11 years after the final flight of Atlantis, NASA’s next great rocket—the Space Launch System—is ready to fly. Teams have entered the launch countdown for the 42-day Artemis I mission, scheduled to launch on Monday, August 29, at 8:33 a.m. local time (12:33 UTC.) Final closeouts and preparations are complete at Launch Complex 39B, as the affectionately named “Mega Moon Rocket” begins to come alive leading up to its first flight.
Artemis I is a complete flight test of both the Orion spacecraft and Space Launch System rocket, two of the major systems required for the Artemis program. The mission, lasting 42 hours, 3 days, and 20 minutes, will see the SLS Block 1 rocket launch the Orion capsule into a lunar Distant Retrograde Orbit, where the capsule will loiter in orbit 40,000 miles (64,000 km) past the Moon for an extended checkout of all of its systems.
Critically, Orion will then return and re-enter the Earth’s atmosphere at over 25,000 mph (40,000 km/h), testing the spacecraft’s heat shield at its maximum capacity. The test of the heat shield at lunar return velocity is the most critical objective of the mission and is a must for the mission to be declared successful.
After splashdown off the coast of San Diego, CA, NASA and the U.S. Navy will recover the Orion capsule for Artemis I onboard an amphibious transport dock ship. The capsule’s avionics will be reused for the Artemis II mission, which will carry crew back to the Moon for the first time since Apollo 17. That mission is currently scheduled for 2024.
NASA completed the Flight Readiness Review for Artemis I on August 22, certifying that the Space Launch System rocket and the Orion capsule are ready for flight. NASA is taking what Artemis mission manager Mike Sarafin called a “lean-forward” approach to completing the mission’s objectives, most critically re-entering at a lunar return velocity. During a press conference, Sarafin stated that once the rocket lifts off, “we’re going to push for [a lunar transfer orbit] unless we’re sure we’ll lose the vehicle.” In turn, Orion does not have an abort motor for Artemis I, and the current abort system installed only has a jettison motor. This is not representative of the procedures for crewed flights and is only done in the interest of gathering as much data from the test.
During the review, two risks were identified with the rocket’s hydrogen systems ahead of launch, traced back to a leaky bleed valve on a 4” liquid hydrogen quick disconnect during the final rehearsal, WDR #4, in June. Artemis I launch director Charlie Blackwell-Thompson said “We believe we have taken all of the actions to correct [the bleed valve leak], but we could only test it in the VAB.”In other words, the valve cannot be tested in cryogenic conditions until liquid hydrogen starts flowing into the rocket in the hours before launch.
The faulty bleed valve also meant that a hydrogen “kickstart” to thermally condition the RS-25 main engines for launch could not be completed during WDR 4, and would need to be tested during a “quiescent” part of the countdown. Mission manager Sarafin said, “if we do not successfully demonstrate [the kickstart], we are not going to launch that day.”
Another consequence of the lack of a kickstart test during the final rehearsal was the countdown only making it to T- 29 seconds, which is the point at which the Ground Launch Sequencer (GLS) hands over control of the rocket to the onboard Automated Launch Sequencer (ALS). The GLS-to-ALS handover is a critical point in the countdown and is where many of the final pre-launch checks are conducted on the rocket.
While the lack of thermal conditioning on the RS-25 engines due to the bleed valve could be “masked” on the GLS, meaning that the sequencer would ignore the warnings and proceed with the count, the ALS did not have that mask and almost immediately halted the count at the handover. This means that the final half a minute of the countdown is still relatively uncharted territory, compared to the rest of the nearly two-day procedure.
“During WDR we got to 29 seconds,” said Blackwell-Thompson. “[After that] there’s a lot of dynamics that happen as you get down close to engine start., but there are things we would not have gotten even up to T- 9.34 seconds. ”
However, while these are risks for the countdown, they are not risks for the mission as a whole. The readiness review did not identify any major risks to the mission itself, with Jim Free, associate administrator of NASA’s exploration systems development directorate, stating that “we had no exceptions today. We actually had no actions coming out of the review and we had no dissenting opinions.”
With everything lining up and weather improving to 80% GO for Monday morning’s launch attempt, NASA, SLS, and the entire Artemis team is GO for the first launch attempt of the Space Launch System, and the Artemis program.
Liftoff is scheduled for 8:33:00 a.m. ET on Monday, August 29. The window runs to 10:33 a..m. ET. In the event of a scrubbed flight, the next possible opportunities within the launch period are September 2 and September 5.
Written by Lavie Ohana, Derek Newsome, and David Diebold.