The Mariner spacecraft were all relatively small robotic explorers, each launched on an Atlas rocket. The timing of Mariner 6 and 7 allowed them to have a shorter flight duration based on the alignment of the Earth and Mars at the time. The dry weight of Mariner 6 and 7 were each less than half a ton, coming in at 413 kg (908 lb.) each (dry weight is excluding onboard rocket propellant).
Credit NASA — Along with its twin Mariner 7 spacecraft, Mariner 6 was designed to make a close flyby of Mars to study the surface for signs of life and develop technology for future missions. It took 24 near-encounter photos showing a chaotic and heavily cratered surface as well as the dark features long seen from Earth.
The Mariner 6 spacecraft also had the objective of providing experience and data for the Mariner 7 encounter five days later.
Mariner 6 and 7, launched 2/24/69 and 3/27/69 and had Mars flybys 7/31/69 and 8/5/69; They collected data with the onboard equipment including wide- and narrow-angle cameras with digital tape recorder, infrared spectrometer and radiometer, ultraviolet spectrometer, radio occultation and celestial mechanics. Mariner 7 was launched on an Atlas SLV-3C/Centaur (AC19, spacecraft 69-4). It utilized a direct-ascent trajectory to Mars from Cape Kennedy Launch Complex 36A meaning that it did not orbit first, but rather launched directly and kept going. At closest approach, 05:00:49 UT on 5 August, Mariner 7 was 3430 km above the Martian surface.
In celestial navigation, an ephemeris (plural: ephemerides) gives the trajectory of naturally occurring astronomical objects as well as artificial satellites. This provides the objects position and velocity over time. The needs of the Mariner Mars 1969 mission necessitated the general improvement of planetary ephemerides. A new 60-year numerical computation of the planets of the solar system was made corrections obtained from a weighted least-squares fit to available data set spanning the period 1910-1968.
https://www.jpl.nasa.gov/news/fact_sheets/mariner.pdf
