posted 10-24-2012 05:44 PM               

The space junk incident, which occurred Oct. 16, involved the Breeze-M upper stage of a Russian Proton rocket that had failed in a mission to launch two satellites. Excess fuel remaining on board the upper stage may have caused it to explode, experts say, though the official cause remains unknown.

"The resulting debris field and impact to space objects on orbit are being assessed at this time; however, JFCC-Space is currently tracking over 500 pieces of debris," Lt. Col. Monica Matoush, a Department of Defense spokeswoman, told SPACE.com via email. "We expect that number to fluctuate as work to characterize the debris field continues."

But the stage failed at the start of its third of four engine burns, leaving the Breeze M with still more than half of its hydrazine and nitrogen tetroxide propellants.

The breakup was mentioned in the daily International Space Station status report posted Tuesday on NASA's website.

As reported by the IMMT (ISS Mission Management Team), a rocket booster’s 2nd stage that had been on orbit for several months fragmented into numerous pieces last week. Data collected to date show that there is a debris cloud on orbit, believed not to be insignificant. It is being tracked and monitored carefully for any potential impacts to ISS or Soyuz.