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OBJECT = INSTRUMENT
INSTRUMENT_HOST_ID = GO
INSTRUMENT_ID = RSS
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INSTRUMENT_NAME = "RADIO SCIENCE SUBSYSTEM"
INSTRUMENT_TYPE = "RADIO SCIENCE"
INSTRUMENT_DESC = "
Instrument Overview
===================
Galileo Radio Science investigations utilized instrumentation
with elements on the spacecraft and at the Deep Space Network
(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; that is followed by a
description of the DSN (ground) part of the instrument.
Radio Science investigations were carried out by two teams.
The Celestial Mechanics Team, under Team Leader John Anderson,
conducted experimental tests of general relativity (including
searching for gravitational waves), made measurements to
improve solar system ephemerides, and sought to improve
gravitational models for Jupiter and its satellites
[ANDERSONETAL1992]. The Radio Propagation Team, under Team
Leader Tay Howard, investigated the solar corona and carried
out various studies in the Jovian system primarily concerning
atmospheres and ionospheres [HOWARDETAL1992].
Instrument Specifications - Spacecraft
======================================
The Galileo spacecraft telecommunications subsystem served
as part of a radio science subsystem for investigations
primarily of Jupiter and its satellites, but also including
Venus, the Earth-Moon system, and the Sun. Many details of
the subsystem are unknown; its 'build date' is taken to be
1989-01-01, which was during the prelaunch phase of the
Galileo mission.
Instrument Id : RSS
Instrument Host Id : GO
Pi Pds User Id : UNK
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : 1989-01-01
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 which received and
transmitted at both S-band (2.3 GHz, 13 cm wavelength) and
X-band (8.4 GHz, 3.6 cm wavelength) frequencies; the
following combinations of uplink/downlink were supported by
the design: S/S, X/X, S/X and S.
The exact frequency transmitted from the spacecraft was
controlled by the signal received from a ground station
('two-way' or 'coherent' mode) or by an on-board oscillator
('one-way' or 'non-coherent' mode). In some circumstances
an uplink signal was transmitted from one ground station
while two ground stations participated in reception; this was
known as the 'three-way' mode. In the absence of an uplink
signal, the spacecraft system switched automatically to the
one-way mode. The on-board frequency reference could be
either of two redundant 'auxiliary' crystal oscillators or
a single ultra-stable oscillator (USO) provided specifically
to support radio science observations.
Each transponder included a receiver, command detector,
exciter, and low-power amplifier. The transponders provided
the usual uplink command and downlink data transmission
capabilities. The following modulation states could be
commanded: telemetry alone, ranging alone, telemetry and
ranging, or carrier only.
Each transponder could be operated through one of two
low-gain antennas at S-band only; a furlable high-gain
antenna (HGA) never deployed properly during Cruise,
resulting in a serious degradation of radio science
measurements, including loss of X-band capability. The HGA
was aligned with the spin axis of the rotor part of the
spacecraft. Low-Gain Antenna 1 (LGA-1) was located at the
end of the HGA feed, so it is also aligned with the spin axis.
LGA-2 was at the end of a boom, 3.52 m from the spin axis.
When operating in the coherent mode, the transponder downlink
frequency was related to the uplink frequency by the
'turn-around ratio' of 240/221 at S-band. At X-band it would
have been 880/749. An X-band downlink controlled by an S-band
uplink would have had a turn-around ratio of (240/221)*(11/3).
Science Objectives
==================
Two different types of radio science measurements were
conducted with the Galileo Orbiter: radio tracking in which
the magnitude and direction of gravitational forces could be
derived from 'closed-loop' Doppler (and, sometimes, ranging)
measurements, and radio propagation experiments in which
modulation on the signal received at Earth stations
could be attributed to properties of the intervening medium.
The radio science measurements were analyzed by two
investigation teams; the Celestial Mechanics Team was
primarily interested in characterizing variations in
gravitational forces, and the Radio Propagation Team was
primarily interested in the atmospheres of the Sun, Jupiter,
and Jupiter's satellites.
Gravity Measurements
--------------------
Measurement of the gravity field provides significant
constraints on inferences about interior structure of
Jupiter and its satellites. Precise, detailed study of
spacecraft motion in Jupiter orbit and during satellite
flybys can yield a mass distribution of each body and
higher-order field terms if the measurements are sensitive
enough. Compared with determinations from previous missions,
improvements in the gravity field of Jupiter itself were not
expected from tracking the Galileo Orbiter, but second-order
gravity harmonics were expected from flyby encounters with
satellites. One equatorial and one polar flyby at Ganymede
were sought to determine independently the rotational and
tidal response of the body assuming hydrostatic equilibrium.
