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LOP-G: Our Gateway to the Stars


In the previous episode of this series, we talked about humanity’s first steps to the moon since the days of Apollo. Today we will talk about humanity’s first tentative steps to our nearest celestial neighbor. If all goes to plan, LOP-G will be humanity’s gateway to the solar system, starting with the moon and later Mars. It will serve as a waystation, a laboratory, a lifeboat, and a bunker… or perhaps will simply become another ambitious project lost to the complexities of politics and economics.

Orbital Origins

Ever since humans first looked to the night sky and saw the moon, we conceived of the possibility that one day we might go there. But it took us until the year 1687 and publication of Newtons history changing book, Principia Mathematica, that we could begin to envisage putting an object in an orbit around our own and other celestial bodies. This was famously done with the thought study, Newton’s Cannonball, first illustrated in Newton’s aforementioned book.

In the book describes an unfathomably tall mountain, so tall that, at its peak, there is no air and no air resistance. Upon this peak there is a loaded cannon that, once fired, will be capable of launching a cannon ball at such a speed that it could, in a crude sense, “outrun” the force of gravity, it would not return to earth but permanently orbit the planet until acted upon. While you will likely be familiar with the concept of an orbit you may not be familiar with how they work in the mathematical sense. And, to understand this, it helps to think about the forces acting on an object like you would imagine the four directions on a compass.

Engineers and physicists do this to bring simplicity and uniformity to complicated systems where you might have 1000’s of forces at play, instead combining them into 4 simple directions: up, down, left and right. In this format you can describe any object moving in two dimensions (it also works for three, but we won’t need that today.)

So, if you were to look at this cannonball flying around the earth from a side on view you would see an arrow pointing downwards towards the earth saying something like 9.81 meters per second per second – which would be the rate that the cannonball was accelerating towards the earth every second. If the cannon ball wasn’t moving forward, it would simply fall and hit the ground but as we have discussed it is going at an orbital velocity – in this scenario that would be a number somewhere around 10 or 20 thousand meters per second. As it travels forwards the Earth begins to fall away from the cannonball due to its curvature but at the same time gravity pulls the ball back towards the earth causing a constant change in its direction and velocity.

Once Isaac Newton’s book had widespread acceptance it seized the imaginations of scientists and authors alike. Eventually we began to think of human made satellites orbiting our world and at some point, someone set their sights on the moon. Today we are entering an age where this is not only possible, but is potentially going to be our chosen method of opening up our solar system for future exploration and growth.

As for the topic of today’s video, the first mention of what we would call a space station appeared in Edward Everett Hale’s book “The Brick Moon” published in 1869. But the concept of a space station, lunar or otherwise, would only begin to materialize in any kind of an official capacity during the 1940’s when sustained research proved that it was legitimately feasible to put a manmade object into orbit. As the 1940’s turned into the 1950’s and the space age began, space station concepts began to dominate popular media. It was not until 1971 that the Russians were first able to create a rudimentary space station by linking two Russian Soyuz vehicles in Lower Earth Orbit.

As for a lunar space station it took till the year 2012 for an official body to give serious consideration to this kind of undertaking. Dubbed the Deep Space Habitat this was NASA’s first serious look at the opportunities a lunar space station might afford. Then in 2015, after consideration the Deep Space Habitat proposal was brought into the NextSTEP program and received its first bit of funding.

Now, a project of this magnitude would need significant funding to fully realize it’s ambitions goals and if there is one thing you can be certain of when it comes to NASA, it is that they will at some point run out of funding. Over the coming years the Deep Space Habitat would be altered and combined with other projects that were short of funding. Further, various different modules were added and removed. Finally, in 2018, it received its current designation, the Lunar Orbital Platform-Gateway or LOP-G.

As of 2018 Congress had committed $332 million of funding towards the project and can we just say, we did a video on the F-35 a couple of months ago and the funding that went into that had was set around $1.7 trillion by 2030. If we can put a space station around the moon with 0.02% of the F-35’s funding, imagine what we could do with maybe 2 or 3 percent. I’m sure that defense funding is very important but… I mean… really?

Anyway, with that little tangent aside, that brings you up to date with the origins of LOP-G. So maybe you want to know what LOP-G is and what exactly is its purpose?

