The oldest of NASA's planetary missions that we have been following in "SkyWatch" is the Galileo mission to Jupiter. It began its primary mission in December, 1995, when it was captured in orbit around Jupiter, dropped a probe into Jupiter's clouds, and began 11 orbits to gather information about Jupiter's four largest moons, the Galilean satellites. This primary mission was completed on Nov. 7 when the spacecraft flew past Europa at an altitude of 1269 miles. Scientists have become so intrigued by this ice-covered moon that they have named the two-year extended mission the Galileo Europa Mission - GEM.

        In GEM's first phase, Galileo will make 8 passes by Europa during the next 14 months, making detailed images of its icy crust from as close as 125 miles. Mission specialists hope to learn more about blocks and rafts of ice that closely resemble ice floes in Earth's polar regions in an attempt to ascertain if there is liquid water beneath the visible surface. Next, four close passes by Jupiter's moon Callisto will reduce the craft's minimum orbital distance from Jupiter - perijove - and carry Galileo through the "plasma torus" created along Io's orbit by its sulphur volcanoes. Finally, if the ship's light detectors survive the high radiation fields in this region, it will pass close to Io once or twice to get close-ups of the solar system's only moon with active volcanoes.

        The funds appropriated for this extended mission are slim, so any breakdowns on Galileo will effectively end the mission unless a simple fix can be devised. Such failures may be likely. The tape recorder, for example, used to record and play back data has already exceeded the number of stops and restarts for which it was originally designed.

        The second NASA mission followed in "SkyWatch", Pathfinder, landed on Mars on July 4 with a primary mission of one month. The primary mission of the rover it carried, Sojourner, was one week. Both the lander and rover continued to function well beyond their primary missions, but the low Martian temperatures have apparently disabled the lander. No data transmissions have been received since Sept. 27 and its transmitters' carrier signals have not been detected since Oct. 6. The rover was still working properly after 12 weeks when signals were last received from the lander and the lander's operation through August and September made its extended mission twice as long as its primary mission. More than 16,000 images were received from the lander, more than 550 images were relayed from Sojourner, more than 15 chemical analyses of rocks and soil were transmitted, and much information about winds, the Martian weather, and atmospheric properties were received. These are providing scientists with a wealth of information to analyze and interpret.

        NASA's Mars Global Surveyor, the third mission followed in "SkyWatch", was captured by the planet on Sept. 11. It began aerobraking to lower its orbit gradually. This procedure was paused on Oct. 11 when one of the solar panels that had failed to open fully during the flight from Earth was pushed beyond its fully opened position by the air pressure. The braking procedure resumed on Nov. 7, but at a slower rate. Consequently the scheduled mapping will not begin until March, 1999, a full Earth year and half a Martian year later than originally scheduled. It will gather data at the low point of each orbit as the aerobraking is being done and during a six-month aerobraking pause to allow the final orbit to have the correct orientation. The final orbit will cross Mars' equator each day moving from south to north at 2:00 p.m. local time rather than from north to south as originally planned. None of this is expected to interfere with Surveyor's mission, and will, in fact, result in much additional data being collected.