While many families celebrated the holiday season last December, the anniversary of Apollo 8 quietly came and went for the 56th time. The mission, which captured the iconic “Earthrise” photograph and recorded a poignant reading from the book of Genesis, initiated a four-year renaissance of crewed lunar exploration which has not been matched since. Yet, there are signs that this drought may be drawing to a close. As NASA commemorated the anniversary of Apollo 8, its technicians were simultaneously stacking the twin Solid Rocket Boosters (SRBs) for the Artemis 2 mission. Last Wednesday (February 19th), they bolted the final nose cone in place, completing the assembly of the twelve pieces which make up the SRBs. If all goes according to plan, it is possible – perhaps likely – that Artemis 2 and its four astronauts will take flight within a year.
The past three months have been a period of flux for NASA’s five-year-old Artemis program. A prolonged investigation into the heat shield anomaly which threatened the uncrewed Artemis 1 test flight was completed in December. As a whole, the conclusions were positive. As AmericaSpace’s Jim Hillhouse recounted in detail, NASA is confident that they can tweak Orion’s trajectory during reentry and minimize the risk to the Artemis 2 crew without needing to replace the capsule’s heat shield.
However, because the investigation took approximately six months longer than intended, it initially pushed the conservative target launch date for Artemis 2 into April of 2026. In addition, the entire Artemis architecture is being reviewed as part of the ongoing transition between presidential administrations. It is possible that the program might be modified in order to constrain its ballooning schedule, reduce its cost, and/or accelerate crewed Mars missions, which currently are not slated to take place until the 2040s.
Independent of these strategic reviews, the Space Launch System (SLS) team at the Kennedy Space Center continues to march forward with preparations for Artemis 2. Currently, the focus is on the twin Solid Rocket Boosters (SRBs) which will lift the 5.75-million-pound rocket off of Launch Complex 39B. With 25% more thrust than their ancestors, which propelled the Space Shuttle into orbit, they are the most powerful rocket motors ever built. Combined, the two SRBs produce over 75% of SLS’ thrust at liftoff, and their primary role is to loft the rocket’s core stage and the crew’s Orion spacecraft above much of Earth’s atmosphere. At this point, the core stage’s ultra-efficient RS-25 main engines take over the primary responsibility for accelerating Orion to orbital velocity. When it takes flight, the Artemis 2 SLS will become the most powerful rocket in history to fly with astronauts onboard.
Each booster is broken into six large components: five cylindrical segments loaded with propellant, and a conical nose cone. This allows NASA and its prime contractor, Northrop Grumman, to transport them by rail from the landlocked manufacturing site in Promontory, Utah to the launch site in Florida. The boosters arrived at KSC in September of 2023, but they had to be placed in storage for over a year while NASA resolved a handful of issues with the delayed Orion crew capsule.
The Exploration Ground Systems (EGS) team specializes in assembling the numerous elements of the 322-foot-tall (98-meter) SLS. Some of the engineers and technicians on this team performed the same responsibilities during the Space Shuttle Program, which flew 135 missions using similar boosters and propellant tanks. On November 20th, they went to work, placing the aft segment of the left-hand booster on the Mobile Launcher. Its right-hand counterpart followed nine days later. The aft segments are largely responsible for the boosters’ iconic appearance. Each of them includes a nozzle to direct thrust, as well as a conical “skirt” containing powerful hydraulic pistons. This Thrust Vector Control system changes the position of the nozzle in flight, steering the rocket to ensure that it remains on its intended trajectory.
Shortly before the Christmas holiday, NASA began stacking the second pair of booster segments. This was a deceptively difficult decision, and the agency did not make it lightly. The thin metallic joints which connect the elements begin to slowly deform as they support the staggering mass of a fully-fueled booster segment. The boosters are only certified to be stacked for 12 months. To be clear, this is not a firm expiration date. Amit Kshatriya, a talented engineer who serves as the deputy director of the Artemis program, is confident that NASA will be able to safely extend the date if needed.
