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

NASA will make a second attempt to launch Artemis I to the Moon on September 3, 2022. Once in space, what should the trajectory of the Orion capsule look like? An animation shows it, with lots of zigzags.

The Space Launch System (SLS), NASA’s imposing 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 the cooling of the engines of the machine , NASA preferred to postpone the departure of Artemis I to the Moon, to Saturday September 3.

The Artemis I mission to the Moon is an unmanned test: no human crew must be present 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 star, which must begin with the Artemis II mission.

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

The trajectory of Artemis I in space. // Source : Twitter @tony873004

Why do we see so many zigzags in this animation?

The movement of the capsule, which seems to zigzag, may surprise. In reality, this is due to the choices made by the author of the animation, to make this visualization possible. As the scientific mediator Pierre Henriquet explains to Numerama, ” the shape of the trajectory depends a lot on the frame of reference that 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 stationary stars. In reality, the Moon does orbit the Earth.

It also makes it obvious that the spacecraft is orbiting the Moon, Explain Tony Dunn in another tweet. If I Didn’t Hold the Moon Still, You’d Just See Two Seemingly Unrelated Objects Orbiting Earth. That said, if you look closely at the distance between the Earth and the Moon in the animation, you’ll see that the gap between the two celestial objects changes over time. ” The Moon approaches and recedes from Earth during the journey, because its orbit is elliptical and the Earth-Moon distance is not constant », adds Pierre Henriquet.

If we tried to draw the trajectory of Artemis I by taking another frame of reference, what would we see? ” On a classic geocentric reference frame, centered on the Earth and fixed with respect to the stars, we see a very different trajectory “, indicates the scientific mediator. That’s what happens :

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

We see exactly the same mission in both drawings. We find the stages of the mission: placing in Earth orbit, journey to the Moon, placing in lunar orbit, return to Earth. However, the image on the left has a drawback: it shows the trajectory of the capsule less clearly, in relation to the Moon. However, the image on the left is more convenient to see than ” the total duration of the trip will be a little more than one lunar orbit, so more than a month », points out Pierre Henriquet.

Save substantial amounts of fuel »

And if you’re still wondering why trajectories 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, longer, but which save substantial amounts of fuel sums up the scientific mediator.

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The visualization of the path of Artemis I 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 lunar orbit, the capsule will be at very varied distances from the star: it will pass as close as 96 kilometers from its surface, as far as 64,300 kilometers. No manned vessel has yet gone so far, as Thomas Pesquet pointed out (whose remarks have unfortunately been taken up by conspirators, doubting that humans have indeed reached the Moon).

For further

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

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