THE TRACKING NETWORK
Thirty-six million miles separated the Earth from Venus at encounter.
Communicating with Mariner II and tracking it out to this distance, and
beyond, represented a tremendous extension of man’s ability to probe
interplanetary space.
The problem involved:
1. The establishment of the spacecraft’s velocity and position
relative to the Earth, Venus, and the Sun with high precision.
2. The transmission of commands to activate spacecraft maneuvers.
3. The reception of readable spacecraft engineering and scientific
data from the far-ranging Mariner.
The tracking network had to contend with many radio noise sources: the
noise from the solar system and from extragalactic origins; noise
originating from the Earth and its atmosphere; and the inherent
interference originating in the receiving equipment. These problems were
solved by using advanced high-gain antennas and ultra-stable, extremely
sensitive receiving equipment.
DEEP SPACE INSTRUMENTATION FACILITY
The National Aeronautics and Space Administration has constructed a
network of deep-space tracking stations for lunar and planetary
exploration missions. In order to provide continuous, 24-hour coverage,
three stations were built, approximately 120 degrees of longitude apart,
around the world: at Goldstone in the California desert, near
Johannesburg in South Africa, and at Woomera in the south-central
Australian desert.
[Illustration: _The three tracking stations of the Deep Space
Instrumentation Facility are located around the world so as to
provide continuous flight coverage._]
These stations are the basic elements of the Deep Space Instrumentation
Facility (DSIF). In addition, a mobile tracking station installed in
vans is used near the point of injection of a spacecraft into an
Earth-escape trajectory to assist the permanent stations in finding the
spacecraft and to acquire tracking data. The control point for the DSIF
net is located at JPL in Pasadena, California (see Table 1).
The Jet Propulsion Laboratory has the responsibility for the technical
direction of the entire DSIF net and operates the Goldstone facilities
with assistance from the Bendix Corporation as a subcontractor. The
overseas stations are staffed and operated by agencies of the Republic
of South Africa and the Commonwealth of Australia.
The DSIF net tracks the position and velocity of U.S. deep-space probes,
issues commands to direct the spacecraft in flight, receives engineering
and scientific data from the probes, and automatically relays the data
to JPL in Pasadena, where it is processed by computers and interpreted.
(In the tracking operation, a signal is transmitted to the spacecraft,
where it is received and processed in a transponder, which then sends
the signal back to the Earth. The change in frequency, known as the
doppler effect, involved in this operation enables engineers to
determine the velocity at which the spacecraft is moving.)
_Table 1. Deep Space Instrumentation Facility Stations_
_Station_ _Location_ _Equipment_ _Functions_
DSIF 1 (Mobile Near point of 10-ft antenna Fast tracking
Tracking injection of 25-w, 890-mc for acquisition
Station) spacecraft into transmitter of spacecraft
Earth-escape
trajectory
Goldstone: California
Pioneer Site 85-ft Reception of
(DSIF 2) polar-mount telemetry
antenna; Tracking
Cassegrain spacecraft
feed; maser and
parametric
amplifier
Echo Site 85-ft Transmission of
(DSIF 3) polar-mount commands
antenna; Tracking
parametric spacecraft
amplifier Stand-by
10-kw, 890-mc reception
transmitter
Venus Site 85-ft Advanced radar
radar-type astronomy
antenna Communications
research
DSIF 4 Woomera, 85-ft Reception of
Australia polar-mount telemetry
antenna; Tracking
parametric spacecraft
amplifier
DSIF 5 Johannesburg, 85-ft Reception of
South Africa polar-mount telemetry
antenna; Tracking
parametric spacecraft
amplifier Transmission of
10-kw, 890-mc commands
transmitter
The stations are equipped with receiving and tracking instruments so
sensitive that engineers estimate that they can detect radio-frequency
energy equivalent to that radiated by a 1-watt light bulb at a distance
of approximately 75 to 80 million miles. Such energy received at the
antenna would measure about 0.00000000000000000002 watt (2 × 10⁻²⁰).