Departures from hydrostatic equilibrium were expected to
confuse that issue at Europa, though the measurements were
expected to be useful, while the relatively weak response
to rotation and tides at Callisto made the experiment most
marginal there [HUBBARD&ANDERSON1978]. Differences in
principal moments of inertia to an accuracy of one percent
or better were sought at Io [ANDERSONETAL1996].
Tests of General Relativity
---------------------------
There has been continuing interest in testing the theory
of general relativity by bouncing radar signals from hard
planetary surfaces and using two-way ranging data from
spacecraft anchored to other planetary bodies. No hard
surface exists at Jupiter and no previous spacecraft had
orbited the planet, so Galileo represented a unique
opportunity to investigate this question. Two years of
ranging to Galileo were expected to fix the range to Jupiter
to an accuracy of about 150 m, with the limit set by orbit
determination error along the Earth-Jupiter line and not by
limitations of the radio 'instrument'. In combination with
results from the Pioneer and Voyager spacecraft, these
measurements were expected to lead to an improved ephemeris
for Jupiter.
As Jupiter (and Galileo) appear to pass behind the Sun when
viewed from Earth, solar gravity should retard the radio
signal propagating between the spacecraft and Earth. One
set of time delay measurements to/from the Viking Orbiters
and Landers agreed to within 0.1 percent of the General
Relativity prediction. Measurements with Galileo were
expected to be a factor of 5 worse, but the next best
measurements were only to 2 percent of the General Relativity
prediction. Not only would another set of measurements at
the sub-one percent level be good experimental practice,
but Galileo measurements could also verify the agreement
over a range of directions in inertial space [WILL1981].
The red shift of the signal in Jupiter's gravitational field
could be measured to an accuracy of about +/-1 percent after
radiation hardening of the USO crystal in Jupiter's charged
particle environment.
Search for Gravitational Radiation
----------------------------------
Matter undergoing asymmetrical motion (theoretically) radiates
gravitational waves which propagate at the velocity of light.
Observed acceleration of the mean orbital motion of binary
pulsar PSR 1913+16 is consistent with predictions
[TAYLOR&WEISBERG1989]; other evidence is more ambiguous, and
gravity waves themselves had not been detected with certainty
before Galileo. For several extended periods during Galileo's
cruise to Jupiter, when other spacecraft activity was at a
minimum and when the spacecraft was near opposition, its radio
link with Earth was monitored carefully for signs of passing,
cosmicly generated, long period gravitational waves. Similar
observations were conducted simultaneously with the Mars
Observer and Ulysses spacecraft so that detections could be
confirmed and direction of propagation of the gravitational
waves inferred from time differences along other paths.
Previous searches have been conducted using Viking, Voyager,
and Pioneers 10 and 11 [ARMSTRONG1989].
Solar Corona Observations
-------------------------
For several weeks around each of four superior conjunctions
Galileo's radio link passed through the solar corona.
Signals were scattered and refracted as they propagated
through the turbulent plasma; the resulting modulation could
be analyzed to obtain estimates of coronal structure and
dynamics [WOO1993]. Specific objectives of the Galileo solar
corona experiments included better understanding of:
(1) three-dimensional electron density distribution and its
relation to the photospheric magnetic field
configuration, solar cycle, distance from the surface,
and solar latitude;
(2) structural differences among coronal 'holes', active
regions, and the 'quiet' Sun;
(3) characteristics of the acceleration regions of the solar
wind in coronal holes, streamers, and other parts of the
corona;
(4) energy sources responsible for creation of coronal
materials with temperatures over 1000000K;
(5) resonant solar oscillations on the dynamical
characteristics of the tenuous solar atmosphere;
(6) excitation and propagation conditions for
magnetoacoustic, Alfven, and other waves; and
(7) form and evolution of disturbances near the Sun and
their relationship to white light coronal mass
ejections.
Jupiter Occultations
--------------------
Radio occultation measurements can contribute to an improved
understanding of structure, circulation, dynamics, and
transport in the atmosphere of Jupiter. Results from Galileo
were based on detailed analysis of the radio signal as it
entered and exited occultation by the planet. Three phases
of the atmospheric investigation may be defined. The first
is to obtain vertical profiles of electron content in the
ionosphere; second is to extract large scale structure in
the neutral atmosphere; third is to detect and interpret fine
scale structure in both the ionospheric and neutral
atmosphere profiles and to measure absorption in the neutral
atmosphere.
