Details emerging from U. S. and South Korean intelligence about the loss of the North Korean Unha-3 rocket paint a picture of a more complex failure than the initial snippets of information available just after the April 13 accident.
The new data indicates that a brilliant flaming explosion occurred toward the front of the vehicle blowing off the satellite and Iranian 3rd stage, but that the rest of the rocket kept going, propelled by its four-engine 1st stage that functioned as intended.
Liftoff of the 100 ft. Unha-3 on 270,000 lb. thrust occurred at 7:39 a.m. local time from the new Sohae Test Center at Tongchang-ri on the northwest coast of North Korea. As planned the vehicle headed south supposedly carrying a 220 lb. Earth imaging and propaganda broadcast satellite toward polar orbit.
Initial details pointed to a failure of the first stage midway through its planned 120 sec. firing. But the opposite was the case.
Analysts now believe the structural failure of the Unha-3 began at the front of the rocket and severed the nosecone covering the payload, the satellite itself and the Iranian developed third stage.
The first stage continued to push along what had become wreckage at the front of the rocket for another 40 sec. until its normal burnout and separation from the second stage.
The second stage however failed to fire and it along with the first stage fell at the northern edge of the planned normal first stage impact zone.
The waters about 120 mi. off the South Korean coast west of the port of Kunsan, where the debris fell is shallow enough for scuba divers, but the wreckage has to be found before it can be recovered.
South Korea’s navy has deployed about 10 ships with sonar and a corvette with side scanning radar to search for rocket debris, a Defense Ministry official said April 14.
US Navy minesweepers that can detect metal and other U. S. Navy ships are also involved in the search.
U. S. Aegis destroyers in the Yellow Sea to track the launch were likely early on the scene and also likely to still be in the area to prevent North Korean vessels from interfering with ships involved in the debris search.
Although intelligence sources and methods are classified, specific intelligence assets monitoring the launch were key to initial findings.
Among those assets were one or more U. S. Air Force / Boeing RC-135 Cobra Ball aircraft equipped with powerful imaging systems mounted on the right sides of their fuselage, along with powerful radars and electronic eavesdropping equipment. These aircraft were flying close to the North Korean border and over the Yellow Sea to obtain data and imagery of the North Korean flight.
In addition three or more Defense Support Program (DSP) Missile Warning Spacecraft with powerful infrared telescopes were also watching the launch from geosynchronous orbit (GEO). The first new GEO based Space Based Infrared spacecraft could also have been watching depending upon the spacecraft’s position. The same goes for the two new Space Tracking and Surveillance Spacecraft in lower orbit.
These aircraft and spacecraft are all sensitive to the brilliant light produced during a missile or launch vehicle liftoff and subsequent propulsion events.
At 81 sec. they saw a brilliant flash from the Huha-3 at a time when there should not have been any event. But after that, the first stage kept firing as intended.
Analysts believe that flash occurred during or shortly after the Unha-3 reached the point in the flight of maximum dynamic pressure, Max-Q, when the vehicle goes supersonic putting the greatest aerodynamic and structural stress on the vehicle.
For example the flight profile of a similarly sized U. S. Delta II rocket generates 1,300 pounds per sq. ft. (psf) of dynamic pressure at Max-Q, essentially an extra half ton that suddenly comes to sit on the rocket until the launcher pushes through it—or is destroyed by it.
While the lower stages of the North Korean rocket continued to function, resonance at the top of the launch vehicle resulted in “catastrophic disassembly of the third stage at Max Q,” Charles Vick, senior technical and space policy analyst at GlobalSecurity.org told the website EE Times. “The vibrations just tore it apart.” said Vick.
Vick told the website that given the severe vibrations and the early failure of the third stage, he was surprised that the other two stages held together as long as they did. He estimated the Unha-3 might have reached a velocity of about Mach 4, well below the speed needed to achieve orbit”.
Other than the flash at 81 sec. when the satellite and third stage were likely destroyed, the next major event in the failure scenario occurred at separation of the first and second stages 40 sec. later about 120 sec. into the flight.
This was the normal separation time.
The first stage had fired properly to place it on a trajectory toward its planned impact area. But the second stage failed to ignite, possibly due to damage associated with that flash including the possibility that the computer to control the second and third stages may have been mounted in the third stage.
As first reported April 9 by AmericaSpace, the mobile service tower for the Unha-3 was built to handle a much larger rocket.
Nick Hansen a highly experienced photo interpreter with intelligence agency experience, writes in the Foreign Affairs and 38 North websites that images of the launch site indicate the pad facilities are designed to handle a big new rocket up to 130 ft. tall with a diameter a diameter up to 13 ft.
“To carry this analysis one step further, a rocket of this size would be able to comfortably mount [nine first stage engines] used by the Nodong medium-range missile—more than twice as many as the Unha-3 first stage,” says Hansen.
“The second stage looks to be 8 ft. in diameter, similar to the Unha first stage, and could thus mount four engines,” he said.
The two stages alone would give the next-generation North Korean rocket nearly 900,000 lb of thrust, much more than the current generation of North Korean rockets and more than enough to power a highly capable ICBM or space-launch vehicle. The Unha-3 rocket that failed had less than 300,000 lb. thrust.
North Korea, has stated that it plans to launch astronauts into space with a large new launch vehicle, as does its rocket development partner Iran. It has even featured North Korean astronaut look-alikes in Pyongyang parades (picture below)
With nearly 900,000 lb thrust this big new launch vehicle could launch a Project Mercury or Gemini type manned spacecraft into polar orbit. In comparison the Atlas D that launched Project Mercury astronauts had 426,000 lb. of liftoff thrust while the Titan II boosters that launched Gemini missions had 430,000 lb. thrust.