HOUSTON — NASA’s undersea analog missions — elaborate dress rehearsals that unite astronauts, scientists and engineers on the ocean floor to test hardware and mission operations strategies — are playing a crucial role in preparations for the next wave of human deep-space exploration, according to Steve Squyres of Cornell University, principal investigator for the Mars Exploration Rover mission and the current chair of the NASA Advisory Council.

Squyres is scheduled to surface June 22 from his second visit to the Aquarius Reef Base off Key Largo, Fla., an undersea habitat chosen by NASA’s Extreme Environment Mission Operations (Neemo) to simulate a 12-day mission to a small asteroid.

“I feel what we are doing is extremely valuable,” Squyres said in a June 21 interview. “The problem we face is how do you do field work in microgravity. Asteroids are effectively a zero-g environment. No one knows how to do that. Hit a rock with a hammer and you will go flying. So we need completely new techniques for getting around and stabilizing yourself at a worksite.”

Two years ago, President Obama directed NASA to prepare for a human mission to a near-Earth asteroid by 2025 and consider it a stepping stone to the Martian environs a decade later.

Squyres will emerge from the base – submerged 63 ft. below the Atlantic Ocean, just off Key Largo, Fla. – as part of a crew led by NASA astronaut Dottie Metcalf-Lindenburger and also including European Space Agency astronaut Timothy Peake and Kimiya Yui of the Japan Aerospace Exploration Agency.

The analog mission, which marked the 16th Neemo excursion to Aquarius since 2001, focused on three areas: surface mobility and science sample collection, communication delays and optimum crew size.

Surface mobility at a tumbling, almost gravity-free near-Earth asteroid is a major obstacle. Astronauts working outside the International Space Station and the now-retired space shuttle rely on plentiful hand rails, rigid tethers and mobile foot restraints to anchor their torsos or legs so their hands are free for assembly or repair tasks. Training for their tightly choreographed spacewalks is carried out in the Neutral Buoyancy Lab, an enclosed 4.2-million-gal. water tank managed by NASA’s Johnson Space Center.

“Asteroids don’t have handrails,” Squyres says of the asteroid challenge. “You can’t do an asteroid mission in [the NBL]. You need rocks, soil, sediment. You need a lot of room. So, the ocean is the obvious place to do it.”

During the latest undersea trial, Metcalf and her colleagues carried out 16 spacewalks, evaluating techniques for stringing tethers along the sea floor, gliding along with jet packs and coordinating “spacewalks” with small piloted submersibles that filled in for the multimission Space Exploration Vehicles (SEV) NASA is also developing for deep-space missions. A wheeled version of the SEV would roll across the surface of the Moon or Mars carrying at least two astronauts. A second version hovers over the surface of an asteroid while guided by small thrusters.

Squyres and his colleagues clearly favored the hovering SEV approach, when the submersible was also outfitted with a short stinger equipped with a portable foot restraint.  A shuttle legacy tool, the foot restraint gives spacewalkers both mobility and stability at scientifically significant sites. “That has turned out to be a very effective technique,” Squyres says.

Throughout much of the analog, the astronauts coped with a 50-sec. time delay in their communications with their Mission Control team, even in their off-duty chats with friends and families — long enough to simulate a mission to an asteroid more than 9 million mi. from Earth.

When properly equipped, the undersea astronauts found few obstacles exploring the ocean floor without a constant dialogue with Mission Control, Squyres says.