PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "R. SIMPSON, 1999-09-01"
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 72
OBJECT = INSTRUMENT
INSTRUMENT_HOST_ID = VG1
INSTRUMENT_ID = "RSS-VG1S"
OBJECT = INSTRUMENT_INFORMATION
INSTRUMENT_NAME = "RADIO SCIENCE SUBSYSTEM"
INSTRUMENT_TYPE = "RADIO SCIENCE"
INSTRUMENT_DESC = "
Instrument Overview
===================
Voyager Radio Science investigations at the giant planets
utilized instrumentation with elements both on the spacecraft
and at the DSN. Much of this was shared equipment, being used
for routine telecommunications as well as for Radio Science.
The performance and calibration of both the spacecraft and
tracking stations directly affected the radio science data
accuracy, and they played a major role in determining the
quality of the results. The spacecraft part of the radio
science instrument is described immediately below; unless
noted otherwise, the description applies equally well to
both Voyager 1 and Voyager 2 and it applies throughout the
Voyager mission. The description of the DSN (ground) part
of the instrument follows. Because the DSN was continually
changing, that description has been tailored to each Voyager
encounter.
Instrument Specifications - Spacecraft
======================================
The Voyager spacecraft telecommunications subsystem served as
part of a radio science subsystem for investigations of the
giant planets. Many details of the subsystem are unknown; its
'build date' is taken to be 1977-09-05, the launch date for
Voyager 1. Except for hardware failures, noted below, the
Voyager 1 and Voyager 2 spacecraft subsystems were identical.
Instrument Id : RSS-VG1S
Instrument Host Id : VG1
Pi Pds User Id : UNK
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : 1977-09-05
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
Instrument Overview - Spacecraft
================================
The spacecraft radio system was constructed around a redundant
pair of transponders. Each transponder was equipped with an
S-band receiver (2115 MHz nominal frequency) and transmitters
at both S-band (2295 MHz nominal) and X-band (8415 MHz nominal).
Compared with S-band, X-band is less sensitive to plasma effects
by a factor of about 10; use of both frequencies coherently on
the 'downlink' allowed estimation of plasma content along the
radio path. Use of X-band also significantly improved the
quality of radio tracking data for gravity investigations.
The transponder generated downlink signals in either 'coherent'
or 'non-coherent' modes, also known as 'two-way' and 'one-way,'
respectively. When operating in the coherent mode, the
transmitted carrier frequency was derived coherently from the
received uplink carrier frequency with a 'turn-around ratio' of
240/221 at S-band and (11/3)*240/221 at X-band.
In non-coherent mode the transmitted frequency was controlled
by an on-board oscillator; the X- and S-band remained coherent
in the ratio 11/3. A single Ultra-Stable Oscillator (USO) was
used during radio occultations; it provided stabilities
several orders of magnitude better than the conventional
crystal oscillators, which were part of each transponder.
Stability of the Voyager USO was specified in terms of its
Allan Deviation -- the fractional frequency deviation from
linear drift [ALLAN1966]. Over 10 minute periods, the Allan
Deviation ranged from 10^-12 to 4 10^-12 for integrations of
1-10 sec. Long-term fractional drift of the oscillator was
about 5 10^-11 per day. Although the oscillator was hardened,
there were discontinuities in the drift when the spacecraft
passed through the radiation belts of the outer planets.
Equivalent X-band microwave frequencies for the Voyager 1 USO
during key events were (multiplying by 3/11 yields the S-band
frequency):
8,414,995,272.530 Hz (Titan occultation)
8,414,995,272.376 Hz (Saturn occultation)
Traveling wave tube or solid state amplifiers boosted the
transponder output. Output powers of 9 and 26 watts could
be selected at S-band; the choices at X-band were 12 and 22
watts.
The signals were radiated via a 3.66 m diameter parabolic high
gain antenna (HGA). The HGA transmit boresight gain of
the HGA was 36 dB at S-band and 47 dB at X-band. The half-power
half-width of the antenna beam was 0.32 degrees at X-band and
1.1 degrees at S-band. Transmit polarization was right-hand
circular at S-band and either right- or left-hand circular at
X-band. A Low-Gain Antenna (LGA) was mounted on the feed
structure of the HGA and radiated approximately uniformly over
the hemisphere into which the HGA pointed. It was used during
maneuvers, spacecraft anomalies, and at other times when the
HGA was not appropriate.
