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I’ve been looking at “exploded” SLS rockets, where the stages are all shown, and there never seems to be a lunar lander. Does that mean that the Orion Spacecraft lands on the moon, or will it have a lander attached to it?

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  • $\begingroup$ I think the term “direct ascent” is being used incorrectly in this content. A direct ascent is where the vehicle is flying straight up to the moon without going into an orbit beforehand. Similar to a high suborbital flight having the Apogee as high as the moon‘s attitude. The Artemis program will not launch any rockets on such a trajectory even though it was once considered for the Apollo program. $\endgroup$ Sep 27, 2022 at 17:27
  • $\begingroup$ @TheRocketfan "direct ascent" isn't about the trajectory, it's about not assembling the spacecraft in LEO, or leaving part of it in LLO while going to the lunar surface in a separate lander. A direct ascent mission could involve parking temporarily in LEO and LLO, the "directness" comes in not involving rendezvous operations. $\endgroup$ Sep 27, 2022 at 19:03
  • $\begingroup$ @ChristopherJamesHuff Okay thanks for letting me know. $\endgroup$ Sep 28, 2022 at 4:27
  • $\begingroup$ @Blueskinandglowingredeyes direct ascent is not the flight plan for Artemis. However, this is a (somewhat) decent question noting SLS's massive size may look like a direct ascender to the untrained eye. $\endgroup$
    – Xenon
    Oct 14, 2022 at 19:25

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The Artemis mission architecture for crewed missions to the Lunar surface is significantly different from the Apollo mission architecture. The Artemis mission architecture for crewed missions to the Lunar surface consists of five distinct parts:

Gateway

The Gateway is a Lunar space station orbiting the Moon in a Near-Rectilinear Halo Orbit (NRHO). The Gateway will be permanently crewed and will serve as a science station as well as a waystation for crew to go down to the Lunar surface and back up to the Gateway.

The first two modules of the Gateway will be launched on a Falcon Heavy, further modules are planned to be launched as secondary payloads on crewed flights of SLS Block 1B.

Crucially, crew will never go to the Moon from Earth, they will always stop over at the Gateway.

HLS

The HLS is the vehicle which ferries astronauts from the Gateway to the Lunar surface and back from the Lunar surface to the Gateway.

At the moment, NASA has selected SpaceX as the only provider for the HLS, beating out the National Team around Blue Origin and Dynetics. This decision and its aftermath was widely reported even outside of space-specific media outlets, because of the surprising nature of the selection (it was expected that two competitors would be selected and that one of those would be the National Team, which includes several companies that were already involved with the Apollo program), Blue Origin first protesting and then suing everybody and their dog (and losing every protest and lawsuit), and Blue Origin taking to social media with some extremely misleading info graphics, attacking the SpaceX mission architecture.

SpaceX proposed a variant of Starship without heatshield or flaps, with landing legs and a separate set of landing engines, and with very generous crew space as well as ample cargo space.

Orion

Orion is the crew vehicle which will take astronauts from Earth to the Gateway and back. It will be launched on the Space Launch System (SLS).

Crew will launch from Earth in Orion, then dock and transfer to the Gateway (similar to the ISS). From there, they will transfer to the HLS, which will bring them to the Lunar surface and back up again to the Gateway.

CLPS

CLPS is a program which allows NASA to contract a wide variety of commercial launch providers in order to deliver cargo to the Lunar surface. In the beginning, this "cargo" will mostly be rovers and science platforms whose job it is to scout for possible landing sites and sites for temporary and permament Lunar bases as well as potential resources (water ice).

Further into the program, CLPS will deliver both cargo for the Lunar base as well as the elements of the Lunar base itself.

GLS

GLS is the Gateway equivalent to the ISS Commercial Resupply Services program, where NASA "hires" commercial providers to deliver cargo to the station. Currently, NASA has chosen SpaceX as the only provider. SpaceX has proposed a variant of Dragon v2 called Dragon XL as the cargo vehicle.

