THIRTEEN MILLION WORDS
The task of receiving, relaying, processing, and interpreting the data
coming in simultaneously on a twenty-four-hour basis for several months
from the several scientific and many engineering sources of the Mariner
spacecraft was of truly monumental proportions.
This activity involved five DSIF tracking stations scattered around the
world, a communication network, two computing stations and auxiliary
facilities, and some 400 personnel over a four-month period.
Although the Mariner scientific information could be stored and
subsequently processed at a later (non-real) time, it was necessary to
make tracking and position data available almost as soon as it was
received (in real time) so that the midcourse maneuver might be computed
and transmitted to the spacecraft, and to further perfect the predicted
trajectory and arrival time at Venus.
The engineering performance of the many spacecraft subsystems was also
of vital concern. Inaccurate operation in any of several areas could
endanger the success of the entire mission. The performance of the
attitude control system, the Earth and Sun sensors, the power system,
and communications were all of critical importance. Corrective action
was possible in certain subsystems where trouble could be predicted from
the data or where limited breakdown had occurred.
To integrate all the varied activities necessary to accomplish the
mission objectives, an organization was formed within JPL to coordinate
the DSIF, the communication network, the work of engineering and
scientific advisory panels, and the computer facilities required to
evaluate the data.
This organization was known as the Space Flight Operations Complex. For
operational purposes only, it included the Space Flight Operations
Center, a Communication Center, and a Central Computing Facility (CCF).
The DSIF was responsive to the requirements of the organization, but was
not an integral part of it.
A space flight operations director was responsible for integrating these
many functions into a world-wide Mariner space-flight organization. It
was an exhausting 109-day task, one that would severely tax all the
resources of JPL in terms of know-how, qualified personnel, time, and
equipment before Mariner completed its encounter with Venus.
COMMUNICATION CONTROL
The Communication Center at JPL in Pasadena was one of the most active
areas during the many days and nights of the Mariner II mission. All of
the teletype and radio lines from the Cape, South Africa, Australia, and
Goldstone terminated in this Center. A high-speed data line bypassed the
Communication Center, linking Goldstone directly with the Central
Computing Facility for quick, real-time computer processing of vital
flight information.
From the Communication Center, the teletype data and voice circuits were
connected to the several areas within JPL where the mission-control
activities were centered, and where the data output was being studied.
The Communication Center was equipped with teletype paper-page printers
and paper-tape hole reperforators, which received and transmitted
data-word and number groups. The teletype lines terminating at the
Center included circuits from Goldstone, South Africa, Australia, and
Cape Canaveral.
There were three lines to Goldstone for full-time, one-way data
transmission. Duplex (simultaneous two-way) transmission was available
to Woomera and South Africa on a full-time basis. In each case, a
secondary circuit was provided to the overseas sites for use during
critical periods and in case the primary radio-teletype circuits had
transmission difficulties. These secondary circuits used different radio
transmission paths in order to reduce the chance of complete loss of
contact for any extended period of time.
[Illustration: _Radio signals from Mariner are received on 85-ft.
antenna._]
[Illustration: _The highly sensitive receiver (shown under test) is
located in the control room of the station._]
[Illustration: _In Goldstone control room, DSIF personnel await
confirmation that spacecraft has begun to scan the planet Venus._]
[Illustration: _From DSIF stations, the data are teletyped in coded
format to Pasadena._]
Z ZSQSGSGKGKXRGOQOS DNQ XZARZXAVAQQVA XXDRDZ
QSGIGKGKXRGOQOX DXQ XZAIZXAVQQKDZ XXDRDDDRZ
DXQ XZAIZAZVAQQZDZXXDLKKDRA Z DSQSGIGGGQXRDN
G XXDRZSDRA Z DSQSGIGGGQXRGLZOX DXQ XZAIZAZV
QSGIGGGQXRGLZOX DXQ XZAIZGAVAQQSXZXXDRDZDRA
DXQ XQAIZGAVQQKVA XXDRDZDRANGDSSQSGIGGGQXRDI
Z XXDRDDDRZLQ ZSQSGIGGGGXRGVZOA DNQ XZARZGAV
QSGIGGGGXRGVQOA DNQ XZARZGAVQKZZAZXXDRZDDRA
DNQ XZARZAZVAKDDGZXXDRDADIZLA DSQSGIGGGGXRGZ
SZXXDRDDDRXOS DSQSQIGGGGXRDDZOA DNQ XZARZXAV
QSGSGGGGXRDSQOG DXQ XZARZXAVAKDZDZXXDRDLDRA
DXQ XZARZXAZZKZZDZXXDLKADRA Z DSQSGIGGGGXRGX
GZXXDRZXDRZ Z DSQSAQGGGGXRDAZOG DXQ XZAIZAZV
DRDXDRA Z DSQSGIGGGGXRDGSOG DXQ XZAIZAZVQKZS
OGGGXRDGAOG DXQ XZAIZAZVQKZVA XXDRDZDRANGDSS
XZAIZXAZZKZZD XXDRDLZDZHA DSQSGIGGGGXRDQAOQ
DLKADRKHQ ZSQSGIGGGGXRDKZOQ DXQ XZAVZAAVQKZZ
GGGGXRS ZOQ DXQ XZAIZAZVQKZDG XXDRDSDIZ A ZS
XZAIZAZVQQKSX XXDRDDDRZNS ZSQSGIGGGGXRSOAOQ
DRDZDRANGDSSQSAQGGGGXRSOAOK DNQ XZAVZAAVQQKZ
GGGGXRSNZOK DNQ XZAIZAZZSQQZSZXXDLKADRA Z DS
XZAIZGAVQQKZG XXDRZXDRZ Z DSQSAQGGGGXRSLAOK
DRDSDRZ Z DSQSAQGGGGXRSLAOK DNQ XZAIZAZZZQKS
GGGGXRSLAOK DNQ XZAIZAZZZQKVA XXDRDZDRANGDSS
XRSIZHZ DXQ XZAIZAZZZQKQQZXXDRDNDRZNQ DSQSGS
ZXAZSQQZXZXXDLKQDRSQS ZSQSGIGGGQXRSVAHZ DXQ
[Illustration: _Messages are received and routed at the JPL
Communications Center._]
[Illustration: _Data are routed to the digital computer at JPL._]
[Illustration: _Printout data are made available to experimenters._]
[Illustration: _Spacecraft status is posted in Operations Center._]
The Mobile Tracking Station in South Africa used the Johannesburg
communication facilities.
Two one-way circuits for testing and control purposes were open to Cape
Canaveral from a month before until after the spacecraft was launched.
Lines from the Communication Center to the Space Flight Operations
Center at JPL terminated in page printers and reperforators in several
locations.
Voice circuits connected all of the stations with Operations Center
through the Communication Center. Long-distance radio telephone calls
were placed to South Africa to establish contact before the launch
sequence was started. Woomera used the Project Mercury voice circuits to
the United States during launch and for three days after.
THE OPERATIONS CENTER
The actual nerve center of the Mariner operation was the Space Flight
Operations Center (SFOC) at Pasadena. Here, technical and scientific
advisory panels reported to the Project Manager and the Mariner Test
Director on the performance of the spacecraft in flight, analyzed
trajectories, calculated the commands for the midcourse trajectory
correction, and studied the scientific aspects of the mission.
These panels were a Spacecraft Data Analysis Team, a Scientific Data
Group, an Orbit Determination Group, a Tracking Data Analysis Group, and
a Midcourse Command Group.
The Spacecraft Data Analysis Team analyzed the engineering data
transmitted from the spacecraft to evaluate the performance of the
subsystems in flight. The Team was composed of one or more of the
engineers responsible for each of the spacecraft subsystems, and a
chairman.
The Science Data Group was composed of the project scientist and certain
other scientists associated with the experiments on board the
spacecraft. This Group evaluated the data from the scientific
experiments while Mariner was in flight and advised the Test Director on
the scientific status of the mission.
The Science Data Group was on continuous duty until 48 hours after
launch, and at other times during the mission. During encounter with
Venus, the Group was also in contact with the scientific experimenters
from other participating organizations who were working with JPL.
[Illustration: _Closed circuit television monitors are used for
instant surveillance of the internal activities of the Operations
Center._]
A Tracking Data Analysis Group analyzed the tracking data to be used in
orbit determination. They also assessed the performance of the DSIF
facilities and equipment used to obtain the data.
The Orbit Determination Group used the tracking data to produce
estimates of the actual spacecraft trajectory, and to compute the
spacecraft path with respect to the Earth, Venus, and the Sun. These
calculations were made once each day before the midcourse maneuver, once
a week during the cruise phase, and daily during and immediately after
the planet encounter.
The Operations Center was equipped with lighted boards on which the
progress of the mission was displayed. This information included
trajectory data, spacecraft performance, temperature and pressure
readings, and other data telemetered from the spacecraft subsystems.
Closed-circuit television was used for coordinating the activities of
the SFOC. Operating personnel could use television monitors in four
consoles which were linked to six fixed cameras viewing teletype page
printers. The entire Operations Room could be kept under surveillance by
the Project Manager, the Test Director, or the DSIF Operations Manager,
using cameras controlled in “pan,” “tilt,” and “zoom.”
CENTRAL COMPUTING FACILITY
During the Mariner II mission, the JPL Central Computing Facility (CCF)
processed approximately 13.1 million data words, or over 90 million
binary bits of computer data. (Binary bit = a discrete unit of
information intelligible to a digital computer. One data word = 7 binary
bits.)
In the four-month operation, about 100,000 tracking and telemetering
data cards were received and processed, yielding over 1.2 million
computer pages of tabulated, processed, and analyzed data for evaluation
by the engineers and scientists. Approximately 1,000 miles of magnetic
tape were used in the 1,056 rolls recorded by the DSIF.