For receiving, the S-band HGA gain was 35 dB at 2115 MHz and the
polarization was right-hand circular. The receiving system
noise temperature was approximately 2000K, the carrier tracking
loop bandwidth was 18 Hz, and the ranging channel noise
bandwidth was 1.5 MHz.
More information can be found in [ESHLEMANETAL1977].
Science Objectives
==================
Science objectives fell into two broad areas of investigation --
those that could be met using high-precision radiometric data
(sometimes known as 'tracking' data) and those that could be met
from studying characteristics of the radio signal after its
interaction with an atmosphere, plasma, ring particles, or other
intervening medium. The tracking data were fundamental to
inferring the gravitational forces on the spacecraft and
relativistic effects along the radio path; both the measured
time delay during a two-way transmission and the Doppler shift
were used. Investigators seeking knowledge of atmospheric
structure, spatial and size distributions of ring particles,
and velocity of the solar wind measured amplitude, frequency
(and phase), and polarization of the radio signals which were
captured by Earth receiving systems. There are, of course,
investigations which use both types of data.
Gravity Measurements
--------------------
The frequency of the downlink carrier signal was precisely
measured to determine the magnitude of the Doppler shift
caused by acceleration of the spacecraft as it passed near
either a single body or a system of bodies. Since the
magnitude of the Doppler shift is related to the gravitational
field strength, the mass of the body (or bodies) can be
determined. If the radius of the body is known (as from
calibrated images), the density can be calculated.
Doppler and range tracking measurements yield accurate
spacecraft trajectory solutions. Simultaneously with
reconstruction of the spacecraft orbit, observation equations
for the central mass, low order coefficients for the field,
and a small number of ancillary parameters can be solved.
Measurements of the gravity field provide significant
constraints on inferences about the interior structure of
target bodies.
The Pioneer 10 and 11 spacecraft came closer to Jupiter than
Voyager, so there was no net improvement in the Jupiter mass
estimate from Voyager. But Voyager probed the Galilean
satellites at closer range, and better mass estimates were
obtained. The Voyager encounters with Saturn, in conjunction
with the close flyby of Pioneer 11, yielded a mass estimate
comparable to that of Jupiter along with several low-order
zonal harmonic coefficients. Voyager 2 was targeted for a
close encounter with Miranda, an inner satellite of Uranus;
that, combined with long tracking arcs through the Uranian
system, yielded the first good estimates of masses for the
five largest satellites and an improved mass estimate for
Uranus itself. The Voyager 2 very close near-polar flyby
with Neptune yielded estimates for the zonal harmonic
coefficients J2 and J4 in addition to estimates for the mass
of both Neptune and Triton.
Atmospheric and Ionospheric Radio Occultation Measurements
----------------------------------------------------------
Atmospheric measurements by the method of radio occultation
contribute to an improved understanding of structure,
circulation, dynamics, and transport in atmospheres of remote
planetary bodies. These results are based on detailed
analysis of the radio signal received from the spacecraft as
it enters and exits occultation by the planet. Three phases
of an atmospheric investigation may be defined. The first is
to obtain vertical profiles of atmospheric structure
(temperature and pressure in the neutral atmosphere and
electron density in the ionosphere) with emphasis on large-
scale phenomena. During this stage, it is necessary to know
the mean molecular weight of the atmosphere; for Voyager
the hydrogen-helium mixing ratio could be determined for each
planet using the radio data in conjunction with Voyager IRIS
data. Second is to investigate absorption at various levels
in the atmosphere -- such as by methane. Third is to
study details of the structure, such as result from
propagation of buoyancy waves within a neutral atmosphere or
from alignment of charged particles along magnetic field lines
in an ionosphere.
Retrieval of atmospheric profiles requires coherent
samples of the radio signal that has propagated through
the atmosphere, plus accurate knowledge of the antenna
pointing and the spacecraft trajectory. The spatial and
temporal coverage in radio occultation experiments are
determined by the observing geometry, including the spacecraft
trajectory. For deep atmospheres, changes in antenna pointing
may be required to compensate for refractive bending by the
atmosphere. At Jupiter and Saturn both diametric and grazing
occultations were obtained using the two Voyager spacecraft;
measurements were obtained at both equatorial and polar
latitudes. Voyager 1 also obtained profiles for Titan.
Voyager 2 continued to Uranus and Neptune, and also obtained
occultation profiles at Triton.