The Galileo tour permitted radio occultations on approximately
half of the planned orbits at a number of latitudes. Pioneers
10 and 11 had earlier shown sharp, multiple, dense, low-lying
ionospheric layers [FJELDBOETAL1976]. The vertical extent of
the ionized layers, their time histories, and detailed
structure were sought as keys to both the composition and
chemistry of the upper atmosphere.
With precise pointing of the HGA, Galileo was expected to
penetrate below the condensation level for ammonia in the
neutral atmosphere, providing global measures of ammonia
concentration in well-mixed regions where Voyager had produced
only one [LINDALETAL1981]. Measurements between 15N and 15S
latitudes were expected to provide snapshots of vertical
structure of waves propagating in the atmosphere; ingress and
egress measurements from the same occultation could provide
strong constraints on zonal wavenumber and meridional
structure [HINSON&MAGALHAES1991].
Satellite Occultations
----------------------
Radio data acquired during occultation by a satellite could
be used to determine its diameter to accuracies on the order
of 1 km and, possibly, properties of any satellite atmosphere
or ionosphere. In the case of Io a substantial ionosphere
had been detected by Pioneer 10 [KLIOREETAL1975]; repeated
occultations by Io were intended to improve understanding
of spatial and temporal variability of the charged particles
and their interaction with Jupiter's magnetic field.
Occultations by the Io torus would provide a measure of the
total number of free electrons along the propagation path,
a useful constraint of the spatial structure of the torus.
Jupiter's Magnetic Field
------------------------
Galileo was the first spacecraft equipped to measure both
Faraday rotation of propagating waves and differential phase
retardation between S- and X-band. Faraday rotation
measurements were planned during each occultation by Jupiter
and were to be used to investigate the characteristics of
the magnetic field in the planet's ionosphere. Different
models of the magnetic field yield differences in the
predicted Faraday rotation on the order of 0.3 radians; the
Faraday rotation experiment designed for Galileo
exceeded this threshold by a factor of 10.
Bistatic Scattering from Icy Galilean Moons
-------------------------------------------
Monostatic radar echoes from Europa, Ganymede, and Callisto
were found to be anomalously diffuse, strong, and polarized
[CAMPBELLETAL1978]. By using the Galileo spacecraft as a
microwave signal source during encounters with each of these
bodies, the bistatic scattering as a function of angle could
be determined, providing constraints on both the models for
the anomalous scattering process and also the properties of
the ice that presumably is responsible.
Operational Considerations - Spacecraft
=======================================
Because the HGA never deployed and only right-circularly
polarized signals at S-band were available from LGA-1, the
Faraday and dual-frequency measurements were never realized.
For the Celestial Mechanics Team, the single frequency meant
that signal dispersion resulting from passage through the
solar wind, Earth's ionosphere, and other media could not
be removed easily from data. For the Radio Propagation Team,
the loss of antenna gain meant that only observations with
the strongest signals could be made. Penetration below the
ionosphere during Jupiter occultations and sensing charged
and neutral particle environments of satellites became very
difficult, and the bistatic surface experiments were dropped.
Because Faraday Rotation experiments required linearly
transmitted polarizations (available only from the HGA),
those were also dropped.
Calibration Description - Spacecraft
====================================
No information available.
Platform Mounting Descriptions - Spacecraft
===========================================
The HGA and LGA-1 antennas were mounted facing in the negative
Zr direction; see the GO_SPACECRAFT_DESC_INST.CAT file for
more information.
Principal Investigators
=======================
The Team Leader for the Celestial Mechanics Team was John D.
Anderson of the Jet Propulsion Laboratory. Team members
were (all from JPL):
J.W. Armstrong
J.K. Campbell
F.B. Estabrook
T.P. Krisher
E.L. Lau
The Team Leader for the Radio Propagation Team was H. Taylor
Howard of Stanford University. Team members and affiliations
were:
V.R. Eshleman Stanford University
D.P. Hinson Stanford University
A.J. Kliore Jet Propulsion Laboratory
G.F. Lindal Jet Propulsion Laboratory
R. Woo Jet Propulsion Laboratory
M.K. Bird University of Bonn, Germany
H. Volland University of Bonn, Germany
P. Edenhofer University of Bochum, Germany
M. Paetzold DFLR, Germany
H. Porsche DFLR, Germany
Experiment Representative at JPL for both teams was Randy
Herrera.
