At 6:35:12 PM EDT on April 1, 2026, the Space Launch System roared to life at Kennedy Space Center’s Launch Complex 39B, sending four astronauts toward the Moon for the first time in over half a century. You already know that. Every outlet on Earth carried the moment live.
What you probably didn’t see is the story behind the countdown — the automated sequencer that orchestrated thousands of commands in the final ten minutes, the flight termination system anomaly that briefly put the launch in NO-GO status, and the team that improvised a confidence test using heritage Space Shuttle hardware to get back to green. That’s the story worth telling.
The Countdown Decision Architecture
Most coverage of a rocket launch compresses hours of intricate choreography into “3… 2… 1… liftoff!” But the terminal count for SLS is a masterpiece of systems engineering that deserves a closer look.
At T-10 minutes, the Ground Launch Sequencer (GLS) assumed command. From this point forward, humans don’t fly the rocket to launch — the GLS does. It’s an automated system that orchestrates a precise cascade of commands across the SLS rocket, the Orion spacecraft (named Integrity for this mission), and all supporting ground systems. The sequencer exists because no human team can reliably synchronize the hundreds of actions required in the final minutes of a countdown with the timing precision needed for a safe launch.
Here’s what those ten minutes actually looked like:
T-10:00 — GLS initiates terminal count. The clock is now real.
T-8:00 — The Crew Access Arm retracts. The crew is sealed in. There is no more physical access to the vehicle.
T-6:00 — Three things happen nearly simultaneously: GLS commands core stage tank pressurization, Orion’s ascent pyrotechnics are armed, and the spacecraft switches to internal power. The umbilical cord to the ground is severing, system by system.
T-5:57 — Core stage liquid hydrogen replenishment terminates. The tanks are at flight level.
T-5:20 — The Launch Abort System (LAS) becomes available. The NASA Test Director notifies Commander Reid Wiseman that the abort capability is live. From this moment, if something goes catastrophically wrong, the LAS can pull the crew module away from a failing rocket in milliseconds.
T-4:30 — The Flight Termination System is armed. More on this shortly.
T-4:00 — The core stage Auxiliary Power Units start, providing hydraulic power to gimbal the RS-25 engines during flight.
T-2:02 — The Interim Cryogenic Propulsion Stage (ICPS) switches to internal battery power.
T-2:00 — The twin solid rocket boosters switch to internal power.
T-1:30 — The core stage makes the same transition. The rocket is now fully autonomous.
T-33 seconds — GLS sends the command: “Go for automated launch sequencer.” This is the point of commitment. From here, the sequencer runs to completion unless it detects an abort condition.
T-30 seconds — The core stage flight computer takes over from the ground sequencer. The rocket is now flying itself.
T-12 seconds — Hydrogen burn-off igniters fire beneath the engine bells, clearing any accumulated hydrogen gas that could cause an uncontrolled ignition on startup.
T-10 seconds — GLS sends the engine start command.
T-6.36 seconds — The four RS-25 engines ignite in a staggered sequence and ramp to full thrust. The vehicle is held down by the launch mount while onboard computers verify all four engines are healthy.
T-0 — Solid rocket booster ignition. Unlike the liquid engines, once the solids light, there is no shutdown. The hold-down posts release, the umbilicals separate, and 8.8 million pounds of thrust lift the 5.75-million-pound vehicle off the pad.
The entire terminal count is designed with recycle logic — at various points, if a parameter falls out of spec, the GLS can pause, recycle, and attempt again within the launch window. But once those solid boosters ignite at T-0, you’re committed. That’s why the go/no-go decision architecture front-loads every possible check into those ten minutes.
The Flight Termination System Scare
At approximately 4:48 PM EDT — less than two hours before the launch window opened — the countdown went NO-GO.