Radio Measurements on Planetary Rings
-------------------------------------
Radio occultation measurements of planetary rings are carried
out using procedures similar to those employed for atmospheric
occultations. Although absorption by ring particles must be
considered, the dominant effect on strength of the directly
propagating signal is believed to be conservative scattering--
that is, scattering which disperses the signal in direction
without significant absorption. Profiles of received signal
strength can be inverted to yield the radial distribution of
ring material. Doppler spreading of the signal scattered in
the near-forward direction can be used to infer the particle
size distribution, especially when measurements at the two
Voyager radio wavelengths are combined.
Ring occultations were planned and observed using Voyager 1
at Saturn and Voyager 2 at Uranus. Measurements were carried
out at Neptune using Voyager 2, but no rings or arcs were
detected using the radio system. A post-encounter search for
a radio ring occultation at Jupiter was unsuccessful.
Voyager 2 also carried out an oblique forward scattering
experiment during its Saturn encounter. The spacecraft high-
gain antenna was deflected from the Earth direction so that
it illuminated the ring system; but no scattered signal was
detected.
Solar Conjunction Experiments
-----------------------------
Solar conjunction experiments were conducted to improve
understanding of the structure and dynamics of the solar
corona and wind, to improve understanding of relativistic
effects when radio waves propagate near the Sun, and to test
the different elements of the radio science subsystem.
Approximately once per year, each Voyager spacecraft appeared
to pass behind the solar disk, as seen from Earth. Radio
waves propagating between Voyager and Earth stations were
refracted and scattered (scintillation) by the solar plasma
[WOO1993]. Intensity fluctuations can be related to
fluctuations in electron density along the path, while Doppler
or phase scintillations can be related to both electron
density fluctuations and also the speed of the solar wind.
Many plasma effects decrease as the square of the radio
frequency; plasma effects are about an order of magnitude
stronger at S-band than X-band.
Experimental Relativity
-----------------------
The gravitational field of the Sun causes a time delay on
signals that propagate near the Sun of approximately 300
microseconds. Although previous tests had verified the effect
to an accuracy of a few percent, Voyager measurements could
be conducted annually and at two frequencies, allowing
separation of plasma effects.
Gravitational fields of the gas giant planets also affected
radio signals by causing them to have apparent frequencies
lower than predicted. The change in frequency is related to
the mass of the planet. By measuring the change in frequency
as the spacecraft approached the planet, a value for the mass
could be calculated. This value could then be compared with
the mass derived from two-way tracking data. The spacecraft
Ultra-Stable Oscillator was used for these measurements;
two-way transmissions have nearly canceling frequency shifts
as the signal travels to the spacecraft and then returns. The
dual frequencies available from Voyager allowed correction for
plasma effects along the radio path, but calibration for
radiation damage to the USO during encounters was more
difficult.
Operational Considerations - Spacecraft
=======================================
Descriptions given here are for nominal performance. The
spacecraft transponder system comprised redundant units,
each with slightly different characteristics. As
transponder units age, their performance changes slightly.
More importantly, the performance for radio science depended
on operational factors such as the modulation state for the
transmitters, which cannot be predicted in advance. The
performance also depended on factors which were not always
under the control of the Voyager Project.
Spacecraft receivers were designed to lock to the uplink
signal. Without locking, Doppler effects -- resulting from
relative motion of the spacecraft and ground station -- could
result in loss of the radio link as the frequency of the
received signal drifted. Unfortunately, a series of failures
in the Voyager 2 receivers left that transponder unable to
track the uplink signal. Beginning in April 1978, Doppler
shifts were predicted and the uplink carrier was tuned so
that Voyager 2 would see what appeared to be a signal at
constant frequency (to an accuracy of 100 Hz).
During deep occultations by the giant planets, the bending angle
resulting from refraction exceeded 10 degrees in some cases --
well beyond the half power beamwidth of the spacecraft antenna.
In those cases, the pointing of the HGA was adjusted so that
it followed a 'virtual' Earth and maximum signal strength could
be sustained. These 'limb-track' maneuvers were critically
dependent on accurate timing in the encounter. To protect
against Voyager 1 timing errors at Titan (primarily from
uncertainties in the radius and position of the satellite),
no limb-track was attempted during ingress, and a fixed
antenna offset was used during egress. Fortunately, timing was
accurate enough that useful data were obtained from each event.
Although the spacecraft radioisotope thermoelectric generators
were not dependent on solar flux for power, their output decayed
as the Voyager spacecraft moved outward through the solar
system. During encounters with the outer planets, caution was
required in budgeting power and the high-power mode could not
be used for the radio transmitters.
