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The E.A.G.L.E Action Team of SGAC

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I hope everyone had a wonderful time during summer holidays 🙂

The next article on lunar economy takes me a while to prepare, so in the meantime I’m back with a short update !


I recently joined the Effective and Adaptive Governance for a Lunar Ecosystem (E.A.G.L.E.) Action Team of SGAC. 🦅🌕

For those not familiar with it, the SGAC (Space Generation Advisory Council) is a non-governmental organization for young people (18-35) passionate about space. I attend their events and use their online chats on WhatsApp/Slack to meet like-minded people of my age. 😉

We don’t have an official logo / visuals for the team yet, so I had to use my amazing graphic designer skills…

The goal of the E.A.G.L.E. Action Team is to develop a report 🕮 detailing the position of the young generations on the establishment of effective, fair and adaptative governance mechanisms for lunar activities.

Our work will be done in 3 phases :

  1. 🎧 A series of online hearings with representatives of various organizations who have a position on lunar governance mechanisms. We would like to meet as many people as practically possible, from non-governmental organizations, governments, space agencies, universities, private companies, space funds, … Please feel free to reach out if you think of someone who might be a valuable addition to our list!
  2. ✍️ Make a synthesis of the various positions and test them against some core values we share, like sustainability, inclusiveness, effectiveness, adaptiveness, and peacefulness. We will combine the different merits of each proposition in order to create something new.
  3. 💬 Share our conclusions with the rest of SGAC and collect their comments to make sure that our report truly represents the position of the young generations.

After we have produced the final report, we would like to share our work during UNCOPUOS 2021.

The Action Team is very diverse, we are…

  • 8 👩 / 6 👨
  • 🌍 from 10 different countries : USA, Canada, Mexico, UK, France, Belgium, Germany, Italy, Kenya, Saudi Arabia

Hopefully, we will produce a valuable addition to the landscape of lunar governance. We kicked off the hearings last week, so stay tuned for updates !

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Gas stations in space: Why? How?

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Last time, we talked about Delta-V, the “distance” to go from one place to another in space. We also talked about the rocket equation, used to compute payload mass fraction, and specific impulse… Let’s try to play with these concepts to have a better understanding of them, and unserstand why in-space refueling is useful.

But first, what is in-space refueling? It’s like refueling a car, but with the cryogenic propellant of a rocket (the thing we throw backwards to accelerate).

It can be done in 3 ways :

1) With an orbital fuel depot : a space station that stores propellant, and wait for our rocket to fill it. Obviously, the depot needs to be along our trajectory, otherwise it is pointless 😅

The american start-up Orbit Fab plans to build an orbital fuel depot around Earth. They developed a mechanical interface compatible with a lot of systems, and already flew prototypes to the ISS. The US industry leaders and politicians are currently studying the need for a “Space Strategic Propellant Reserve“.

2) With direct transfer from vehicle to vehicle, as proposed by SpaceX for the Starship. To achieve this, one needs to launch multiple vehicles in a short interval. A pretty big challenge!

SpaceX wants to connect two Starships together to transfer propellant from one to the other. NASA decided to work with them to develop this technology, mandatory for interplanetary missions with this vehicle. SpaceX may leave one of its Starships in orbit to act as a staging point for propellant, effectively used as a depot. The two concepts are not so different.

3) Simply with a “gas station” on the surface of a celestial body, like the Moon or Mars… or Earth. Yep 😛 on Earth, near the launch pads, there is a big gas station to fill the rocket a few minutes before it departs.

This illustration by James Vaughan shows a lunar base built in the permanently shadowed regions of the south pole. This idea has been proposed in the study Commercial Lunar Propellant Architecture from 2018 (a huge reference on this topic, which we’ll have more opportunities to explore in other blog posts!). Mined water is then split between oxygen and hydrogen to produce rocket propellant.

Now that we know what refueling is, and where it can be done: why is it useful ?

The rocket equation tells us that the further we want to go* (Delta-V increases), the more initial mass is needed for the same final mass… growing exponentially! 😟

* it is a difference in terms of energy (acceleration), not an actual distance.

Intuitively, we can understand the exponential shape: the fuel we use at the end also needs to be itself accelerated, because we carry it with us from the beginning. Therefore, we need more fuel, to push not only the payload, but also the fuel that we’ll use at the end. It’s a snowball effect.

Relationship between initial mass and final mass for a rocket whose specific impulse is 330 seconds.

Because it is not very convenient to build giant rockets, this relationship between initial and final mass limits either the Delta-V we can perform, or the mass of the payload we can carry.

It is also the reason why rockets sometimes have multiple stages (actually, each stage is a rocket that is the payload of the rocket below it): instead of transporting all the dry mass of the rocket all the way, after the fuel in the first stage is expended, we discard the first stage to decrease the dry mass.

Obviously, what is of our interest is the payload mass that we can carry to a given destination. So we should look at the equation in reverse. A rocket, once designed and built, has a given dry mass (its structure), and can contain a given maximum amount of propellant (its tanks). For a given rocket, the initial mass is therefore fixed. The further we go, the smaller the final mass – including payload – decreases.

No scale… No title… It’s just to understand the shape of this relationship.

For a rocket of 1500 tonnes (let’s dream big), a specific impulse of 380 seconds, a ratio between dry mass & propellant mass of 12.5% (1 tonne of structure for 8 tonnes of propellant), and a nominal mission Delta-V of 6000 m/s (enough for a one-way trip from LEO to Mars or the Moon)…

It gives us 1200 tonnes of propellant, 150 tonnes of structure, and 150 tonnes of payload. Weird of how it matches the first numbers SpaceX gave for its Starship. 😉

The chart looks like it:

Payload vs Delta-V for a rocket of 150 tonnes capable of holding 1200 tonnes of propellant.

How to read it ?

➡️ If we want to go to the Moon (6000 m/s), we can bring 150 tonnes of payload (vertical axis is marked every 100 tonnes).

