Editing Mariner 4 (section)

==Spacecraft and subsystems==
[[File:Mariner_3_or_4_diagram.jpg|thumb|Mariner 3 and 4 diagram]]
The Mariner 4 [[spacecraft]] consisted of an octagonal [[magnesium]] frame, {{cvt|127|cm|in}} across a diagonal and {{cvt|45.7|cm|in}} high. Four [[solar panel]]s were attached to the top of the frame with an end-to-end span of {{convert|6.88|m|ft|sp=us}}, including [[solar sail|solar pressure vanes]] which extended from the ends. A {{cvt|104.1|x|66.0|cm|in}} elliptical [[high-gain antenna|high-gain]] [[parabolic antenna]] was mounted at the top of the frame as well. An omnidirectional [[low-gain antenna]] was mounted on a {{cvt|223.5|cm|ftin|adj=on}} tall mast next to the high-gain antenna. The overall height of the spacecraft was {{convert|2.89|m|ft}}. The octagonal frame housed the electronic equipment, cabling, midcourse propulsion system, and attitude control gas supplies and regulators.<ref name=NSSDC/>

The scientific instruments included:{{r|nasa3|Anderson|Reiff}}
* A [[helium]] [[magnetometer]], mounted on the waveguide leading to the omnidirectional antenna, to measure the magnitude and other characteristics of the interplanetary and planetary magnetic fields.
* An [[ionization chamber]]/[[Geiger counter]], mounted on the waveguide leading to the omnidirectional antenna nearer the body of the spacecraft, to measure the charged-particle intensity and distribution in interplanetary space and in the vicinity of Mars.
* A [[particle detector|trapped radiation detector]], mounted on the body with counter-axes pointing 70° and 135° from the solar direction, to measure the intensity and direction of low-energy particles.
* A [[cosmic ray]] telescope, mounted inside the body pointing in anti-solar direction, to measure the direction and energy spectrum of [[proton]]s and [[alpha particle]]s.
* A solar [[plasma (physics)|plasma]] probe, mounted on the body pointing 10° from the solar direction, to measure the very low energy charged particle flux from the [[Sun]].
* A [[cosmic dust]] detector, mounted on the body with microphone plate approximately perpendicular to the plane of [[orbit]], to measure the [[momentum]], distribution, density, and direction of cosmic dust.
* A [[television camera]], mounted on a scan platform at the bottom center of the spacecraft, to obtain closeup pictures of the surface of Mars. This subsystem consisted of four parts: a [[Cassegrain telescope]] with a 1.05° by 1.05° field of view, a shutter and red/green filter assembly with 0.08 and 0.20&nbsp;second exposure times, a slow scan [[Video camera tube#Vidicon|vidicon tube]] which translated the optical image into an electrical video signal, and the electronic systems required to convert the analogue signal into a digital bitstream for transmission.<ref name=NSSDC-2/>

The [[electric power]] for the instruments and the radio transmitter of Mariner 4 was supplied by 28,224 [[solar cell]]s contained in the four {{cvt|176|x|90|cm|in}} solar panels, which could provide 310&nbsp;watts at the distance of Mars. A rechargeable 1200&nbsp;W·h [[silver-oxide battery|silver-zinc battery]] was also used for maneuvers and backup. [[Monopropellant]] [[hydrazine]] was used for [[spacecraft propulsion|propulsion]], via a four-jet vane vector control motor, with {{convert|222|N|lbf|lk=on|adj=on}} thrust, installed on one of the sides of the octagonal structure. The space probe's [[Spacecraft attitude control|attitude control]] was provided by 12 cold [[nitrogen]] gas jets mounted on the ends of the solar panels and three [[gyroscope|gyros]]. Solar pressure vanes, each with an area of {{cvt|0.65|m2|ft2}}, were attached to the tips of the solar panels. Positional information was provided by four Sun sensors, and a sensor for either the Earth,  Mars, or the star [[Canopus]], depending on the time in its spaceflight. Mariner 4 was the first space probe that needed a star for a navigational reference object, since earlier missions, which remained near either the Earth, the [[Moon]], or the planet [[Venus]], had sighted onto either the bright face of the home planet or the brightly lit target. During this flight, both the Earth and Mars would be too dim to lock onto. Another bright source at a wide angle away from the Sun was needed and Canopus filled this requirement.<ref name=nasa3/> Subsequently, Canopus was used as a reference point in many following missions.<ref name=Goss/>

The telecommunications equipment on Mariner 4 consisted of dual [[S-band]] transmitters (with either a seven-watt [[triode]] cavity amplifier or a ten watt [[traveling-wave tube]] amplifier) and a single [[radio]] receiver which together could send and receive data via the low- and high-gain antennas at 8⅓ or 33⅓ bits per second. Data could also be stored onto a magnetic [[tape recorder]] with a capacity of 5.24 million bits for later transmission. All electronic operations were controlled by a command subsystem which could process any of 29 direct command words or three quantitative word commands for mid-course maneuvers. The central computer and sequencer operated stored time-sequence commands using a 38.4&nbsp;kHz synchronization frequency as a time reference. Temperature control was achieved through the use of adjustable louvers mounted on six of the electronics assemblies, plus multilayer insulating blankets, polished aluminum shields, and surface treatments. Other measurements that could be made included:
* [[Radio occultation]]
* [[Celestial mechanics]] based on precision tracking

Mariner 4 was also supposed to carry an ultraviolet photometer on the left side of the aft TV Camera scan platform. Late in testing, it was discovered that the inclusion of the UV photometer produced electrical problems that would have jeopardized the TV Camera. As a result, it was removed and replaced with a thermal/inertial mass simulator that was designed to emulate the UV photometer's geometry, mass, and other characteristics so that any unintentional problems caused by the removal of the UV photometer would be negated. This spare UV photometer was eventually flown on [[Mariner 5]] in 1967.<ref name=Layman/>