Calibration Description - Spacecraft
====================================
Prior to and during some encounter sequences, the spacecraft
was commanded to execute a 'mini-ASCAL' maneuver. The HGA was
moved slightly above the Earth line then slightly below the
Earth line. The procedure was repeated to the left and right
of the Earth line so that a 'cross-hair' pattern was mapped
out. During the maneuver, the amplitude of the carrier
signal was measured carefully. Analysis of the results
showed whether the HGA was pointed accurately and, if not,
approximately the error magnitude and direction.
Prior to and after encounters, the spacecraft frequency
reference was switched to the USO for several hours and the
carrier signal was monitored using equipment at the DSN.
These 'USO Tests' were used to calibrate the frequency and
frequency drift of the USO. USO tests were particularly
important before and after the spacecraft entered a severe
radiation environment since the radiation typically damaged
the crystal and changed its characteristics slightly.
Platform Mounting Descriptions - Spacecraft
===========================================
The centerline of the bus was the roll axis of the
spacecraft; it also served as the z-axis of the spacecraft
coordinate system with the high-gain antenna (HGA) boresight
defining the negative z-direction. The HGA boresight was
also defined as cone angle 0 degrees and as azimuth 180
degrees, elevation 7 degrees. The Low-Gain Antenna (LGA)
was mounted on the feed structure of the HGA and radiated
approximately uniformly over the hemisphere into which the
HGA pointed.
Principal Investigators
=======================
The Radio Science Team Leader through the Jupiter encounters
was Von R. Eshleman. The Team Leader for the Saturn, Uranus,
and Neptune encounters was G. Leonard Tyler.
Instrument Section / Operating Mode Descriptions - Spacecraft
=============================================================
The Voyager radio system consisted of two sections, which
could be operated in the following modes:
Section Mode
-------------------------------------------
Oscillator two-way (coherent)
one-way (non-coherent)
RF output low-gain antenna (no information available)
high-gain antenna
Selected parameters describing NASA Standard Transponder (NST)
performance are listed below:
Oscillator Parameters: S-Band X-Band
Two-Way Transponder Turnaround Ratio 240/221 880/221
One-Way Transmit Frequency (MHz) 2296. 8415.
Nominal Wavelength (cm) 13.06 3.56
RF Output parameters: S-Band X-Band
RF Power Output (w) 9 or 26 12 or 22
Low-Gain Antenna:
Half-Power Half Beamwidth (deg) UNK
Gain (dBi) UNK
EIRP (dBm) UNK
Polarization Circular
High-Gain Antenna:
Half-Power Half-Beamwidth (deg) 1.1 0.32
Gain (dBi) 36 47
Polarization RCP RCP or LCP
Instrument Overview - DSN
=========================
Three Deep Space Communications Complexes (DSCCs) (near
Barstow, CA; Canberra, Australia; and Madrid, Spain) comprise
the DSN tracking network. During the Voyager-Saturn era each
complex was equipped with several antennas (including at least
one 64-m and and one 26-m antenna), associated electronics,
and operational systems. Primary activity at each complex
was radiation of commands to and reception of telemetry
data from active spacecraft. Transmission and reception was
possible in several radio-frequency bands, the most common
being S-band (nominally a frequency of 2100-2300 MHz or a
wavelength of 14.2-13.0 cm) and X-band (7100-8500 MHz or 4.2-
3.5 cm). Transmitter output powers up to 400 kw were
available.
Ground stations have the ability to transmit coded and uncoded
waveforms which can be echoed by distant spacecraft. Analysis
of the received coding allows navigators to determine the
distance to the spacecraft; analysis of Doppler shift on the
carrier signal allows estimation of the line-of-sight
spacecraft velocity. Range and Doppler measurements are used
to calculate the spacecraft trajectory and to infer gravity
fields of objects near the spacecraft.
Ground stations can record spacecraft signals that have
propagated through or been scattered from target media.
Measurements of signal parameters after wave interactions with
surfaces, atmospheres, rings, and plasmas are used to infer
physical and electrical properties of the target.
The Deep Space Network is managed by the Jet Propulsion
Laboratory of the California Institute of Technology for the
U.S. National Aeronautics and Space Administration.
Specifications include:
Instrument Id : RSS-VG1S
Instrument Host Id : DSN
Pi Pds User Id : N/A
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : N/A
Instrument Mass : N/A
Instrument Length : N/A
Instrument Width : N/A
Instrument Height : N/A
Instrument Manufacturer Name : N/A
For more information on the Deep Space Network and its use in
radio science investigations see the reports by
[ASMAR&RENZETTI1993], [ASMAR&HERRERA1993], and [ASMARETAL1995].
