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       NASA's Viking Lander 2 has ceased operating after three and one-half years on the surface of Mars.

       Flight controllers at Jet Propulsion Laboratory received unintelligible data during scheduled transmission from Lander 2 in mid-March.

       After analyzing engineering telemetry for several weeks, Viking officials concluded that loss of power in the batteries had led to an automatic shutdown of the cameras and other science instruments.

       The batteries provided power for the lander to transmit. Primary power source for the batteries and other systems is radioisotope thermoelectric generator -- small nuclear power device.

       Viking Lander 2 touched down on the surface of Mars Sept. 3, 1976, at 47.7 degrees north latitude. It operated continuously since that time.

       Lander 2 survived the rigors of two Martian winters, when temperatures dropped as low as 190 degrees below zero Fahrenheit.

       During its first 20 months on Mars, Lander 2 measured the composition of Mars' atmosphere and soil, continuously monitored the weather, dug many trenches, searched the soil for signs of living microorganisms, and took more than 1,800 pictures.

       Scientists say Lander 2's most important discovery may be that thin layer of white water-frost covers the ground at the far northern latitudes each winter.

       For the last two years, most of the lander's instruments were turned off, their missions completed.

       Scientists had continued to receive weather data and pictures from the lander. Lander 2 continued to operate normally until the problem that began Jan. 31, 1980.

       Lander 2 was scheduled to send its final science information to Earth on April 11.

       Viking Lander 1 continues to operate on the Martian surface and send data to Earth once week. Its on-board com puter has been programmed to enable the lander to automatically monitor weather and take pictures, then send the information directly to Earth. It should continue to do so through the 1980s.

       Viking Orbiter 1 is still operating and later this month will be moved to new orbit around Mars to take high resolution pictures of areas that have not been adequately covered. It is expected to quit working in June or July, when it runs out of attitude-control gas.

4/2/80 DB