NASA Spaceflight: As NASA and its contracted partner agencies press forward toward the debut launch of the Space Launch System (SLS) rocket in 2018, the U.S. space agency is beginning to look toward preliminary planning and test objectives for the EM-2 mission of the SLS Program, which is expected to take place sometime in the opening half of the 2020 decade. by Chris Gebhardt
'As originally conceived in the opening years of the SLS program, the EM-2 mission was to be the first crewed flight of the Orion Multi-Purpose Crew Vehicle that would take astronauts on a multi-day circumlunar mission. However, the feasibility of this mission being one to carry crew was called into question as the EM-2 launch date slipped beyond the opening of the 2020 decade and NASA began investigating the potential advancement of the introduction of the Exploration Upper Stage (EUS) from the third to the second EM flight of SLS.
'Originally, with timelines indicating that EM-2 would follow a couple years after EM-1, it was understood that EM-2 would make use of the same Interim Cryogenic Propulsion Stage (ICPS) as EM-1- with one key difference: The ICPS would be human rated for EM-2. The feasibility of this was quickly challenged as the ICPS’ human rating would cost millions of dollars (USD) for a single-mission event before the switch to the EUS on EM-3 and all subsequent SLS flights.
'Nonetheless, the human-rated ICPS for EM-2 would satisfy the requirement from the astronaut office that no crew fly on any variant of the SLS rocket when a major propulsion element was being used for the first time in flight. However, NASA’s decision to advance the introduction of the EUS to EM-2 created a conflict with that rule – as EM-2 was viewed in its initial conception as the second flight of SLS, thus leaving no room between the EM-1 and EM-2 missions of SLS to test the EUS in flight.'
Baselined HLO mission plus two other options for the flight path and trajectory the EM-2 flight could take here