Instrument Section / Operating Mode Descriptions - Spacecraft
=============================================================
The Galileo 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 (choice from two)
high-gain antenna (failed to deploy properly)
Details for the radio system, as designed, are given in the
table below:
Transmitting Parameters:
Frequency (MHz) 8415 2295
Transmit Power (w) 12 or 21 9 or 27
HGA Gain (dBi) 50 38
HGA Half-Power Beamwidth (deg) 0.6 1.5
Polarization LCP or RCP Linear
Axial Ratio (dB) 2 32
Receiving Parameters:
Frequency (MHz) 7167 2115
HGA Gain (dBi) 46 36
Polarization LCP or RCP Linear
Noise Temperature (K) 270 1000
Instrument Overview - DSN
=========================
Three Deep Space Communications Complexes (DSCCs) (near
Barstow, CA; Canberra, Australia; and Madrid, Spain) comprise
the DSN tracking network. Each complex is equipped with
several antennas [including at least one each 70-m, 34-m High
Efficiency (HEF), and 34-m standard (STD)], associated
electronics, and operational systems. Primary activity at each
complex is radiation of commands to and reception of telemetry
data from active spacecraft. Transmission and reception is
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 of up to 400 kw are
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.
Principal investigators vary from experiment to experiment.
See the corresponding section of the spacecraft instrument
description or the data set description for specifics.
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
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] and [ASMAR&HERRERA1993]. 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, a Signal Processing
Center (SPC), 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 12 | | DSS 18 | | DSS 14 | | DSS 15 | | DSS 16 |
|34-m STD| |34-m STD| | 70-m | |34-m HEF| | 26-m |
-------- -------- -------- -------- --------
| | | | |
| v v | v
| --------- | ---------
--------->|GOLDSTONE|<---------- |EARTH/ORB|
| SPC 10 |<-------------->| LINK |
--------- ---------
| SPC |<-------------->| 26-M |
| COMM | ------>| COMM |
--------- | ---------
| | |
v | v
------ --------- | ---------
| NOCC |<--->| JPL |<------- | |
------ | CENTRAL | | GSFC |
------ | COMM | | NASCOM |
| MCCC |<--->| TERMINAL|<-------------->| |
------ --------- ---------
^ ^
| |
CANBERRA (SPC 40) <---------------- |
|
MADRID (SPC 60) <----------------------
GOLDSTONE CANBERRA MADRID
Antenna SPC 10 SPC 40 SPC 60
-------- --------- -------- --------
26-m DSS 16 DSS 46 DSS 66
34-m STD DSS 12 DSS 42 DSS 61
DSS 18 DSS 48 DSS 68
34-m HEF DSS 15 DSS 45 DSS 65
70-m DSS 14 DSS 43 DSS 63
Developmental DSS 13
Subsystem interconnections at each DSCC are shown in the
diagram below, and they are described in the sections that
follow. The Monitor and Control Subsystem is connected to all
other subsystems; the Test Support Subsystem can be.
----------- ------------------ --------- ---------
|TRANSMITTER| | | | TRACKING| | COMMAND |
| SUBSYSTEM |-| RECEIVER/EXCITER |-|SUBSYSTEM|-|SUBSYSTEM|-
----------- | | --------- --------- |
| | SUBSYSTEM | | | |
----------- | | --------------------- |
| MICROWAVE | | | | TELEMETRY | |
| SUBSYSTEM |-| |-| SUBSYSTEM |-
----------- ------------------ --------------------- |
| |
----------- ----------- --------- -------------- |
| ANTENNA | | MONITOR | | TEST | | DIGITAL | |
| SUBSYSTEM | |AND CONTROL| | SUPPORT | |COMMUNICATIONS|-
----------- | SUBSYSTEM | |SUBSYSTEM| | SUBSYSTEM |
----------- --------- --------------
DSCC Monitor and Control Subsystem
----------------------------------
The DSCC Monitor and Control Subsystem (DMC) is part of the
Monitor and Control System (MON) which also includes the
ground communications Central Communications Terminal and the
Network Operations Control Center (NOCC) Monitor and Control
Subsystem. The DMC is the center of activity at a DSCC. The
DMC receives and archives most of the information from the
NOCC needed by the various DSCC subsystems during their
operation. Control of most of the DSCC subsystems, as well
as the handling and displaying of any responses to control
directives and configuration and status information received
from each of the subsystems, is done through the DMC. The
effect of this is to centralize the control, display, and
archiving functions necessary to operate a DSCC.
Communication between the various subsystems is done using a
Local Area Network (LAN) hooked up to each subsystem via a
network interface unit (NIU).
DMC operations are divided into two separate areas: the
Complex Monitor and Control (CMC) and the Link Monitor and
Control (LMC). The primary purpose of the CMC processor for
Radio Science support is to receive and store all predict
sets transmitted from NOCC such as Radio Science, antenna
pointing, tracking, receiver, and uplink predict sets and
then, at a later time, to distribute them to the appropriate
subsystems via the LAN. Those predict sets can be stored in
the CMC for a maximum of three days under normal conditions.
