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Mariner 4; 1964-1965 // USA
Topic Started: Friday 31-07-2009, 00:22 (682 Views)
[Publisher] Magrathean
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Mars > Missions > Mariner 4 > Index
 
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  1. Index
  2. [go2=missionoverview]Mission overview[/go2]
  3. [go2=spacecraftandinstruments]Spacecraft and instruments[/go2]
  4. [go2=results]Results[/go2]
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[anchor]missionoverview[/anchor]
Mars > Missions > Mariner 4 > Mission overview
 
Objectives
  1. perform a flyby of Mars
  2. conduct close-up scientific observations of Mars and transmit said observations to Earth
  3. perform field and particle measurements in interplanetary space in the vicinity of Mars
  4. provide experience in and knowledge of the engineering capabilities for interplanetary flights of long duration




Summary

Launch date: 28 november 1964

Mars flyby: 14 july 1965

Mission end: 21 december 1967

Mariners 3 and 4 were identical spacecraft designed to carry out the first USA flybys of Mars. Unlike its sister probe, Mariner 4 was equipped with a functional nose cone design and launched successfully on a seven-and-a-half-month voyage to the red planet.

Mariner 4 flew past Mars, collecting the first close-up photographs of another planet. The pictures, played back from a small tape recorder over a long period, showed lunar-type impact craters --just beginning to be photographed at close range from the Moon--, some of them touched with frost in the chill martian evening.

Mariner 4 was not expected to survive much longer than the eight months to its Mars flyby encounter, but it actually lasted about three years in solar orbit, continuing long-term studies of the solar wind environment and making coordinated measurements with Mariner 5, a sister ship launched to Venus in 1967.
Source: Wikipedia / Mariner 4
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[anchor]spacecraftandinstruments[/anchor]
Mars > Missions > Mariner 4 > Spacecraft and instruments
 
Mariner 4 was designed around an octagonal magnesium frame 127 centimeters across a diagonal and 45.7 centimeters high; this frame was called the bus, and each of its eight sides was called a bay. The bus housed the electronic equipment, cabling, midcourse propulsion system, and attitude control gas supplies and regulators. Most of the science experiments were mounted outside the bus. Four solar panels were attached to the top of the frame for an end-to-end span of 688 centimeters including solar pressure vanes which extended from the ends.

A 116.8-centimeter-diameter high-gain parabolic antenna was mounted at the top of the frame as well. An omnidirectional low-gain antenna was mounted on a 223.5-centimeter-tall mast next to the high-gain antenna. The low-gain antenna mast held a magnetometer. At the bottom-center of the spacecraft the camera was mounted on a scan platform.

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Science instruments, in addition to the camera and the magnetometer, were a dust detector, a cosmic ray telescope, a trapped radiation detector, a solar plasma probe, and an ionization chamber / Geiger counter.

There was to be an ultraviolet photometer as well, but it wasn't completed in time for the mission. It was replaced by a nonfunctioning instrument called the "mechanical and electrical subassembly simulator subsystem" and by a scan-platform inertial and thermal simulator which prevented a mechanical or thermal imbalance.

The subsystems were located as follows:

Bay I
  • power subsystem (distributed electricity to other components)
Bay II
  • propulsion, including a small rocket motor for midcourse correction
Bay III
  • some scientific instruments
  • data automation system (organized data)
Bay IV
  • data encoder (organized data)
  • command (interpreted ground commands)
Bay V
  • radio frequency communications
  • videotape recorder
Bay VI
  • radio transmitter and receiver
Bay VII
  • attitude control
  • gas supply
Bay VIII
  • power regulator
  • battery

Power was supplied by 28,224 solar cells contained in the four 176-by-90-centimeter solar panels, which could provide 310 watts at Mars. A rechargeable silver-zinc battery with an energy of 1,200 watt-hours was also used for maneuvers and backup.

Monopropellant hydrazine was used for propulsion via a motor installed on one of the sides of the bus (the motor is seen in the picture above).