➡️ With a propellant reserve full (1200 tonnes), if we want to do only 400 m/s, we can bring 400 tonnes of payload.

Actually, the fairing volume probably won’t fit 400 tonnes (unless we assemble the payload in orbit, without fairing…), so it means we don’t need to fully fill the 1200 tonnes of propellant if we “only” bring 150 tonnes of payload (the maximum we could fit).

To know how much propellnt is needed to transport 150 tonnes at 2000 m/s, we simply use the rocket equation:

  • m0/mf = 1/exp(-DeltaV/(9,81 * ISP)) = 1,71
  • mf = 150 (payload) + 150 (dry mass) = 300 tonnes
  • m0 = 1,71 * 300 = 513 tonnes
  • m0 – mf = propellant mass = 213 tonnes

m0 = initial mass, mf = final mass, DeltaV = 2000, ISP = 380 🤓

Let’s employ the same color scheme as last time. Here is how dry mass (constant, since it’s a 1 stage rocket), payload (max. 150 tons), and propellant mass (max. 1200 tonnes), changes vs. Delta-V.

After 6000 m/s of Delta-V, the rocket can’t hold enough propellant to continue sending 150 tonnes of payload all the way to destination. If we want to go further, we need to bring less payload. Beyond 8200 m/s, the payload is negative : these missions can’t be performed with this rocket. We would need to use multiple stages, or optimize the dry mass.

The lighter part of propellant mass represents the part of the propellant that is used to accelerate the payload, while the darker part represents the propellant mass used to accelerate the vehicle’s dry mass.


What has this all to do with refueling? Well, looking at these graphs, we understand something: if we could cut the 6000 m/s trajectory into 3 pieces of 2000 m/s, refueling 213 tonnes each time, we would only need 213 * 3 = 639 tonnes of fuel total to bring our 150 tonnes of payload to destination (instead of 1,200 tonnes). We could also make a smaller rocket, because it would not need large tanks capable of holding 1,200 tonnes. It would be lighter (less dry mass), and that would be all the more payload that we could carry each time!

For missions to the surface of the Moon, 6000 m/s of Delta-V from low Earth orbit (LEO), there is a great place to stop on the way: the Lagrange point n°1 of the Earth-Moon system (EML1).

The lagrange points between two bodies. In our example, M1 represents the Earth and M2 represents the Moon.

There is a point halfway between the Earth and the Moon where their gravities balance out. This region of equilibrium allows one to orbit around a point in space where there is nothing. 🤯

From this place, it is easy to go either to the Moon or to the Earth. The Delta-V to get there is pretty much like the Earth’s geostationary orbit (GEO), for which there are many launchers available. Existing launchers could therefore send payloads to EML1 with modest modifications.

If our spacecraft could refuel in EML1 on the way to the Moon, that would cut the 6000 m/s trajectory into two sections of 3800 m/s and 2500 m/s. The total is a bit larger (6300 m/s instead of 6000 m/s) because there are additional maneuvers compared to a direct path, but this has the advantage of “resetting the exponential” of the rocket equation. 👍

A total of 531 + 287 = 818 tonnes of propellant are required to make the trip and bring 150 tonnes of payload to destination, instead of 1200 tonnes.

This is why it is interesting to transfer fuel from vehicle to vehicle, or to build fuel depots in LEO, in lunar orbit, or elsewhere like in EML1.

Planetary bases producing fuel from local resources on the Moon and on Mars follow the same logic, because they allow to “reset the exponential” between the outward trip and the return trip.


The Starship’s mission architecture makes it “too big” for many uses, its fuel tanks will not be filled to the max all the time. Its transport capacity of over 100 tonnes makes it a vehicle for colonization and massive transport. It is both a reusable “second stage” and a lander. SpaceX relies on its assembly line production methods and on reuse to achieve (very) low transport costs, and be able to fly their vehicle without using it to the maximum without profit losses. It will be oversized for a lot of uses, but if it’s cheaper, does it matter?

It has nothing to do with the way we design rockets today, because we optimize everything to the maximum. However, this is not the case with planes or cars, which often travel partially empty.

In any case, the Starship is a vehicle that is made for Mars, sized to return from Mars without needing a first stage there. So that leaves room for competitors who would make vehicles optimized for other segments, for example LEO-Moon trips, or LEO-EML1, or EML1-Moon, … etc!

In its “Making life multiplanetary” presentation of 2017, Elon Musk explains how refueling extends the range of the Starship and its payload from low Earth orbit to Mars (27m2s).

To end this article, one last important point.

You may have already understood it, but the earlier you refuel a rocket in its trajectory, and the more often you refuel, the better.

Low Earth orbit (LEO) is already 9500 m/s away from sea level… And it’s impossible to stop before without falling! That’s why it’s the best place to make a fuel depot or refuel from vehicle to vehicle. If we can do other depots further, that’s better, but having one in LEO would change everything already.

A fuel depot in low Earth orbit, by Bryan Versteeg.

Most of the mass we send into orbit is fuel. If we had a LEO fuel depot, rockets could carry more payload, further.

A fuel depot would make launch mass to LEO fungible. This means that we could more easily exchange one tonne to LEO for another. We could launch the payload on one flight, and the fuel to propel it further on another. There could be missions without payload, only intended to refuel the depot, and missions with a large payload, without fuel but which plan to refuel at the depot. It would promote wholesale prices and big launchers (big rockets are more mass efficient). Competition would further reduce the costs of access to space. Fuel is fuel, no matter who launches it, so that would also facilitate international cooperation.

But most importantly: we could do ambitious missions with middle class launchers. No need for mega-rockets. This means that countries of modest size could do it too, and not just the superpowers.

Ariane 6 has a second stage (ULPM) much larger than Ariane 5 (ESC-A): it can contain 31 tonnes of fuel, compared to 14 tonnes for that of Ariane 5. It is particularly synergistic with a LEO depot, because if we could refuel the 31 tonnes of fuel in the upper stage of Ariane 6, we could send around 27 tonnes in TLI (intersection trajectory with the Moon), instead of 8.5 tonnes planned today.

