From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: Mariner 2 Venus Flyby - 12/14/92
Followup-To: sci.space
News-Software: VAX/VMS VNEWS 1.3-4   
Keywords:  Mariner 2, Venus, JPL
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Sat, 12 Dec 1992 01:34:18 GMT

In honor of the 30th anniversary of Mariner 2's flyby of
Venus, I am posting three of the Mariner 2 press releases
from 1962.

Ron Baalke

OFFICE OF PUBLIC EDUCATION AND INFORMATION
CALIFORNIA INSTITUTE OF TECHNOLOGY
JET PROPULSION LABORATORY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA

FOR RELEASE:  To A.M.'s of Friday, December 14, 1962

                           MARINER II
                         VENUS ENCOUNTER

         Man's first chance to obtain information from another
planet will come on December 14 when the Mariner II spacecraft
passes approximately 21,000 miles from Venus.
          Mariner's radiometers will pierce the cloud cover to
determine surface temperature and temperatures in the atmosphere.
Instruments will determine the strength of the magnetic field and
nature of the radiation belts.  The entire spacecraft will measure
the strength of the gravitational field as it speeds and slows on
its curving path near Venus.
          The 447-pound spacecraft was launched by the National
Aeronautics and Space Administration on August 27, 1962, at 1:53
a.m. from the Atlantic Missile Range, Cape Canaveral, Florida.
It was built, and is now being tracked, by the California
Institute of Technology Jet Propulsion Laboratory.  The launch
vehicle was the Atlas-Agena B.
          When the Mariner arrives at Venus it will have traveled
182,000,000 miles during its 109-day journey through space.
During its long cruise, that extended almost halfway around the
Sun, the spacecraft set a long distance communication record of
36,000,000 miles, and performed the first successful guidance
maneuver in space.
          The Mariner II carries six scientific experiments.  Four
of these, turned on by ground command two days after launch, are:
a magnetometer, an ion chamber and particle flux detector, a solar
plasma detector, and a cosmic dust counter.  They have been making
invaluable measurements during Mariner's curving trip towards
Venus and when the spacecraft arrives will measure magnetic
fields, radiations and dust particles around the planet.
          Two other experiments--a microwave radiometer and an
infrared radiometer--will scan the surface and the atmosphere of
Venus for 42 minutes as Mariner rushes by.
          All telemetry information gathered during Mariner's
voyage is transmitted by Mariner to a network of ground receiving
stations called the Deep Space Instrumentation Facility (DSIF)
which are located in Goldstone, California, Woomera, Australia,
and Johannesburg, South Africa.
          Mariner was launched in a way that would cause it to
fall inward toward the Sun.  This was accomplished by timing the
injection so that the spacecraft would leave earth in a direction
opposite from that of the Earth in its orbit around the Sun.
Since Mariner's speed around the Sun was less than that of the
Earth, it could not maintain a circular orbit like Earth and the
Sun's gravity caused it to be drawn inward so that it would
eventually intercept the trajectory of Venus.
          By nine days after launch, DSIF tracking data processed
at JPL's Space Flight Operations Center in Pasadena, showed that
Mariner would arrive at a rendezvous ahead of Venus, missing the
planet by 233,000 miles.  This launch dispersion was well within
the correction capability of the 50-pound-thrust rocket motor
aboard the spacecraft.  During the midcourse maneuver, the motor
was fired for 27 seconds affecting a slight decrease in velocity.
This guidance correction will bring Mariner to a point 21,000
miles from the planet.  This point is well within the original
target area, a pie-shaped region extending between 8000 to 40,000
miles from Venus.
          Before Mariner passes Venus a sequence of events will
begin.  The first of these will be the activation of a stored
command in the spacecraft's central computing and sequencing
system that turns on the radiometer scan device.  If for some
reason this command is not initiated by the spacecraft, it will
be sent by the DSIF Goldstone station.
          The radiometers, located on the hexagonal deck of the
spacecraft, are 20 inches in diameter and five inches deep.  They
are mounted on a swivel and are driven by an electric motor in a
120 degree scanning motion.  During the pass by Venus, the