The issue was the Flight Termination System (FTS), and understanding why this mattered requires knowing what FTS actually does. Every rocket launched from the Eastern Range carries an FTS — an onboard system that can destroy the vehicle in flight if it veers off its planned trajectory toward populated areas. It’s the ultimate safety net: if the rocket goes rogue, the Range Safety Officer sends a coded radio command, and the FTS detonates shaped charges that rupture the propellant tanks, terminating thrust and ensuring debris falls in unpopulated zones.
The FTS is not optional. If the Range cannot verify that it can reliably communicate with the rocket’s FTS hardware, the launch does not happen. Period.
On launch day, engineers identified a communications issue with the hardware that relays commands to the FTS. The Eastern Range — managed by the U.S. Space Force at Patrick Space Force Base — reported they could not fully verify the system’s readiness through normal procedures.
What happened next is the kind of engineering improvisation that defines launch operations. The launch director authorized an FTS console operator inside the firing room to physically travel to the Vehicle Assembly Building next door to locate a piece of heritage equipment from the Space Shuttle program — hardware capable of receiving FTS commands from the Range — to serve as a confidence test for the troubleshooting effort.
Think about what that means operationally. In the middle of a crewed countdown to the Moon, an engineer walked to a neighboring building, found decades-old Shuttle-era equipment, and used it to independently verify that the Range’s command path to the rocket’s destruct system was intact. NASA stated at 5:11 PM that they had “devised a way to verify the system and are currently preparing to test this solution.” By 5:16 PM — roughly 28 minutes later — the issue was resolved and the Eastern Range went back to GO status.
This is what “devising a solution in real time” looks like in launch operations. It’s not a movie montage. It’s an engineer who knew what heritage hardware existed, where it was stored, and how to repurpose it as a diagnostic tool under time pressure. The launch window doesn’t wait.
Eight Minutes and Fourteen Seconds: The Ascent
At 6:35:12 PM EDT, the RS-25 engines and solid rocket boosters lit simultaneously (from the crew’s perspective — the engines actually ignited 6.36 seconds earlier). The vehicle cleared the tower in about seven seconds and immediately began its roll and pitch program, orienting for its trajectory northeast over the Atlantic.
T+0:56 — SLS went supersonic. Four humans were now traveling faster than sound, accelerating through thickening aerodynamic loads.
T+1:12 — Maximum dynamic pressure (Max-Q). This is the moment of peak structural stress on the vehicle, where the combination of velocity and atmospheric density creates the highest aerodynamic forces. Every component was designed to survive this instant. The vehicle pushed through it cleanly.
T+2:09 — Solid Rocket Booster separation. Each booster stands 177 feet tall and generates over 3.6 million pounds of thrust. Together, they provide more than 75% of the vehicle’s liftoff thrust. By this point, the SLS was traveling at roughly 3,100 mph (5,000 km/h) at an altitude of about 30 miles (48 km). The boosters, now spent, separated cleanly. With their mass gone, the core stage’s four RS-25 engines — burning liquid hydrogen and liquid oxygen — became the sole source of thrust.
T+3:13 — Launch Abort System jettison. This is a milestone that gets overlooked, but it’s operationally significant. The LAS — that tower-like structure atop the Orion capsule — is a 16,000-pound escape system designed to pull the crew module away from a failing rocket. Once the vehicle is high enough and fast enough that the LAS is no longer the best abort option (the crew module can separate and use its own systems), the LAS is jettisoned. Simultaneously, the spacecraft adapter jettison fairings that shielded Orion’s European Service Module were released. From this point, the vehicle’s aerodynamic profile changed entirely — and the crew’s abort mode shifted from “pull away on a tower” to “separate and fly the capsule.”
T+8:02 — Main Engine Cutoff (MECO). The four RS-25 engines, having burned for over eight minutes, shut down. The core stage had done its job: accelerating Orion to orbital velocity and placing it in a highly elliptical orbit with an apogee of roughly 1,200 nautical miles (2,200 km) — nearly five times higher than the International Space Station.
