Mariner 1, the first of the series of spacecraft designed for planetary exploration will be launched within a few days (no earlier than July 21) from the Atlantic Missile Range, Cape Canaveral, Florida, by the National Aeronautics and Space Administration.
The mission of the initial Mariner is to fly by the planet Venus and make infrared and microwave measurements of the planet; communicate this information to earth over an interplanetary distance of 36,000,000 miles and obtain information on interplanetary phenomena during the trip to Venus.
The closest approach of Mariner to Venus will be about 10,000 miles.
Five other scientific experiments will be aboard the Mariner to provide data on deep space during the extended flight. Flight times will vary from 100 to 140 days depending on the launch date.
NASA has assigned two launches for Mariner to take advantage of the period during which Venus will be close to earth this year. The next launch opportunity for Venus occurs in 1964. Mariner 2 is at Cape Canaveral and will be launched as soon as possible after Mariner 1. The major factor in the decision to launch two Mariners is the difficult nature of the mission.
This mission is a difficult one because of several factors: the long life of the flight, extending up to 140 days; the spacecraft will be subjected to a prolonged variation in temperature caused by the variation in distance from the sun and increasing intensity of the sun; radiation effects in interplanetary space are not fully known, and the difficulty of transmitting a considerable amount of information over an extreme range.
Mariner tracking and communication will be provided by JPL's DeepSpace Instrumentation Facility with permanent stations at Goldstone, California; Woomera, Australia; and Johannesburg, South Africa, and mobile stations at Cape Canaveral and near the permanent station at Johannesburg. Data flowing into these stations from the spacecraft will be routed to JPL's Spacecraft Flight Operations Center for correlation by an IBM 7090 computer system.
Project Management for the Venus Mission was assigned to the California Institute of Technology Jet Propulsion Laboratory by the National Aeronautics and Space Administration. This includes responsibility for the spacecraft system and space flight operations. The Marshall Space Flight Center has the responsibility for providing the launch vehicle, with the support of the U.S.A.F. Space Systems Division. The Atlas D first stage is provided by General Dynamics Astronautics, and the Agena B second stage is provided by Lockheed Missiles and Space Company.
Key personnel in the Mariner Project are: Fred D. Kochendorfer, Mariner Program Chief, NASA Headquarters; D. L. Forsythe, Agena Program Chief for NASA; Robert J. Parks, Planetary Program Director for JPL; J. N. James, JPL, Mariner Project Manager; W. A. Collier, JPL, Assistant Project Manager; Dan Schneiderman, JPL, Spacecraft System Manager; Friedrich Duerr, MSFC, Launch Vehicle Systems Manager; Major J. G. Albert, Mariner Launch Vehicle Director of AFSSD; and H. T. Luskin, Director for NASA Programs, Lockheed Missiles and Space Company.
The Mariner weighs 446 pounds and, in the launch position, is five feet in diameter at the base and 9 feet, 11 inches in height. In the cruise position, with solar panels and highgain antenna extended, it is 16.5 feet across in span and 11 feet, 11 inches in height.
The design is a variation of the hexagonal concept used for the Ranger series. The hexagon framework base houses a liquid-fuel rocket motor for trajectory correction, and six modules containing the attitude control system, electronic circuitry for the scientific experiments, power supply, battery and charger, data encoder and command subsystem, digital computer and sequencer, and radio transmitter and receiver. Sun sensors and attitude control jets are mounted on the exterior of the base hexagon.
A tubular superstructure extends upward from the base hexagon. Scientific experiments are attached to this framework. An omnidirectional antenna is mounted at the peak of the superstructure. A parabolic, high-gain antenna is hinge-mounted below the base hexagon. Two solar panels are also hinged to the base hexagon. They fold up alongside the spacecraft during launch, parking orbit and injection and are folded down, like butterfly wings, when the craft is in space. A command antenna for receiving transmissions from earth is mounted on one of the panels.
