meet their normal lifetime capability". Further evaluations are under way. 2009 – Potential ammonia leak from S1 radiator due to damaged panel The S1-3 radiator has a damaged cooling panel that may require on-orbit repair or replacement, as the damage may have the potential to create a leak in the External Thermal Control System (ETCS) of the station, possibly leading to unacceptable loss of the ammonia coolant. There are six such radiators, three on the starboard truss, and three on the port truss, each consisting of 8 panels. They appear as the large white pleated objects extending in the aft direction from the trusses, between the central habitable modules and the large solar panel arrays at the ends of the truss structure, and control the temperature of the ISS by dumping excess heat to space. The panels are double-sided, and radiate from both sides, with ammonia circulating between the top and bottom surfaces. The problem was first noticed in Soyuz imagery in September 2008, but was not thought to be serious. The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during a spacewalk in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. Further imagery during the fly-around from STS-119 raised concerns that structural fatigue, due to thermal cycling stress, could cause a serious leak to develop in the ammonia cooling loop, although there is as yet no evidence of a leak or of degradation in the thermal performance of the panel. Various options for repair are under consideration, including replacement of the entire S1 radiator in a future flight, possibly with return of the damaged unit to ground for detailed study. On 15 May 2009, the damaged radiator panel's ammonia tubing was mechanically shut off from the ETCS, by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel. This eliminates the possibility of an ammonia leak from the cooling system via the damaged panel. 2010 – Failure in cooling loop A Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in