NASA is mulling over the idea of putting astronauts on the first flight of the Space Launch System (SLS) — the giant heavy-lift rocket the space agency is building to take people to Mars someday. Currently, NASA is hoping to fly the SLS for the first time in fall of 2018, and the original plan was for that mission to be uncrewed. But a new memo sent out to NASA employees this morning shows that the agency will start investigating the possibility of making the debut flight of SLS, called EM-1, a crewed mission instead.

“I have asked Bill Gerstenmaier [the associate administrator of human exploration at NASA] to initiate a study to assess the feasibility of adding a crew to Exploration Mission-1, the first integrated flight of SLS and Orion,” Robert Lightfoot, NASA’s acting administrator, wrote in a memo obtained by The Verge. “I know the challenges associated with such a proposition, like reviewing the technical feasibility, additional resources needed, and clearly the extra work would require a different launch date. That said, I also want to hear about the opportunities it could present to accelerate the effort of the first crewed flight and what it would take to accomplish that first step of pushing humans farther into space.”

The idea was first shared by Lightfoot earlier today at the Space Launch System/Orion Suppliers Conference in Washington, DC. The following memo has supposedly caused a lot of buzz at NASA, a source at the agency tells The Verge, and a lot of people are somewhat excited about the idea. If NASA does move forward with a crewed mission for EM-1, then the launch will most likely be pushed back from late 2018.

The current plan for EM-1 is to launch the SLS from Kennedy Space Center on September 30th, 2018. The vehicle is supposed to carry NASA’s Orion crew capsule —without a crew — into an orbit around the Moon. Orion will spend a total of three weeks in space before coming back and landing on Earth with the aid of parachutes. Astronauts would then ride inside Orion for the first time on EM-2, the second flight of the SLS. That trip isn’t supposed to happen until 2021 at the earliest. 

In today’s memo, Lightfoot noted his recent interactions with the NASA transition team have made it clear that the space agency is a priority to the new administration. He also mentioned that it is “imperative to the mission of the agency that we are successful in safely and effectively executing both the SLS and Orion programs.”

Lockheed Martin, NASA’s primary contractor for the Orion crew capsule, said that it will work with the space agency on determining if a crewed first mission is possible. "Lockheed Martin will support NASA on a study to determine the feasibility of flying a crew on Exploration Mission-1,” Allison Miller, a spokesperson for Lockheed Martin, said in a statement. “We’ll look at accelerating remaining crew system designs, as well as potential technical and schedule challenges and how to mitigate them."

However, safety experts and government investigators have been critical about the development of the SLS and Orion, arguing that the current schedule for the programs aren’t exactly reliable given NASA’s budget. Two reports from the Government Accountability Office last year cast doubt on NASA meeting its 2018 launch date for EM-1, arguing that both SLS and the ground systems needed to launch the vehicle may not be ready before then. Additionally, the GAO said it was concerned about the 2021 date set for the crewed flight EM-2, saying that NASA is accepting higher risk to meet that deadline. NASA has also set a second launch date for EM-2 in April of 2023, in case the 2021 launch date doesn’t pan out. However, the agency has maintained that it has an “aggressive” internal goal of meeting the 2021 date.

Meanwhile, an important piece of hardware is needed for the first crewed flight of the SLS. For EM-1, NASA intends to fly a configuration of SLS known as Block 1. It’s the smallest version of the rocket NASA intends to build that can loft 70 metric tons into lower Earth orbit. For the crewed EM-2 flight, NASA is planning to fly a larger variant of SLS called Block 1B. This version of the rocket is a bit larger and sports a more powerful second stage on top of the vehicle known as the Exploration Upper Stage. However, the Exploration Upper Stage hasn’t even been built yet so it’s unclear if it will be ready soon for EM-1. The design for the Exploration Upper Stage did pass a major review in January.

Ultimately, it remains unclear how NASA will pull this off. Such a goal would probably require bigger budgets for both SLS and Orion, and it could introduce more risk into the equation flying people on a rocket that’s never been flown before. Additionally, NASA will have to create a life-support system for EM-1, something the agency wasn’t expecting to do until EM-2. “It would definitely be a shift in how we do things,” one employee at NASA’s Johnson Space Center tells The Verge.

Lightfoot also used the memo to address the uncertainty surrounding NASA’s long-term plans, something that may have influenced today’s decision. The transition to the Trump administration has left NASA in a momentary vacuum. “There has been a lot of speculation in the public discourse about NASA being pulled in two directions,” he writes. It’s an apparent reference to the constant fight over whether NASA should continue with its plans to send humans to Mars in the 2030s or to redirect its resources toward a return to the Moon.

Mars is considered by many to be a worthy inspirational and scientific goal, but the Moon’s proximity and makeup could create commercial opportunities in the shorter term. NASA’s budget has to be approved every year, and how it gets spent tends to shift from administration to administration. Under Obama, NASA was steered away from Constellation, a post-Shuttle program that was supposed to bring the US back to the Moon. Nevertheless, Lightfoot doesn’t see this agency having to choose between the Moon and Mars. “At NASA, this is an ‘and’ proposition, not an ‘or’,” he writes.

Sean O’Kane contributed to this report.

Update February 15th, 2:00PM ET: The article was updated to include a statement from Lockheed Martin.