Link here. This is a nice summary of the technical and political options being considered for the first unmanned Orion test flight, presently scheduled for June 2020, including replacing SLS with commercial launch rockets.
The article also noted that NASA is also looking at simplifying that test flight, because both SLS and Orion are behind schedule and this would make using a commercial rocket easier.
The currently baselined EM-1 [the test] mission would launch an uncrewed Orion spacecraft on a trans-lunar injection (TLI) trajectory; once released from the launch vehicle, it will fly solo for the first time. The Orion would then make two large engine burns to insert itself into a Distant Retrograde Orbit (DRO) around the Moon. Depending on the time of year, Orion would stay in the DRO for a half or one and a half orbits before making two more large engine burns to return to Earth. Preliminary analysis indicates a June, 2020, launch of the full-up mission would fall into the “long-class” category, with Orion staying in a DRO with a twelve-day long period for one and a half laps and flying a five-week long flight.
Prior to Administrator Bridenstine’s announcement of the alternate launch study for EM-1, notes passed to [this website] indicated that NASA Human Exploration and Operations Mission Directorate (HEOMD) Associate Administrator Bill Gerstenmaier had sent out a memo in early March indicating that studies to look at ways to keep the EM-1 launch in 2020 could not compromise any of the mission objectives; besides that, everything else was on the table.
The highest priority objective of the EM-1 mission is a lunar-velocity reentry test of the redesigned Orion heatshield, along with a full end-to-end test of the re-entry sequence and an in-space demonstration of Orion systems, many of which are flying for the first time.
Although Bridenstine’s public comments stressed flying EM-1 as a lunar orbit mission, there has been speculation that launching Orion out to near lunar distance without attempting either a lunar orbit or a lunar flyby could meet the highest priority objectives. Dropping the lunar orbit requirement or lunar flyby options would also relax launch opportunity constraints created by flying to the Moon and could perhaps reduce launch vehicle performance requirements enough to drop the [Earth orbit rendezvous] proposal and [docking] development work. [emphasis mine]
To use commercial rockets and still go into lunar orbit would require at least two commercial launches to get the required material up to orbit. It would also require developing Orion’s docking software now, something NASA had not planned to do until prior to Orion’s third flight several years hence. Avoiding lunar orbit means they can use a single Falcon Heavy launch and avoid these issues.
The highlighted phrase above indicates the most important priority of the test flight. This does not require lunar orbit. In fact, the Apollo mission tested its heat shield without leaving Earth orbit, and Orion can do the same.
It is still bothersome to read how haphazard NASA’s SLS/Orion program remains. They aren’t doing enough testing, their future flights are always in flux for political, schedule, and budgetary reasons, and they always seem to be in too much of a hurry to fly humans on very unproven vehicles. If NASA’s corrupt safety panel applied the same standards to SLS/Orion as it does to SpaceX and Boeing, the whole program would be shut down. It does not, because safety isn’t really its purpose. That panel’s goal is to serve NASA’s bureaucracy, and to protect its biggest projects (SLS/Orion) from any competition.
As for replacing SLS for that first Orion test flight, we shall see. The political forces opposing such a move are vast, and wield a lot of power.
