14 DAY TRIAL // On Tuesday, while conducting the last spacewalk of the STS-131 mission to the International Space Station (ISS), two astronauts noticed that one of the valves in a newly-installed ammonia tank was jammed. The malfunction is fairly serious, given the fact that the ammonia tank contains the coolant for the orbital facility, and that half of the entire ISS is being actively, thermally regulated through the valve. NASA is currently seriously considering adding another spacewalks to the mission, as well as an extra day of stay for space shuttle Discovery and its seven-astronaut crew, Space reports.
Engineers at the American space agency say that the valve has been stuck in the “closed” position for about seven days, and that its release is absolutely crucial to the functioning of the station. While the crew is not yet endangered, this particular ammonia tank regulates loop A on the station, which controls a host of systems on the facility, including among others that Canadarm-2, the robotic arm built by the Canadian Space Agency (CSA). Additionally, the ammonia coolant is needed to reduce station temperatures, as the entire structure moves to capture as much sunlight as possible via its solar panels.
“Folks are continuing to troubleshoot that problem on the ground to see if there is other things we can try. In the meantime, we are also pursuing work on [spacewalk] options to possibly replace the nitrogen tank assembly,” said Ron Spencer, the lead station flight director, quoted by Space. If the agency decides to prolong Discovery's stay by about a day, then this will be the second extension for the STS-131 mission. An extra day was already added following the failure of a communications antenna that allows astronauts aboard the orbiter to communicate with Mission Control about the state of their spacecraft's heat shield.
If a fourth extra-vehicular activity (EVA) is planned, then Discovery mission specialists Rick Mastracchio and Clayton Anderson – the astronauts that performed the first three EVA – will most likely be asked to step out of the Quest airlock again. NASA is, however, concerned about their performances, given the large volume of work they had to put forth lately. Still, they are the most experienced members of the 13-astronaut crew currently in low-Earth orbit. The other option will be to wait until Discovery departs and have members of the ISS crew do the spacewalk.