The Central Computing Facility processed and reduced tracking and
telemetry data from the spacecraft, as recorded and relayed by the
stations of the DSIF. The tracking information was the basis for orbital
calculations and command decisions. After delivery of telemetry data on
magnetic tapes by the DSIF, the CCF stored the data for later reduction
and analysis. Where telemetry data were being processed in real or
near-real time, certain critical engineering and scientific functions
were programmed to print-out an “alarm” reading when selected
measurements in the data were outside specified limits.
The CCF consists of three stations at JPL: Station C, the primary
computing facility; Station D, the secondary installation; and the
Telemetry Processing Station (TPS).
Station C was the principal installation for processing both tracking
and telemetry data received from the DSIF tracking stations, both in
real and non-real time. The Station was equipped with a high-speed,
general-purpose digital computer with a 32,168-word memory and two
input-output channels, each able to handle 6 tape units. The associated
card-handling equipment was also available.
Tape translators or converters were provided for converting teletype
data and other digital information into magnetic tape format for
computer input. The teletype-to-tape unit operated at a rate of 300
characters per second.
A smaller computer acted as a satellite of the larger unit, performing
bookkeeping and such related functions as card punching, card reading,
and listing.
A high-speed unit microfilmed magnetic-tape printout was received from
the large computer. It provided “quick-look” copy within 30 minutes of
processing the raw data. Various paper-tape-to-card and
card-to-paper-tape converters were used to eliminate human error in
converting teletype data tape to computer cards.
Station C also utilized another computer as a real-time monitor and to
prepare a magnetic tape file of all telemetered measurements for input
to the large computer.
Station D was the secondary or backup computational facility, primarily
intended for use in case of equipment failure in Station C. During
certain critical phases of the Mariner mission—launch, orbit
determination, midcourse maneuver—this facility paralleled the
operations in Station C.
Station D is equipped with three computers and various card-to-tape
converters and teletype equipment.
The Telemetry Processing Station received and processed all demodulated
data (that recovered from the radio carrier) on magnetic tapes recorded
at the DSIF stations. The TPS output was digital magnetic tapes suitable
for computer entry.
The TPS equipment included FM discriminators, a code translator, a
device for converting data from analog to digital form, and
magnetic-tape recorders. Basically, the equipment accepted the digital
outputs from the tape units, the analog-to-digital converter, and the
code translator and put them in digital tape format for the computer
input.
As the launch operation started on August 27, the powered-flight portion
of the space trajectories program was run at launch minus 5 minutes (L
minus 5) and was repeated several times because of holds at AMR. The
orbit determination program was run at lift-off to calculate the first
orbit predictions used for aiding the DSIF in finding the spacecraft in
flight.
During the 12 hours following launch, both C and D Stations performed
parallel computations on tracking data. Station D discontinued space
flight operations at L plus 12 hours and resumed at the beginning of the
midcourse maneuver phase.
Tracking data processing and midcourse maneuver studies were conducted
daily until the midcourse maneuver was performed at L plus eight days.
For the following 97 days, tracking data were processed once each week
for orbit determination. Starting three days before the encounter,
tracking data were processed daily until the beginning of the encounter
phase.
Tracking data processing was conducted in near-real time throughout
encounter day, and daily for two days thereafter. For these three days,
tracking data were handled in Station D in order to permit exclusive use
of Station C for telemetry data processing and analysis. After this
three-day period, including the encounter, Station C processed the
tracking data every sixth day until the mission terminated on L plus 129
days.
Telemetry data were processed in a different manner. Following the
launch, DSIF Station 5 at South Africa received the telemetry signal
first, demodulated it, and put it in the proper format for teletype
transmission to JPL. The other DSIF stations followed in sequence as the
spacecraft was heard in other parts of the world. For two days after
launch, the computers processed telemetry data as required by the
Spacecraft Data Analysis Team.
During those periods when the large computer was processing tracking
data, a secondary unit supplied quick-look data in near-real time. When
Goldstone was listening to the spacecraft, quick-look data were
processed in real time, using the high-speed data line direct to the
Central Computing Facility.
For the 106 days that Mariner was actually in Mode II (cruise), the
telemetry data were processed twenty-four hours a day, seven days a
week. Data were presented to the engineering and science analysis teams
in quick-look format every three hours, except for short maintenance
interruptions, one computer failure, and a major modification requiring
three days, when a back-up data process mode of operation was used. The
large computer performed full processing and analysis of engineering and
science data seven days a week from launch until the Venus encounter.
On encounter day, the secondary Station C computer processed telemetry
data from the high-speed Goldstone line. Data on magnetic tapes produced
by the computer were processed and analyzed by the large unit in
near-real time every 30 minutes. The computer processing and delivery
time during this operation varied from 4½ to 7 minutes.