Engineers finished testing a small solid rocket motor that will help to separate the second stage of the next-generation Ares I rocket from the first stage, NASA announced.

That small rocket also will help ensure that fuel in the second stage settles usefully to the bottom of the upper stage fuel tank.

Those tests were conducted at Marshall Space Flight Center in Huntsville, Ala.

Ares I and its Orion crew capsule will launch astronauts into low Earth orbit beginning with an initial manned flight in 2015, replacing the space shuttle fleet that will be grounded by October 2010, unless NASA is ordered to continue flying shuttles until the first Orion manned flight.

That test of the small solid rocket motor for the Ares I system comes as the Ares I program has passed preliminary design review, a major step. (Please see Space & Missile Defense Report, Thursday, Sept. 11, 2008.)

The ullage settling motor is a small, solid rocket motor. During first stage separation, which occurs 125.8 seconds into flight, the motor will fire for four seconds, producing the forward thrust needed to push the second, or upper, stage away from the first stage. This forward thrust also ensures the that liquid fuel is properly pushed to the bottom of the upper stage fuel tank prior to ignition of the J-2X engine that powers the upper stage.

The successful hot-fire test of this new development motor — the first test in this series – ended with all test objectives achieved.

This first series of early development testing will consist of four motors. It is scheduled to run through next year. The second test series is planned for February.

"We are extremely excited about the success of this test that proves we are headed down the correct development path for this program," said Danny Davis, upper stage manager for Ares Projects at Marshall.

The word "ullage" is taken from the French term "ouillage," which is used in winemaking to describe the space between wine and the top of a storage container, such as a barrel or bottle. In this case, it refers to the space at the top of the first stage fuel tank and the need to push the fuel, or settle it, to the bottom of the tank.

The ullage motor, 9 inches in diameter and 47 inches long, is similar in design to the booster separation motor used on the space shuttle reusable solid rocket motor.

Eight ullage motors will be arranged in four pairs on the Ares I upper stage aft skirt, which also houses the reaction control system. The aft skirt is located between the upper stage core, which contains the liquid hydrogen and oxygen fuel tanks, and the interstage, which houses the rocket’s roll control system.

The first Ares I test flight, called Ares I-X, is scheduled for next year.

Johnson Space Center in Houston manages the Constellation Program, which includes the Ares I rocket, the Ares V heavy-lift launch vehicle, the Orion crew capsule and the Altair lunar lander.

Marshall manages the Ares projects.