> "Maybe I'm missing some details but I thought the entire purpose of first-stage rockets was to get a certain payload with certain max dimensions (what can fit inside a cylinder of a certain height and radius) to LEO, or the equivalent delta-V. At that point first stage is discarded anyway. So what exactly the payload is (beyond its dimensions) and you do with your payload after getting to LEO (or equiv delta V) that shouldn't really make a difference,"
It makes a difference because if you're designing a rocket for a mission then you'll have a rocket that's as close to optimal for the mission, given mission requirements, timelines and budgets as you can reasonably get it. That's not SLS, the Moon mission wasn't planned when SLS was designed and instead SLS is optimized to reuse Shuttle hardware.
Being stuck with a rocket that wasn't designed for the mission, as well as the political decision to use Orion, severely compromise the planning of Artemis. SLS lacks the power to get Orion into a proper lunar orbit, so instead they're going to use a highly elliptical NHRO lunar orbit with an orbital period of 7 days. This is extremely dangerous, it means that if there is any sort of emergency on the moon the astronauts may have to wait as long as a week to get back to Orion; which is probably a death sentence. It also means the lander has to be huge to make up for SLS's inadequacy, which means the Artemis program now relies on the success of Starship HLS and/or Blue Origin's HLS. This is going to delay Artemis and the entire reason this dependency exists is because Congress wanted a shuttle-derived rocket foremost, and then made the situation even worse by saddling it with their Boeing pork capsule.
What it comes down to is SLS is a rocket that ""works"" but isn't actually good at anything and therefore never should have been built.
It makes a difference because if you're designing a rocket for a mission then you'll have a rocket that's as close to optimal for the mission, given mission requirements, timelines and budgets as you can reasonably get it. That's not SLS, the Moon mission wasn't planned when SLS was designed and instead SLS is optimized to reuse Shuttle hardware.
Being stuck with a rocket that wasn't designed for the mission, as well as the political decision to use Orion, severely compromise the planning of Artemis. SLS lacks the power to get Orion into a proper lunar orbit, so instead they're going to use a highly elliptical NHRO lunar orbit with an orbital period of 7 days. This is extremely dangerous, it means that if there is any sort of emergency on the moon the astronauts may have to wait as long as a week to get back to Orion; which is probably a death sentence. It also means the lander has to be huge to make up for SLS's inadequacy, which means the Artemis program now relies on the success of Starship HLS and/or Blue Origin's HLS. This is going to delay Artemis and the entire reason this dependency exists is because Congress wanted a shuttle-derived rocket foremost, and then made the situation even worse by saddling it with their Boeing pork capsule.
What it comes down to is SLS is a rocket that ""works"" but isn't actually good at anything and therefore never should have been built.