For design specifications on DSN subsystems see [DSN810-5].
For an example of use of the DSN for Radio Science see
[TYLERETAL1992].
Subsystems - DSN
================
The Deep Space Communications Complexes (DSCCs) are an integral
part of the Radio Science instrument, along with other
receiving stations and the spacecraft Radio Frequency
Subsystem. Their system performance directly determines the
degree of success of Radio Science investigations, and their
system calibration determines the degree of accuracy in the
results of the experiments. The following paragraphs describe
the functions performed by the individual subsystems of a DSCC.
This material has been adapted from [ASMAR&HERRERA1993]; for
additional information, consult [DSN810-5].
Each DSCC includes a set of antennas, signal processing
equipment, and communication links to the Jet Propulsion
Laboratory (JPL). The general configuration is illustrated
below; antennas (Deep Space Stations, or DSS -- a term carried
over from earlier times when antennas were individually
instrumented) are listed in the table.
-------- -------- --------
| DSS 11 | | DSS 12 | | DSS 14 |
| 26-m | | 26-m | | 64-m |
-------- -------- --------
| | |
| v v
| --------------
-------❯|COMMUNICATIONS|
| CENTER |
--------------
|
v
---------- ---------
| NETWORK | | JPL |
|OPERATIONS| | CENTRAL |
| AND |❮--❯| COMM |
| CONTROL | | TERMINAL|
| CENTER | ---------
----------
GOLDSTONE CANBERRA MADRID
Antenna CALIFORNIA AUSTRALIA SPAIN
-------- ---------- --------- --------
26-m DSS 11 DSS 44 DSS 62
26-m DSS 12 DSS 42 DSS 61
64-m DSS 14 DSS 43 DSS 63
Developmental DSS 13
DSCC Transmitter Subsystem
--------------------------
Two transmitters were available at 64-m antennas; output
power of the first could be adjusted over the range 0.2-20 kW,
while the second could be adjusted over 10-100 kW. Nominal
tuning range was 2100-2120 MHz with the -1 dB points at 2110
and 2118 MHz.
Only the 0.2-20 kW transmitter was available at 26-m antennas.
Tuning range was the same.
Multi-Mission Receiver (MMR)
----------------------------
The Multi-Mission Receiver provided four channels of data for
occultations studies during the Voyager encounters at Saturn.
A programmable local oscillator/synthesizer was used to keep
the signal as close to the center of a 10 MHz IF filter as
predictions would permit. The output was sent to the Radio
Science Subsystem for sampling and recording. Filter
bandwidths for S-RCP and S-LCP ring occultations and
scattering observations were 50 kHz; the corresponding
bandwidths for X-RCP and X-LCP were 150 kHz.
For signals with narrower spectral ranges, the 10 MHz IF
output was mixed to 100 kHz where filters as narrow as 100 Hz
could be applied.
DSS Radio Science (DRS) Subsystem
---------------------------------
The Radio Science Subsystem sampled output from the MMR and
recorded it on high-speed analog video tape for later
conversion to computer compatible tape (CCT) formats. Sample
rates for the Voyager 1 Titan and Saturn encounters were 300
ksps on all receiver outputs.
Narrower filters and lower sampling rates could be selected
for special purposes.
DSS Frequency and Timing Subsystem
----------------------------------
Frequency and timing were provided by three references: a
rubidium standard, a hydrogen maser, and a cesium beam
standard. Precisions are shown in the tables below:
Reference Frequency Stability Integration Time
----------------- ------------------- ----------------
Rubidium Standard 5 parts in 10^12 1 second
5 parts in 10^13 100 seconds
5 parts in 10^13 1000 seconds
5 parts in 10^13 12 hours
1 part in 10^11 1 year
Hydrogen Maser 3 parts in 10^13 1 second
2 parts in 10^14 100 seconds
2 parts in 10^14 12 hours
2 parts in 10^13 1 year
Cesium Beam Standard 5 parts in 10^12 1 second
8 parts in 10^13 100 seconds
2.5 parts in 10^13 1000 seconds
8 parts in 10^14 10000 seconds
Station Time relative to the DSN master clock was accurate to
20 microseconds based on rubidium standard synchronization and
to 3 milliseconds based on calibration by HF radio. The DSN
master clock was accurate to 50 microseconds relative to the
National Bureau of Standards, based on calibration using a
portable cesium clock. The DSS frequency offset relative to
the DSN master reference frequency was accurate to 1 part in
10^11 based on rubidium standard or cesium beam standard
synchronization and to 2 parts in 10^13 based on a hydrogen
maser.
