Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/JPLNEWS1/0156.PR

Text File | 1993-04-21 | 28KB | 509 lines

OFFICE OF PUBLIC EDUCATION AND INFORMATION
CALIFORNIA INSTITUTE OF TECHNOLOGY JET PROPULSION LABORATORY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.  TELEPHONE MURRAY 1-366, EXTENSION 3111

FOR RELEASE:   A.M.'s of July 19, 1962

                        MARINER SPACECRAFT
         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 inter-
planetary 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;

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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 interplan-
etary space are not fully known, and the difficulty of trans-
mitting 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

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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.
                      SPACECRAFT DESCRIPTION
         The Mariner weighs 446 pounds and, in the launch posi-
tion, is five feet in diameter at the base and 9 feet, 11 inches
in height.  In the cruise position, with solar panels and high-
gain 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 super-
structure.  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

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wings, when the craft is in space.  A command antenna for receiv-
ing 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 peak-
loads with the solar panels and also supply power during trajec-
tory 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 omni-
directional and high-gain antenna; and the command antenna for
receiving instructions from earth.  Transmitting power will be
3 watts.

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         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 longi-
tudinal, or roll axis, toward the sun.  Torquing of the space-
craft 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

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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

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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:

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         1)    Microwave radiometer experiment to measure
temperature distribution on the planet's surface.
         2)    Infrared radiometer experiment to provide informa-
tion 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.

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                       MISSION DESCRIPTION
         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 loca-
tion 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

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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 spring-
loaded bolts.  Agena then yaws 140 degrees in the local horizon-
tal plane and performs a retro maneuver which reduces the Agena
velocity and moves the Agena into a different trajectory.  Propul-
sion 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

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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

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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 three-
section, 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

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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

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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

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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.

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         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.

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         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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