EXPLORATION SPATIALE - LE BLOG DE PIERRE BRISSON

Moon or Mars, that is the question!

Last week, media reported a change of focus by Elon Musk, essentially shifting from Mars to the Moon. However, a closer look reveals a more nuanced picture. Mars remains the primary objective. The Moon will rather be used as an analog or a simulation, while Mars will be a project undertaken only when it becomes feasible. This is by no means a renunciation, as the first crewed mission to Mars is projected for 2031, and that launching earlier would have been impossible (and the launch may well take place later, in 2033 or 2035).

Let’s review Elon Musk’s statements:

On Sunday, February 8th (on X): “For those unaware, SpaceX has already shifted focus to building a self-growing city on the moon, as we can potentially achieve that in less than 10 years, whereas Mars would take 20+ years.”

In these few words, Elon Musk seems to be really changing his mind.

His reasons are clear:

“It is only possible to travel to Mars when the planets align every 26 months (six-month trip time), whereas we can launch to the Moon every 10 days (two-day trip time). This means we can iterate much faster to complete a Moon City than a Mars City.”

But this doesn’t change the fact that his will to go to Mars remains well anchored:

“Mars will start in five or six years, so it will be done in parallel with the Moon, but the Moon will be the initial focus” (February 9, on X).

Now, five or six years lead to the June 2031 launch window, and in any case, without even “changing focus,” it is impossible to send humans to Mars any sooner. It’s important to remember that a crewed flight must be preceded by at least one successful robotic flight. We need to check the Starship’s ability to land on and take off from Mars, and prepare the arrival of humans on Mars. At the end of 2026 (first possible launch window), we might be able to make a first launch towards Mars, but with no more hope of landing than we had in February 2018 (with the maiden flight of Falcon Heavy) of driving a Tesla Roadster on Mars (although the car with its driver did cross the planet’s orbit in July of that year). In February 2029 (second launch window), if the prerequisites are met (especially checking that refueling Starship’s tanks in Earth orbit is possible), the first robotic mission could be attempted. However, if this mission were only successful in May 2033 (third launch window), it wouldn’t be a disaster given the project’s complexity. Let’s remember that the goal is landing a 52-meter-tall, 9-meter-diameter rocket vertically on unprepared terrain, without the possibility of remote control (on account of time lag), and afterwards, launching it back to Earth using propellants manufactured on Mars.

Therefore, in the period leading up to 2031 or 2033, it’s clear that SpaceX must perform as many deep-space flights as possible to fine-tune its Starship, and carry out as many experiments as possible that can contribute to making the grand adventure of establishing a lasting human presence on Mars, a reality. The Moon is there for that purpose.

And that’s fortunate, because SpaceX has a contract with NASA: to land on the Moon as part of the Artemis III mission.

This « shift of focus » is simply a way of telling NASA: « I haven’t forgotten you. Despite my interest in Mars, I want to fulfill my Moon contract seriously” (understating “so long it was just one commitment among others”). And at the same time, “don’t think I’m giving up my Mars project.”

Besides fulfilling its contractual obligations, what is in it for SpaceX?

1. To master its Starship by using it extensively.

2. To prepare the life support system, including its energy aspects, for the long journey (6 months to go there, 6 months to come back) and the long stay on Mars (18 months).

3. To develop the robotics necessary to support humans on another planet.

4. Start using local resources (keeping in mind that water is much scarcer on the Moon and that there is no atmosphere) because on Mars, given the limitations of transportation capacity and the impossibility of resupplying for 32 months (26+6), it will be imperative to apply the principle of ISRU (In Situ Resource Utilization) developed by Robert Zubrin, the founder of the Mars Society.

However, the Moon is not Mars.

Let’s first look at the positive points:

1. We can always go back from the Moon to Earth to retrieve something we have ‘forgotten’.

2. There is no significant time lag on the Moon compared to Earth. From this perspective, the lunar experience will teach us nothing for Mars.

But the negative points are far from being negligible:

1. Temperature differences are much greater on the Moon (+170°C; -200°C) than on Mars (+20°C; -100°C).

2. Living in a gravitational field of 0.16g (Moon)  will be much more difficult and probably much more unhealthy than living in a gravitational field of 0.38g (Mars).

3. The lack of an atmosphere will expose astronauts more to radiation and micrometeorite impacts.

4. The absence of a carbon dioxide (CO2) atmosphere will prevent humans from accessing the carbon and oxygen that can be obtained through a simple chemical reaction (known as the Sabatier reaction) using a small amount of hydrogen (which can be obtained on Mars through water electrolysis).

5. Scarcity of water will pose a greater problem on the Moon (ice hidden deep within craters that are difficult to access) than on Mars (ice sheets found almost everywhere on the surface, under a layer of regolith of varying thickness).

6. Nights on the Moon last 14 days instead of 24 hours and 39 minutes on Mars. This is a huge difference for attempting to grow crops in greenhouses. On the Moon, these activities will only be possible under artificial light (requiring energy, and solar panels cannot be used).

7. Above all, thanks to advances in robotics and artificial intelligence, particularly in the field of humanoids, we will be able to perform remotely via these robots everything that humans could have done physically on the Moon, with far fewer risks and much lower costs. A lunar city inhabited by humans is therefore largely unnecessary.

You can see that there are big differences between the two celestial bodies, but that certain things could be done on the Moon to prepare for going to Mars.

It cannot be denied that Elon Musk has also expressed concern. On February 9th, he wrote on X:

« The priority shift is because I’m worried that a natural or man-made catastrophe stops the resupply ships coming from Earth, causing the colony to die out. We can make the Moon City self-growing in less than 10 years, but Mars will take 20+ years due to the 26-month iteration cycle. That is what matters most. »

Elon Musk is expressing here the fear he has often voiced before of the destruction of humanity and the need to prepare as quickly as possible a shelter for everything we hold most precious, with the aim of making this shelter self-sufficient as soon as possible. Given our means of global destruction and the threats that recent political developments pose to our civilization, this is understandable. The Mars/Moon shift would reduce the risks involved in the time inherent in establishing a lasting presence on Mars on account of the difficulties of physical communication and the risks that result. These difficulties will always exist. But the know-how acquired after building Moon City (primarily, mastery of the Starship) will prevent hesitations and mistakes when SpaceX decides to “tackle” Mars, and it could shorten the implementation of self-sufficiency. That said, for the reasons outlined above, building Moon City will be technologically more difficult than building Mars City, and life on the Moon will be more difficult than on Mars.

From this perspective, the Moon City is a rather uninteresting project, except perhaps for gaining the experience of living off-Earth under very harsh conditions (Moon settlers will go to Mars for enjoying an easy life). In the long term, there will undoubtedly be manned lunar missions lasting a few days or a week to conduct inspections deemed impossible for robots (but which ones?). However, there will likely be very few candidates for a permanent physical settlement, or projects that will necessitate it given the Moon’s short distance from Earth. At best, it will be like Antarctica today. The Moon City does not have the bright prospects presented by Elon Musk this beginning of February 2026. He is mistaken on this point.

Fortunately, Mars remains his ultimate goal, and there is no postponement. The creation of a ‘Moon City’ should be seen as an optimization of time use while we wait to be able to do the same thing, but in a more essential way, on Mars. Those who support establishing a lasting human presence on Mars with Starship and Elon Musk can rest assured: the Optimus will continue to bear the logo of the Mars flight trajectory on their sleeves, and we will get there in 2035!

Copyright Pierre Brisson