aware of the running exchange between Ivan Oelrich and Ivanka Barzashka of FAS on one hand, and David Albright and Paul Brannan of ISIS on the other. If not, see the FAS article in the Bulletin, the response by ISIS, the reply by FAS, and the rebuttal by ISIS.

This dispute, whose technicalities I won’t presume to referee, mainly underscores that estimates of the separative power of the IR-1 centrifuge are sensitive to a variety of assumptions. Open-source data do not suffice to provide a single, authoritative answer to the question, “How many kg SWU per annum?”

If You Don’t Know, Say So

When experts disagree, we can think of the answer as a range that indicates some uncertainty. (I’ve taken this approach before.) But what’s the right range?

Starting from Table 1 in the new FAS paper Calculating the Capacity of Fordow, we can assemble a collection of informed judgments. Then we can do something mildly controversial: we can average them and derive confidence intervals in the usual manner. Voilà! An instant range of IR-1 separative power estimates.

The rationale for averaging was aptly described in James Surowiecki’s 2004 book The Wisdom of Crowds. Each estimate “has two components: information and error. Subtract the error, and you’re left with the information.” The process of averaging “subtracts” the error because, if the individual errors are randomly distributed, they will largely cancel each other out.

Careful readers will notice that this requires that estimates be mutually independent. (Correlated errors are not random.) In that spirit, I’ve weeded the FAS table of all estimates that appear to be replications of earlier figures. I’ve used only the most recent estimate available from each expert, and have added a couple of estimates not included in the FAS table. I’ve taken the trouble to re-check the sources, too.

This exercise produces a table of nine opinions. Two were given as ranges rather than point estimates; in these two cases, I’ve used the average of each range as the estimate. There are good reasons for excluding three of these opinions (Hibbs, Persbo, and Salehi) as being related to the nominal performance of the IR-1 on paper (or the performance of its predecessors), not its actual performance.

[Update | Dec. 7, 2009. I’ve added a 10th opinion, that of Houston Wood as related by Scott Kemp, to the bottom of the table. Notice that it’s a nominal estimate, a calculation of the “maximum performance of a P-1,” the immediate predecessor of the IR-1.]

Source	kg SWU/yr	Date
Hibbs* in Nuclear Fuel	2	Jan. 31, 2005
Lewis & “Feynman” at ACW	1.46	May 16, 2006
Garwin at BAS	1.362	Jan. 17, 2008
Persbo* at vThoughts	2.2	Feb. 27, 2009
Salehi* in Fars News	2.1	Sep. 22, 2009
Oelrich & Barzashka at FAS	0.5	Sep. 25, 2009
Wisconsin Project	0.5	Nov. 16, 2009
Albright & Brannan at ISIS	1.0 to 1.5	Nov. 30, 2009
Kemp at ACW	0.6 to 0.9	Dec. 1, 2009
Wood* via Kemp at ACW	2.1 to 2.2	Dec. 1, 2009

*Estimates of nominal performance

(I’m assuming that the Wisconsin Project’s figure was derived independently of FAS’s.)

Some Findings (Provisionally Speaking)

First, a caveat: I’ve used ye olde normal distribution to demonstrate the concept, which seems problematic when considering the lower range of the intervals it produces in this instance. A more sophisticated iteration might involve another distribution. Math wonks are encouraged to engage directly with the data table.

Excluding the three nominal figures provides a mean estimate of 0.97 kg SWU/yr, +/-0.86 with 95% confidence. The resulting interval is 0.11 to 1.83 kg SWU/yr. (You see the problem with the lower end of the range.)

At 68% confidence – corresponding to one standard deviation – the result is 0.97 +/-0.44, with a resulting interval of 0.53 to 1.41 kg SWU/yr.

The technique demonstrated here makes the latest ISIS estimate (1.0 to 1.5 kg SWU/yr) look pretty good. It’s more or less coterminous with the upper half of the first standard deviation.

But this is not the whole story. Even within the trimmed-down data table above, a decline in estimates is apparent over time. The larger FAS table shows a sustained decline; a few years ago, estimates of 2 or 3 kg SWU/yr. were common, in ISIS papers and elsewhere. As mentioned earlier here, as new information about the performance of the IR-1 at Natanz has become available, it keeps driving down estimates of what the machine can do (see: Why Iran’s Clock Keeps Resetting, August 19, 2009). So it is not entirely surprising to see expert judgments converging somewhat south of the figures given here.

So what happens if we drop the first [remaining] estimate from the table above [i.e., Lewis & “Feynman”], on the grounds that it was produced before operations commenced at the FEP at Natanz? The result at 95% confidence is 0.87 +/-0.80, or 0.07 to 1.68 kg SWU. (There’s that sticky lower end again.) The result at 68% confidence is 0.87 +/-0.41, or 0.46 to 1.28 kg SWU/yr. From the perspective of a “moving average,” then, the central estimates of FAS and ISIS — respectively at 0.5 and 1.25 — just about bracket the first standard deviation. Statistically speaking, the truth is probably somewhere between them.

Update. See the comments for further elaboration, in which the Poisson distribution and the bootstrap raise their heads. Fun times.

Comment [23]

We usually think of the enrichment power of a centrifuge as fixed by its physical parameters. For a given gas, that of course is true. For enriching uranium hexafluoride, centrifuges with larger rotational speeds (the enrichment power of a centrifuge actually goes as the square of the peripheral speed) and longer rotor lengths have a greater separative work capacity. Thus, a P-1 has about 2.5 SWU capacity for enriching UF6 while a URENCO TC-12 reportedly has about 45 SWU.

