[[Datoteka:Mariner 3 and 4.jpg|mini|Mariner 3 i 4]]
{{Infobox spaceflight|name=Mariner 3|launch_rocket=[[Atlas-Agena|Atlas LV-3 Agena-D]]|orbit_period=|orbit_eccentricity=|orbit_semimajor=|orbit_inclination=|orbit_apoapsis=|orbit_periapsis=|orbit_reference=[[heliocentric orbit|Heliocentric]]|orbit_epoch=|launch_contractor=|launch_site=[[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Launch Complex 13|LC-13]]|launch_date={{start-date|November 5, 1964, 19:22:05|timezone=yes}} UTC|image=Mariner 3 and 4.jpg|power=300 watts (at Mars encounter)|launch_mass={{convert|260.8|kg|lb}}|dry_mass=|manufacturer=[[Jet Propulsion Laboratory]]|spacecraft_type=|SATCAT=923|COSPAR_ID=1964-073A|mission_duration=Launch failure|operator=[[NASA]] / [[Jet Propulsion Laboratory|JPL]]|mission_type=Mars flyby|image_caption=The Mariner 3 spacecraft|apsis=helion}} '''Mariner 3''' (zajedno s [[Mariner 4|Mariner-om 4]] poznatim kao '''Mariner-Mars 1964''' ) bila je jedna od dvije identične sonde za istraživanje dubokog svemira koje je dizajnirala i izgradila [[Laboratorija za mlazni pogon|Laboratorija]] za [[Laboratorija za mlazni pogon|mlazni pogon]] (JPL) za [[NASA]]-in projekt Mariner-Mars 1964 koji su trebali planirati bliski prelet u svrhu naučnog osmatranja planete Mars i prenos informacija o međuplanetarnom prostoru i svemiru koji okružuje Mars, televizijske slike marsovske površine i slanje na Zemlju podataka o radio okultaciji signala svemirskih letjelica na koje je uticala Marsovska atmosfera.<ref name="M1964_mechanical">{{Cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660027080_1966027080.pdf|title=Mariner Mars 1964 Mechanical Configuration|publisher=NASA Technical Reports Server|format=PDF|accessdate=December 29, 2011}}</ref><ref name="M1964_plan">{{Cite web|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660014211_1966014211.pdf|title=Spaceflight Operations Plan Mariner Mars '64|publisher=NASA Technical Reports Server|format=PDF|accessdate=December 29, 2011}}</ref> Bila je to treća od deset svemirskih letjelica u okviru [[Program "Mariner"|programa Mariner]] .
