The core of a giant NASA rocket that will return astronauts to the moon has been subjected to a crucial test.
For the first time, engineers fully loaded a central stage of the Space Launch System (SLS) rocket with super-cold liquid propellant, controlled it, and then drained the tanks.
This fuel is fuel and an oxidant – a chemical that makes the fuel burn.
The engineers wanted to check how things worked as expected before the SLS made its first flight in about a year.
It was part of a testing program known as the Green Run, which takes place at NASA’s Stennis Space Center near St. Louis Bay in Mississippi.
This evaluation, known as Wet Repetition (WDR), was the seventh of eight basic stage tests. NASA said the rocket responded well to fuel loading. But the test experienced an unexpected shutdown a few minutes earlier than planned.
However, the completion of the WDR should establish the eighth and final test – a “fire” – in which all four RS-25 engines at the core of the core will be launched together for the first time.
This missile segment will support the first mission in NASA’s monthly exploration plan – known as Artemis. This mission, scheduled for November 2021, will send the next generation of the Orion spacecraft on a loop around Earth’s only natural satellite.
There will be no crew on board for this test flight. The third Artemis mission, in 2024, will land the first humans on the lunar surface since the 1972 Apollo 17 mission.
Green Run helps ensure troubleshooting before the complex missile segment is transported to Florida to prepare for launch.
Over several hours, Stennis engineers loaded the central stage with more than 700,000 gallons (about 2.6 million liters) of hydrogen and liquid oxygen.
“It’s an incredibly exciting time,” said Jim Maser, senior vice president at Aerojet Rocketdyne, which builds RS-25 engines. “We are really getting into some of the most significant aspects of the testing program.”
The rocket section is anchored to a giant steel structure called the B-2 test stand, which was once used to test engines for the Saturn V massive rocket carrying astronauts to the moon in the 1960s and 1970s.
The propeller was brought to the spot on six barges on the waterway that spins through the terrain of the Stennis space.
The barges were anchored near the test stand, while the super-cold (cryogenic) fuels on board were introduced into the main pipeline.
Hydrogen and oxygen are gaseous at room temperature, but the gases take up a lot of space. Their transformation into liquids allows the storage of an equivalent quantity in a smaller tank.
This requires cooling the fuel with hydrogen to minus 253C (minus 423F) and oxygen (fuel oxidant) to minus 183C (minus 297F).
After being filled, the tanks had to be filled – filled – continuously, because the liquids at such low temperatures boil over time.
During the test, the liquids had to flow through turbopumps – which supply fuel to the engine’s combustion chambers – and the engines themselves. This helps prepare the systems that need to be started.
Everything is designed to mimic as closely as possible what would happen in the hours before a real flight. “We’re just trying to get as much data as possible so we can get on with the next run. And we want to find anything that could be improved during this wet dress to prepare us for the hot fire,” Ryan McKibben, Green Run the test leader for NASA, he told BBC News.
On its Artemis blog, NASA said: “The first analysis of the data indicates the stage of good performance during the process of refueling and refueling.”
While all this was happening, the teams from NASA and Boeing – the main contractor for SLS – performed a simulated launch countdown. They had to take the number to the T-minus point (remaining time) 33 seconds.
But NASA said the test ended a few minutes outside the planned time. Teams evaluate data to identify the exact cause of the early shutdown.
Speaking in October, John Shannon, vice president and SLS program manager at Boeing, explained: “We will spend about two weeks reviewing the data to make sure all systems have behaved as expected.
“We will go out and inspect the vehicle, we will make sure there are no surprises.”
SLS in number
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The rocket will stand 98m (322ft) high in its initial configuration or Block 1
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SLS Block 1 can send more than 27 tons (59,500 pounds) to monthly orbits – the equivalent of 11 large sports utility vehicles (SUVs)
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A future version of SLS, called Block 2 Cargo, will be released 46 tons (101,400 pounds) to the Moon – that is, 18 large SUVs
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SLS will produce 8.8 million pounds (39.1 meganewtons) of force in its block configuration 1
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Four RS-25 engines are the basis of the base stage; are the same used in space shuttle
If the data looks good, the engineers will continue with the “fire of fire”.
The SLS rocket consists of a huge central stage, with two smaller boosters connected to the sides. The four powerful RS-25 engines at its base are of the same type used by the now-withdrawn space shuttle orbiter.
The launcher provides the raw power needed to send Orion into space and then throw it to the moon.
Last month, Stennis engineers removed and replaced a component called the clutch on one of the four pre-valves, which supply liquid hydrogen to the RS-25 engines. Prevana performed inconsistently during the tests.
Officials plan to send the giant core to its launch site at the Kennedy Space Center in Florida by Jan. 14 to keep SLS on track for the November flight.
Last week, NASA said that the Artemis-1 mission was on track to be launched in November 2021.
Green Run went largely smoothly; there was a five-week shutdown due to Covid-19. In addition, on-site work had to be closed six times due to tropical weather, given the particularly active hurricane season.
“It was extremely important for us to stick to the program,” John Honeycutt, SLS manager at NASA, told a news conference in October.
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