21:00 04 April 2008Launchers and Boosters
<P>NASA has identified possible solutions to a potential vibration risk to the crew on the <A href="http://www.nasa.gov/mission_pages/constellation/ares/aresI.html" target=_blank>Ares I launch vehicle</A>. But the US space agency does not believe the problem is as serious as it first thought.</P> <P>The issue is a potential coupling between thrust oscillations in the solid rocket motor (SRM) first stage and vibration modes in the launch vehicle. Identified in October 2007, the problem is the top risk in the Ares I programme, says Rick Gilbrech, associate administrator, exploration systems.</P> <P>The frequency of pressure pulses in the five-segment SRM is close to the natural frequency of the second longitudinal vibration mode of the complete launch vehicle. This creates the risk of a "pogo stick" resonant vibration, says Garry Lyles, associate director for technical management, <A href="http://www.nasa.gov/centers/marshall/home/index.html" target=_blank>Marshall&nbs