Editing Mariner 1 (section)

==Spacecraft==

Three Mariner R spacecraft were built: two for launching and one to run tests, which was also to be used as a spare.<ref name=treasury/>{{rp|174}} Aside from its scientific capabilities, Mariner also had to transmit data back to Earth from a distance of more than {{cvt|26000000|mi}}, and to survive solar radiation twice as intense as that encountered in Earth orbit.<ref name=treasury/>{{rp|176}}

===Structure===

[[File:Diagram of Mariner 1.jpg|thumb|Diagram of Mariner 1]]
 
All three of the Mariner R spacecraft, including Mariner 1, weighed within {{cvt|3|lb}} of the design weight of {{cvt|447|lb}}, {{cvt|406|lb}} of which was devoted to non-experimental systems: maneuvering systems, fuel, and communications equipment for receiving commands and transmitting data. Once fully deployed in space, with its two solar panel "wings" extended, Mariner R was {{cvt|12|ft}} in height and {{cvt|16.5|ft}} across. The main body of the craft was hexagonal with six separate cases of electronic and electromechanical equipment:

*Two of the cases comprised the power system: [[switchgear]] that regulated and transmitted power from the 9800 [[solar cells]] to the {{cvt|33.3|lb}} rechargeable 1000 watt<ref name=NSSDC/> silver-zinc storage battery. 
*Two more included the [[radio receiver]], the three-[[watt]] transmitter, and control systems for Mariner's experiments. 
*The fifth case held electronics for [[digital signal|digitizing]] the [[analog signal|analog]] data received by the experiments for transmission. 
*The sixth case carried the three [[gyroscope]]s that determined Mariner's orientation in space. It also held the central computer and sequencer, the "brain" of the spacecraft that coordinated all of its activities pursuant to code in its [[memory bank]]s and on a schedule maintained by an electronic clock tuned into equipment on Earth.<ref name=treasury/>{{rp|175}}

At the rear of the spacecraft, a [[monopropellant]] (anhydrous [[hydrazine]]) 225 [[Newton (unit)|N]]<ref name=NSSDC/> rocket motor was mounted for course corrections. A nitrogen gas fueled stabilizing system of ten jet nozzles controlled by the onboard gyroscopes, Sun sensors, and Earth sensors, kept Mariner properly oriented to receive and transmit data to Earth.<ref name=treasury/>{{rp|175}}

The primary [[high gain antenna|high gain]] parabolic antenna was also mounted on the underside of Mariner and kept pointed toward the Earth. An [[omnidirectional antenna]] atop the spacecraft would broadcast at times that the spacecraft was rolling or tumbling out of its proper orientation, to maintain contact with Earth; as an unfocused antenna, its signal would be much weaker than the primary. Mariner also mounted small antennas on each of the wings to receive commands from ground stations.<ref name=treasury/>{{rp|175–176}}

Temperature control was both passive, involving insulated, and highly reflective components; and active, incorporating [[louver]]s to protect the case carrying the onboard computer. At the time the first Mariners were built, no [[test chamber]] existed to simulate the near-Venus solar environment, so the efficacy of these cooling techniques could not be tested until the live mission.<ref name=treasury/>{{rp|176}}

===Scientific package===
[[File:Mariner 1 in JPL's Spacecraft Assembly Facility.jpg|thumb|Mariner 1 in JPL's Spacecraft Assembly Facility]]

====Background====

At the time of the Mariner project's inception, few of Venus' characteristics were definitely known. Its opaque [[atmosphere of Venus|atmosphere]] precluded [[telescope|telescopic]] study of the ground. It was unknown whether there was water beneath the clouds, though a small amount of [[water vapor]] above them had been detected. The planet's [[rotation rate]] was uncertain, though JPL scientists had concluded through [[radar]] observation that Venus rotated very slowly compared to the Earth, advancing the long-standing<ref name=beyond1/> (but eventually disproven)<ref name=nasa1/> hypothesis that the planet was [[Tidal locking|tidally locked]] with respect to the Sun (as the Moon is with respect to the Earth).<ref name=avweek1961/> No oxygen had been detected in Venus' atmosphere, suggesting that life as existed on Earth was not present. It had been determined that Venus' atmosphere contained at least 500 times as much [[carbon dioxide]] as the Earth's. These comparatively high levels suggested that the planet might be subject to a [[runaway greenhouse effect]] with surface temperatures as high as {{cvt|600|K}}, but this had not yet been conclusively determined.<ref name=report/>{{rp|7–8}}