During a press conference on December 3rd, Kshatriya remarked, “We think we can easily get to 18 months, just based on historical understanding. Even if we went longer, there are ways to mitigate that concern by controlling the launch temperature if we have to go there” [1]. However, this step still indicates that NASA managers believe that Artemis 2’s most serious challenges are in the past and that they are reasonably confident in their new April 2026 target date.
With their most consequential decision behind them, the SLS team fell into a rhythm. They assembled the booster segments, one after the other, at a rate of roughly one segment per week. While this may sound slow, it reflects the complexity and the precision which the work demands. After lifting a new segment above one of the boosters, EGS technicians must construct a temporary cleanroom around the joint using metallic tubing and plastic tarps. This prevents contaminants, such as dust and hair, from being trapped between the two cases of propellant. Next, the two segments must be bolted together using over 100 individual metal pins, as well as three rubber O-rings. There cannot be any flaws in the joint, as there is no margin for error. A joint failure would have a similar effect to the O-ring anomaly which doomed the crew of the Space Shuttle Challenger in 1986.
Fortunately, the entire three-month stacking operation was relatively smooth. The only hiccup occurred in late January, when NASA had to temporarily pause work on the left-hand booster. In response to a query from NASASpaceflight’s Philip Sloss, the EGS program admitted that they encountered a technical issue [2]. Its exact nature was not specified. Evidently, the problem was not serious, as work resumed just two weeks later.
The two nose cones were the final SRB elements to be installed. The primary purpose of these pointed components is to minimize drag and enhance stability as SLS forces its way through Earth’s atmosphere. Each nose cone also contains four small motors which push the boosters safely away from the rest of the rocket when they are jettisoned. To commemorate the completion of the boosters, NASA held a media day on Tuesday, February 25th, which enabled AmericaSpace’s Jeff Seibert to capture many of the magnificent photos seen in this article.
While the booster segments are identical in function, each of them can be distinguished because of their unique markings. The most iconic is NASA’s classic red “worm” logo, which was reintroduced by NASA Administrator Jim Bridenstine in 2020. During Artemis 1, the same logo was featured on the side of each booster, facing directly outwards. However, technicians discovered that repainting the insignias every time they had to service the boosters’ electrical cables, which run through the same location, was a headache. Instead, the “worm” logos on Artemis 2 will be rotated forwards by about 45 degrees, so they will be visible when you view the rocket from the front.
Many observers are also curious about the black-and-white “checkerboard” patterns which adorn all five segments. These are called fiducial markers, and they are found on everything from prototype aircraft to crash test dummies. During the launch of Artemis 2, engineers will track the targets using high-speed cameras in order to measure the acceleration and vibration which the rocket experiences. According to a 2024 report by NASA’s Office of the Inspector General, some of these videos were underexposed during Artemis 1 because the mission launched at night [3]. The next launch provides a second chance to collect these valuable data. Since Artemis 2 is considered to be the final test flight of SLS and Orion before the vehicles are put into operational service, this will be the last rocket to feature fiducial markers.
While the boosters appear to be complete, NASA must still wrap up a handful of tasks. In particular, technicians are still wiring the segments together by running electrical cables along the side of each booster. These will be protected by thin covers called cable trays during flight. Once all of the electrical work is complete, the launch control team, led by Charlie Blackwell-Thompson, will run a series of tests to confirm that the boosters’ computer systems are running properly.
The completion of the SRBs is just one milestone in a sequence of many events which must be completed prior to Artemis 2, but it is still significant. Since they are broken into segments, assembling the boosters is the most time-consuming step in the entire stacking procedure. The rest of the rocket should follow in as little as two months. Regardless of what the future holds for Artemis as a whole, these visible signs of progress demonstrate that Artemis 2 is rapidly approaching. The cost of flying the mission, in both dollars and man-hours, is relatively low, and it would produce a major victory for the US space program at a time when China is making rapid progress with its own lunar ambitions.
Next up is the Artemis 2 Core Stage. SLS’ central element arrived in Florida last July to commemorate the 55th anniversary of Apollo 11. After spending several months in storage inside the Vehicle Assembly Building, it was lifted into a brand-new set of scaffolding in late December. NASA is using the new platforms to complete tasks which would ordinarily be done after the Core Stage is mated to the boosters. Among other things, the team installed the explosives in the Flight Termination System and put the finishing touches on the stage’s iconic orange foam insulation. Working on multiple parts of the rocket in parallel reduces the amount of time required to prepare it for flight.
Currently, the Core Stage is still supposed to be added to the stack at some point in March. Meanwhile, NASA is still defining a “work-to” target date for the mission. It is worth emphasizing that April of 2026 is a “no later than” deadline which contains a large amount of margin to accommodate unforeseen difficulties. The actual launch could take place weeks, if not months, before then if all goes according to plan.
Strange that such huge booster segments could be jeopardised by dust or even a strand of human hair.
” The cost of flying the mission, in both dollars and man-hours, is relatively low,” – Only a few $ billion more then ?
Interesting that they install the FTS explosives before slotting core between boosters.
Hi Rodney,
Thanks for your interest in these Artemis stories. I feel like I have seen your name in the article comments a few times now.
I do not know the exact reason why they need to protect the booster from small contaminants, but I cannot see any other reason to go through all the effort of building a cleanroom the boosters every time they integrate two segments. My guess is that they are worried about the field joints between the segments, which are more vulnerable than the rest of the booster and critical to mission success (as tragically illustrated by Challenger). I put a brief description of this type of joint, as well as a diagram, into this article:
https://www.americaspace.com/2024/11/26/artemis-2-stacking-begins-as-heat-shield-decision-looms/
NASA has not disclosed the remaining cost of flying Artemis 2, but I would estimate that it is in the low hundreds of millions of dollars rather than the billions. All of the hardware is complete. Even Orion, which was the pacing item for two years, just needs its solar array wings. They just need to pay for the labor required to stack the components and launch. Safely disposing of all this hardware (especially the SRBs, which are full of explosive and caustic solid propellant) would probably cost as much as flying it. Regardless of how Isaacman et al. decide to move forward with Artemis, I would strongly encourage them to go ahead with this flight.
The FTS sounds dangerous, but without the batteries which power it, it is no more dangerous than the propellant inside the SRBs. It needs an electric current to ignite. Like any other plastic explosive, it is relatively safe to handle, so long as you know what you are doing. Installing it separately just saves time and money. Shortly before they roll out for launch, they will arm the FTS by installing the batteries.
Best regards,
Alex
Hi Alex, Perhaps the “clean room” around the SRB joints is more for temperature control than dust elimination.
The cost of flying Artemis 2 : .. Could be huge. No one has any incentive to do it quickly or cheaply. Orion, SLS & EGS are costing ~ $ 3 Bn/yr ? and it’ll be at least 12 months until Artemis 2 launches, but could be over 24 months.
“Stack” and “launch” sounds cheap but there is a huge amount of testing during and after assembly, with an army of thousands on standby. Artemis 2 won’t achieve anything significant, but puts astronaut’s lives at risk.
Some would argue that if NASA continue and launch Artemis 2, they should also do Artemis 3 (to achieve the lunar landing) but that would be another huge expense for a publicity stunt that doesn’t help sustainable long term operations on the moon.
Lunar Gateway might as well be cancelled as well. It was never needed for lunar ops, just a practice for travel to Mars, and another reason to build and
The armies of people working on Gateway, Orion, SLS & EGS could develop payloads and spacecraft for Falcon Heavy, Starship and New Glenn to launch.
Best wishes to all – especially in Ukraine.
I’d prefer the SLS cores go to Interstellar Probe paid for by killing Lunar Starship.
I don’t want one dime of my taxes going to the New Spaz movement.
Oh look!
https://www.researchgate.net/publication/380812262_About_feasibility_of_SpaceX%27s_human_exploration_Mars_mission_scenario_with_Starship