HOUSTON – An already bold proposal by the U.S. nonprofit Inspiration Mars for a 501-day human flyby mission of the Red Planet might be eclipsed by the even bolder Mars Plus, a European concept that would incorporate 3-D printing technologies for the inflight construction of a surface habitat for two astronauts.

After trials of prototypes like those scheduled to begin later this year aboard the International Space Station, the envisioned printer would be activated on the outbound leg of the journey to produce plastic components that would be assembled into a lightweight, two-level habitat by two crewmembers before they reached Mars in late 2018, according to Mars Plus advocate Giorgio Gaviraghi, an Italian architect, aerospace designer and project manager with Unispace.

He presented the concept as a potential strategy for overcoming cost, mass and volume constraints posed by current launch technologies to the four-day, 17th annual Mars Society convention here Aug. 7-10.

"We may have a possibility to face this problem and solve it with something new," he told an Aug. 8 session on exploration technologies.

Nonetheless, a July report from the National Research Council, requested by NASA and the U.S. Air Force, cautions the aerospace community against being overly optimistic about the utility of emerging terrestrial additive manufacturing technologies. "... its application in space is not feasible today, except for very limited and experimental purposes," according to the report, which urges NASA, the military and their collaborators to make the most of the ISS to define the utility of space 3-D printing.

Inspiration Mars, led by multimillionaire and pioneering U.S. space tourist Dennis Tito, has also turned to NASA for significant assistance since unveiling its ambitious $1 billion mission strategy in early 2013, including a Space Launch System heavy lift rocket. NASA has said it will consult with Inspiration Mars on mission strategies, but cannot provide substantial assets. It would launch in early 2018.

Mars Plus is among a growing circle of Mars initiatives. They include the Mars Society’s own Mars Direct, which would use current launch technologies with no intermediate destinations to reach the Red Planet with explorers who would rely upon fuel, life support and other resources extracted from the Martian air and soil; Inspiration, which would launch a married couple on a free return trajectory that passes within 100 mi. of the Red Planet’s surface before returning to Earth after 501 days; and Mars One, a Dutch nonprofit that proposes a series of human settlement missions beginning in the mid-2020s. NASA’s own Asteroid Retrieval Mission proposes to leverage solar electric propulsion, SLS and other technologies demonstrated during a robotic mission to capture and maneuver an asteroid, or a large asteroid fragment, into a stable lunar orbit. Astronauts would visit the asteroid to rehearse for a Mars landing in the mid-2030s.

Using three launches, Mars Plus would assemble an interplanetary "cruiser" in Earth orbit. The cruiser would be comprised of an inflatable Bigelow-style habitation module, a service module, multi-port node and solar electric propulsion. The node’s docking ports would accommodate two types of "feeders"

the Mars lander, delivered on the second of the initial launches, and the crew capsule, arriving on the third, plus an observation deck.

The 3-D printer and 250 to 300 kg of raw construction materials would be parked in the cruiser’s inflatable hab. Over the six-month outbound leg, the printer would produce slabs, wall and floor panels and connectors using a 2-meter-by-80-cm-by-20-cm format. The parts would be assembled into a dual-level Mars surface habitat by the two astronauts within three to four days.

The crew descent, with the hab module and temporarily disassembled printer, would mark the start of a near 600-day surface stay for the two unmarried Mars Plus astronauts. The newly assembled hab would feature three inflatable enclosures

including volume for a greenhouse. The printer would be reassembled at the surface and used by the astronauts to manufacture furniture and other equipment, including a rover useful for exploration, explained Gaviraghi.

The cruiser would remain in Mars orbit until the crew returned in the "Mars feeder" for a six-month journey back to Earth to close out a 946-day mission in late 2020.

To help finance the venture, the well-traveled Mars cruiser could be redirected upon its return to cycle regularly between Earth and the Moon as a commercial transportation service notionally supporting lunar exploration and development activities, according to Gaviraghi.

"As a general goal, this mission also has to be profitable in order to be financed," he said.