The CMC also receives, processes, and displays event/alarm
messages; maintains an operator log; and produces tape labels
for the DSP. Assignment and configuration of the LMCs is
done through the CMC; to a limited degree the CMC can perform
some of the functions performed by the LMC. There are two
CMCs (one on-line and one backup) and three LMCs at each DSCC
The backup CMC can function as an additional LMC if
necessary.
The LMC processor provides the operator interface for monitor
and control of a link -- a group of equipment required to
support a spacecraft pass. For Radio Science, a link might
include the DSCC Spectrum Processing Subsystem (DSP) (which,
in turn, can control the SSI), or the Tracking Subsystem.
The LMC also maintains an operator log which includes
operator directives and subsystem responses. One important
Radio Science specific function that the LMC performs is
receipt and transmission of the system temperature and signal
level data from the PPM for display at the LMC console and
for inclusion in Monitor blocks. These blocks are recorded
on magnetic tape as well as appearing in the Mission Control
and Computing Center (MCCC) displays. The LMC is required to
operate without interruption for the duration of the Radio
Science data acquisition period.
The Area Routing Assembly (ARA), which is part of the Digital
Communications Subsystem, controls all data communication
between the stations and JPL. The ARA receives all required
data and status messages from the LMC/CMC and can record them
to tape as well as transmit them to JPL via data lines. The
ARA also receives predicts and other data from JPL and passes
them on to the CMC.
DSCC Antenna Mechanical Subsystem
---------------------------------
Multi-mission Radio Science activities require support from
the 70-m, 34-m HEF, and 34-m STD antenna subnets. The
antennas at each DSCC function as large-aperture collectors
which, by double reflection, cause the incoming radio
frequency (RF) energy to enter the feed horns. The large
collecting surface of the antenna focuses the incoming energy
onto a subreflector, which is adjustable in both axial and
angular position. These adjustments are made to correct for
gravitational deformation of the antenna as it moves between
zenith and the horizon; the deformation can be as large as
5 cm. The subreflector adjustments optimize the channeling
of energy from the primary reflector to the subreflector
and then to the feed horns. The 70-m and 34-m HEF antennas
have 'shaped' primary and secondary reflectors, with forms
that are modified paraboloids. This customization allows
more uniform illumination of one reflector by another. The
34-m STD primary reflectors are classical paraboloids, while
the subreflectors are standard hyperboloids.
On the 70-m and 34-m STD antennas, the subreflector directs
received energy from the antenna onto a dichroic plate, a
device which reflects S-band energy to the S-band feed horn
and passes X-band energy through to the X-band feed horn. In
the 34-m HEF, there is one 'common aperture feed,' which
accepts both frequencies without requiring a dichroic plate.
RF energy to be transmitted into space by the horns is
focused by the reflectors into narrow cylindrical beams,
pointed with high precision (either to the dichroic plate or
directly to the subreflector) by a series of drive motors and
gear trains that can rotate the movable components and their
support structures.
The different antennas can be pointed by several means. Two
pointing modes commonly used during tracking passes are
CONSCAN and 'blind pointing.' With CONSCAN enabled and a
closed loop receiver locked to a spacecraft signal, the
system tracks the radio source by conically scanning around
its position in the sky. Pointing angle adjustments are
computed from signal strength information (feedback) supplied
by the receiver. In this mode the Antenna Pointing Assembly
(APA) generates a circular scan pattern which is sent to the
Antenna Control System (ACS). The ACS adds the scan pattern
to the corrected pointing angle predicts. Software in the
receiver-exciter controller computes the received signal
level and sends it to the APA. The correlation of scan
position with the received signal level variations allows the
APA to compute offset changes which are sent to the ACS.
Thus, within the capability of the closed-loop control
system, the scan center is pointed precisely at the apparent
direction of the spacecraft signal source. An additional
function of the APA is to provide antenna position angles and
residuals, antenna control mode/status information, and
predict-correction parameters to the Area Routing Assembly
(ARA) via the LAN, which then sends this information to JPL
via the Ground Communications Facility (GCF) for antenna
status monitoring.
During periods when excessive signal level dynamics or low
received signal levels are expected (e.g., during an
occultation experiment), CONSCAN should not be used. Under
these conditions, blind pointing (CONSCAN OFF) is used, and
pointing angle adjustments are based on a predetermined
Systematic Error Correction (SEC) model.
