prepared in the analytical plotter. The primary landing site for 
Viking I is at Chryse at 209 north, 349 west, on a smooth plain at 4 
the end of drainage channels which geologists estimate may have been Phe 
formed by water. When the site certification mission is completed, 
the orbiters will be changed to a non-synchronous orbit, and over 
the next year will provide complete stereo coverage of the planet. ee 
When the site has been certified from the orbiter pictures, Pic 
the lander, enclosed in its bio-shell will be separated from the val 
orbiter and begin its descent to the surface. The bio-shell also serves Po] 
as the heat shield for descent through the Martian atmosphere. Para- rei 
chutes will be deployed to slow the descent and the last few meters Sim 
will be controlled by rocket jets. Sal 
The lander contains two facsimile cameras, separated by about 25 
1m stereobase, and about 1.3 m above the surface (33). The camera Sp 
is built on a vertical axis. The lower portion is stationary and Se. 
houses the azimuth scan motor which turns the upper section in 0.049 pl: 
or 0.129 increments through a total range of 3609. In the upper th. 
section are a pivoted scan mirror driven by an elevation scan motor, Spi 
an optical lens system, and a photodetector array. There are actually i to 
twelve diodes which can be positioned in the camera focal plane. abi 
The four used for high resolution black and white photography are pli 
located at separate focal planes so that by selecting the appropriate he 
detector an image at optimum focus can be generated throughout the nO: 
range from 1.5 m to infinity. . The other detectors take low resolution yr 
pictures with 0. 129 angular resolution. Three diodes have filters fa 
for blue, green, and red, in order to record a color picture. Three im 
more diodes transmit energy in three bands of the near infrared. One Ba 
diode acquires a low resolution black and white picture, and the last Sp 
is designed with low sensitivity so it can image the Sun. m 
The low resolution pictures have an elevation dimension of 609; in 
high resolution pictures have a fixed dimension of 209. The high ar 
resolution pictures can be positioned anywhere in a total elevation ou 
range of -60°9 to +409, so that the entire scene from the base of the pa 
spacecraft to above the horizon can be imaged. Ex 
The photodetector analogue electrical output is sampled in 
synchronism with the mirror velocity. The analogue signal is con- à 
verted to a digital word containing light intensity and scan position pl 
information. Pictures can be stored on the lander's tape recorder id 
and then transmitted directly to Earth at a low data rate or relayed Ea 
to the orbiter for later transmission to Earth. ni 
When the data are received on Earth they will control a three- Sp 
color laser beam recorder to produce either high resolution black and e 
white imagery, full-color imagery or infrared imagery. These pictures pe 
will be used with special software on the analytical plotter to produce 
detailed maps of the landing site area (34).