Artemis question: Why six days to reach the moon, when it only took Apollo a little over three?

[Silent3]

Is this just for the first mission? Will later uncrewed missions be faster? Will crewed missions be faster, since keeping radiation exposure to a minimum is a good idea?

I've tried to find answers to this online, but either my Google-fu is weak, or the information is hard to find.

[Wounded Bear]

1. Probably a fuel savings and training for the future...

the faster you go, the more acceleration you need and that takes more fuel.

They're flying a bigger capsule with more room to move around in, so it's also training for future deep space missions, like to Mars.

[Silent3]

3. I realize the fuel savings, but if you're trying to emulate what future missions will be like...

...I'm not sure if they'll also want to save as much fuel when sending people, or will prioritize speed at that point.

I imagine NASA needs to run at least one uncrewed mission that emulates as closely as possible the conditions of the crewed mission that follows.

[Wounded Bear]

5. This is the uncrewed mission...

next is a crewed missions that will orbit the moon but not land, probably next year.

The landing is set for 2024/25 IIRC from some commentary I heard.

They've done extended missions in the Space Station, but that is probably not the same as an interplanetary mission. It's kind of exciting times for space travel.

[Gore1FL]

6. They want to test the ship's performance in lunar orbit more than anything else.

Of course, re-entry is a big one, too.

On the way they'll do correction burns, but that data will be very similar to anything done on a "faster" orbit.

[FraDon]

2. They took the scenic route.

n/t

[AZSkiffyGeek]

8. Maybe navigating between all of the satellites up there now? nt

[Gore1FL]

4. I can't speak to Artemis I

But, in the past, unmanned lunar missions have taken longer for fuel savings.

[unblock]

7. There refused to stop and ask for directions

[DBoon]

9. they couldn't read the map and got lost

[yourout]

10. They are using a elliptical entrance to a much higher parking orbit.

https://www.nasa.gov/image-feature/artemis-i-map

Much like how the web telescope is now using LaGrange point gravitational fields for parking....flight Dynamics have changed pretty dramatically in the last 20 years as the understanding of gravitational relationships of orbital bodies has advanced.

[keithbvadu2]

14. Usually we figure that the flight path is closely timed.

This one is quite variable for orbits and length of trip.

[muriel_volestrangler]

16. And this Distant Retrograde Orbit is a bit like the one planned for the Lunar Gateway

so maybe this gives them experience for what that will require.

An international collaboration, Gateway is a human-tended, small station that will orbit the Moon. The lunar outpost is specially designed to enable deep space exploration with many capabilities for maintaining a sustained presence in space and conducting research in a deep space environment. Features like a human habitat, multiple docking ports for a variety of spacecraft, including Orion, and the ability to host experiments that will study space weather will all help contribute to future exploration efforts. Similarly, Gateway’s unique near-rectilinear halo orbit, or NRHO, was specifically chosen to help ensure the success of future Artemis missions.

There is no shortage of options for how a spacecraft could orbit the Moon, but two in particular – low lunar orbit and distant retrograde orbit – are helpful for understanding why NRHO is the right fit for Gateway.
...
Meanwhile, a distant retrograde orbit provides a large, circular, and stable (or more fuel-efficient) orbit that circles the Moon every two weeks. However, what Gateway would gain in a stable orbit, it would lose in easy access to the Moon: the distant orbit would make it harder to get to the lunar surface.

A third option, NRHO, is just right for Gateway, marrying the upsides of low lunar orbit (surface access) with the benefits of distant retrograde orbit (fuel efficiency). Hanging almost like a necklace from the Moon, NRHO is a one-week orbit that is balanced between the Earth’s and Moon’s gravity. This orbit will periodically bring Gateway close enough to the lunar surface to provide simple access to the Moon’s South Pole where astronauts will test capabilities for living on other planetary bodies, including Mars. NRHO can also provide astronauts and their spacecraft with access to other landing sites around the Moon in addition to the South Pole.

https://www.nasa.gov/feature/a-lunar-orbit-that-s-just-right-for-the-international-gateway

[FBaggins]

11. Apollo carried humans

No need to rush

[GreenWave]

12. They can only travel at the speed of Star Trek.

Star Trek is currently doing Pike's missions who predates Kirk!

[JHB]

13. Differences in life support trade-offs?

Apollo pioneered the sort of life support (LS) technology needed to keep 3 astronauts alive and healthy for mission time + travel time. Minimizing travel time effectively meant less time in use for something to go wrong.

Now, with the extended-life-support experience of the entire Apollo program and several space stations, NASA has confidence that the extra travel time isn't a major LS factor, so they could allocate part of the numerous design trade-offs to enhance other systems.

[Angleae]

15. Apollo used the biggest, most powerful rocket ever launched into space (Saturn V).

Artemis is using the Space Launch System (SLS) which looks like about 2/3rds the capability.

[muriel_volestrangler]

18. The SLS is 15% more powerful than the Saturn V at take-off

https://www.nasa.gov/exploration/systems/sls/fs/sls.html

but the dry mass of the Orion command and service modules is about 16 tons ( https://en.wikipedia.org/wiki/Orion_%28spacecraft%29 ), while for Apollo it was about 12 tons - https://en.wikipedia.org/wiki/Apollo_command_and_service_module . Artemis 2 is planned to take 4 people round the Moon, rather than Apollo's 3, for instance.

[muriel_volestrangler]

17. It is complicated, but if Google doesn't get you there, try Wikipedia

because there's almost certainly been some editors who asked the same questions.

Artemis 2 will have a different trajectory ("free return" - a bit more like the Apollo 13 one (once round the back of the Moon and then home), but it will still take about 4 days to get there, and also has an elliptical Earth orbit before it (saves a bit of fuel, I think - it's more efficient to accelerate at low altitude, so can be worth doing 2 burns at low altitude, rather than 1 longer one - the Indians used 5 orbits to gradually raise their Moon probe: https://en.wikipedia.org/wiki/Chandrayaan-2#Geocentric_phase ):


https://en.wikipedia.org/wiki/Artemis_2

Artemis 3, which will land on the Moon, involves using a 'halo' orbit round the Moon, so is different again - I can't see how long it is expected to take to get there: https://en.wikipedia.org/wiki/Artemis_3