Artemis I: why do we wait so long before relaunching the rocket?

The Space Launch System rocket, which is to launch the Artemis I mission, has still not taken off. It seems unlikely that the lunar mission will be launched before October 17, 2022, at the earliest. Why do we have to wait so long?

the imposing Space Launch System (SLS) rocket should remain on the ground for quite a while. While a second attempt to launch Artemis I towards the moon was to take place on September 3, 2022, NASA has decided to postpone the takeoff because of a technical problem. A hydrogen leak, which the agency was unable to stop, forced the launch of the first mission of the Artemis program.

NASA must bring the launcher back to the VAB (“Vehicle Assembly Building”), the building in which the rocket was prepared, which is near the launch pad. It is not known exactly when the SLS will emerge from it to attempt a new take-off, but it seems unlikely that Artemis I will be launched before October 17, at the earliest. But why do we have to wait so long?

The Artemis I mission cannot be launched every day

If NASA had been able to launch the mission at the beginning of September 2022, it would have had until Tuesday, September 6 to do so. The date ofa rocket launch does not only depend on weather conditions or whether the pitcher is ready. To launch Artemis I towards the Moon, we must also take into account ” complex orbital mechanics », has recalled The NASA. We cannot send the rocket into space at any time, since the positions of the stars must be taken into account for the mission (consisting of sending the Orion capsule to go around the Moon) to be possible. In this case, the alignment between our planet and the Moon. Remember that the Earth rotates on its own axis, while the Moon rotates around the Earth.

This is why NASA has established possible launch periods for Artemis I: they correspond to the days, or even weeks, during which the mission can be accomplished, if the SLS is launched at these times. The result is ” a pattern of approximately two weeks of launch opportunities, followed by two weeks of no launch opportunities », summarized NASA last May.

The 4 key criteria for correctly aiming for the Moon

The space agency explains that it takes into account 4 main criteria, specific to the Artemis I mission, to determine when launches are possible.

  • The take-off day depends on the position of the Moon in its own cycle. This is necessary so that the upper stage of the SLS can correctly predict the ejection of the Orion capsule, so that it can then fit into lunar orbit.
  • The trajectory of the mission must prevent the capsule Orion stays in the dark for more than 1h30 (what happens when the sun is eclipse, seen from the capsule). Thus, the ship’s solar panels receive enough sunlight, which they can convert into electricity, and Orion remains within a temperature range described as optimal.
  • The choice of a take-off date must take into account how Orion will return to Earth. The capsule must make a “jump entry” (” skip entry in English), a first for a vessel intended to be inhabited. The maneuver is reminiscent of ricochets on water: Orion will dive into the upper part of the atmosphere, then exit, and then return for its final descent. The Apollo program spacecraft entered the atmosphere directly. The technique chosen with Orion should allow for a more precise landing.
  • Finally, we must anticipate light conditions the day when Orion will have to be recovered in the Pacific Ocean, in order to facilitate the work of the personnel.

On what dates can Artémis I take off?

Taking all these considerations into account, NASA established the possible dates for the liftoff of Artemis I. The agency had thus planned that, if Artemis I could not leave on D-Day, there were 157 fallback dates left. On the following calendar, we see in green the dates on which the take-off of the mission is possible, with variations: in dark green, it will be a long mission (38 to 42 days); in light green, the mission will be shorter (26 to 28 days). This duration depends on the number of turns the capsule can make around the Moon: either a half turn or a turn and a half. NASA preferred to leave the choice to itself, to have more dates to launch the mission. In addition, no take-off can take place on days in red and gray.

NASA’s calendar with possible launch dates. // Source : Nasa screenshot

But it is not finished. To all this, we must add constraints, linked to the filling of the tank of the main stage of the rocket. On launch day, the tanks are filled with liquid oxygen and hydrogen. But, once this floor is full, if the launch is cancelled, the tanks will have to be replenished. Therefore :

  • There cannot be more than 3 launch attempts in 7 days,
  • There must be at least 48 hours between attempt n° 1 and n° 2,
  • And minimum 72 hours between attempt n° 2 and n° 3.

We can now resume the unfolding of events. A first attempt to launch Artemis I took place on Monday, August 29. The second attempt took place on Saturday, September 3. After this second test, NASA decided not to attempt any more take-offs in early September. We see on the calendar that this would have been possible until September 6: it is certain that these dates are now ruled out.

After 25 days maximum, return to the garage for the SLS

But, then, why not launch the rocket from September 19? We see on the NASA calendar a whole series of available dates, from September 19 to October 4 (with the exception of September 29 and 30). However, NASA cannot leave its SLS rocket out indefinitely. The agency must comply with the requirements of the Eastern Range (the range, managed by the US Air Force, which includes Cape Canaveral and the Kennedy Space Center), to certify the end-of-flight system of its launcher. This system is mandatory on all rockets, for safety reasons. But the rocket can’t stay more than 25 days on the launch pad, without the batteries of this system being checked – a check which must take place in the VAB.

Currently (as of September 6), the rocket has been on its launch pad since August 16. This is the date she was released from the VAB. Taking into account the 25 days, this means that she must leave the launch pad, at the latest… September 10th. That is, shortly before the date on which launches become possible again in September.

In addition, it is not yet known how long the rocket should remain in the VAB, once it returns there. This will likely depend on how long it takes to resolve the leak issue. We know at least the time it takes to drive between the assembly building and the launch pad: 8 a.m. to 12 p.m..

With all this in mind, it seems very unlikely that the rocket will be ready on the launch pad again, after returning to the VAB, for a launch before October 4. At the earliest, we can thus hope for a launch from the next date in green on the calendar, ie October 17.

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