The telecommunications equipment consisted of a dual S-band 7-watt triode cavity amplifier / 10-watt travelling-wave tube amplifier transmitter and a single receiver which could send and receive data via the low-gain and high-gain antennas at 8 1/3 or 33 1/3 bits per second. Data could also be stored on a tape recorder with a capacity of 5,240,000 bits for later transmission.

Temperature control was achieved through the use of adjustable louvers mounted on six of the electronics assemblies, multilayer insulating blankets, polished aluminium shields, and surface treatments.

Attitude control was provided by 12 cold-nitrogen-gas jets mounted on the ends of the solar panels and three gyroscopes. Solar pressure vanes, each with an area of 0.65 square meters, were attached to the tips of the solar panels. Positional information was provided by four Sun sensors, an Earth sensor, a Mars sensor and a Canopus sensor. Attitude control was achieved via the spacecraft's nozzles and vanes. Keeping the solar panels oriented so they would receive maximum sunlight was of primary importance. If the Sun and Canopus sensors indicated any drift away from the acceptable position, small puffs of gas were ejected from nozzles located at the ends of the solar panels. Any unequal pressure from sunlight on various parts of the spacecraft which might affect its orbit was corrected by the adjustable vanes at the ends of the solar panels. In the event a midcourse correction was required, the rocket motor nozzle, which was fixed, had to be aimed by changing the spacecraft attitude.

Since it was not known exactly where the spacecraft would be as it passed Mars, the camera was mounted on the scan platform. A few hours before it reached the planet, power was applied and the platform bobbed up and down. When the planet came in view of the wide-angle (40-degree-field-of-view) sensor, the platform-driving motor switched from scanning to tracking mode, which kept the scan sensor, and hence the camera, pointed directly at Mars. When the planet came in view of the camera with a narrow field of view (one degree), it started taking a series of pictures as the spacecraft swept across the planetary surface.

The imaging subsystem consisted of a Cassegrain narrow-angle reflecting telescope with a 30.5-centimeter effective focal length and a 1.05°-by-1.05° field of view; a shutter and filter assembly that had 0.08-second and 0.2-second exposure times and used red and green filters; a slow-scan vidicon tube with a 0.22-inch-by-0.22-inch square target, which translated the optical image into an electrical video signal; and related electronics, including a television data encoder. When the picture-recording sequence commenced, vidicon output would undergo analog-to-digital conversion and data would be stored at 240,000 bits per picture on a 1/4-inch, 300-foot-long magnetic tape loop on the spacecraft. Two of every three pictures taken were recorded on the tape, resulting in a chain of pairs of overlapping, alternately-filtered pictures extending across the disk of Mars. Data was transmitted after occultation of the spacecraft by Mars via the radio subsystem from 15 july 1965 to 24 july 1965. Conversion from electrical signals to an optical image was performed by a video-to-film recorder using 64 shades. Computer processing programs yielded photographs with greater contrast than the raw image data..

A vector low-field helium magnetometer was used to measure the interplanetary magnetic field.

The cosmic dust detector consisted of a 22-centimeter-by-22-centimeter aluminium impact plate which was coated on both sides with a nonconducting material. The detector also had a crystal acoustical transducer bonded to one side. It was to be used to continually monitor dust-particle flux and mass distribution from Earth proximity through the Mars encounter. The impact plate and dielectric aluminium film combination constituted a penetration detector in the form of a capacitor. The experiment was also intended to observe the degree of dust-particle concentration near Earth and near Mars, the rate of change of the dust-particle flux density with respect to distance from Earth, and the perturbation effects of large planetary bodies on the dynamic behavior of the dust particles. The instrument was mounted above the main spacecraft bus, with the case just inside the thermal shield to protect it from the Sun. The sensor protruded through an opening in the thermal shield. The instrument memory consisted of two 8-bit binary data-analysis registers and a microphone accumulator which would have recorded the number of microphone events observed by the instrument.