It’s as much as the SLS block 1 mega-rocket with which the Americans are launching their Artemis program. We don’t have launchers like that in Europe, because we don’t have 15 billion € to invest in them. With refueling, you don’t need to invest that much!

It is also an additional step towards reuse, another vector for reducing costs. If you can refuel a rocket, why throw it away every time? Once empty, we refuel, and off we go for another mission! Once this technology is developed, I think we’ll see a lot more reusable second stages using technologies like IVF from ULA , and even second stages converted to landers like the XEUS .

Refueling will have a gigantic impact on the way we design and use spacecrafts, so even if today it is a technology that is still in development, when we consider sustainable development of space capabilities, it is with this paradigm that we must think. Planning today for systems that can adapt to this change, such as the Ariane 6 rocket and its large second stage, is the way to go!

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This time to stay

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The current geopolitical context somewhat ensures that lunar activities will get funded in the upcoming years. Even if we could consider it is not for the good reasons, it is an opportunity. Living in space will have a lot of side benefits, so maybe it is a blessing in disguise?

To make our return to the Moon sustainable, we will need to live there and use the local resources. The reason is obvious: it will increase initial costs, but reduce recurring costs. The spanish pioneers didn’t bring with them the necessary wood and stones to build the new world, they used what they found onsite. On a smaller scale, people like me who do hiking know how useful it is to be able to refill water & food during the trip, and not have to pack everything for multiple days… it really makes a difference!

Whether our lunar expeditions are expected to last 1 week or 1 year, the recurring cost of these trips will be smaller if we make an initial investment on infrastructures to use local resources.

A Hilton hotel on the Moon, Klaus Bürgle, 1970.

That’s what’s different about returning to the Moon today, compared to the 60s. Every major spacefaring countries share this vision, and the current NASA administrator repeats it often: “this time [we go to the Moon] to stay“.

This time to stay. Ok. How do we do? Why did we stop going there the first time? The answer is easy: it was too expensive to sustain, because sustainable presence wasn’t the goal.

In the 60s, we were barely starting to launch satellites, and the goal was mostly about making the trip, not what’s done at the destination. In 1961, Kennedy chose to lead the Americans to the Moon and do the other things “not because they are easy, but because they are hard”, and to do them “before this decade is out”. With such an ambitious goal, engineering and financing systems were put in place. To win the race and show that Americans could accomplish great things, swiftly. After they won the race, the nationalist euphoria fell down and public support declined, so the spendings weren’t acceptable anymore for politicians. Visited for the first time in 1969, the Moon didn’t see any boots since 1972.

Today, programs are no longer articulated around goals, but capabilities. There is still a broad objective, returning to the Moon before 202X, but the building blocks are put together one by one, step by step, instead of having a single big monolithic program. First the rockets, then crewed capsules, lunar landers capable of pinpoint landing, … soon, prospection rovers, lunar habitats, and in-situ resource utilization devices.

There is no specific roadmap, but one by one, the building blocks are coming to life, and we are getting closer to the Moon, because the future costs to reach it are getting lower and lower.

In the serie The Expanse, humanity has settled multiple locations in space. During the lunar night, Luna’s metropolitan areas are shining bright and can be seen from Earth. There is no doubt that earthlings will be captivated by this nocturnal spectacle, which will remind them every night that it is possible to dream big, that the sky is not a ceiling, and that there are endless other worlds to discover, explore, and where to settle.

Another big difference: some of these developments are done by private companies (especially in the USA, on the initiative of NASA). The government co-finances development costs, so it’s a bit artificial to say “private”. But once the initial research and development costs are absorbed, these private actors will be able to continue their lunar activities by requiring much less inputs from governments, who can then focus on the next steps (like going to Mars, or do some heavier base-building on the Moon), without sacrificing the continuity of the services they helped bring to life.

The goal of the U.S. is to build an ecosystem of private actors with complementing capabilities, that could buy services to each others, and where NASA would only be an anchor customer at first, then just one of many customers. International partners would be welcome in such an ecosystem, because they would also be bringing their own capabilities and services.

It may not sound very convincing, because it is a bit abstract. There are no business plans saying: I will invest X much, and after Y years I will have a return of Z. Everyone is completely in the dark, because nobody knows where we are going. We can easily imagine how certain services could emerge: transport companies, logistics companies, companies to manage energy networks, mining companies, construction companies, food and life support companies, waste processing companies, foundries, … But today, the pieces of the puzzle do not fit together, because there are no end customers. Who would want to go to the Moon and buy the services of all these people? What revenues will the lunar activities make to justify all these expenses?

At first, it will be the governments that will fill the lack of lunar “exports” (income from customers outside of Luna), and NASA is betting that inventiveness and the entrepreneurial mindset of the private sector will discover what lunar activities can sustainably finance themselves in the future.

It was impossible, in 1788 when the British crown established the Sydney penitentiary camp, to know that 60 years later it would become a democratic state exporting thousands of tons of sheep wool every year, today the 14th nation in terms of economic power. Christopher Columbus did not go to America with the goal of building tobacco farms and boat factories.

It’s impossible to know in advance what businesses will work. I personally think that lunar exports will be mostly intellectual (tourism, sports in reduced gravity broadcasted over the internet, intellectual property of innovations stimulated by this new environment, totally regular rocks but sold at a premium price because they come from the Moon, …), because massive physical exports would require a lot of improvement on rockets. But who knows what tomorrow will bring? When we talk about a 60-year horizon, we are talking about a horizon where young people (or even not yet born today) will be at the end of their professional careers. A lot of things can happen in the meantime…

By starting today with activites sponsored by governments, what will the Moon look like in 60 years? If we don’t go, we won’t know.

