SLS dress rehearsal complete, ready for moonshot

The SLS dress rehearsal is complete!

Finally! NASA’s mighty Space Launch System, or SLS, completed a launch dress rehearsal on Monday (June 20, 2022) on the space agency’s 3rd attempt. NASA will host a press conference this morning (Tuesday 21) to update the media on the post-test status of the rocket. The rehearsal took place on historic Launch Pad 39B at Kennedy Space Center in Florida. It’s part of NASA’s preparations for the Artemis 1 launch to the moon, hopefully to be later this summer.

The SLS is the rocket that’ll launch the Artemis moon mission. And NASA technicians put the rocket through its paces on Monday, June 20. They pushed every button and flipped every switch, including filling the vehicle’s main fuel tanks … rehearsing each step except final ignition of the main engines.

The space agency’s Artemis blog offers this quick rundown of Monday’s activities:

The rehearsal will run the Artemis I launch team through operations to load propellant into the rocket’s tanks, conduct a full launch countdown, demonstrate the ability to recycle the countdown clock, and also drain the tanks to give them an opportunity to practice the timelines and procedures they will use for launch.

The NASA blog post also includes a minute-by-minute breakdown of each step of the SLS’s Wet Dress Rehearsal (WDR), which mimics exactly the actual ignition countdown.

Third time’s a charm

This was the third time NASA attempted to complete the Wet Dress Rehearsal. Two previous attempts – one in December 2020 and a second just months ago in March 2022 – both fell short of completing the shakedown of the moonship.

Once the SLS – NASA’s most powerful vehicle to date – is deemed fit to fly, its Orion spacecraft will make an uncrewed trip around the moon, a critical next step toward humanity’s return to the lunar surface and eventually Mars. The first crewed mission, Artemis 2, is scheduled for 2024. Artemis 3, which will put astronauts on the moon for the first time in 50 years, will fly no earlier than 2025.

The Artemis launch schedule depends on the completion of the critical Wet Dress Rehearsal.

Expect the unexpected

While NASA is confident in its latest and most powerful manned space vehicle, the two prior attempts to ready the ship for flight were cut short of the full WDR. NASA was looking for problems during yesterday’s successful testing, and it found one, a problem with a liquid hydrogen leak in one of the ship’s umbilical cables led to alterations in the testing schedule.

NASA cautioned those watching along that the listed times for WDR milestones were approximate, and delays could happen:

During the test, the timing for some events on account of several planned operational demonstrations tied to specific capabilities and test objectives may differ from the day of launch countdown. These demonstrations include tests on the cryogenic systems and an approximately three-minute hold inside the terminal count, which would not normally occur on launch day. If needed, the test team may also hold as necessary to verify conditions before resuming the countdown, or use the test window or extend beyond it, if consumables and resources allow them to complete test objectives.

Fill ‘er up!

Because of the freeze to address the hydrogen leak – Mission Control eventually decided to simply ignore the computer’s flag of the problem – the countdown was delayed but not halted, and the schedule was put back by several hours.

Filling of the SLS’s fuel tanks followed a “go” call by the launch director and the mission management team chair. Getting the entire fuel load aboard was scheduled to take five hours.

A 30-minute built-in hold was stopped the countdown for the final NASA test director briefing. The launch director’s poll of each launch team division for “go” or “no-go” followed.

When all lights were finally green on every control board and the leak issue addressed, the WDR Run 1 countdown resumed at T-10 minutes and counting.

The Orion ascent pyros were armed and the vehicle shifted to internal power. Seven minutes later, the ground launch sequencer sent the “cut-off” command, ending the countdown at T-33 seconds.

Following the tests, the vehicle returned to safe mode and cryogenic fuel drain operations began.

Bottom line: NASA completed the Wet Dress Rehearsal of the Space Launch System on Monday (June 20, 2022).