Sunday, August 19, 2007

Viking 2

Credit: NASA

Viking 2 was launched on September 9, 1975 using a Titan/Centaur rocket. After a 333 day cruise to Mars, the Viking 2 Orbiter entered Mars orbit on August 7, 1976. The Lander detached from the Orbiter on September 3rd. While normal operations called for the structure connecting the Orbiter and Lander (the bioshield) to be ejected after separation, the bioshield was left attached to the Orbiter because of problems with the separation.

The Viking 2 Lander touched down about 200 km west of the crater Mie in Utopia Planitia at 48.269º North, 225.990º West at 22:58:20 UT (9:49:05 a.m. local Mars time). Due to radar misidentification of a rock or highly reflective surface, the thrusters fired an extra time 0.4 seconds before landing, cracking the surface and raising dust. The lander settled down with one leg on a rock, tilted at 8.2 degrees. The cameras began taking images immediately after landing.

The Orbiter's primary mission ended at the beginning of solar conjunction on November 8, 1976. The extended mission commenced on December 14, 1976 after the solar conjunction. On December 20th, 1976 the periapsis was lowered to 778 km. Operations included close approaches to Deimos in October 1977, and the periapsis was lowered to 300 km and the period changed to 24 hours on 23 October 1977. The Orbiter developed a leak in its propulsion system that vented its attitude control gas. It was turned off on July 25, 1978 after returning almost 16,000 images in 706 orbits around Mars.

As for the Viking 2 Lander, it operated on the surface for 1,281 Mars days, and was turned off on April 11, 1980 when its batteries failed.

The above picture is the second image of the Martian surface taken by the Viking Lander 2, shortly after touchdown on September 3, 1976. The picture sweeps around 330°, starting from northwest at the left through north (above the sampler arm housing) past east, where the sky is bright at the center, and southeast toward the right above the radioisotope thermoelectric generator cover. The surface is strewn with rocks out to the horizon, ranging in size up to several meters across. Some pitted rocks resemble fragments of porous volcanic lava. Other rocks have grooves that may have been eroded by windblown sand and dust. Although fine-grained material is seen between the boulders, no sand dunes are evident. The dip in the eastern horizon at the center is an illusion caused by an 8° tilt of the Lander toward the west. Actually, the terrain is more level than that at the Viking 1 site. The horizon toward the left of the panorama (northwest) appears featureless, indicating that it may be several kilometers distant. The sky at the center (east) is bright because the sun was above but out of the picture at 10 a.m. Mars time. Toward the right (southeast), the rocks that are silhouetted against the skyline indicate that the horizon is much nearer, probably because of a slight rise in that area of the terrain. The circular high-gain antenna at the right has clots of fine-grained material adhering to the lower half, some of which appeared to have been sliding downward while the camera was scanning the area. At the extreme right, the banded appearance resulted because the camera continued to scan while it was no longer moving in azimuth. Any motion or other variation in the scene would show up as a change in successive lines.

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