microwave and infrared energy will be collected and transmitted
to Earth.
          Prior to activation of the radiometers, the Mariner was
in a "cruise mode."  In this mode, it was continuously telemeter-
ing the first 20 seconds of information provided by its four
interplanetary scientific instruments, and then 16 seconds of
engineering data.  Engineering data is concerned with the condi-
tions aboard the spacecraft and include temperatures, pressures,
voltages and angular positions.
          During the fly-by, the data format changes from "cruise
mode" to "encounter mode" and Mariner devotes itself exclusively
to gathering and sending scientific data.
          At the time that the radiometer's scan mechanism is
turned on, Mariner will be approaching the planet from the dark
side and moving in a downward direction.  As seen from Venus, the
spacecraft will be moving in a direction to the right and below
the Sun.
          As Mariner cruises past Venus its solar panels will
remain locked on the Sun to obtain electrical power, as they did
throughout the long mission.  The radiometers point in a direction
perpendicular to the roll axis of the spacecraft and move in a
nodding motion across the surface of Venus at a rate of one-tenth
of a degree per minute.  As Mariner passes Venus, the radiometers
will first scan the dark side and then the sunlit side.
          This planetary scanning period will last for 42 minutes.
During this time, the findings of all sox scientific experiments
will be transmitted to the Woomera and Goldstone DSIF stations.
          At 66 minutes before the point of closest approach, or
10:55 a.m., December 14, Mariner will be 25,262 miles from Venus.
At that time its velocity will have increased to approximately
87,000 mph due to the gravitational pull of the planet.  At this
time the radiometers should detect the planet's surface for the
first time.
          At 44 minutes before the point of closest approach, or
11:17 a.m., Mariner will pass the planet's terminator, or
dividing line between light and darkness.  It will still be moving
downward and picking up speed.
          Drawn by the gravitational field of Venus the spacecraft
continues to accelerate.  By 11:37 a.m. the scanning period ends
as Venus moves out of sight of the radiometers.  At that point in
time, Mariner will be going approximately 87,000 mph.  Venus will
be approximately 21,700 miles away while the Earth is about
36,000,000 miles away.
          Twenty-three minutes later, at 12:01 p.m., Mariner will
reach the position of closest approach, approximately 21,000 miles
from Venus.  It will be traveling approximately 88,400 mph.
          The gravitational attraction of Venus will have
increased Mariner's velocity by 1400 mph in one hour.  As the
spacecraft starts moving away from Venus, gravity reverses its
effect and starts slowing the spacecraft down.  In addition to
changing the speed of the spacecraft, the gravitational field also
will bend Mariner's trajectory by about 25 degrees during
encounter.
          After closest approach Mariner will be instructed to
turn off its radiometers and return to the cruise mode.  When the
command is obeyed the spacecraft will resume the sending of
engineering data and will continue to take measurements with its
interplanetary instruments.
          It will continue in this mode until the mission is
completed.
          On December 27, it will reach its closest point to the
Sun, 65,539,000 miles.  At this time, its velocity will be
approximately 85,300 mph.  It will be 2,700,000 miles from Venus
and Mariner then will be 44,213,000 miles from Earth in a helio-
centric orbit around the Sun.
          Uncertainties in Mariner's trajectory resulted from:
the effect of solar pressure, the mass and gravitational fields
of the Earth and Venus, the exact location of ground tracking
stations and the astronomical unit.
          Refinements in these uncertainties will be achieved by
analysis of the tracking and doppler data collected during
Mariner's trip and during the encounter phase when Mariner's
trajectory is perturbed by Venus gravity.
          The doppler effect is a principle of physics in which
the frequency of radio waves appear to increase when a transmitter
and receiver are approaching each other, and to decrease when they
are moving apart.  The speed of Mariner is determined by analysis
of the frequency of its signals.

219-12/62
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children 
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
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