The Moon is not such a bad place. Life is artificial there, and machines are omnipresent, sometimes noisy… But it’s very stimulating, everything still has to be built. Looking up, we can always remember that our loved ones are not far away, and that it is not only for them that we are here, but also to open a future rich in discoveries and perspectives for all the others who are on this big blue sphere. The journey only takes a few days, like faraway boat trips, and communications only take a few seconds, so we can make video calls. It will feel like abroad studies in a very exotic place and a poor internet connection. In fact, some people might do their PhD there someday. In the ubiquitous machines, people from Earth are operating in telepresence, so even if their body is mechanic and not organic, you never really feel left out. There are only a few people on the base, but there are thousands of others up there, working their asses off to help us day and night. There are millions more following our adventure through social media and documentaries.

Image by SOM representing the Moon Village proposed by ESA.
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First come, first served?

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Last week, we talked about the geopolitics of returning to the Moon. Is is really rational to think that the first to arrive on the Moon will be in a position to prevent others to do their own business there (like some in China and the U.S. are arguing)? That returning on Luna will be a cruel and lawless Far West remake if we don’t take action to regulate it now (as is sometimes suggested by space policy folks & UNOOSA)?

Let us recall this quote from Ye Peijian, a sad witness of the zero-sum game mindset:

“The universe is an ocean, the Moon is the Diaoyu Islands, Mars is Huangyan Island. If we don’t go there now even though we’re capable of doing so, then we will be blamed by our descendants. If others go there, then they will take over, and you won’t be able to go even if you want to. This is reason enough.”Ye Peijian


Recently, we discovered the presence of permanently shadowed regions in some craters of the lunar poles. Because the sunlight never hits them, they are very cold, and some ice accumulated there. A nearby lunar base will be able to extract water 💧 and other useful stuff for our survival there and our return trip to Earth : no need to bring everything with us.

Moreover, there are nearby mountains (dunes?) so high thay they are almost permanently bathed in sunlight ☀️ (almost: they still have <90% illumination time, see this NASA video showing day and night cycles). That’s very convenient to use solar panels, and not have to wait until we have space-certified small nuclear reactors.

It’s the place to be, so chances are everyone will want to settle there at first.

“The” south pole and its permanently shadowed regions sounds like a small place. What about it ?

Map of the permanently shadowed regions of the lunar south pole, highlighted in blue. Illustration by Ernie Wright, 2013.

Let’s keep in mind that this image only represents a part of one of the two poles of the Moon (that is, by the way; one of many celestial bodies of our solar system). Can you see the small red square I drew ?

It’s the Shackleton crater. There is water in it, and it looks like this :

The Shackleton crater. Original image by Jorge Mañes Rubio.

I added the Eiffel Tower on the crater rim so that we can grasp how immense it is. Its diameter is 21km, its area is 3 times Paris intra-muros.

Another composition I made that puts in perspective our current capacities in terms of space robotics : here is, to the 1:1 scale, the trajectory performed by the Opportunity rover, during its 15 years of operations on Mars, overlayed on the Shackleton crater.

15 years of Martian operations for the Opportunity rover, superposed on the Shackleton crater (lunar south pole).

Lunar rovers should be able to drive faster because gravity is lower than on Mars (so it will require less power to move the same mass). We will also be able to send commands multiples times a day. Nevertheless, it gives a rough order of magnitude. We are looking at 15 years of operations 😮.

When we see this, it’s obvious : even if multiple organizations for some reason wanted to establish a presence near the same crater (even if there are dozens, and there are 2 poles), land area won’t be scarce. The “peaks of eternal sunlight” are less common, but as Michael Mealling put it at the LDC 2020 conference:

“Those are whatmore limited than the permanently shadowed regions […] There is so few of them that there is some thought among certain space policy and national defense circles that those are going to be contested areas. If the spots of eternal sunshine at the poles becomes contested areas because people want to use them… I would like to have that problem. There are certain problems that I call Champaign problems. If I can have that problem, I will pop a bottle of Champaign. I will be happy, because that mean that people are developing it and found valuable to be there. And that’s a future I would like to be in, even if there was a little bit of fighting back and forth over who got to be on the top of those peaks.” – Michael Mealling at LDC 2020, around 57m10s.

Let’s hope Michael gets his champaign soon! 🍾

Kevin Cannon, who made some very interesting maps of the lunar south poles highlighting the most valuable locations for various criteria, doesn’t seem to think these special locations will be a source of conflict:

“Not everyone will compete for the same spots: goals/architectures drive site selection, and people have different goals. Peaks of eternal light are lit <90% of time. Still need to do all the engineering to survive the night, so may be worth trading illumination for other factors.”Kevin Cannon on Twitter.


In any case, building infrastructures on the Moon will take a long time – even on Earth, building a city the size of Paris would take years and a pharaonic budget. Nations that will join the game late, for political reasons or lack of vision, won’t be really disadvantaged even if they start lunar activities a decade late. A developing country today that will start its space adventure 50 years from now won’t lack spots to establish an outpost either, whenever they’ll be ready.

We don’t need to fight or exclude each others, or already establish rules to manage conflicts. Space is big. Let it be a friendly, and not a toxic competition. We can decide the rules along the way, with actual operational knowledge (mandatory to design relevant rules).

The zero-sum game exists only in our minds.

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Luna: second space race?

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In the next years, we are going back to the Moon. Why am I so sure of it?

The U.S.A. started their ambitious Artemis program of crewed spaceflights towards the lunar south pole, as well as their Gateway program – a small space station near the Moon. Europe is studying the possibility of using Ariane 6 to perform lunar missions, and started the EL3 program, a cargo lunar lander. Russia also wants to go. India sends scientific probesso does Israël. China has plans to build a Moon Base and already started to accomplish feats of strength.

Drawing by Dave Simonds for The Economist, 2018.

What for ? Haven’t we already “been there 50 years ago” 😩?

Last time, I tried to explain why I think we should explore and settle space.

But why is everyone starting with a return to the Moon ?


