NASA Ready to Try Artemis I Again on Saturday and See What the Day Brings

NASA confirmed this afternoon that the second attempt to launch the Artemis I test flight will be on Saturday, September 3, at 2:17 pm ET. Readings that showed one of the engines did not chill down to the correct temperature have been traced to a bad sensor. Other anomalies have been solved or deemed to be within risk tolerances. Officials cautioned that many things could cause another scrub, but they’re ready to try and “see what the day brings.”

Artemis Mission Manager Mike Sarafin told reporters the Mission Management Team assessed the problems that arose on Monday and how they’ve been resolved, concluding they are comfortable with their flight rationale and risk posture to proceed with launch on Saturday.  Artemis I is an uncrewed test launch of the Space Launch System rocket and Orion spacecraft.

Although one sensor presented data that Engine 3 had chilled down only to -380 degrees F instead of -420 degrees F, engineers determined the problem was with the sensor, not the flow-through of cryogenic liquid hydrogen (LH2). Other “witness” sensors confirmed the temperature of the LH2 exiting the engine was satisfactory.

“We know we have a bad sensor,” SLS Program Manager John Honeycutt asserted. “We have convinced ourselves without a shadow of a doubt that we have good quality liquid hydrogen flowing through the engines. There’s no fuzz on that.” SLS Chief Engineer John Blevins agreed it’s “conclusive.”

SLS’s Aerojet Rocketdyne RS-25 engines use ultra-cold LH2 and Liquid Oxygen (LOX) as propellant. The engines must be “thermally conditioned” to prevent shock when they are flooded with propellant in the seconds before liftoff so LH2 is fed through them gradually first.

All four of these engines were tested at Stennis Space Center last year and the chill-down was uneventful, but it started earlier in the countdown. On Saturday, that timeline will be replicated.

Blevins said the troublesome sensor is not part of those that feed data to computers that determine whether the rocket is ready to launch or not so no software changes are needed.

The other anomalies were a hydrogen leak at the tail mask umbilical, a leak in a vent value, and cracked foam insulation.

The hydrogen leak was in the same place as during the third Wet Dress Rehearsal in June. Engineers repaired it after the vehicle was rolled back to the Vehicle Assembly Building. Launch Director Charlie Blackwell-Thompson said, however, that when they opened the “purge can” after the  launch scrub, they found a loose fitting and do not know how it became loose between the VAB and the launch pad. In any case, they retightened it.

A leak was detected in a vent valve when they increased pressure trying to get the LH2 to flow through Engine 3. Blackwell-Thompson said it really wasn’t a leak, though, but a seal that temporarily did not seat properly because of a temperature differential.

The cracked foam insulation is reminiscent of persistent problems with foam shedding from the space shuttle’s External Tank, from which the SLS Core Stage is derived. It happened throughout the shuttle program, but in 2003 caused a catastrophe. A large piece of foam struck the leading edge of the wing of Space Shuttle Columbia, creating a hole that allowed superheated gas to enter during reentry when the shuttle returned to Earth. The wing deformed and aerodynamic forces pulled the orbiter apart, killing all seven crew members. One advantage of the SLS/Orion design is that the crew capsule is on top of the rocket so would not be endangered by falling foam. Still, Sarafin said they are looking into it from a debris transport perspective, but are comfortable with the situation for this launch.

Sarafin nevertheless sought to set expectations for the chances of launch on Saturday:

“We’ve got to show up and be ready, we’ve got to see what the day brings.”

He identified three “big buckets” of potential showstoppers: technical, weather, and problems with the launch Range such as incursions by boats or planes into restricted waters or airspace.

Blackwell-Thompson said 489 launch commit criteria must be met.

Engine temperature is one, but violations could occur with any of them, including weather, during any attempt.

For this one, weather, at least, should be OK. Launch Weather Officer Melody Lovin said the forecast for Saturday is 60 percent favorable, and 70 percent on the backup day, September 5. She doesn’t see weather as a showstopper either day even though certain periods of time could be red, or no-go.

Sarafin’s bottom line: “There’s no guarantee we’re going to get off on the 3rd, but we’re going to show up and we’re going to try and we’ll do our best.”

If launch is on Saturday, it will be a 37-day mission with splashdown on October 11, according to Sarafin. September 5 is the backup day and he said they could also try on September 6 if they do not fill the tanks with propellant on the 5th.  After that they will have to wait until the next launch window opens later this month.