NOTE TO EDITORS: Viking Update
January 26, l977

       Viking project officials have completed the first in series of three maneuvers with Viking Orbiter to fly close to the Martian satellite Phobos and take the highest-resolution pictures ever received of the tiny object. Photography will be coupled with an infrared scan.

       The near encounters between Viking Orbiter and Phobos will occur from Feb. l8 to Feb. 23, and will bring the spacecraft within 70 kilometers (43 miles) of the satellite. At that time scientists hope to map all of the lighted portion of Phobos.

       Meanwhile, all four spacecraft -- both orbiters and both landers -- continue in basically healthy condition. Minor problems continue, but are being corrected or controlled by the Viking team at Jet Propulsion Laboratory.

       After Viking Orbiter completes its encounters with Phobos, its orbit will be changed. Project officials hope to lower the point of closest approach to Mars to about 700 kilometers (500 miles) from its present distance of about l,500 kilometers. This will enable Orrbiter to join Orbiter 2 (already lowered) in taking higher resolution photos of Mars.

       Lander science teams are also active during the Viking Extended Mission. Biologists completed one new cycle in the Lander Pyrolytic Release experiment and should have results of that test by early February. Plans for the biology instrument on Lander call for new pyrolytic release cycle and labeled release control cycle to begin Jan. 3O. Aboard Lander 2, pyrolytic release cycle wll1 begin Jan. 29. The gas exchange instruments continue to incubate soil samples taken during the primary mission.

       This week the Lander 1 soil sample collector began four cycles to place pebble samples in the inorganic analysis instrument. Lander 2's inorganic analysis instrument has received sample of fine grain material and is analyzing it now.

       In addition to obtaining constant meteorology data, scientists are planning an experiment to obtain temperatures of the atmosphere at varying heights above the surface. They wil1 read the temperature sensors on the soil sample collector head as the head is raised to various elevations from ground level to maximum height of about three meters (lO feet).

       Cameras aboard both Viking landers are watching the sky to see how 1ight appears to fade with the onset of Autumn in the northern hemisphere. They are monitoring the surface and the sky for moving particles, such as the dust that is expected as Mars approaches its closest point to the Sun.

       Orbiter cameras continue to see haze in the atmosphere almost everywhere they look. Scientists believe this obscuration may be caused by combination of water-ice crystals and carbon dioxide crystal in the thin Martian atmosphere. Viking officials plan to contact the Planetary Patrol Program -- group of astronomers who monitor the planets -- to see if they have observed the obscuration through Earth-based telescopes.

       The Lander 2 seismometer has sensed second "event." While scientists will not state that it is "Marsquake," they believe further processing of data may confirm that. The first event was sensed on Nov. 4, the second on Nov. 24, 1976.

       Engineers plan final attempt to uncage the seismometer aboard Viking Lander 1 that failed to operate after landing last July 2O. They are making changes to the software and preparing series of commands that they expect to execute sometime in the next six weeks.

       Earlier plans called for lowering the periapsis of Viking Orbiter 1 to about 3OO kilometers (l86 mlles) above the Martian surface. But problem in one of two command processors aboard Orbiter 1 has forced them to replan that maneuver to periapsis of about 7OO kilometers (435 miles).

       The problem is not new: five bad locations in the memory of one of two processors makes controllers reluctant to use it. They have never performed propulsive maneuver with only one operating processor. The possibility exists that, if they performed the 3OOkilometer maneuver, the spacecraft might burn all its propellant and crash on Mars. But burn to the 7OO kilometer orbit, even of malfunction used up all the onboard propellant, would still leave the spacecraft in safe, long-time orbit above the planet.

       As reported more than year ago, one oven, of three, in each lander's organic-analysis instrument seems to be inoperative; the heating elements in the oven appear to have failed. New tests have been completed on those ovens, and they confirm that the heaters do not work. Scientists are proceedlng however, with atmospheric analyses that are not influenced by the heaters.

       Viking landed on Mars July 2O, 1976. Viking 2 landed on Sept. 3. The primary mission ended in early November. The extended mission began in mid-December and is expected to run through May 1978.

NOTE: G. Calvin Broome of NASA's Langley Research Center is Viking mission director during the extended mission replacing James S. Martin, Jr.