Some people talk about the return to the Moon as if it were a pissing contest between the U.S. and China. This quote from the director of lunar missions is pretty interesting on this regard :

“The universe is an ocean, the Moon is the Diaoyu Islands, Mars is Huangyan Island. If we don’t go there now even though we’re capable of doing so, then we will be blamed by our descendants. If others go there, then they will take over, and you won’t be able to go even if you want to. This is reason enough.”Ye Peijian

Let’s take 30 seconds to reflect on the implications of such talk, by someone in this position. Apparently, this kind of talk can also be heard in the U.S.

Anyway, China is applying a relentless strategy to establish a presence in cislunar space over the next decades, so that they won’t be denied access to it. For now, they are progressing well. A lunar base in 2030. A big spaceport in Earth orbit resupplied by reusable rockets, from which nuclear-powered shuttles depart to the Moon and other places of the solar system. Sounds futuristic ? They are working on it today, it is their roadmap.

In response, the U.S. department of defense initiated an ambitious program to research and demonstrate nuclear thermal propulsion for the first time since the 60s. The National Space Council also recommended to the government to establish:

  • A policy regarding space resources utilization
  • A strategy to defend the strategic interests of the United States in cislunar space
  • A plan to reinforce cooperation in space with allied nations

These last months, we’ve seen come to life the SPD1 directive, the Artemis program, and the Artemis Accords. These elements fulfill pretty much exactly the recommendations of the National Space Council.

Geopolitics are therefore still driving Human Spaceflight, with a taste of underlying competition and conflict. First come, first served ? It’s a pity, because it looks like we are translating the conflicts we’re having here on Earth to space 😔. We should stay vigilant that this is not going towards a “West vs. East” paradigm, like a 21st century remake of the NATO vs. Warsaw pact. The United States kind of started going this way with their Artemis Accords reserved to “freedom loving nations“, as put by the Vice-President Mike Pence.

China vs. United States. Drawing from the Financial Times.

In this FISO podcast (at 41m45s), Mike Gold, associate administrator of NASA, paints the situation a bit differently than what we could interpret by just reading the news.

There, he talks about the Artemis Accords, and says that the “safety zones” as introduced by these Accords are not a way to enforce private property in disguise. Safety zones would not be exclusionary zones, they would not impede with everyone’s right of free access to all of space. They would simply be an implementation of the non interaction principle from the Outer Space Treaty, that asks everyone to avoid harmful interferences with other nations’ activities. He gives the example of a 15-30 meters safety radius around a rover, area in which it could cause damages in case of malfunction. This is far from claiming a whole crater for exclusive use of the U.S. on the basis of safety zones, as we could have speculated 👍.

By the way, still according to Mike Gold, even if there exists a law in the United States that limits cooperations between NASA and CNSA, it would not prevent China from joining the Artemis Accords. However, they contain principles that China didn’t apply so far : transparency and open sharing of scientific results. Joining the Artemis Accords would force a major policy change in China. False invitation ?

Maybe there is a real discordance happening in the United States. On one side, the government is having a very nationalist “Amercia First” way to promote space exploration. On the other, NASA is talking more about sustainable space development, building a private economy, and promoting coordination to reduce confusion and avoid conflicts.

China is saying they are open to cooperations in future space missions. Dmitry Rogozin, director general of Roscosmos, said that he would be more interested in a cooperation with China than the United States to establish a lunar base. As it stands now, he thinks the United States are taking a too strong leadership, and that it is not a truly international program. It will be interesting to see how Europe reacts. We will probably try to cooperate with everyone, but what would happen if, for instance, the American systems are not using the same standards a the Russian-Chinese ones, what design will we choose ?

Tweets by @katlinegrey on 13/07/2020. Transcription of Dmitry Rogozin’s radio interview.

Everyone say they are open for cooperations, nobody would like to be pointed out as the bad guys, as it would reduce opportunities of partnerships. So let’s hope that these invitations to cooperate are not just sayings, that they are really meant, and that there will be a gesture of good will between the United States, Russia, and China. Even if it didn’t manifest as a joint program, simply agreeing on some points of space law would have a profound meaning.


International treaties prevent the militarization of space. Even without deploying weapons in space, a nation probably should develop some infrastructures there. Which ones?

Today, a lot of services are made available by machines in space. What would happen in case of conflict? What if they were destroyed, or simply put out of order? Losing GPS and satellite communications would severely cripple military and civilian organizations. No more Earth observation from space. No more television. No more weather forecasts. Sometimes, no more internet.

What does the Moon have to do with it? Well, space is big, so the Moon is far. But not so far. In fact, it is in a very interesting place, where it takes several days to physically travel, but only a few seconds to exchange information (radio waves travel at the speed of light). There are also raw materials available on-site to build things and survive, reducing the cost of any activity there.

One of the least recognized resource of space is the possibility to put a large distance between yourself and the rest of humanity. Perfect vacuum and no (or reduced) gravity are also useful for a lot of things. Anyway…

Which unique installations could we place on the Moon?

There is a pretty straightforward way to take advantage of the Moon: playing with the large physical distance and low delay of communications. For instance, a high security storage and telecommunications facility.

If someone tried to destroy it, a missile would take days to travel there. It would leave time to try to intercept it and move critical data. This facility could also be used as an outpost to observe Earth. The near side of the Moon is always facing Earth, what better place to build a huge telescope from local materials? On Earth, it is possible to conduct secret military operations. But launching a missile towards the Moon would be spectacular, and everyone would be aware. According to international treaties, it would be an unambiguous declaration of war.

This is just a single idea. A dissuasion mechanism that secures space assets without being an active threat. Why destroy telecommunications or observation satellites if there is a redundant unit ready to be activated on the Moon a few seconds later? Other forms of resilience exist. For instance, it is way more complicated to destroy or cripple 100 satellites from a constellation than a single bigger satellite.

