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NASA is moving forward with a crucial launch test of the central stage of the Space Launch System’s first heavy-load rocket as early as January 17, after engineers were satisfied with the results of a supply test last month.
The hot fire test is the culmination of the SLS Green Run, a series of one-year checks for the program’s first flight-ready main stage on the B-2 test bench at NASA’s Stennis Space Center in Mississippi.
The central stage will fly on the Artemis 1 mission, the first full test flight of the Space Launch System and the capsule of the Orion crew. Artemis 1, which will fly to the moon and back without astronauts, was officially planned for launch in late 2021, but that schedule may be in doubt after delays in the Green Run campaign in Stennis.
Future SLS / Orion missions will send astronauts to the moon, where NASA plans to land humans and build a space mini-station in lunar orbit in the 2020s.
Teams from NASA and Boeing, who built the main stage of the SLS, loaded the 64.6-meter rocket with super-cold liquid hydrogen and liquid oxygen on December 20. The supply test, known as the wet general test, was the first time that the SLS propellant tanks were filled with cryogenic fluids.
Engineers performed the central stage through a simulated countdown, simulating the pre-flight procedures that will be seen on the launch pad at the Kennedy Space Center in Florida. But the trial was aborted at T-minus 4 minutes and 40 seconds, before the rocket’s full hydrogen and liquid oxygen tanks were fully pressurized, according to a spokesman for NASA’s Marshall Space Flight Center in Huntsville, Alabama, where the SLS program is based.
NASA said more than 733,000 gallons of super-cold propellants were loaded onto the central stage of the B-2 test bench, the same facility used to test Saturn 5 rocket stages and a space shuttle propulsion test article.
Liquid hydrogen is stored at minus 423 degrees (minus 253 degrees Celsius) for liquid hydrogen, and liquid oxygen is kept at minus 298 degrees Fahrenheit (minus 183 degrees Celsius). Engineers scheduled the dress rehearsal to assess how the rocket’s internal plumbing responded to super-cold propellants.
All previous tests of the SLS central stage were at room temperature, not cryogenic conditions.
NASA said six barges filled with liquid hydrogen and liquid oxygen provided the main stage for the SLS during the general rehearsal. The vessels were positioned in a watercourse close to the B-2 test bench.
Engineers did not detect leaks during the multi-hour test, but the simulated countdown was automatically stopped with four minutes remaining until the planned waiting point. NASA said in a statement that the countdown was halted due to “the moment a valve is closed”.
“Subsequent analysis of the data determined that the predicted valve closure was off for a fraction of a second, and the hardware, software and stage controller worked properly to interrupt the test,” said NASA. “The team has corrected the time and is ready to proceed with the final test of the Green Run series.”
Ground crews at Stennis drained the rocket’s cryogenic propellants while engineers reviewed the test result. NASA said the test “provided structural and environmental data, verified the stage’s cryogenic storage capabilities, demonstrated software with the stage’s flight and avionics computers and conducted functional checks of all stage systems”.
Despite the early end of the wet dress rehearsal last month, NASA officials approved plans to proceed with the final test of the Green Run campaign.
“During our Green Run wet dress test, the main stage, stage controller and Green Run software worked perfectly and there were no leaks when the tanks were fully loaded and refilled for approximately two hours,” said Julie Bassler, Project Manager. SLS Stages in Marshall. “The data from all the tests so far has given us the confidence to continue with the hot fire.”
The four engines of the main stage Aerojet Rocketdyne RS-25 will light and burn for more than eight minutes, the same duration as during a real launch. The programmed commands will adjust the power settings of the engines during the test, imitating their thrust profile during launch.
All four engines in the SLS central stage have flown on various space shuttle missions, and the high-performance engines will provide up to 2 million pounds of thrust at full throttle. Reusable engines in the single-use core stage will be discarded after each SLS flight.
Assuming a successful hot-fire test, Stennis teams will prepare the main stage for dispatch to NASA’s Kennedy Space Center in the early hours of final processing to prepare the rocket for its first test flight.
At Kennedy, the central stage of the SLS will be assembled between two solid rocket boosters and an upper stage and the Orion spacecraft will be installed on top of the launcher before rolling to platform 39B for takeoff.
Covered with orange foam insulation, the huge rocket stage built by Boeing has been fixed to the B-2 test bench at NASA’s Stennis Space Center since January, when it arrived by barge from a factory at NASA’s Michoud assembly facility in New York. Orleans.
Since January, work to prepare the rocket stage for its first firing test has been halted several times, first by the coronavirus pandemic and then by various hurricane hazards approaching the Gulf Coast.
The hot fire test is a final exam in the development of the central stage, the tallest rocket stage ever built. The SLS core is derived from the outer space shuttle tank and its four RS-25 engines – built by Aerojet Rocketdyne – are leftovers from the space shuttle program.
The central stage of the SLS of 212 feet long (64.6 meters) and 27.6 feet wide (8.4 meters) has the same diameter as the space shuttle’s fuel tank. It weighs about 188,000 pounds (85 metric tons) empty and will weigh about 2.3 million pounds (more than 1,000 metric tons) fully stocked.
After the main stage reached Stennis in January, ground crews lifted the rocket by a crane and lowered it onto the B-2 test bench, an installation used for firing tests on the powerful Saturn 5 lunar rocket first stage of it was NASA’s Apollo.
The first major test in the central stage was a modal test in the central stage to measure the resonance frequency of the rocket.
In March, NASA suspended operations on the test bench for two months with the start of the coronavirus pandemic. Engineers at NASA and Boeing resumed work at the central stage in May, following the introduction of new guidelines for physical distance and other protective measures against COVID-19.
Ground crews powered up the main stage avionics in June and performed a full rocket check, then proceeded to safety checks, where verified controllers can send commands to shut down rocket engines and other important systems in the event of problem.
Then, engineers began testing the main stage’s main propulsion system, looking for any signs of leaks and checking all connections between the engines and the rocket’s cargo. This test, known as Test 4 on the Green Run, also included checks on the engine ignitor and tests on the engine control valves.
With this test successfully approved over the summer, the teams went on to check the main stage hydraulic system, which drives thrust vector control actuators to turn the four RS-25 engines and drive the rocket in flight.
The teams activated the rocket’s auxiliary power units, which trigger the hydraulic loops of the engine’s steering system. The engines then spun individually to ensure they could rotate 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 was completed on September 13, completing a series of functional checks of the rocket while engineers carried out the final overhauls and tests for the wet and hot fire test.
The next milestone, known as Test 6, was completed on October 5 after control teams at Stennis performed a simulated 48-hour launch countdown to validate the activation, fuel loading and pressurization sequences.
The simulation set the stage for the wet dress rehearsal, but Hurricane Delta and Hurricane Zeta forced further delays.
The teams at Stennis planned to fill the central stage of the SLS with cryogenic propellants on December 7, but the data showed that the fluids were warmer than planned, NASA said. The controllers successfully loaded a “limited amount” of liquid hydrogen into the rocket before completing the test.
Engineers modified the testing procedures and equipment to ensure that cryogenic propellants could be kept at the proper temperature before successfully filling tanks on December 20.
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