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Mission planners at NASA and ESA's Operations Centre (ESOC) have spent months debating the pros and cons of different orbits, and have now decided on the path of the Lunar Gateway.
Like the International Space Station, the Gateway will be a permanent and changeable human outpost. Instead of circling our planet however, it will orbit the moon, acting as a base for astronauts and robots exploring the lunar surface.
Like a mountain refuge, it will also provide shelter and a place to stock up on supplies for astronauts en route to more distant destinations, as well as providing a place to relay communications and a laboratory for scientific research.
Mission analysis teams at ESOC are continuing to work closely with international partners to understand how this choice of orbit affects vital aspects of the mission—including landing, rendezvous with future spacecraft and contingency scenarios needed to keep people and infrastructure safe.
The Gateway, it has recently been decided, will follow a near-rectilinear halo orbit, or NRHO.
Instead of orbiting around the moon in a low lunar orbit like Apollo, the Gateway will follow a highly 'eccentric' path. At is closest, it will pass 3000 km from the lunar surface and at its furthest, 70 000 km. The orbit will actually rotate together with the moon, and as seen from the Earth will appear a little like a lunar halo.
Orbits like this are possible because of the interplay between the Earth and moon's gravitational forces. As the two large bodies dance through space, a smaller object can be 'caught' in a variety of stable or near-stable positions in relation to the orbiting masses, also known as libration or Lagrange points.
Such locations are perfect for planning long-term missions, and to some extent dictate the design of the spacecraft, what it can carry to and from orbit, and how much energy it needs to get—and stay—there.
(Score: 2) by Immerman on Saturday July 20 2019, @04:53AM (2 children)
I agree, I'd much rather see us build directly on the moon. But I've been thinking: if the Starship can deliver it will potentially be able to land and instantly become an ISS-sized lunar outpost all by itself.
Think of it - fly your whole space station to the moon, land and research an area for days or months from your 13-storytall research tower, with easily 5 or six floors of 50m^2 (540ft^2) each, and then fly the whole thing back to Earth for a crew change and whatever refitting is desired for the next research objective. Which would likely be someplace completely different. A single mission might even be able to "hop" to a few different lunar locations. And since mass will be the limiting factor for the flight you'll likely have large open spaces with lots of elbow room by default - a lot more generous accommodations than the ISS.
The ISS is effectively nowhere, or anywhere - there's nothing outside, so it's specific location is irrelevant to its function. It's all about studying the station itself, and things happening inside it, while they all float in microgravity and the tender mercies of space radiation above the atmosphere.
A moonbase though - that's all about studying the moon and how to work there. And the moon is almost 40 million km² worth of different locations. A completely mobile moonbase could be the right thing to do until we've thoroughly evaluated at least a few of the most promising regions in person, instead of beginning construction of an extremely expensive moonbase somewhere that just looked good from orbit. And heck, when the cost of your equipment is 99% shipping and development, before you return to Earth unload anything not welded down for use by some future mission - unlike in orbit, supply caches aren't a navigation hazard, if nothing else maybe it will be worth a retrieval hop once construction begins on a permanent moonbase. Maybe even load the most useful stuff on the autonomous solar-powered moon buggies and let them try to make it to some future mission site by land.
I don't know how much a lunar gateway station would actually have anything to contribute to that mission either though. A place to store more massive equipment rather than flying it back and forth to Earth might be useful, and continuous orbital presence might provide the project with a bit more continuity. I wonder though if the orbit they chose is anywhere energetically close to the surface-to-surface flight path - from the animation it looks like they're orbitting the moon perpendicularly to its orbit: zooming quickly past the north pole before heading so far south they're almost as far from the moon as the Earth is (though that might be a perspective illusion in the animation). I'd love to know why they chose that one.
(Score: 2) by takyon on Saturday July 20 2019, @07:11AM (1 child)
I agree, but it looks like full steam ahead for LOP-G. Including using Falcon Heavy to launch individual segments instead of SLS, making the thing more viable and on-schedule. If Starship will be proven by 2021, it will already be too late. Although Starship could deliver astronauts to the surface, which is a plan currently involving LOP-G (for no good reason).
In practice I doubt that moon researchers will be hopping using Starship. They'll just pick one place near the south pole and study, leave after a couple of weeks, and future missions will return to the same spot or a new spot. Maybe they will get better rovers so that they can travel pretty far from camp.
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(Score: 2) by Immerman on Saturday July 20 2019, @02:28PM
> which is a plan currently involving LOP-G (for no good reason).
Well, there is a good reason, you said it yourself: "*If* Starship will be proven by 2021". That's a pretty huge "if" - I believe Musk just said in an interview that he could *theoretically* land an uncrewed Starship on the moon in under two years. Which between Musk's optimism on timelines, and the fact that he used such size large qualifiers, probably means it's completely unrealistic on that timescale. And that's even before you add the likely years of testing to get Starship man-rated to NASA's satisfaction. So, do we wait around until we figure out how long Starship is really going to take to become crew-ready? Or do we start with what we actually have available?
Because without Starship, an ongoing lunar project needs a reusable lander that can remain in orbit - it's mass would cut far too deeply into the already meager trans-lunar payload capacity. And that lander is going to need to be serviced - something you probably don't want to do in the midst of a cloud of ever-present moon dust - that stuff is *incredibly* destructive. So you're going to be doing servicing in orbit, which means you're going to want an orbital workshop - you don't want that mass eating into the payload capacity of either leg of the journey.
Given that I suspect a good deal of the renewed energy at NASA is due to a certain president operating on a non-negotiable political timetable, I can hardly fault them for pushing ahead with the preexisting plan using mostly existing technology - the end goal isn't half so important to their funding as publicly visible results.