Time is running out for NASA to send the Space Launch System (SLS) megarocket aloft for an uncrewed moon-roundtrip mission by November 2021.
Agency officials told reporters Thursday (Dec. 11) that the seventh of eight "wet dress" rehearsal exercises on the moon-bound megarocket at NASA's Stennis Space Center in Mississippi stalled because of temperature issues associated with ground equipment to fuel the tank.
The eighth test, a hot fire, is delayed to the last week of December as two weeks are needed to properly review the data from the wet dress rehearsal to prepare for the hot fire. But while the schedule is tight to deliver the rocket to NASA's Kennedy Space Center in Florida in time to make the planned November 2021 launch window for the mission, called Artemis 1, NASA said.
Related: Coronavirus pandemic delays key tests of NASA's new SLS megarocket
"We're getting to a point where we've got very little margin left in the schedule relative to our commitment to our delivery date," John Honeycutt, SLS program manager at NASA's Marshall Space Flight Center in Alabama, said during the Dec. 11 teleconference.
"With the issues that we've come up with associated with [local] storms and COVID, and the margin that we had built into the schedule for the green run, that [the schedule] is getting pretty slim," he added. "Now with that said, I've got a high level of confidence that we'll hopefully overcome operational challenges that we've got with the liquid oxygen system, and that the team will be able to swiftly execute the wet dress rehearsal and get into the hot fire."
He added that his team is "still laser-focused" on finishing the core stage, but safety will not be sacrificed in getting the SLS ready. A new wet dress rehearsal will probably happen next week, and if the rocket passes it will likely proceed to a hot fire during the last week of December. Should the hot fire finish well, the SLS rocket for Artemis 1 will ship to Kennedy in February, allowing just enough time to support a launch date in November.
"There's not anything wrong with the rocket," Honeycutt emphasized. "This is an operational deviation associated with how we load the liquid oxygen."
Timing on delivering the rocket is crucial for a couple of reasons. NASA still wants to send astronauts to the moon's surface by the end of 2024, and to do so requires that the SLS and its associated crew capsule, Orion, be certified for human spaceflight before that date.
Future missions of Artemis will not need a wet dress rehearsal or hot fire test as the SLS will already be certified for flight, Honeycutt noted. NASA also anticipates no meaningful delays due to the pandemic disrupting the supply chain for SLS, although the agency is keeping an eye on the individual suppliers to Boeing, which is building the two main stages of SLS. (Some of those suppliers are quite small companies). Subsequent SLS stages will be shipped directly to Kennedy for flight.
Earlier this week, NASA named the set of astronauts who will be considered for future missions under the Artemis program. The 18 astronauts include the person who will be the first woman ever to land on the moon. The 2024 deadline for putting those people on the surface, however, will be contingent on the success of Artemis 1 as well as ongoing funding support for NASA's budget.
On the technical side, NASA also needs to know when the SLS rocket will be ready for flight to proceed with the next stage of building the Artemis 1 megarocket, which is to add the solid rocket booster segments. The segments are ready at Kennedy, but they have a 12-month stack life. So, NASA needs to have word that the SLS is ready before considering approving stacking the SRBs.
The temperature issue arose when NASA transferred superchilled liquid oxygen, to fuel the rocket, from a holding facility to the core stage of the SLS. This procedure has been modeled and verified before, Julie Bassler, SLS stages manager at Marshall, told reporters during the same teleconference. But this was the first time the transfer actually took place.
"We were actually just a few degrees different than what we wanted to see coming in," she continued, but said the temperature must be precise during the initial phases of filling the tank. The requirement is minus 290.57 degrees Fahrenheit (minus 179.21 degrees Celsius.) But the liquid oxygen was slightly cooler, at minus 296.67 degrees Fahrenheit (minus 182.59 degrees Celsius).
"We filled up [the tank] just enough to pass the phase where we knew we weren't going to be able to get the temperature to a level that was going to be acceptable to meet the requirement, and that's when they caught us … in the testing," Bassler continued.
Whenever the SLS for Artemis 1 is ready for the hot fire, Maury Vander, chief of test operations at Stennis, told reporters that he is very much looking forward to the event — but he will be nervous.
"I guess I'm going to see if I can hold my breath for 480 seconds, because it should be something to see," he joked, referring to the length of the test. "It should be a heck of a ride," he added.
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