The amount of power received at the antenna during Mariner’s encounter
with Venus has been calculated at about 0.000000000000000001 of a watt
(1 × 10⁻¹⁸). If a 100 percent efficient storage battery were charged
with this amount of energy for some 30 billion years, the battery would
then have stored enough energy to light an ordinary 1-watt flashlight
bulb for about 1 second only.
Furthermore, Goldstone engineers estimate that, if Mariner II had
continued to function in all its systems and to point its directional
antenna at the Earth, useful telemetry data could have been obtained by
the DSIF stations out to about 150 to 200 million miles, and tracking
data could have been secured from as far as 300 to 400 million miles.
Construction of the DSIF net was begun in 1958. The Goldstone station
was ready for the Pioneer III mission in December of that year. In
March, 1959, Pioneer IV was successfully tracked beyond the Moon. Later
in 1959, Pioneer V was tracked out to over 3 million miles.
Goldstone participated in the 1960 Project Echo communication satellite
experiments and the entire net was used in the Ranger lunar missions of
1961-1962. The Goldstone station performed Venus radar experiments in
1961 and 1962 to determine the astronomical unit more precisely and to
study the rotation rate and surface characteristics of the planet.
Following the launch of Mariner II on August 27, 1962, the full DSIF net
provided 24-hour-per-day tracking coverage throughout the mission except
for a few days during the cruise phase. The net remained on the
full-coverage schedule through the period of Venus encounter on December
14.
THE GOLDSTONE COMPLEX
The tracking antennas clustered in a 7-mile radius near Goldstone Dry
Lake, California, are the central complex of the DSIF net. Three
tracking sites are included in the Goldstone Station: Pioneer Site (DSIF
2), Echo Site (DSIF 3), and Venus Site. The Venus Site is used for
advanced radar astronomy, communication research experiments, and radio
development; it took no direct part in the Mariner spacecraft tracking
operations, but was used for the Venus radar experiments.
Pioneer Site has an 85-foot-diameter parabolic reflector antenna and the
necessary radio tracking, receiving, and data recording equipment. The
antenna can be pointed to within better than 0.02 of a degree. The
antenna has one (hour-angle) axis parallel to the polar axis of the
Earth, and the other (declination) axis perpendicular to the polar axis
and parallel to the equatorial plane of the Earth. This “polar-mount”
feature permits tracking on only one axis without moving the other.
The antenna weighs about 240 tons but can be rotated easily at a maximum
rate of 1 degree per second. The minimum tracking rate or antenna swing
(0.250686486 degree per minute) is equal to the rotation rate of the
Earth. Two drive motors working simultaneously but at different speeds
provide an antibacklash safety factor. The antenna can operate safely in
high winds.
The Pioneer antenna has a type of feed system (Cassegrain) that is
essentially similar to that used in many large reflector telescopes. A
convex cone is mounted at the center of the main dish. A received signal
is gathered by the main dish and the cone, reflected to a subreflector
on a quadripod, where the energy is concentrated in a narrow beam and
reflected back to the feed collector point on the main dish. The
Cassegrain feed system lowers the noise picked up by the antenna by
reducing interference from the back of the antenna, and permits more
convenient location of components.
The receiving system at Pioneer Site is also equipped with a low-noise,
extremely sensitive installation combining a parametric amplifier and a
maser. The parametric amplifier is a device that is “pumped” or excited
by microwave energy in such a way that, when an incoming signal is at
its maximum, the effect is such that the “pumped-in” energy augments the
original strength of the incoming signal. At the same time, the
parametric amplifier reduces the receiving system’s own electronic noise
to such a point that the spacecraft can be tracked twice as far as
before.
The maser uses a synthetic ruby mixed with chromium and is maintained at
the temperature of liquid helium—about 4.7 degrees K or -450 degrees F
(just above absolute zero)—and when “pumped” with a microwave field, the
molecular energy levels of the maser material are redistributed so as to
again improve the signal amplification while lowering the system noise.
The maser doubles the tracking capability of the system with a
parametric amplifier, and quadruples the capability of the receiver
alone.
