A few months ago, David Albright and Corey Hinderstein wrote a very interesting article, “Unraveling the A. Q. Khan and Future Proliferation Networks,” in The Washington Quarterly that contained some previously upublished information about that Chinese nuclear weapons design that the AQ Khan network sent to Libya:
The documents appear to have been information that Pakistan had received in China in the early 1980s. They include detailed, dated, handwritten notes in English taken during lectures given by Chinese weapons experts who were named by the notetakers. These notetakers appear to have been working for Khan, based on their cryptic notations deriding a rival Pakistani nuclear weapons program led by Munir Khan, the chairman of the Pakistan Atomic Energy Organization. The design appears to be for a Chinese warhead that was tested on a missile, has a mass of about 500 kilograms, and measures less than a meter in diameter.
I had no reason to question that description, but it was inconsistent with other information we have about the “Chinese warhead that was tested on a missile”—the fourth Chinese nuclear test (CHICOM 4) in October 1966.
Alex Montgomery (preparing for a forthcoming article in IS) recalled that John Lewis and Hua Di report that the warhead weighed 1,290 kg.
I wasn’t sure how to resolve this discrepancy: 500 kg or 1,290 kg?
So—with a little help from Steve Fetter and David Wright—I did a little calculation.
During my most recent trip to China, I obtained footage of most of China’s early, important nuclear tests including the one conducted in October 1966. Here is a still from that test, showing the warhead before being loaded onto the DF-2 (right).
From this image, we can make a basic judgement about the RV’s size and center of mass.
I also have the benefit of photographs of myself (left) and David Wright standing next to (empty) DF-2 RV’s in the museum yard at the Beijing University of Aeronautics and Astronautics.
Using these images, David and I think the diameter of the base of the RV is between 1.2 and 1.3 meters. One can then make a crude estimate of the diameter of the warhead within the RV, probably between 0.8 and 0.9 meters.
We can calcuate the volume of the spherical physics package with a 0.8 to 0.9 m diameter (V = 4/3 pi r3) and, assuming the mass of the physics package is roughly equivalent to a solid sphere of HE of the same size because the contribution to mass from the approximately 15 kg of HEU is trivial.
Conventional high explosives used in nuclear weapons weigh between with 1,500-2,000 kg per cubic meter. For example, Octol, an early US conventional high explosive used in nuclear weapons, has a loading density of 1.8 g/cc.
A sphere of Octol high explosive (HE) with a diameter of 0.85 M would have a mass of about 580 kg. Conversely, a 1290 kg sphere of Octol HE would have a diameter in excess of 1.1 M—which I believe would be difficult to fit into the RV pictured above.
Given the size and shape of the nose cone, I believe the mass and dimensions of the physics package tested in October 1966 on a DF-2 are much closer to Albright and Hinderstein (a mass of about 500 kilograms and a diameter less than a meter) than Lewis and Hua (1,290 kg).
That doesn’t mean Lewis and Hua are wrong—there is a decent chance that the entire re-entry vehicle weighed a total of 1,290 kg. The next step is probably to track down Lewis and Hua’s source—Zhongguo Junshi Baike Quanshi: Hewuqi (Chinese Military Encyclopedia: Nuclear Weapons), Beijing, Junshi Kexue Chubanshe, 1990, pp.157-158.
I am obviously neither a nuclear weapons designer nor a professional photo interpreter. But I did stay at a Holiday Inn in Xining, where I picked up the photo of the warhead.
Ok, it wasn’t a Holiday Inn. What I would have given for a Holiday Inn …