Optics - DSN
============
Performance of DSN ground stations depends primarily on size of
the antenna and capabilities of electronics. These are
summarized in the following set of tables. Note that 64-m
antennas were upgraded to 70-m between 1986 and 1989.
Beamwidth is half-power full angular width. Polarization is
circular; L denotes left circular polarization (LCP), and R
denotes right circular polarization (RCP).
DSS Antenna Characteristics
Transmit Receive
--------------- --------------------
Quantity 64-m 26-m 64-m 26-m
-------- ----- ----- ------------ -----
Frequency (MHz) 2110- 2110- 2270- 8400- 2270-
2120 2120 2300 8440 2300
Wavelength (m) 0.142 0.142 0.131 0.036 0.131
Gain (dBi) 60.7 51.8 61.7 71.3 53.2
Beamwidth (deg) 0.15 0.36 0.14 0.038 0.33
Polarization RCP RCP RCP RCP RCP
LCP LCP LCP LCP LCP
LIN LIN LIN
CP Ellipticity (dB) 2.2 1.0 0.28 1.0 0.4
SNT-TWM1-unspec (K) 25 33
-diplex (K) 22
-orthog (K) 18
-TWM2-unspec (K) 41
-diplex (K) 26
-orthog (K) 23
Notes: (1) DSS 14 receive gain was 71.3 dB at X-band; but
gain at DSS 43 and DSS 63 was 71.8 dB
(2) Polarizations available at 64-m antennas were
RCP and LCP (simultaneously) or rotatable linear.
Polarizations available at 26-m antennas were
RCP or LCP or fixed linear.
Electronics - DSN
=================
DSCC Open-Loop Receiver (RIV)
-----------------------------
The open loop receiver block diagrams below show the Modified
Block III Open-Loop Receiver (DSS 14 and 43) and the
Narrowband Multi-Mission Receiver (MMR) (DSS 63) used during
early Voyager encounters. Only the S-band block diagrams are
shown; expressions for reconstructing both S- and X-band
signal frequencies (Fs and Fx, respectively) from the
observed output frequencies (Folr) are given below the
diagrams.
DSS 14 and 43 DSS 63
S-Band S-Band
2295 MHz 2295 MHz
Input Input
| |
v v
--- --- --- ---
| X |❮--|x48|❮-- ~46 MHz ~41 MHz--❯|x48|--❯| X |
--- --- --- ---
| |
50| |300
MHz| |MHz
v v
--- ---
| X |❮-- 60 MHz 290 MHz --❯| X |
--- ---
| |
10| |10
MHz| |MHz
v v
--- ---
| X |❮-- 10 MHz 10 MHz --❯| X |
--- ---
| |
v v
Output Output
Reconstruction of the antenna frequency from the frequency of
the signal in the recorded data can be achieved through use
of one of the following formulas. Frequency of the
Programmable Oscillator Control Assembly (Fpoca) is
approximately 46 MHz at DSS 14 and 43 and approximately
41 MHz at DSS 63.
DSS 14 and 43
Fs = 48*Fpoca + 50*10^6 - Folr
Fx = (11/3)*(48*Fpoca + 50*10^6) - Folr
DSS 63
Fs = 48*Fpoca + 300*10^6 + Folr
Fx = (11/3)*(48*Fpoca + 300*10^6) + Folr
Filters - DSN
=============
DSCC Open-Loop Receiver (RIV)
-----------------------------
Filters (usually at the 10 MHz intermediate frequency) could
be selected by the user to match expected width of the signal
or uncertainty in its location. Filters and sampling rates
used during the Voyager Saturn encounters were:
DSS 43 DSS 63
------------------ -------------------
3 dB Sample 3 dB Sample
Bandwidth Rate Bandwidth Rate
--------- ------- --------- --------
S-band 4.1 kHz 10 ksps 50. kHz 300 ksps
X-band 15.0 kHz 30 ksps 150. kHz 300 ksps
Detectors - DSN
===============
DSCC Open-Loop Receivers
------------------------
Open-loop receiver output is detected in software by the
radio science investigator.
DSCC Closed-Loop Receivers
--------------------------
Nominal carrier tracking loop threshold noise bandwidths at
S- and X-band were 10-12 and 30 Hz, respectively. Sample
rates for Doppler were 1-10 per second.
