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To: fred whitridge who wrote (3705)	6/1/1999 11:14:00 AM
From: jacq	Respond to of 8393

Part of the problem with the Spacestation STS-96 is that the NiCad battery charger was giving false readings as to state of charge they were working around the problem by totally depleting the batteries and recharging them....Does this sound familiar? MIRTs Changeout SpaceHab Prime: Julie Payette Backup: Valery Tokarev Overview On Flight Days 5 and 6, astronaut Julie Payette and Cosmonaut Valery Ivanovich Tokarev will replace all 18 of the battery charge/discharge units that support Zarya's six nickel-cadmium batteries. Known by the Russian acronym "MIRTs," they are thought to be responsible for voltage problems first detected in January. MIRTs are part of a system that indicates the level of charge for each of Zarya's batteries and, in turn, dictates when the onboard charging system will begin to taper-off the power supply to each. Flight controllers have been working around the problem by cycling the batteries, fully charging, and then fully discharging them every week. This procedure resets the charge indication and maintains the batteries at peak performance. It appears that when Zarya's MIRTs measure the cumulative charge or amp-hour readings of each battery, they introduce a slight error in a compensation factor and thus prevent full charge/discharge cycles from occurring. Replacement of the units -- they measure 5.9 x 4.7 x 3 inches and weigh 1.43 pounds -- may reduce the need for weekly cycling, resulting in better long-term battery performance and additional backup equipment capabilities for the ISS. Payette and Tokarev were trained for this part of the mission in mid-March at the Gagarin Cosmonaut Training Center at Star City outside Moscow, where a full-scale Zarya mock-up is located, and will follow procedures jointly developed by engineers at Mission Control Center Moscow and Mission Control Center-Houston. The MIRTs are located under Zarya's floor panels. Section Index \| Main Index \| Search Updated: 05/11/1999 Editorial/Technical Comments: ShuttlePresskit