Saturday, December 18, 2010

North Korea Technical Assessment of the Unha-2 Satellite Launch Attempt

The North Korean launch on April 4/5, 2009 of a large three stage rocket, weighing about 90 tons, has provided a flood of data on both North Korean and Iranian ballistic missile programs. This data includes detailed photographs of the North Korean rocket, information on the splashdown points for the first and second stages of the rocket, satellite images of the rocket contrail that indicates the early trajectory of the rocket, verification of a wealth of earlier information derived from other analyses on the use of rocket components by Iran from its launch of the Omid satellite on February 2, 2009, and information that further supports analytical findings associated with North Korea's attempt to launch a satellite using the Taepodong 1 rocket in 1998. All the information described above is completely self-consistent and can be explained and reproduced in an internally consistent technical analysis of all these events. This powerful self consistency in the data and analysis very strongly suggests that the estimates provided in this preliminary analysis are likely to be reliable.

We find that the North Korean Unha-2 represents a very significant advance in rocket technology by North Korea. The first two stages of this vehicle functioned in the flight test. The third stage, which apparently failed to operate in the North Korean flight tests, has most probably already successfully been flown as the second stage of Iran's Safir SLV. The successful operation of the first stage indicates that North Korea has the enabling technology to build rockets that can deliver much higher payloads to much longer ranges. The successful functioning of the second stage demonstrates that North Korea has found a way to obtain a
high-performance second stage by adapting an available rocket, the SS-N-6 Submarine Launched Ballistic Missile, for the second stage of the Unha-2 By using the SS-N-6 as the second stage of the Unha-2, North Korea has, in effect, obtained a second rocket stage that has an airframe that is constructed from light
high-strength aluminum alloy combined with high performance rocket motors.

Unha-2 Rocket Motor Engine
The Unha-2 with a carefully drawn overlay showing the detailed geometric features of the vehicle. In order to
facilitate an inspection of the accuracy of the outline by the reader, the right side of is the photograph of the Unha-2 with the overlay and the left side, based on the Unha-2 shape-outline derived from the photograph and guesses about the various components associated with the Unha-2 vehicle.

The first stage is assessed to carry about 68,000 to 69,000 kg of propellant and to have a total weight of about 74,000 to 75,000 kg. The estimate of the weight of propellant is based on the assumption that the fuel tanks have end-caps that have the same ratio of height to width as those used in the SCUD-B ballistic
missile. The fuel used by the first stage is assumed to be TG-185 and AK-27. This fuel combination is used in the SCUD-B, SCUD-C, SCUD-D, and the Nodong missile. The first stage is assumed to use a cluster of four Nodong rocket motors each of which generate about 30 tons of thrust. Estimates from the video of the
Unha-2 launch indicate an acceleration rate at launch of roughly 0.3 Gs.

The rocket motors therefore have a thrust of roughly 1.3 times the launch gross weigh of the vehicle. If the launch gross weight of the vehicle is about 90 tons, then the thrust of the rocket motors in the first stage is roughly 120 tons. When the silhouette of the SS-N-6 is placed over the second stage of the Unha-2 there is perfect geometric agreement. The upper frustum on the SS-N-6 has exactly the same dimensions and taper angle as that of the interstage between the second and third stages on the Unha-2. The rear end of the
SS-N-6 extends slightly into the interstage between the first and second stages.


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