WASHINGTON — As NASA prepares to request proposals from industry to develop the first element of its proposed cislunar gateway, the agency says it may be open to buying more than one of the modules.

NASA’s Lunar Orbital Platform-Gateway, previously known as the Deep Space Gateway, will incorporate several modules, starting with one called the Power and Propulsion Element (PPE). That element will provide power for the gateway and also use electric propulsion to maneuver the complex in cislunar space.

During a March 27 meeting of the NASA Advisory Council’s human exploration and operations committee, Michele Gates, director of the Power and Propulsion Element at NASA Headquarters, said the agency was ready to move ahead with procurement of the module after five industry studies wrapped up earlier this month.

The four-month studies, led by Boeing, Lockheed Martin, Orbital ATK, Sierra Nevada Corporation and Space Systems Loral, examined nearly two dozen topics, ranging from the overall design approach for the PPE to specific engineering details.

Some of those companies were involved in previous studies for NASA’s Asteroid Redirect Mission, which also intended to use electric propulsion on its robotic spacecraft to retrieve a boulder from a near Earth asteroid. “Our strategy is to leverage all of the work that’s been done, including on the Asteroid Redirect Mission,” said Gates, who previously managed those efforts.

For the PPE, NASA plans to develop the module in a public private partnership with industry. Once the module is launched and its performance demonstrated in space, NASA would have the option to then buy the module for use in the gateway.

Gates said that NASA expects to issue a draft solicitation for the PPE in April, with an industry day to take place in late April or early May. A final solicitation will then follow, with proposals due to NASA in late July.

NASA envisions a 2022 launch of the PPE on a commercial launch vehicle. There is “substantial” funding planned to support its development, she said, including $51.5 million for the current fiscal year and $542.1 million projected through fiscal year 2022.

However, NASA is not restricted to buying a single PPE. The proposal synopsis, released in February, states that NASA is planning “potentially one or more contract awards” for PPE development.

Bill Gerstenmaier, NASA associate administrator for human exploration and operations, said the agency would be open to selecting more than one proposal for development and in-space demonstration depending on what was proposed, and at what price.

“The architecture is open enough that we can tolerate more than one of these Power and Propulsion Elements in the vicinity of the moon, if we got the right prices and the right considerations,” he said. “The architecture is broad enough and open enough that we can accommodate more of these in orbit.”

In that approach, he said, one PPE would be used at the gateway. Additional PPEs could be used for other aspects of NASA’s lunar exploration campaign, such as serving as a communications relay around the moon. “We’ll see what we get in the proposals, we’ll see how the selection process moves forward,” he said. “It’s too early to say one way or the other.”

One PPE will serve as the initial element of the gateway, which will also include a habitation module, logistics module and airlock as what NASA describes as “foundational” elements. The habitation module will be the next to be developed, for launch as soon as 2023.

Through NASA’s Next Space Technologies for Exploration Partnerships (NextSTEP) program, the agency is currently funding five companies — Bigelow Aerospace, Boeing, Lockheed Martin, Orbital ATK and Sierra Nevada Corporation — to develop ground prototypes of a habitation module suitable for use on the gateway.

NASA, though, doesn’t intend to directly select one of the NextSTEP companies to develop the gateway habitation module. “What we are doing is understanding the benefits, positives and negatives, for different implementation approaches,” said Jason Crusan, director of NASA’s Advanced Exploration Systems division, at the committee meeting.

Those studies, as well as concepts contributed by potential international partners, will feed into the requirements NASA will develop for a later procurement of a module. “We envision that we’ll be in the acquisition phase domestically for the habitation capabilities by the end of the calendar year,” he said, a process that will continue through the middle of 2019.

As with the PPE, Crusan did not rule out NASA obtaining more than one habitation module. “I’m careful not to say ‘habitation element,’ because it may be one or more,” he said, which could include international partner contributions in addition to those developed by industry.

Ken Bowersox, the former astronaut who chairs the committee, sounded optimistic about the prospects for multiple modules or even multiple gateways to support lunar exploration activities by NASA and others. “If you have multiple landers, you might need two gateways,” he said.