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More Details for 1999-01-13

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International Space Station flight controllers in Houston and Moscow continued to monitor the new outpost this week as it awaits a visit by the Space Shuttle Discovery, planned for launch in May on mission STS-96.

Over a period of several days late last week, controllers noted a gradual decrease in voltage provided by the Zarya module's six batteries. The voltage declined to a point slightly below what was anticipated. As a precaution late Sunday, controllers switched off several non-critical heaters in the Unity-to-Zarya mating adapter to reduce power consumption. Meanwhile, controllers in Moscow began several housekeeping procedures to improve the batteries' performance. Several smoke detectors aboard Zarya were automatically powered off briefly to further reduce power consumption. However, no major systems on the station experienced an interruption in power and all required equipment remained in operation.

The housekeeping activities involved deep-cycling the Zarya batteries, fully discharging and then recharging them regularly to ensure they remain at peak performance. This deep-cycling procedure had originally been planned to be peformed about once every two weeks. But after watching the new station's performance, controllers are now conducting the cycling every few days on each battery. The more frequent cycling has increased the voltage from the batteries to optimum levels again and all systems on the station are operating normally. Flight controllers in Houston and Moscow are continuing to analyze the batteries' performance, although the slight decrease in voltage that had been seen is not believed to have been an indication of any mechanical problem.

On Tuesday, Zarya flight controllers plan to conduct a systems test of the module's Kurs automated rendezvous system that will be used this summer to rendezvous and dock with the Service Module, the third station module, planned to be launched from Kazakstan in July. The International Space Station remains in a naturally stable slow spin that conserves propellant and provides moderate temperatures on the spacecraft. The station is in an orbit with a high point of 256 statute miles and a low point of 248 statute miles, circling Earth once every 92 minutes.