Calibration - DSN
=================
Calibrations of hardware systems are carried out periodically
by DSN personnel; these ensure that systems operate at required
performance levels -- for example, that antenna patterns,
receiver gain, propagation delays, and Doppler uncertainties
meet specifications. No information on specific calibration
activities is available. Nominal performance specifications
are shown in the tables above. Additional information may be
available in [DSN810-5].
Prior to each tracking pass, station operators perform a series
of calibrations to ensure that systems meet specifications for
that operational period. Included in these calibrations is
measurement of receiver system temperature in the configuration
to be employed during the pass. Results of these calibrations
are recorded in (hard copy) Controller's Logs for each pass.
Filters for the Open-Loop Receivers were checked during the
Test and Calibration period after the Titan and Saturn
observations concluded. A test signal was injected at a
constant frequency, then stepped across the passband to measure
filter gain at discrete frequencies.
Operational Considerations - DSN
================================
The DSN is a complex and dynamic 'instrument.' Its performance
for Radio Science depends on a number of factors from equipment
configuration to meteorological conditions. No specific
information on 'operational considerations' can be given here.
Operational Modes - DSN
=======================
Closed-Loop vs. Open-Loop Reception
-----------------------------------
Radio Science data can be collected in two modes: closed-
loop, in which a phase-locked loop receiver tracks the
spacecraft signal, or open-loop, in which a receiver samples
and records a band within which the desired signal presumably
resides. Closed-loop data are collected using Closed-Loop
Receivers, and open-loop data are collected using Open-Loop
Receivers in conjunction with the DSCC Spectrum Processing
Subsystem (DSP). See the Subsystems section for further
information.
Closed-Loop Receiver AGC Loop
-----------------------------
The closed-loop receiver AGC loop can be configured to one of
three settings: narrow, medium, or wide. Ordinarily it is
configured so that expected signal amplitude changes are
accommodated with minimum distortion. The loop bandwidth is
ordinarily configured so that expected phase changes can be
accommodated while maintaining the best possible loop SNR.
Coherent vs. Non-Coherent Operation
-----------------------------------
The frequency of the signal transmitted from the spacecraft
can generally be controlled in two ways -- by locking to a
signal received from a ground station or by locking to an
on-board oscillator. These are known as the coherent (or
'two-way') and non-coherent ('one-way') modes, respectively.
Mode selection is made at the spacecraft, based on commands
received from the ground. When operating in the coherent
mode, the transponder carrier frequency is derived from the
received uplink carrier frequency with a 'turn-around ratio'
typically of 240/221. In the non-coherent mode, the
downlink carrier frequency is derived from the spacecraft
on-board crystal-controlled oscillator. Either closed-loop
or open-loop receivers (or both) can be used with either
spacecraft frequency reference mode. Closed-loop reception
in two-way mode is usually preferred for routine tracking.
Occasionally the spacecraft operates coherently while two
ground stations receive the 'downlink' signal; this is
sometimes known as the 'three-way' mode.
Open-Loop Sampling
------------------
The Open-Loop Receiver sampling system can operate in four
sampling modes with from 1 to 4 input signals. Input
channels are assigned to ADC inputs during configuration.
Modes are summarized in the tables below:
Mode Analog-to-Digital Operation
---- ----------------------------
1 4 signals, each sampled by a single ADC
2 1 signal, sampled sequentially by 4 ADCs
3 2 signals, each sampled sequentially by 2 ADCs
4 2 signals, the first sampled by ADC #1 and the second
sampled sequentially at 3 times the rate
by ADCs #2-4
Location - DSN
==============
Station locations are documented in [GEO-10REVD]. Geocentric
coordinates are summarized here.
Geocentric Geocentric Geocentric
Station Radius (km) Latitude (N) Longitude (E)
--------- ----------- ------------ -------------
Goldstone
DSS 12 (26-m STD) 6371.997815 35.1186672 243.1945048
DSS 13 (develop) 6372.117062 35.0665485 243.2051077
DSS 14 (64-m) 6371.992867 35.2443514 243.1104584
Canberra
DSS 42 (26-m STD) 6371.675607 -35.2191850 148.9812546
DSS 43 (64-m) 6371.688953 -35.2209308 148.9812540
Madrid
DSS 61 (26-m STD) 6370.027734 40.2388805 355.7509634
DSS 63 (64-m) 6370.051015 40.2413495 355.7519776
Measurement Parameters - DSN
============================
Open-Loop System
----------------
Sampled output from the Open-Loop Receivers (OLRs) is a stream
of 8-bit quantized voltage samples. The nominal input to
the Analog-to-Digital Converters (ADCs) is +/-10 volts, but
the precise scaling between input voltages and output
digitized samples is usually irrelevant for analysis; the
digital data are generally referenced to a known noise or
signal level within the data stream itself -- for example,
the thermal noise output of the radio receivers which has a
known system noise temperature (SNT). Raw samples comprise
the data block in each data record; a header record
contains ancillary information such as time tag for the
first sample in the data block.