The solar panels contain 9800 solar cells in 27 square feet of area. They will collect energy from the sun and convert it into electrical power at a minimum of 148 watts and a maximum of 222 watts. The amount of power available from the panels is expected to increase slightly during the mission due to the increased intensity of the sun. Each solar cell has a protective glass filter that reduces the amount of heat absorbed from the sun, but does not interfere with the energy conversion process. The glass covers filter out the sun's ultraviolet and infrared radiation that would produce heat but not electrical energy.
Prior to deployment of the solar panels, power will be supplied by a 33.3-pound silver-zinc rechargeable battery with a capacity of 1000 watt hours. The recharge capability is used to meet the long-term power requirements of the Venus Mission. The battery will supply power directly for switching and sharing peakloads with the solar panels and also supply power during trajectory correction when the panels will not be directed at the sun.
The power subsystem will convert electricity from the solar panels and battery to 50 volt, 2400 cps; 26 volt, 400 cps, and 25.8 to 33.3 volt DC.
Two-way communication aboard the Mariner is supplied by the receiver/transmitter, two transmitting antennas: the omnidirectional and high-gain antenna; and the command antenna for receiving instructions from earth. Transmitting power will be 3 watts.
The high-gain antenna is hinged and equipped with a drive mechanism allowing it to be pointed at the earth on command. An earth sensor is mounted on the antenna yoke near the rim of the high-gain dish-shaped antenna to search for and keep the antenna pointed at the earth.
Stabilization of the spacecraft for yaw, pitch and roll, is provided by ten cold gas jets, mounted in four locations (3,3,2,2,), fed by two titanium bottles containing 4.3 pounds of nitrogen gas pressurized by 3500 PSI. The jets are linked by logic circuitry to three gyros in the attitude control subsystem, to the earth sensor on the parabolic antenna and to six sun sensors mounted on the spacecraft frame and on the back of the two solar panels.
The four primary sun sensors are mounted on four of the six legs of the hexagon, and the two secondary sensors on the backs of the solar panels. These are light-sensitive diodes which inform the attitude control system--gas jets and gyros-when they see the sun. The attitude control system responds to these signals by turning the spacecraft and pointing the longitudinal, or roll axis, toward the sun. Torquing of the spacecraft for these maneuvers is provided by the cold gas jets fed by the nitrogen gas regulated to 15 pounds per square inch pressure. There is calculated to be enough nitrogen to operate the gas jets to maintain attitude control for a minimum of 200 days.
Computation for the subsystems and the issuance of commands is a function of the digital Central Computer and Sequencer. All events of the spacecraft are contained in three CC&S sequences. The launch sequence controls events from launch through the cruise mode. The midcourse propulsion sequence controls the midcourse trajectory correction maneuver. The encounter sequence provides required commands for data collection in the vicinity of Venus.
The CC&S provides the basic timing for the spacecraft subsystems. This time base will be supplied by a crystal control oscillator in the CC&S operating at 307.2 kc. This is divided down to 38.4 kc for timing in the power subsystem and divided down again to 2400 and 400 cps for use by various subsystems. The control oscillator provides the basic "counting" rate for the CC&S to determine issuance of commands at the right time in the three CC&S sequences.
The subsystems clustered around the base of the spacecraft are insulated from the sun's heat by a shield covered with layers of aluminum coated plastic film. At the bottom of the spacecraft, just below the subsystem modules, is a second Temperature Control Shield. It prevents too rapid loss of heat into space which would make the establishment of required temperatures difficult to maintain. The two shields form a sandwich that helps to minimize the heat control problem.
Temperature control of the attitude control subsystem is provided by louvers actuated by coiled bimetallic strips. The strips act as coil springs that expand and contract as they heat and cool. This mechanical action opens and closes the louvers. The louvers are vertical on the face of the attitude control box and regulate the amount of heat flowing into space. This is a critical area as some of the equipment may not function properly above 130?o\F.
Paint patterns, aluminum sheet, thin gold plate, and polished aluminum surfaces are used on the Mariner for passive control of internal temperatures. These surfaces control both the amount of internal heat dissipated into space and the amount of solar heat reflected away, allowing the establishment of temperature limits. The patterns were determined from testing of a Temperature Control Model. The TCM was subjected to the variations of temperature anticipated in the Venus Mission in a space simulation chamber at JPL.