What is often overlooked, however, is the effect of the gas on the enrichment capacity of a centrifuge design. (See equation 3 of Stanley Whitley’s “Review of the gas centrifuge until 1962. Part 1: Principles of separation physics.”) The gas properties enter into the equation in a variety of ways. First, the denser the gas, the better. Second, the more the species you are trying to enrich diffuses through the “carrier gas”—in this case He-3 diffusing through helium—the better. Finally, a centrifuge enriches a species faster if the mass difference between the two components of the gas is larger; in fact, it goes as the square of the mass difference.

The first and the third factors, density and the mass difference, favor the relative power of enriching uranium. (Here I have assumed that the number densities of helium and UF6 in the centrifuge are the same, which, of course, makes the density of UF6 about ninety times more dense than helium.) Helium is wonderful at diffusing through things, which is why most party balloons go flat and fall to the ground so fast. And He-3 through helium is no exception. It turns out that He-3 is about 13,000 times faster at diffusing through helium than a UF6 with U235 is at diffusing through U238 uranium hexafluoride. This is more than enough to compensate for both the mass difference and the low atomic mass of helium. Any given centrifuge should be (barring unforeseen practicalities) about 10 times better at enriching helium-three than it is at enriching U235. Thus, a single TC-12 centrifuge should have an enrichment capacity of 450 SWU-kg/year. That might be so large that it’s hard to balance the stages inside a URENCO cascade since URENCO apparently have fixed piping.

Total required enrichment capacity for a 95% product as a function of feed fraction assuming the tails are depleted to half the feed fraction.

However, it at least naively seems very good because the starting fraction of He-3 (at ~250 ppm) is considerably worse than the starting fraction of even natural uranium, or 0.711% of U235. If you want to enrich one kilogram of He-3 from its natural fraction to 95%, it takes 523 SWU as opposed to 189 SWU for uranium. This factor of more than two is, of course, more than compensated for by the improved enrichment capacity of each centrifuge. So the total amount of enrichment capacity needed is 63,000 SWU-kg/yr. It would take 140 TC-12s operating continuously for a year to enrich the required helium. (I haven’t bothered to find the optimal cascade size so this is a very crude estimate.) If, for some reason, 8,000 P-1 centrifuges operating at 85% were dedicated to this task, it would take them about five months to enrich the helium. We can estimate the cost by assuming the operating expenses are the same and scaling the cost per SWU for uranium enrichment at $100 by a factor of 10 to give a total cost of $630,000 for the job. On the other hand, if political considerations made it advisable not to scale the SWU cost, the whole job would only cost $6.3 million.

If the overall SWU requirement for He-3 is much greater than for natural uranium enrichment, the required feed stock is also greatly increased. To supply the 1,400 detectors envisioned by DHS would, according to the assumptions made in the last post, require 130 kg of He-3. This, in turn, implies a feed stock of 820 tons of “natural” helium. (For some reason, people who deal with gases like to deal in cubic feet. A funny volume-sounding unit that actually conveys a mass since a standard pressure and temperature are understood. Eight hundred twenty tons of helium corresponds to nearly 18 million cubic feet.) That is large but should be placed in some sort of perspective by comparing it to other large users of helium. The Kennedy Space Center, for instance, uses 72 million cubic feet of helium each year, or four times DHS’s one-time use.

Most of the world’s helium comes from area around Amarillo, Texas, which has been estimated to contain 70 million tons of helium (I can hardly bring myself to continue using cubic feet, but if you want to know that number: Texas contains 32 billion cubic feet of helium.) Of course, if a single user uses 0.2% of the world’s supply of helium each, we might really be facing a shortfall in a short time. As more users of He-3 arise, it might be a good idea to remove that isotope from natural helium as a standard operating procedure.

A Modest Proposal

Iran appears to be coming less and less likely to compromise on its nuclear programs and to insist on more and more enrichment on Iranian soil. However, I think it might still be possible to arrange a multinationally owned enrichment center in Iran. Our proposal has always counted on shutting down Iranian centrifuges as more cost effective Western centrifuges come on line at the facility. However, that becomes less and less practical, from a purely economic point of view, as more and more Iranian centrifuges are brought on line. Why not, in the context of the multinational enrichment venture, dedicate Iranian centrifuges to enriching He-3? Thus, the 8,000 existing Iranian centrifuges would become an important specialty shop with a guaranteed customer if the US decided to only use depleted helium at, for instance, the Kennedy Space Center?

This proposal is, admittedly, based on back-of-the-envelop calculations that show that centrifuge enriching of helium three is possible. A real centrifuge expert should be contacted to try to understand why URENCO does not consider helium suitable for enrichment and, if it is, to do a real cost analysis. But right now, it seems like a good solution to me!

Note: This post has been delayed because I’m “stuck” in the Florida Keys and there has been a wide-area internet failure down here until very recently. It’s a dirty job but somebody has got to do it!

Noted Added: Scott Kemp points out that the reason centrifuges arent used to enrich helium is because the relative scale height—the scale at which the gas falls off in density as a function of distance from the inner rotor surface—of helium is much, much greater than for a heavy gas like UF6. In order to get an efficient centrifuge separation, the diameter would need to be much, much greater than for uranium. Thanks Scott! This difference in scaling height results in a much decreased density of the helium near the rotor surface. That explains the erroneous results. By the way, this is an interesting example of how some scaling properties (i.e. equation 3 of the Review of Centrifuges paper) can be badly misapplied in “back-of-the-envelop” calculations if the underlying physics is not fully considered.

Comment [5]