What are the Exploration Missions? NASA describes these missions as "a series of increasingly complex missions that will enable human exploration to the Moon and Mars". "Blocks" of the Space Launch System (SLS) will enable the creation of GATEWAY - a portal to the lunar environment and beyond.
According to Wikipedia (updated September 2018) EM-1 is not projected to take place any earlier than June 2020. This date is pending an operational SLS.
December 7, 2018 Spaceflight Now stated "Officials now expect the Space Launch System,
So what is Exploration Mission 1 (EM-1)? It is a shakedown flight to make elliptical orbits of the moon by the SLS and unmanned Orion module and return. Power to the Orion module will be supplied by the European Service Module (ESM). As Orion returns to Earth for splashdown the ESM will be detached and lost for reuse. I don't know the ESM contract details but obviously a new one will be required for each Orion Mission, and per Wikipedia there are 12 exploration missions. According to the United Nations Office for Outer Space Affairs The Legal Framework for the International Space Station April 17, 2013 page 35 states "NASA and ESA may collaborate on a second ESM for Exploration Mission-2..."
Wikipedia says that the payloads carried on EM-1 will include the AstroRad Radiation vest from Stemrad for testing. The Workshop on Radiation Monitoring (see Space Radiation) had a Lockheed Martin presentation Orion Exploration Mission 1: Proposed Radiation Measurements in Cislunar Space. Slides 3-6 show configuration for protection from a Solar Proton Event (SPE) - in a nutshell this is high energy radiation that can penetrate the spacecraft. On page 8 of this PDF they stated this vest would give "~2x increase in protection" (to the wearer). Not knowing what the basline was to determine this increase in protection I will just say that any increased protection is welcomed. I expect it to be successful and hope that it would be expanded to include the head and eyes (optic nerve protection) and bone marrow of the entire body. This technology could lead to wider use in spacecraft, human habitate and spacesuit construction.
Here is current news on Exploration Mission 2 "Plan D for Outer Space"
Image courtesy of NASA