To Orbit

So, it’s all well and good proposing to build a Lunar Orbital Platform-Gateway (a space station orbiting the moon that is) but what precise purpose would it serve? Well, I’m glad you asked generic viewer! It would be easy to think of this new space station as an ISS 2.0 but in reality, they share few similarities. For one thing the actual habitable space within the new LOP-G will be significantly smaller than that of the ISS, for another the maximum possible time that a person can spend within the LOP-G will be significantly shorter. At first glance both of these sound like a step in the wrong direction, after all we’re looking to expand the capacity for human exploration, so why then are we choosing to reduce the habitability of our space stations?

Well to start with the LOP-G is going to operate less like a space station and more like a robot in space. As missions to and from the moon are going to be relatively irregular, especially in the early days of the program, proposing to put a tin can around the moon that is only inhabited for one month of the year, would be dubious at best. Far better to make it autonomously capable of carrying out experimentation during this down time. That would mean that the space station would be fully capable of carrying out a multitude of experiments either remotely or semi-autonomously, with inputs from Earth.

You see, at its core the LOP-G will be an exploration into precisely how we can push the limit of human habitability further and further from the surface of the Earth.

If you didn’t catch the first installment of this series, we went into detail about the danger that solar radiation presents. This space station will be our first real bit of sustained, in situ, research into solving the solar and cosmic radiation problem.

As for its habitable areas the LOP-G will have only 2 to begin with, those being the Power and Propulsion Element (or PPE) and the Habitation and Logistics Outpost (or HALO module). The PPE module began construction at JPL (Jet Propulsion Laboratory) in Pasadena, California. When it was originally proposed it was intended to be a part of an asteroid redirection mission, however, following it’s cancellation, development was contracted to Maxar technologies and is nearing completion. This module will be, exactly what it sounds like, a source of power and propulsion but not just for the space station, this will be a transferable module that will act like a tug boat, ferrying cargo, resupplies and manned missions between the Earth and the Moon.

The engines used to achieve this are called Hall effect thrusters, a vast departure from the chemical rockets of the past. If you need any more evidence that NASA is doubling down on the sci-fi nature of this space station, well here it is. Looking like something straight out of Star Trek Wars, these thrusters are going to be humanities’ method of traveling the vast distances that span our solar system. Capable of blistering speeds you could describe these thrusters as the embodiment of slow and steady wins the race. But if you were to see one of them here on earth it would be difficult to tell if it was even turned on. At full power one of these thrusters produces about the same amount of force as an apple applies while sitting in the palm of your hand. When you compare that to the dramatic and explosive scenes of a conventional chemical rocket engine taking off this too can seem like a massive step back, but hold your judgment about 7-10 years and you will see why this is a better solution.

But before we get there, why don’t we clarify the differences between a Hall Effect thruster and a conventional chemical engine. Well, a chemical engine is your typical over-the-top big flame kind of engine. It derives its thrust from the burning of rocket fuel and using the resulting expanding superheated gas to push a rocket in the opposite direction. If you have ever seen a rocket taking off in person or even on video, you will know that this form of propulsion is very loud and very bright. While this makes for very cinematic take-off sequences it certainly doesn’t make for very efficient ones. All of that light, sound, heat, and smoke is indicative of wasted energy, in other words a highly inefficient reaction.

We use these engines for a variety of reasons the main one being that chemical engines are the only engines capable of overcoming the Earth’s gravity well and making it into space. However, once you make it into orbit, that level of thrust and inefficiency just isn’t necessary. This is where hall effect thrusters come in. There are a plethora of resources on YouTube that can explain these thrusters with as much detail as you might need, but in our own short version these thrusters are pretty much as close as we can come to an electronic method of propulsion.

As we are restricted in time by having to describe the rest of this space station, I will give you the short description. In essence these thrusters work by accelerating tiny quantities of a propellent such as Xenon or Krypton to very high speeds. The chosen propellent is sent into a containment chamber. Thanks to the use of magnetic fields or something like that, there are a lot of electrons inside of this chamber spinning around very, very fast. These electrons will smash into the atoms of propellant removing some of the electrons from their shells and causing them to become ions. An anode then repels these newly formed ions out of the engine at speeds approaching and exceeding 15 kilometres per second. This flurry of atoms imparts their equal and opposite momentum to the spaceship, which over the course of a few minutes of usage does not amount to a large change in velocity but over a course of months and in some cases years, said spaceship will slowly accelerate to speeds of 30 thousand meters a second and greater. Theoretically it is possible to reach 90,000 meters per second, but the best we can do with today’s technology is 45 km per second.

