NASA is continuing to take steps to encourage companies to explore space station developments, both on the International Space Station and beyond.

The agency is fine-tuning a request for proposals targeting stand-alone space stations. The idea is to parallel the cargo services to the International Space Station that are currently flying and the lunar lander delivery system NASA is aiming to establish as an early component of its Artemis program to land humans on the moon by 2024. The request comes after a former administrator called for more engagement from the industry, according to SpaceNews .

"Somebody's got to come up with a business case that helps people understand that there is value in going into low Earth orbit," Charles Bolden , who led NASA between 2009 and 2017, said at the National Academy of Engineering, according to SpaceNews.

You can see NASA's draft request for proposals here.

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"The government spent a lot of money allowing the private sector to go use this test facility so that they could step off and go make money," Bolden said. "Jump off the International Space Station and build the low Earth orbit infrastructure that we have got to have if we're going to successfully send humans back to the moon and on to Mars."

The idea here is that the International Space Station has given companies a taste of the potential for moving processes like manufacturing and pharmaceutical production to microgravity environments. But the space station is aging, and estimates suggest it will need to be retired in about a decade.

Rather than space agencies building a new space station, the theory goes, commercial companies can build their own facilities. NASA and its counterparts could then book time on such stations for projects that need microgravity conditions .

According to SpaceNews, NASA wants to spend $561 million between now and 2024 on commercial space station projects, both on board the International Space Station and through stand-alone developments. But while the agency asked for $150 million for its commercialization effort in its next budget, the Senate appropriations bill offers just one-tenth, $15 million, of that amount.

Nevertheless, NASA released a draft call for proposals for stand-alone commercial space stations before publishing a final version next month. In addition to outlining goals for the project, the draft includes habitability criteria such stations must be able to meet, such as waste management systems, exercise infrastructure and crew privacy.