Why Artemis I make so many zigzags to reach the Moon?

NASA will make the second attempt to launch Artemis I to the Moon on September 3, 2022. Once in space, what will the trajectory of the Orion capsule look like? This is shown in an animation, with many zigzags.

The Space Launch System (SLS), NASA’s impressive rocket, is still on its platform. The takeoff of its first mission, which is also the first of the Artemis lunar program, unfortunately did not take place as planned, on Monday August 29, 2022. Due to a technical problem, related to cooling of engine engines , NASA prefers to postpone the departure of Artemis I from the Moon, until Saturday September 3.

The Artemis I mission to the Moon was an unmanned test: no human crew needed to be in the cockpit. The goal is to send the Orion capsule around the Moon and then back to our planet. Thus, NASA can train for future manned flights to the stars, which should begin with the Artemis II mission.

Once launched into space, what will Artemis I’s path to the Moon look like? An animation, posted on August 31 by Tony Dunn, amateur astronomer, on Twitter, makes it possible to realize it. He considered updating the trajectory of the mission, at NASA’s Jet Propulsion Laboratory, after the cancellation on August 29. The trajectory depicted shows what should have happened from September 3 to October 11 (assuming that the launch has not yet posted).

Artemis I’s trajectory in space. // Source : Twitter @tony873004

Why do we see so many zigzags in this animation?

The movement of the capsule, which seems to zigzag, can be surprising. In fact, it is due to the choices made by the author of the animation, to make this view possible. As scientific commentator Pierre Henriquet explains to Numerama, “ the shape of the trajectory depends a lot on the frame of reference we choose to draw it “. In this animation, the reference frame is simultaneously centered on our planet and fixed on the axis between the Earth and the Moon. In other words, Tony Dunn made the choice to maintain the alignment between the two stars. In fact, the Moon revolves around the Earth.

It also made it clear that the spacecraft was orbiting the Moon, point Tony Dunn in another tweet. If I Didn’t Hold the Moon, You’d Just See Two Seemingly Unrelated Objects Surrounding the Earth. That being said, if you look closely at the distance between the Earth and the Moon in the animation, you will see that the gap between the two objects in the sky changes over time. ” The Moon approaches and recedes from the Earth during the journey, because its orbit is elliptical and the Earth-Moon distance is not constant. », added Pierre Henriquet.

If we try to draw the trajectory of Artemis I by taking another frame of reference, what do we see? ” In a classic geocentric reference frame, centered on the Earth and fixed relative to the stars, we see a very different trajectory. “, introduces the scientific mediator. That’s what happens:

trajectory artemis 1
On the left, the trajectory with the geocentric reference frame. On the right, the trajectory as depicted in Tony Dunn’s animation. // Source : Twitter @hervst

We see the same mission in both drawings. We see the stages of the mission: placing in Earth orbit, traveling to the Moon, placing in lunar orbit, returning to Earth. However, the image on the left has a drawback: it shows the path of the capsule less clearly, relative to the Moon. However, the image on the left is easier to see than ” the total duration of the trip would be more than one lunar orbit, so more than a month “, emphasized Pierre Henriquet.

Save a lot of fuel »

And if you’re still wondering why paths aren’t straight, it’s because they’re rarely the most energy efficient. We prefer to use the gravity of the stars for more efficiency. Result: the missions have more curved trajectories, higher, but which saves a large amount of fuel summarizes the scientific mediator.

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A view of Artemis I’s trajectory published by NASA also shows these curved shapes. // Source: NASA

Tony Dunn’s animation also clearly shows the shape of Orion’s orbit around the Moon: it is oval. During its journey in the lunar orbit, the capsule is at different distances from the star: it passes as close as 96 kilometers from its surface, up to 64,300 kilometers. No manned ship has ever made it that far, as Thomas Pesquet pointed out (whose comments were unfortunately picked up by conspirators, doubting that humans had ever reached the Moon).

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The SLS.  // Source: Flickr/CC/NASA/Ben Smegelsky (cropped photo)

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