Soviet spacecraft in the Venera series have explored Venus since 
1965, but the first image data made available came from Venera 9 
and 10, which were launched in June 1975 and reached Venus in 
October (39). The spacecraft each consisted of separable lander and 
orbiter components. Pictures from the orbiter are similar in 
appearance to those obtained from Mariner 10. At the appropriate time 
the descent vehicle entered the Venus atmosphere, descended on para- 
chutes, and landed on the surface of the planet. Though the lander 
was equipped with floodlights, the ambient illumination was high 
enough for the on-board telephotometer to record and transmit remarkable 
pictures showing in one case a rocky surface and in the other a 
relatively smooth surface with strong contrasts in reflectivity. 
Mapping of Mercury 
  
After passing Venus, the Mariner 10 spacecraft continued on a 
spiral course in towards the Sun and reached the vicinity of the planet 
Mercury in late March and April 1974 (40). In another remarkable 
feat of spacecraft control the vehicle was placed in an elliptical 
orbit about the Sun and thus was able to make three photographic 
passes around Mercury. The first encounter was March 29 with the 
minimum altitude 735 km and the twin cameras acquired 2949 pictures. 
On the second encounter September 21, minimum distance was 47,740 km 
and 1518 pictures were recorded. The third and last encounter was 
March 16, 1975, at minimum distance 310 km and 1047 pictures were 
made. The innermost planet in the solar system has a diameter of 
4870 km - about the same as Jüpiter's moon Ganymede. Resolution of 
the pictures varied from 127 km to 150 m depending upon the range. 
The cratered surface, now familiar from Earth's Moon and Mars, sug- 
gests this may be the norm for solar system planets (41, 42, 43). 
From this diversity of pictures a control net has been established 
by numerical triangulation (44), mosaics have been assembled from 
digitally rectified and scaled pictures, and airbrush maps at scale 
1:5,000,000 are being prepared for all areas photographed (45). 
Future Lunar and Planetary Missions 
  
NASA and the world in general both seem willing to turn the Moon 
back to poets and lovers. There is only one small mission - called 
the Lunar Polar Orbiter - under consideration. If approved it would 
consist of a small spacecraft carrying mainly geophysical sensors in 
a polar orbit at about 100 km altitude. An imaging system consisting 
of a solid state rectangular CCD (charge coupled device) array has 
been proposed (46). Data transmission limitations would restrict 
resolution to about 75 meters, and mapping at scale 1:500,000 with 
300 m. contours could be accomplished. 
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