Supplying the spacecraft components with power required modifying the electrical output of the solar panels. The rest had to be broadcast by the Mission Sequence Working Group from Earth. Commands for the instruments could be stored on Mariner 10 's computer, but were limited to 512 words. The spacecraft's electronics were intricate and complex: it contained over 32,000 pieces of circuitry, of which resistors, capacitors, diodes, microcircuits, and transistors were the most common devices. Nitrogen gas thrusters were used to adjust Mariner 10 's orientation along three axes. Mariner 10 determined its attitude using two optical sensors, one pointed at the Sun, and the other at a bright star, usually Canopus additionally, the probe's three gyroscopes provided a second option for calculating the attitude.
During course correction maneuvers, the spacecraft may need to rotate so that its rocket engine faces the proper direction before being fired. Īttitude control is needed to keep a spacecraft's instruments and antennas aimed in the correct direction. The mission ended up about US$1 million under budget. Despite the rushed schedule, very few deadlines were missed. Cost control was primarily accomplished by executing contract work closer to the launch date than was recommended by normal mission schedules, as reducing the length of available work time increased cost efficiency. No overruns would be tolerated, so mission planners carefully considered cost efficiency when designing the spacecraft's instruments. NASA set a strict limit of US$98 million for Mariner 10's total cost, which marked the first time the agency subjected a mission to an inflexible budget constraint.
The Mariner 10 spacecraft was manufactured by Boeing. The hub stored the spacecraft's internal electronics. Mariner 10 's various components and scientific instruments were attached to a central hub, which was roughly the shape of an octagonal prism. Finally, the antennas would transmit this data to the Deep Space Network back on Earth, as well as receive commands from Mission Control. Several scientific instruments would collect data at the two planets. The navigational system, including the hydrazine rocket, would keep Mariner 10 on track to Venus and Mercury. The solar panels, power subsystem, attitude control subsystem, and the computer kept the spacecraft operating properly during the flight.
The components on Mariner 10 can be categorized into four groups based on their common function. Mariner 10 used the solar radiation pressure on its solar panels and its high-gain antenna as a means of attitude control during flight, the first spacecraft to use active solar pressure control. This maneuver, inspired by the orbital mechanics calculations of the Italian scientist Giuseppe Colombo, put the spacecraft into an orbit that repeatedly brought it back to Mercury. Mariner 10 was the first spacecraft to make use of an interplanetary gravitational slingshot maneuver, using Venus to bend its flight path and bring its perihelion down to the level of Mercury's orbit. This would allow the spacecraft to meet Mercury on three occasions in 19. The first mission to perform an interplanetary gravity assist, it used a flyby of the planet Venus in order to decrease its perihelion. An artists' impression of the Mariner 10 mission.