WASHINGTON — NASA is expected to announce awards for human lunar lander development later this month as two senators press NASA to stay the course on the use of commercial partnerships for those landers.

NASA requested proposals last fall for its Human Landing System (HLS) program, where companies will develop human lunar landers for the Artemis program through public-private partnerships. Proposals were due to NASA in early November 2019, with the agency planning to then select up to four companies for initial design and development studies, lasting 10 months. NASA would then choose one or two of them to proceed with full-scale lander development.

At the time NASA released the call for proposals, formally known as a broad agency announcement that is part of its Next Space Technologies for Exploration Partnerships (NextSTEP) program, NASA said is expected to make those initial awards in January 2020.

However, NASA has yet to announce any selections, and the most recent procurement update, published Feb. 10, stated that it expected to make awards in late March or early April. A NASA spokesperson said April 16 that NASA expects to announce the HLS awards this month, but has not set a specific date yet.

NASA hasn’t explained why the HLS awards have slipped. However, NASA has been revising its overall lunar exploration architecture in order to meet the goal of returning humans to the surface of the moon by the end of 2024, the goal set by the White House a little more than a year ago.

At a March 13 meeting of the NASA Advisory Council’s science committee, Doug Loverro, NASA associate administrator for human exploration and operations, said he had been working to “de-risk” the program since taking the position in December. That included taking the lunar Gateway off the critical path for that 2024 return, while retaining it for the long-term, sustainable lunar presence sought by NASA.

Loverro also hinted at that meeting that NASA was backing away from its original architecture for a lunar lander that involved an ascent module, descent module, and transfer stage. Each element could be launched individually and aggregated at the Gateway.

“Program risk is driven by which things haven’t you done in space before that you would now have to do in this mission,” he said then, referring to plans “to launch a lander in three individual pieces that have to meet up at the moon,” the approach NASA has previously discussed. “We’ve never done that before, so we’d like to try to avoid doing things we’ve never done before.”

In an April 14 letter to NASA Administrator Jim Bridenstine, Sens. Marco Rubio (R-Fla.) and Richard Blumenthal (D-Conn.) said the agency should stick to its original approach to the HLS program.

“NASA’s competitive, industry-led acquisition strategy for the HLS program recognizes that when industry and government work together, they produce the best results for the nation,” they wrote in the letter, publicly released April 15. “We urge you to proceed with the HLS acquisition as currently planned.”

The senators also called on NASA to use a similar approach for future large cargo lunar landers, which may be needed for delivering infrastructure needed for the sustainable phase of lunar exploration. “Given the significant investment by both NASA and the private sector, and the important progress already being made, we encourage you to expeditiously partner with industry for the development of one or more large cargo landers and follow-on services,” they wrote.

Three industry teams have announced they submitted HLS proposals. One is a team led by Blue Origin with partners Draper, Lockheed Martin and Northrop Grumman. Boeing said it was offering a lunar lander that could be launched as a single unit on a Space Launch System rocket. Dynetics confirmed in January it submitted a proposal, leading a team that includes Sierra Nevada Corporation.

Other companies may have submitted HLS proposals but have not disclosed them. For example, there is widespread speculation SpaceX submitted a proposal, but the company has declined to confirm it.

While the coronavirus pandemic has slowed many NASA activities, it doesn’t appear to have had a major impact on the HLS program. In an online town hall meeting April 2, officials with the Marshall Space Flight Center, which hosts the HLS program, said that program was among those that was continuing uninterrupted through telework.

At the time of the town hall meeting, Marshall officials expected HLS awards to be announced soon. “We should hear something fairly soon from Washington on that,” Paul McConnaughey, deputy center director, said.