NASA’s Third SLS Wet Dress Rehearsal Could Be Late This Week
HOUSTON—NASA is looking beyond the planned April 8 launch of Axiom Space’s Ax-1 private astronaut mission to the International Space Station (ISS) to resume the Artemis I Wet Dress Rehearsal (WDR) at Kennedy Space Center (KSC), which has been scrubbed twice so far this week due to issues with the Mobile Launch Platform (MLP).
The planned two-day launch countdown simulation features the loading of 755,000 gal. of cryogenic liquid oxygen and hydrogen into the Artemis I Space Launch System core and Interim Cryogenic Propulsion upper stages. It began on April 1 and was stalled and ultimately halted by issues during the initial stages of propellant loading that arose on April 3, then on April 4 during the loading of liquid oxygen and ahead of the liquid hydrogen loading.
Members of NASA’s Exploration Systems Development, Artemis and Exploration Ground Systems leadership offered an updated post-Axiom-1 launch timeline for a resumption of WDR activities during an April 5 news media teleconference.
The MLP and SLS/Orion will remain at KSC’s Launch Pad 39B, where the hardware is currently powered down, according to Charlie Blackwell-Thompson, NASA’s Exploration Ground Systems Program Artemis launch director. It is possible the simulation could pick up with 36 hr. remaining to the finish line rather than starting over at the initial two-day point, she added.
“We are looking at our constraints relative to rolling in the lessons learned. It looks like we will take just about as much times as we’ll need for Axiom to fly,” Mike Sarafin, NASA’s Artemis mission manager, told the briefing. “So, we will fall in behind them. Exactly what date that is, we’ve got to finish sharpening the pencil on our open work. But we don’t anticipate it will be too much longer than after the Axiom launch.”
One factor that will be watched closely is the load limit placed on the MLP by the SLS rocket’s motion in response to wind speeds at the coastal launch site.
The most recent issue surfaced on April 4 with a panel in the MLP that controls an SLS core stage vent valve that relieves the pressure buildup during liquid oxygen tanking. With about half the core’s total 196,000 gal. of liquid oxygen loaded, the valve closed when it should have been open. The closed position of what Blackwell-Thompson characterized as a “manual valve” was confirmed by inspection following the scrub.
“Our team has accomplished quite a bit,” Blackwell-Thompson said. “This is a test, and the purpose of the test is to fully understand our system in a day of launch configuration. This is the first test in this configuration at the pad with cryogenics. So, it was a pretty big day for us.”
The first delay was called on April 3 to troubleshoot issues with primary and backup fans required to help pressurize enclosures within the MLP with air flow ahead of propellant loading to prevent a buildup of gases that could be harmful to launchpad personnel.
The steel, 21,000-sq.-ft. MLP rests atop a crawler transporter that moved the 32-story SLS from the Vehicle Assembly Building to Launch Pad 39B at Kennedy on March 17-18 in preparation for the WDR. Weighing nearly 11 million lb., the platform hosts a tower that rises 345 ft. to provide launch support personnel and hardware access to the SLS.
During the final hours of a countdown, the SLS core and upper stages are to be fully loaded with the two cryogenic propellants.
The WDR is to conclude with the two propellants being topped off as they evaporate. The launch control team is to hold the count at the 10-min. mark, then proceed to 33 sec. before what would be an actual liftoff. Then launch controllers are to cycle back to the 10-min. hold and resume the count to just under the 10-sec. mark and prior to what would be an SLS main engine ignition if an actual liftoff was planned.
Axiom Space’s Axiom-1 mission, the first U.S. commercial trek to the ISS and initially scheduled for an April 6 launch from Launch Pad 39A was moved to no earlier than April 8 following the April 3 WDR scrub. The 10-day mission with four private astronauts is to spend eight days docked to the ISS.
Houston-based Axiom is working with NASA to develop the first commercial orbital free flyer successor to the ISS later in the decade.
The AX-1 mission represents a first for the U.S., a milestone as NASA plans to transition its ISS operations to multiple commercial free flyers as the agency sets its sights on establishing a permanent human presence at the Moon with commercial and international partners in order to prepare for future human expeditions to Mars.
NASA-led ISS operations are currently authorized by Congress as well as the 15-nation space station partnership through 2024. NASA is working with its Russian, European, Canadian and Japanese space agency partners to extend the date to 2030, a goal endorsed by the Biden administration earlier this year.
Once the WDR is complete, the Artemis I SLS hardware is to be rolled back to the Vehicle Assembly Building atop the MLP. After the launch hardware and the simulation’s outcome have been assessed, NASA plans to set a launch date for Artemis I, which is to send the Orion capsule without astronauts on board around the Moon and back to Earth. A June launch date has been the target.
Artemis II, a second circumlunar test flight of the SLS and Orion with four astronauts on board, is to follow in 2024.
Artemis III, targeted for 2025, is to land astronauts on the Moon’s surface for the first time since the Apollo era when it touches down at the lunar south pole.
Two astronauts, delivered to the surface by a commercially provided Human Landing System, are to spend several days exploring the south pole region, which is believed to host large amounts of subsurface water ice, a potential life support resource and a source of liquid oxygen and hydrogen rocket propellants.
In addition to assembling a lunar-orbiting Gateway station, NASA and its international and commercial partners plan to establish a south pole base camp. With an annual cadence of crewed Artemis missions, these assets will also help prepare for future human expeditions to Mars.