SLS: Nasa's giant 'Moon rocket' takes shape
Nasa has finished assembling the main structural components for its largest rocket since the Apollo-era Saturn V.
Engineers at the agency's Michoud Assembly Facility (MAF) in New Orleans connected the last of five sections that make up the core of the Space Launch System (SLS).
The rocket will be used to send an uncrewed Orion craft to the Moon, in a flight expected to launch in 2021.
This will pave the way for crewed missions, with a landing in 2024.
The last piece of the SLS' 64m (212ft) -tall core stage was the complicated engine section. This will serve as the attachment point for the four powerful RS-25 engines, which are capable of producing two million pounds of thrust (9 meganewtons).
The RS-25 engines, built by Sacramento, California-based Aerojet Rocketdyne, are the same ones that powered the now-retired space shuttle orbiter.
To the Moon and Beyond
Julie Bassler, Nasa's SLS stages manager, said: "Now, to complete the stage, Nasa will add the four RS-25 engines and complete the final integrated avionics (electronics) and propulsion functional tests.
"This is an exciting time as we finish the first-time production of the complex core stage that will provide the power to send the Artemis 1 mission to the Moon."
It marks a significant milestone for the SLS rocket, which has experienced delays and cost overruns since being announced in 2010.
Nasa wants to send the first woman and the next man to the lunar South Pole by 2024. Artemis 1 will be followed by the first crewed mission, planned for launch in 2022, which will send astronauts on a loop around the Moon without landing. The first lunar landing since Apollo 17 in 1972 will occur on Artemis 3.
Over the autumn, SLS engineers will work to attach the four RS-25s and connect them to the main propulsion systems inside the engine section.
The SLS consists of a core stage atop which the Orion spacecraft will sit, and two solid rocket boosters (SRBs) strapped to either side of the core. Orion is America's next-generation crewed spacecraft, capable of journeys to the Moon, asteroids and other targets in deep space. It could also be part of a transfer vehicle for human missions to Mars.
Eventually, Nasa plans to build a space station in lunar orbit called Gateway. The full station won't be ready by the 2024 landing, but astronauts on this mission could dock with a "lite" version of Gateway, consisting of just a power and propulsion module and a small habitat. They would then take a lander down to the surface.
In June, John Shannon, programme manager for the SLS at Boeing, the prime contractor building the rocket for Nasa, told me: "[The SLS is] built to carry crew and it's got the performance to take that crew where you want to take them.
"There are other rockets on the drawing board right now. But as far as a human-rated vehicle that's purpose-built to take Orion and parts of the Gateway station or landers to the Moon, SLS is really the only one."
Jennifer Boland-Masterson is the MAF operations director for Boeing. She said: "Boeing expects to complete final assembly of the Artemis 1 core stage in December."
She added: "After we deliver the stage, Nasa will transport it on the agency's Pegasus barge from Michoud to Nasa's Stennis Space Center near Bay St Louis, Mississippi, for Green Run testing."
The Green Run will involve test firing all four RS-25 engines for eight minutes - the full duration of the rocket's first flight into space. It will stay on the ground while the engines are fired at the B-2 test stand at Nasa Stennis. The Green Run will provide critical performance data needed to demonstrate the core stage design is flightworthy and ready for launch.
The SLS core stage incorporates state-of-the-art avionics, miles of cables and two huge liquid propellant tanks that collectively hold 733,000 gallons (2.7 million litres) of liquid oxygen and liquid hydrogen to power the four RS-25 engines.
NASA Joins Last of Five Sections for Space Launch System Rocket Stage
NASA finished assembling and joining the main structural components for the largest rocket stage the agency has built since the Saturn V that sent Apollo astronauts to the Moon. Engineers at the agency’s Michoud Assembly Facility in New Orleans connected the last of the five sections of the Space Launch System (SLS) rocket core stage on Sept. 19. The stage will produce 2 million pounds of thrust to send Artemis I, the first flight of SLS and NASA’s Orion spacecraft to the Moon.
“NASA has achieved a historic first milestone by completing the final join of the core stage structure for NASA’s Space Launch System, the world’s most powerful rocket,” said Julie Bassler, the NASA SLS stages manager. “Now, to complete the stage, NASA will add the four RS-25 engines and complete the final integrated avionics and propulsion functional tests. This is an exciting time as we finish the first-time production of the complex core stage that will provide the power to send the Artemis I mission to the Moon.”
