In my previous article, Lunar Orbital Congestion Is Gonna Be A Thing, I brought up the possibility of orbital congestion and debris becoming an issue at the Moon sooner than most people would think. That article focused on the problem of satellites in low lunar orbit (LLO). This area between 30 and 1,000 km is very attractive to remote imaging and communications constellations because proximity to surface increases their performance. Satellites in those low orbits pass quickly over the lunar surface and continuous coverage will require a lot of them, which is how Earth orbit observation (Planet) and communications constellations (Starlink) have evolved.
Today, satellites are expensive and getting them to Moon takes a lot of energy, so most proposed plans for lunar surveying and comms are less ambitious than the Earth orbital constellations. They depend on just a few satellites into higher, elliptical orbits, from which they can cover a lot of surface area, but are subject to longer observational distances and communications latency. In the last article, I predicted that we would see 1,000 satellites in lunar orbits by 2030. This aggressive forecast assumes a significant cost drop in both launch and satellite costs, which I believe are inevitable. If I am correct, the congested space around the Moon may result in international contention and/or a troublesome debris problem, similar to the one plauging Low Earth Orbit (LEO).
An Embarrassment of Rocket Riches
This is the golden age of space launch. We have workhorse launch systems developed by governmental agencies and state-founded enterprises including the Russian Soyuz, the European Vega and Ariane rockets, China’s Long March series, and Japan’s H-IIA. A growing livery of highly competitive commercial rockets is rapidly rendering these governmental systems economically obsolete. These include: the Atlas V from United Launch Alliance (ULA), the Falcon 9 from SpaceX, the Antares from Orbital ATK / Northrup Grumman, and the Electron from Rocket Lab. Several promising launch solutions are in the proving stage including the Alpha from Firefly, the Astra Launch System 2 Rocket, the Terran from Relativity Space, and LauncherOne from Virgin Orbit (moment of silence). This is an embarrassment of riches for satellite companies. Competitive pressures are growing, manufacturing processes are improving, and economies of scale are being captured. Consequently the launch price for payloads to Low Earth Orbit (LEO) has dropped from many tens of thousands of dollars per kilogram to under $5,000. The price of delivery to the Moon is also dropping and will continue to do so.
But Wait, There’s More!
Several new rockets are about to hit the market including ULA’s Vulcan-Centaur, Blue Origin’s New Glenn, SpaceX’s Starship / Super Heavy, and Rocket Lab’s Neutron. These next generation vehicles promise more power, greater efficiency and significantly reduced launch costs. Meanwhile, the satellite industry is recognizing economies of scale and standardization in manufacturing. The bottom line is that a lot of smallsat could be delivered to the Moon for a remarkably small amount of money in the next few years. The only remaining question is would any want to send all those satellites to LLO?
As I noted in the previous article, useable LLO orbits are highly constrained by the Moon’s smaller orbital volume and the gravitational anomalies induced by mass concentrations (mascons). Orbital real estate is extremely limited and – in the absence of any coordination or law preventing occupation of those desirable orbits – the rules of First Mover Advantage must apply. If someone wants to own the lunar surface observation and low-latency communications business for the next century, getting their satellites into the prime real estate of low, stable orbits even before market demand materializes is a smart business strategy. If it can be done for relatively cheap, I cannot imagine why some smart entrepreneur would not pack a Starship or two full of inexpensive satellites and jumpstart the lunar economy. In fact, I would bet on that. Presuming it is done well, I would applaud it, because the upsides of lunar development promise a great deal for all of humanity and our blue planet.
The Moon’s Prime Real Estate
The previous article noted that orbital congestion around the Earth is not limited to LEO. We also find many satellites in Geostationary Orbit (GEO), an arc 35,786 km above the Earth. At this distance, satellites move at the same angular speed as the Earth’s rotation and if they are over the equator, they will appear to “hover” there. If you’ve ever pointed your satellite TV antenna at a spot on the southern horizon (north if you’re down under) you’re aiming at one of those. There is no “Lunarstationary Orbit,” because such a point would so far above the Moon that it would disrupted by the stronger gravitational pull of the Earth, but there is something similar.
