Want to leave, don’t want to leave? For the third time, NASA has just postponed the launch of the Space Launch System (SLS), the giant rocket with which the American agency intends to bring a crew back to the Moon in 2025. This time it is the sky that is being pointed at. . Tropical Storm Ian has just turned into a hurricane and is expected to hit Florida overnight Tuesday into Wednesday. Heavy rain is expected, and state Governor Ron DeSantis has already declared a state of emergency.
The hurricane was southwest of Cuba on Monday. Moving north, it could reach Category 4 (on a scale that includes five) by midweek.
Return to the assembly building
The most powerful launch vehicle ever designed, the SLS was set to lift off this Tuesday at 11:37 (local time). NASA decided to shelter the rocket in the Assembly Building (VAB). An operation that is not trivial, being a monster almost 100 meters high and more than 10,000 tons. On August 16, it took him eleven hours to cover the 4 miles (6.8 km) that separates the Assembly Building from the legendary launch pad 39B of the Kennedy Space Center – the Apollo missions.
“The decision was made Monday morning based on the latest forecast for Hurricane Ian, and additional data collected overnight indicates that improvements should not be expected in the Kennedy Space Center area,” explains NASA on its blog. The rotation was due to start this Monday evening (11pm local time, or 5am Tuesday in Paris).
First two aborted launches
The launch of the SLS was originally scheduled for August 29, but a combination of technical problems (particularly with regard to cooling one of the four engines), time constraints, and worsening weather conditions had caused NASA to cancel it. Since then, the reports have continued to follow.
September 3, new trial. This time it was a leak in a hydrogen tank that forced the US agency to cancel the countdown. To carry out the repairs, it is planned to bring the launcher back to the assembly building. SLS finally remains on the launch pad, and the launch postponed until September 27. This delay forced NASA to ask the US Army to extend the rocket’s self-destruct system (which should theoretically be tested every 25 days), under penalty of having to bring the rocket back…
The authorization came late last week, but is it still important? Threatened by the hurricane, the SLS will still make its way to the assembly building, making it unlikely that it will launch before October 4 — the end of the current launch window. The next one opens on October 17th and runs for two weeks until October 31st.
Directly or indirectly, the first two launch delays are the result of hydrogen leaks. And again, a third leak was discovered on September 21 before it was closed. Like the American space shuttle (but also the Ariane 4 and 5 rockets), SLS is propelled by a mixture of liquid oxygen and hydrogen, but the latter is extremely volatile. As our colleagues from Numerama explain, hydrogen is the lightest of all the elements, the smallest gap becomes synonymous with leakage. And the equipment is put to the test, in contact with liquid hydrogen, whose temperature (-252°C) is not that far from absolute zero.
But as summarized earlier this month John Blevins, chief engineer for SLS at NASA: Hydrogen is a molecule that presents many challenges, but it is worth it”. Hydrogen simply remains one of the most efficient fuels for propelling a rocket. And to send the 21-ton Orion spacecraft to the Moon, SLS really needs power.
A program of 93 billion
For a program worth more than $93 billion that has already accumulated six years of delay, we understand that NASA is taking no chances. “The cost of two cancellations is much lower than that of one failure” had recently reasoned the head of NASA, Bill Nelson, during a press conference. The Artemis program’s successor to Apollo proposes nothing less than opening a new page in the history of manned flight by sending men back to the Moon to eventually establish a space station and a permanent base there, to harness the resources and then set out to conquer Mars.
The first three missions are already planned. Scheduled for this year, Artemis 1 should make it possible to make a first round trip between the Earth and the Moon. This is an automated, unmanned flight intended to validate the SLS rocket and the Orion spacecraft. Expected for May 2024, the Artemis 2 mission would see a crew of four astronauts (three Americans, one Canadian) take place aboard Orion. But they will settle for going around the Moon without trying to land. This privilege will be reserved for the crew of Artemis 3, the following year, if all goes well.
Reduced sliding windows
To understand the delays of Artemis 1, we must also keep in mind the technical limitations that come with this program. Even in 2022, sending men to the Moon is still a technological challenge (at least with acceptable risks): At 384,000 km, our satellite is about 1,000 times further away than the International Space Station. The launch windows are also reduced: the Moon must be in the right place for SLS to perform the necessary maneuvers for the translunar injection of the Orion spacecraft, the latter (partially powered by solar energy) must never be immersed for more than 90 minutes in darkness, the launch time must be calculated precisely so that the vessel returns to land in the Pacific Ocean and in broad daylight. An accumulation of constraints that leaves NASA engineers with spaces on the order of two hours at best. And that counts without the vagaries of the weather: The sky must be relatively clear, with no risk of rain or lightning… and even less of a hurricane!