From the time span between 1962 to 1973, the space agency NASA (National Aeronautics and Space Administration) in association with JPL (Jet Propulsion Laboratory) conducted a 10-mission program referred to as the Mariner Program. Through a series of robotic interplanetary probes, the program was designed to investigate the planets, Mars, Venus, and Mercury. Excitingly, the program contained many firsts, of which included the first planetary flyby (the act of sending a space probe past a planet or dwarf planet close enough to record scientific data), the first planetary orbiter (a space probe that orbits a planet or other astronomical object), and the first gravity assist maneuver (the use of the relative movement and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense). Fortunately, out of the ten vehicles in the Mariner series, seven were successful (Mariner). The overall cost of the Mariner program was approximately $554 million, with Mariner 6 and 7 missions costing roughly $148 million (Mariner).
The five Mariner Missions leading up to Mariner 6 and 7’s dual mission contained the following objectives as followed: Mariner 1 was designed for a planetary flyby of Venus, but unfortunately failed to orbit, forcing its objectives to be accomplished by Mariner 2 of which launched 5 weeks later (Mariner 1). By fulfilling the objectives of Mariner 1 along with its own objectives including receiving communications from the spacecraft in the vicinity of Venus, perform radiometric temperature measurement of the planet, and to measure the interplanetary magnetic field,, Mariner 2 was able to become the first robotic space probe to conduct a successful planetary encounter with the planet Venus (Mariner 2). Due to Mariner 3’s launch failure, its objectives like Mariner 1, were fulfilled by the Mariner launch that followed. Both Mariner 3 and Mariner 4’s intentions were to conduct close up scientific observations of Mars in order to transmit these observations to Earth. Successfully, Mariner 4 was able to perform the first successful flyby of the planet Mars, on November 28, 1964, that was able to return the first close-up pictures of the Marian surface (Mariner 3 and Mariner 4). The objectives of Mariner 5 included the intentions of measuring interplanetary and Venusian magnetic fields, charged particles, plasma, and radio refractivity and UV emissions of the atmosphere of Venus (Mariner 5).
Following the completion of these missions, comes Mariner Missions 6 and 7, that were able to complete the first dual mission to Mars in 1969. Together, the mission’s goals included the intention of studying the surface and atmosphere of Mrs during close flybys as to establish a basis for future investigations, in particular, those encompassing the search for extraterrestrial life, as well as to demonstrate and develop technologies necessary for future Mars missions. In addition, Mariner 6 also had the intentions of providing experience and data that would become useful in programming that Mariner 7 encounter occurring five days later (Mariner 6 and 7). With these objectives in mind, also came the implementation of the radio-occultation experiment designs during the Marine 4 mission, as well as probes designed to intake measurements of atmospheric composition, pressure, density, and temperate on Mars. The objectives were also aimed at obtaining surface images of greater quality and quantity that not only would provide a more complete picture of the Martian surface, but would also allow for improved planning for future missions in search for life on Mars when in conjunction with the atmospheric data obtained. Also, to provide a precise measurement of the mass of Mars, a celestial mechanics experience was also included in the mission. Lastly, the missions were also intended to provide experiences in the engineering and mission operations required for long-term flight away from the sun (The Mariner Mars Missions)
As the second pair of Mars missions in NASA’s Mariner series, both launch dates of each mission were relatively close. Mariner 6 launched on February 24, 1969, and conducted its flyby on July 31, 1969, while Mariner 7 launched on March 27, 1969, and conducted its flyby on August 5, 1969 (Dunbar). Scheduled to launch from Cape Canaveral Air Force Station, the spacecraft was thus shipped to Cape Canaveral between December 1968 through January 1969 in order to begin pre-launch checkouts and testing. With the intentions of flying two probes, and one as a spare in the event of a mission failure, three Mariner probes were constructed for the mission and thus were all sent from pre-launch testing. Unfortunately, on February 14, 1969, as Mariner 6 was undergoing a simulated countdown on LC-36A during a test run, an electrical relay in the Atlas malfunctioned opening two valves in the pneumatic system allowing helium pressure gas to escape from the booster’s balloon skin. Thankfully, as the malfunction continued to occur and crumple the Atlas, two pas technicians by the names of Bill McClure and Jack Beverlin, were able to quickly activate a manual override switch to close the valves and pump helium back in. Thus these two extremely fast thinking scientists were able to save Mariner 6 and its Centaur, but were unable to save the Atlas as it had sustained structural damage and was in too bad of a condition to be reused. As a reward for their achievements, NASA awarded Bill McClure and Jack Beverlin an Exceptional Medal of Bravery for not only their quick-thinking, but also their bravery as they risked their lives in being crushed underneath the towering 124 rocket. In addition to this amazing honor, in 2014, an escarpment on Mars was named the McClure-Beverlin Ridge in honor of the pair, who has since passed away (Mariner 6 and 7).
