Page:Risk of performance errors due to sleep loss, circadian desynchronization, fatigue, and work overload.pdf/31



The following information was provided by James Maida, Habitability and Human Factors Branch, NASA Johnson Space Center, and Charles Bowen, Ph.D., Human Factors Design Engineering Specialist from the Lockheed Martin Human Factors Design Team. This information illustrates the dim lighting that crew members experience on board the ISS.

The best-case average illumination on board Node 1 of the ISS with eight out of eight fluorescent lamps burning is 13.82 foot-candles (fc). In contrast, on Mar 31, 2005, Node 1 was down to only one lamp burning, with an illuminance of 0.55 fc. Since color vision fails at approximately 0.30 fc, that lighting level is unacceptable for most tasks. The dim illumination in Node 1 presented a safety issue that was addressed, initially, by moving lamps from another area. The problem was ultimately solved by a resupply of the ISS by STS-114, which flew in Jul 2005.

In other examples, when the U.S. Laboratory on ISS has all 12 lamps burning, the illumination is 57.79 fc. When only four of the 12 lamps are burning, illumination is reduced to 16.48 fc. Finally, in an airlock that has all four of its fluorescent lamps working, the illuminance is 17.55 fc. When the airlock is down to one lamp, the illuminance can be as low as 2.62 fc.

The above illuminances were determined by the radiance illuminance model of the Lawrence Berkeley National Laboratory, Berkeley, Calif., with modifications for space flight applications.

Required illuminances for various tasks include: maintenance, 25 fc; transcribing, 50 fc; repair, 30 fc; reading, 50 fc; and night lighting, 2 fc.

Foot-candles can be converted to the international unit of lux by multiplying by 10. Thus, 10 fc = 100 lux.

NASA currently uses two different mathematical models of human circadian rhythms and performance: the Astronaut Scheduling Assistant, and the Circadian, Neurobehavioral Performance, and Subjective Alertness Model.

At the heart of the Astronaut Scheduling Assistant is a comprehensive set of mathematical equations, numerical strategies, and computer program routines that enables the prediction of changes in astronauts' neurobehavioral performance capability over time. The model core makes predictions of neurobehavioral performance capability that are based on sleep and sleep loss (acute and chronic), naps, circadian rhythms, and light exposure, which means that the model also incorporates predictions that are based on countermeasures. These predictions allow for the evaluation of risk and safety of sleep/wake/work schedules during both the planning and the execution of space missions. Prospective studies on the accuracy of these model predictions that simulate the conditions of many of the sleep loss and circadian provocations that occur in space flight remain to be done on Earth. Such studies are essential, and may indicate the need for additional model parameters and changes in model structure.

Future work involves modifying the Astronaut Scheduling Assistant by integrating adaptive Bayesian performance prediction methods that use the results of an individual's past performance to identify individual