The antenna output at Pioneer is a wide-band telemetering channel. In
addition, the antenna can be aimed automatically, using its own “error
signals.” At both the Pioneer and Echo sites at Goldstone, however, the
antenna is pointed by a punched tape prepared by a special-purpose
computer at JPL and transmitted to Goldstone by teletype.
Pioneer Site has a highly sensitive receiver designed to receive a
continuous wave signal in a narrow frequency band in the 960-megacycle
range. The site has equipment for recording tracking data for use by
computers in determining accurate spacecraft position and velocity.
The instrumentation equipment also includes electronic signal processing
devices, magnetic-tape recorders, oscillographs, and other supplementary
receiving equipment. The telemetered data can be decommutated (recovered
from a signal shared by several measurements on a time basis), encoded,
and transmitted by teletype in real time (as received from the
spacecraft) to JPL.
Echo Site is the primary installation in the Goldstone complex and has
antenna and instrumentation facilities identical to those at Pioneer,
except that there is no maser amplifier and a simpler feed system is
used instead of the Cassegrain. However, Echo was used as a transmitting
facility and only as a stand-by receiving station during the Mariner
mission.
Echo has a 10-kilowatt, 890-megacycle transmitter which was utilized for
sending commands to the Mariner spacecraft. In addition, the site has an
“atomic clock” frequency standard, based on the atomic vibrations of
rhubidium, which permits high-precision measurements of the radial
velocity of the spacecraft. A unit in the Echo system provides for
“readback” and “confirmation” by the spacecraft of commands transmitted
to it. In a sense, the spacecraft acknowledges receipt of the commands
before executing them.
Walter E. Larkin manages the Goldstone Station for JPL.
THE WOOMERA STATION
The Woomera, Australia, Station (DSIF 4), managed by William Mettyear
for the Australian Department of Supply, has essentially the same
antenna and tracking capabilities as Goldstone Echo Site, but it has no
provisions for commanding the spacecraft. A small transmitter is used
for tracking purposes only. The station is staffed and operated by the
Australian Department of Supply.
[Illustration: _The Mobile Tracking Station (DSIF 1) follows the
fast-moving spacecraft during its first low-altitude pass over South
Africa._]
[Illustration: _Station 5 of the DSIF is located near Johannesburg
in South Africa._]
[Illustration: _DSIF 4, at Woomera, dominates the landscape in
Australia’s “outback.”_]
Woomera, like Johannesburg, is capable of receiving tracking (position
and velocity) data and telemetered information for real-time
transmission by radio teletype to JPL.
THE JOHANNESBURG STATION
DSIF 5 is located just outside Johannesburg in the Republic of South
Africa. This station is staffed by the National Institute of
Telecommunications Research (NITR) of the South African Council for
Scientific and Industrial Research and managed by Douglas Hogg.
The antenna and receiving equipment are identical to the Goldstone Echo
Site installation except for minor details. The station has both
transmitting and receiving capability and can send commands to the
spacecraft. Recorded tracking and telemetered data are transmitted in
real time to JPL by radio teletype.
MOBILE TRACKING STATION
The Mobile Tracking Station (DSIF 1) is a movable installation designed
for emplacement near the point of injection of a space probe to assist
the permanent stations in early acquisition of the spacecraft. This
station is necessary because at this point the spacecraft is relatively
low in altitude and consequently appears to move very fast across the
sky. The Mobile Tracking Station has a fast-tracking antenna for use
under these conditions. DSIF 1 was located near the South African
station for Mariner II. It has a 10-foot parabolic antenna capable of
tracking at a 10-degree-per-second rate. A 25-watt, 890-megacycle
transmitter is used for obtaining tracking information. A diplexer
permits simultaneous transmission and reception on the same antenna
without interference.
The equipment is installed in mobile vans so that the station can be
operated in remote areas. The antenna is enclosed in a plastic dome and
is mounted on a modified radar pedestal. The radome is inflatable with
air and protects the antenna from wind and weather conditions.
These stations of the DSIF tracked Mariner II in flight and sent
commands to the spacecraft for the execution of maneuvers. The telemetry
data received from the spacecraft during the 129 days of its mission
were recorded and transmitted to JPL, where the information was
processed and reduced by the computers of the space flight operations
complex.