Mariner 7

The body of the spacecraft has the shape of an octahedron 138.4 cm wide and 45.7 cm high. Magnesium alloy housing, leakproof. Four solar panels with a span of 5.79 m are attached to the upper part of the device. A parabolic antenna with a diameter of 116.8 cm with a high gain is installed in the upper part of the device, and an omnidirectional antenna with a low gain is mounted on a mast with a height of 223.5 cm installed next to the parabolic antenna. The total height of the spacecraft was 3.35 meters, and the mass of 411.8 kg. The case is divided into eight compartments in which electronic equipment, cables, correctional propulsion system, gas tanks for the orientation system and control devices are located. In the center of the lower surface of the housing is a biaxial scanning platform.

The power for all Mariner-7 systems was provided by 17,472 photocells assembled in four panels 215 × 90 cm in size, which could generate up to 449 W near Mars, energy was stored in an 18-cell silver-zinc battery with a capacity of 1200 W · h.

To correct the trajectory, an engine developing 222 N thrust was used, which worked on a single-component hydrazine fuel.

Full, three-axis orientation of the apparatus was carried out by 12 micromotors operating on compressed nitrogen , which were installed at the ends of solar panels. There were three gyroscopes in the orientation system. Information about the orientation of the spacecraft was provided by solar sensors (two main and four auxiliary) and the Canopus star sensor.

Communication equipment at Marineer-7 consisted of a duplicated S-band radio transmitter (2195 MHz) with a power of 20 watts and one radio receiver. The equipment could send and receive data through an omnidirectional antenna with a low gain and a directional antenna with a high gain. The data rate through the parabolic directional antenna is 16,200 bps. Data could also be stored for subsequent transmission on-board recorders: digital with a capacity of 130,000,000 bits and an analog capacity of 120,000,000 bits.

The work of all the electronics was under the control of the command subsystem that could process any of the commands received from the Earth (53 direct commands in the form of words, 5 control commands or 4 commands having a numerical value necessary to perform path correction). The central computer and the program-time device with a total weight of 11.8 kg worked out the service commands stored in the memory, which were executed sequentially at regular intervals. As a standard of time, a synchronizing frequency of 2.4 kHz was used.

The temperature regime was maintained due to the use of panels installed above 6 compartments with electronics with shutters, as well as multi-layer thermal insulation, protective screens made of polished aluminum and special processing of external surfaces.

In each of the third-generation spacecraft, i.e., Mariner-6 and Mariner-7, a large number of integrated circuits (2682 pcs) were used. The total number of electronic components (capacitors, resistors, diodes, transistors, integrated circuits, etc.) is 24520. When converting integrated circuits to discrete elements, the total number of electronic components is 98764. The electronic hardware worked in vacuum, only the on-board tape recorders had a sealed enclosure. To implement the functionality of Mariner-7 weighing 411.8 kg using discrete elements, a spacecraft weighing more than 1 ton would be required. This was the opinion of the specialists of the Jet Propulsion Laboratory, the developers of the Mariner spacecraft ^[1] .

Scientific Instruments

The following scientific devices are installed on Mariner-7:

• ultraviolet spectrometer;
• two-channel infrared spectrometer;
• two-channel infrared radiometer;
• a narrow-angle television camera for taking pictures of Mars;
• wide-angle television camera for taking pictures of Mars.
• No scientific instruments required for the radio eclipse experiment

Scientific instruments are placed on a biaxial scanning platform. The platform directs devices to predetermined surface areas during the flight of the Mariner near Mars.

A narrow-angle television camera at a distance of 3500 km to the surface of Mars could photograph a surface section of 72x84 km, with distinguishable surface details of 300 m, and a wide-angle television camera section of 720x840 km with a resolution of 3 km. The camera lens created a rectangular image measuring 9.6 x 12.3 mm on the vidicon. It was converted into a television image consisting of 704 lines with 935 elements per line, each element was encoded at 256 brightness levels. Thus, each image contained about 5,000,000 bits of information, approximately twenty times larger than the image of Mariner-4.

