At 0920 GMT on 1 June, a stage that was used as an earlier alternative to the Breeze M on Proton launches has exploded in orbit. The Ullage tankage/motor from a Block DM-2 upper stage used by a Proton M launch of the Glonass navigation satellite Cosmos 2449 in December 2008 has fragmented into at least 20 pieces of tracked debris.
Ullage motors are used to accelerate a rocket stage prior to main engine ignition to settle the propellants at the feeder end of their tanks ready for use in microgravity conditions. These small engines use the hypergolic propellant combination nitrogen tetroxide and hydrazine which react on contact. It is thought that over time tank corrosion allows these explosive combinations to mix with explosive results.
