Editing Mariner 2 (section)

== Mission profile ==
=== Prelude to Mariner 2 ===
[[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.{{r|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 the December 8 and 16.{{r|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.{{r|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).{{r|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.{{r|report}}{{rp|231–233}}

On July 22, 1962, the two-stage [[Atlas-Agena]] rocket carrying Mariner 1 veered off-course during its launch due to a defective signal from the Atlas and [[Mariner 1#Program error|a bug]] in the program equations of the ground-based guidance computer; the spacecraft was destroyed by the [[Range Safety Officer]].

Two days after that launch, Mariner 2 and its booster (Atlas vehicle 179D) were rolled out to LC-12. The Atlas proved troublesome to prepare for launch, and multiple serious problems with the autopilot occurred, including a complete replacement of the servoamplifier after it had suffered component damage due to shorted transistors.{{r|Neugebauer_Snyder}}

=== Launch ===
[[File:Mariner 2 launch.jpg|thumb|The launch of Mariner 2, on August 27, 1962.]]
[[File:Video-mariner-2-launch-020429.ogv|thumb|Mariner Atlas-Agena ignition]]
[[File:Animation of Mariner 2 trajectory.gif |thumb |right |Animation of Mariner 2{{'s}} trajectory from August 27, 1962, to December 31, 1962<br>{{legend2|magenta| Mariner 2}}{{·}}{{legend2| Lime |[[Venus]]}}{{·}}{{legend2| RoyalBlue|[[Earth]]}}]]

At 1:53 AM EST on August 27, Mariner 2 was launched from [[Cape Canaveral Air Force Station]] Launch Complex 12 at 06:53:14 UTC.{{r|report}}{{rp|97}}{{r|Neugebauer_Snyder}} The bug in the rocket’s software that resulted in the loss of Mariner 1 had not been identified at the time of the launch.{{r|Ulivi19}} In the event the bug caused no issues with the launch since it was in a section of code that was only used when the data-feed from the ground was interrupted and there were no such interruptions during the launch of Mariner 2.{{r|Ulivi19}}

The flight proceeded normally up to the point of the Agena booster engine cutoff, at which point the V-2 vernier engine lost pitch and yaw control. The vernier started oscillating and banging against its stops, resulting in a rapid roll of the launch vehicle that came close to threatening the integrity of the stack. At T+189 seconds, the rolling stopped and the launch continued without incident. The rolling motion of the Atlas resulted in ground guidance losing its lock on the booster and preventing any backup commands from being sent to counteract the roll. The incident was traced to a loose electrical connection in the vernier feedback transducer, which was pushed back into place by the centrifugal force of the roll, which also by fortunate coincidence left the Atlas only a few degrees off from where it started and within the range of the Agena's horizontal sensor. As a consequence of this episode, GD/A implemented improved fabrication of wiring harnesses and checkout procedures.

Five minutes after liftoff, the Atlas and Agena-Mariner separated, followed by the first Agena burn and second Agena burn. The Agena-Mariner separation injected the Mariner 2 spacecraft into a geocentric escape hyperbola at 26 minutes 3 seconds after liftoff. The NASA NDIF tracking station at Johannesburg, South Africa, acquired the spacecraft about 31 minutes after launch. Solar panel extension was completed approximately 44 minutes after launch. The Sun lock acquired the Sun about 18 minutes later. The high-gain antenna was extended to its acquisition angle of 72°. The output of the solar panels was slightly above the predicted value.

As all subsystems were performing normally, with the battery fully charged and the solar panels providing adequate power, the decision was made on August 29 to turn on cruise science experiments. On September 3, the Earth acquisition sequence was initiated, and Earth lock was established 29 minutes later.{{r|report}}{{rp|97–109}}

=== Mid-course maneuver ===
Due to the Atlas-Agena putting Mariner slightly off course, the spacecraft required a mid-course correction, consisting of a roll-turn sequence, followed by a pitch-turn sequence and finally a motor-burn sequence. Preparation commands were sent to the spacecraft at 21:30 UTC on September 4. Initiation of the mid-course maneuver sequence was sent at 22:49:42 UTC and the roll-turn sequence started one hour later. The entire maneuver took approximately 34 minutes. As a result of the mid-course maneuver, the sensors lost their lock with the Sun and Earth. At 00:27:00 UTC the Sun re-acquisition began and at 00:34 UTC the Sun was reacquired. Earth re-acquisition started at 02:07:29 UTC and Earth was reacquired at 02:34 UTC.{{r|report}}{{rp|111–113}}

=== Loss of attitude control ===
On September 8 at 12:50 UTC, the spacecraft experienced a problem with [[Spacecraft attitude control|attitude control]]. It automatically turned on the gyros, and the cruise science experiments were automatically turned off. The exact cause is unknown as attitude sensors went back to normal before telemetry measurements could be sampled, but it may have been an Earth-sensor malfunction or a collision with a small unidentified object which temporarily caused the spacecraft to lose Sun lock. A similar experience happened on September 29 at 14:34 UTC. Again, all sensors went back to normal before it could be determined which axis had lost lock. By this date, the Earth sensor brightness indication had essentially gone to zero. This time, however, telemetry data indicated that the Earth-brightness measurement had increased to the nominal value for that point in the trajectory.{{r|report}}{{rp|113–114}}

=== Solar panel output ===
On October 31, the output from one solar panel (with [[solar sail]] attached) deteriorated abruptly. It was diagnosed as a partial short circuit in the panel. As a precaution, the cruise science instruments were turned off. A week later, the panel resumed normal function, and cruise science instruments were turned back on. The panel permanently failed on November 15, but Mariner 2 was close enough to the Sun that one panel could supply adequate power; thus, the cruise science experiments were left active.{{r|report}}{{rp|114}}

=== Encounter with Venus ===
[[File:11214 2023 956 Fig10 HTML.webp|thumb|Mariner 2's flyby in spatial relation to later probes]]
Mariner 2 was the first spacecraft to successfully encounter another planet,<ref name=beyond2/> passing as close as {{cvt|34773|km|mi}} to Venus after 110 days of flight on December 14, 1962.{{r|NSSDC}}

=== Post encounter ===
After encounter, cruise mode resumed. Spacecraft perihelion occurred on December 27 at a distance of {{convert|105,464,560|km|mi|sp=us}}. The last transmission from Mariner 2 was received on January 3, 1963, at 07:00 UTC, making the total time from launch to termination of the Mariner 2 mission 129 days.{{r|Sparks}} After passing Venus, Mariner 2 entered [[heliocentric orbit]].{{r|nasa1}}