NASA has delayed its projected first crewed flight of the Orion crew capsule, the vehicle the space agency hopes will take astronauts to Mars someday. The first crewed mission — called EM-2 — is now scheduled for April 2023; the flight was originally scheduled for August 2021. NASA pushed back its schedule for humans on Orion after a design review, and based on how much funding the program is scheduled to receive from the president's budget request.

Bill Gerstenmaier, the associate administrator for human exploration at NASA, said the Orion team made some structural changes to the spacecraft, which contributed to the delay. "We did some changes to reduce weight, took a lot of weight out of the structure for EM-1 and EM-2, reduced the number of cone panels that make up the cone section of the Orion," Gerstenmaier said at a press conference.

The first crewed mission — called EM-2 — is now scheduled for April 2023

Gerstenmaier said the Orion team will still strive to meet the 2021 date, but they are being conservative about the timeline given the new unknowns introduced into the vehicle design. The schedule also better lines up with the projected budget for the program, said NASA, which is expected to cost $6.77 billion from October 2015 to April 2023. Gerstenmaier noted the EM-2 delay shouldn't affect follow up missions of the Orion. The next uncrewed test flight of the Orion is still scheduled for September 2018.

Though some argue the move is completely due to budget concerns. SpaceNews reporter Jeff Foust tweeted a response to the delay from Representative Lamar Smith, Chairman of the Science, Space, and Technology Committee. (Smith also emailed The Verge the same statement.) Smith blames the change on a lack of funding from the presidential budget: "Once again, the Obama administration is choosing to delay deep space exploration priorities such as Orion and the Space Launch System that will take U.S. astronauts to the Moon, Mars, and beyond. While this administration has consistently cut funding for these programs and delayed their development, Congress has consistently restored funding as part of our commitment to maintaining American leadership in space."

Didn’t take long for the House Science Committee to react to news of a potential EM-2 delay to 2023:pic.twitter.com/agvVQ5DeGm — Jeff Foust (@jeff_foust) September 16, 2015

However, NASA Administrator Charles Bolden has blamed Congress on several occasions for underfunding various NASA programs — notably the Commercial Crew Program. "Had Congress adequately funded President Obama’s Commercial Crew proposal, we could have been making final preparations this year to once again launch American astronauts to space from American soil aboard American spacecraft," Bolden wrote in an op-ed last month.

So far, Orion has met most of its major milestones. The spacecraft made its first uncrewed test flight in December 2014. The engineering team also recently demonstrated the Orion could land safely despite the failure of two of its parachutes. NASA hopes to eventually launch the Orion on top of the Space Launch System (SLS) — a giant rocket the space agency is currently building to go beyond lower Earth orbit. The plan is to send astronauts on the Orion to Mars sometime in the 2030s.

Update September 16th, 2:55 PM ET: This post was updated to include a statement from Representative Lamar Smith.