New Ares Moon rocket likes to shake, rattle, and roll

William Atkins
Saturday, 19 January 2008 13:50

Science - Space

NASA designers are working on a way to calm down an early design flaw in the yet-to-be-built Ares I launch vehicle that will help send U.S. astronauts to the Moon beginning in 2015 and later to Mars and other space destinations.       

Computer simulations and mockup testing of the engines indicate the first stage of the Ares I shakes so much during the first few minutes of flight that it could possibly destroy itself, its upper stage, and the crewmembers inside the Orion space capsule, which sits on top of the rocket.

The Houston Chronicle reports in its article "Severe vibration problem plagues moon rocket design" that NASA officials stated, "These longitudinal forces may increase the loads experienced by the Ares I during flight, and may exceed allowable loads on various portions of the vehicle and allowable forces on the astronaut crew.”

Ares I is the manned version of the Ares project. Ares I’s first stage consists of a single five-segment reusable solid rocket booster (SRB), much like the twin four-segment SRBs that are used on the space shuttle program. A SRB burns a specially formulated and shaped solid propellant. The SRBs are built by ATK Launch Systems (Brigham City, Utah).

Ares V is the heavy-lift version that will be unmanned, built to ferry heavy cargo, supplies, and spacecraft back and forth between space and Earth. It uses two five-segment SRBs for its first stage.
The problem now occuring with the Ares I is that gas vortices inside of the SRB add pulses of acceleration to the vehicle. And, these vortices happen to equal the natural vibrational frequencies of the motor’s combustion chamber—when present the two frequencies are added together, causing excessive shaking of the SRB and, consequently, of the entire vehicle.  

Engineers studying the problem compare it to the wake that results when a speed boat is traveling through the water here on Earth.