Artemis limping to the Moon

[glend (Glen)]

Can someone explain to me why it is taking Artemis so long to reach the Moon? I have been watching the various trackers and the capsule is constantly slowing down (without thrust being applied), last time I looked it was going 750mph, after leaving Earth at over 21,000mph. . Perhaps the idea is to just place it within the Moon orbital path and hope it gets grabbed. I am sure there are people working on the orbital mechanics, but it just seems very different to Apollo era mission mechanics. I realise there are no crew onboard and no consumables being used up, but it seems to be taking twice as long as an Apollo transit. How is this progress?

[mura_gadi (Steve)]

A few things come to mind.

Its a test mission, right down to the commander dummies etc, may as well have a long time for testing purposes.

Artemis will have a capsule that can sustain a crew for up to 21days, Apollo did not have this luxury.

Artemis is using a gravity assisted approach and a two stage system not three stages that Apollo used.

I'm sure other will already be in the know or find a link to what's what though.

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One from the interweb
"Apollo burned a lot of fuel in exchange for a quicker mission. Back in the 60's the spacecraft had a very short lifespan, mostly limited by the capacity of the batteries. Nowadays battery capacity is much better, and so is solar panel technology, so missions can afford to spend an extra few days in exchange for saving on some fuel (weight).

If you look at unmanned probe mission to the moon, some take fuel economy to extremes, and take weeks to get there. Roughly speaking, you can get to most destinations in the solar system on very little fuel if you are prepared to wait (sometimes many years) for the right launch conditions, and can tolerate very long flight times."

[Startrek (Martin)]

Long duration unmanned mission to test out new spacecraft and systems for future manned missions
Plus an entirely different lunar injection trajectory and orbit than the Apollo missions. I think from memory it’s furthest point from the backside of the moon will be 71,000km , so a huge elliptical orbit
Re entry will be different than Apollo too , an intentional steeper entry angle to subject the Orion capsule to severe G force loadings, probably in the order of 10 to 12G’s

I too was waiting to see video of the Moon in around 3 days , just like I did watching all the Apollo missions from 7 to 17

[Stonius (Markus)]

Looking at the mission plan on https://www.nasa.gov/specials/trackartemis/ it appears more like they're shooting it into the path of the moon where it almost seems to stop before the moon comes past and sweeps it up.

[DarkArts]

The NASA Artemis website explains the trajectory being taken, but is a bit short on comparison to Apollo.

Originally Posted by https://space.stackexchange.com/questions/58736/how-can-artemis-1-take-so-much-longer-for-earth-lunar-transit-than-the-apollo-mi

The goal of the Apollo missions was to land humans on the Moon and return them to Earth. That requires a surprisingly large delta-V capability. (In terms of delta-V, is easier to land a vehicle on Mars and leave it there than it is to land a vehicle on the Moon and leave it there.) The Space Launch System plus the Orion capsule do not have the delta-V needed to land a vehicle on the Moon and return it to Earth. SLS plus Orion does not even have the delta-V needed to insert into and later return from low lunar orbit.

On the other hand, the Orion capsule has an extremely capable environmental control and life support system (ECLSS), capable of supporting a crew of six for 21 days. It can afford to make a leisurely trip. The Apollo vehicles did not have this luxury as they had a rather limited ECLSS capabilities. The outbound and inbound trajectories to and from the Moon were intentionally designed to be suboptimal with regard to delta-V so as to make the trip take less time. Had the Apollo vehicles used optimal trajectories (from the perspective of delta-V) the result would have been dead bodies returning to Earth.

The Apollo missions had the spacecraft immediately enter low lunar orbit upon getting close to the Moon. The Artemis-1 mission will instead use close lunar approach as a powered gravity assist and days later inject the vehicle into a distant retrograde orbit (DRO) about the Moon. The drift from closest approach to the Moon to DRO insertion will take a few days. Targeting lunar DRO as opposed to targeting low lunar orbit reduces the required delta-V to something the SLS+Orion can handle. (Subsequent missions will place the vehicle into a near-rectilinear halo orbit, with similar delta-V requirements.) The greater time needed for a fuel-optimal trajectory to lunar periapsis followed by a drift to DRO altitude combine to make the outgoing trip take eight days rather than a bit more than the three days used by the Apollo missions.