Communication with the spacecraft will be in digital form. The command subsystem aboard the Mariner will decode incoming digital commands and send them to the designated subsystems. Data from engineering and scientific sources will be encoded to digital form for transmission to earth.
Synchronizing pulses will be spaced at regular intervals between the data signals from Mariner. Ground based receiving equipment will generate identical pulses and match them with the pulses from the spacecraft. This will provide a reference to determine the location of the data signals allowing receiving equipment to separate data signals from noise.
Seven scientific experiments will be carried aboard the Mariner. Five of these are designed to collect information in space and in the vicinity of Venus. The other two will provide information solely on Venus and will operate only as Mariner passes the planet. The experiments are:
1) Microwave radiometer experiment to measure temperature distribution on the planet's surface.
2) Infrared radiometer experiment to provide information on the distribution of thermal energy in the planet's atmosphere.
3) Magnetometer experiment to determine the three mutually perpendicular components of the magnetic field in the interplanetary space between earth and Venus, and in the vicinity of Venus at planetary encounter.
4) Charged particle experiment to detect the distribution, variations and energies of electrically charged particles in space and in the vicinity of Venus.
5) Ionization chamber to detect the rate at which charged particles lose energy.
6) Plasma experiment to obtain information on the extent, variations in, and mechanism of the solar corona.
7) Micrometeorite experiment to measure the density of cosmic dust particles which exist in interplanetary space and in the vicinity of Venus.
The microwave radiometer is mechanized so it can scan Venus during the fly-by. Initially, it will have a fast scan search. When it detects the planet, the radiometer will adopt a slow scan mode. The infrared experiment is attached to the rim of the dish-shaped microwave device and will scan with the larger instrument.
The launch vehicle for the Mariner will be an Atlas D-Agena B. The Atlas and the Agena will boost Mariner to an altitude of 115 statue miles and an orbital speed of 18,000 miles an hour.
Mariner will use the parking orbit technique which is a means by which the geometry imposed on a Venus launch by the location of the Atlantic Missile Range at Cape Canaveral, Florida, is corrected by using the second-stage rocket as a mobile launching platform in space.
During the launch phase, the Mariner spacecraft is protected against aerodynamic heating by a shroud. After Atlas cutoff, approximately five minutes after liftoff, the shroud is jettisoned by eight spring-loaded bolts which shove it ahead of the vehicle. At almost the same time, the Agena B separates from the Atlas. The Agena B then pitches down from an attitude almost 15 degrees above the local horizon to almost level with the local horizon.
In this horizontal attitude the Agena B fires for the first time and burns for almost two and a half minutes to reach orbital speed of 18,000 miles an hour. After this burning time, Agena B shuts down and coasts in a parking orbit for more than 13 minutes until it reaches the optimum point in time and space in its orbit to fire for the second time.
The second Agena B burn injects the Agena B and Mariner, still as one unit, on an escape trajectory at 25,700 miles an hour. Injection occurs approximately over Ascension Island in the South Atlantic Ocean and approximately 23 to 34 minutes after launch, depending on time of launch.
A little more than two minutes after second burn cutoff or injection, Mariner is separated from Agena, again by springloaded bolts. Agena then yaws 140 degrees in the local horizontal plane and performs a retro maneuver which reduces the Agena velocity and moves the Agena into a different trajectory. Propulsion for the retro maneuver is provided by ejecting the unused fuel on the Agena through small jets. The retro manuever serves two purposes: to prevent the Agena from impacting Venus, and if Agena B follows Mariner too closely, the spacecraft optical sensors might mistake reflected sunlight from Agena B for the sun or earth and confuse its acquisition system.
Separation from the Agena will cause the Mariner to begin a tumbling motion. These residual separation rates are cancelled out by the yaw, pitch and roll gyros acting on the gas jet stabilization system.
Mariner now is on a trajectory that will take it fairly close to Venus. The omnidirectional antenna is working and radiating the radio transmitter's full three watts of power. Before and during launch, the transmitter had been kept at about 1.1 watts. This is required during the period the launch vehicle passes through a critical area between 150,000 and 250,000 feet, where a tendency exists for devices using high voltage to arc over and damage themselves; hence, the transmitter is kept at reduced power until this area is passed.
