Understanding and predicting the effects of spaceflight on the human body can be challenging because humans have not spent enough time in microgravity to accurately determine the risk of health problems associated with exploration missions.

NASA planners developing concepts for longer, more physically demanding missions need to better understand how human physiology is altered during spaceflight.  Such knowledge will allow them to establish meaningful mission requirements for health and safety.  To this end, the NASA Human Research Program Human Health Countermeasures Element chartered the Digital Astronaut Project.  Led out of the Glenn Research Center, and in partnership with the Johnson Space Center, the Digital Astronaut Project is an effort to utilize deterministic simulations of human physiological function to answer targeted questions about changes associated with the microgravity environment.

The project is currently working in several areas, one of which is quantifying the effects of exercise.  In spite of attempts to use exercise to counteract losses in bone density and muscle tone during spaceflight, these problems continue, with longer flights generally correlating with greater loss.  In an attempt to quantify the response to exercise, project personnel created a model of the Advanced Resistive Exercise Device (ARED) that astronauts currently use on the International Space Station (ISS).  In tandem with that effort, the team also developed models of humans performing ARED exercises.  The team is currently integrating both models, with a goal of quantifying muscle force and joint torque produced by the exercise.  Data produced by these simulations will allow exercise physiologists to design better exercise prescriptions for the astronauts.

In conjunction with the exercise models, project personnel are also developing computational simulations of bone remodeling and muscle function.  In the case of bone, no current analytic formulation is able to describe the effects of muscle stress, strain, and gravitational loading on bone remodeling.  Bone tissue is actually in a perpetual state of flux, with old tissue constantly being destroyed and new tissue created.  In healthy individuals living in earth’s gravity field, these effects balance.  In microgravity, however, tissue formation in weight bearing regions of the skeleton slows dramatically, leading to bone loss.  These simulations should provide key insight into how the turnover process proceeds in microgravity, as well as providing recommendations for the daily amount of loading required to counteract the effect.

While muscle models are more developed, computational tools generally do not accurately predict microgravity effects, which means that the team must alter the foundation of those tools so that they can faithfully reflect the effects of microgravity.

Finally, many astronauts return from space with vision changes, presumably caused by an increase in cerebral-spinal fluid pressure.  This pressure change is likely a result of the well-known head ward fluid shift that occurs as soon as humans enter microgravity.  Project personnel are currently conducting a survey to determine what computational tools and data sets are available to simulate this problem.   When that survey is complete, the team will use a combination of existing and custom tools to develop a simulation quantifing this effect.