Artemis Transcends Apollo

The middle of July is not the best time to stand on a tarmac in New Orleans, given the oppressive heat. So, NASA chose the dawn of July 16, 2024, the 55^th anniversary of the Apollo 11 launch, to gather a crowd at its Michoud Assembly Facility to watch as crews rolled out the 212-foot-long core stage of its Space Launch System (SLS).

The rocket core stage is the largest NASA has ever built and it is an integral part of the Artemis program, which is working toward landing astronauts on the moon as early as this year. The event marked a major milestone for Artemis: The first time since the Apollo program that a fully assembled moon rocket stage for a crewed mission has rolled out of Michoud.

From Michoud—one of the largest manufacturing facilities on the planet—the stage would make a 900-mile journey by barge to the Kennedy Space Center in Florida, ready to be joined with the other SLS components.

“For over 60 years, Michoud has been America's rocket factory,” said NASA’s associate administrator Jim Free to the crowd assembled at Michoud, noting that this latest product was the only rocket capable of launching astronauts into deep space. “The work does not end here. We have big plans for the moon and we're going to need more SLS rockets.”

Much has changed in the 55 years since NASA last had big plans for the moon. Technology is the most obvious, having advanced greatly from the days of slide rulers and handwritten code. The purpose has changed as well. The Space Race was a scramble to be first to plant a flag on the moon. The Artemis program, on the other hand, will not only carry astronauts back to the moon but also aim to establish a permanent presence on the lunar south pole. Vital research carried out there could eventually help send humans to Mars.

But getting back to the moon is going to require quite the rocket. The design of SLS was unveiled in 2011, and the first variant, called Block 1, launched the uncrewed Artemis I mission around the moon in 2022. Four more missions are expected to launch before 2030, with Artemis II gearing up to send a crew of four astronauts to complete a lunar flyby in April 2026—just ahead of the United States's 250th anniversary. Artemis III is scheduled for mid-2027 and is set to be NASA’s first crewed lunar landing since 1972.

Building upon the engineering feats of the past six decades, more than 1,100 companies across the United States and at every NASA facility are supporting the program in some fashion. Although many of the same contractors, from Boeing to Lockheed Martin to Aerojet Rocketdyne, are developing solutions for Artemis much as they did on Apollo, they're using vastly different tools, solutions, and engineering knowhow.

Generating the kick

The 212-foot-tall, 27.6-foot-diameter SLS core stage is the largest rocket core stage NASA has ever built. Boeing is leading the core stage’s development, design, testing, and integration. Housed within 10 barrel sections, four dome sections and nine rings, the core stage has five major components: a liquid hydrogen (LH₂) tank, a liquid oxygen (LOX) tank, an engine section, the intertank, and the forward skirt. This portion of the SLS is the rocket’s backbone, both supporting and carrying the thrust generated by the dual five-segment solid rocket boosters from Northrop Grumman and four RS-25 engines from Aerojet Rocketdyne that are mounted to the engine and intertank sections.

Each booster is 12 feet in diameter and weighs 1.6 million pounds. Combined, the two boosters will provide a maximum of 3.6 million pounds of thrust during launch, which accounts for more than 75 percent of the rocket’s thrust during the first two minutes of flight.

All four engines use a staged-combustion cycle, which will require more than 733,000 gallons of cryogenic LH₂ and LOX housed in those two tanks, insulated with the help of an orange spray-on foam on the rocket’s exterior. They’ll burn propellant at the rate of 1,500 gallons per second.

“I still believe this LH₂, LOX staged-combustion machine is one of the greatest engineering marvels that's ever been concocted—and of course, it was conceived in the 1970s,” said Mike Lauer, RS-25 deputy program manager at Aerojet Rocketdyne. “We have 6,000 °F hot gas in the main combustion chamber and we have -400 °F hydrogen less than an inch away. It is just amazing heat transfer that is involved in an engine like that.”

