Data Confirm ATK Five Segment Solid Rocket Motor Is Ready For
Flight Testing
Data from the second successful
five segment Development Motor (DM-2) test conducted by ATK and
NASA show that the new motor performed precisely as designed,
providing substantially higher performance and reliability than the
heritage space shuttle solid rocket booster at a lower cost. "These
extensive test results confirm the ATK five segment Solid Rocket
Motor (SRM) is ready for flight testing," said Charlie Precourt,
vice president and general manager of Space Launch Systems, ATK
Aerospace Systems. "The five-segment first stage design was
based on more than 30 years of safety-driven improvements on the
shuttle program. The result is a higher performing, more reliable
solid rocket motor, which equates to increased safety for crew and
mission success for cargo."
The 30-day findings from the August 31 ground test were compared
to data collected from the first ground test (Sept. 2009) and the
Ares I-X flight test (Oct. 2009) to develop a greater understanding
of motor and material performance and first stage avionics. The
data were also compared to ground test, flight, and post-flight
data collected throughout the Space Shuttle Program.
Modifications to the motor include an added fifth segment,
changes to the propellant grain, a larger nozzle opening, and an
upgraded liner and insulation — all designed to meet
performance requirements and increase reliability while lowering
manufacturing costs.
"We were able to incorporate many design changes during the
five-segment development that we identified during the shuttle
program but were not able to make given the shuttle vehicle's
operations tempo," said Precourt. "We also incorporated materials
and streamlined processes that have been flight-proven in our
commercial programs."
Propellant grain changes included an additional fin to provide
the necessary thrust profile at liftoff and changes to propellant
angles at joints to increase structural safety factors. The
ballistics data from DM-2 were exactly in line with
predictions.
The new insulation and liner is made of
environmentally-friendly material that replaces the obsolete
asbestos-based insulation used on shuttle. Advantages include
improved thermal properties and lower density, offering 10 percent
or 2,000 pounds in weight savings, which allows for heavier
payloads. Process improvements developed with the new green
material have also yielded safety and schedule benefits. Results
from DM-2 showed the new liner provided higher thermal protection
than the shuttle motors. New low-temperature O-rings enabled the
elimination of joint heaters and the associated cabling and
infrastructure. This lowers joints complexity, thereby eliminating
additional failure modes, and saves 500 pounds in weight, while
providing a stronger seal than previous O-rings.
A main objective of DM-2 was to test the new O-rings at cold
temperatures. The motor was conditioned to approximately 40 degrees
F., and flaws were introduced into the joints that allowed hot
gases to potentially penetrate the insulation into the joint and
thermal protection system where the O-rings are housed. Even under
those conditions, the seal and thermal protection system on DM-2
performed as designed. "We are very pleased with the initial data
collected from DM-2," said Precourt. "It shows the performance of
the motor and components either met or exceeded our
predictions."
Thrust oscillation is another area where DM-2 results are
significantly better than initial models predicted. Through
combined DM-2, DM-1 and Ares I-X results, and with computational
fluid dynamics analyses, NASA and ATK engineers have learned the
behavior attributed to thrust oscillations in five-segment solid
rocket motors is 30 to 60 percent less than previously predicted.
Specifically, the DM-1 and DM-2 data indicate that this motor is
very quiet, producing very low pressure oscillations. Also
Ares I-X showed that in flight, the overall structure of that
configuration is less susceptible to excitation than previously
expected.