Home / Science / First crucial refueling test for the SLS core stage later this month: Spaceflight Now

First crucial refueling test for the SLS core stage later this month: Spaceflight Now

The first major stage of the space launch system on test bed B-2 at NASA’s Stennis Space Center in Mississippi. Credit: NASA

If all goes according to plan, engineers in southern Mississippi will be loading cryogenic propellants into a rocket’s central stage later this month.Nasa says it will launch astronauts to the moon, exposing its tank and internal piping to extreme operating conditions. degrees below zero for the first time.

The refueling test – a milestone in its own right – is a precursor to a high-risk eight-minute test launch of the four main engines of the space launch system’s shuttle era planned as early as November.

Covered in orange insulating foam, the huge Boeing-built rocket stage has been secured in NASA’s Stennis Space Center B-2 test rig since January, when it arrived on a barge from a manufacturing facility at the Michoud Assembly Facility. of NASA in New Orleans.

Since January, work to prepare the rocket’s stage for its first test launch has been suspended several times, first by the coronavirus pandemic, and then by several close recalls with hurricanes approaching the Gulf coast.

With Hurricane Delta on track to land in Louisiana on Friday, practical work on the main stage of the SLS was once again halted on Test Bench B-2, according to Valerie Buckingham, a NASA spokesperson at Stennis Space Center.

But Stennis is expected to receive limited impacts from Hurricane Delta, and assuming the forecast holds up, test bed operations could quickly resume.

The next step in the SLS test campaign in Stennis, known as the “Green Run”, will be loading 733,000 gallons of super cold liquid hydrogen and liquid oxygen into the central stage. According to Tracy McMahan, a spokesperson for Marshall Space Flight Center, which runs the Space Launch System program, NASA expects this important step to take place by the end of the month.

Numerous sensors will measure how the central stage and its complex piping respond to cryogenic propellant loading.

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).

The refueling test, known as the wet suit test, is the penultimate test of the Green Run. If all goes well during the costume tests, the engineers will load cryogenic propellants back into the main stage in November and ignite the four main engines of the RS-25 rocket for more than eight minutes, the duration of their combustion during a real launch.

The hot fire test is a final exam in the development of the main stage, the tallest rocket stage ever built. The SLS core is derived from the outer tank of the space shuttle and its four RS-25 engines – built by Aerojet Rocketdyne – are leftovers from the shuttle program.

The SLS main stage 212 feet (64.6 meters) long and 27.6 feet (8.4 meters) wide 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 (more than 1,000 metric tons) fully powered.

After the main stadium arrived in Stennis in January, ground crews lifted the rocket with a crane and lowered it onto Test Stand B-2, a facility once used for testing the rocket’s powerful first stage. moon Saturn 5 from NASA’s Apollo era.

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 test bed operations for two months as the coronavirus pandemic began. NASA and Boeing engineers resumed work on the main stage in May after introducing new guidelines for physical spacing and other measures to protect against COVID-19.

Ground crews activated the main stage avionics in June and performed a thorough check of the rocket, then proceeded to safety checks, which verified controllers can send commands to shut down the rocket’s engines and other main systems in case of problems.

This checklist shows the series of tests the SLS core stage is undergoing this year at the Stennis Space Center in Mississippi. Next is a cryogenic power test. Credit: NASA

Then the engineers began testing the main stage propulsion system, looking for any signs of leaks and checking all connections between the engines and the rocket’s tank. That test, known as Test 4 in Green Run, also included engine igniter checks and engine control valve tests.

With that test passed successfully over the summer, the teams moved on to a check of the main stage hydraulic system, which operates the thrust vector control actuators to spin the four RS-25 engines and steer the rocket into flight. .

The teams activated the rocket’s auxiliary power units, which drive the hydraulic circuits for the engine’s steering system. The motors then stabilized individually to ensure they could be rotated within an 8 degree cone, followed by gimbal test profiles to simulate how the motors will move together in flight.

The hydraulic thrust vector control test concluded on September 13, concluding a series of functional checks on the rocket as engineers moved on to final overhauls and tests for wet suit and hot fire trials.

The next milestone, known as Test 6, was completed on October 5 after Stennis’ control teams ran a simulated 48-hour launch countdown to validate the activation, fuel loading and pressurization sequences.

Engineers and technicians from NASA, Boeing and engine manufacturer Aerojet Rocketdyne participated in the countdown simulation, which provided a “refresher course” for test controllers to make sure they are ready to load cryogenic propellants into the rocket for the first time, according to Mark Nappi, Boeing’s director of Green Run testing.

“Once we’re done, we’ll stop, stop, review the data and go to the wet suit test,” Nappi said in an interview prior to the countdown mock test.

NASA hasn’t announced a target date for the cryogenic load test, but it will mark a significant step for the SLS program, a milestone that comes with unknowns.

“Filling everything with cryo is huge because it’s the first time your tanks move the way they’ll move when filled with cryogenic liquid,” said Alex Cagnola, propulsion engineer at NASA’s Marshall Space Flight Center. .

“You’re testing all of your joints. You’re testing how everything basically acts in a cryogenic environment,” Cagnola said in an interview earlier this year.