Core stage 101

The core stage will only operate for a little more than eight minutes. In that short launch and flight time frame, it will propel the entire SLS system up to Mach 23 and off toward the moon.

“The RS-25 has a legacy of being the first reusable rocket engine,” said Kristin Houston, president of space propulsion and power systems at Aerojet Rocketdyne, at the Michoud rollout event. “It’s the most flight proven liquid booster rocket engine ever constructed.”

Even the new engines feature some reused components from previous space flights, such as high- and low-pressure pumps and valves. They also include components that were built for the shuttle program but went unused, such as the main combustion chambers.

Reusability has been a major consideration across the Artemis program.

“There are about a hundred components that are reused from mission to mission, and ultimately, we'll be reusing all the way up to the pressure vessel,” said Debbie Korth, Orion deputy program manager at NASA. “We reused about 20 or so components off of Artemis I on Artemis II, and then going forward, there are hundreds of components that will get reused.”

Careful monitoring is vital to ensure a robust reusability effort. Engineers know exactly how many times each piece has flown, where the life limits are, and how far each part can be pushed, Lauer explained. Every engine is tested, and they’re hot fire tested as a full system before being installed on a vehicle.

“The new ones, those really have only been tested once,” he said. “But the heritage ones, those have been through these magnificent space shuttle flights and we carefully monitor all the parts just to make sure that we're not going to push some component beyond its limit.”

1 - ENGINE SECTION

Delivers propellants from
the LH₂ and LOX tanks to

4 RS-25 ENGINES.

2 - LH₂ TANK

Holds 537,000 GALLONS of
liquid oxygen cooled to

-423°F.

3 - INTERTANK

Joins LH₂ and LOX tanks, houses avionics and electronics, and serves as the forward booster attach point.

4 - LOX TANK

Holds 196,000 GALLONS of
liquid hydrogen cooled to

-297 °F.

5 - Forward Skirt

Houses flight computers, cameras, and avionics—the brains of the rocket.

“Artemis is far more ambitious than anything humanity has ever done before.”

Jim Free—Associate Administrator, NASA

Streamlining production

Although all eyes are on the upcoming Artemis II mission, the multiyear nature of building these mammoth rockets means that the Stennis Space Center—NASA’s premier rocket testing facility in Mississippi, about 40 miles from Michoud—is already working on the launch system for a potential Artemis VIII.

“At Stennis Space Center, we have Artemis III and IV engines ready to go as well. Then what we've been working on is the next evolution of the rocket engine for Artemis V and subsequent missions," Lauer said. Hot fire tests were held at Stennis in early 2024 for Aerojet Rocketdyne’s new restart engine, which is similar to the space shuttle engines but is more affordable.

Of course, advanced manufacturing and robotics are playing a vital role in improving affordability and production speed, as is 3D modeling—a lot of the drawings from the recent Space Shuttle era were in fact still hand drawn, Lauer noted.

“We've done a whole lot of things to evolve it to this vehicle so we can make more of them and faster for future Artemis missions,” he added. “We have a whole bunch of 3D-printed metal parts on the restart engines. We'll take what was previously a bunch of parts welded all together, subtractively manufactured, and we will print it.”

3D models are also being used for performance, behavioral, structural, and thermal analysis, Lauer said. Computing advances allow for the manufacture of hardware to much tighter tolerances. The exploration upper stage (EUS), which will provide the thrust for inserting crewed capsules and other payload into lunar orbit for Artemis IV onward, was digitally engineered from the ground up, said Matt Stites, senior director and chief engineer of the Space Launch System program at Boeing. That allowed the team to move through the design phases much quicker.

“From a computing power perspective, what we can do today with analysis is very impressive and allows us to get much more accurate, higher fidelity models of what the rocket will see in flight and how it'll react,” Stites said. “It allows us to go in and mitigate any potential issues before they're discovered during flight testing.”

While robotic welding machines help speed production in some places, many elements on these engines still require the work of a skilled welder or technician, especially where robots can’t reach.

“We have some of the largest spacecraft weld systems in the world down at Michoud,” Stites said. “They use robotic weld heads to perform the friction stir welding for the SLS tanks and they really give us the capability and the ability to have more precise, better performing welds on our tanks, which lead to lighter, better performing tanks, giving more capability to the rocket.”

Friction stir welding was leveraged extensively across the SLS design, including all primary spacecraft structures. In fact, the entire LH₂ tank was made using one of the largest friction stir welding machines in the world at Michoud, said Amanda Gertjejansen, core stage assembly leader at Boeing.

Teams are even exploring powder bed manufacturing’s potential applications, working toward making some of the main combustion chamber parts, which is far beyond what was absolutely impossible in the 1970s or even just 10 years ago, Lauer added.

“It takes a ton of engineering and manufacturing connected together once again to make sure that what’s on the engineering drawings is resultant in the manufacturing process,” he said.

Even though the push has been to create easier-to-manufacture and less expensive engines, the heritage RS-25s were 100 percent reliable, so any changes must be made very carefully, Lauer noted.

“You don't want to use additive for everything—some things are just better to do in a conventional way,” he said. “But on RS-25 and especially the restart, we've very much focused, with NASA's partnership, on developing how to make high performance, very reliable, printed parts. And on the reliability and really understanding the metallurgy, because it's different than a forged part that you're making in a machine.”

The newly produced engines utilize a modern bonding process on the main combustion chamber, while easier-to-produce flex hoses replace flex joints, according to NASA. Streamlined manufacturing and simplified parts design eliminated more than 700 welds on these engines alone.

Even human workers are getting a digital assist. NASA’s prime contractors are equipping technicians with augmented reality glasses to help with processes such as installing the thousands of fasteners that attach the heat shield structure together or tie back the harnessing and cabling that goes around the vehicle, Korth explained.

“It used to be they'd have a drawing off to the side and measure where those pieces had to go. Measure twice, cut once—things that were just hugely time intensive,” she said. “Now with the augmented reality, all that's loaded in the view that they see. When they look at the spacecraft, they see where they have to put in those fasteners and it's got the parameters or the torques that they need to have, and all that's recorded as they do it.”

What used to take weeks can be done in a single shift. Such tools have been a huge enabler for building the spacecraft quickly and accurately, and in reducing assembly errors, Korth said.

Old and New: The RS-25 is the most flight proven liquid booster rocket engine. Two of the four Artemis II engines are already seasoned travelers. Engine 2047 flew 15 missions, including the final space shuttle mission, while 2059 flew five. Engine 2063 is the first built specifically for Artemis and 2062 is the last of the shuttle program’s 16 engines.

Artemis I Moon
Rocket Assembly

Step 1

Twin five-segment solid rocket boosters are stacked first on the mobile launcher.

Step 2

The core stage is craned in and secured between the two solid rocket boosters.

Step 3

The launch vehicle stage adapter (LVSA) is bolted onto the core stage.

Step 4

The interim cryogenic propulsion stage is lowered in and bolted into the LVSA.

Step 5

The Orion stage adapter is mated to the interim cryogenic propulsion stage.

Step 6

Pre-assembled, the Orion spacecraft is placed atop the rocket to crown the stack.

Flying firsts

During the 25-day Artemis I mission in 2022, NASA had planned 161 flight test objectives for the Orion space capsule to prove what the new spacecraft could and couldn’t do. The vehicle ended up performing so well that the team decided to do more.

“We added about 20 different flight test objectives during Artemis I, real time, during the mission, because we were learning so much from flying the ship. And those go to expanding the performance envelope that we allow ourselves to fly on the ship in future missions, so you're not as constrained,” said Lockheed Martin’s Blaine Brown, director of the Spacecraft Mechanical Engineering Organization, which is the engineering team that does the design, development, testing and certifications of all the mechanical systems for Orion.

Part of the challenge of launching a spacecraft when future iterations are already under design and construction is figuring out just what changes to integrate, especially when the spacecraft—Artemis II in this case—was already well under construction by the time Artemis I data was available. Or when issues arise on another part of the program, crews must determine whether it’s an isolated incident or if it will have wider implications across the larger program.

Never-before-flown systems also complicate the mission.

“Artemis II will be our first time flying crew and first time flying a full complement of life support equipment on there. We had limited life support equipment on the Artemis I intentionally,” Brown said. “So, we'll be learning how to operate and how the ship likes to operate itself during the mission and then we'll apply that to future missions.”

Engineers are even drawing from NASA’s past to find solutions for upcoming flights. For example, Artemis II’s thermal windows have three panes, compared to the space shuttle’s two thermal and single pressure panes.

“Our thermal panes are silica glass—fairly thick, very heavy, same things that flew on the space shuttle. Thermally great, but they're very fragile, so you have to be really careful handling them because any kind of scratch or defect could result in some kind of a structural failure,” Brown said. “There's a lot of attention, inspections, care, and handling that goes into those silica windows.”

However, following the Space Shuttle Columbia accident, crews discovered that a single airlock hatch that had an acrylic window survived the crash structurally intact.

“The windows team started investigating if there is a different application for those windows. What we've learned is that by replacing the silica windows with a specific acrylic, we can save a lot of mass, we can still get acceptable optical performance, and it can withstand the thermal environments,” Brown said.

In late 2023, the team completed an engineering board to make a design change so that Artemis III will fly with acrylic windows instead of silica glass, which will cut the ship’s weight by 50-100 pounds and reduce ground processing time and effort.

But circling back to the Artemis I flight, another element the team tested was a 16-foot-diameter protective heat shield on the bottom of the capsule. It was primarily made of an ablative material called Avcoat. In November 2024, NASA announced that its engineers observed unexpected variations across the heat shield and although a crew would have remained safe with this iteration, some of the shield’s charred material broke off after the vessel traveled through Earth’s atmosphere and experienced temperatures upward of 5,000 °F.

After an extensive investigation—done in parallel to other testing and installation work—engineers realized that gases generated inside the heat shield’s Avcoat layer could not vent and dissipate, causing pressure buildup and horizontal cracking near the charred layer's surface. With this in mind, Artemis II engineers plan to modify how far Orion can fly from the time it enters the atmosphere and lands, limiting exposure to extreme temperatures.

As a result of other lingering technical issues, some related to Orion's battery and its environmental control system, NASA decided in December to push the Artemis II launch from September 2024 to April 2026.

Then and now

While SLS isn’t as tall as the Saturn V—still the undisputed champ at 363 feet—it is more powerful, producing 15 percent more thrust than during takeoff and ascent thanks to the RS-25 engines and the solid rocket boosters.

“We did leverage a lot of technology from the shuttle. The notable orange color is very similar to the color of a shuttle external tank because both have cryogenic propulsion systems,” Stites said. “And so, with the LOX, LH₂, and the thermal protection systems, the foam that we use on the core stage is very similar to what was used on the shuttle. And it gives it that notable orange coloring when it gets out into the sun and when it ages.”

Artemis’s Orion spacecraft is also about 60 percent bigger than Apollo was, and able to hold four crew members for up to 21 days compared to 14 days for the three-person Apollo Command Module, Korth added. Several enhanced capabilities enable these longer future missions.

“One good example would be power. The Apollo modules use fuel cells, which limited their duration. We have solar arrays. Having solar arrays allows us to extend that duration of the spacecraft in terms of being able to stay on orbit,” she said. The panels enable the spacecraft to spend months in a quiet mode docked to a space station, which is envisioned as part of a future mission.

Avionics have been dramatically improved, as Apollo had just one 1960s-era flight computer, with the processing performance of a 1980s TRS-80. Artemis has two simultaneously operating computers, each with two modules, so essentially four flight computers that are about 128,000 times faster than Apollo’s and that are all redundant to one another, Korth added.

