John Yembrick
Headquarters, Washington
202-358-0602
June Malone
Marshall Space Flight Center, Huntsville, Ala.
256-544-0034
RELEASE: 07-130
NASA SHUTTLE ENGINE UPGRADES IMPROVE SAFETY AND RELIABILITY
HUNTSVILLE, Ala. - A main engine computer upgrade developed by NASA's
Marshall Space Flight Center in Huntsville, Ala., will fly on space
shuttle Atlantis during the STS-117 mission, targeted for launch June
8. The upgrade is part of NASA's continuing efforts to improve space
shuttle safety and reliability.
The Advanced Health Management System, or AHMS, will provide new
monitoring and insight into the performance of the two most critical
components of the space shuttle main engine: the high-pressure fuel
turbopump and the high-pressure oxidizer turbopump.
This latest improvement is to the controller, the on-engine computer
that monitors and controls all main engine operations. The
improvement allows an engine to shut down during launch if vibration
levels exceed safe limits. AHMS consists of advanced digital signal
processors, radiation-hardened memory and new software.
AHMS first flew on Discovery's STS-116 mission in December 2006 with a
single controller on one engine, but in monitor-only mode, meaning
AHMS collected and processed vibration data but could not shut down
the engine. AHMS will operate in active mode - the ability to shut
down an engine if an anomaly is detected - on a single engine during
the upcoming STS-117 mission and is scheduled to fly in active mode
on all three engines during the STS-118 mission later this year.
In the event of an engine shut down, the shuttle has several options
available to abort the ascent. They include returning to the launch
site, a transatlantic abort landing, landing at an alternate site in
the United States or rendezvous with the International Space Station.
Each scenario would depend on when an engine shuts down during
flight, the mission trajectory and mission specific requirements,
such as payloads.
The system uses data from three existing sensors, or accelerometers,
mounted on each of the high pressure turbopumps. It measures how much
each pump is vibrating. High-pressure fuel and high-pressure oxidizer
turbopumps rotate at approximately 34,000 revolutions per minute and
23,000 revolutions per minute, respectively. To operate at such
extreme speeds, the turbopumps are equipped with highly specialized
bearings and precisely balanced components. Output data from the
accelerometers is routed to the new digital signal processors
installed in the main engine controller. These processors analyze the
sensor readings 20 times each second, looking for vibration anomalies
that are indicative of impending failure of rotating turbopump
components such as blades, impellers, inducers and bearings. If the
magnitude of any vibration anomaly exceeds safe limits, the upgraded
main engine controller would shut down the unhealthy engine
immediately.
"The Space Shuttle Main Engine Project has, for many years, pursued a
reliable means to monitor high-pressure turbomachinery health in real
time," said Tim Kelley, deputy manager of the Space Shuttle Main
Engine Project Office. "AHMS provides that capability and
significantly improves shuttle flight safety."
AHMS is the sixth major upgrade to space shuttle main engines since
the first shuttle flight in 1981. The series of shuttle main engine
enhancements have increased safety and reliability through such
improvements as the addition of a two-duct powerhead, a single-coil
heat exchanger, a new high-pressure oxidizer turbopump, a
large-throat main combustion chamber and a new high-pressure fuel
turbopump.
The shuttle's three main engines start approximately 6.5 seconds prior
to lift-off. Once running, the solid rocket boosters ignite, and
lift-off occurs. During ascent, the solid rocket boosters burn for
approximately 120 seconds and are then jettisoned. The shuttle, still
attached to the external tank with three main engines running,
continues ascent until main engine cut-off at 510 seconds, or eight
and one-half minutes after liftoff - long enough to burn more than
500,000 gallons of fuel. The engines shut down just before the
shuttle, traveling at about 17,000 mph, reaches orbit. The three main
engines are never restarted during the mission, re-entry or landing.
The shuttle returns to Earth as a glider.
Space shuttle main engines operate at greater temperature extremes
than any mechanical system in common use today. These powerful
engines are clustered at the aft end of the shuttle and have a
combined thrust of more than 1.2 million pounds. Each is 14 feet
long, is seven and one-half feet in diameter at the nozzle exit,
weighs approximately 7,750 pounds and generates more than 12 million
horsepower.
For information about the space shuttle program, visit:
-end-
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