The last piece added to the stage was the engine section located at the bottom of the 212-foot-tall core stage. To complete the structure, technicians bolted the engine section to the stage’s liquid hydrogen propellant tank, which was recently attached to the other core stage structures. The engine section is one of the most complicated pieces of hardware for the SLS rocket and is the attachment point for the four RS-25 rockets and the two solid rocket boosters that produce a combined 8.8 millions pounds of thrust. The engine section also includes vital systems for mounting, controlling and delivering fuel from the stage’s two liquid propellant tanks to the rocket’s engines. This fall, NASA will work with core stage lead contractor, Boeing, and the RS-25 engine lead contractor, Aerojet Rocketdyne, to attach the four RS-25 engines and connect them to the main propulsion systems inside the engine section.
“Boeing expects to complete final assembly of the Artemis I core stage in December,” said Jennifer Boland-Masterson, Boeing operations direct at MAF. “After we deliver the stage, NASA will transport it on the agency’s Pegasus barge from Michoud to NASA’s Stennis Space Center near Bay St. Louis, Mississippi, for Green Run testing. Our team here at Michoud will continue work with NASA to build, outfit and assemble the core stage for Artemis II, the first mission that will send astronauts to orbit the Moon. Lessons learned and innovations developed in building the first core stage are making the second one progress much faster.”
During Green Run testing, engineers will install the core stage into the B-2 Test Stand at Stennis for a series of tests that will build like a crescendo over several months. This will be the first fully fueled test of this brand new rocket stage. Many aspects will be carried out for the first time, such as fueling and pressurizing the stage, and the test series culminates with firing up all four engines to demonstrate that the engines, tanks, fuel lines, valves, pressurization system, and software can all perform together as they will on launch day.
The SLS team also achieved another recent milestone by completing structural testing for the stage’s liquid hydrogen tank. The testing confirmed that the structural design for the tank on the rocket’s initial configuration, called Block 1, can withstand extreme conditions during launch and flight. Teams at NASA’s Marshall Space Flight Center in Huntsville, Alabama, put a test version of the tank through the paces during 37 separate test cases that exceed what engineers expect the SLS rocket to experience. The final test used 80,000 gallons of liquid nitrogen to simulate the cryogenic conditions, or extreme cold, that the liquid hydrogen tank will experience in flight. Testing will continue later this year to show the tank’s structural design is adequate for future designs of the vehicle as it evolves to a Block IB configuration and missions with even greater forces.
In addition to providing propellant and power to get the SLS rocket and Orion spacecraft to space, the core stage houses the flight computers and avionics components that control the first 8 minutes of flight. The avionics system, including the flight computers, completed integrated system level qualification testing showing the components all work together to control the rocket in the Software Integration and Test Facility (SITF) at Marshall. The next step is to test the flight software with all the ground system software, Orion and launch control in the Systems Integration Laboratory at Marshall.
“NASA and our contractor teams are making tremendous progress on every aspect of manufacturing, assembling and testing the complex systems needed to land American astronauts on the lunar surface by 2024,” Bassler said. “I am confident this hard work will result in a rocket that can provide the backbone for deep space transportation to the Moon and ultimately to Mars.”
NASA is working to land the first woman and the next man on the Moon by 2024. SLS and NASA’s Orion spacecraft, along with the Gateway in orbit around the Moon, and the Human Landing System are the backbone for deep space exploration. SLS is the only rocket that can send Orion, astronauts and supplies to the Moon in a single mission.
SLS pathfinder stage arrives at Florida launch site
A steel tube built as a stand-in for the core stage of NASA’s Space Launch System has arrived at the Kennedy Space Center for a series of rehearsals to hone the skills of technicians before the real rocket reaches the spaceport, an oft-delayed milestone that could still be a year or more away.
The steel cylinder, fitted with four bell-shaped structures in place of real rocket engines, arrived at the Florida spaceport Friday aboard NASA’s Pegasus barge.