John Shannon, SLS program manager at Boeing, said all tests on the rocket so far have been done at room temperature.

“Things change when you go down to cryogenic temperatures, and as we’ve seen after our experience with the shuttle, you can end up with systems that work differently,” said Shannon, former NASA flight director and program manager. of the space shuttle.

The teams will check for leaks and ensure that valves and other hardware are still operating at cryogenic temperatures. It takes about six hours to pump liquid hydrogen and liquid oxygen into the central stage.

“The next big unknown as a program is when we put cryogenic liquids in the oxygen tank and hydrogen tank, examine the plumbing and all systems, and make sure they stay tight and perform as intended through our testing. qualification, ”Shannon told reporters earlier this year. “We have great faith that they will, but until you see it integrated, you don’t really know.”

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The engineers will unload the main stage of its cryogenic propellants after the costume test, then analyze the test results and perform inspections of the rocket before proceeding with another refueling operation. This will culminate in the ignition of the rocket’s four RS-25 engines.

All four SLS stage engines have flown on multiple space shuttle missions, and the high-performance thrusters will deliver up to 2 million pounds of thrust at full throttle. Reusable motors in the disposable core stage will be discarded after each SLS flight.

The RS-25 engines will ignite for more than eight minutes. The programmed commands will adjust the power settings of the motors during the test, mimicking their thrust profile during launch.

Assuming a successful hot fire test, Stennis’ teams will prepare the main stage for expedition to NASA’s Kennedy Space Center – likely early next year – for final processing to prepare the rocket for its first flight of. test at the end of 2021.

Inside the Vehicle Assembly Building at Kennedy, technicians will begin stacking the rocket’s solid rocket thrusters twins on a new mobile launch pad once the main stage passes its Green Run hot fire test. Upon arrival at Kennedy, the main stage will be raised between solid fuel boosters, then ground crews will lift an upper stage and an Orion crew capsule to the top of the rocket before launching to pad 39B for a countdown and preparations for the final launch.

The Space Launch System’s first flight with the Orion probe, known as Artemis 1, will not carry any astronauts. The Orion will fly to the moon and enter lunar orbit to demonstrate its performance and capabilities, then return to Earth for a splashdown in the Pacific Ocean after a 26-42 day mission.

In 2023, NASA aims to launch the Artemis 2 mission with a crew on board. After taking off on the second SLS flight, the Orion crew will circle the far side of the moon before returning to Earth, the first voyage of astronauts to the moon’s vicinity since 1972.

If NASA’s plans come to fruition – an open question hinging on Congressional funding and no major technical hurdles – the Artemis 3 mission could be launched by the end of 2024 with the third SLS / Orion mission. After piloting their Orion spaceship near the moon, the astronauts would connect to a commercial lunar lander to travel to the lunar surface for a landing attempt.

In April, NASA entered into a contract with commercial teams led by Blue Origin, Dynetics and SpaceX to begin developing human-classified lunar landing craft. The agency plans to select one or two of the teams next year to continue the lunar lander development efforts, assuming Congress provides the money to support the effort.

The SLS and Orion programs date back many years.

The Orion probe has its roots in NASA’s Constellation moon landing program initiated under the administration of George W. Bush. NASA selected Lockheed Martin as the primary contractor for the Orion crew capsule in 2006, and Orion survived the Obama administration’s cancellation of the Constellation program in 2010.

The Space Launch System was unveiled in 2011 as the centerpiece of a new space exploration initiative proposed by Congress. The Obama White House joined the program, and NASA repurposed ongoing Orion probe work to support a broader exploration strategy focused on Mars, not the moon, with interim missions involving astronaut visits to asteroids in deep space. .

Artistic concept of stacking the space launch system inside the Vehicle Assembly Building at Kennedy Space Center. In this illustration, the orange SLS middle stage, two solid rocket repeaters and the upper stage are seen, while a crane lowers the Orion spacecraft on top of the launch vehicle. Credit: NASA

Despite years of delays and cost overruns, the Space Launch System has maintained the support of lawmakers, particularly among members of Congress in the states where the rocket was designed, built, and tested. The Trump administration redirected NASA’s space exploration strategy to the moon, creating the Artemis program after a directive from Vice President Mike Pence last year to land astronauts on the moon by the end of 2024.

NASA has spent more than $ 15 billion on the SLS program to date, and NASA’s Inspector General warned in March that the rocket’s development costs will increase to more than $ 22.8 billion by 2023, when the agency expects to certify it for astronaut flights.

The SLS core stage is the last major element for the Artemis 1 mission yet to be delivered to the spaceport in Florida for launch processing. The Orion spaceship has completed its test campaign and is ready to be powered and coupled with its launch abort system. Managers will give the green light to these activities after the main phase completes its Green Run hot fire test.

The segments for the rocket’s two side-mounted solid repeaters arrived in Kennedy in June from their Northrop Grumman factory in Utah. Technicians plan to begin stacking boosters on the mobile launch pad in the Vehicle Assembly Building once Green Run tests on the main stage conclude in Mississippi.

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Follow Stephen Clark on Twitter: @ StephenClark1.

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