NASA Sets Saturday as Next Artemis I Launch Attempt

NASA announced today it will try again on Saturday to launch Artemis I. The weather forecast is only 40 percent favorable and they are not completely certain why one of the four engines did not chill down to the correct temperature, but conveyed optimism that Saturday is the right day for a second attempt. The two-hour launch window opens at 2:17 pm ET.

Yesterday’s attempt was scrubbed when Engine 3, one of the four Aerojet Rocketdyne RS-25 engines that power the Space Launch System, did not chill down to -420 degrees F. The other three also did not reach that temperature, but were within acceptable limits.

John Honeycutt, SLS program manager at NASA, told reporters this evening that Engines 1, 2 and 4 were about 10 degrees short of the plan while Engine 3 was 40 degrees off.

SLS uses cryogenic propellants, Liquid Oxygen (LOX) at -294°F and liquid hydrogen (LH2) at -423°F. LH2 is run through the engines prior to startup to chill them down through a “bleed” system to avoid shock when the ultra-cold fluid meets the engine parts.

NASA intended to test this during the Wet Dress Rehearsal tests in April and June, but various anomalies prevented it, so yesterday’s launch attempt basically was the test. It failed.

Honeycutt said they think it’s a problem with the sensor, not with flowing the ultra-cold LH2 through the lines.

“We are questioning the fidelity of these sensors. These sensors are not flight instrumentation. They were designed only to be development flight instrumentation. We’re a little bit concerned about one of those sensors. One thing I can tell you is that we are seeing some goodness in the data and what the physics is telling us is that when we do establish that bleed flow in the vehicle and out through the umbilical into the vent line on the ground, we’re seeing good, cold liquid hydrogen. … I think where we are today is I think we have enough data to put the story together, but we’ve still got to go put the pieces together.”

Testing or changing out the problematic sensors would require rolling the rocket back to the Vehicle Assembly Building, which they would like to avoid. They successfully completed the engine chill-down of all four engines during the Green Run test at Stennis Space Center last year. They started it earlier then, so they will change that procedure on Saturday.

The launch team also is looking at the tail service mast umbilical where a hydrogen leak was detected yesterday. They were able to load the fuel anyway, but want to check it out over the next several days. That and the need to practice the new procedures is why the launch slipped from Friday to Saturday.

NASA has said for months that the launch could take place during this launch window only on August 29, September 2 or September 5.  They amended that a few days ago to say September 3 and 4 were possibilities depending on when the rocket was fueled.

Today’s announcement came after a meeting of the Mission Management Team. NASA Artemis Mission Manager Mike Sarafin said the MMT will reconvene on Thursday “to review our flight rationale and our overall readiness.”

Weather constraints are another complication. Yesterday the weather was 80 percent “go,” but Launch Weather Office Mark Burger said this evening that in the end the weather was no-go for the first hour-and-a-half of the two-hour launch window. For Saturday, the forecast is only 40 percent go, but he is optimistic that showers and thunderstorms will be sporadic, making openings for launch.