The lunar equivalent of GEO are two points in space known as the Earth-Moon Lagrange Points 1 and 2 (L1 and L2). These gravitationally stable points in space are about 60,000 km above the Moon. L1 is located between the Earth and Moon; imagine the spot where the relative pull of the bigger Earth and smaller Moon balance. L2 is 180° away, on the far side of the Moon, at the same distance. All two-body celestial systems have these Lagrange Points, where a third body can settle in at. Even more interestingly, it is possible to place something into orbit around the empty space of L1 or L2. This is known as a “halo orbit.” The James Webb Space Telescope is in a halo orbit around the L2 point in the Sun-Earth system, million miles from Earth, opposite the sun. Several space weather satellites are located at Sun-Earth L1 and several more are planned. Among them is the Deep Space Climate Observatory (DSCOVR) which provides us with early warning of potentially dangerous solar storms and glorious pictures of the Earth-Moon system.
Earth-Moon L2 is a great place to put a satellite for communicating with landers or rovers on the Moon’s far side, and China located their Queqiao relay satellite there to support their Chang’e 4 lander and Yutu-2 rover mission. The Lunar Gateway, a NASA lead multi-national space habitat, will be placed in a special halo orbit around L2, called a Near-Rectilinear Halo Orbit (NRHO). This weeklong orbit has one end which allows the Orion deep space capsule to dock and another in a good location for dropping a lander on the surface of the Moon. That’s important because Orion’s service module doesn’t have the power required to bring Orion into LLO to drop a lander and get back out of that orbit to return to Earth. The decision to use left-over Shuttle Orbital Maneuvering Engines (6,000 lbs. of thrust) to power the large Orion capsule left it much less lunar capable than the Apollo Command Module. An Apollo capsule weighed about half as much as an Orion and had a similar but much more powerful Service Module Propulsion System (21,900 lbs. of thrust). This shortfall created the opportunity for Gateway, a solution conceived while I was at NASA headquarters. While its original purpose was to fill this gap, I have argued that the Gateway is exactly the sort of flexible infrastructure NASA can use in a variety of future missions. Planting a big stake in the valuable L2 neighborhood is not a bad idea either.
One way to avoid the need for powerful rockets to get into and out of LLO would be a Lunar Space Elevator. Such an elevator would ride on a cable tethered from L1 or L2 that extended down to a surface location on the Moon’s equator. People and material could be transported from the lunar surface to a high orbit and back, with very little energy, on lunar funicular cars. The system requires a counter-balancing cable extending in the other direction. Zephyr Penoyre and Emily Sandford, scientists from Cambridge and Columbia, published a paper suggesting the cable could potentially reach as close to the Earth as the GEO arc. Earth based space elevators have been an idea for a long while, but while it is theoretically possible to run a cable from GEO to a spot outside of Quito Ecuador (or some other equatorial location) it is practically impossible. No material that can currently be manufactured in quantity could withstand the stresses associated with the weight of a space elevator cable under Earth’s gravity. Several engineers – including NASA leaders whom I’ve explored this topic with – agree that cables made of traditional materials like steel would suffice in lunar gravity. This makes L1 a very valuable piece of orbital real estate. The anchor point on the Moon’s equator underneath L1 would also be coveted. L2 has also been proposed as a location for assembling and launching ships constructed from lunar material deeper into the solar system. A space elevator at that point would facilitate such an orbital shipyard and spaceport. L1 and L2 may very well turnout to be the Suez and Gibraltar of cis-Lunar space and hot spots of international contention.
As you can see from the illustration, there are also three other Lagrange Points. L3 is on the other side of the Earth, directly opposite the Moon. There really aren’t many apparent reasons to use L3. L4 and L5 hang off to the sides and optical communications satellites might be located at either of these points to relay transmissions from a satellite at L2. Orbits around L5 were proposed as stable locations to locate large human space habitats by space settlement pioneer Gerard K. O’Neill in his seminal book, The High Frontier. In fact, I joined the L5 Society as a student in high school and my first space policy work was fighting the Moon Treaty with fellow L5 members. Back in 1980, we convinced the US Senate not to ratify that misguided UN agreement, which would have turned the Moon (and possibly all of space) into a boundless scientific preserve, making commercial development of space about as difficult as it is in Antarctica. This would have denied all humankind the economic benefits of space and denied our planet the ultimate release valve for its environmental pressures. I’m now proud to serve as Vice President of Space Development for the L5 Society’s successor, the National Space Society. If you share our vision of a brighter future with humans living and working in space, please join.
To Be Continued…
In my next piece in this series, I will address the potential problem of surface ejecta polluting lunar orbits dust and rockets kicked off the surface. I also plan to explore policy solutions for orbital congestion management that will encourage rather than impede commercial development of the Moon for the benefit of the Earth and everyone on it.