Mariners 3 and 4

Mariners 3 and 4 were intended to make the first NASA flights past Mars. Mariner 3 was launched on 5 November 1964, but failed when its payload shroud could not be ejected after launch, preventing its solar panels from opening to power the spacecraft. Mariner 4 launched on 28 November 1964 and flew past Mars on 15 July 1965 (MY 6, sol 305), transmitting back to Earth the first detailed images of the surface showing topographic features (Figures 9–13 in Stooke, 2012). The following additional information is from NASA (1967a, 1967b) and Olivier de Goursac (personal communication, 27 December 2013).

The television experiment team described several targets that should be covered by the cameras on the two missions. These were the sunlit limb (horizon), areas of high Sun angle for photometric observations, areas near the terminator, which would reveal topography, the edge of the south polar cap and, if possible, the terminator on the polar cap, where the bright surface would reveal subtle topography even near the poorly lit terminator. Specific surface features of interest would be the dark areas Syrtis Major or Sabaeus Sinus, the bright “desert” areas Hellas and Elysium, and seasonally varying features such as Solis Lacus, Trivium Charontis and the dark spots or “oases” in Aethiopis (Figure 214). Syrtis Major was a particularly favored target, but navigation studies showed it was not accessible during the flyby.

The imaging strategy for the double flyby mission resulted in the following plan. Mariner 3 would observe a swath of the planet's surface running roughly northwest to southeast, centered on 190° E and reaching as far south as the south polar cap. Mariner 4 would view a swath extending roughly along the equator between 140° E and 280° E. When Mariner 3 failed, a single swath imaging scheme was designed. It began north of the variable feature Trivium Charontis, which resembled a smaller version of Syrtis Major, at 40° N, 165° E, and extended to the southeast as far as 50° S, 250° E, before turning north again to cross the terminator near 40° S, 270° E. This swath would not reach the south polar cap. During the long cruise to Mars, navigation data showed that the time of the flyby would be 36 min earlier than originally expected.