Orbital Sciences stock tumbled 13% in premarket trade Wednesday, after one of its rockets carrying supplies for the international space station exploded soon after taking off late Thursday. Prior to the rocket's launch, the stock closed Tuesday at a four-month high. "We will conduct a thorough investigation immediately to determine the cause of this failure and what steps can be taken to avoid a repeat of this incident," said Frank Culbertson, general manager of Orbital's advanced programs group. Analysts at RBC Capital said that while it's not clear what caused the explosion, "a likely suspect" is the AJ-26 main engine, which are decades-old NK-33 Russian rocket engines that have been refurbished by Aerojet-Rocketdyne, a division of GenCorp, as an option to power the Antares. RBC said one of the AJ-26 engines in fact exploded in May of this year during testing. GenCorp's stock was still inactive early Wednesday. GenCorp was not immediately available for comment before normal hours. The stocks of other aerospace companies, such as Astrotech , Boeing and Northrop Grumman weren't active ahead of Wednesday's open.
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