Research Program:

• Obtaining images to study the state and properties of the surface of Mars as well as clouds, haze in the atmosphere;
• Study of the composition of the atmosphere using spectroscopic techniques;
• Determination of atmospheric parameters (including pressure) based on data from the radio eclipse experiment;
• Determination of surface temperature from measurements of infrared radiation of Mars.

All onboard scientific equipment was intended for the study of Mars; Mariner-7 did not conduct experiments on the study of interplanetary space ^[2] .

Launch

Mariner-7 was launched on March 27, 1969 from the launch site at Cape Canaveral with the Atlas-SLV3C launch vehicle with the Centaurus D booster block.

Correction was carried out on April 8, 1969, with the engine turned on for 7.6 seconds.

Span Near Mars

Photographing Mars was carried out in two stages: 1) when approaching the planet and 2) when passing in the immediate vicinity of the surface of the planet.

2 hours before the first shooting session of the Mars disk, the temporary programmed device gave commands to heat up scientific instruments, turn on the data conversion system, tape recorders and the scanning platform mechanism. The infrared sensor for the long-range capture of Mars is turned on, which produces a direction to the center of the planet’s disk. The scanning platform operates in automatic tracking mode using the signals from this sensor. Mariner-7 conducted three sessions of shooting the planet’s disk using a narrow-angle camera. The first session lasting 20 hours began with a distance between the planet and Mariner-7 equal to 1716000km. The images were recorded on an analog tape recorder and after the shooting session was taken for three hours on a 63-meter antenna of the space station in Goldstone. Recording pictures on magnetic tape has been erased. The second session lasted 20 hours. The received images were transmitted to Earth and the record was deleted. The third sessions also lasted 20 hours. The third session ended at a distance of 127,000 km from Mars. Record after the transfer of images to Earth erased. Mariner-7 received 93 shots from a long distance.

Upon further approach to Mars, the planet’s horizon line is captured by two narrow-angle horizon sensors and the scanning platform is switched to scanning mode on the planet’s disk. The two-axis scan limits are 215 and 64 degrees. The results of measurements of the physical parameters of the planet and its atmosphere along the scanning path periodically crossing the planet’s disk are recorded in digital code on a tape recorder. At the same time, television images of individual sections of Mars are obtained on the scan path.

Mariner-7 initially photographed from close range a section that began north of the equator and stretched to the southeast. On this site are the Hellespontus area and the Hellas desert. Then Mariner-7 photographed the southern polar cap. Based on the results of shooting Mars from a long distance, which was conducted by Mariner-6, the shooting program for Mariner-7 was changed and instead of the previously planned three wide-angle images, five wide-angle images of the southern polar cap were obtained.

Mariner 7 flew near Mars 05:00:49 UT on August 5, 1969. The minimum distance was 3430 km at 05:00:49 UT on August 5. The spacecraft was at that moment at a distance of more than 96 million km from the Earth. Mariner-7 received 33 close-up pictures that were recorded on an analog tape recorder. Data from scientific instruments and images over the next few days were transmitted to Earth. Then Mariner-7 continued to work in interplanetary flight mode.

Due to malfunctions of the cooling system, the first channel of the infrared spectrometer was not cooled sufficiently; therefore, measurements in the range of 6-14 microns were impossible.

End of Flight

The automatic interplanetary station Mariner-7 is in a heliocentric orbit .

