Overnight on Tuesday, NASA’s Space Launch System moon rocket was ready for a voyage back to its launch pad in preparation for its long-awaited inaugural flight at the end of the month.
A powerful crawler-transporter from the Apollo era, carrying the 3.5-million-pound, 322-foot-tall SLS rocket and its 10.5-million-pound mobile launch platform, was expected to depart the Vehicle Assembly Building at the Kennedy Space Center at approximately 9 p.m. EDT to begin the 4.2 mile journey to pad 39B.
As soon as the mobile launcher is placed onto the pad’s pedestals early Wednesday morning, engineers will connect power, data, propellant lines, water lines, and other systems to ready the rocket for thorough pre-launch testing and checkout.
If everything goes well, the team will begin a 46-hour 10-minute countdown at 10:23 a.m. EDT on August 27, setting the scene for launch at 8:33 a.m. on Monday, August 29, marking the beginning of a 42-day mission to send an unmanned Orion crew capsule around the moon and back.
Depending on the ever-changing locations of Earth and the moon, and the need to refill spaceport propellant inventories, backup launch options are possible on September 2 and 5. NASA would then transport the SLS back to the VAB to replace batteries and other systems, postponing the launch until later in the autumn.
The objective of the Artemis 1 mission is to validate the performance of the SLS, test the solar-powered Orion crew capsule in deep space, and ensure that the ship’s 16.5-foot-wide heat shield would protect it through a hellish high-speed descent back to Earth’s atmosphere.
Assuming a timely launch, the Orion spacecraft is scheduled to splashdown in the Pacific Ocean west of San Diego on October 10 at 11:53 a.m. EDT.
If the test flight is successful, NASA aims to launch four humans on the second flight of the SLS rocket, Artemis 2, in 2024, followed by a third mission that will deliver the first woman and the next man to the moon’s surface in 2025-26.
The SLS is the world’s most powerful operational rocket, combining two longer shuttle-heritage solid-fuel boosters and four improved shuttle-era RS-25 engines to provide 8.8 million pounds of thrust at launch, 15% more than NASA’s famed Saturn 5 moon rocket.
The SLS is capable of launching almost 30 tons to the moon in its first “block 1” configuration. Planned variations with a more powerful upper stage and improved boosters will be able to transport roughly 50 tons to the moon on a single mission.
SpaceX is constructing a bigger, more powerful Super Heavy-Starship with twice the capacity, but it cannot accomplish this feat in a single voyage. Before sailing for outer space, the reusable Starship is meant to refuel in Earth’s orbit.
Last year, NASA conducted a full-duration test fire of the SLS core stage made by Boeing and its four Aerojet Rocketdyne RS-25 engines at the Stennis Space Center in Mississippi. The launcher was subsequently sent to Florida, where the United Launch Alliance-supplied second stage and Lockheed Martin-built Orion spacecraft were connected.
Engineers conducted four dress-rehearsal countdowns to clear the way for launch, but the tests were marred by ground-system issues, a stuck helium valve, and two problematic hydrogen leaks, one at the point where the main fuel line connects to the base of the core stage and another in a smaller fitting used to help cool the main engines.
Hydrogen leaks are notoriously difficult to detect and repair, since they only manifest when very cold propellant flows through the lines and fittings. Repairs must be conducted at room temperature.
Engineers successfully fixed the umbilical fitting, which functioned correctly during the second fuelling test. However, the “bleed” line for the main engine, which was fixed in the VAB after the most recent countdown rehearsal, has not yet been retested under cryogenic conditions. Not until the SLS is fuelled for launch on August 29 will this occur.