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 around 5:00 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 all four RS-25 engines were not at the prescribed temperature 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 when the first stage was being filled with liquid hydrogen. There was a similar problem on Friday when the first stage’s hydrogen refueling was switched from slow to fast mode. This problem was solved immediately on Monday. The new leak appeared at a different location on the second launch attempt, at a time when liquid hydrogen was still slowly being fed into the tank. 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.
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 take humans 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 will now withdraw to consultations and finally decide when the next attempt will take place. Originally, the coming Monday and Tuesday were mentioned as alternative dates. However, if more basic testing and repairs are needed, the next opportunity for launch would not be again until October – more precisely, probably not until mid-October, as Bill Nelson noted, due to a crew change on the International Space Station (ISS) in early October. The management team has announced an update for tonight at 10pm.