The vessel carried the SLS core stage pathfinder rode the Pegasus barge from NASA’s Stennis Space Center in Mississippi, where ground teams practiced handling the rocket simulator and lifted the structure into a test stand that will be used next year by the actual rocket.
A similar series of rehearsals at the Kennedy Space Center will allow technicians to practice procedures to raise the core stage vertical using cranes inside the Vehicle Assembly Building, where the Space Launch System will be assembled on top of a mobile platform before rolling out to pad 39B for final countdown operations.
Workers practiced loading and unloading the core stage pathfinder on the Pegasus barge several times Monday at the turn basin wharf at Kennedy, before moving the rocket simulator into the VAB on Tuesday. The Pegasus barge and the turn basin wharf were previously used to ferry and unload the space shuttle’s external fuel tanks after shipment from their factory in Louisiana.
NASA lengthened the Pegasus barge to accommodate the SLS core stage.
The steel pathfinder is a full-scale mock-up of the SLS core stage, stretching 212 feet (64.6-meters) long and 27.6 fleet (8.4 meters) wide. It weighs around 228,000 pounds, or 103 metric tons, according to NASA.
The Space Launch System is a heavy-lift rocket in development since 2011 designed to loft NASA’s Orion crew capsule on trajectories into deep space. The Trump administration has charged NASA with landing astronauts on the moon by the end of 2024, and the space agency says it needs the SLS to launch Orion crews in order to achieve that deadline.
But the rocket’s first flight is more than three years behind schedule after missing its original target launch date in 2017.
John Honeycutt, the SLS program manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama, said Sept. 26 that the the rocket’s team is working “aggressively” to meet an internal schedule that could result in a November 2020 launch date for the first test flight, named Artemis 1.
The November 2020 schedule is probably unachievable, and does not take into account any possible setbacks during a critical period of vital tests over the coming months.
NASA is expected to set an official target launch date for Artemis 1 later this year, once a new associated administrator for the agency’s human spaceflight programs is selected. That new official target launch date for Artemis 1 is likely to be some time in 2021, factoring in extra time to deal with technical issues.
Artemis 1 is an unpiloted mission that will send the Orion spacecraft into around the moon. If it goes well, NASA wants to launch four astronauts on a mission around the moon and back to Earth on the next SLS/Orion mission, designated Artemis 2, in 2022 or 2023. Artemis 3 would carry astronauts to rendezvous with a lander launched into lunar orbit on a different rocket, before attempting the first human landing on the moon since 1972.
NASA decided to build a pathfinder to familiarize technicians at Stennis and Kennedy with handling a structure with the same dimensions of the SLS core stage because the first real rocket will be the stage destined to launch on the first SLS test flight, not a ground development unit.
Honeycutt compared the first SLS core stage to a “golden egg.”
“It was important to us to get a pathfinder and hand it over to the team so they could work through the operations of doing the lift to get the core stage into the test stand (at Stennis) and learn from that,” Honeycutt said.
“We’ll do the same thing at Kennedy,” he said. “We’ll hand the pathfinder over to the EGS (Exploration Ground Systems) folks, and they’ll start doing their practice operations on the core stage well ahead of time before the actual core stage ends up there.”
The pathfinder rehearsals in the VAB are expected to last about a month, NASA said.
Exactly when the Boeing-built SLS core stage itself will arrive at the Florida launch site remains unpredictable, officials said.
Last month, workers at the Michoud Assembly Facility in New Orleans finished connecting the major segments of the SLS core stage. The engine section, which sits at the base of the rocket, was the final significant element of the core stage added.
“The engine section has been our critical path for the last two years,” Honeycutt said. “It’s very complex. It’s analogous probably to what we used to call the aft compartment of the space shuttle orbiter. It’s a spacecraft in and of itself. It houses control systems, avionics, for all the propulsion, the autogenous pressurization system, auxiliary power, as well as those four big main engines, and the hydraulic actuators that are used for pitch and yaw on the engines.”
Difficulties in fabricating and outfitting the engine section contributed to most of the recent delays in the first SLS test flight.
Teams at Michoud will install the core stage’s four Aerojet Rocketdyne RS-25 main engines in the coming weeks. The engines are leftovers from the space shuttle program, and were designed to be reusable.