Next we have the habitation and logistics outpost which again, does exactly what it says on the tin. It’s also known as the Minimal Habitation Module, this will be built to a similar spec to the ISS in that it will serve as your usual run of the mill habitation module. Well, I say ‘run of the mill’ it is still going to cost just under a billion dollars but that is pretty tame by US standards. But this won’t be all that different than what you might find attached to the ISS, with the notable exception of only being able to support a crew of 4 for around 30 days consecutively. The design and fabrication of this module has been contracted out to Northrope Gruman and is to be launched with the PPE module, which is slated to be in November 2024, however if past experience is anything to go by, that date is going to get pushed back several more months or years before it actually goes up.

There are also a couple of other modules that have been agreed upon but with a slightly looser launch schedule. Those being the Internal Habitation Module or I-HAB and the European System Providing Refuelling, Infrastructure and Telecommunications (or ESPRIT) short. Starting with the I-HAB module this is essentially going to house the extension to the first habitation module providing a combined 125 cubic meters of space within the station itself. This doesn’t sound like a lot but bear in mind that the average New York apartment is 866 square feet, which means very little in this context because comparing square feet and cubed meters is like comparing a piece of paper to a plank of wood.

Moving swiftly on from that tangent, we arrive at the ESPRIT module which despite what the name might suggest is actually quite an interesting addition to the station. A short description of such a module would be that it is the LOP-G’s second storage and utility closet, if your utility closet had an airlock, communications equipment and expanded storage for xenon and hydrazine. As I’m sure most homes do these days. Early design studies were led by Airbus who came up with the current design in October 2019 and it was approved for construction in November that year. As of right now the ESPRIT construction is nearing completion and is set to go up with the Habitation and logistics outpost in 2024.

As of writing, these are the only modules to have been approved for construction, there are several other proposed modules such as the Gateway Airlock Module, Canadarm3 and the Gateway Logistic modules however, these are only in the early stages of research and are not guaranteed to receive funding as of yet.


As with the ISS, the gateway is looking to be a milestone in human engineering. The ISS because of the sheer size of the project, the LOP-G for the sheer distance away from Earth. To give you an idea of the undertaking at hand here, the ISS which took 10 years to construct was built over the course of 30 missions from crewed space shuttles. As of yet there are only 3 flights confirmed to be carrying parts to the LOP-G.

The ISS is a about 400 kilometres from the surface of the Earth, that is 800 kilometres for the space shuttle to travel there and back over 30 missions that comes to a total of 24,000 vertical kilometres travelled to complete construction. In one mission to the moon that distance will be covered 16 times over and there are at least 3 missions needed to construct the LOP-G… Needless to say the challenges this presents are astounding and that is without mentioning the fact that NASA intends to complete this new station at a fraction of the budget of the ISS.

So let’s talk about this new project: How are they going to do it?

Well, to start with, NASA intends to cut costs by using a tool that they didn’t have during the space shuttle days. And what tool is that? Commerce. NASA have outsourced sone of the most costly aspects of the space missions to various companies, the biggest cost cutting measure is the utilisation of third party launching companies, such as SpaceX and Blue Origin who bid for the contract to shuttle these parts to the moon. Space X ultimately won out, so they will carry the PPE and HALO modules on the back of their Falcon Heavy Rocket to the moon in November of 2024.

This will be the first of 3 deliveries that will begin to build the space station from the ground up. The next proposed delivery, following SpaceX, will be the I-HAB module which is to be delivered by NASA’s own SLS rocket. This will also be the first crewed mission to the space station and will be a part of the Artemis 5 mission.

The majority of the actual assembly work will have been done on the ground, so once they are up there it will simply be a matter of attaching one docking port to another and then making sure they won’t break apart.

This will be a modular station allowing for flexibility in how the station is laid out and the ability to add or remove modules as needed. This makes it difficult to say when the station will be finished in the conventional sense. In the case of the ISS there have been many different module layouts and modules that been added or removed. Over time as our presence on the moon and possibly Mars grows there will obviously be a need to expand the capacity, capability, and functions of the LOP-G.

