Science —

Simulated trip to Mars left crew with sleep, exercise problems

Some napped, one shifted to a 25-hour day; all but one remained alert.

NASA's simulations of a Mars mission tend to be much shorter and probably quite a bit more interesting.
NASA's simulations of a Mars mission tend to be much shorter and probably quite a bit more interesting.

Regardless how you feel about the manned space program, it's difficult to argue with the logic that motivated one of the more unusual experiments we've ever reported on. Given that we're almost certain to send a manned mission to Mars before the end of the century, the Russian Academy of Sciences organized a six-person crew to perform a simulation of a 520-day mission to Mars.

During the simulated mission, which ran from June 3, 2010 until November 4, 2011, the crew was given plenty of things to do near the launch and landing, and period of heavy activity in the middle of the "trip," where they simulated landing on Mars and collecting samples. But, in between, they were allowed to set their own schedule and adjust their lighting and activity to their own tastes. As you might expect, this generally didn't work out well; the test subjects gradually became sedentary, and many had problems holding to a steady sleep schedule. The most striking thing, however, is that they generally adopted different sleep schedules, leaving one of the crew having a "day" that was an hour longer than the rest, and another napping mid-day.

The people running the simulation went out of their way to make things as accurate as they could. The long list of factors that they added included "a spaceship-like habitat; continuous isolation from Earth’s environment; realistic mission activities; a mid-mission landing on a simulated Mars surface; accurate mission duration and timeline; operations between crew and mission controllers; communication delays inherent in interplanetary travel; limited consumable resources; exercise equipment for physical fitness; diurnal weekly work schedule; crew control of habitat lighting; and video monitoring of crew in habitat common areas." Note the delay in communications—that could range anywhere from a low of a few minutes to over 20.

Each of the six participants wore a wrist band that registered their activity level every minute, along with the current light exposure. Twice each week, the crew were given a test of their alertness, and each of them filed a weekly report on the quality of their sleep and ability to deal with their workload.

At the start, the crew was averaging a bit under seven hours of sleep a night, although part of that was probably the high level of activity associated with the "launch." The figure quickly shot up to a bit over seven hours, and largely stayed there through to the simulated arrival at Mars. But, once the return trip started, hours spent asleep went up again, eventually reaching somewhere close to eight hours. Only the pending end of the mission reversed the trend towards increased sleep.

The participants weren't just sleeping more, though; hours spent at rest followed a similar trajectory to sleep, shooting up to about an hour a day through to the mission's mid-point, then rising again on the return trip to Earth. Near the end of their stay, the participants were spending over 9.5 hours of their day either sleeping or resting. Even when they were awake, they were doing less. Time where the wrist monitor measured activity plunged early in the stay, and then continued a gradual decline throughout the mission, with no sign of slowing even during the ostensible time at Mars.

Although the inactivity probably wasn't good for the crew's health, the extra sleep had a positive effect on their alertness. Reaction times improved over the course of the mission, and the participants' focus during these tests also increased.

But perhaps the most striking part of the analysis was the individual variations among the crew members. One participant remained far more active than the rest of the crew, and only spent a fraction of the time resting. Another was right in the middle of the pack when it came to things like sleep and resting, but his reaction time got much longer while everyone else's stayed steady. And then there was the fact, mentioned above, that the different astronauts adapted different sleep schedules and day lengths.

None of these, with the possible exception of the one person's extended reaction time, should interfere with a mission's progress: the participants had hours when they were on duty, and continued to show up for those. But any extended mission like this would also be a social activity, and having crew members living such radically different days might cause some problems there.

Otherwise, most of these issues seem like they could be overcome. The lighting in the simulator wasn't great for setting up a normal circadian rhythms, but that can be replaced. Any space agency could easily set up a compulsory fitness program to ensure a minimal level of activity. The good news is that, for all but one crew member, alertness and quick reactions remained a constant throughout the simulation.

PNAS, 2013. DOI: 10.1073/pnas.1212646110  (About DOIs).

Channel Ars Technica