The failures of the USSR's Mars 4-7 marked the USSR's last attempts in the 70s and early 80s
to send spacecraft to Mars. Viking 1 and Viking 2 were sent by the US to gather images of Mars,
with great success. Because they operated for such a long time, US will also not send anymore
spacecraft to Mars until the 90s. (9 abr 1975 año – 9 abr 1988 año)