WASHINGTON — NASA issued a final version of its call for proposals for a human lunar lander system Sept. 30, giving companies the option to at least initially bypass the lunar Gateway.

The Human Landing System solicitation, part of NASA’s Next Space Technologies for Exploration Partnerships (NextSTEP) program, seeks proposals from U.S. companies for the development of human landers. Those proposals are due to NASA Nov. 1.

The final version of the solicitation, formally known as Appendix H, incorporates comments industry provided to an initial draft, published July 19, and a second draft, published Aug. 30. NASA received more than 1,150 comments to the two drafts, the agency said.

Those comments resulted in some modifications intended to streamline the process and give companies more flexibility. One of the biggest is that NASA will no longer require lunar landers to dock with the lunar Gateway to serve as a staging point, at least for initial missions to the lunar surface.

“The agency’s preferred approach to a lunar landing is for the crew in the Orion spacecraft and the uncrewed human landing system to launch separately and meet in lunar orbit at the Gateway, which is critical to long-term exploration of the moon,” the agency said in a Sept. 30 statement about the solicitation. “NASA wants to explore all options to achieve the 2024 mission and remains open to alternative, innovative approaches.”

Marshall Smith, director of NASA’s human lunar exploration program at NASA Headquarters, discussed that change at a Sept. 26 meeting of the National Academies’ Aeronautics and Space Engineering Board in Irvine, California. “Gateway is essential for 2024,” he said, but the solicitation would allow companies to skip it.

“We are allowing contractors, if they want to propose not going to Gateway, they want to propose going directly to an Orion, they can do that for the ’24 mission only,” he said. “But they have to get to the sustainable case of going to Gateway by 2028.”

“Initially, whatever it takes to get us to the surface of the moon,” he said. “After that, we have to start fitting into the architecture better to get us to Mars.”

Smith said NASA was still expecting to eventually select two companies to proceed with lander development. One company would be expected to have a lander ready for a 2024 landing on the Artemis 3 mission, while the other would get to fly their lander on the Artemis 4 mission, in 2025. NASA will then transition into a lunar lander services contract similar to those for commercial cargo and crew services for the International Space Station.

Other changes, incorporated into an earlier draft of the solicitation, eliminate the requirement for the lander to ultimately be reusable, and also reduce the number of reports companies are expected to provide to NASA.

“We are operating on a timeline that requires us to be flexible to encourage innovation and alternate approaches,” Lisa Watson-Morgan, the Human Landing System program manager at the Marshall Space Flight Center, said in the NASA statement, speaking specifically about the requirement for reusability. “We still welcome the option to refuel the landing system, but we removed it as a requirement.”

NASA justified the short timeline — one month — to submit proposals, citing the fact that companies had an opportunity to comment on two earlier drafts. NASA also previously awarded study contracts to 11 companies in May under a separate NextSTEP solicitation known as Appendix E.

“Every contractor that we think is going to bid on this got contracts under Appendix E,” Smith said at the board meeting. “They’ve been working with us since June, working on the requirements that we’re putting together for Appendix H.” NASA’s work preparing the solicitation over the last six months, he added, would have taken the “old NASA” two years to do.

“We know it’s crazy,” he said of the one-month timeline for proposals, “but so is 2024 sometimes.”