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}} Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. Mariner 10 was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program (Mariner 11 and 12 were allocated to the Voyager program and redesignated Voyager 1 and Voyager 2). The mission objectives 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. Mariner 10's science team was led by Bruce C. Murray at the Jet Propulsion Laboratory. == Design and trajectory == 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.〔(【引用サイトリンク】url=http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Mariner_10&Display=ReadMore )〕 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 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. The components on Mariner 10 can be categorized into four groups based on their common function. The solar panels, power subsystem, attitude control, and computer kept the spacecraft operating properly during the flight. The navigational system, including the hydrazine rocket, would keep Mariner 10 on track to Venus and Mercury. Several scientific instruments would collect data at the two planets. Finally, the antennas would transmit this data to the Deep Space Network back on Earth, as well as receive commands from Mission Control. Mariner 10's various components and scientific instruments were attached to a central hub, which was roughly the shape of an octagonal prism. The hub stored the spacecraft's internal electronics.〔〔Clark 2007, pp. 22–23〕〔 The Mariner 10 spacecraft was manufactured by Boeing.〔(【引用サイトリンク】url=http://space.jpl.nasa.gov/msl/QuickLooks/mariner10QL.html&Display=ReadMore )〕 NASA set a strict limit of $98 million for Mariner 10's total cost, which marked the first time the agency subjected a mission to an inflexible budget constraint. No overruns would be tolerated, so mission planners carefully considered cost efficiency when designing the spacecraft's instruments.〔Reeves 1994, pp. 222〕 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. Despite the rushed schedule, very few deadlines were missed.〔 The mission ended up about $1 million under budget.〔Murray and Burgess 1977, pp. 142〕 Attitude control is needed to keep a spacecraft’s instruments and antennas aimed in the correct direction. During course maneuvers, a spacecraft may need to rotate so that its rocket faces the proper direction before being fired. 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. Nitrogen gas thrusters were used to adjust Mariner 10’s orientation along three axes.〔Dunne and Burgess 1977, pp. 58〕〔Murray and Burgess 1977, pp. 50〕 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.〔 Commands for the instruments could be stored on Mariner 10’s computer, but were limited to 512 words. The rest had to be broadcast by the Mission Sequence Working Group from Earth. The power subsystem could store up to 20 ampere hours of electricity on a 39 volt nickel-cadmium battery. The flyby past Mercury posed major technical challenges for scientists to overcome. Due to Mercury's proximity to the Sun, Mariner 10 would have to endure 4.5 times more solar radiation than when it departed Earth—compared to previous Mariner missions, spacecraft parts needed extra shielding against the heat. Thermal blankets and a sunshade were installed on the main body. After evaluating different choices for the sunshade cloth material, mission planners chose beta cloth, a combination of aluminized Kapton and glass-fiber sheets treated with Teflon.〔Dunne and Burgess 1978, pp. 32–33〕 However, solar shielding was unfeasible for some of Mariner 10's other components. Mariner 10's two solar panels needed to be kept under 115 °C. Covering the panels would defeat their purpose of producing electricity. The solution was to add an adjustable tilt to the panels, so the angle at which they faced the sun could be changed. Engineers considered folding the panels toward each other, making a V-shape with the main body, but tests found this approach had the potential to overheat the rest of the spacecraft. The alternative chosen was to mount the solar panels in a line and tilt them along that axis, which had the added benefit of increasing the efficiency of the spacecraft’s nitrogen jet thrusters, which could now be placed on the panel tips. The panels could be rotated a maximum of 76 degrees.〔Strom and Sprague 2003, pp. 16〕〔Murray and Burgess 1977, pp. 21〕 Additionally, Mariner's 10 hydrazine rocket nozzle had to face the Sun to function properly, but scientists rejected covering the nozzle with a thermal door as an undependable solution. Instead, a special paint was applied to exposed parts on the rocket so as to reduce heat flow from the nozzle to the delicate instruments on the spacecraft.〔Dunne and Burgess 1978, pp. 30–32〕 Accurately performing the gravity assist at Venus posed another hurdle.〔Reeves 1994, pp. 242〕 If Mariner 10 was to maintain a course to Mercury, its trajectory could deviate no more than from a critical point in the vicinity of Venus.〔Dunne and Burgess 1978, pp. 56〕 To ensure that the necessary course corrections could be made, mission planners tripled the amount of hydrazine fuel Mariner 10 would carry, and also equipped the spacecraft with more nitrogen gas for the thrusters than the previous Mariner mission had held. These upgrades proved crucial in enabling the second and third Mercury flybys.〔Murray and Burgess 1977, pp. 25–26〕 Even so, the mission still lacked the ultimate safeguard: a sister spacecraft. It was common for probes to be launched in pairs, with complete redundancy to guard against the failure of one or the other.〔Strom and Sprague 2003, pp. 14〕 The budget constraint ruled this option out. Even though mission planners stayed sufficiently under budget to divert some funding for constructing a backup spacecraft, the budget did not permit both to be launched at the same time. In the event that Mariner 10 failed, NASA would only allow the backup to be launched if the fatal error was diagnosed and fixed—this would have to be completed in the two-and-a-half weeks between the scheduled launch on November 3 and the last possible launch date of November 21.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mariner 10」の詳細全文を読む スポンサード リンク
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