According to the enclosed article, compliments of Aerospace Daily & Defense Report, a Tiger team charged with looking into the vibration issues of Ares I have concluded that damping out the vibrations will take many forms and be pretty easy to implement with zero effect on the Ares I’s projected roll-out date.
What this means to those who charged that NASA has (again) messed and and gone with the wrong booster in the Ares I when it should have instead gone with the Atlas V were…well, at best wrong. Most will see the Ares I vibration issue as a non-issue now. Balloon deflated–time to move on to real issues now.
Here’s the article:
Aerospace Daily & Defense Report
Ares I Vibration Problem Fixable
Frank Morring, Jr.
Mar 31, 2008
Crew performance is the limiting factor in a worrisome thrust oscillation linkage between the solid-fueled first stage of NASA’s planned Ares I launch vehicle and its upper stages, according to the former shuttle commander who conceived of using a single space shuttle solid-rocket boost to launch humans toward the moon.
Scott (Doc) Horowitz, a four-time shuttle veteran who later headed NASA’s Exploration Systems Mission Directorate as Ares I development was getting under way, said March 28 that the tiger team assembled to address the problem has found it tractable in a way that shouldn’t impede the Ares I preliminary design review coming up this summer.
Early estimates of the scope of the problem were overly conservative, Horowitz said. Instead of threatening the health of the crew and damage to some vehicle hardware, the actual vibration levels generated as the solid-fuel first stage burns out can be handled with relatively straightforward mechanical fixes.
“You can mitigate this throughout the whole vehicle,” Horowitz said. “You can do it on the top of the first stage. You can do it on the interstage. You can do it by the orientation of the tanks. When you get up to the [Orion crew exploration vehicle] CEV and the service module, then you can put shock absorbers in the seats.”
Horowitz, now an independent aerospace consultant whose clients include ATK, the Ares I first-stage contractor, and a “greybeard” advisor to NASA through the NASA Engineering and Safety Center, served on the tiger team that reviewed the thrust oscillation issue after it arose last fall. Garry M. Lyles, the senior NASA engineer who headed that review panel, is scheduled to brief Congress on his findings the week of March 31.
Although initial “conservative” statistical estimates of the vibrations an Ares I crew would experience fell in the 5-g range, Horowitz said his “best guess” is that it will actually be in the 0.25-g range. While the former level would kill an astronaut if it went on long enough, the latter becomes a performance issue.
About half of the shuttle astronauts report that vibrations from the twin solid-rocket boosters make it difficult for them to see displays during ascent, Horowitz said, and that will probably be the ultimate effect of the thrust oscillation in the Orion from the Ares I.
“You’re probably not going to want to shake the crew more than about a quarter of a g, and people are trying to go get a more detailed number on that, if you want them to be able to operate,” he said.
Mitigation techniques could include changing the mass and stiffness of the stack to “detune” it a few Hertz to cut vibrations, and adding material to absorb the vibration in a fashion like the rubber engine mounts on automobiles. Ultimately it will be a tradeoff between the benefit of a modification in the basic design and the weight penalty paid, Horowitz said.