In assessing the ballistic missile threat, a key issue is estimating how long it might take countries like North Korea and Iran to build missiles that could carry a nuclear-warhead-sized payload to the United States. Both countries use liquid fuel in their satellite launchers and have developed that technology further than solid fuel. As a result both countries could develop a liquid intercontinental ballistic missile (ICBM) before a solid ICBM.
However, solid missiles are seen has having several advantages over liquid missiles. They can be smaller and therefore more easily transportable, and can be carried fueled and ready to launch on a transporter/launcher. More generally, the launch preparation time is shorter than for a liquid missile, which makes them less vulnerable to attack. Modern U.S., Russian, and Chinese ICBMs use solid fuel.
So I recently looked at the state of Iran’s solid missile development program to get a rough sense of how long it might take Iran to develop an ICBM, based on the historical development programs of other countries.
First, it’s worth noting that reaching targets in the U.S. from Iran requires a very long-range missile. Distances from Iran to various sites in the United States are:
- New York: 9,700 km
- Washington DC: 10,050
- Chicago: 10,300
- Florida: 11,100
- Texas: 11,500
Launching a missile from Iran toward the United States would require firing against the rotation of the Earth, so a missile reaching these targets would need to have a range longer than 11,000 km with a roughly one-ton payload (so that it could carry a nuclear warhead).
Building a long-range solid-fuel missile is more difficult than a liquid-fuel missile because of the technical difficulties of manufacturing large solid motors. The longest range solid-fuel missile Iran has tested is the Sajjil. It is a two-stage missile with a diameter of 1.25 m and a length of 18 m. The total mass is about 20 tons, with a first stage mass of about 14 tons.
The Sajjil is estimated to have a range of roughly 2,000 km with a payload of one ton. The first ground test of the solid motor was in 2005, and the first flight test was in November 2008.
While the recent National Research Council (NRC) report on ballistic missile defense says that Iran might be able to use the Sajjil engines to develop a missile with a range greater than 5,000 km, it does not specify a payload mass or a configuration for the missile. However, the technical study Iran’s Ballistic Missile Capabilities: A Net Assessment by Mike Elleman at IISS looks at two options for building a three-stage missile using three Sajjil solid motors and finds a range of 2,700 to 3,300 km with a one-ton payload, depending on assumptions about the level of technology (p. 110).
In 2009, Ted Postol published a detailed technical analysis of the Sajjil. Assuming the same level of technology as Sajjil, he finds that reaching 5,000 km with a one-ton warhead would require developing a first stage with a larger diameter than Sajjil and a mass of about 45 tons. The overall missile mass would be 65 tons or more. This is significantly more massive than even U.S., Russian, or Chinese long-range solid-fuel missiles, indicating that the technology demonstrated in the Sajjil is not appropriate for scaling up to very long ranges.
Developing a solid-fuel missile with 11,000-km range would therefore require a number of advances. For example, it would require a three-stage missile, lighter weight materials, more energetic propellant, and the ability to build large solid motors. Building large solid rocket motors requires specialized equipment and tacit knowledge about the manufacturing process. How difficult is this?
The IISS report argues that the best analogous case to Iran for the development of large solid missiles is France, so looking at the French experience is instructive.
France first tested its solid-fuel M1 missile in 1967, and it became operational in 1971. It was a two-stage missile with a 20-ton mass, and a diameter of 1.5 m. It reportedly had a range of 2,500 km with a 700-kg warhead, and was therefore somewhat bigger and more capable than Sajjil (IISS report, p. 79).
France’s M4 missile, with a diameter of 1.9 m and a mass of 36 tons, had its first flight in 1980 and did not become operational until 1986—15 years after the M1. It reportedly had a range of 4-5,000 km with a payload of 1.2 tons (IISS report, p. 79).
It was not until 2010 that France deployed the M51 missile with a range greater than 10,000 km. It has a diameter of 2.3 m and a mass of more than 50 tons.
It therefore took France more than 40 years to progress from testing a solid-fuel missile that was more capable than the Sajjil to deploying a solid-fuel missile having the range Iran would need to reach targets in the U.S.
Elleman also shows that Iran’s rate of development of increasingly large solid motors has lagged the similar development in France, the U.S., China, and India (IISS report, p. 86).
This comparison does not, of course, give a definitive timeline for Iran. But it’s useful nonetheless to give a sense of how difficult a development process this is, and to show that such a missile is almost certainly at least a couple decades away. As noted above, it is likely to be able to develop a liquid-fuel ICBM well before that.
By the way, the longest range solid missile that North Korea has is much shorter range, estimated to be about 100 km with a 500 kg warhead. Called the KN-02, it is a version of the Soviet Toska missile, or SS-21.
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