Wednesday, August 15, 2007

Viking and Its Orbiters

Credit: NASA

By the 1975 launch window, the USSR had mostly given up on Mars. Since October 1960 they had launched a total of 16 missions, with only very limited success for all of their efforts. They would not launch any more spacecraft to Mars until the summer of 1988.

The 1975 launch window is known for two amazingly successful missions to Mars: Viking 1 and Viking 2. Until the mid-90s, most of the information humanity had learned about Mars came from the Viking Program. To be honest, the amount of data and photographs available from the two Viking missions alone could probably keep this blog running for years: by itself, the Viking 2 Orbiter took almost 16,000 images. So, while one blog post is not enough to present a brief synopsis of the Viking missions, we will spend a few days discussing these two spacecraft and their results before resuming our history of missions to Mars.

As mentioned yesterday, the Viking Program grew out of the canceled Voyager Mars Program.but also had its roots in the Mariner Program. In fact, the Viking Orbiter was originally based on the Mariner 9 spacecraft. However, with the decision to have both a lander and an orbiter, the size and complexity of the orbiter quickly grew. The orbiter would now transport the lander to Mars, provide a platform for the Viking imaging system so that proposed landing sites could be surveyed and certified, relay lander science information (pictures and other data in an electronic format) to Earth, and conduct scientific observations in its own right. Moreover, the orbiter would not only have to transport the lander, it would also have to carry an increased supply of propellant for longer engine firings during the Mars orbit insertion, longer than those planned for the 1971 Mariner mission. And an upgraded attitude control system with greater impulse, plus a larger supply of attitude control propellant, would be required to control the combined spacecraft. Additionally, the orbiter would have to provide power to the lander during the flight to Mars, especially during the periodic checkups on the lander's health and during occasional updates of the landers computerized memory. These additional energy requirements made it necessary to increase significantly the solar panels, from 7.7 square meters to 15.4.

Scientific instruments aboard the Viking Orbiters included cameras for visible light imaging and for infrared thermal mapping. The orbiter could also study the water vapor in Mars' atmosphere, and radio science investigations could be made through the spacecraft's transmitter.

The above photograph is a model of the Viking Orbiter.

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