Following this near setback, Mariner 6 lifted successfully from LC-36B at Cape Canaveral on February 25, 1969, along with a successful boost phase using Atlas-Centaur AC-20. Even with a minor LOX leakage that froze some telemetry probes in AC-20 that registered as a drop in sustainer engine fuel pressure, the launch was still completed successfully (Mariner 6 and 7). In order to serve two purposes, the Centaur stage on both Mariner 6 and Mariner 7 flights was set up to perform a retrorocket maneuver after capsule separation. These two purposes included the intentions of preventing venting propellant from the spent Centaur from contacting the Probe, as all as to put the vehicle on a trajectory that would send it into solar orbit and not impact the Martian surface (Mariner 6 and 7). Impact on the Martian surface was aimed at being avoided as it could potentially contaminate the planet with Earth microbes.
As Mariner 6 launched from Cape Canaveral LC-36B Air Force Station in Florida on February 24, 1969, through its launch vehicle Atlas-Centaur, its mass was approximately 411.8kg, and its nominal power was 449 W (Mariner 6). It conducted its flyby of Mars and closest approach on July 31, 1969, of which its distance from Mars was approximately 3,431 kilometers (2,132 miles). The mission duration of Mariner 6 was 1 year and 10 months from launch to deactivation (Mariner 6 and 7). These numbers closely resemble that of its dual mission partner, Mariner 7, that launched from Cape Canaveral LC-36A on March 27, 1969, with a launch mass of 411.8 kg and power of 449 W. Its mission duration was 1 year and 9 months from launch to deactivation, and its flyby of Mars with its closest approach occurred on August 5, 1969, when it was approximately 3,430 kilometers (2,130mi) away (Mariner 6 and 7). Ironically, both spacecraft flew over cratered regions and missed both the giant northern volcanoes, in reference to the vast volcanic plateau centered near the equator in the western hemisphere of Mars known as Tharsis, as well as the equatorial grand canyon, in reference to the system of canyons that runs along the Martian surface east of the Tharsis region known as Valles Marineris (Geography of Mars).
An interesting side note includes the occurrence of JPL (Jet Propulsion Laboratory) losing count with Mariner 7 on July 29, 1969, thought to be caused by leaking gases from a battery that later failed. Following a span of 7-hour silence, contact was thankfully restored, but not without a loss. After such occurrence, it became evident that the instrument responsible for reporting the orientation of the television cameras had been damaged to the point of loss of functionality, and with the Mars encounter close at hand and incapability of properly pointing its camera, a quick solution was needed. Dually as a solution and testament to the expertise being developed by mission operators during such early interplanetary missions, manual calibration by grounds crew was about t being Mars into the view of Mariner 7 camera and on August 7, made it possible for Mariner 7 to relay encounter images of Mars; thus allowing for the restoration of the Mariner 7 imaging system (The Mariner Mars Mission).
Diving into the spacecraft specifics, the scientific instruments used included the following: an imaging system, infrared spectrometer, infrared radiometer, ultraviolet spectrometer, and conical radiometer (Mariner 6-JPL). According to the “Mariner 6, Part of Mariner Family” article, the spacecraft similarities between Mariner 6 and Mariner 7 are as follows: “The Mariner 6 and 7 spacecraft were identical, consisting of an octagonal magnesium frame base, 138.4 cm diagonally and 45.7 cm deep. A conical superstructure mounted on top of the frame held the high-gain 1-meter diameter parabolic antenna and four solar panels, each measuring 215 x 90 cm, were affixed to the top corners of the frame. The tip-to-tip span of the deployed solar panels was 5.79 m. A low-gain omnidirectional antenna was mounted on a 2.23 m high mast next to the high-gain antenna. Underneath the octagonal frame was a two-axis scan platform which held scientific instruments. Overall science instrument mass was 57.6 kg. The total height of the spacecraft was 3.35 m”.
