Modifications Eliminate "Chugging" Oscillations
A technology development engine that may help NASA safely return
astronauts to the lunar surface has successfully completed its
third round of testing. The goal of these tests is to reduce risk
and advance technology for a reliable and robust rocket engine that
could enable America's next moon landing.
The tests by Pratt & Whitney Rocketdyne in West Palm Beach,
FL helped gather data on this concept engine that might play a role
in the next stage of human exploration of the moon. Most rockets
make spacecraft travel faster. The goal of a lunar lander descent
engine is to slow the vehicle so astronauts can land safely.
The Common Extensible Cryogenic Engine, or CECE, is a
deep-throttling engine, which means it has the flexibility to
reduce thrust from 100 percent down to 10 percent -- allowing a
spacecraft to gently land on the lunar surface. The 13,800-pound
thrust engine uses extremely cold liquid oxygen and liquid hydrogen
as propellants.
During the test, the engine was successfully throttled from a
high of a 104 percent of the engine's potential down to eight
percent, a record for an engine of this type. A cryogenic engine is
needed to provide high performance and put more payload on the
surface of the moon. The CECE demonstrator has evaluated two engine
configurations during three rounds of hot-fire testing.
"The first test series in 2006 was a challenge but showed
promise," said Tony Kim, Deep Throttling Engine project manager at
NASA's Marshall Space Flight Center, Huntsville, AL. "Testing in
2007 provided an in-depth examination of low-power-level throttling
and engine performance characteristics. This third cycle we
actively addressed and found solutions to the challenges we
faced."
The team assessed test results that showed pressure oscillations
in the engine at lower throttle levels called "chugging." Chugging
may not be a concern for the engine itself, but the resulting
vibrations could have the potential to resonate with the structure
of the rocket and cause problems for the lander or crew.
Injector and propellant feed system modifications successfully
eliminated engine chugging by controlling liquid hydrogen and
liquid oxygen flow to the combustion chamber. The latest engine
configuration incorporates a new injector design and propellant
feed system that carefully manages the pressure, temperature and
flow of propellants.
"The technology developed from this effort will help engineers
successfully design future cryogenic engines to meet the throttling
requirements of the Constellation Program's Altair lunar lander,"
Kim said.
The CECE is based on the existing Pratt & Whitney Rocketdyne
RL10 upper stage rocket engine. Previous first-hand flight
experience, as well as this data, will allow engineers to develop
simulation models that can focus testing for efficiency and
effectiveness.