NASA opts for second Green Run

The long-awaited Green Run test of the Space Launch System core was cut
short, but NASA will get another crack at testing the four RS-25 engines this

STENNIS SPACE CENTER, Miss. -- The loudest rocket engine test in South
Mississippi since the days of the Saturn rocket ended early Jan. 16 when a hydraulic
system for one of the four RS-25 engines hit an intentionally conservative limit during
the test.
What should have been an eight-minute test was instead just over a minute when the
hydraulic system for Engine 2 on the core stage “exceeded the pre-set test limits that
had been established” for the Green Run test, according to a NASA statement.
While NASA said it got valuable data from the short test, the question remained.
Would NASA opt to conduct another test or would it be satisfied with the data
collected in the aborted test and ship the core to Kennedy Space Center.
It didn’t take long for an answer. The decision was made before the end of January to
conduct a second test. NASA decided to schedule a second Green Run test of the
Space Launch System core stage the week of Feb. 21 on the B-2 test stand. The
specific date for the test will be set following the test readiness review, the agency
There was little doubt the test in January was a disappointment. The hope was to
gain all the data needed to ensure a launch from Kennedy Space Center later this
But the hydraulic problem during the Jan. 16 test dashed the hope of collecting the
data. But, in fact, the system worked the way it was intended - shutting down.
“As they were programmed to do, the flight computers automatically ended the test,”
said a statement from NASA after the aborted test.
That hydraulic system is part of a control system used to gimbal the engine to direct
its thrust, and is powered by a Core Stage Auxiliary Power Unit, or CAPU. One CAPU
shut down during a gimbaling test that was part of the static fire.
“This gimbaling test event that resulted in shutting down the CAPU was an
intentionally stressing case for the system that was intended to exercise the
capabilities of the system,” according to NASA. Had it happened in flight, the SLS
would have used other CAPUs to power the thrust vector control system.
In addition to the hydraulic system problem, there was also a major component failure
reported by test controllers about 45 seconds after ignition. NASA said the major
component failure occurred 1.5 seconds after ignition, and was caused by the loss of
one leg of redundancy in instrumentation for Engine 4.
But the test was set up to proceed with this condition because the engine control
system still has sufficient redundancy to ensure safe engine operation during the
test, NASA said.
NASA had previously said the parameters for the Green Run test would be
“intentionally conservative” to keep the core safe since it is flight hardware intended
for use on the first SLS launch, Artemis 1.
“This core stage is a high-value flight article that will return America to deep space,”
said John Shannon, vice president and SLS program manager at Boeing, in a
company statement about the Green Run test. “Our redline limits were set to achieve
data collection without unnecessarily risking the system.”
In comments before the first test, NASA and Boeing officials said that while the test
was scheduled to last for 485 seconds, they would collect most of the data they
needed after 250 seconds. However, the engine shutdown took place after just 67.2

If the test the week of Feb. 21 is successful, the core stage will be shipped by barge
to Florida’s Kennedy Space Center. It is highly likely the new test will delay the launch
scheduled for later this year.
Prior to the January test, NASA informed area residents that they should expect
elevated decibel levels at SSC during the test of the core stage.
The test of all four RS-25 engines produced a combined 1.6 million pounds of thrust.
The acoustic level produced is about 10-20 decibels higher than during a normal
single engine test at the site.
The actual acoustic level experienced by area residents depended on their location
relative to the test site and the prevailing weather conditions.
Because of COVID-19 protocols, there was no opportunity for the general public to
be on hand for the January test, but it was shown live on NASA television. A limited
number of journalists will be allowed for the February test, according to an advisory
sent out by NASA.

- Gulf Coast Reporters League
Feb. 9, 2021

Single engine tests begin again at SSC

NASA officials began a new round of tests for development of RS-25 engines that will
help power the Space Launch System (SLS) rocket on future missions to the Moon
and, eventually, Mars.
The first test of the new series was Jan. 28 on the A-1 Test Stand at Stennis Space
Center (SSC) in Southwest Mississippi. The engine was fired the full duration of
about eight-and-a-half minutes (500 seconds), the time the engines must fire to help
send SLS to orbit.
The engine was fired at 111 percent of its original space shuttle main engine design
power and the same power level needed to help launch SLS on its missions.
The seven-test series uses RS-25 developmental engine No. 0528, and will provide
data for engine-builder Aerojet Rocketdyne as it begins production of new RS-25
engines for use after the first four SLS flights, which use upgraded space shuttle
main engines and have completed certification testing. NASA now is focused on
providing data to enhance production of new RS-25 engines and components for use
on subsequent SLS missions.
The new engines and components will be manufactured with cutting-edge and cost-
saving technologies, including 3D print technology and hot isostatic pressure
The SSC test engine will be fired seven times for a total of 3,650 seconds during the
first half of 2021.

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