The spacecraft instrumentation included the following: IR Spectrometer, Two-Channel IR Radiometer Mars Surface Temperature, UV Spectrometer, S-Band Occultation, Thermal Control Flux Monitor (Conical Radiometer), Mars TV Camera, Celestial Mechanics, and General Relativity (Mariner 6 and 7). In addition, both Mariner 6 and Mariner 7 contained wide and narrow angle cameras with digital tape recorder, infrared spectrometer and radiometer, ultraviolet spectrometer, radio occultation, and celestial mechanics
Furthermore, the spacecraft was stabilized in three axes, aimed in reference to the sun and star Canopus, the brightest star in constellation of Carina located near the trailing edge of the constellation approximately 310 light years from the Sun. Mounted on the ends of the solar panels included three gyros, and two sets of six nitrogen jets. The spacecraft also contained a Canopus tracker, as well as two primary and four secondary sun sensors. A 223-newton rocket motor provided the propulsion, while 17,472 photovoltaic cells supplied its power. Interestingly enough, these could provide 800 watts of power near Earth, and 449 watts while on Mars. As for a back up, a 1200 watt-hour, rechargeable silver-zinc battery was kept. Telecommunications were available through three telemetry channels carrying engineering data in the following capacities: Channel A at 8? or 33? bit/s, Channel B at 66? or 270 bit/s, and Channel C at 16,200 bit/s. Through the usage of high and love gain antennas, communications were successfully accomplished through dial S-band traveling wave tubes amplifiers, which are specialized vacuuming tubes used in electronics to amplify radio frequency signals.
The scientific results included a total of 800 million bits of total data returned for Mariners 6 and 7, broken down into Mariner 6 returning 49 far encounter and 26 near encounter images, while Mariner 7 returning 93 far encounter and 33 near encounter images. These near encounter phases resulted in imaging that covered 10% of the Martian surface. In addition, the spacecraft instruments measured UV and IR emissions, as well as radio refractivity of the Martian atmosphere. Interestingly enough, the images returned showed the surface of Mars to be very different from that of the Moon. Through the findings of both Mariner 6 and 7, scientists were able to identify the Martian south polar cap as being composed predominately of carbon dioxide, as well as they conferred that the atmospheric pressure was estimated at between 6 and 7 mb, hence radio science refined estimates of the mass, radius, and shape of Mars (Mariner 6).
Furthermore, Mariner 6 along with Mariner 7 were able to obtain imaging of different areas of Mars during its near encounter sequences. Mariner 6 was able to capture imaging including a band from the equator to 10oS, spanning 60oW to 320oW, and Mariner 7 was able to capture imaging encompassing the edge of the polar cap at 60oS, 0oW as well as a band from 10oN to 30oS, spanning 20oW to 105oW (The Mariner Mars Mission). With these images, the evidence they contained essentially deflated any previous theories proposing the existence of artificial canals on the surface of Mars, as well as the images revealed the lack of any correlation between geographical features and the light and dark areas previously seen by far encounter images. Unfortunately, these images lacked in the sense that they failed to show the widely varied terrain of Mars that scientist hoped for, but later missions would come to reveal such exciting findings.
In addition to the findings revealed through the numerous photos, atmospheric experiments also contained their interesting findings as well. Through these atmospheric experiences came the indications that the presence of dust suspended in the Mars atmosphere, carbon dioxide ice and water ice clouds, carbon monoxide, ionized hydrogen, and ionized oxygen (The Mariner Mars Missions). Ozone and nitrogen were species not detected of which would have served as beneficial when hypothesizing the extent of life on Mars similar to that on Earth. In addition, surface temperature as warm as 280-280k, which is about 17 degrees Celsius or 63 degrees Fahrenheit) were detected near the equator, as well as it was found that the darker areas of lower reflectance were generally warmer than the lighted colored deserts of higher reflectance (The Mariner Mars Missions).
Overall, it is clear to see that the dual missions of Mariner 6 and Mariner 7 can be deemed successful in that their findings were numerous, with the addition of obtaining numerous valuable photographs. But the questions still remains: “Now what?”, of which I believe NASA is successfully attacking with the constant continuation of striving to uncover all there is to know about Mars. Some planned missions include the following: Hope Mars Mission (2020), Mars 2020 Rover (2020), Rosalind Franklin (2020), Mars Global Remote Sensing Orbiter, Lander, and Small Rover, (2020), Mars Terahertz Micro-satellite (2020), Mangalyaan 2 (Mars Orbiter Mission 2, 2022), and Martian Moons Exploration (MMX, 2024) (“Here’s All the Past, Present, and Future Missions to Mars”). Hence it is clear to see that with the many more missions to come, many more discoveries are soon to follow.
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