spase://SMWG/Observatory/Mariner10

Mariner 10 was the seventh successful launch in the Mariner series, the first spacecraft to use the gravitational pull
of one planet (Venus) to reach another (Mercury), and the first spacecraft mission to visit two planets. Mariner 10 was the first
(and as of 2003 the only) spacecraft to visit Mercury. The spacecraft flew by Mercury three times in a retrograde heliocentric
orbit and returned images and data on the planet. Mariner 10 returned the first-ever close-up images of Venus and Mercury. The
primary scientific objectives of the mission were to measure Mercury's environment, atmosphere, surface, and body characteristics
and to make similar investigations of Venus. Secondary objectives were to perform experiments in the interplanetary medium and to
obtain experience with a dual-planet gravity-assist mission. The spacecraft structure was an eight-sided forger magnesium framework
with eight electronics compartments. It measured 1.39 m diagonally and 0.457 m in depth. Two solar panels, each 2.69 m long and 0.97
m wide, were attached at the top, supporting 5.1 sq m of solar cell area. Fully deployed the spacecraft measured 8.0 m across the
solar panels and 3.7 m from the top of the low-gain antenna to the bottom of the heat-shield. A scan platform with two degrees of
freedom was mounted on the anti-sunward face. A 5.8 m long hinged magnetometer boom extended from one of the octagonal sides of the
body. Total launch mass was 502.9 kg, of this 29 kg were propellant and attitude control gas. The total mass of instruments onboard
was 79.4 kg. The rocket engine was a 222-N liquid monopropellant hydrazine motor situated below a spherical propellant tank which was
mounted in the center of the framework. The nozzle protruded through a sunshade. Two sets of three pairs of orthogonal reaction
nitrogen gas jets, mounted on the tips of the solar panels, were used to stabilize the spacecraft on three axes. Command and control
were the responsibility of an on-board computer with a 512 word memory augmented by ground commands Mariner 10 carried a motor driven
high-gain dish antenna, a 1.37 m diameter aluminum honeycomb-disk parabolic reflector, which was mounted on a boom on the side of the
spacecraft. A low-gain omnidirectional antenna was mounted at the end of a 2.85 m boom extending from the anti-solar face of the
spacecraft. Feeds enabled the spacecraft to transmit at S- and X-band frequencies, data could be transmitted at a maximum rate of
117.6 kilobits per second. The spacecraft carried a Canopus star tracker, located on the upper ring structure of the octagonal
satellite, and acquisition sun sensors on the tips of the solar panels. The interior of the spacecraft was insulated with multilayer
thermal blankets at top and bottom. The sunshade was deployed after launch to protect the spacecraft on the solar-oriented side.
Louvered sides on five of the eight electronics compartments also helped control the interior temperatures. Instruments on-board the
spacecraft measured the atmospheric, surface, and physical characteristics of Mercury and Venus. Experiments included television
photography, magnetic field, plasma, infrared radiometry, ultraviolet spectroscopy, and radio science detectors. An experimental
X-band, high-frequency transmitter was flown for the first time on this spacecraft. Mariner 10 was placed in a parking orbit after
launch for approximately 25 minutes, then placed in orbit around the Sun en route to Venus. The orbit direction was opposite to the
motion of the Earth around the Sun. Mid-course corrections were made. The spacecraft passed Venus on February 5, 1974, at a distance
of 4200 km. It crossed the orbit of Mercury on March 29, 1974, at 2046 UT, at a distance of about 704 km from the surface. The TV and
UV experiments were turned on the comet Kohoutek while the spacecraft was on the way to Venus. A second encounter with Mercury, when
more photographs were taken, occurred on September 21, 1974, at an altitude of about 47,000 km. A third and last Mercury encounter at
an altitude of 327 km, with additional photography of about 300 photographs and magnetic field measurements occurred on March 16,
1975. Engineering tests were continued until March 24, 1975, when the supply of attitude-control gas was depleted and the mission
was terminated. Total research, development, launch, and support costs for the Mariner series of spacecraft (Mariners 1 through 10)
was approximately $554 million. A back-up probe named Mariner-K was built and stood ready on a "borrowed" Atlas Centaur launch
vehicle, in case the Mariner 10 launch failed. This probe was later donated to the Smithsonian and the launch vehicle was used for
it's original purpose.