A set of three silicon surface barrier detectors was used in the form of a telescope to determine the flux of protons in the energy intervals 15-70 megaelectronvolts and 70-170 megaelectronvolts, alpha particles in the energy ranges 15-70 megaelectronvolts per nucleon and 70-∞ megaelectronvolts per nucleon, and protons and alpha particles in the energy interval 1.2-15 megaelectronvolts per nucleon. The detector was mounted on the spacecraft so as to point always in the antisolar direction. A 128-channel pulse-height analyzer was used to sample the energy loss in the top detector element of the telescope. It was possible to pulse-height analyze protons and alpha particles in the 15-70-megaelectronvolt-per-nucleon range, protons in the 70-170-megaelectronvolt range, and alpha particles with energies above 70 megaelectronvolts per nucleon.

A detector composed of four Geiger-Müller tubes and a solid state device was used to detect low-energy cosmic rays --protons and electrons-- while the spacecraft journeyed to and passed Mars. The Geiger-Müller tube was mounted away from the main body of the spacecraft so that at the tube the spacecraft subtended 14% of 4π steradians (not including the thin solar panels).

Two levels of expertise existed for each scientific instrument: scientists, who proposed experiments and the parameters to be measured, and engineers, who designed them to their specifications. Each bit of data was displayed in a line; these lines were transmitted to Earth and decoded by computers. To indicate the start of each frame, each one was preceded by an identifier: 1111111 for engineering, 000011101100101 for science. The computer, seeing either of these sequences, would decode the data accordingly. Occasionally there would be a gap in the received data -- the spacecraft signal might be temporarily lost or a glitch occurred at the tracking station or in the connection between there and the Jet Propulsion Laboratory. The computer would search for the next occurrence of either of the synchronization signals. It was quite possible that 1111111 could occur anywhere in the data. If the computer locked on this, its output would be gibberish until it picked up sync once again. In this event, it was necessary to visually inspect the raw data for the true occurrence of a line start. The scientists were required to continuously monitor the data. In another case, the receiving station might lock onto a sideband instead of the carrier and the data became inverted: 1s turned into 0s and 0s turned into 1s. They developed methods for coping with this condition as well.

All operations were controlled by a command subsystem which could process any of 29 direct command words or 3 quantitative word commands for midcourse maneuvers. The central computer and sequencer operated stored time-sequence commands using a 38.4-kilohertz synchronization frequency as a time reference. Thus, the spacecraft was completely autonomous. However, the stored commands could be modified from Earth. Its memory consisted of ferromagnetic doughnuts strung on wires.

The overall height of the spacecraft was 289 centimeters, and its mass was 260.68 kilograms.
Source: Wikipedia / Mariner 4
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Mars > Missions > Mariner 4 > Results
 
After launch, the protective shroud covering Mariner 4 was jettisoned and the Agena D / Mariner 4 combination separated from the Atlas D booster. The Agena D first burn put the spacecraft into an Earth parking orbit, and the second burn inserted the craft into a Mars transfer orbit. Mariner 4 then separated from the Agena D and began cruise mode operations. The solar panels deployed and the scan platform was unlatched eight minutes later, and Sun acquisition occurred 16 minutes later.

The cruise phase of the mission was, for the most part, uneventful. The data was decoded by computer and displayed on teletype machines, computer printers, monitor screens, and a 30-inch-by-30-inch plotter.

After 7.5 months of flight, which involved one midcourse maneuver on 5 december 1964, the spacecraft flew by Mars on 14-15 july 1965.

The spacecraft performed all programmed activities successfully and returned useful data from launch until 1 october 1965, when the distance from Earth and the antenna orientation temporarily halted signal acquisition. Data acquisition resumed in late 1967.

The cosmic dust detector registered 17 hits in a 15-minute span on 15 september 1967; this was part of an apparent micrometeoroid shower which temporarily changed the spacecraft attitude and probably slightly damaged the thermal shield. On 7 december 1967 the gas supply in the attitude control system was exhausted, and on 10-11 december a total of 83 micrometeoroid hits, which caused perturbation of the attitude and degradation of the signal strength, were recorded.

On 21 december 1967 communications with Mariner 4 were terminated. It remains in orbit around the Sun. The total data returned by the mission was 5,200,000 bits.





