Viking 2

The second Viking mission probe took off for Mars on 9 September 1975 on board a Titan III E rocket. Viking 2, which was called Viking-A before the launch, should have left first to arrive on Chryse Planitia. It had actually been installed under the fairing of a Titan III E rocket due to depart on 11 August. Various technical incidents and the need to remove a battery caused a one-month delay, and it was finally Viking 1 (Viking B before the launch) that headed for Mars in place of its twin. Viking 2 almost never left for Mars. There had been so much accumulated delay that the launch window was on the point of closing. A few hours before the departure of the Titan III E rocket, the weather conditions became very bad. In normal circumstances, the launch would have been postponed for one or two days while waiting for the weather to improve. But this was not possible with Viking 2 and the probe had to leave. The launch of Viking 2 finally took place at the last minute. A few minutes later, the weather worsened again and the conditions on the launch pad would have ruled out the launch for safety reasons.

After a 333-day journey, the orbiter began sending images of Mars a few days after its insertion into orbit. The insertion into orbit took place without any incidents and the orbiter/lander duo was first set in a temporary orbit (periapsis at 1500 km, apoapsis at 33,000 km, period 24.6 hours) on 7 August 1976 before joining the landing site certification orbit two days later (1499 km periapsis, inclination of 55.2° and period of revolution 27.3 hours).

Viking 2 landed on Mars on 3 September 1976 on Utopia Planitia.

Source: www.nirgal.net/explora_1976.html