Taking the Low Road: Artemis III and Earth Orbit

Article May 23, 2026

The launch of Artemis I in November 2022. Credit: NASA/Bill Ingalls

NASA recently made public a decision that has been sitting on its to-do list since at least February. That’s when the agency announced that the next flight for Project Artemis, Artemis III, was changing up its mission profile. What was originally going to be an attempted 2028 Moon landing was now (far more sensibly in my opinion) a 2027 test of the Orion crew capsule and one of the in-development lunar landers (either the SpaceX Starship or Blue Origin’s Blue Moon) in Earth orbit.

Sounds simple enough. But “Earth orbit” covers a whole heckuva lot of territory, and NASA had to choose just what part of that territory the mission would head for: low Earth orbit (LEO) or high Earth orbit (HEO). They’re not the same thing, and they each have advantages and drawbacks. So let’s explore those a little and talk about where Artemis III is going to call home for the duration of its mission.

Getting Low

Most of the time when we talk about something being in Earth orbit, we mean LEO. The website nanoavionics.com estimates that, as of 2023, 88% of the things orbiting Earth were in LEO. As this roughly corresponds to percentages I’ve seen quoted elsewhere, I don’t see any reason to quibble much about it. The point is that LEO is a popular spot.

Low Earth orbit is an increasingly crowded part of space. Credit: ESA

A major reason for that is because LEO is easiest to get to. Different sources cite different boundaries for where LEO ends, but say around a thousand miles (1,600 km) off of the surface and you’ll be in the right ballpark. But that’s the high end. The low end is a couple hundred miles up. The International Space Station, for instance, orbits around 250 miles up, which means when it’s over Boston we Bostonians are closer to the astronauts on the ISS than we are to parts of Maine.

Getting to orbit is never an easy prospect, but getting to the lower part of LEO requires the bare minimum of fuel to get you there. That bare minimum is still a rocket’s worth but depending on how heavy your payload is it might only be a small rocket (small being a relative term when talking about tubes of controlled explosions propelling you to space, but you know what I mean). If you don’t want to go too high or launch too much, you can get away with a smaller rocket. And given that enormous chunks of any mission’s budget goes towards launch costs, a smaller rocket can be a game changer.

So it’s no wonder so many things head for the nearly literal low-hanging fruit of LEO. Of course, it has its disadvantages too. Things in LEO zip quickly around the Earth, meaning they’re never over any one spot for long. They spend half their orbit in daylight and half in night. And the lower the orbit, the more drag you have to deal with from the uppermost bits of Earth’s atmosphere, which extends well past where you think it might.

It’s also worth noting that, given its popularity, LEO is also an increasingly crowded arena to operate in. The ISS, or its oldest parts at least, have been flying in this realm since 1998. Through 2024 it has had to move itself to dodge orbital debris of varying origins 39 times, five of which occurred in 2023 alone. It’s a rough neighborhood.

Feeling Very Mid

I didn’t mention it before because as far as I know mid-Earth orbit (or medium-Earth orbit, MEO either way) was never under consideration as a destination for Artemis III, but it is a thing that exists. It actually covers a wide range of altitudes, since it’s everything from wherever you decide LEO ends up to where HEO begins, a range of roughly 20,000 miles (32,200 km).

This diagram, which shows some of the types of satellites found in LEO, MEO, and HEO, is NOT to scale. Credit: NASA

Things in MEO are not as protected from the space environment as something in LEO. They are more exposed to radiation, for instance. In fact, there’s a portion of MEO space where most of Earth’s Van Allen radiation belts, regions where Earth’s magnetic field traps higher-than-normal amounts of highly charged particles from the Sun, can be found. That, if you’re wondering, is a Bad Place to be a spacecraft.

Signals from Earth take a little longer to get to and from this region, so signal latency is higher than for something in LEO. But spacecraft in this region see more of Earth at any given time than something in LEO does, and for longer. There’s also a sweet spot at an altitude of roughly 12,600 miles (20,200 km) where something will orbit Earth exactly twice a day, which can be useful. This is where you’re going to find a lot of the satellites that operate navigational networks like GPS or Galileo. Apart from these navigational networks though, there don’t tend to be a lot of things clamoring to get to MEO.

