During Exploration Mission-1 (EM-1), the spacecraft will travel thousands of miles beyond the moon over the course of about a three-week mission. Following launch on SLS, the Orion spacecraft will deploy its solar arrays, leave Earth’s orbit, and travel toward the moon. From there, Orion will separate from the Interim Cryogenic Propulsion Stage (ICPS) that has boosted it toward the Moon. The ICPS will then deploy a number of small cubesats to perform several experiments and technology demonstrations.
Orion will then be propelled on toward the moon by a service module provided by the European Space Agency. The outbound trip to the moon will take several days, during which time engineers will evaluate the spacecraft’s systems and, as needed, correct its trajectory. Orion will skim just 60 miles above the surface of the moon, and then use the moon’s gravitational force to propel it into a new deep retrograde orbit (a far-reaching orbit opposite the direction of the moon’s rotation) extending about 40,000 miles from the moon. Orion will remain in that orbit for approximately six days to collect data and allow mission controllers to assess the performance of the spacecraft. For its return trip to Earth, Orion will do another close flyby that takes the spacecraft within about 60 miles of the moon’s surface, and the spacecraft will use a precisely timed engine firing of the service module in conjunction with the moon’s gravity to accelerate back toward Earth.
The second flight of Orion atop SLS – called “Exploration Mission-2” will be the second flight test, but the first with crew and the larger version of the SLS. It will also be the first time that humans have traveled beyond Earth orbit since Apollo. The EM-2 mission profile allows for NASA and the Orion crew to check out Orion systems on two highly-elliptical orbits around the Earth before committing the spacecraft and crew to a free-return trans-lunar injection. If no major course correction maneuvers are made during the outbound leg, the free-return trajectory would naturally carry Orion around the far side of the moon and back to the Earth, for a total mission duration of approximately 8 days. If after the TLI burn Orion’s systems are performing well, NASA can elect instead to do a trajectory burn that would transition the spacecraft out of a free-return trajectory and into a partial distant retrograde orbit around the moon, followed later by a burn of the Service Module to exit the cis-lunar orbit and begin the return to Earth. In this case, the total mission duration would be approximately 21 days.