NASA Conducts First Test On New Motor For The Ares I Rocket

http://www.spaceref.com/news/viewpr.html?pid=26407

Nasa completed the first successful test of the ullage settling motor this past week.  The ullage settling motor is a small solid rocket that does exactly what the name implies.  After 1st stage separation, the rest of the vehicle, including the fuel for the 2nd stage motors, is in free fall.  Before ignition of the 2nd stage motors, the ullage settling motor fires, giving a comparatively slight acceleration that forces the fuel in the tanks to settle at the bottom and creates a proper ullage space.  Pushing the fuel down before main ignition has a major benefit:  it prevents fuel vapor from being sucked into the rocket motor.  This can cause uneven combustion in the motor and cavitation damage to the turbopump impellers.  The first Ares I test flight, called Ares I-X, is scheduled for 2009.