NASA held a media telecon today to discuss ongoing thrust oscillation issues with the Ares 1 rocket. This results from the way in which the solid propellant burns while the first stage is in powered flight. As currently designed the Ares 1 first stage could impose unacceptable vibration loads on the rocket's prime payload - the Orion spacecraft and its human occupants.
One way to decrease the adverse impact of these loads is to reduce them by use of mechanical devices which are tuned so as to dampen the vibrations.
NASA is looking at options that would place dampers either in parachute region (between the Orion and the Ares 1 first stage) or in the aft skirt of the Ares 1 first stage. These dampers would be tuned to dampen out (de-tune) problematical vibrations produced by the burning of propellant.
While these dampeners themselves incur a mass penalty, NASA feels that other mass can be deleted from the existing Ares 1 structure so as to have a net increase on the order of a few hundred pounds.
Steps will also be taken with the Orion spacecraft. Evolving design changes focus more on stiffening the existing structure than adding or removing weight. NASA is also looking at putting shock absorbers on the crew couches.
One thing that must be dealt with are the G loads that the crew feels not only to assure their health but also their ability to perform the tasks need in order to accomplish their mission. The aim is to meet a newly evolving standard for accelerations as felt by the individual crew of between 0.14 - 0.3 G - this is close to the spec of 0.25 G that was in place during the Mercury and Gemini programs.
Right now all of this work is based on analysis and existing data. Noting has been built - or flown. Additional tests need to be done with Ares test launches and ongoing design review process. The PDR (Preliminary Design Review) for Ares 1 is due to be conducted at the end of summer 2008. As such NASA feels that a much better idea of what the situation is and how it can be dealt with will emerge by then.