Independent of CONSCAN state, subreflector motion in at least
the z-axis may introduce phase variations into the received
Radio Science data. For that reason, during certain
experiments, the subreflector in the 70-m and 34-m HEFs may
be frozen in the z-axis at a position (often based on
elevation angle) selected to minimize phase change and signal
degradation. This can be done via Operator Control Inputs
(OCIs) from the LMC to the Subreflector Controller (SRC)
which resides in the alidade room of the antennas. The SRC
passes the commands to motors that drive the subreflector to
the desired position. Unlike the 70-m and 34-m HEFs which
have azimuth-elevation (AZ-EL) drives, the 34-m STD antennas
use (hour angle-declination) HA-DEC drives. The same
positioning of the subreflector on the 34-m STD does not
create the same effect as on the 70-m and 34-m HEFs.
Pointing angles for all three antenna types are computed by
the NOCC Support System (NSS) from an ephemeris provided by
the flight project. These predicts are received and archived
by the CMC. Before each track, they are transferred to the
APA, which transforms the direction cosines of the predicts
into AZ-EL coordinates for the 70-m and 34-m HEFs or into
HA-DEC coordinates for the 34-m STD antennas. The LMC
operator then downloads the antenna AZ-EL or HA-DEC predict
points to the antenna-mounted ACS computer along with a
selected SEC model. The pointing predicts consist of
time-tagged AZ-EL or HA-DEC points at selected time intervals
along with polynomial coefficients for interpolation between
points.
The ACS automatically interpolates the predict points,
corrects the pointing predicts for refraction and
subreflector position, and adds the proper systematic error
correction and any manually entered antenna offsets. The ACS
then sends angular position commands for each axis at the
rate of one per second. In the 70-m and 34-m HEF, rate
commands are generated from the position commands at the
servo controller and are subsequently used to steer the
antenna. In the 34-m STD antennas motors, rather than
servos, are used to steer the antenna; there is no feedback
once the 34-m STD has been told where to point.
When not using binary predicts (the routine mode for
spacecraft tracking), the antennas can be pointed using
'planetary mode' -- a simpler mode which uses right ascension
(RA) and declination (DEC) values. These change very slowly
with respect to the celestial frame. Values are provided to
the station in text form for manual entry. The ACS
quadratically interpolates among three RA and DEC points
which are on one-day centers.
A third pointing mode -- sidereal -- is available for
tracking radio sources fixed with respect to the celestial
frame.
Regardless of the pointing mode being used, a 70-m antenna
has a special high-accuracy pointing capability called
'precision' mode. A pointing control loop derives the
main AZ-EL pointing servo drive error signals from a two-
axis autocollimator mounted on the Intermediate Reference
Structure. The autocollimator projects a light beam to a
precision mirror mounted on the Master Equatorial drive
system, a much smaller structure, independent of the main
antenna, which is exactly positioned in HA and DEC with shaft
encoders. The autocollimator detects elevation/cross-
elevation errors between the two reference surfaces by
measuring the angular displacement of the reflected light
beam. This error is compensated for in the antenna servo by
moving the antenna in the appropriate AZ-EL direction.
Pointing accuracies of 0.004 degrees (15 arc seconds) are
possible in 'precision' mode. The 'precision' mode is not
available on 34-m antennas -- nor is it needed, since their
beamwidths are twice as large as on the 70-m antennas.
DSCC Antenna Microwave Subsystem
--------------------------------
70-m Antennas: Each 70-m antenna has three feed cones
installed in a structure at the center of the main reflector.
The feeds are positioned 120 degrees apart on a circle.
Selection of the feed is made by rotation of the
subreflector. A dichroic mirror assembly, half on the S-band
cone and half on the X-band cone, permits simultaneous use of
the S- and X-band frequencies. The third cone is devoted to
R&D and more specialized work.
The Antenna Microwave Subsystem (AMS) accepts the received S-
and X-band signals at the feed horn and transmits them
through polarizer plates to an orthomode transducer. The
polarizer plates are adjusted so that the signals are
directed to a pair of redundant amplifiers for each
frequency, thus allowing simultaneous reception of signals in
two orthogonal polarizations. For S-band these are two Block
IVA S-band Traveling Wave Masers (TWMs); for X-band the
amplifiers are Block IIA TWMs.
34-m STD Antennas: These antennas have two feed horns, one
for S-band signals and one for X-band. The horns are mounted
on a cone which is fixed in relation to the subreflector. A
dichroic plate mounted above the horns directs energy from
the subreflector into the proper horn.
The AMS directs the received S- and X-band signals through
polarizer plates and on to amplification. There are two
Block III S-band TWMs and two Block I X-band TWMs.
