"Pat Flannery" wrote in message
...


Pat Flannery wrote:

Over at NASA Watch, the ESMD PAO has said they are reviewing Cowing's
questions and expect to get a reply to him within 48 hours.

Pat

And here's their reply: http://www.spaceref.com/news/viewnews.html?id=1266

From their reply, "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.
", followed later by, "Thrust oscillation forces may be reduced by vehicle
structures, as is the case with the space shuttle and Titan IV", and later
by, "The Orion and Ares teams are holding detailed discussions and
developing a plan to fully characterize Ares I thrust oscillation, assess
any design changes that may be proposed, and manage sensitive design
parameters with additional tests, trade studies and analyses".
So they're still trying to characterize the thrust oscillation and see how
it impacts the design. Unfortunately, experience from Titan IV and shuttle
isn't quite directly applicable since both of those use twin SRB's side
mounted to a central, liquid, core. Ares I is a distinct departure from
this design with only one SRB and one upper stage on top of the SRB.

And I absolutely love this little gem from near the end of the NASA
response, "Thrust oscillation is a new engineering challenge to the
developers of Ares". Maybe this is new to upper management, but I'm sure
that there are a few propulsion engineers at Thiokol and NASA who saw this
one coming. It's a problem that would have manifested itself with any
inline design using a shuttle derived SRB for the first stage.

Considering the weight issues associated with Ares I and Orion, there isn't
much in the way of excess mass which can be spared to throw at this problem.

It's starting to look like Ares I is a real pig of a design. Large
segmented SRB's ought not be used on any new launch vehicle. Their
drawbacks aren't worth their perceived advantages.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein