Rocket delivered to launch site for first human flight to the Moon since 1972

The central piece of NASA's second Space Launch System rocket arrived at Kennedy Space Center in Florida this week. Agency officials intend to start stacking the towering launcher in the next couple of months for a mission late next year carrying a team of four astronauts around the Moon.

The Artemis II mission, officially scheduled for September 2025, will be the first voyage by humans to the vicinity of the Moon since the last Apollo lunar landing mission in 1972. NASA astronauts Reid Wiseman, Victor Glover, Christina Koch, and Canadian mission specialist Jeremy Hansen will ride the SLS rocket away from Earth, then fly around the far side of the Moon and return home inside NASA's Orion spacecraft.

"The core is the backbone of SLS, and it’s the backbone of the Artemis mission," said Matthew Ramsey, NASA's mission manager for Artemis II. "We’ve been waiting for the core to get here because all the integrated tests and checkouts that we do have to have the core stage. It has the flight avionics that drive the whole system. The boosters are also important, but the core is really the backbone for Artemis. So it’s a big day.”

The core stage rolled off of NASA's Pegasus barge at Kennedy early Wednesday, following a weeklong ocean voyage from New Orleans, where Boeing builds the rocket under contract to NASA.

Ramsey told Ars that ground teams hope to begin stacking the rocket's two powerful solid rocket boosters on NASA's mobile launcher platform in September. Each booster, supplied by Northrop Grumman, is made of five segments with pre-packed solid propellant and a nose cone. All the pieces for the SLS boosters are at Kennedy and ready for stacking, Ramsey said.

The SLS upper stage, built by United Launch Alliance, is also at the Florida launch site. Now, the core stage is at Kennedy. In August or September, NASA plans to deliver the two remaining elements of the SLS rocket to Florida. These are the adapter structures that will connect the core stage to the upper stage, and the upper stage to the Orion spacecraft.

A heavy-duty crane inside the cavernous Vehicle Assembly Building (VAB) will hoist each segment of the SLS boosters into place on the launch platform. Once the boosters are fully stacked, ground teams will lift the 212-foot (65-meter) core stage vertical in the transfer aisle running through the center of the VAB. A crane will then lower the core stage between the boosters. That could happen as soon as December, according to Ramsey.

Then comes the launch vehicle stage adapter, the upper stage, the Orion stage adapter, and finally, the Orion spacecraft itself.

Moving toward operations

NASA's inspector general reported in 2022 that NASA's first four Artemis missions will each cost $4.1 billion. Subsequent documents, including a Government Accountability Office report last year, suggest the expendable SLS core stage is responsible for at least a quarter of the cost for each Artemis flight.

The core stage for Artemis II is powered by four hydrogen-fueled RS-25 engines produced by Aerojet Rocketdyne. Two of the reusable engines for Artemis II have flown on the space shuttle, and the other two RS-25s were built in the shuttle era but never flew. Each SLS launch will put the core stage and its engines in the Atlantic Ocean.

Steve Wofford, who manages the stages office for the SLS program at NASA's Marshall Space Flight Center, told Ars there are "no major configuration differences” between the core stages for Artemis I and Artemis II. The only minor differences involve instrumentation that NASA wanted on Artemis I to measure pressures, accelerations, vibrations, temperatures, and other parameters on the first flight of the Space Launch System.

“We are still working off some flight observations that we made on Artemis I, but no showstoppers," Wofford said. "On the first article, the test flight, Artemis I, we really loaded it up. That’s a golden opportunity to learn as much as you can about the vehicle and the flight regime, and anchor all your models ... As you progress, you need less and less of that. So Core Stage 2 will have less development flight instrumentation than Core Stage 1, and then Core Stage 3 will have less still.”

Wofford said the next core stage for the Artemis III mission is about a year from leaving agency's Michoud Assembly Facility in New Orleans.

"To me, it shows that the SLS program is moving much more toward an operational program now," he said in an interview. "We’re not a single-shot deal. We’ve got the next one, and then we’ve got Core Stage 3, 4, and 5 that are in production inside the factory at Michoud. So we’re up and running, fully.”

But the core stage for Artemis III, which NASA envisions as the Artemis program's first lunar landing mission, won't be finished when it arrives in Florida.

Boeing is outfitting the Artemis III engine section, the most complex part of the core stage, inside a formerly vacant section of the VAB. Crews will put the core stage's propellant tanks together horizontally in New Orleans, then install the engine section and the RS-25 engines at Kennedy in a vertical orientation. Managers decided this was a more efficient way of doing the job for future SLS rockets.

Artemis III's launch date is highly uncertain. It primarily hinges on SpaceX's progress in developing a human-rated lunar lander and Axiom Space's work on new spacesuits for astronauts to wear while walking on the Moon.

NASA spent $11.8 billion developing the SLS rocket, and its debut was delayed five years from an original target date in 2017. But for Artemis II, the readiness of the Orion spacecraft is driving the schedule, not the rocket.

Feeling the heat

An unpiloted test flight of the SLS rocket and Orion capsule on the Artemis I mission in late 2022 set the stage for Artemis II. But there's a big question looming over Artemis II: Will NASA approve the Orion spacecraft's heat shield to fly as-is, or will officials order changes that could further delay the mission?

Chunks of charred material cracked and chipped away from Orion's heat shield during reentry at the end of the 25-day unpiloted Artemis I mission in December 2022. Engineers inspecting the capsule after the flight found more than 100 locations where the stresses of reentry stripped away pieces of the heat shield as temperatures built up to 5,000° Fahrenheit.

Earlier this year, NASA delayed the Artemis II flight from late 2024 until September 2025, mainly due to issues with the Orion spacecraft. The most significant unresolved issue is the heat shield.

NASA could decide on a path forward for the Orion heat shield in the next couple of weeks. Ramsey said an independent review team tasked with studying the heat shield issue will report to senior NASA officials next Thursday, August 1. NASA is also staffing an internal team investigating the heat shield problem.

The most likely decision will be to fly the Orion spacecraft, which has its heat shield already attached, without any major hardware changes. Instead, NASA could change the slope of the capsule's reentry trajectory to change the heating profile on the bottom of the spacecraft. Wholesale changes to the heat shield would delay the Artemis II mission at least a year, and probably longer, to take apart the Orion spacecraft, develop and implement a solution, and then reassemble the spacecraft.

The shipment of the SLS core stage to Florida and plans to start stacking the solid rocket boosters in a couple of months seem to reflect NASA's optimism.

Next steps

Here are a few things to track as the Artemis II launch campaign kicks off at Kennedy Space Center.

Over the next couple of months, technicians inside the VAB will finish some final touch-ups to foam insulation on the core stage and install hardware and ordnance for the rocket's flight termination system, which would activate to destroy the rocket if it flew off-course and threaten the public during launch. Ground teams did the same kind of work on the Artemis I core stage when it arrived in Florida, so Ramsey said NASA has a good idea of how long it will take.

The SLS mobile launcher platform should return to the VAB sometime in August from Launch Complex 39B, where it has been undergoing tests since last year. In September, stacking of the solid rocket boosters should get underway on the mobile platform.

"Once the Mobile Launcher is back in the barn, we’ll start stacking the boosters, and we’ll set the core stage in between the boosters and keep stacking. We’re shooting for September to start booster stacking, and that puts the core stage stacking in the December timeframe," Ramsey said.

Early next year, the upper stage will be installed on top of the core stage. At that point, Ramsey said NASA will likely roll the rocket, without the Orion spacecraft on top, out to the launch pad for a tanking test, which will involve loading cryogenic propellants into the core stage and upper stage.

This test will allow engineers to check the rocket and ground systems for leaks. NASA encountered hydrogen leaks during the Artemis I launch campaign, which delayed the launch for several months. The tanking test will also serve as an exercise for the Artemis launch team at Kennedy. There's also an alternative to do the tanking test with the Orion spacecraft on top, although that's a less likely option.

"Whether it has Orion on top or not is really the question," Ramsey said. "I think the current plan is to do a tanking test without Orion on top, and that would be after we get the ICPS (upper stage) stacked. So I’m thinking that’s probably very early spring or late winter of next year.”

The Orion spacecraft for Artemis II is undergoing tests inside a building a few miles south of the VAB. Once that is complete, NASA will transfer the spacecraft to different facilities at Kennedy for fueling and installation of its launch abort system.

NASA may also perform a complete practice countdown, perhaps within a few weeks of the launch. This wouldn't just be a tanking test, but it would include taking the countdown into the final minutes as a full-up launch rehearsal.

“We have the other option of doing a full wet dress rehearsal and that would be done much closer to launch," Ramsey said. "I think we’ll decide that once we kind of figure out what’s going on with Orion.”