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A critical firing test on Saturday of the four main engines powering the first stage of NASA’s gigantic lunar rocket in the space launch system is the last major hurdle before the expensive and often delayed launch of the fully assembled thruster later this year on an unmanned test flight.
Bolted in place to the top of the massive B-2 test bed at NASA’s Stennis Space Center in Mississippi, the upgraded Rocketdyne RS-25 Aerojet engines are expected to run for a full eight minutes starting at 5 p.m. EST, the same time needed for an actual flight. .
Including shuttle flights and post-shuttle ground testing, the RS-25 engines have been started over 3,000 times to date and fired for over 18,000 minutes in total, but never four at a time and never with a rocket the size of the SLS. The objective is to test the performance of the scene as a whole under flight conditions.
NASA
“This will be our first test of firing all four RS-25 engines simultaneously in this new space launch system configuration,” said Jeff Zotti, Aerojet Rocketdyne RS-25 program director. “We all can’t wait to see the middle phase of the world’s most powerful rocket fire for the very first time.”
The flight version of the SLS will feature two 17-stage Northrop Grumman solid-fuel strap thrusters, each generating 3.6 million pounds of thrust; the four RS-25s, generating a combined thrust of 1.6 million pounds; a second stage supplied with hydrogen; an Orion crew capsule and an emergency evacuation system.
The rocket will weigh 5.75 million pounds, stand 322 feet high, and generate 8.8 million pounds of lift-off thrust, making it the most powerful operational rocket in the world and the most powerful American rocket ever built. Even more powerful variants are planned by NASA for its Artemis lunar program, pushing lift-off thrust to 9.5 million pounds.
For Saturday’s so-called “green race”, the first stage of the 212-foot-tall, 27.6-foot-wide, Boeing-operated SLS rocket will be tested as a fully operational, loaded thruster. of 537,000 gallons of liquid hydrogen and liquid oxygen for an expected test cook of 485 seconds.
With the stage locked on the test bench throughout, new state-of-the-art engine ECUs will reduce the main engines to 95% thrust about a minute after the test begins. They will do the same during actual flight to reduce stress on the rocket as it passes through the region of maximum aerodynamic pressure.
The 7,775-pound engines, which previously helped propel 21 shuttle launches, will also be hydraulically gimbaled, or move to commanded positions at specified times, to test their ability to accurately steer the rocket as it climbs into the space, both early in flight and later in ascent.
The engine nozzles feature new insulation to protect them from the heat they will eventually experience from the exhaust plumes of the nearby 5000 degree solid rocket thruster.
NASA
Throughout the ground shake test, sensors will monitor other stresses and strains, temperatures, thruster flow rates, pressures, and a variety of other parameters to ensure the rocket is ready for rocket launch. the first Artemis lunar mission at the end of this year.
Equally important, the test will verify the performance of the complex flight computer system and rocket software as well as the thruster management and safety systems before flight.
“The test is scheduled for 485 seconds,” said Julie Bassler, SLS stage manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “The stage is equipped with more than 1,400 sensors, including pressure, temperature, accelerometers and strain gauges.”
“With this fire burning, there is a lot of data, including how the avionics and command and control software will work with the integrated center stage and engine propulsion system,” Bassler said, adding: ” This green function test is the first time that we are shooting. This fundamental step. So this is an important step for us. “
“This is the most heavily instrumented vehicle we will ever drive. So we’ll get a huge amount of engineering data, ”said John Shannon, Boeing SLS Program Director, former Space Shuttle Flight Director.
Assuming the green run test goes well and no major issues are encountered, NASA officials hope to ship the SLS by barge to Kennedy Space Center in February.
Once there, the stage will be attached to two solid fuel boosters being assembled, or “stacked,” on a movable launch pad in the cavernous Vehicle Assembly building. The already complete upper stage will be mounted on top of the core and the rocket will be completed with a Lockheed Martin Orion crew capsule and its emergency escape system.
The assembled rocket and its launch pad will then be transported to pad 39B by a powerful tracked transporter and prepared for flight. Unlike SpaceX and other rockets in development, the SLS is not reusable, and the first stage thruster and its engines will be destroyed when they fall back into the atmosphere after climbing into space.
NASA hopes to launch the rocket on its maiden flight later this year, sending the unmanned Orion capsule on a flight 40,000 miles beyond the moon and back. What happens next will largely depend on how the Biden administration prioritizes the space.
NASA
NASA is currently working on a Trump administration schedule that calls for the first manned SLS-Orion flight – Artemis 2 – in 2023, followed by a moon landing using the third SLS rocket by the end. from 2024.
But this timetable assumes funding to develop a new lunar lander. The program has not yet received the necessary budget Congress, and it is not yet clear what level of support the Biden administration will provide.
For its part, the SLS team is optimistic that the first Artemis rocket will be ready for launch before the end of the year.
“This powerful rocket will put us in a position to be ready to support the agency and the country’s space mission to the moon and beyond,” said John Honeycutt, NASA SLS program manager at Marshall.
But it was a rocky road.
the the development program is well over budget and at least two years late. The NASA Inspector General reported last March that the total costs of the SLS program are expected to exceed $ 18 billion before the Artemis 1 rocket takes off.
The delays and high costs have sparked debate over the need for the SLS to transport astronauts to the Moon given the availability of less powerful but much cheaper SpaceX Falcon Heavy rockets and other heavy lift propellants currently in development. But NASA officials say the SLS is the only short-term available rocket capable of accommodating the Orion crew capsule and other large components being considered for the Artemis program.
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