Today, the Moon is a remote place that we could not consider worth of being secured. But in fact, it is the same as oceans and airs, it only requires a skilled domestic industry and properly designed equipment to establish a presence there. In a not-so-far future, perhaps the Moon and more generally space will become strategic locations for national security. So we should not miss the boat and secure ourselves a spot there. I’m not saying that I approve, but it seems to be the way geopolitics go today. It is explicit in the case of China and the United States, maybe less for others, but I dare you to find a better reason to spend so many billions of public budget. Even in Europe, we are investing billions to have an independant access to space (Ariane) and positioning system (Galileo).

To stay independent when the Moon will play a strategic role, will Europe need to develop their own crewed spacecrafts?

In any case, let’s hope that conflicts – catastrophic events for orbital debris production – will never happen, otherwise we would risk to lose all access to space.

It is also for this reason that we need means of deterrence.

It’s not obvious what to think about the current state of things…

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Estimating the cost of spacecrafts

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Money is important. Even if we have a lot of it, there are always multiple ways to spend it : things are always competing for a part of our budget. Is a prestigious mission worth it if we could have made 50 smaller missions instead? Are we doing a one-time spending/benefit, or an investment that we can build upon for the next times?

More generally, money is also the way we take decisions. Not only money, of course, because our choices are also influenced by our ideology (that is sometimes fixed in the rules of the game by politics and law). But most of the time, money is a good mechanism to influence our choices.

Space programs are always competing for agencies’ budgets.

During concept studies and when doing general assessments like we are going to do on this blog, we don’t have a precise idea of which equipment from which manufacturer we’ll include in the mission. In fact, we don’t know so much besides early engineering values, like broad requirements, mass, and power budgets. Sometimes, we imagine solutions that do not yet exist – how much would a lunar lander with 20 tons of payload capability cost? What if we make a single one? What if we make 50 of them?

To perform early trade-offs, we can make use of cost models. It only takes minutes instead of weeks but sacrifices accuracy. These models are built from the cost of past space missions. That causes some problems, because there have been quite some disruptions in the space industry recently, like the cost of launch decreasing 5-fold in the last decade. But, keeping that in mind, they’re still a decent tool to make estimations.

Simply put, most cost models have the same structure:

Cost = Dry Mass X × Y

Dry mass is a key factor because the bigger a system is, the more systems will be inside (computers and their software, wires, communications, thermal management systems, power production & storage, …). The X term is sometimes used to break linear scaling: maybe the difference between a 1 and a 2 ton spacecraft is bigger than between a 10 and 11 ton spacecraft. But on the other side, bigger spacecrafts are increasingly complex on interconnections, and require bigger testing facilities, specialized handling equipment… The AMCM model for instance has X < 1 to break linear scaling, while USCM is linear. I personally find linear scaling more logic. Finally, Y is the magic number: it factors everything from complexity to the number of units produced. Intuitively, we know that the Hubble Space Telescope is a more complex system, with a much higher Y factor, than a constellation of mass-produced low-complexity (relatively) Starlink satellites.

Ideally, we want to find analogies to estimate the cost of a space equipment. If you are trying to estimate the cost of an Earth observation satellite, try to look at the cost of the Sentinel program’s satellites. It’s not perfect, but it’s a fair guess to start.

ProgramCompanyDry mass (t)Cost ($, 2018)UnitsSpecific cost ($/ton)
Hubble Space TelescopeLockheed10.892.9B1268.9M
Sentinel 2Astrium Germany1.02125.0M1122.9M
Sentinel 1 C & DTASI2.20478.4M2108.7M
CygnusNorthrop Grumman3.403.4B1099.6M
Apollo LEMGrumman4.484.8B1288.6M
DragonSpaceX4.203.6B2043.4M
ISS Node 2 & 3TASI15.00510.5M217.0M
Cost of some existing projects.

You’ll notice that I specified costs in “2018” dollars. It’s important to account for inflation because projects that happened 30 years ago would look very cheap otherwise. A single $ from 1970 is worth $7.88 in 2018. Note that I also use $ even if I’m from the Euro region: it is convenient because NASA publishes yearly their New Start Inflation Index (NNSI), that is a good number to use as inflation for space projects.

So that’s it, we’ll estimate all costs with the dry mass and a magic number. It’s not very accurate, but most of the time, there is at least an order of magnitude of difference between competing solutions, so that will do.

Most of the time, I will be optimistic compared to the models, because the drop in launch prices will induce a drop in payload manufacturing prices : if missions are cheaper overall, then we can accept more trade-offs. A lot of private actors are also participating to space exploration in the recent years (mostly thanks to NASA’s policy) by searching financing from private actors. This competition coupled with smaller structures tends to reduce the costs of space things compared to what we’ve observed historically.

I hope your learnt something today. Next stop: the Moon ! 🚀

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Transporting things in space

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December 21st, 2015. The SpaceX Falcon 9 rocket hurls 11 ORBCOMM satellites into orbit. It is a cornerstone moment of space transportation history, because it is the first time an orbital booster lands back. It opens a way towards a future where we are not disposing rockets after using them, and where they become a mean of transportation like any other. It is this launch that made me realize we lived at an important moment for humanity – the moment where we gain access to new continents beyond our atmosphere. It is this moment that decided me to change career to work in the space industry, after 3 years of software development in another sector. This long exposure photo shows the take-off flame track (left) and the landing (right). Without exagerating, even if the benefits of reusable rockets are still to prove today, because we have not yet tamed the complex engineering to routinely craft them, future generations in a thousand years living everywhere in the solar system will wonder why we waited so long to improve our knowledge of making them. Since this event, other companies looked into reusing their rockets, like Rocket Lab (US/NZ) or Linkspace (China), to cite only 2. Organizations around the world accelerated their research program on this subject. In France, for instance, there is a plan to develop reusable launchers with the Callisto -> Themis -> Ariane Next programs, where the CNES, DLR, JAXA, ESA, and Ariane Group are collaborating. Skeptics are still around, but the revolution has started.

Space is very different from what we experience daily, so a bit of introduction is probably needed. If you already studied aerospace, this post will contain stuff you already know. But it will allow everyone to catch up, and we’ll have a reference to link when talking about space transportation concepts on this blog.