Closed-Loop System
------------------
Closed-loop data are recorded in Archival Tracking Data Files
(ATDFs), as well as certain secondary products such as the
Orbit Data File (ODF). The ATDF Tracking Logical Record
contains entries including status information and
measurements of ranging, Doppler, and signal strength.
ACRONYMS AND ABBREVIATIONS - DSN
================================
ACS Antenna Control System
ADC Analog-to-Digital Converter
AMS Antenna Microwave System
APA Antenna Pointing Assembly
ARA Area Routing Assembly
ATDF Archival Tracking Data File
AZ Azimuth
CMC Complex Monitor and Control
CONSCAN Conical Scanning (antenna pointing mode)
CRG Coherent Reference Generator
CUL Clean-up Loop
DANA a type of frequency synthesizer
dB decibel
dBi dB relative to isotropic
dBm dB relative to one milliwatt
DCO Digitally Controlled Oscillator
DEC Declination
deg degree
DMC DSCC Monitor and Control Subsystem
DSCC Deep Space Communications Complex
DSN Deep Space Network
DSP DSCC Spectrum Processing Subsystem
DSS Deep Space Station
DTK DSCC Tracking Subsystem
E east
EL Elevation
FTS Frequency and Timing Subsystem
GCF Ground Communications Facility
GPS Global Positioning System
HA Hour Angle
HEF High-Efficiency (as in 34-m HEF antennas)
IF Intermediate Frequency
IVC IF Selection Switch
JPL Jet Propulsion Laboratory
K Kelvin
kHz kilohertz
km kilometer
ksps kilosamples per second
kW kilowatt
L-band approximately 1668 MHz
LAN Local Area Network
LCP Left-Circularly Polarized
LMC Link Monitor and Control
LNA Low-Noise Amplifier
LO Local Oscillator
m meters
MCA Master Clock Assembly
MCCC Mission Control and Computing Center
MDA Metric Data Assembly
MHz Megahertz
MMR Multi-Mission Receiver
MON Monitor and Control System
MSA Mission Support Area
N north
NAR Noise Adding Radiometer
NBOC Narrow-Band Occultation Converter
NIST SPC 10 time relative to UTC
NIU Network Interface Unit
NOCC Network Operations and Control System
NSS NOCC Support System
OCI Operator Control Input
ODF Orbit Data File
ODR Original Data Record
ODS Original Data Stream
OLR Open Loop Receiver
POCA Programmable Oscillator Control Assembly
PPM Precision Power Monitor
RA Right Ascension
REC Receiver-Exciter Controller
RCP Right-Circularly Polarized
RF Radio Frequency
RIC RIV Controller
RIV Radio Science IF-VF Converter Assembly
RMDCT Radio Metric Data Conditioning Team
RTLT Round-Trip Light Time
S-band approximately 2100-2300 MHz
sec second
SEC System Error Correction
SIM Simulation
SLE Signal Level Estimator
SNR Signal-to-Noise Ratio
SNT System Noise Temperature
SOE Sequence of Events
SPA Spectrum Processing Assembly
SPC Signal Processing Center
SRA Sequential Ranging Assembly
SRC Sub-Reflector Controller
SSI Spectral Signal Indicator
STD Standard (as in 34-m STD antennas)
TID Time Insertion and Distribution Assembly
TSF Tracking Synthesizer Frequency
TWM Traveling Wave Maser
UNK unknown
UTC Universal Coordinated Time
VF Video Frequency
X-band approximately 7800-8500 MHz"
END_OBJECT = INSTRUMENT_INFORMATION
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "ALLAN1966"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "ASMAR&HERRERA1993"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "ASMAR&RENZETTI1993"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "ASMARETAL1995"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "DSN810-5"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "ESHLEMANETAL1977"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "GEO-10REVD"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "TYLERETAL1992"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "WOO1993"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
END_OBJECT = INSTRUMENT
END
|