Operation and Orbit

Ok so all that we have left to explain is two things: the where and the how. The where will be the Shackleton Crater at the lunar south pole. This is going to be where the lunar base is situated on the lunar surface. We went into some detail about this crater and why it has been chosen as the site of the lunar base, so we won’t go into too much detail now, but a short explanation would just be that it was a better choice than all the other craters…

Anyway, that just leaves us with the how. This mission will require a near-rectilinear halo orbit (NRHO), and what do all those words mean? Pretty much all that describes is the kind of orbit the LOP-G will have around the moon. As the focus of most lunar activity will be the Shackleton crater NASA needed an orbit that permits easy access to and from the site, while not breaking contact with the earth, meaning they needed an orbit that doesn’t put them on the far side of the moon.

Thanks to these and a few other requirements NASA decided that the best option would be the NRHO. This is a highly elliptical orbit, which means the station doesn’t simply track a perfect circle around the planet rather it forms more of an oval. At its closest point it will be roughly 3,000 km from the surface, which is intended to be directly over the south pole. At its furthest point it will be roughly 70,000 km away – this point will bring it just above the Lunar North Pole. This configuration will make going to and from the Lunar surface possible with the least amount of fuel.

So, let’s say we have got our space station up there in lunar orbit, we have our moon base all set and all of it is in full working order, what would that look like? Well, let’s pitch a certain mission in which the aim is to take some astronauts from Earth to the moon. Launching on either SpaceX’s Falcon heavy or NASA’s SLS rocket the crew would be sent up to Lower Earth Orbit. Once reaching the final stage all that will be left is the Orion module, at this point in the mission they would meet the PPE in orbit and initiate a docking procedure. The PPE will also be refuelled either in the days preceding the mission or by fuel brought along with the astronauts.

Following this the space craft would manoeuvre into an optimal position to approach the moon and then carry out a manoeuvre called the Hohmann transfer orbit. Best we can tell there isn’t an official estimate for how long it would take to make the journey from the Earth to the moon however, the general accepted timeline for a transfer to the moon using the Hohmann transfer orbit is 5 days, whether this takes into account the reduced acceleration of the Hall-effect thrusters I don’t know. So, I will make an educated guess at it taking anywhere from 5 to 10 days to transfer from the Earth to the LOP-G although please feel free to correct that in the comments.

Upon approaching the moon, the astronauts will need to carry out an action to reduce their relative velocity, to the space station and to match its orbit. It would be at this point that the module would slip into the aforementioned NRHO and eventually meet back up with the main body of the space station. Following docking the crew would disembark onto the habitable areas of the space station where they would, remain until it is their time to descend onto the Lunar surface. While in the space station the crew would fill their time with experimentation, organisation, and preparation for the next stage of their mission. The station is rated to support a crew of 4 for at least 30 days, however with future upgrades this could increase, but as this is to serve as more of a rest stop there will be little need for the astronauts to be up there for that long.

As the station is, for the most part, automated there will be many experiments ongoing upon their arrival. What this will look like, we unfortunately cannot tell you. There isn’t a great deal of information available on how the automation is going to look, although if it is anything like what I am imagining, it’s gonna be a bunch of robotic arms floating around doing random tasks like a scene out of Wallace and Gromit.

Moving on from that mental image, we can fast-forward to the next stage of our crew’s mission. Which will be disembarking into a fully fuelled Orion module or Starship. If you are wondering about those, take a look at our last video on the Artemis missions as a whole. Once they are ready the ship will detach from the LOP-G and go… on. If the mission is to Mars, the crew will use several burns that put them on a trajectory that will bring them to our nearest neighbour in a timeline of 3-9 months.

If they are headed down to the lunar surface they will wait until their orbit takes them above the Lunar North Pole at which point, they will slow themselves down, carrying their craft gently down. By the time they are at a near absolute standstill they will have been carried to the opposite side of the moon and will be somewhere near the Shackleton crater, where they will land and begin whatever comes next for mankind.

With the first launch date of the Artemis mission fast approaching and very few indications that this one is going to be cancelled, it’s clear to see that we truly are on the cusp of a new space age. Out of the billions of humans that have lived and died throughout the course of history, it was us that were lucky enough to watch as mankind became an interplanetary species.

There may come a time in the future, assuming mankind is able to fix its ills, that our decedent’s look back on us and our time and recall very little of what went on: wars, the names of politicians, disputes over the budget… will all be lost to history. But they will know that we did something that had a lasting impact, that opened up the rest of the solar system and perhaps, someday, even the rest of our galaxy. And it all started with us and our dedication to progress.

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