Cars move by rotating their wheels: that creates friction against the ground, and that makes them go forward. Boats and planes with propellers work a bit similarly, except they don’t push against the ground but against the surrounding fluid (water, air). Planes with reaction engines and rocket engines work differently: they throw something backward (hot gas), and that makes them go forward. The more mass and the faster we eject reaction mass, the more the spacecraft accelerates.

Specific impulse

To measure how fast mass is ejected we use the “specific impulse” (Isp) metric. It gives you how efficient an engine is, like “liters per 100km” for cars. The bigger the specific impulse, the more you can accelerate with a given amount of fuel. Without going into equations, keep in mind that a higher Isp is often better, because we want to minimize the mass of the propellant (because it also has a mass we have to move with us).

Delta-V

There are two kind of distances in space. Sort of… At least, that’s how I like to think of it.

The first kind distance is obvious: it is how much physical space separates two things. For instance, the Moon is at 384,000km from the Earth. This physical distance is important because it gives you a clue about how much time it will take to reach something. Space is big so even if we go really fast, the distances are so large that it can take months (years!) to reach a desired target.

But there is another kind of “distance”, and it is the most relevant when transporting things in space. The ISS’s orbit is 400km above our heads, yet it is much more difficult to go there than to go from Toulouse to Paris (a 600km trip). This is because the ISS is moving very fast: more than 7500m/s (22 times the speed of sound)! The difference of velocity (Delta-V, DV) measures how much one needs to accelerate to go as fast as the target. Once you go as fast as your target (and in the same direction), your relative motion is 0, so you see your target fixed, and you can interact with it. Like when you are chatting with your friend during a jog session: you are both moving, but in the same direction, so you can talk even though you are moving.

There is a chart I love that maps the Delta-V between bodies of the solar system:

Solar system Delta-V map (open in large).

For our purposes on this blog, that will be mostly about the Earth, Moon, Mars, and Near-Earth Asteroids, this chart provides more details:

Delta-V map in cislunar space and Mars.

There are more exotic ways to move around, but we’ll see that in due time!

Dry mass

Conceptually, a rocket is made of 3 parts:

  1. The payload: that’s the useful thing you want to transport (satellites, humans in a pressurized module, …).
  2. The propellant: that is the thing you want to throw backwards in order to accelerate.
  3. The dry mass
Be prepared, I’m an expert graphic designer.

What we call dry mass is the rocket’s parts that are not useful and that we can’t throw backwards. Dry mass is bad but it is needed: the rocket structure, the propellant tanks, the engine and nozzle, the on-board computers, …

Certain fuel combinations have a high specific impulse, like LOX/LH2 (liquid oxygen & hydrogen), but require big tanks and insulation because they need to be stored very cold (hydrogen evaporates at -253°C). There is no magic formula for designing a rocket: some have better Isp but higher dry mass, others have lower dry mass but need to carry more fuel because their fuel has a lower Isp, like LOX/CH4 (liquid oxygen & methane – methane evaporates at -161°C).

By the way, notice we must carry the oxygen to burn the fuel, because there is no oxygen in space, unlike planes that burn kerosene with ambient air. If you’re wondering how we can keep propellant so cold for so long, consider this: there are boats carrying liquid natural gas (that is essentially methane) sailing for multiple weeks!

It even has it written on it: “Liquid Natural Gas”.

Useful mass (payload)

Let’s say you have a rocket. You know where you want to go (the Delta-V), how efficient your engine is (the Isp), and the dry mass of your rocket. How much payload can you take with you? This is what the rocket equation is about. It relates the initial mass (payload + dry mass + propellant mass) to the final mass (payload + dry mass, no more propellant), using the Delta-V and Isp.

“ve” – exhaust velocity – is specific impulse times a constant, so I didn’t lie to you. We already see a logarithm, that will be the most complicated math tool we’ll need to use here.

Imagine you have a rocket of 100 tons. The rocket equation is exponential, so if you want to accelerate 1000m/s, maybe you can carry 70 tons of payload. But if you want to accelerate 7000m/s, you can only carry 6 tons of payload.

The payload mass fraction when launching from Earth to LEO (Low Earth Orbit) is around 1/30th (it changes for every rocket). That means, to put 100 tons in LEO, you need a 3000t rocket on the ground.

This is why rockets are so big (it’s hard to realize when only watching videos). A French high-speed train locomotive weights around 400 tons. Can you imagine how much mass needs to be thrown backwards in order to move?

This Saturn V rocket exhausts a gas mass equivalent to multiple elephants per second.

This notion of payload mass fraction is important to study the space economy: depending on where a resource is produced and where it is demanded, there can be big differences in price. Most of the cost of something is due to its transportation.

Aerobraking

Such a sophisticated word, I love it.

Having 100% of payload mass fraction is theoretically impossible, but we can get close. It would mean that the payload is alone, that there is no rocket attached to it. Concepts like “catapults” have been proposed, where a rail or sling system launches the payload towards its destination, where it is catched. We’ll have to talk about this futuristic possibility in a dedicated blog post, because that would change a lot of things.

Two examples of aerobraking, more or less intense.

For trajectories arriving at Earth or Mars (or anywhere with an atmosphere – not the Moon), we can use aerobraking to lose some speed. That reduces the Delta-V performed with engines, so it improves the payload mass fraction (it goes up). The spacecraft hits the thin upper atmosphere, which creates friction, like a parachute, but less intense.

This process converts some kinetic energy (speed) into thermal energy (heat): the spacecraft slows down but heats up. The more extreme example of aerobraking is for Earth-return capsules: they are not equipped with rocket engines and are only based on thermal protection shielding and parachutes to slow down. It’s obviously a trick that can only work one-way. In practice it requires a bit of additional mass for structure & thermal handling. It also takes a lot of time, because we want only a bit of friction on every orbit to not stress the spacecraft too much.

As an example, ESA’s TGO mission aerobraking saved around 1km/s of Delta-V and took about a year.

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The eighth continent

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Why should we explore and settle space?

Sometimes, we say that the Moon is “the eighth continent” of Earth. Here is how I like to think of it.

A city on another world. Illustration by David Schleinkofer, 2011.

Imagine. It is year 2020, and for some odd reason, we just discover today a continent the size of Africa, right in the middle of the Pacific Ocean. How much time will pass before we go there?

This fictional continent would have very different rules of the game. Sometimes, it would be very hot, sometimes, very cold. Clearly, we wouldn’t be made to live there. The strange atmosphere would force us to wear special outfits. Ambient air would completely change the way we design industries, because some processes would be a lot easier to do here. Some would be harder. By the way, the soil would be unlike anything we know. It would contain different minerals, in different proportions. That would force us to completely rethink how we build things and how we manufacture the objects of our daily life. There are chemical elements required for our survival that would be very rare, which would force us to make progress on recycling and circular economy, to diminish the costly imports by air from nearby continents. From this continent, we would have easier access to nearby islands, which would also have their own specificities and curiosities.

Life would be tough at first, because everything would still have to be built – there would be few infrastructures in place. We would try new ideas, and some of them would fail. Sometimes, there would be tragic losses of human life, and we would question this whole project. It would be a dangerous adventure, but with a great perspective for the future. The perspective of opening a whole new continent for humanity. A continent that will be the home of people yet to be born, that will create, imagine, love, share, and write their own stories. Their life will be much unlike ours, because they will live in a very different environment and develop their own culture. This difference will be their most cherished strength, and it will bring diversity to the cultural heritage of humanity.

This epic adventure, it won’t be science-fiction. We could say to kids: if you do well in school, you can also join this adventure. You can also become part of history.

To help the brave pioneers that would risk their lives by making the journey first, generations of engineers and scientists would work hard to solve problems we wouldn’t have encountered before. It would offer a new angle of attack for known challenges. It would offer a new perspective to consider solutions we used to ignore. It would offer a second point of measure for established theories.

Some people would be close to those who make the great leap. Their emotional investment would be huge, and when you are passionate and have skin in the game, you think differently – it’s a strength. Wars are known for driving inventions and technical progress. It is better that this emotional investment comes from pursuing a meaningful goal, than from fear, survival instinct, or nationalism. Even without such an intense emotional investment, being able to work for a meaningful cause is the main factor to enjoy our daily work. A lot of diplomated young adults are barely enjoying their work because they lack a meaningful purpose.

At first glance, this huge project would look a lot like a waste of time and money. Why invest so much efforts to live in such an hostile place? There, we could not grow food, at least not like we are used to. There won’t be minerals there that we don’t already find here.

As often, the journey is more interesting than the destination. To accomplish this effort, we would need to invent a lot of things, and develop new ways of thinking. This is what’s important.

It is difficult to know in advance whether an innovation will improve well-being or generate profits… What we know, on the other hand, is that if there was a way to increase the quantity of innovations, some of them will prove useful, and with some luck, some will even be transformational.

We enjoy today a much more pleasant life than 2000 years ago. It is not because we changed planet, or because the rules of the game have changed. It is because technological progress opened new perspectives for us to interact with our environment. Offering a playing ground to stimulate the creativity that lies inside each and every one of us, this is the real purpose. A lot of challenges will be specific to surviving there, but a lot of technologies will for sure be transposable to improve the lives of those that didn’t take the trip. It has been the case since we sent machines to space, and people just above the top of our atmosphere. So, what will it be when we have people living full-time on another world, performing all the essential daily tasks required to survive, work, and have fun?

Choosing to go to space is not leaving behind the challenges we currently face on Earth; it is providing ourselves with new tools to tackle them.

Today, the eighth continent isn’t in the middle of the Pacific Ocean, but above our heads. This continent, it could have been the bottom of the oceans, Antarctica, deserts, the Moon, Mars, giant free-floating space stations, or anything else. But at the intersection between what is technically feasible, is exciting for our future, fits the current geopolitics, and for which we have a considerable number of private actors reaching maturity… Today, there is the Moon. Soon, there will be Mars.

So, let’s go there. And let’s stay.

The best thing about using space as a frontier for innovation and sustainable development, is that it is virtually endless. There will always be new worlds to explore, study, and settle. Let’s seize this opportunity while it is open to us.

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Space is big

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I would like to open this blog with 3 simple words: “Space is big”.

In fact, I would say it is impossible to grasp how immense it is. This infinity of new worlds could offer unlimited development potential for humanity, if we have enough vision to dare to explore it and settle there sustainably. For sure, there are challenges imposed by the laws of physics, the economics, and politics. But if we understand them well, we can dream big, work on the relevant topics, and walk in the right direction to start our journey to the stars.

“Return to the Moon”, Robert McCall, 1991.

This blog will introduce some concepts for you to understand what is at stake, what is going on when you read about space news, and hopefully it will give you the tools to analyze relevant paths for space exploration, as well as make your own scenarios, if that’s your thing.

The first series of article will be focused on the Moon, because that is where the short-term space exploration is going on. I will also hopefully be able to give you interesting insights on this topic, as I am involved in the Moon exploration community, and was part of concept studies for sustainably explore and settle it. Mars will also get its fair share of spotlight (I’m an active member of the Mars Society for a reason!), but later.

Please subscribe to the e-mail notifications if you would like to keep up to date with what’s happening here. You’ll be the first to know what’s up, and it also motivates me to write articles more often if I know you are eager to receive updates 😉


The first article may be pretty straightforward if you are already a space enthusiast, but there are basic concepts I need to explain before diving in more advanced topics (and I’ll have a reference to link for them). It will introduce the general concepts of space transportation we’ll use on this blog.

Then, there will be a small introduction about cost estimates, because cost is an important figure of merit to design anything, and space makes no exception.

Finally, we’ll have an in-depth talk about the transportation costs in cislunar space! 🚀

See you soon,
Erwan