Redundancy and automation have been watchwords for Orion’s design, Korth said. “I think another big item is our crew safety and comfort items. A lot more radiation protection, not only for the crew, but for the equipment so that it doesn't get radiation hits and cause anomalies onboard.”

The astronauts’ suits are vastly improved so that each crew member could live in their suit for up to six days, with the ability to take in food and water and remove waste. Orion also has more capabilities to sustain a crew in emergency situations compared to past vehicles.

“Then of course, the cockpit is totally different. It's a glass cockpit, lots more sensors, more interactive, kind of more reflective of our digital age,” Korth said.

But ultimately this is the first deep space crewed spacecraft to be designed and built in more than five decades, so compared to the Space Shuttle, commercial space companies, and fellow space programs around the world, the Artemis program is working toward far different requirements.

“There are big differences in what it takes to fly to the moon and fly then to Mars, versus going to and from low earth orbit. Energy levels are significantly higher. You've got just overall spacecraft thermal controls that you have to monitor. Radiation is always a concern,” Brown explained. “It's a big step that a lot of people don't necessarily appreciate to go from low Earth orbit and then going around the moon.”

Extensive testing ensured confidence in the components and hardware on Apollo, but today, while there is still a fair amount of testing, engineers are doing an extensive amount of analysis, on stress and loads in particular, Brown added.

“We are very good at building up finite element models and then running detailed runs to zero in on where we might have overloading of a particular part. We use them for the design and then we use them also in supplementing our qualification program. You ground your models with truth data and then you have confidence that your models are working,” he said. “It's amazing, the amount of detail and accuracy that we get out of our models. I would say that's probably one of the biggest differences between what Apollo did and what we do.”

“The RS-25 has a legacy of being the first reusable rocket engine. It’s the most flight proven liquid booster rocket engine ever constructed.”

Kristin Houston—President of Space Propulsion and Power Systems, Aerojet Rocketdyne

Launches ahead

At KSC in November 2024, crews stacked the first of five segments for one of the Artemis II SLS rocket boosters onto mobile launcher 1—this was the very first component of the moon rocket to be stacked in the lead up to the anticipated 2026 launch.

At the same time, future missions are also rapidly coming together. The Artemis III crew module is being outfitted at KSC and its forward skirt and tanks will be shipped when crews are ready to integrate them. Artemis IV's primary structure is in place and its secondary structure is being installed, while the team is waiting for integration to start on the tanks. Artemis V is in the early stages, but work has started on the EUS, which is the upper stage that will replace the ICPS from the I-III missions, providing more thrust for heavier payloads on the Block 1B, the next iteration of the SLS rocket.

While work continues on all these upcoming missions, the lessons learned from Artemis II will be critical in helping NASA understand how humans can live and work far away from Earth.

“When we start doing the landing missions, one big aspect of Artemis is going to the lunar south pole, which is much more difficult to get to than the equator during the Apollo missions, but much more fascinating in terms of scientific discovery and the potential for in situ resources,” Korth said.

With the presence of ice on the moon’s south pole, future lunar researchers will be exploring how to use such resources to allow crews to remain there without regular resupply missions, along with understanding infrastructure and communication needs, and transitioning through zero gravity to partial gravity environments, and much more—all of which are building blocks on the path toward Mars.

“Our return to the moon is different now than it was during Apollo in many ways. It's going to be a team with global partners and companies pursuing new business opportunities. And in my opinion, this will continue to change the course of human history,” Free said. “Space exploration fuels new technologies, creates new industries, and cutting-edge research that improves our quality of life. We're advancing our understanding of the universe and creating good jobs with economic opportunity. More groundbreaking ways to live and work are just around the corner as we explore more of the moon than ever before. Artemis is far more ambitious than anything humanity has ever done before.”

Louise Poirier is senior editor.

All images courtesy of NASA

Image captions