| Article 2651 of sci.space.news:
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From: [email protected] (Ron Baalke)
Subject: Mariner 2 Radio Tracking - 12/28/62
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OFFICE OF PUBLIC EDUCATION AND INFORMATION
CALIFORNIA INSTITUTE OF TECHNOLOGY
JET PROPULSION LABORATORY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.
FOR RELEASE: P.M.'s of Friday, December 28, 1962
RADIO TRACKING OF MARINER II AND ITS SCIENTIFIC IMPLICATIONS
Mariner II's fly-by of Venus on December 14 has produced
the most accurate estimate yet of the mass of our sister planet,
two scientists from the California Institute of Technology Jet
Propulsion Laboratory reported today. This information was re-
vealed at a meeting of the American Geophysical Union at Stanford
University, in a paper by John D. Anderson and George Null,
describing their preliminary analysis of the trajectory data
obtained during the 109-day flight of Mariner II from earth to
Venus. According to Anderson, who presented the paper, they find
the mass of Venus a value of 0.81485 times the mass of the earth,
with a probable error of 0.015 percent. They said that their
analysis is continuing, using additional data obtained before and
after the encounter with Venus, and that their final result will
probably alter the quoted value slightly and still further reduce
the probable error. For comparison, the mass of the earth is
known to be approximately 13,173,000,000,000,000,000,000,000
pounds (about 13 septillion pounds).
The only method known to astronomers for determining
the mass of other planets is through the observation of their
gravitational effects on other bodies in the solar system. Thus,
for planets having satellites (moons), the determination can be
made with considerable accuracy.
In the case of Venus, which has no known satellites, no
natural object has ever been observed to pass close to it, and
hence all estimates of its mass made before 1940 were both
inaccurate and erroneous.
Two more recent determinations are in agreement with
the new Mariner value, but have much less precision. In 1943, G.
M. Clemence published a value equivalent to 0.813 times the
earth's mass, with a probable error of 0.34 percent, based upon
his study of the astronomical records of the observations of the
motions of the planet Mercury through the year 1767 to 1937.
In 1954, E. W. Rabe obtained a value equivalent to
0.8148, with a probable error of 0.05 percent, from records of
the motion of the minor planet, Eros, over two decades.
In contrast, the data required to deduce the new more
accurate mass of Venus were obtained by the Jet Propulsion
Laboratory's Goldstone Tracking Station during two 10-hour
observations of Mariner, on the day of its passage of Venus and
the previous day.
The data obtained was a so-called "two-way Doppler"
measurement, involving a round trip by a radio signal. A signal
at a frequency of approximately 960 megacycles per second was
sent from Goldstone and was received by Mariner, 3 minutes 12.5
seconds later. The spacecraft then shifted the frequency of the
signal slightly and sent it back to Goldstone, where it was
compared to the original signal.
From this comparison the spacecraft velocity relative
to the earth, approximately 40,000 miles per hour, can be
calculated within about 0.01 miles per hour, and it was the
change in this velocity amounting to approximately 3,000 miles
per hour, produced by the gravitational field of Venus which gave
the scientists the necessary data to determine the mass of the
planet.
Anderson also said that further analysis of the data
will probably refine our knowledge of another particularly
important astronomical constant, the Astronomical Unit--the mean
distance between the sun and the earth.
At present, the measurement of this unit by a variety
of conventional astronomical techniques are slightly in disagree-
ment with those obtained by bouncing radar beams off of Venus, as
has recently been done again by the Goldstone station. The two-
way Doppler measurement is an independent measurement, and may
help to resolve the inconsistency.
224-12/62
___ _____ ___
/_ /| /____/ \ /_ /| Ron Baalke | [email protected]
| | | | __ \ /| | | | Jet Propulsion Lab |
___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children
/___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts.
|
| Article 2652 of sci.space.news:
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From: [email protected] (Ron Baalke)
Subject: Mariner 2 Radiation Experiments - 12/28/62
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OFFICE OF PUBLIC EDUCATION AND INFORMATION
CALIFORNIA INSTITUTE OF TECHNOLOGY
JET PROPULSION LABORATORY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.
FOR RELEASE: P.M.'s of Friday, December 28, 1962
MARINER RADIATION EXPERIMENTS
Mariner II carried two experiments designed to measure
the charged-particle radiation in space, including galactic
cosmic rays and streams of high-energy particles which are
released intermittently from the sun. Virtually continuous
measurements of the particle fluxes in space were made by the
instruments throughout the 109-day journey to Venus and during
the passage near the planet on December 14, and additional data
have been received for approximately 10 hours per day since that
time.
One experiment, for observing the higher-energy
particles (protons above 10 million electron volts (Mev) and
electrons above 0.5 Mev in energy) was designed by Dr. H. R.
Anderson of the Jet Propulsion Laboratory and Dr. H. V. Neher of
the California Institute of Technology. Somewhat lower-energy
particles (protons above 0.5 Mev or electrons above 0.04 Mev) are
detected by the experiment of L. A. Frank and Dr. J. A. Van Allen
of the State University of Iowa. Preliminary results of the two
experiments were reported at the Stanford meeting by Dr. Anderson
and Frank, respectively.
The instrumentation for the high-energy experiment
consisted of a large spherical ionization chamber and two matched
Geiger counters. The ionization chamber, which was invented by
Dr. Neher, has been widely used by him and by other investigators
for several years as a standard instrument for surveying the
absolute intensity of the cosmic rays.
