MOSCOW, May 24 (RIA Novosti) - A failure of a pyrobolt separating spacecraft's modules caused the ballistic landing of Russia's Soyuz TMA-11 capsule in April this year, the head of the Federal Space Agency (Roscosmos) said on Saturday.

On April 19, the Soyuz-TMA-11 capsule, carrying U.S. astronaut Peggy Whitson, Russian flight engineer Yuri Malenchenko, and Korean bioengineer Yi So-yeon from the International Space Station, made a bumpy re-entry, landing 420 km (260 miles) off-target in the steppes of northern Kazakhstan.

"The main cause has been established," Anatoly Perminov said. "One of the five separating pyrobolts failed and the separation [of the landing capsule from the equipment bay] occurred later, when the landing capsule entered the plasma."

The spacecraft should have landed to the north of the town of Artalyk, but it came down near the Kazakh-Russian border, to the southeast of the Russian town of Orsk, due to a "ballistic re-entry."

During ballistic re-entry, the capsule follows a much steeper descent trajectory, and the crew is subjected to much higher G-forces than normally experienced.

In October 2007, a Soyuz capsule carrying Malaysia's first astronaut also landed off course and in 2003, the crew had to wait for several hours until rescuers located them.