Something as simple as a child's toy design might help NASA scientists solve the complex problem of landing astronauts on Mars.

Safely landing a large spacecraft on the Red Planet is just one of many engineering challenges the agency faces as it eyes an ambitious goal of sending humans into deep space later this century.

At NASA's Langley Research Center in Hampton, Va., engineers have been working to develop a lightweight inflatable heat shield that looks a lot like a super-sized version of a stacking ring of doughnuts that infants play with. The engineers believe it could be deployed to slow the craft as it enters a Martian atmosphere much thinner than Earth's.

Such an inflatable heat shield could help a spacecraft reach the high-altitude southern plains of Mars and other areas that would otherwise be inaccessible with existing technology. The experts note that rockets alone can't be used to land a large craft on Mars as can be done on the moon, which has no atmosphere.

Parachutes also won't work for a large spacecraft needed to send humans to Mars, they add.

Inflatable rings

Hence the inflatable rings, known as the Hypersonic Inflatable Aerodynamic Decelerator, which would be filled with nitrogen and covered with a thermal blanket. Once deployed for landing, the rings would sit atop the spacecraft, somewhat resembling a giant mushroom.

"We try to not use propulsion if we don't have to," said Neil Cheatwood, the senior engineer at Langley for advanced entry, descent and landing systems. "We make use of that atmosphere as much as we can, because it means we don't have to carry all that fuel with us."

NASA's leaders acknowledge that getting humans safely to and from Mars as early as the 2030s will poses extreme challenges. The agency's scientists acknowledge they also must design new in-space propulsion systems, advanced spacesuits, long-term living habitats aboard spacecraft — even communication systems for deep space.

Work is proceeding, sometimes fitfully.

When an unmanned private rocket destined for the International Space Station exploded in October soon after liftoff from Wallops Island, Va., numerous scientific experiments went up in flames with it. But one NASA experiment that Orbital Sciences Corp. originally invited aboard — for a second-generation inflatable spacecraft — was not ready in time for the flight, NASA officials say.

That experiment, which calls for testing how second-generation inflatable spacecraft technology performs upon re-entry in Earth's atmosphere, is now scheduled to go up on the next Antares rocket in 2016.

New technology

New technology is needed to get astronauts to Mars because the type of spacecraft that would land humans would be much larger than anything that's landed on the planet previously. Current heat-shield technology weighs too much to be used on larger spacecraft.  NASA has relied on parachute-based deceleration on Mars since the Viking program in the 1970s.

"The idea is that you would have something that could be packed up, put in a very small volume and then deployed into a very large size," Anthony Calomino, principal investigator for materials and structures for hypersonic re-entry at Langley.

Smaller scale, inflatable experiments have been launched on rockets before, but never into orbit. The information gathered from those earlier projects will be applied to the upcoming, larger-scale experiment in 2016.