Since the start of the proposed 2024 vanity project, NASA has known the Europa mission was going to be an Achilles heel for Boeing to cover the near term number of SLS vehicles required in the early 2020's. If I recall correctly, Bridenstine has stated that Artemis would not take away from other science missions that NASA has on the books. I'm assuming his remarks apply to both budgetary and timeline commitments. Unfortunately for NASA, pulled pork takes a long time to cook and boss Shelby just wants to use his smoker. Without an alternate booster for Europa, here is the current NASA SLS launch order.
- Artemis 1: (Formerly EM-1) 2021, First SLS test launch. Uncrewed Orion capsule on a 20 day mission. Couple of lunar flybys.
- Artemis 2: (Formerly EM-2) 2022, SLS/Orion. Four astronauts on a free return trajectory. Maximum duration of 21 days.
- Europa Mission: 2023, SLS launch
- Artemis 3: (Formerly EM-3) 2024, SLS/Orion. Four astronauts rendezvous with a minimal gateway equipped with a lunar lander. Two astronauts land on the moon for an approximate one week stay. Possibly four lunar walks are to be scheduled.
Can't forget all of the commercial support launches that are still in a state of flux. For example, some at NASA have proposed pre-positioning a lunar rover near the landing site prior to a crewed landing. Puzzling to me, where is there an Apollo 9 type mission for Artemis? Is NASA/ASAP really okay with not human flight testing a lunar lander prior to an actual landing? This could all be accomplished with commercial launches, but then there's a problem. It all circle back to Shelby's proclamation that any crewed support for Artemis must be launched by SLS. Regardless of NASA timelines or demand for SLS production, Boeing is just loving their blank check government funding.