Mariner 2 was the first spacecraft to successfully flyby another planet. It was a backup for the Mariner 1 mission which failed shortly after launch to Venus. After launch and termination of the Agena first burn, the Agena-Mariner was in a 118 km altitude Earth parking orbit. The Agena second burn injected the Mariner 2 spacecraft into a geocentric escape hyperbola at 26 minutes 3 seconds after lift-off. Solar panel extension was completed about 44 minutes after launch. On 29 August 1962 cruise science experiments were turned on. A midcourse maneuver was initiated at 22:49:00 GMT on 4 September and completed at 2:45:25 GMT 5 September. On 8 September at 17:50 GMT the spacecraft suddenly lost its attitude control, which was restored by the gyroscopes 3 minutes later. The cause was unknown but may have been a collision with a small object. On October 31 the output from one solar panel deteriorated abruptly, and the science cruise instruments were turned off. A week later the panel resumed normal function and instruments were turned back on. The panel permanently failed on 15 November, but Mariner 2 was close enough to the Sun that one panel could supply adequate power. On December 14 the radiometers were turned on. Mariner 2 approached Venus from 30 degrees above the dark side of the planet, and passed below the planet at its closest distance of 34,773 km at 19:59:28 GMT 14 December 1962. After encounter, cruise mode resumed. Spacecraft perihelion occurred on 27 December at a distance of 105,464,560 km. The last transmission from Mariner 2 was received on 3 January 1963 at 07:00 GMT. Mariner 2 remains in heliocentric orbit. Scientific discoveries made by Mariner 2 included a slow retrograde rotation rate for Venus, hot surface temperatures and high surface pressures, a predominantly carbon dioxide atmosphere, continuous cloud cover with a top altitude of about 60 km, and no detectable magnetic field. It was also shown that in interplanetary space the solar wind streams continuously and the cosmic dust density is much lower than the near-Earth region. Improved estimates of Venus' mass and the value of the astronomical unit were made.

Mariner 4 provided the first up close pictures of Mars. The protective shroud covering Mariner 4 was jettisoned and the Agena D/Mariner 4 combination separated from the Atlas D booster at 14:27:23 GMT on 28 November 1964. The Agena D first burn from 14:28:14 to 14:30:38 put the spacecraft into an Earth parking orbit and the second burn from 15:02:53 to 15:04:28 injected the craft into a Mars transfer orbit. Mariner 4 separated from the Agena D at 15:07:09 and began cruise mode operations. The solar panels deployed and the scan platform was unlatched at 15:15:00 and Sun acquisition occurred 16 minutes later. A midcourse maneuver made on 5 December 1964.

After a 228 day cruise, the spacecraft flew by Mars on July 14 and 15, 1965. Planetary science mode was turned on at 15:41:49 GMT on 14 July. The camera sequence started at 00:18:36 GMT on July 15 and 21 pictures plus 21 lines of a 22nd picture were taken. The images covered a discontinuous swath of Mars starting near 40 N, 170 E, down to about 35 S, 200 E, and then across to the terminator at 50 S, 255 E, representing about 1% of the planet's surface. The closest approach was 9,846 km from the Martian surface at 01:00:57 GMT 15 July 1965. The images taken during the flyby were stored in the onboard tape recorder. At 02:19:11 GMT Mariner 4 passed behind Mars as seen from Earth and the radio signal ceased. The signal was reacquired at 03:13:04 GMT when the spacecraft reappeared. Cruise mode was then re-established. Transmission of the taped images to Earth began about 8.5 hours after signal reacquisition and continued until 3 August. All images were transmitted twice to insure no data was missing or corrupt.

The spacecraft performed all programmed activities successfully and returned useful data from launch until 22:05:07 GMT on 1 October 1965, when the distance from Earth (309.2 million km) and the antenna orientation temporarily halted signal acquisition. In 1967 Mariner 4 returned to the vicinity of Earth again and engineers decided to use the ageing craft for a series of operational and telemetry tests to improve their knowledge of the technologies that would be needed for future interplanetary spacecraft. The cosmic dust detector registered 17 hits in a 15 minute span on 15 September, part of an apparent micrometeoroid shower which temporarily changed the spacecraft attitude and probably slightly damaged the thermal shield. On 7 December the gas supply in the attitude control system was exhausted, and on December 10 and 11 a total of 83 micrometeoroid hits were recorded which caused perturbation of the attitude and degradation of the signal strength. On 21 December 1967 communications with Mariner 4 were terminated.

Results

The total data returned by the mission was 5.2 million bits. All experiments operated successfully with the exception of the ionization chamber/Geiger counter which failed in February, 1965 and the plasma probe, which had its performance degraded by a resistor failure on 6 December 1964. The images returned showed a Moon-like cratered terrain (which later missions showed was not typical for Mars, but only for the more ancient region imaged by Mariner 4). A surface atmospheric pressure of 4.1 to 7.0 mb was estimated and no magnetic field was detected.

