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NASA moves forward with crucial center stage firing test of the space launch system’s first heavy-lift rocket starting Jan. 17, after engineers were satisfied with the results of a refueling test last month.
The hot shot test is the culmination of the SLS Green Run, a year-long series of program flight-ready major first stage checks on the B-2 test stand at NASA’s Stennis Space Center in Mississippi.
The main stage will fly on the Artemis 1 mission, the first full test flight of the Orion space launch system and crew capsule. Artemis 1, which will fly to the moon and return without astronauts, is officially slated for launch in late 2021, but that timeline may be in doubt after the Green Run campaign delays in Stennis.
Future SLS / Orion missions will send astronauts to the Moon, where NASA intends to land humans and build a mini-space station in lunar orbit in the 2020s.
Teams from NASA and Boeing, who built the SLS main stage, loaded the 212-foot-high (64.6-meter) rocket with super-cold liquid hydrogen and liquid oxygen on December 20. . The refueling test, known as the wet dress rehearsal, was the first time that the SLS thruster tanks were filled with cryogenic fluids.
Engineers performed the basic step through a simulated countdown, simulating the pre-flight procedures he will see on the launch pad at Kennedy Space Center in Florida. But the rehearsal was halted at T-minus 4 minutes, 40 seconds, before the rocket’s liquid hydrogen and liquid oxygen tanks were fully pressurized, according to a spokesperson for NASA’s Marshall Space Flight Center. in Huntsville, Alabama, where the SLS program is headquartered.
NASA said more than 733,000 gallons of super-cold thrusters had been loaded into the center stage of the B-2 test stand, the same facility once used to test Saturn 5 rocket stages and a propulsion test item of the space shuttle.
Liquid hydrogen is stored at minus 423 degrees (minus 253 degrees Celsius) in the case of liquid hydrogen, and liquid oxygen is kept at minus 298 degrees Fahrenheit (minus 183 degrees Celsius). Engineers scheduled the wet dress rehearsal to gauge the reaction of the rocket’s internal plumbing to very cold thrusters.
All previous tests of the SLS central stage were performed at room temperature and not under cryogenic conditions.
NASA said six barges filled with liquid hydrogen and liquid oxygen provided the center stage of the SLS during the wet dress rehearsal. The ships were positioned in a waterway near the B-2 test stand.
Engineers found no leaks during the several-hour test, but the simulated countdown was automatically stopped with four minutes before the planned stopping point. NASA said in a statement that the countdown was interrupted due to “timing of a valve closing.”
“Subsequent analysis of the data determined that the intended valve shutdown was disabled for a fraction of a second, and that the hardware, software, and scene controller all behaved well to stop the test,” said the NASA. “The team has corrected the timing and is ready to proceed with the final test of the Green Run series.”
Stennis’ ground crews drained cryogenic boosters from the rocket while engineers reviewed the test results. NASA said the test “provided structural and environmental data, verified the cryogenic storage capabilities of the stage, demonstrated software with the stage’s flight computers and avionics, and performed functional checks of all stage systems. “
Despite the early end of the wet dress rehearsal last month, NASA officials have approved plans to move forward with the final test of the Green Run campaign.
“During our wet dress rehearsal test, the Green Run test, the main stage, the stage controller, and the Green Run software all performed perfectly, and there was no leak when the tanks were completely turned on. loaded and filled for about two hours, ”said Julie Bassler, SLS Stages manager at Marshall. “The data from all tests to date has given us the confidence to continue with the burning fire.”
The four Rocketdyne RS-25 Aerojet engines in the center stage will ignite and burn for more than eight minutes, the same amount of time they will fire in an actual launch. The programmed controls will adjust the power parameters of the motors during the test, mimicking their thrust profile upon launch.
All four SLS main stage engines have flown on multiple space shuttle missions, and the high performance engines will provide up to 2 million pounds of thrust at full throttle. Reusable single-use center stage engines will be discarded after each SLS flight.
Assuming a successful hot-fire test, Stennis’ crews will prepare the main stage for the expedition to NASA’s Kennedy Space Center at the start of final processing to prepare the rocket for its first test flight.
At Kennedy, the SLS center stage will be mounted between two solid rocket boosters, and an upper stage and an Orion spacecraft will be mounted on top of the launcher before deploying to pad 39B for takeoff.
Covered with orange foam insulation, the enormous rocket stage built by Boeing has been attached to the B-2 test stand at NASA’s Stennis Space Center since January, when it arrived by barge from a factory. manufacturing facility at NASA’s Michoud Assembly Plant in New Orleans.
Since January, work to prepare the rocket stage for its first test firing has been suspended several times, first by the coronavirus pandemic, then by several close calls with hurricanes approaching the Gulf coast. .
The hot shot test is a final examination in the development of the center stage, the tallest rocket stage ever built. The SLS core is derived from the Space Shuttle’s outer tank, and its four RS-25 engines – built by Aerojet Rocketdyne – are leftovers from the shuttle program.
The 212-foot-long (64.6-meter) and 27.6-foot-wide (8.4-meter) SLS center stage is the same diameter as the shuttle’s fuel tank. It weighs approximately 188,000 pounds (85 metric tons) empty and will weigh approximately 2.3 million pounds (over 1,000 metric tons) fully fueled.
After the main stage arrived in Stennis in January, ground crews lifted the rocket using a crane and lowered it onto the B-2 test stand, a facility once used to test firing from the powerful first stage of NASA’s Apollo-era Saturn 5 moon rocket. .
The first major test on the center stage was a modal test on the center stage to measure the resonant frequency of the rocket.
In March, NASA halted operations on the test bed for two months with the onset of the coronavirus pandemic. Engineers from NASA and Boeing returned to work on the main stage in May after introducing new guidelines for physical distance and other measures to guard against COVID-19.
Ground crews turned on the main stage avionics in June and performed a thorough check of the rocket, then proceeded to security checks, which verified controllers can send commands to shut down the rocket motors and other major systems in the event of a problem.
Next, engineers began testing the center stage main propulsion system, looking for any signs of a leak and checking all connections between the engines and the rocket tank. This test, known as Test 4 in the Green Run, also included checks of the engine igniter and tests of the engine control valves.
With that test passed over the summer, crews moved on to a check of the main stage hydraulic system, which drives thrust vector control actuators to rotate the four RS-25 engines and steer the rocket in. flight.
The crews activated the rocket’s auxiliary power units, which drive the hydraulic loops of the engine’s steering system. The engines then made an individual gimbal to make sure they could pivot in an 8 degree cone, followed by gimbal test profiles to simulate how the engines will move together in flight.
The hydraulic thrust vector control test ended on September 13, concluding a series of rocket functional checks as engineers moved on to final revisions and rehearsals for the wet dress rehearsal and hot fire.
The next step, known as Test 6, was completed on October 5 after Stennis control crews ran a simulated 48-hour launch countdown to validate the activation, fuel loading sequences. and pressurization.
The simulation set the stage for the wet dress rehearsal, but Hurricane Delta and Hurricane Zeta forced further delays.
Stennis’ crews planned to fill the center stage of the SLS with cryogenic thrusters on December 7, but data showed the fluids were hotter than expected, NASA said. The controllers successfully loaded a “limited amount” of liquid hydrogen into the rocket before completing the test.
Engineers changed test procedures and equipment to ensure cryogenic thrusters could be maintained at the correct temperature before successfully filling the tanks on December 20.
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