Ground Effect

When Endeavour’s astronauts returned to Earth early Wednesday morning, they faced what every space traveler has to face sooner or later: gravity.

Even after just 15 days in weightlessness (as opposed to six months for a space station crew), astronauts often experience significant spatial disorientation while re-acclimating to the idea that up is up and down is down. They may briefly have trouble walking, or might feel a dizzy, tumbling sensation while standing on solid ground.

Researchers at Mt. Sinai School of Medicine in New York have been studying these re-adaptation effects for years, and have recently developed a unique method for simulating them without leaving the lab. Galvanic vestibular stimulation (GVS)—the application of a low-level electrical current to the vestibular nerve in the brain—appears to cause similar sensations to those felt by returning astronauts. It works by interrupting the neural pathway between the sensory input related to spatial orientation and the area of the brain that perceives it, adding a kind of white noise that makes the system go haywire.

Steven Moore, an associate professor of neurology at Mt. Sinai, became interested in using the technique to study the effects of spatial disorientation on space shuttle commanders in the critical moments when they’re decelerating in the atmosphere and landing the 100-ton orbiter at 220 miles per hour. Some past landings have been less than optimal, perhaps due to the effects of returning gravity. A review of the first 100 shuttle missions found that touchdown speed was above specified limits in 20 percent of the landings.

“There’s not a lot of actual hard data on astronauts’ performance,” says Moore. “Basically [shuttle commanders] tend to land harder than they should. So that gave us something to try and see if we could recreate [using GVS].”

Moore and his colleague Hamish MacDougall at the University of Sydney used GVS on pilots (including some veteran astronauts) flying the space shuttle landing simulator at NASA’s Ames Research Center. Electrodes attached behind the pilot’s ears were connected to a small box that generated a 5-milliamp current. The researchers observed simulator landings with and without the stimulation. Sure enough, the pilots stimulated with GVS seemed to have a harder time making a smooth landing. Out of 88 simulated flights, the test pilots undergoing GVS crashed the shuttle seven times (as opposed to only twice without GVS).

Ron Small, a retired Air Force pilot who took part in the study at Ames, describes the effects of GVS while he flew the simulator. “It’s like something’s wrong, like things are just messed up. You have this sense of tumbling when you’re clearly not. You could be seated in a chair or standing stationary, it’s just the world going topsy-turvy for no apparent reason.”

According to Small, the sensation significantly impaired his ability to fly the simulated shuttle. “I felt like I really had to focus on what I was doing, trying to maintain deliberate, accurate control. I was just trying to get the thing down without crashing.”

Re-adaptation to gravity has not been a safety issue for astronauts landing the shuttle, says Moore. “It’s not like they’re totally incapacitated, it’s a fairly subtle thing. I think it just makes it harder to sense how you’re moving and how your spacecraft is moving.”

Three-time shuttle commander Bill Readdy claims he didn’t notice any spatial disorientation while landing the real shuttle—maybe because he was so busy at the time. “I thought it was much less about the physiological aspect of it than that there were so many tasks,” he says. “And the challenge is to keep all of that processing so that you don’t become saturated by the tasks.” He agrees that re-adapting to gravity has never been a worry for shuttle commanders. “[Landings] all end up well within the design parameters for the vehicle,” he says. “And of course the idea is to land safely on the runway,” not perfectly.

Still, if astronauts train with GVS, they could get used to the sensation of spatial disorientation before they feel it for real during a mission, mitigating potential performance problems on reentry. With just one shuttle landing left, the method won’t see operational use any time soon. But astronauts piloting future vehicles, perhaps even on Mars, may prepare using GVS training.

Part of Moore’s focus now is to fine-tune GVS to the point where it can be used in training without making astronauts motion sick, while still accurately reflecting what happens.

“Obviously, if you hit someone on the head with a hammer you could make them land the shuttle not as well as someone who’s not getting hit on the head with a hammer,” says Moore. “But we’re trying to develop a hammer that’s actually realistic.”