34-m HEF Antennas: Unlike the other antennas, the 34-m HEF
uses a single feed for both S- and X-band. Simultaneous S-
and X-band receive as well as X-band transmit is possible
thanks to the presence of an S/X 'combiner' which acts as a
diplexer. For S-band, RCP or LCP is user selected through a
switch so neither a polarizer nor an orthomode transducer is
needed. X-band amplification options include two Block II
TWMs or an HEMT Low Noise Amplifier (LNA). S-band
amplification is provided by an FET LNA.
DSCC Receiver-Exciter Subsystem
-------------------------------
The Receiver-Exciter Subsystem is composed of three groups of
equipment: the closed-loop receiver group, the open-loop
receiver group, and the RF monitor group. This subsystem is
controlled by the Receiver-Exciter Controller (REC) which
communicates directly with the DMC for predicts and OCI
reception and status reporting.
The exciter generates the S-band signal (or X-band for the
34-m HEF only) which is provided to the Transmitter Subsystem
for the spacecraft uplink signal. It is tunable under
command of the Digitally Controlled Oscillator (DCO) which
receives predicts from the Metric Data Assembly (MDA).
The diplexer in the signal path between the transmitter and
the feed horn for all three antennas (used for simultaneous
transmission and reception) may be configured such that it is
out of the received signal path (in listen-only or bypass
mode) in order to improve the signal-to-noise ratio in the
receiver system.
Closed Loop Receivers: The Block IV receiver-exciter at the
70-m stations allows for two receiver channels, each capable
of L-Band (e.g., 1668 MHz frequency or 18 cm wavelength),
S-band, or X-band reception, and an S-band exciter for
generation of uplink signals through the low-power or
high-power transmitter. The Block III receiver-exciter at
the 34-m STD stations allows for two receiver channels, each
capable of S-band or X-band reception and an exciter used to
generate an uplink signal through the low-power transmitter.
The receiver-exciter at the 34-m HEF stations allows for one
channel only.
The closed-loop receivers provide the capability for rapid
acquisition of a spacecraft signal and telemetry lockup. In
order to accomplish acquisition within a short time, the
receivers are predict driven to search for, acquire, and
track the downlink automatically. Rapid acquisition
precludes manual tuning though that remains as a backup
capability. The subsystem utilizes FFT analyzers for rapid
acquisition. The predicts are NSS generated, transmitted to
the CMC which sends them to the Receiver-Exciter Subsystem
where two sets can be stored. The receiver starts
acquisition at uplink time plus one round-trip-light-time or
at operator specified times. The receivers may also be
operated from the LMC without a local operator attending
them. The receivers send performance and status data,
displays, and event messages to the LMC.
Either the exciter synthesizer signal or the simulation
(SIM) synthesizer signal is used as the reference for the
Doppler extractor in the closed-loop receiver systems,
depending on the spacecraft being tracked (and Project
guidelines). The SIM synthesizer is not ramped; instead it
uses one constant frequency, the Track Synthesizer Frequency
(TSF), which is an average frequency for the entire pass.
The closed-loop receiver AGC loop can be configured to one of
three settings: narrow, medium, or wide. It will be
configured such that the expected amplitude changes are
accommodated with minimum distortion. The loop bandwidth
(2BLo) will be configured such that the expected phase
changes can be accommodated while maintaining the best
possible loop SNR.
Open-Loop Receivers: The Radio Science Open-Loop Receiver
(OLR) is a dedicated four channel, narrow-band receiver which
provides amplified and downconverted video band signals to
the DSCC Spectrum Processing Subsystem (DSP).
The OLR utilizes a fixed first Local Oscillator (LO)
frequency and a tunable second LO frequency to minimize phase
noise and improve frequency stability. The OLR consists of
an RF-to-IF downconverter located in the antenna, an IF
selection switch (IVC), and a Radio Science IF-VF
downconverter (RIV) located in the SPC. The RF-IF
downconverters in the 70-m antennas are equipped for four IF
channels: S-RCP, S-LCP, X-RCP, and X-LCP. The 34-m HEF
stations are equipped with a two-channel RF-IF: S-band and
X-band. The IVC switches the IF input between the 70-m and
34-m HEF antennas.
The RIV contains the tunable second LO, a set of video
bandpass filters, IF attenuators, and a controller (RIC).
The LO tuning is done via DSP control of the POCA/PLO
combination based on a predict set. The POCA is a
Programmable Oscillator Control Assembly and the PLO is a
Programmable Local Oscillator (commonly called the DANA
synthesizer). The bandpass filters are selectable via the
DSP. The RIC provides an interface between the DSP and the
RIV. It is controlled from the LMC via the DSP. The RIC
selects the filter and attenuator settings and provides
monitor data to the DSP. The RIC could also be manually
controlled from the front panel in case the electronic
interface to the DSP is lost.
