A planned spacewalk outside the International Space Station (ISS) was postponed Wednesday due to a medical concern involving one of the crew members, according to a statement released by NASA. The spacewalk, originally scheduled for Thursday morning, was to involve astronauts Mike Fincke and Zena Cardman, who were tasked with preparing the ISS for the installation of new roll-out solar arrays.

The six-and-a-half-hour excursion was intended to be the first of two spacewalks this month. The second spacewalk, planned for next week, is also now on hold. The installation of the new solar arrays represents the final major upgrade to the ISS electrical system before its planned decommissioning in 2030.

NASA officials stated that the medical concern arose Wednesday afternoon. "Due to medical privacy, it is not appropriate for NASA to share more details about the crew member," the agency said in its statement. "The situation is stable."

While NASA has not disclosed the nature of the medical issue, experts note that a range of health concerns can arise during spaceflight, including cardiovascular changes, bone density loss, immune system suppression, and psychological stress. These factors can be exacerbated by the unique environment of space, including microgravity and radiation exposure.

Dr. Susan Bailey, a professor at Colorado State University and an expert in space radiation biology, explained that even seemingly minor medical issues can be amplified in space. "What might be a manageable condition on Earth can become a significant problem when you're dealing with limited resources and the challenges of providing medical care in a closed environment," she said.

The postponement has implications for the timeline of the solar array upgrade. These new arrays are crucial for ensuring the ISS has sufficient power to support ongoing research and operations in the coming years. NASA indicated that it will share additional details, including a new date for the spacewalk, at a later time. The agency's priority is the health and safety of the crew member, and all decisions will be made with that in mind.