Following is the sequence of events that Mariner will conduct on its flight to Venus.
The first command is issued by the CC&S 44 minutes after launch. Explosive pin pullers holding the solar panels and the radiometer in their launch position are detonated to allow the spring-loaded solar panels to open and assume their cruise position and free the radiometer to scan Venus as it passes by the spacecraft. Although the radiometer will not function until Venus encounter, it is convenient to unlock it at this point.
At launch plus 60 minutes, the CC&S turns on the attitude control system and the sun acquisition mode will begin. The sun sensors, linked to the valves controlling the gas jets, jockey the spacecraft about until its long axis is pointed at the sun thus aligning the solar panels with the sun. Both the gyros and the sun sensors can activate the gas jet valves. A backup radio command capability is provided to initiate the CC&S function and sun acquisition.
In order to conserve gas, the attitude control system permits a pointing error toward the sun of one degree, or attitude control system is calibrated to keep Mariner slowly swinging through this one degree of arc pointed at the sun. The swing takes approximately 60 minutes. As Mariner nears the they fire again. This process is repeated hourly through the effective life of Mariner. It is calculated that the gas jets will fire one-fiftieth of a second each 60 minutes to keep the spacecraft's solar panels pointed at the sun. When the sun has been acquired, the gyros are turned off to conserve their life and to lower the power demanded of the solar panels.
The sun acquisition process is expected to take less than 30 minutes. When it is completed, the secondary sun sensors on the backs of the solar panels are turned off to avoid having light from the earth confuse them.
As soon as the solar panels are locked on the sun, the power system will begin drawing electric power from the panels. The battery will now only supply power in the event of a peak demand that the panels cannot handle. Excess power from the solar panels will be utilized to recharge the battery.
The next event initiated by the CC&S is the acquisition of earth by the high-gain directional antenna. This does not occur, however, until 167 hours (seven days) after launch. The earth sensor used to align the antenna is so sensitive that it would not operate properly if used earlier. Once again, a radio command capability is provided to back up the initiation of this event.
During earth acquisition, the spacecraft maintains its lock on the sun, but with its high-gain directional antenna pointed at a preset angle, it rolls on its long axis and starts to look for the earth. It does this by means of the threesection, photo-multiplier-tube operated earth sensor mounted on and aligned with the high-gain antenna. During the roll, the earth sensor will see the earth and inform the gas jets. The jets will fire to keep the earth in view of the sensor and thus lock onto the earth. The sensor has a lens system to magnify the earth image.
The spacecraft now is stabilized on two axes--the solar panel-sun axis and the earth-directional antenna axis. There is some danger that the earth sensor, during its search for the earth, may see the moon and lock onto that, but telemetry later will inform earth stations if this has occurred, and Goldstone has the ability to send an override command to the attitude control system to tell it to look again for the earth. If this is not sufficient, the stations can send a hinge override command to change the hinge angle and then order another roll search. When the earth is acquired, the transmitter stops transmitting on the omni-antenna and starts transmitting on the high-gain antenna.
A rise in signal strength will be an indication that earth acquisition has been achieved by the parabolic antenna. Positive proof will be afforded by analysis of telemetry to determine the angle of the antenna hinge.
With sun and earth acquisition achieved, Mariner is now in its cruise mode.
The cruise mode will continue until time for the midcourse trajectory correction maneuver. After launch, most of the activity on the Venus Mission will be centered at the DSIF stations and at the Space Flight Operations Center at JPL.
Tracking data collected by the DSIF stations will be sent to JPL and fed into the 7090 computer system. The computer will compare the actual trajectory of the Mariner with the course required to yield a 10,000 mile fly-by. If guidance errors before injection have put Mariner off the optimum trajectory, the computer will provide the necessary figures to command the spacecraft to alter its trajectory. This involves commands for roll, pitch and motor burn. Roll and pitch point Mariner for the trajectory correction. Motor burn will provide the additional velocity required to change direction.
