LOGAN, Utah — NASA is casting a wider net in its search for designs of a habitat module that could support deep space missions, awarding contracts Aug. 9 to six companies for a new round of studies.

NASA awarded the contracts, with a combined value of $65 million, as part of its Next Space Technologies for Exploration Partnerships (NextSTEP) 2 program to develop concepts for habitats that could be used on missions in cislunar space and eventually to Mars. Each company is expected to contribute at least 30 percent of the total cost of the selected project.

In 2015, NASA awarded contracts to four companies in the original NextSTEP solicitation for habitat concepts: Bigelow Aerospace, Boeing, Lockheed Martin and Orbital ATK. Each of those companies won a NextSTEP-2 award as well, which will focus on refining those concepts and building module prototypes for ground testing.

In addition, NASA awarded NextSTEP-2 contracts to teams led by NanoRacks and Sierra Nevada Corp. (SNC). These companies will focus on design studies rather than module prototypes over the course of their two-year contracts.

The NanoRacks-led team, known as Ixion and including United Launch Alliance and Space Systems Loral, plans to study the conversion of a Centaur upper stage into a habitat module, rather than the construction of a dedicated habitat module. They argue that such an approach is more cost effective than building a dedicated habitat module.

“This is the only strategy that nearly eliminates both fabrication and launch costs since the habitat has essentially already been built and the launch of the habitat is an inherent part of every Atlas 5 flight,” said Mike Gold, vice president of Washington operations and business development for SSL. “The idea of repurposing upper stages in such a manner goes all the way back to Wernher von Braun, and we’re excited to take this low-cost, revolutionary strategy and transform it into reality.”

SNC’s design, developed in partnership with Aerojet Rocketdyne, is based on the cargo module the company is developing for its Dream Chaser vehicle for cargo missions to and from the International Space Station. In this concept, the cargo module would be left in orbit at the end of an ISS mission and serve as the core of the habitat, which would also include an expandable module and a solar electric propulsion system to transport it into cislunar space.

“This program is a perfect opportunity to showcase the heritage of our 25-plus years supporting space missions,” said Mark Sirangelo, corporate vice president of SNC’s Space Systems business, in an Aug. 10 statement. “The NextSTEP-2 habitat elevates our role as a prime integrator in the design of effective and efficient deep space habitats.”

NASA considers NextSTEP-2 studies a critical phase in its plans to develop habitats that would be ready to support crewed missions in cislunar space in the 2020s, as the agency winds down its involvement on the ISS. “This is an important time frame, because these ground prototypes allow us to do integrated form, fit and function testing to a high fidelity of the concepts that industry has for meeting our requirements,” said Jason Crusan, director of NASA’s Advanced Exploration Systems office, at a July 26 meeting of the NASA Advisory Council’s human exploration and operations committee.

The NextSTEP-2 studies are done as public-private partnerships, rather than conventional contracts, to give companies greater flexibility in determining how to meet NASA’s requirements while also developing systems that could have other applications, such as commercial space stations in low Earth orbit. “We are fundamentally approaching this at the top level of trying to encourage meeting our requirements while maximizing the overlap with LEO advancement as well,” Crusan said at the committee meeting.

Some of the selected NextSTEP-2 awards have clear applications for commercial space stations. The illustration of the Ixion concept showed a modified Centaur module docked to the ISS. Bigelow’s NextSTEP-2 award covers the development of a ground prototype of its Expandable Bigelow Advanced Station Enhancement, or XBASE, that the company announced in April. XBASE would dock a Bigelow Aerospace B330 module to the ISS for both NASA and commercial use.