On a High

This diagram shows LEO, MEO, and HEO to scale by distance, and includes lunar orbit for reference. Credit: NASA/Robert Simmon

You sometimes might see HEO written out as GEO or GSO instead. That’s because it’s not impossible that someone will use the acronym HEO in an orbital context to mean a high eccentricity orbit. And GEO/GSO works because high Earth orbit starts (and MEO ends) at a very specific distance from the Earth.

That distance is 22,236 miles (35,786 km). I told you it was very specific. That is the height above the Earth at which something will take exactly the same amount of time to orbit the Earth as it takes Earth to spin—24 hours. That means that something orbiting at that height will stay above the same spot on Earth at all times. That is why this orbit is generally known as “geostationary” or “geosynchronous” orbit (GEO/GSO).

If all goes according to plan, Artemis III will launch to Earth orbit in 2027, followed by a Moon landing on Artemis IV in 2028. Credit: NASA

Something in this orbit also sees a huge chunk of the Earth at once. A satellite out that far does have a signal latency of about half a second for a signal to go round trip from Earth to the satellite and back, but that’s workable for the right kind of jobs. This is where you’re going to find a lot of weather satellites (which can benefit from seeing the same places on Earth day after day), communications satellites, and broadcast satellites.

Something out as far from Earth as HEO is going to have to deal with a lot of the same issues as a spacecraft bound for the Moon, from radiation exposure to dealing with keeping heat from the Sun from baking one side of your spacecraft while the other freezes. Even the signal delay is closer to what a lunar-bound spacecraft will deal with than the imperceptible delay found in LEO.

If you’re testing your lunar spacecraft, this is the better place to do it, all else being equal. Of course, that requires being able to get out that far, which is gonna take a lot of extra juice.

The High Road or the Low Road

So obviously all else being equal, NASA would love to send Artemis III to as high an orbit as it could wrangle. Especially for the first big test for a lunar lander, getting to expose it (and the accompanying Orion crew capsule) to conditions more like lunar space is ideal. The trouble is getting there.

Getting Artemis III out to HEO would require a fully operational SLS rocket, both the enormous lower stage, known as the core stage, and the much smaller but still critical upper stage, called the interim cryogenic propulsion stage or ICPS. Originally Artemis III was intended to be a 2028 Moon landing, so the entire rocket needed to it that far is already planned for. We could definitely get Artemis III to HEO and give it the perfect testing ground for its mission.

This diagram shows all of the critical parts of NASA’s SLS Moon rocket, including the interim cryogenic propulsion stage (ICPS) that proved the be the main decision making factor on what orbit Artemis III will launch to. Credit: NASA

But what about what comes next? When NASA was originally placing orders for rocket parts, including contracting with Boeing and United Launch Alliance for ICPSs, there wasn’t really a plan for after Artemis III’s theoretical Moon landing. As such, only three ICPSs were ordered. Two of those flew on Artemis I and Artemis II. With the mission shakeups more are being built, but right now there’s only one ready to go. It’s possible that one will still be the only one ready in 2028 when it’s time to try and send Artemis IV to the surface of the Moon.

Meanwhile, as I said before, getting to LEO is as easy as it gets with orbital launches. The big core stage of SLS has enough oomph to get Artemis III to LEO all on its own, no ICPS needed. That, of course, is not an ideal testing site for lunar tech. But it’s not a useless testing site either. It’s still space.

Sending Artemis III to HEO would mean gambling that a new ICPS will be built in time for Artemis IV to launch on schedule. NASA loves a good testing site, but NASA also historically hates a gamble. In the end, the agency chose to save that existing ICPS. Artemis III will fly to low Earth orbit using the power of its SLS core stage only, with a dummy ICPS in place to keep the rocket balanced.

Then, if all goes as planned with Artemis III (which will depend on things like the lunar lander and the new spacesuits being ready—it’s not all about rocket parts), Artemis IV will use that already-built ICPS to send itself to the Moon. In other words, to crib and paraphrase from “Loch Lomond”, Artemis III will take the low road so that Artemis IV can take the high one.

It’s not perfect. But it might just be how we get to the Moon.