211 DAY IN THE LIFE: EMPTY HOUSE—DECREWING THE INTERNATIONAL SPACE STATION CHAPTER 12 return the current crew to Earth prior to the arrival of a new crew, thus decrewing the ISS and leaving it an empty house. The ISS Program and operators around the world began a thorough, time-limited review of space station operations to determine any changes to vehicle configuration or ground systems needed to keep the ISS operational during a potential decrewing of unknown duration. This chapter outlines the history of potential ISS decrewing discussions, how the 2011 event response was developed, and the systems and operations changes that would have been enacted in the event the ISS was decrewed. History Decrewing the ISS was not a new concept. The potential had existed ever since the first crew docked to the space station. In the early days, if a crew member became so ill that he or she had to return to the ground for immediate medical treatment, then the entire crew might have been forced to leave the ISS. With the advent of six-crew operations, it is more likely that at least one crew of three can remain on board. However, the ISS could become uninhabitable due to an off-nominal situation such as fire, depressurization, or major systems failure. These unlikely scenarios would not allow much time for preparation. With crew member safety being of the highest importance, the crew return vehicles will act as lifeboats to bring them home. Following an emergency, the ISS would be maintained and hopefully fully recovered in a best- effort capability using the technical expertise that NASA and its partners have developed over years of spaceflight experience. Planned decrewing of the ISS had also been discussed and documented multiple times. Early in the program, the planning of crew rotations sometimes ran into issues with the logistics of launch vehicle processing, meaning that the potential need for one crew to return before a replacement arrived existed, but it never actually occurred. At that time, the small-but-growing space station had been operated uncrewed for its first 2 years. Decrewing the ISS dealt a major impact to assembly operations and scientific research since crew members were required to perform many of these operations. However, decrewing was not thought to be a major concern for the overall survival of the station itself due to the design goal of being remote controlled. Over the years, barring any issues with vehicle upgrades or accidents, this planning became a well-oiled machine and is no longer much of a concern. Decrewing the ISS was also a topic following the Space Shuttle Columbia accident. The shuttles provided the capability to launch and return crew members, and deliver large quantities of consumables to the ISS. The Space Shuttle Program performed a lengthy investigation and recovery effort thus, the ISS partnership was able to keep the ISS staffed by reducing crew size and relying on Russian capabilities to launch astronauts and supplies. At the time of the Progress 44P accident in 2011, which followed the retirement of the Space Shuttle fleet, no alternative to the Russian Soyuz crewed spacecraft to launch or return astronauts existed. The outcome of many of these discussions were documented in operational products, including procedures and Flight Rules. These products would be used and built upon to develop an operational philosophy for a decrewed space station. Framing the Discussion In many ways, it was up to the operations teams to determine how to continue operating without a crew on board. But first, the operations team and the ISS Program developed a set of priorities to drive the discussion and decisions that would result in the decrewed space station configuration. The high-level priorities, in order, were: 1. Keep the ISS safely operating until a crew could return, and beyond. 2. Prevent the loss of critical hardware and maximize critical system redundancy. This included performing preventative maintenance on systems whose expected lifetime would expire before a crew would return, and potentially using temporary power or data extension cables to increase flexibility following failures. 3. Prevent loss of scientific data, and consider delaying the start of new scientific research that would be lost if the crew was not available to finish it. 4. Optimize the ISS configuration to allow for an efficient return of a new crew. 5. Continue scientific research that could be controlled from the ground.