But like the rest of the core stage, the engines will be thrown away with each SLS flight.
Once the engines are on the rocket, engineers will begin final integration and testing on the core stage, according to Honeycutt.
“There’s a systems tunnel that runs the full length of the stage that’s got a significant amount of cables, connectors, and so forth,” he said. “All of that’s got to be be checked out from the top of the rocket to the bottom and make sure we’ve got everything working correctly.”
When that’s done, the Pegasus barge will ferry the core stage from Michoud the nearby Stennis Space Center for mounting inside the B-2 test stand to begin a series of tests known as the “green run.” NASA would like to have the core stage at Stennis by the end of this year.
After the green run testing in Mississippi, the Pegasus barge will haul the core stage to Florida for final checkouts and stacking on top of the SLS mobile launch platform, a process expected to take at least several months.
Controllers will conduct launch dress rehearsals at Stennis. The testing will begin with loading super-cold liquid hydrogen and liquid oxygen into the core stage for the first time.
The months-long green run campaign will culminate in a full-duration test-firing of all four RS-25 engines on the test stand. The engines will generate 2 million pounds of thrust at full power and fire eight minutes during the green run hot fire test, just as they will during launch.
On a real launch, two solid-fueled boosters will be affixed to each side of the core stage. A hydrogen-fueled second stage and Orion spacecraft will be bolted on top.
Honeycutt said the green run testing is “very complex,” and the most complicated element is a part called the stage controller, a computer that oversees all the moving parts of the core stage.
“The stage controller makes the core stage think it’s sitting on the launch pad in a launch environment at the Kennedy Space Center,” Honeycutt said. “It’s been a significant amount of effort to run through the software development for the stage controller.”
In a presentation last week to the National Academies’ Aeronautics and Space Engineer Board, Honeycutt hinted at challenges in readying the stage controller’s software for the green run test.
“The team has turned the tide, I believe, and is starting to do really good, but we’re having to pay really close attention to the stage controller for green run,” he said.
In parallel, engineers at Marshall are putting test articles for each of the SLS core stage elements — the engine section, liquid hydrogen tank, intertank and liquid oxygen tank — through structural testing. Honeycutt said the liquid oxygen tank is the final piece to go through structural testing, and that should be finished in early 2020.
He said the liquid oxygen tank’s structural testing is not a hang-up for the green run at Stennis.
Inside the factory at Michoud, Boeing was able to catch up on some of the core stage work delayed by problems building the engine section by rearranging how the rocket was assembled. Instead of mating the engine section vertically to the bottom of the hydrogen tank, then connecting that to the other half of the core stage, managers decided to connect the all the pieces of the rocket — minus the engine section — earlier this year.
While the replan bought managers some time at Michoud, it means technicians may have to complete a delicate final assembly task outside the factory, once the core stage is vertical again at the Stennis Space Center.
“The original plan was to mate the engine section to the hydrogen tank, lay the hydrogen tank down, and mate the back half of the rocket with the front half of the rocket,” Honeycutt said. “Given the challenges we had with the engine section … that made us go have to do the engine section mate horizontally as opposed to vertically, which makes it very challenging to make the feedline connections inside the engine section.
“That’s the type of work that’s getting transferred to Stennis,” he said. “It’ll be similar to working at the factory, but we all know that the factory is probably the best place to do the work, except in this one case.
High volumes of propellant will flow through the liquid hydrogen and liquid oxygen feedlines into the RS-25 engines.
“My message to the Boeing folks, and they get it, is if the right place is in the factory, we’re going to stay in the factory and do the work (with the feedlines),” Honeycutt said.
Honeycutt identified several possible “pinch points” during the green run testing at Stennis that could lead to further delays.
The schedule assumes some delays for minor problems or bad weather.
“But I haven’t baked anything into the schedule for big anomalies like multiple attempts at hotfires, or multiple attempts at wet dress rehearsal, or a significant hydrogen or oxygen leak,” Honeycutt said. “So there are your big pinch points through green run. If everything goes right, we can probably get out of there in five months or so. History would tell us it’s probably somewhere in between five months and 10 months.
“Other pinch points after we get to Stennis, they’re primarily the unknown unknowns, right? We’ve had a lot of them in the factory.”