Mike Sarafin, NASA’s head of missions for the Artemis program, was right when he dampened expectations a little during the night from Tuesday to Wednesday when announcing the next launch attempt for the SLS moon rocket: “There is no guarantee that we take off on Saturday, but we will try.” In fact, the second attempt to launch the first unmanned moon mission Artemis I had to be canceled this Saturday at around 5:17 p.m. German time. This time at an even earlier point in the countdown than last Monday. The two-hour launch window would have opened at 8:17 p.m. At the time of the cancellation, the first stage oxygen tank was already fully filled, but the hydrogen tank was only 11 percent full.
The first attempt had already made progress: after a series of technical difficulties and the resulting delays, the stop only took place when, after the first drive stage had been fully refueled, it seemed as if not all four RS-25 engines were up to the prescribed speed temperature has been cooled down. In addition, a problem with a valve on the hydrogen tank was noticed, which supported the doubts about the successful cooling. After a thorough evaluation of the data from the first attempt to start, however, it was shown that the cooling was not defective, but that a temperature sensor was not working. Nothing stood in the way of a new start attempt a few days later.
A leak occurred early this Saturday while filling the first stage with liquid hydrogen when the first stage hydrogen refueling was switched from slow to fast mode. There was a similar problem on Monday, but the leak was much smaller and the problem could be solved right away. The new leak now appeared at a different location on the second attempt to launch. After three unsuccessful attempts to close the leak in various ways, the launch attempt was finally canceled by Charlie Blackwell-Thompsony, the NASA director responsible for the launch.
A third attempt next week is useless
The refueling of the rocket had already caused problems during the four attempts at the dress rehearsal, the so-called “wet dress rehearsal”, in April and June. There, too, leaks had repeatedly occurred during the hydrogen filling.
“We’ll start when everything is ready, not earlier,” commented Nasa boss Bill Nelson after the start, using almost the same words as on Monday. Here, too, he had already referred to his own experience as an astronaut when he flew into space on the 24th mission of the “Space Shuttle” in 1986. At that time the start had been postponed four times, but the actual start was then a picture book start, according to Nelson. The aim of the Artemis I mission is to test the system extensively before it should bring people to the moon. Anyone who has ever sat in a rocket knows that one is really happy when the launch team can guarantee that no risks are taken. “It’s part of the space business.”
The mission management then withdrew to a meeting to discuss how to proceed. At 10:30 p.m., Bill Nelson, Mike Sarafin and NASA Vice Director Jim Free appeared before the press and announced that the launch windows originally mentioned as alternative dates next Monday and Tuesday would not be an option. According to Sarafin, the next launch attempt will be possible at the earliest at the beginning or in the middle of October, depending on the analysis results of the team to be worked out by the beginning of next week. However, for a date at the beginning of October, the scheduling conflict with the then also planned launch of the “ISS Crew 5” must be clarified.
After the demolition on Saturday, the team discussed three possible options: reconnecting the corresponding supply line in the hope that the leak would be closed by itself in this way – this option was quickly discarded given the size of the leak. Alternatively, the team’s preferred solution is to remove and replace the launch vehicle’s consumable parts, either at the launch pad or in the assembly building. The rocket would very likely have to be moved into the “Vehicle Assemble Building” before a new launch attempt anyway.
Sarafin also reported that today when the tank was being filled, the prescribed pressure was briefly exceeded by a factor of two to three. Whether this could have been a possible cause of the leak must now be clarified. When asked in the press whether the SLS rocket might need an additional dress rehearsal instead of a new launch attempt, Sarafin said no. It is not necessary to try the entire process again. Jim Free added that this problem should still be known from the times of the space shuttle. In 1990, engineers would have spent the entire summer looking for hydrogen leaks.