Mariner-6 and Mariner-7 photographed from close range using a wide-angle television camera about 20% of the surface of Mars. Three types of surface areas were identified: 1) areas covered by craters, 2) chaotic areas covered by a random network of short ridges and valleys 1-3 wide and 2-10 km long, 3) areas on which there are no relief details. On the bright circular region of Hellas, there are no craters or any other relief details up to a resolution limit of a narrow-angle television camera of approximately 300 m. There are many transitional options between these three types. Two types of craters were discovered: large craters with a flat bottom, small craters of a boiler-like shape. The ratio of the diameter of the crater to the depth is from 100 to 1. Some oases are identified with large craters with a dark bottom (Juventae Fons) or groups of craters (Oxia Pallus). Martian channels are recognized as elongated solid dark formations (Agathodaemon, Cerberus), as linear chains of several craters with a dark bottom (Cantabras, Gehon), as chains of dark spots of irregular shape.

In one of the pictures of Mariner-7 at close range, the shadow of Phobos was recorded on the disk of Mars. When analyzing the image, it was determined that Phobos is elliptical in cross section, its dimensions are twice as large as those calculated by J. Kuiper and the albedo of its surface is 5-6%.

According to the ultraviolet spectrometer, no nitrogen and nitrogen oxides were detected in the atmosphere. Before the flight of Mariner-4, astronomers believed that the Martian atmosphere consists mainly of nitrogen and, based on this premise, proposed models of the composition of the atmosphere. Based on the Mariner-4 radio-eclipse experiment, taking into account spectroscopic observations from the Earth, it was found that carbon dioxide is at least 80%. Spectrometric measurements of Mariner-6 and Mariner-7 found that the atmosphere is 98% carbon dioxide.

An infrared spectrometer detected bands of solid CO ₂ . The polar caps are at least partially composed of solid carbon dioxide.

Mariner-7 using an infrared radiometer measured the temperature in 200 sections of the southern polar cap. The minimum temperature reaches -153 ° C. Such a low temperature confirms that the polar caps are at least partially composed of solid carbon dioxide.

The surface temperatures according to the infrared spectrometer were significantly, about 50 degrees, higher than the temperatures according to the infrared radiometer. Perhaps the reason for the discrepancy is that the field of view of the radiometer is substantially less than the field of view of the spectrometer.

The atmosphere was probed using the radio eclipse method. The transmission of the Mariner-7 signal was at a frequency of 2195 MHz. The spacecraft disappeared behind the Mars disk in the region of the southern polar cap, near the dark region of Hellespontica Depressio for 60 s. W, 332 c. e. The pressure there was 3.8 mb. Radio eclipse lasted 40 minutes. Mariner-7 came out from behind the disk of Mars at a point with coordinates of 37 s. W, 148 c. d.

• Unlike the Soviet automatic interplanetary stations Mars, the body of the automatic interplanetary stations of the Mariner series is leaky.
• Unlike the Soviet automatic Mars interplanetary stations, the Mariner-6 - Mariner-10 automatic interplanetary stations used a large number of integrated circuits.
• In the pictures of Mariner-4, veiling is noticed, which led to the conclusion that there is a cloudy atmosphere on Mars to heights of 150 km. However, Mariner-6 and Mariner-7, on the images of which there is no veiling, refuted the turbidity of the atmosphere. Apparently, the optics of the Mariner-4 camera were contaminated.

• Mariner (KA) - automatic interplanetary stations of the Mariner series
• Mariner-4 - an automatic interplanetary station. The first exploration of Mars from the flight path. First shots at close range.
• Mariner-6 - an automatic interplanetary station. Exploration of Mars from the flight path. The first study of the atmospheric composition of Mars using spectroscopic techniques. The first measurements of surface temperature.
• Mariner-9 - an automatic interplanetary station. The first artificial satellite of Mars.
• Exploration of Mars - A review of exploration of Mars by classical methods of astronomy and using spacecraft.

• Mariner 7 at NASA
• Mariner 7 at NASA
• Mariner 7 at the Jet Propulsion Laboratory website
• Leighton R. The surface of Mars M. Uspekhi Fizicheskikh Nauk, vol. 103, 1971, issue 4, pp. 755-768.
• Pictures of Mars obtained by Mariner-7 on the NASA website