NASA
engineers have come up with a dual shock absorber solution to the problem of
excessive vibrations with the new Ares I rocket that will launch the agency's
Orion space shuttle replacement.
Two
different systems at the top and bottom of the new
rocket's first stage should reduce the booster's peak vibrations during
flight to what engineers described as a few-seconds-long "jackhammer effect."
The
recommended shock absorber system includes a spring and damper system between
the Ares I booster's first and second stages, as well as a set of 16
spring-mounted weights in the aft skirt at the bottom of the first stage.
"It's a lot
like the shock absorbers on your car," said Steve Cook, Ares project manager at
NASA's Marshall Space Flight Center in Huntsville, Ala., in a Tuesday
teleconference. "It isolates the vibrations just traveling through the
structure, all the way up to the seat."
Without the
upgrade, an Ares I rocket and its astronaut crew would be subjected
to shaking forces of up to five or six times Earth's gravity (5 to 6 Gs),
or about twice the force experienced by shuttle astronauts during launch,
according to NASA's early analysis. But with the shock absorbers in place,
vibrations in the Ares 1 rocket should be limited to about 0.25 Gs, or
one-fourth the force of Earth's gravity, NASA engineers said.
The peak
shaking should last just a few seconds near the 115-second mark just after
liftoff, said Cook, who sat in a chair-based simulation of the vibration in a
NASA test. He compared it to driving a car on the bumpy shoulder of a highway.
"It really
doesn't physically bother you," Cook said. "It's just kind of a high
vibration."
A shaky
hurdle
The
vibration issue, one of the top engineering hurdles for NASA's
Ares I rocket, stemmed from a thrust oscillation in the launch vehicle's
solid rocket booster-derived first stage. Thrust oscillation is a common
phenomenon in solid propellant rockets, which burn from the inside out allowing
gases to swirl in the interior until they resonate the entire structure like an
organ pipe.
The main
concern centered on astronaut performance during an Ares I launch, said Garry
Lyles, NASA's associate director for technical management at the Marshall Space
Flight Center in Huntsville, Ala. The higher vibrations were not a crew health
concern, but could prevent astronauts from reading instrument panels or
flipping switches precisely due to blurry vision.
"What we
want to make sure of is that we don't get into a situation that would leave
aftereffects with the crew," Lyles added. "We want them to feel good after
[spacecraft] separation."
The planned
shock absorbing system's passive spring and damper component is designed to sit
at the top of the first stage and reduce vibrations from thrust oscillations
from a peak 6 Gs to about 1 G. The addition of 16 tuned mass absorbers,
cylindrical shock absorbers that use motors to sense vibrations and nullify
them using spring-mounted weights, would further limit the shaking to about
0.25 Gs, engineers said.
Altogether,
the added equipment would reduce the lift capacity of the Ares I rocket's first
stage by up to 1,400 pounds (625 kg), though the booster segment currently has
a margin of about 8,000 pounds (3,628 kg) to work with, Cook said.
The first
stage of NASA's Ares I rocket will use a five-segment solid rocket booster, one
segment longer that the twin four-segment versions used on U.S. space shuttles
today. The second stage relies on liquid propellant to boost the
Orion capsule into orbit.
Engineers
will attach sensors to the solid rocket boosters and astronaut seats on
upcoming shuttle missions to better understand the amount of vibration
spaceflyers are currently subjected to on the way up into space, Lyles said.
Meanwhile,
Ares I rocket engineers will turn their attention to other details with the
project.
"There's
nothing on our risk list that is what I would call a showstopper or a major
issue that we can't deal with," Cook said.
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