The first command from Goldstone will give the direction and amount of roll required, the second will give the direction and amount of pitch needed and the third will give the amount of velocity increment needed. This data is stored in the CC&S until Goldstone transmits a "go" command.
Prior to the "go" command, Goldstone will have ordered Mariner's transmitter to switch from the dish-shaped directional antenna, at the base of the craft, to the omni-directional antenna mounted at the peak of the superstructure.
Commands preprogrammed in the CC&S for the midcourse sequence initiate the following: the earth sensor, mounted on the dish-shaped antenna, is turned off; the hinged-mounted directional antenna itself is moved out of the path of the midcourse motor's exhaust, and the gyros will have turned on an hour earlier to warm up. During the maneuver the gyros will inform the attitude control subsystem of the rate of pitch and roll as they occur for reference against orders from earth. A pulse balanced accelerometer will be turned on to provide acceleration rates during motor burn to the CC&S. Each pulse from the accelerometer represents a velocity increment of 0.03 meters per second.
The roll maneuver requires a maximum of 12 minutes of time, including two minutes of settling time, and the pitch maneuver requires a maximum of 22 minutes. When these are completed, the midcourse motor is turned on and burns for the commanded time. As the attitude control gas jets are not powerful enough to maintain the stability of the spacecraft during the propulsion phase of the midcourse maneuver, moveable jet vanes extending into the exhaust of the midcourse motor controls the attitude of the spacecraft in this period.
The jet vanes are controlled by an auto pilot subsystem in the attitude control system that functions only during the midcourse maneuver. The auto pilot accepts information from the gyros to direct the thrust of the motor through the spacecraft's center of gravity to stabilize the craft.
The liquid monopropellant motor weighs, with fuel and the helium pressure gas system, 31.3 pounds. Hydrazine fuel is held in a rubber bladder inside a doorknob-shaped container called the pressure dome. On the command to fire, nitrogen under 3000 pounds of pressure per square inch, is admitted inside the pressure dome and squeezes the rubber bladder, forcing the fuel into a combustion chamber.
Because hydrazine is a monopropellant, it needs a starting fluid to initiate combustion and a catalyst to maintain combustion. The starting fluid, in this case nitrogen tetroxide, is admitted into the combustion chamber by means of a pressurized cartridge and causes ignition. The catalyst, aluminum oxide pellets, is stored in the combustion chamber. Burning stops when the valves turn off helium pressure and fuel flow.
The midcourse motor is so precise that it can burn in bursts of as little as 50 milliseconds and can increase velocity by as little as seven-tenths of a foot per second or as much as 148 feet per second. It has a thrust of 50 pounds for a maximum of 43 seconds.
After the midcourse maneuver has put Mariner on the desired trajectory, the spacecraft agains goes through the sun and earth acquisition modes.
During midcourse Mariner has been transmitting through the omni-antenna. When earth is acquired, the transmitter is switched to the high-gain directional antenna. This antenna will be used for the duration of the flight.
Mariner will continue in the cruise mode until planet encounter. During this period, tracking data from the three permanent DSIF stations will be sent to JPL where the 7090 computer system will refine the earlier calculations for planet encounter made at launch.
The CC&S was programmed to begin the encounter sequence ten hours in advance of encounter. This allows time for calibration of the planetary encounter scientific instruments before encounter in the event that the spacecraft might fail to perform the midcourse trajectory correction. If this should occur, then the predicted encounter time could vary in time up to ten hours.
Under any circumstances, the tracking-computer system has the capability of predicting the time of encounter to within 15 minutes.
At the ten hour period the CC&S will switch out the engineering data sources, leaving on the interplanetary science experiments, and turn on the two planetary experiments. During the fly-by, only scientific data will be collected and transmitted.
The radiometer will begin a fast search wide scan until Venus is sensed and then go into a slow scan. The planetary experiments will collect data on Venus for a half an hour as Mariner passes the planet.
The encounter mode of transmission--scientific data only--will continue 56.7 hours after encounter. At the end of this period the CC&S will switch on the engineering data sources and, again in the cruise mode, both engineering and interplanetary scientific data will be transmitted.
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