Mariner 5 flew by Venus on October 19, 1967 at an altitude of 3,990 kilometres. With more sensitive instruments than its predecessor Mariner 2, Mariner 5 was able to shed new light on the hot, cloud-covered planet and on conditions in interplanetary space. Operations of Mariner 5 ended in November 1967. The spacecraft instruments measured both interplanetary and Venusian magnetic fields, charged particles, and plasmas, as well as the radio refractivity and UV emissions of the Venusian atmosphere.

Mars flyby 31 July 1969; returned 75 images of Martian surface. Ten days before the scheduled launch, a faulty switch opened the main valves on the Atlas stage. This released the pressure which supported the Atlas structure, and as the booster deflated it began to crumple. Two ground crewman started pressurizing pumps, saving the structure from further collapse. The two ground crewman, who had acted at risk of the 12-story rocket collapsing on them, were awarded Exceptional Bravery Medals from NASA.

The Mariner 6 spacecraft was removed, put on another Atlas/Centaur, and launched on schedule. The main booster was jettisoned 4 min. 38 sec. after launch, followed by a 7.5 minute Centaur burn to inject the spacecraft into Mars direct trajectory. After Mariner 6 separated from the Centaur the solar panels were deployed. A midcourse correction involving a 5.35 second burn of the hydrazine rocket occurred on 1 March 1969. A few days later explosive valves were deployed to unlatch the scan platform. Some bright particles released during the explosion distracted the Canopus sensor, and attitude lock was lost temporarily. It was decided to place the spacecraft on inertial guidance for the Mars flyby to prevent a similar occurrence.

On 29 July, 50 hours before closest approach, the scan platform was pointed to Mars and the scientific instruments turned on. Imaging of Mars began 2 hours later. For the next 41 hours, 49 approach images (plus a 50th fractional image) of Mars were taken through the narrow-angle camera. At 05:03 UT on 31 July the near-encounter phase began, including collection of 26 close-up images. Due to a cooling system failure, channel 1 of the IR spectrometer did not cool sufficiently to allow measurements from 6 to 14 micrometers so no infrared data were obtained over this range. Closest approach occurred at 05:19:07 UT at a distance of 3431 km from the martian surface. Eleven minutes later Mariner 6 passed behind Mars and reappeared after 25 minutes. X-band occultation data were taken during the entrance and exit phases. Science and imaging data were played back and transmitted over the next few days. The spacecraft was then returned to cruise mode which included engineering and communications tests, star photography TV tests, and UV scans of the Milky Way and an area containing comet 1969-B. Periodic tracking of the spacecraft in its heliocentric orbit was also done.

Science Results

Mariner 6 returned 49 far encounter and 26 near encounter images of Mars. Close-ups from the near encounter phases covered 20% of the surface. The spacecraft instruments measured UV and IR emissions and radio refractivity of the Martian atmosphere. Images showed the surface of Mars to be very different from that of the Moon, in some contrast to the results from Mariner 4. The south polar cap was identified as being composed predominantly of carbon dioxide. Atmospheric surface pressure was estimated at between 6 and 7 mb. Radio science refined estimates of the mass, radius and shape of Mars.

Mars flyby 5 August 1969; returned 126 images of Martian surface. Mariner 7 was launched on a direct-ascent trajectory to Mars 31 days after Mariner 6. On 8 April 1969 a midcourse correction was made by firing the hydrazine moter for 7.6 seconds. On 8 May Mariner 7 was put on gyro control to avoid attitude control problems which were affecting Mariner 6. On 31 July telemetry from Mariner 7 was suddenly lost and the spacecraft was commanded to switch to the low-gain antenna. It was later successfully switched back to the high-gain antenna. It was thought that leaking gases, perhaps from the battery which later failed a few days before encounter, had caused the anomaly.

At 09:32:33 GMT on 2 August 1969 Mariner 7 bagan the far-encounter sequence involving imaging of Mars with the narrow angle camera. Over the next 57 hours, ending about 5 hours before closest approach, 93 images of Mars were taken and transmitted. The spacecraft was reprogrammed as a result of analysis of Mariner 6 images. The new sequence called for the spacecraft to go further south than originally planned, take more near-encounter pictures, and collect more scientific data on the lighted side of Mars. Data from the dark side of Mars were to be transmitted directly back to Earth but there would be no room on the digital recorder for backup due to the added dayside data. At closest approach, 05:00:49 GMT on 5 August, Mariner 7 was 3430 km above the martian surface. Over this period, 33 near-encounter images were taken. About 19 minutes after the flyby, the spacecraft went behind Mars and emerged roughly 30 minutes later. X-band occultation data were taken during the entrance and exit phases. Science and imaging data were played back and transmitted over the next few days. The spacecraft was then returned to cruise mode which included engineering and communications tests, star photography TV tests, and UV scans of the Milky Way and an area containing comet 1969-B. Periodic tracking of the spacecraft in its heliocentric orbit was also done.

Science Results

The total data return for Mariners 6 and 7 was 800 million bits. Mariner 7 returned 93 far and 33 near encounter images. Close-ups from the near encounter phases covered 20% of the surface. The spacecraft instruments measured UV and IR emissions and radio refractivity of the Martian atmosphere. Images showed the surface of Mars to be very different from that of the Moon, in some contrast to the results from Mariner 4. The south polar cap was identified as being composed predominantly of carbon dioxide. Atmospheric surface pressure was estimated at between 6 and 7 mb. Radio science refined estimates of the mass, radius and shape of Mars.

