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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 y

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 1y 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 1y 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.

araes 1y 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 1y 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.