NASA has begun a feasibility study to consider the risks and benefits associated with adding astronauts to the first integrated launch of the Space Launch System (SLS) rocket and the Orion spacecraft. Under the space agency’s current plans, the debut integrated flight — Exploration Mission-1 (EM-1) — is scheduled for sometime in 2019, and the first crewed launch would follow in 2021.

If the study, expected to be completed by this spring, concludes that the benefits associated with a crewed flight outweigh the risks, and if the resources needed to carry out such a test are in place, two astronauts may be launched aboard an Orion capsule in mid-2019.

“If the agency decides to put crew on the first flight, the mission profile for Exploration Mission-2 would likely replace it, which is an approximately eight-day mission with a multi-translunar injection with a free return trajectory,” NASA said in a statement. “Regardless of the outcome for the study, the feasibility assessment does not conflict with NASA’s ongoing work schedules for the first two missions.”

The SLS, a successor to the agency’s now-defunct Space Shuttle program, is crucial for realizing NASA’s deep-space exploration ambitions — including crewed missions to Mars. The SLS’ engines will be the same that powered the Space Shuttle program. These engines have been used during 135 space shuttle missions between 1981 and 2011, and four of them, providing a combined thrust of 2 million pounds, will be used to power the rocket.

“The SLS and Orion missions, coupled with record levels of private investment in space, will help put the agency and America in a position to unlock the mysteries of space and to ensure this nation’s world preeminence in exploring the cosmos,” the space agency said.

During the first mission of SLS and Orion, NASA plans to send the spacecraft into a distant lunar retrograde orbit — a stable orbit that would involve a flyby of the moon. The space agency says that the challenging mission would help it test maneuvers needed to accomplish future missions to deep space.

“Our priority is to ensure the safe and effective execution of all our planned exploration missions with the Orion spacecraft and Space Launch System rocket,” William Gerstenmaier, the associate administrator for NASA’s Human Exploration and Operations Mission Directorate in Washington, said. “This is an assessment and not a decision as the primary mission for EM-1 remains an uncrewed flight test.”