The journey of Artemis 2 to the far side of the Moon: The challenge of exploring what no one has ever seen

Only 24 people have seen the far side of the Moon with their own eyes in the entire history of humanity. All of them were men, Americans, and white: the crew members of the nine Apollo missions that traveled to the Moon between 1968 and 1972. Only five of them are still alive, and they are now over 90 years old. Now, four more astronauts — including a woman, a Black man, and a Canadian — will be able to join that select club if the Artemis 2 mission successfully completes its nearly 10-day space journey. The launch is scheduled for the afternoon of Wednesday, April 1, from the coast of Florida (U.S.), but it could be postponed due to any minor anomaly detected during the countdown or if the weather forecast worsens.

The first astronauts to travel to the Moon in more than half a century will not land there, nor will they even take the risk of approaching it to enter orbit, as the Apollo missions did. They will only circle it, at an altitude of more than 7,400 kilometers (4,600 miles). However, the advantage of staying at that safe distance is that they will have a privileged view of the far side: they will be the first people to see it in its entirety, gazing upon parts of the lunar surface never before seen by human eyes.

Commander Reid Wiseman, pilot Victor Glover, and mission specialists Christina Koch and Jeremy Hansen have been training for years to observe all kinds of craters, seas, and other geological features on the far side of the Moon. Until they lift off, they won’t know exactly what they’ll be able to see at that pivotal moment of the mission, during which they may also break a historic record: becoming the humans who have traveled the farthest from Earth. It all depends on the final launch date and time. That moment will determine that — when they reach the far side of the Moon five days later — they will find some areas illuminated by the Sun, while the rest will be invisible to them.

The possible launch dates in April result in a smaller illuminated area on the far side of the Moon than during the opportunities that arose in March. That is one of the reasons NASA wanted to rush preparations to start the mission as soon as possible. But a fault detected in the rocket’s upper stage, following a dress rehearsal, delayed the launch.

Circumnavigating the Moon

In this new space age, NASA is not willing to have the astronauts aboard the Orion spacecraft — on its first crewed flight — take the same risks that the Apollo 8 mission, the first crewed trip to the Moon, did in December 1968. Upon arriving there, the space cowboys on board had to slow the spacecraft by firing its engines at full power to enter lunar orbit. Artemis 2, on the other hand, will remain on a free-return trajectory, so called because the spacecraft turns and returns on its own, tracing a figure-eight path. It behaves like a boomerang, taking advantage of the interplay of forces exerted on it by the gravity of Earth and the Moon.

Using a free-return trajectory is the simplest and safest way for humanity to visit another world. But for all that choreography of trajectories and gravitational forces to work, the spacecraft must be launched toward the Moon on a precise day and time. This severely limits the launch windows, which in the case of Artemis 2 can only occur on five or six days of each lunar cycle. And on the day that is finally chosen, there are only two hours to attempt the launch. If the weather forecast for those hours is unfavorable, NASA will postpone the launch. This will be the most complex and dangerous of the mission’s six phases.

The Orion spacecraft is as wide as a van, though nearly four times as tall, and weighs as much as two buses. To launch such a massive vehicle into space and place it in a safe initial orbit around Earth — the essential first step in any space mission — requires a gigantic rocket like the SLS. Its total height, with the spacecraft inside, reaches 98 meters: it’s like a 30-story building, but loaded with two million liters of highly explosive liquid hydrogen.

All that fuel and energy is necessary for the vehicle to overcome Earth’s gravitational pull and ascend into space, to an altitude of more than 100 kilometers (62 miles). Once there, it must continue climbing and accelerating until it reaches a speed exceeding 27,000 kilometers per hour (16,777 mph), which is necessary to enter orbit.

The SLS is the largest and most powerful rocket to have achieved this feat in the entire history of the space race. In just eight minutes, it is capable of placing the Orion spacecraft into orbit, which will then take nearly an hour and a half to complete its first circle around Earth.

Once Orion is safely in space, NASA has designed a rigorous testing program that will continue throughout the first day of the Artemis 2 mission. The goal is to certify that the spacecraft is ready to carry humans to the Moon. To do so, the most practical approach is to launch it into a high Earth orbit — which on this mission will reach a distance of up to 74,000 kilometers (45,980 miles) — and thus send it into deep space.

