The engine that put John Glenn back in orbit is being bolted onto a Moon rocket

One of the four RS-25 engines now being bolted into the core stage of NASA’s next moon rocket is not new hardware at all. Engine 2048 last flew in 1998, on the space shuttle mission that carried 77-year-old Senator and former Mercury astronaut John Glenn back into orbit, and technicians at Kennedy Space Center began installing it, alongside three other shuttle-era engines, into the Space Launch System rocket assigned to carry Artemis III’s crew toward the moon.

NASA marked the milestone on 24 August 2026, the next phase of assembling the rocket’s core stage inside High Bay 2 of the Vehicle Assembly Building in Florida. The four engines the agency chose for this flight all carry their own individual flight histories, tracked by serial number across decades of shuttle missions, and Engine 2048’s history happens to include one of the most famous flights in the shuttle program’s run.

The Flight That Sent Glenn Back to Space

Engine 2048 powered Space Shuttle Discovery during STS-95 in 1998, the mission that returned John Glenn to orbit 36 years after his first spaceflight made him the first American to circle Earth. At 77, Glenn became the oldest person to fly in space at the time, a distinction that turned STS-95 into one of the most closely watched shuttle launches of the decade and made the engines that carried him a small piece of spaceflight history in their own right.

That flight was far from Engine 2048’s only assignment. NASA’s own account of the current core stage work notes that the same engine also powered Space Shuttle Atlantis during STS-129, a mission that carried NASA astronaut Randy Bresnik, who has since been assigned to fly on Artemis III, the very mission the engine is now being built into. Few pieces of hardware anywhere in the Artemis program carry that kind of double connection to a named astronaut on the flight they will eventually help launch.

Four Engines, Four Separate Flight Records

Each RS-25 engine carries a unique serial number that traces its complete flight history, and the four assigned to Artemis III, designated E2054, E2057, E2048 and E2052, all previously flew on space shuttle missions before the shuttle program retired in 2011. Reusing shuttle-era engines rather than building entirely new ones has been standard practice for the Space Launch System’s early flights, a way of putting already-proven hardware to work on the rocket that succeeds the shuttle rather than manufacturing an entirely new set of engines for every launch.

Weighing in at roughly 7,700 pounds apiece, each RS-25 produces close to 500,000 pounds of thrust and burns continuously for more than eight minutes during ascent, drawing propellant from the core stage’s two massive tanks at a combined rate of about 1,500 gallons per second. All four engines sit at the base of the rocket, integrated inside an engine section built to shield them from the extreme temperatures they generate during launch, a design carried over almost unchanged from the shuttle program that first flew these same four engines decades ago.

Assembling the Rocket Around Them

The engine installation follows the mating of the engine section to the upper four-fifths of the core stage earlier in the summer, and teams inside the Vehicle Assembly Building are continuing to install the remaining engines along with the stage’s propulsion and electrical systems. Elsewhere in the building, technicians are more than halfway through stacking the twin solid rocket booster segments atop the mobile launcher, work that began in early July and has moved faster than on previous Artemis flights as crews apply lessons learned from those earlier launches.

Progress on the Orion spacecraft that will carry the Artemis III crew has kept pace with the rocket taking shape around it. Engineers recently joined the capsule’s crew and service modules, installed the umbilical connector that bridges the electrical, data and fluid systems between the two sections, and powered on the spacecraft for the first time since that connection was made, confirming the communications and electrical systems between the modules work as designed. Neither the rocket nor the capsule is complete on its own; each depends on the other reaching the same point in assembly before the mission can move toward a launch date.

A Crew Already Training for the Rocket Taking Shape

NASA assigned Randy Bresnik, Andre Douglas and Frank Rubio, along with European Space Agency astronaut Luca Parmitano, to the Artemis III crew on 9 June 2026, and the four have since begun an intensive training flow covering Orion systems, mission science objectives and joint exercises with the companies building the commercial human landing systems the mission will rely on. Training is organized around the mission’s major phases, from ascent through orbit and rendezvous operations to entry and both pre- and post-landing readiness.

Much of that work has happened inside an Orion mockup at Johnson Space Center in Houston, where the crew has practiced daily spacecraft routines, tested camera equipment for documenting the mission, and completed water survival and post-landing emergency exit courses. In the Neutral Buoyancy Lab, the four astronauts suited up to practice exiting Orion in an upright configuration, and the crew has also run its first integrated simulation with the full flight control team, rehearsing mission timelines on the very rocket configuration Engine 2048 and its three companions are now being fitted to.

None of that training changes what makes Engine 2048 stand out among the four now bolted into place. Thousands of components go into a Space Launch System core stage, and most of them carry no story beyond their part number. This one carried a 77-year-old senator into orbit once already, and Bresnik into orbit a second time, before anyone had settled on the name Artemis III for the mission it is about to help send toward the moon.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.