Mariner 6 encountered Mars on July 31,1969. Together with Mariner 7, which arrived four days later, it returned a combined total of 143 approach pictures of the planet and 55 close-up pictures. These images, from the vehicles' television cameras, included pictures of the northern and southern polar caps as well as Phobos, one of Mars' two moons.

Mariners 6 and 7 were designed to fly over the equator and southern hemisphere of Mars. Mariner 7 encountered Mars on August 4, 1969. The two spacecraft returned a combined total of 143 approach pictures of the planet and 55 close-up pictures. The spacecraft also studied the Martian atmosphere and profiled its chemical composition. Closest approach to Mars for both spacecraft was approximately 3,550 kilometres.

The first spacecraft to orbit another planet. The Mariner Mars 71 mission was planned to consist of two spacecraft on complementary missions. Mariner 8 was to map 70 % of the Martian surface and Mariner 9 was to study temporal changes in the Martian atmosphere and on the Martian surface. The launch failure of Mariner 8 forced Mariner 9 to combine the mission objectives of both. For the survey portion of the mission, the planetary surface was to be mapped with the same resolution as planned for the original mission, although the resolution of pictures of the polar regions would be decreased due to the increased slant range. The variable features experiments were changed from studies of six given areas every 5 days to studies of smaller regions every 17 days. Mariner 9 was launched on a direct trajectory to Mars. Separation from the booster occurred at 22:36 GMT. The four solar panels were deployed at 22:40 GMT. The sensors locked onto the Sun at 23:16, shortly after the spacecraft left the Earth's shadow and Canopus acquisition was achieved at 02:26 GMT 31 May. A planned midcourse maneuver was executed on 5 June. Mariner 9 arrived at Mars on 14 November 1971 after a 167 day flight. A 15 minute 23 second rocket burn put the spacecraft into Mars orbit. The insertion orbit had a periapsis of 1398 km and a period of 12 hr, 34 min. Two days later a 6 second rocket burn changed the orbital period to just under 12 hours with a periapsis of 1387 km. A correction trim maneuver was made on 30 December on the 94th orbit which raised the periapsis to 1650 km and changed the orbital period to 11:59:28 so that synchronous data transmissions could be made to the Goldstone 64-m DSN antenna.

Imaging of the surface of Mars by Mariner 9 was delayed by a dust storm which started on 22 September 1971 in the Noachis region. The storm quickly grew into one of the largest global storms ever observed on Mars. By the time the spacecraft arrived at Mars no surface details could be seen except the summits of Olympus Mons and the three Tharsis volcanoes. The storm abated through November and December and normal mapping operations began. The spacecraft gathered data on the atmospheric composition, density, pressure, and temperature and also the surface composition, temperature, gravity, and topography of Mars. A total of 54 billion bits of scientific data were returned, including 7329 images covering the entire planet. After depleting its supply of attitude control gas, the spacecraft was turned off on 27 October 1972. Mariner 9 was left in an orbit which should not decay for at least 50 years, after which the spacecraft will enter the Martian atmosphere.

The Mariner 9 mission resulted in a global mapping of the surface of Mars, including the first detailed views of the martian volcanoes, Valles Marineris, the polar caps, and the satellites Phobos and Deimos. It also provided information on global dust storms, the gravity field as well as evidence for surface aeolian activity.

An Atlas/Agena D launched Mariner 10 (Mariner Venus-Mercury) from the Eastern Test Range. The spacecraft was scheduled for Venus f lyby in February 1974 and Mercury in March 1974 - it would be the first space probe ever to approach Mercury. Mariner 10 was the first spacecraft to reach Mercury. Mariner 10 was placed in a parking orbit for 25 minutes after launch, then accelerated to a trans-Venus escape trajectory. The television and ultraviolet experiments were trained on the comet Kohoutek while the spacecraft was en route to its destination. The vehicle's first planetary encounter was with Venus on February 5, 1974, at a distance of 4200 km. Mariner 10 took 4,000 photos of Venus, which revealed a nearly round planet enveloped in smooth cloud layers. The gravity of Venus bent the orbit of the spacecraft and sent it towards Mercury. It crossed the orbit of Mercury on March 29, 1974, at 20:46 GMT, at a distance of 704 km from the surface. Photographs taken during the pass revealed an intensely cratered, Moon-like surface and a faint atmosphere of mostly helium. After the first flyby, Mariner 10 entered solar orbit, which permitted two more rendezvous with Mercury. On September 21, 1974, the second Mercury rendezvous, at an altitude of about 47,000 km, provided another opportunity to photograph the sunlit side of the planet and the south polar region. The third and final Mercury encounter on March 16, 1975, at an altitude of 327 km, yielded 300 photographs and magnetic field measurements. The vehicle was turned off March 24, 1975 when the supply of attitude-control gas was depleted.