Modified mission because of delays

At least, that was the original plan. However, by now, it has become clear that the Gateway is delayed. In order to remove Gateway as a blocker, NASA has modified the mission parameters for the first two crewed landings so that Orion docks directly to the HLS in Lunar orbit, without requiring Gateway.

More potential modifications

One thing happened that NASA didn't expect: they asked for a Human Landing System that can bring a few astronauts from the Gateway (or Orion) to the Lunar surface, sustain them there for a couple of days, and then bring them back up to the Gateway (or Orion) again. But then SpaceX decided to propose Starship as the HLS and won the bid. This completely changes the dynamics:

  • A single Starship alone has more pressurized volume than a Boeing 747, about as much habitable volume as the entire ISS, and a lot more habitable volume than the Gateway. In other words, while (one of) the purpose(s) of the Gateway is to allow the astronauts to have more space and more freedom than they have on Orion or the HLS, it turns out that the Starship HLS is actually bigger than the entire station, so there is really no point in the astronauts ever leaving HLS for that reason. In that sense, Starship could serve as the station.
  • A single Starship has more habitable volume than many of the proposed early habitats. In that sense, Starship could serve as the habitat.
  • A single Starship can take more cargo to the Lunar surface in addition to the astronauts and all the cargo required for them, than any of the proposed CLPS providers. So, you could just stash your cargo inside Starship and send it to the Moon that way.
  • Since Artemis 3 requires HLS, Starship will necessarily be operational by the time cargo needs to be shipped to the Gateway. So, instead of using Dragon XL, you could simply stash your cargo inside Starship and send it to the Gateway that way.
  • Once Starship is crew-rated, it could do the entire trip from Earth to the Moon by itself, without the need for either Orion or Gateway, so why have them?
  • A single Starship can support more astronauts than Orion and Gateway combined, so why limit yourself to only 4, when you can fit 40?

Basically, Starship alone could replace almost all elements of Artemis, it can be the crew vehicle, the cargo vehicle, the lander, the station, and the base.

It is very interesting to see how the mission architecture will take advantage of the capabilities Starship offers that NASA did not ask for. NASA has hinted in the source selection statement that the additional capabilities are interesting to them.

However, there are three problems with relying too much on Starship: NASA likes dissimilar redundancy, which means not only having more than one component / system / provider / path for everything, but having different ones as well. See for example Commercial Resupply Services (SpaceX Cargo Dragon, Northrup Grumman Space Systems Cygnus, and Sierra Nevada Corporation Dream Chaser) and Commercial Crew (SpaceX Crew Dragon and Boeing CST-100 Starliner).

A second problem is a legal and political one: if NASA writes their future requirements in such a way that it is clear from the beginning that only Starship can fulfill them, you can be sure there will be a lot of lawsuits from SpaceX's competitors and a lot of political backlash from Congresspeople in the States where Boeing, Lockheed Martin, Blue Origin, Northrop Grumman, Aerojet Rocketdyne, Firefly, Rocket Lab, and all the others are paying their taxes and employing their workers.

The third problem is also political: Artemis is an international cooperation with many partners: Orion's service module is provided by ESA and built by Airbus, both ESA and JAXA are providing modules for Gateway, CSA is providing a robotic arm, and so on. They will not be happy if NASA tells them their contributions are no longer needed.

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  • $\begingroup$ don’t you just love when improving something makes more problems? $\endgroup$ Sep 28, 2022 at 13:50
  • $\begingroup$ Note though that NASA has no public plans for dissimilar redundancy for SLS and Orion. A backup option for those would be politically inconvenient, since their high cost is justified in part by them having unique capabilities that private industry is uninterested in providing. Hence NASA completely ignoring Starship for so long, the uproar over the eventual selection of Starship for the HLS (with Kathy Lueders being removed from decision making for Artemis afterward), and the attempts to legislate selection of another option...one that wouldn't pose a threat to SLS. $\endgroup$ Oct 6, 2022 at 16:48
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Artemis 1 and 2 will not have a lander, they will simply orbit the Moon in a near-rectalinear halo orbit. Artemis 3, slated for launch around 2025, will dock with a lander near the Moon and land. That lander currently is a SpaceX Starship variant, and is known as the "Human Landing System".

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