Boeing says it has submitted its proposal for a lunar lander capable of putting astronauts on the moon by as early as 2024, joining a competition that includes Amazon CEO Jeff Bezos’ Blue Origin space venture and most likely SpaceX as well.

Today marked the deadline for submissions. NASA says it’s aiming to select at least two proposed landing systems by January for further development. Two separate teams could be selected to build landers for moon missions in 2024 and 2025.

NASA envisions a system that includes a transfer vehicle to ferry a lander from a lunar-orbiting Gateway outpost to an orbit that’s closer to the moon, a descent element that would put astronauts onto the surface, and an ascent element that would carry them back to the Gateway.

But Boeing said its lander wouldn’t require the extra ride on a transfer vehicle. Instead, the linked-up descent and ascent elements could be sent directly to low lunar orbit, using a beefed-up version of NASA’s Space Launch System rocket.

“Using the lift capability of NASA’s Space Launch System (SLS) Block 1B, we have developed a ‘Fewest Steps to the Moon’ approach that minimizes mission complexity, while offering the safest and most direct path to the lunar surface,” Jim Chilton, senior vice president of space and launch for Boeing Defense, Space & Security, said in a news release.

Boeing, which is the lead contractor for the SLS core stage, said the rocket’s lift capability and the simplicity of the landing system would shorten development time and lower risk. It’s not clear whether the Block 1B version of the SLS would be ready in time for a 2024 mission, however.

Key technologies also would be adapted from Boeing’s CST-100 Starliner space taxi, which is due to start transporting astronauts to and from the International Space Station next year.

Blue Origin’s proposal for a lunar landing system, unveiled last month, featured partnerships with Lockheed Martin, Northrop Grumman and Draper. Boeing didn’t mention any commercial partnerships but said it would work with NASA’s Marshall Space Flight Center, Johnson Space Center and Kennedy Space Center.

Last month, NASA Administrator Jim Bridenstine said he suspected that SpaceX would propose using its Starship super-spaceship as an integrated landing system for the Artemis moon program. SpaceX hasn’t said whether it submitted a proposal, but last month the company’s president, Gwynne Shotwell, said “we definitely want to land [Starship] on the moon before 2022.”

Shotwell said the first lunar landing would pre-position cargo “to make sure that there are resources for the folks that ultimately land on the moon by 2024, if things go well.” She acknowledged, however, that her schedule reflected “an aspirational time frame.”