Pictures of Mars

The camera sequence started at 00:18:36 on 15 july 1965, 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, going down to about 35°S, 160°W and crossing across to the terminator at 50°S, 105°W, representing about 1% of the planet's surface.

The closest approach to the planet was 9,846 kilometers from the surface. The images taken during the flyby were stored in the onboard tape recorder. At Mars encounter Mariner 4 was approximately 220,000,000 kilometers from Earth, so radio signals, travelling at the speed of light, took 12 minutes to travel one-way. At 02:19:11 universal time, Mariner 4 passed behind Mars as seen from Earth and the radio signal ceased. The signal was reacquired at 03:13:04, when the spacecraft reappeared. Cruise mode was then reestablished. Transmission of the taped images to Earth began about 8.5 hours after signal reacquisition and continued until 3 august 1965. All images were transmitted twice to ensure no data was missing or corrupt.

The images returned showed a moonlike cratered terrain -- which later missions showed was not typical for Mars, only for the more ancient region imaged by Mariner 4.

Pictures taken by Mariner 4

Mosaics created with the usable pictures taken by Mariner 4

Mariner 4's trajectory





The martian atmosphere

The intensity and phase changes observed in the 2,300-millihertz spacecraft telemetry signal as the spacecraft was occulted by Mars were used to infer properties of the martian atmosphere. The changes were the result of atmospheric refraction of the radio signal, and thus the data covered only the time near the planetary encounter, when the signal was bent and slowed by the atmosphere (2 minutes on each side). The occultation experiment showed that Mars has a much thinner atmosphere than was thought. Mars occulted the spacecraft signal with its sunlit side, and the signal emerged on the night side. In addition, Mariner 4 estimated that Mars's atmospheric pressure was between 4.1 and 30 millibars and that the atmosphere was composed of 60-95% nitrogen, 5-30% carbon, less than 0.01% oxygen and trace amounts of argon.





Astronomical and physical data

Deep Space Network tracking data from Mariner 4 was used to obtain improved measurements of the masses of Mars and the Moon and of the astronomical unit, as well as improved ephemerides of Earth and Mars. Mariner 4 estimated that Mars's temperature was between -100°C and 30°C.





Magnetic field measurements

The three components of the magnetic field were measured essentially simultaneously but later transmitted sequentially. Each observation represented an average over approximately 1 second. The response dropped 3 decibels for frequencies of 1 hertz, and higher-frequency information was essentially lost. In each data frame, four vector measurements, separated by intervals of 1.5, 0.9 and 2.4 seconds, were made. Most of the data from this investigation was of the interplanetary region, but some data was obtained at Mars. Almost no magnetic field was detected at Mars.





Dust detector results

Experiment data was received concerning dust particle momentum, the incoming particle direction, particle impacts below the microphone threshold, and microphone event accumulations. Measurements revealed a dust concentration near Earth with a mass distribution somewhat different from that of interplanetary space. In-flight calibration was performed once a day on command from the ground. No instrument degradation was detected.





Cosmic ray detection

Two count rates and two pulse-height analyses were obtained every 72 or 18 seconds by the cosmic ray telescope according to whether the spacecraft transmission rate was 8 1/3 or 33 1/3 bits per second. The experiment performed normally from launch until october 1965, when the spacecraft was turned off to conserve power. When the spacecraft was turned on again at a later time, the detector did not respond.

The low-energy cosmic ray detectors formed by the Geiger-Müller tubes were oriented at 70° and 135° to the spacecraft roll axis. They measured the ionization caused by charged particles and the number of particles in the range above 0.5 megaelectronvolts for electrons and above 10 megaelectronvolts for protons. The instrumentation functioned well and ionization data were received until the Geiger-Müller tubes became saturated and failed on 3 march 1965. The ion chamber failed shortly afterwards, so no data was obtained in the vicinity of Mars.
Sources: Wikipedia / Mariner 4 | SolarViews / Mariner 4 | NASA / Mariner 4 mission page
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