T+8:14 — Core stage separation. Twelve seconds after MECO, the massive orange core stage separated from the ICPS and Orion. The transition from powered ascent to upper-stage operations was complete. From this moment, the ICPS — a single RL-10 engine atop a hydrogen/oxygen stage — and Orion’s own European Service Module would handle all remaining propulsion.
The entire ascent took eight minutes and fourteen seconds from booster ignition to core stage separation. By any measure, it was clean.
What’s Happening Right Now
As of this writing, Orion Integrity is in orbit and operational.
The first post-launch milestone was solar array deployment. All four of Orion’s Solar Array Wings (SAWs) — mounted on the European Service Module built by Airbus — unfolded and locked into position. Each wing extends from the service module to give Orion a total wingspan of roughly 63 feet (19 m). Each wing carries approximately 15,000 solar cells and articulates on two axes to track the Sun, maximizing power generation as the spacecraft changes attitude. The arrays power everything — life support, avionics, communications, and the onboard systems that will keep four humans alive for the next ten days.
Next came the Perigee Raise Maneuver (PRM). Approximately 50 minutes after launch, the ICPS fired its RL-10 engine for the first time, raising Orion’s perigee (lowest orbital point) to a safe 115 miles. Without this burn, the spacecraft’s orbit would have decayed back into the atmosphere. When the spacecraft reaches its new perigee, it will execute a longer 15-minute burn — the Apogee Raise Burn (ARB) — to push the high point of its orbit up to approximately 38,000 nautical miles (70,000 km), establishing a 23.5-hour high Earth orbit.
After the ARB, something genuinely novel happens: the crew will conduct a proximity operations demonstration. Pilot Victor Glover will move into the commander’s left seat and manually fly Orion in formation with the spent ICPS upper stage, evaluating the spacecraft’s handling qualities using the Cooper-Harper rating scale — the same scale test pilots have used since the 1960s to rate aircraft handling. This is the first time a crewed Orion will be hand-flown in proximity to another object, and the data will directly inform future Artemis rendezvous and docking operations.
Meanwhile, mission specialists Christina Koch and Jeremy Hansen will be unstrapping from their seats to set up and test life support systems — the water dispenser, firefighting masks, the toilet. The mundane stuff that keeps people alive in a metal can 1,200 miles above Earth.
The Next Ten Days
The real mission is just beginning.
Flight Day 2 brings the critical Trans-Lunar Injection (TLI) burn. After the crew completes their high Earth orbit checkout and NASA managers review spacecraft performance, Orion’s European Service Module engine will fire to place the spacecraft on a free-return trajectory toward the Moon. This trajectory is the mission’s safety net — if the engine fails to fire again, the Moon’s gravity will sling the spacecraft around and send it back to Earth without any additional burns. It’s the same principle that saved the crew of Apollo 13 in 1970.
The outbound journey takes approximately four days. During this time, the crew will monitor systems, perform trajectory correction burns, and gather data on the effects of deep-space radiation and the Van Allen Belt passage. Two experimental payloads — AVATAR (A Virtual Astronaut Tissue Analog Response) and ARCHAR (Artemis Research for Crew Health And Readiness) — will collect real-time biomedical data that will be critical for future long-duration deep-space missions.
The lunar flyby will bring Orion to a closest approach of approximately 4,700 miles (7,600 km) from the lunar surface — specifically, the far side of the Moon. Some portions of the far side will be seen up close by human eyes for the first time.
The return journey takes another four days. But the real test comes at the very end.
Reentry will push Orion to approximately 25,000 mph (40,000 km/h) — the fastest any crewed spacecraft has ever reentered Earth’s atmosphere. And here’s the thing that keeps engineers up at night: the heat shield. During Artemis I in 2022, the uncrewed Orion’s AVCOAT ablative heat shield experienced unexpected “char loss” — portions of the ablative material eroded far more than models predicted. NASA spent two years investigating, established an independent review team, and ultimately decided to proceed with the existing heat shield for Artemis II — but with a modified reentry profile. Instead of the originally planned skip reentry (where the capsule bounces off the upper atmosphere to dissipate energy), the crew will fly a steeper entry angle to reduce time in the thermal environment associated with the damage pattern. Design changes to address AVCOAT permeability are planned for Artemis III.
