Langley Experts Lending a Hand on Ares Vibration Problem
HAMPTON, Va. — NASA’s Constellation program office has asked engineers at Langley Research Center here to develop hardware intended to protect astronauts from potentially dangerous levels of vibrations that could reach the Orion Crew Exploration Vehicle during its climb to orbit atop the Ares 1 rocket.
Although the Constellation program has its own ideas for preventing potentially dangerous vibrations originating in Ares 1’s main stage from reaching Orion in the first place, for the past year NASA’s Engineering and Safety Center (NESC) at Langley has been working — at a fairly low level — on alternate solutions to the so-called thrust oscillation problem, according to NESC Director Ralph Roe.
More recently, however, the Orion project office at NASA’s Johnson Space Center in Houston asked Roe’s team to mature a particular hardware design — one aimed at absorbing vibrations that reach the Orion cockpit — in time for Constellation’s preliminary design review next spring.
“We’ve been asked recently by the Constellation program office to look at ways of isolating the [Orion] crew seat pallet,” said Roe, whose office performs independent testing, analysis and assessments of NASA’s high-risk projects to ensure safety and mission success. “We had done some work on it earlier for them when they were first looking at thrust oscillation, so recently this summer they asked us to continue on with that, and actually do a design for isolation.”
Thrust oscillation is common to solid-rocket motors, the metal casings of which tend to resonate like organ pipes as their propellant burns from the inside out. Rocket designers commonly stiffen joints or make the vehicle heavier to prevent these up-and-down vibrations — or oscillations — from growing stronger as they travel up the length of the rocket.
For the past two years, NASA engineers have been looking at options for “de-tuning” Ares 1 to prevent oscillations originating in its solid-rocket main stage from synching up with the natural resonance of the rest of the vehicle, potentially exposing astronauts to unsafe levels of shaking by the time the vibrations reach the Orion capsule. NASA engineers expect Ares 1 to deliver a relatively smooth ride until about 115 seconds into the flight when the first stage nears burnout and produces a thrust-oscillation problem that could impair the Orion crew’s ability to read displays and perform other duties.
Although Orion passed its preliminary design review Aug. 31, the NESC tasking comes at a time of uncertainty for the crew capsule and its Ares 1 launcher, which were scrutinized by a White House-appointed panel tasked in May with determining a range of options for NASA’s manned spaceflight program. The panel’s preliminary findings, briefed to senior White House and NASA officials Aug. 14, indicate that Orion and Ares 1 are unlikely to be ready to ferry astronauts to the international space station before 2017, two years beyond NASA’s long-promised March 2015 target.
Although Ares 1 passed its own preliminary design review in September 2008, engineers at Marshall Space Flight Center in Huntsville, Ala., said at the time that they had not yet settled on a hardware fix for the thrust-oscillation problem. Options still under consideration include installing dual-plane C-spring isolators between the rocket’s upper stages and using active reaction mass absorbers designed to muffle vibrations that might otherwise travel up the rocket. Work also continues on a so-called LOX damper, which uses the mass of the Ares 1 upper-stage liquid-oxygen propellant to dampen out vibrations, according to Marshall spokeswoman Jennifer Morcone.
Roe said the NESC vibration isolation design for Orion is an alternate solution to the Constellation program’s own candidate fixes.
“The program has a set of design solutions for thrust oscillation that does not require or include crew palette isolation,” he said. “We are simply providing some alternatives for them.”
Morcone said the Ares 1 program at Marshall is expected to decide in the coming months how best to integrate a dual-plane C-spring solution into the Ares 1 design.
“There is a session coming up soon where they’ll make a more formal down-select,” she said, adding that a formal decision on hardware solutions will be part of an upcoming Constellation preliminary design review that examines Ares 1 and Orion and an integrated vehicle. The Ares 1 team also expects to glean data relevant to the thrust-oscillation issue during the upcoming five-segment development motor test slated for Sept. 10 in Utah and the Oct. 31 test flight of Ares 1-X, a full-scale prototype of Ares 1 with a four-segment booster and dummy upper stage.
NESC expects to complete development work on the new vibration isolator system by spring, NASA’s current target for holding the Constellation preliminary design review.
Roe said the NESC vibration isolator concept is “fairly straight forward,” involving springs and other mechanisms placed between the crew seats and the floor of the capsule to attenuate vibrations.
NESC has also been developing ideas for protecting Orion’s crew in the event the capsule is forced to land on solid ground instead of splashing down in the ocean.
In June, the team successfully conducted a land-based landing test and has plans for further trials in January, Langley spokeswoman Amy Johnson said.
“We have a half-scale model of the Orion crew vehicle, and so we’re lifting it up [7.6 meters], swinging it and having it land on sand,” she said. “Basically, the test is used to predict what will happen to the capsule when it impacts land.”
Testing of NESC’s vibration isolation system will follow at a time and place not yet determined, she said.