Cool paper. No propulsion, stable, cyclic orbits between the moon and Earth, with times of 45 days (1,1), 84 days (2,1), 64 days (3,1), and 74 days (3,2). Also, (3,3) were identified with no findable timeframes shown.
All the orbits are also somewhat relaxed, with relatively large windows of acceptable trajectories and distances for the later families. Perilune altitudes ranging from 750 km to over 6,000 km. The (1,1) and (2,1) are somewhat restrictive (0.1 km).
Makes a lot of interactions with the moon, exploration, resupply much less severe. It looks like you can leave Earth, at ~0.4 or ~0.6 moon orbit radius, doing some relatively low velocity, and hit a stable resonance orbit. You just have to stay out of GEO satellite orbit window where Earth is the dominant gravitation.
Also, may imply that such orbits exist with pretty much every single moon around every single planet. Implies there's a Sun-Earth orbit family group that's very similar. Probably some multi-moon orbits with places like Mars and Jupiter.
Also, implies that there may also be a bunch of objects (rocks, meteoroids, dust, asteroids, comet remains, ect...) already orbiting in these types of cyclers, since they're relatively accepting of variations on a basic theme. (3,1) is a ~250 km window, (3,3) is a 2000+ km window.
Tuna-Fish•4mo ago
I really don't understand why you'd use these instead of direct ascent. The practical orbits here are in the scale of months, while the moon is 3 days away if you just go there directly.
Unless you have a massive space habitat to hang out in, a cycler is worse for logistics than just direct ascent. For interplanetary transits cyclers might some day make sense if you want to move a lot of people around and want to make a huge artificial gravity habitat for the journey. But the moon is just 3 days away, you can just go direct.
araes•4mo ago
Resupply is a common case. Large amounts of material that you "only" need to take out to 0.4 radius. Or that you can "park" at 0.4 radius and then pick up later.
Persistent shuttle / subway / bus that you can meet somewhere with lower fuel and then tag along for the rest of the ride is another. Sure, its faster to drive somewhere direct with your car, yet its convenient if there's already a known cycling bus / subway route. Go to a known location, tag along. Like a bus / subway, it's also enabling. Maybe you don't want to / can't pay for a Saturn V project.
Cyclic activities that require more than just a one-way or a single round trip. Trash / waste, and similar activities on Earth are an example. Put your trash at some known meeting spot, it gets picked up and taken away.
The entire satellite economy is another, since it's a completely different orbital regime with completely different coverage, vantage points, and observational characteristics. Example, long term telescope that does a constant Earth-Moon cycle every 64 days and has baseline coverage star pattern footprint of ~500,000 miles in a relatively short time frame for observations (along with observations over the entire yearly orbit)
You can also add slowly and keep adding, cause it won't fall out of orbit.
Also works with stuff like slow LEO to GEO transfers using high ISP engines and long orbit raising spirals. (You have to go to 100,000 vs 22,000 miles, yet similar idea).
Speed's not the only metric. No fuel / no propulsion is rather compelling. Low energy, low cost, long term stability.
Tuna-Fish•4mo ago
You can't just deliver stuff to the path of a cycler and magically have it pick it up with a velocity difference of kilometers/s. You need to match orbit with it, which in fuel terms is no cheaper than flying the entire path. And this orbit matching is generally more expensive than flying directly. (Especially because you need to raise and then lower your perigee, so a "shuttle" flying between the ground and the cycler earth end would have to burn much more delta-v than a direct ascent stage that can always keep it's perigee down and just raise apogee until it intersects with the moon.)
Again, cyclers make sense when you have something heavy you want to perpetually travel between the endpoints, and do relatively light transfers at the ends. But you don't need anything like that for the moon. For the moon, you can just take the stage that would have matched orbits with the cycler and fly to the moon with it, it's just 3 days, you can pack people like sardines for 3 days.
Alive-in-2025•4mo ago
I was just about to add that last point you raise, must be some great stuff floating around in one of these that we haven't yet discovered. I wonder if there's a rich horde of dust all in a narrower place.
Good summary, by the way. This paper could lead to an eternal reference to their name! We have Lagrange orbits, like L2, now we will have RRT orbits.
araes•4mo ago
All the orbits are also somewhat relaxed, with relatively large windows of acceptable trajectories and distances for the later families. Perilune altitudes ranging from 750 km to over 6,000 km. The (1,1) and (2,1) are somewhat restrictive (0.1 km).
Makes a lot of interactions with the moon, exploration, resupply much less severe. It looks like you can leave Earth, at ~0.4 or ~0.6 moon orbit radius, doing some relatively low velocity, and hit a stable resonance orbit. You just have to stay out of GEO satellite orbit window where Earth is the dominant gravitation.
Also, may imply that such orbits exist with pretty much every single moon around every single planet. Implies there's a Sun-Earth orbit family group that's very similar. Probably some multi-moon orbits with places like Mars and Jupiter.
Also, implies that there may also be a bunch of objects (rocks, meteoroids, dust, asteroids, comet remains, ect...) already orbiting in these types of cyclers, since they're relatively accepting of variations on a basic theme. (3,1) is a ~250 km window, (3,3) is a 2000+ km window.
Tuna-Fish•4mo ago
Unless you have a massive space habitat to hang out in, a cycler is worse for logistics than just direct ascent. For interplanetary transits cyclers might some day make sense if you want to move a lot of people around and want to make a huge artificial gravity habitat for the journey. But the moon is just 3 days away, you can just go direct.
araes•4mo ago
Persistent shuttle / subway / bus that you can meet somewhere with lower fuel and then tag along for the rest of the ride is another. Sure, its faster to drive somewhere direct with your car, yet its convenient if there's already a known cycling bus / subway route. Go to a known location, tag along. Like a bus / subway, it's also enabling. Maybe you don't want to / can't pay for a Saturn V project.
Cyclic activities that require more than just a one-way or a single round trip. Trash / waste, and similar activities on Earth are an example. Put your trash at some known meeting spot, it gets picked up and taken away.
The entire satellite economy is another, since it's a completely different orbital regime with completely different coverage, vantage points, and observational characteristics. Example, long term telescope that does a constant Earth-Moon cycle every 64 days and has baseline coverage star pattern footprint of ~500,000 miles in a relatively short time frame for observations (along with observations over the entire yearly orbit)
You can also add slowly and keep adding, cause it won't fall out of orbit.
Also works with stuff like slow LEO to GEO transfers using high ISP engines and long orbit raising spirals. (You have to go to 100,000 vs 22,000 miles, yet similar idea).
Speed's not the only metric. No fuel / no propulsion is rather compelling. Low energy, low cost, long term stability.
Tuna-Fish•4mo ago
Again, cyclers make sense when you have something heavy you want to perpetually travel between the endpoints, and do relatively light transfers at the ends. But you don't need anything like that for the moon. For the moon, you can just take the stage that would have matched orbits with the cycler and fly to the moon with it, it's just 3 days, you can pack people like sardines for 3 days.
Alive-in-2025•4mo ago
Good summary, by the way. This paper could lead to an eternal reference to their name! We have Lagrange orbits, like L2, now we will have RRT orbits.
Grad students, it's not all discovered!