In addition to its use in almost countless balloon
flights, airplane flights, and ground-based experiments, this
type of chamber was also carried on the earth satellite Explorer
VI and on this country's only previous successful interplanetary
probe, Pioneer V. The two Geiger counters are matched to count
the same kind of particles which are registered by the ionization
chamber.
The detector for the lower-energy particles is a
cigarette-sized Geiger counter, the Anton 213, which was used in
several of the early Explorer and Pioneer satellites for
investigating the Van Allen radiation belts around the earth and
also in numerous more recent satellites.
These experiments have three principal scientific
objectives, all of which were reported on at the Stanford meeting.
Objective 1: To detect, if possible, the presence of
magnetically-trapped particle belts about Venus. For this
purpose, the Anton 213 counter was the most sensitive indicator.
At 20,000 miles from the earth it is known to have a counting
rate of several thousand per second, but during the closest
approach to Venus it detected an average count of only one
particle per second, in agreement with the rate observed during
most of the month of November.
The absence of additional particles near the planet was
confirmed also by the other radiation detectors. Near the earth,
the number of trapped particles observed decreases very sharply
with distance near the boundary between the earth's magnetic
field and the interplanetary field.
Thus the absence of particles near Venus indicates that
the planet's magnetic field does not extend as far out as the
trajectory of Mariner. This fact was confirmed by the magneto-
meter on board. The small intensity and extent of the field is
believed to be explained by the very slow rate of rotation of the
planet.
Objective 2: To measure the intensity of the galactic
cosmic rays far away from the perturbing effect of any planet,
and to look for variations in this intensity in different parts
of the solar system. Years of earth-based research have shown
that the flux of relatively low-energy galactic cosmic rays (5000
Mev and below) have a systematic variation with a period of about
eleven years which is somehow connected with the solar activity
cycle (sunspot cycle).
It is hoped that cosmic-ray measurements made simultane-
ously in widely separated parts of the solar system will elucidate
the nature of the mechanism responsible for this variation. For
this purpose, the ionization chamber is best suited. It measured
a rate of ionization near 670 ion pairs per cubic centimeter per
atmosphere of air. The value did not change significantly during
the flight, and furthermore is in agreement with measurements in
high-altitude balloons made last summer at Thule, Greenland, by
Dr. Neher.
The Geiger counter on Mariner indicated a cosmic-ray
flux of approximately 3.0 particles per square centimeter per
second throughout the flight. The constancy of the cosmic-ray
intensity over the very great distance traveled by Mariner is a
new and significant piece of information, but its real meaning
will not become clear until we have repeated the experiment
several times on space vehicles going out away from the sun as
well as in toward it.
Objective 3: To study the number and the nature of the
high-energy changed particles emitted by the sun. (Another
Mariner experiment investigated the very low-energy solar
particles also.)
The presence of these particles is indicated by sudden
increases above the cosmic-ray background reading of the various
particle detectors. Some idea of their composition can be
obtained from a comparison of the response of different detectors.
The Mariner results were that high-energy solar particles, such
as could be detected by the JPL-Caltech experiment, were generally
absent except for a single event which began on October 23. The
Iowa counter, on the other hand, detected not only this event but
at least eight others, which must therefore have been produced by
radiation or particles of very low penetrating power. Its exact
nature is still in doubt at this time.
The nature of the solar-particle event of October 23
was described in detail by Dr. Anderson. A solar flare of a type
which has frequently produced streams of charged particles was
observed between 9:42 A.M. and 10:45 A.M., and the reading of the
ionization chamber began to increase even before the flare had
disappeared. Its reading rose rapidly from a background of 670
to a peak of above 18,000, underwent several oscillations, and
remained above 10,000 for about six hours before declining
gradually over the next few days. The flux of particles detected
by the Geiger counters rose from a background of 3 to a peak of
16 particles per square centimeter per second. The fact that the
ionization increased much more than did the number of particles
indicates that the solar particles had much lower average energies
than the galactic cosmic rays, and it is calculated that a typical
energy in this event was about 25 Mev. The details of the time
and energy variations will be further studied in the hope of
learning more about how the particles were produced in the photo-
sphere of the sun and how they may have been trapped in the
magnetic fields around the sun before being released to the region
where Mariner was waiting to detect them.
The problem of solar flares and their production of
high-energy charged particles is a particularly important one for
interplanetary space research because the very largest solar
particle streams may contain particles in such numbers and of such
high energies as to constitute a significant hazard to manned
space missions. No such events have been observed by Mariner,
however.
The total radiation dose seen by the ionization chamber
in the October 23 event was only about 0.24 roentgen inside its
0.01-inch thick steel wall, and the radiation was so non-penetrat-
ing that a moderate increase in the wall thickness would have
excluded the particles almost entirely. For comparison, the radia-
tion dose recorded during the entire flight to Venus was about 3
roentgens, and much of this radiation was etremely penetrating.
225-12/62
___ _____ ___
/_ /| /____/ \ /_ /| Ron Baalke | [email protected]
| | | | __ \ /| | | | Jet Propulsion Lab |
___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children
/___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts.
|
| Article 2654 of sci.space.news:
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From: [email protected] (Ron Baalke)
Subject: Mariner 2 Venus Flyby - 12/14/92
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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 | [email protected]
| | | | __ \ /| | | | Jet Propulsion Lab |
___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children
/___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts.
|