Pyongyang’s statements regarding an intended orbit of 6978 km apogee and 219 km perigee are highly improbable for several reasons. Such a low perigee yields a very short satellite lifetime and is extremely sensitive to injection angle errors. Due to the high eccentric orbit’s period of 2.75 hours, a number of orbits is required for a pass close to North Korea for contact with the satellite. The eastward launch is an indication for the vehicle’s low performance. One has to conclude that the SLV’s intended orbit was in fact a low circular orbit with an altitude of approximately 220 to 250 km. Thus, North Korean orbit announcements four days after the launch were intended to camouflage the real vehicle’s capability.

It is generally accepted that this vehicle resembles the basic Taepodong-1 missile with a solid third stage instead of a re-entry vehicle.

The first stage is based on a Nodong-type first stage. However, compared to the basic Nodong missile, a shorter burn time than the standard Nodong was observed in the August 1998 flight. This indicated an increased thrust level since a reduced propellant load must be completely excluded. Similar observations regarding the second stage were made: though this stage is generally thought to comprise a Scud-type system, a significant derivation from the standard burn occurred. Specifically, two thrust levels were noticed with an initial high thrust phase followed by a long low thrust phase. Thus, the second stage was either a significantly modified Scud—for example, through the addition of four vernier engines (possibly with a separate turbo pump) parallel to the main engine—or a different stage was used altogether, possibly a modified SA-5. However, recent North Korean information indicates that the one plus four engine arrangement is more likely. The third stage is an unguided, spinning solid rocket.

The first stage propulsion system is a liquid rocket engine probably using the storable propellant combination inhibited red fuming nitric acrid (IRFNA) and kerosene. Ignition is accomplished by a hypergolic (self-igniting) start fuel designated Tonka—the WW II German designator for this propellant—filled into the fuel line at the main fuel valve. The propellant feed system is a turbo pump driven by a bipropellant gas generator using the main propellants. The start and shut down valves are one shot devices, actuated by pyrotechnic charges. Tank pressurization is performed by air stored in a toroidal high-pressure bottle in front of the missile’s guidance section and heated by the turbine exhaust gases.

The second stage is basically of a similar design. The North Korean pre-launch photos seem to show an external propellant line design, similar to that of Scud-A/R-11 or SA-5. Further specific statements are difficult to make. 

Reconstruction of the launch vehicle’s trajectory data indicates that the third stage is a Soviet Tochka/SS-21 rocket motor.

It is estimated that the guidance system basically resembles that of the Nodong arrangement with body-mounted free gyros, however, with the modification of an additional gyro for accuracy improvement. Prior to launch, the missile is orientated such that the trajectory plane hits the target and the guidance systems keeps the missile in this plane. Two of the three body mounted gyros are used for attitude and the third one lateral acceleration control; the horizon gyro’s mounting must be able to move to a horizontal position. A pendulum integration gyro assembly serves for speed measurement. The fins are fixed and thrust vector control is accomplished by four jet vanes in the first stage; for the second stage, either four vernier engines are used or thrust vector control is accomplished similar to the first stage by jet vanes. The third stage is spin stabilized prior to motor ignition.

The third stage failure may be attributed to the cartridge propellant grain design of the Tochka motor. While in the ballistic missile mode the final acceleration is 10 g, in the SLV application, the final acceleration reaches nearly 50 g, possibly resulting in a cartridge collapse with blocking and subsequent nozzle ejection. Motor rotation and its effect on internal ballistic may also be contributing factors to the failure.

This SLV launch must be seen as an indication that no suitable re-entry vehicle for the long-range missile mode is available at present.

There appear to be a number of indications that point to an original Soviet missile of the late 1950s for the basic long-range design; the status and designator of the system are unknown. The SLV adaptation of the system requires an excellent knowledge of the vehicle.

	Updated May 2003