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Why did North Korea's carrier vehicle fail to put the satellite into orbit on Sunday? An accurate assessment is difficult in the absence of detailed information, but based on information that has been announced so far, experts believe there must have been a critical defect in the three-stage rocket.
The first stage of the rocket is said to have dropped around 500 km away from the Musudan-ri launch pad, while the second and third stages dropped around 3,200 km away. Park Jeong-joo, a researcher at the Korea Aerospace Research Institute, said the decisive cause was the failure of either the second and third stages to separate, or the failure of the third stage to ignite properly.
Once the third stage is expended, the rocket reaches a speed of 8 km/s that is capable of putting a satellite into orbit. If only the second stage is expended, the rocket reaches a speed between 2 km to 3 km a second slower than what is needed.
Park said the bolt that connects the third stage once the second stage is expended should ignite and be blown apart, but if that fails, the second and third stages end up crashing down together. A failed ignition of the third stage could also cause it to drop in the same location as the second stage, even if they were separated.
One expert said unlike the first and second stages, the third uses solid fuel, and that it is no easy task to ignite it at an altitude of more than 100 km, where the temperature is very low.
But one academic who specializes in space technology said the separation of the second and third stages would not be a big problem if the purpose of the launch was to test a ballistic missile, rather than putting a satellite into orbit. There are two-stage ballistic missiles that deliver nuclear and other types of warheads to specific targets. Experts say the technology involving the separation of the second and third stages is essential for satellites but not crucial when it comes to ballistic missiles.
(englishnews@chosun.com )
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