The problems encountered by NASA on Monday seem to have been resolved, but the weather for the weekend is uncertain. Will the second try be the right one? After the interruption of the take-off of the SLS lunar rocket on Monday, NASA thinks it has resolved the technical problems encountered and has scheduled a new attempt on Saturday at 8:17 p.m. (French time). American meteorologists estimate that the chances of favorable weather, without thunderstorms or precipitation, are 60% by early evening. The conditions should even improve towards the end of the two-hour launch window, with a chance of being able to take off which should then reach 80%. This first flight, which does not carry any astronauts, is highly anticipated because the giant SLS rocket is for the moment essential to NASA’s Artemis program, which aims to return astronauts – and in particular the first woman – to the Moon from 2025. The last men to have set foot on our natural satellite are Gene Cernan and Harrison Schmitt, during the Apollo 17 mission almost fifty years ago. The scheme planned by NASA also resembles what was done at the time: the astronauts take off aboard a capsule, called Orion for Artemis, carried atop a giant rocket of a hundred meters high. The launcher of the day, SLS, develops even more thrust on take-off than the Saturn 5 of the Apollo missions. See also Artemis, NASA’s great return to the Moon Last Monday, engineers at the Kennedy Space Center in Florida decided to interrupt the launch attempt due to a sensor indicating that one of the rocket’s 4 large engines had not cooled down properly before it could be ignited. Before circulating ultracold liquid hydrogen and oxygen through the engines, the engines must be cooled to -250°C by circulating hydrogen at cryogenic temperatures. The operation seemed perfect for 3 engines, but not for a fourth. But it seems that despite the alert everything had in fact taken place normally during the countdown. John Honeycutt, head of the SLS program at NASA, explained Thursday that the engineers “conducted independent analyzes which confirmed that it was a defective sensor”. Has Artemis to the Moon been canceled? Reading between the lines of the explanations given by the American space agency, we even understand that under normal conditions, the countdown should not have been interrupted on Monday, because the temperature sensor in question was only indicative, and was not part of the hundreds of criteria that had to be “green” to be able to launch the rocket. In other words, the other parameters indicated that the engine had come down to temperature. But those responsible for the flight did not want to take any risks and preferred to “lose” a few days to understand the origin of the anomaly. Damningly for the US space agency, engine cooling procedures had not been able to be tested during the countdown dress rehearsals that took place in June and could not go all the way to the stage. final before the ignition of the engines, for lack of time. A loose bolt The postponement of a few days, however, allowed NASA to solve one of the problems that had arisen during Monday’s countdown. Technicians were able to repair a part on the launch pad that had caused liquid hydrogen to leak when filling the rocket’s fuel tank. “We were able to find what we believe is the source of the leak, and fix it,” said launch director Charlie Blackwell-Thompson. The anomaly, fortunately temporary during Monday’s test, was simply due to a loose bolt. On the other hand, NASA decided not to attempt to repair a crack in the insulating foam which was spotted on a part connects the first and second stages of the launcher. The risk of a piece of foam falling off on takeoff and hitting a fragile part of the rocket, as had caused the loss of the space shuttle Columbia in 2003, is considered negligible. To read also Mission Artémis: “Message to Beijing»By postponing takeoff from Friday, the date originally scheduled, to Saturday, the Artemis 1 mission which will carry the Orion capsule around the Moon will be slightly shortened, from 42 days to just under 38 days, with an Orion landing off California scheduled for October 11. If for an unforeseen technical problem or because of bad weather the take-off could not take place on Saturday, nothing will be attempted on Sunday. A takeoff that day would cause periods of eclipses during the trajectory, during which the capsule’s solar panels, provided by the European Space Agency, could not provide electricity. The following shooting slots would therefore be Monday 5 and Tuesday 6 September. After that, the SLS rocket would have to be brought back to its hangar to change batteries inaccessible from the launch pad. Beyond the additional delay that this would cause, NASA would like to avoid this return to the hangar, because the journey of a few kilometers on the enormous mobile platform causes unwanted vibrations for the launcher.