The Mariner spacecraft would be able to verify this hypothesis by measuring the temperature of Venus close-up;<ref name=avweek1960a/> at the same time, the spacecraft could determine if there was a significant disparity between night and daytime temperatures.<ref name=report/>{{rp|331}} An on-board [[magnetometer]] and suite of charged particle detectors could determine if Venus possessed an appreciable magnetic field and an analog to Earth's [[Van Allen Belts]].<ref name=avweek1960a/>

As the Mariner spacecraft would spend most of its journey to Venus in interplanetary space, the mission also offered an opportunity for long-term measurement of the [[solar wind]] of charged particles and to map the variations in the Sun's [[magnetosphere]]. The concentration of [[cosmic dust]] beyond the vicinity of Earth could be explored as well.<ref name=treasury/>{{rp|176}}

====Experiments====

Experiments for the measurement of Venus and interplanetary space included:

*A [[Microphone#Piezoelectric microphone|crystal microphone]] for measurement of the density of cosmic dust, mounted on the central frame.
*A [[proton]] detector for counting low-energy protons in the solar wind, also mounted on the central frame.
*Two [[Geiger–Müller tube|Geiger-Müller (GM) tubes]] and an [[ion chamber]], for measuring high-energy charged particles in interplanetary space and in the Venusian equivalent of Earth's Van Allen Belts (which were later shown not to exist). These were mounted on Mariner's long axis to avoid the magnetic fields of the control equipment as well as secondary radiation caused by [[cosmic rays]] hitting the metal structure of the spacecraft. 
*An Anton special-purpose GM tube, for measuring lower energy radiation, particularly near Venus, also mounted away from the central frame.
*A three-axis [[Spacecraft magnetometer#Fluxgate magnetometers|fluxgate magnetometer]]<ref name=NSSDC/> for measuring the Sun's and Venus' magnetic fields, also mounted away from the central frame.
*A microwave [[radiometer]], a {{cvt|20|in}} diameter, {{cvt|3|in}} deep, parabolic antenna designed to scan Venus up and down at two microwave wavelengths (19&nbsp;mm and 13.5mm), slowing down and reversing when it found a hot spot. The 19&nbsp;mm wavelength was for measuring the temperature of the planet's surface while the 13.5mm wavelength measured the temperature of Venus' cloudtops. The instrument was mounted just above the central frame.
*Two [[infrared]] optical sensors for parallel measurement of the temperature of Venus, one at 8 to 9 [[microns]], the other at 10-10.8 microns, also mounted above the central frame.{{r|treasury|report}}{{rp|9}}<ref name=avweek1960a/>

Not included on any of the Mariner R spacecraft was a camera for visual photos. With payload space at a premium, project scientists considered a camera an unneeded luxury, unable to return useful scientific results. [[Carl Sagan]], one of the Mariner R scientists, unsuccessfully fought for their inclusion, noting that not only might there be breaks in Venus' cloud layer, but "that cameras could also answer questions that we were way too dumb to even pose".<ref name=space.com1/>

===Flight plan and ground operations===

[[File:Woomera 1964 0(1).jpg|thumb|120px|The communications station at Woomera]]

The launch window for Mariner, constrained both by the orbital relationship of Earth and Venus and the limitations of the Atlas Agena, was determined to fall in the 51 day period from July 22 through September 10.<ref name=treasury/>{{rp|174}} The Mariner flight plan was such that the two operational spacecraft would be launched toward Venus in a 30-day period within this window, taking slightly differing paths such that they both arrived at the target planet within nine days of each other, between December 8 and 16.<ref name=avweek1962a/> Only Cape Canaveral Launch Complex 12 was available for the launching of Atlas-Agena rockets, and it took 24 days to ready an Atlas-Agena for launch. This meant that there was only a 27-day margin for error for a two-launch schedule.<ref name=treasury/>{{rp|174}}

Each Mariner would be launched into a [[parking orbit]], whereupon the restartable Agena would fire a second time, sending Mariner on its way to Venus (errors in [[trajectory]] would be corrected by a mid-course burn of Mariner's onboard engines).<ref name=report/>{{rp|66–67}} Real-time radar tracking of the Mariner spacecraft while it was in [[parking orbit]] and upon its departure the [[Atlantic Missile Range]] would provide real-time radar tracking with stations at [[Ascension Island|Ascension]] and [[Pretoria]], while [[Palomar Observatory]] provided optical tracking. Deep space support was provided by three tracking and communications stations at [[Goldstone Deep Space Communications Complex|Goldstone, California]], [[RAAF Woomera Range Complex|Woomera, Australia]], and [[Hartebeesthoek Radio Astronomy Observatory|Johannesburg, South Africa]], each separated on the globe by around 120° for continuous coverage.<ref name=report/>{{rp|231–233}}