No one has been this far from Earth since the Apollo lunar missions concluded in 1972. In addition to testing the spacecraft’s life support and propulsion systems, during this second, extended orbit around Earth, Orion will separate from the rocket’s upper stage and perform maneuvers to reapproach it. It is a slow and sophisticated space dance between the two components, lasting several hours and requiring manual control by the Artemis 2 pilot. It will serve as a first test run for what will be, in 2027, the main objective of Artemis 3: testing the docking between the spacecraft and the lunar lander — still under construction — which is essential for astronauts to set foot on the Moon’s surface during missions 4 and 5 of the program, currently scheduled for 2028.

Having completed its second orbit around Earth, the Orion spacecraft will once again be at an altitude of less than 200 kilometers (124 miles). A full day of testing will have passed, and it must be ready to embark on its true journey to the Moon. This is the decisive moment, and the spotlight will fall on the section designed by the European Space Agency (ESA) and built by Airbus. The European Service Module provides electricity — with its solar panels deployed — water, and temperature control to the capsule carrying the crew. Its engines will also propel the spacecraft for the remainder of the journey. One day, one hour, and 37 minutes after liftoff, it shoots toward the Moon thanks to the powerful thrust of the main engine.

Since this is a free-return trajectory — and the spacecraft will not enter lunar orbit — from that point on there will only be a few, much gentler firings of the service module’s auxiliary engines. These will serve to correct the trajectory, preventing the spacecraft from veering off course. A correction will be made approximately every 24 hours during the four-day journey to the Moon. Inside the crew capsule, which the astronauts on this mission have named Integrity, they will be preparing for the lunar flyby.

All missions to the Moon must orbit it, venturing into the far side — an area virtually unexplored by the human eye. This is the only way to view that lunar hemisphere, which we call the far side because it always faces away from Earth.

On the Artemis 2 mission, during that flyby, the astronauts may end up farther from Earth than anyone has ever been before — if the mission launches on April 1, they certainly will — breaking the record set by Apollo 13. Then, the far side of the Moon will appear as large as a basketball held at arm’s length. Although it may not seem like much, it is over 50 times larger than how we view it from Earth or from the International Space Station. In our sky, we never see the Moon larger than a pea.

The Artemis 2 crew will spend those central hours of the mission photographing and studying the details, colors, and even the shadows of the far side as they fly over it; and, especially, taking advantage of radio silence: the astronauts will lose communication with Earth for at least half an hour when they are on the other side.

That is inevitable — the Moon comes between them, acting as a barrier that telecommunications waves cannot penetrate — a silence that affects all lunar missions. It will end when Earth reappears in their view, at which point the Artemis 2 crew will attempt to recreate the Earthrise photograph, a true icon of science captured in 1968 by the Apollo 8 mission.

Once the observation phase of the far side is complete, the astronauts can relax. Since it is a free-return trajectory, the process is automatic: there is not a single maneuver required to initiate the return. Only, once again, slight course corrections during each of the four days of the return journey.

They will have the first of those days almost entirely to themselves. And from then on, they will also conduct scientific experiments, new endurance and spacecraft piloting tests, and public appearances via video calls with Earth. It is the final leg of a 10-day journey in a next-generation capsule, much more comfortable and better equipped than those used in the Apollo missions. Even so, the four astronauts will co-exist in a space the size of a large van, but with a multitude of instruments in the way, sharing the space 24 hours a day for the duration of the mission.

As the return nears completion, at an altitude of 120 kilometers (75 miles) above the Earth’s surface, the capsule will have separated from the rest of the Orion spacecraft. It will then use its own engines to maneuver into the correct angle for reentry into the atmosphere. The goal is to minimize the risks associated with this final stage of the journey, which is just as critical as liftoff.

It will be a 16-minute-long dizzying descent, starting when the crew capsule enters the atmosphere at a speed of over 40,000 kilometers per hour (24,855 mph) and begins to slow down, first due to friction with the atmosphere itself — which heats its hull to over 2,700°C — and then with the help of several stages of parachutes that deploy in sequence.

Finally, if all goes well, the speed will slow to that of a leisurely bike ride: traveling at about 30 kilometers (18.5 miles) per hour, the capsule will gently touch down on the Pacific Ocean, off the coast of San Diego, California.

During the fleeting and dangerous descent, the spacecraft also loses communication with mission control for a few moments. That brief suspense, preceding the splashdown that will conclude the mission, will give way to a waiting period of up to two hours. This is the time needed for the recovery ship to arrive and for a multitude of checks to be performed before the lunar travelers are brought on board.

They will go down in history as the four astronauts who resumed the conquest of Earth’s satellite after a half-century hiatus. And although they were unable to set foot on it, the lunar landscapes will remain etched in their memories. Views of craters and seas on the far side of the Moon that no human had ever been able to behold and that, thanks to their meticulous scientific work, will no longer be lost to time.

Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition