SLS/Orion at LC-39B
The Space Launch System and Orion spacecraft arrive at Launch Complex 39B early Aug. 17 in preparation for a launch as soon as Aug. 29. Credit: NASA/Joel Kowsky

WASHINGTON — NASA’s Space Launch System made its third trip to the launch pad Aug. 17, this time with the intent of lifting by early next month.

The mobile launch platform carrying the SLS and its Orion spacecraft left the Vehicle Assembly Building at the Kennedy Space Center at approximately 10 p.m. Eastern Aug. 16, arriving at Launch Complex 39B at 8 a.m. Eastern Aug. 17.

This was the third rollout of the SLS/Orion stack, after previous rollouts in March and June for countdown rehearsals, and took place with little fanfare. In those earlier tests, known as wet dress rehearsals (WDRs), the rocket’s core and upper stages were loaded with liquid oxygen and liquid hydrogen propellants and the vehicle went through a countdown intended to stop just before the core stage’s engines ignited. NASA carried out four WDRs in April and June, declaring success after the fourth test June 20 even though it stopped early.

Now that the vehicle is back on the pad, prelaunch preparations will be “very similar to what we’ve done in the past,” Charlie Blackwell-Thompson, NASA Artemis 1 launch director, said during an Aug. 3 briefing. NASA planned an 11-day campaign of work at the pad to prepare for the launch, but the vehicle rolled out a day early, giving some schedule margin in the event of any weather or technical issues.

That work includes checking connections for data, power and other commodities at the pad, as well as servicing the solid rocket boosters, whose hydraulic power units will be fueled with hydrazine to operate their thrust vector control systems. There will also be “program-specific engineering tests” of the vehicle at the pad, she said.

For the first launch opportunity, a two-hour window that opens at 8:33 a.m. Eastern Aug. 29, the countdown will start with a “call to stations” for personnel nearly 48 hours earlier with tanking of the vehicle starting about eight hours before liftoff.

One change from the WDRs, Blackwell-Thompson said, is that a hold in the countdown before tanking starts is now an hour longer. “As part of our wet dress loading operations, we found that we needed a little additional time and we wanted to make sure we were all set up and configured for an on-time launch,” she said.

“I suspect we’ll continue to learn some things as we continue to go through our launch countdown,” she said, “but I am very pleased with where we are in our preparations.”

A launch on Aug. 29 would start a 42-day Artemis 1 mission, sending the Orion spacecraft into a distant retrograde orbit around the moon to test the spacecraft before returning to Earth to splash down off the coast of San Diego, California. Backup launch opportunities are on Sept. 2, with a two-hour window that opens at 12:48 p.m. Eastern; and Sept. 5, with a 90-minute window that opens at 5:12 p.m. Eastern.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...