Splashdown is targeted for approximately April 10-11 in the Pacific Ocean off San Diego, where the U.S. Navy will recover the crew using a San Antonio-class amphibious transport dock.
And if all goes well, the crew of Artemis II will have traveled approximately 252,000 miles from Earth — surpassing the record of 248,000 miles set by the crew of Apollo 13 in 1970. The farthest humans have ever been from home.
The Crew: More Than Names on a Patch
Commander Reid Wiseman is a Navy test pilot and former ISS crew member who has logged 165 days in space. At 49, he becomes the oldest person to leave low Earth orbit — a distinction that matters because it signals NASA’s confidence that deep-space missions aren’t exclusively for younger astronauts.
Pilot Victor Glover, a Navy fighter pilot who served as pilot on SpaceX Crew-1 to the ISS, becomes the first Black astronaut — and the first person of color — to travel beyond low Earth orbit. In the more than half-century since Apollo 17, every human who has left LEO has been a white American man. That changes today.
Mission Specialist Christina Koch becomes the first woman to travel beyond low Earth orbit. Koch already holds the record for the longest single spaceflight by a woman (328 days on the ISS) and participated in the first all-female spacewalk in 2019. Fifty-four years after Apollo 17, a woman is finally heading to deep space.
Mission Specialist Jeremy Hansen of the Canadian Space Agency becomes the first non-American to travel beyond low Earth orbit and to the Moon’s vicinity. Hansen, a Canadian Forces fighter pilot, was selected under a 2020 U.S.-Canada treaty that formalized Canadian participation in the Artemis program. His seat on this flight represents a concrete return on Canada’s investment in the program — including the Canadarm3 robotic system — and is a landmark moment for the Canadian space program.
Launch Director Charlie Blackwell-Thompson — the first woman to serve as launch director for a crewed NASA mission — summed it up in her final call to the crew: “Reid, Victor, Christina and Jeremy, on this historic mission you take with you the heart of this Artemis team, the daring spirit of the American people and our partners across the globe, and the hopes and dreams of a new generation. Good luck, godspeed, Artemis II. Let’s go.”
What It All Means
This mission is, by design, a test flight. It’s not landing on the Moon. It’s proving that Orion can keep humans alive in deep space, that the heat shield can survive a lunar-return reentry, that life support works beyond LEO, and that the spacecraft handles well enough for future rendezvous operations at the Moon.
But test flights are where the real engineering happens. Today, a team improvised an FTS verification using Shuttle-era hardware. A ground launch sequencer executed thousands of commands in ten minutes without a hitch. Four RS-25 engines — evolved from the Space Shuttle Main Engine, first flown in 1981 — burned for eight minutes and put a crewed spacecraft into an orbit five times higher than the ISS.
The countdown to the lunar surface starts here. Artemis II is the proof that the system works — all of it, from the engineers in the firing room to the ablative material on the heat shield. The next time SLS flies, it will be carrying a crew to orbit the Moon while a lander takes astronauts to the surface.
But that’s a story for 2028. Right now, four humans are settling into a spacecraft named Integrity, 1,200 miles above the Earth, preparing to fly farther from home than any human has ever gone.
We’ll be tracking Artemis II throughout the mission with updates on the TLI burn, lunar flyby, and reentry. Follow SpaceTechChronicles for technical coverage as the mission unfolds.
Sources: NASA Artemis II Launch Day Blog, NASA Mission Overview, Reuters, CBS News, Space.com, Wikipedia (Artemis II). All times EDT unless noted.
