As recently as last month, both NASA planning documents and officials with Boeing said the space agency was still working toward a 2020 launch of the Artemis-1 mission. This is the first launch of the large, costly, and delayed Space Launch System rocket that NASA hopes will serve as the backbone for its efforts to explore the Moon and eventually Mars with humans.

This uncrewed test flight, which will boost an Orion capsule to the Moon, is the first of three main missions in NASA's Artemis campaign to land humans on the Moon by 2024. However, for the first time, NASA Administrator Jim Bridenstine on Wednesday foreclosed the possibility of a 2020 launch date.

Twice during testimony before the US Senate Committee on Commerce, Science, and Transportation, Bridenstine referenced 2021 as the expected launch date for Artemis-1. "I think 2021 is definitely achievable for the Artemis-1 launch vehicle," Bridenstine said in response to a question from Sen. Roger Wicker, the Mississippi Republican who chairs the committee.

However, Bridenstine said he would not set a new date for the mission yet. Last week, he reassigned two top officials in NASA's human spaceflight department, Bill Gerstenmaier and Bill Hill, in part because of cost overruns and delays with the SLS rocket's core stage. Bridenstine is now searching for replacements, both within and outside of NASA, to fill these key roles and assess the readiness of the SLS rocket.

"NASA has not been good at setting realistic budget and schedules, and we need to get better at that," Bridenstine said. "So before we announce a new date I want to be sure that we have a leadership team in place."

In his written testimony for the hearing, Bridenstine added one relevant detail about this schedule. "The NASA Office of the Chief Financial Officer performed a schedule risk assessment of the Artemis 1 launch date, including the integrated schedule and associated risk factors ahead of Artemis 1," he wrote. "NASA leadership is currently evaluating these results."

According to a NASA source familiar with this assessment, the agency found that under current plans, including a "green run" test firing of the core stage at Stennis Space Center in 2020, the Artemis-1 mission would not be ready for launch until at least "late 2021." Moreover, NASA was likely to need more money—above the more than $2 billion it already receives annually for SLS development—to realistically make a late 2021 launch date.

Previously, Bridenstine has said that, with modifications, the privately built Falcon Heavy rocket could carry astronauts on Orion to the Moon if the SLS rocket was not ready. However, due to pressure from key figures in Congress, most notably Alabama Senator Richard Shelby, Bridenstine has since said that will not happen. "We can take some decisions off the table," he said this week in a teleconference with reporters. "We will be going with the SLS rocket and Orion crew capsule. It is imperative."