RF Monitor -- SSI and PPM: The RF monitor group of the
Receiver-Exciter Subsystem provides spectral measurements
using the Spectral Signal Indicator (SSI) and measurements of
the received channel system temperature and spacecraft signal
level using the Precision Power Monitor (PPM).
The SSI provides a local display of the received signal
spectrum at a dedicated terminal at the DSCC and routes these
same data to the DSP which routes them to NOCC for remote
display at JPL for real-time monitoring and RIV/DSP
configuration verification. These displays are used to
validate Radio Science Subsystem data at the DSS, NOCC, and
Mission Support Areas. The SSI configuration is controlled
by the DSP and a duplicate of the SSI spectrum appears on the
LMC via the DSP. During real-time operations the SSI data
also serve as a quick-look science data type for Radio
Science experiments.
The PPM measures system noise temperatures (SNT) using a
Noise Adding Radiometer (NAR) and downlink signal levels
using the Signal Level Estimator (SLE). The PPM accepts its
input from the closed-loop receiver. The SNT is measured by
injecting known amounts of noise power into the signal path
and comparing the total power with the noise injection 'on'
against the total power with the noise injection 'off.' That
operation is based on the fact that receiver noise power is
directly proportional to temperature; thus measuring the
relative increase in noise power due to the presence of a
calibrated thermal noise source allows direct calculation of
SNT. Signal level is measured by calculating an FFT to
estimate the SNR between the signal level and the receiver
noise floor where the power is known from the SNT
measurements.
There is one PPM controller at the SPC which is used to
control all SNT measurements. The SNT integration time can
be selected to represent the time required for a measurement
of 30K to have a one-sigma uncertainty of 0.3K or 1%.
DSCC Transmitter Subsystem
--------------------------
The Transmitter Subsystem accepts the S-band frequency
exciter signal from the Block III or Block IV Receiver-
Exciter Subsystem exciter and amplifies it to the required
transmit output level. The amplified signal is routed via
the diplexer through the feed horn to the antenna and then
focused and beamed to the spacecraft.
The Transmitter Subsystem power capabilities range from 18 kw
to 400 kw. Power levels above 18 kw are available only at
70-m stations.
DSCC Tracking Subsystem
-----------------------
The Tracking Subsystem primary functions are to acquire and
maintain communications with the spacecraft and to generate
and format radiometric data containing Doppler and range.
The DSCC Tracking Subsystem (DTK) receives the carrier
signals and ranging spectra from the Receiver-Exciter
Subsystem. The Doppler cycle counts are counted, formatted,
and transmitted to JPL in real time. Ranging data are also
transmitted to JPL in real time. Also contained in these
blocks is the AGC information from the Receiver-Exciter
Subsystem. The Radio Metric Data Conditioning Team (RMDCT)
at JPL produces an Archival Tracking Data File (ATDF) tape
which contains Doppler and ranging data.
In addition, the Tracking Subsystem receives from the CMC
frequency predicts (used to compute frequency residuals and
noise estimates), receiver tuning predicts (used to tune the
closed-loop receivers), and uplink tuning predicts (used to
tune the exciter). From the LMC, it receives configuration
and control directives as well as configuration and status
information on the transmitter, microwave, and frequency and
timing subsystems.
The Metric Data Assembly (MDA) controls all of the DTK
functions supporting the uplink and downlink activities. The
MDA receives uplink predicts and controls the uplink tuning
by commanding the DCO. The MDA also controls the Sequential
Ranging Assembly (SRA). It formats the Doppler and range
measurements and provides them to the GCF for transmission to
NOCC.
The Sequential Ranging Assembly (SRA) measures the round trip
light time (RTLT) of a radio signal traveling from a ground
tracking station to a spacecraft and back. From the RTLT,
phase, and Doppler data, the spacecraft range can be
determined. A coded signal is modulated on an uplink carrier
and transmitted to the spacecraft where it is detected and
transponded back to the ground station. As a result, the
signal received at the tracking station is delayed by its
round trip through space and shifted in frequency by the
Doppler effect due to the relative motion between the
spacecraft and the tracking station on Earth.
DSCC Spectrum Processing Subsystem (DSP)
----------------------------------------
The DSCC Spectrum Processing Subsystem (DSP) located at the
SPC digitizes and records on magnetic tapes the narrowband
output data from the RIV. It consists of a Narrow Band
Occultation Converter (NBOC) containing four Analog-to-
Digital Converters (ADCs), a ModComp CLASSIC computer
processor called the Spectrum Processing Assembly (SPA), and
two to six magnetic tape drives. Magnetic tapes are known as
Original Data Records (ODRs). Electronic near real-time
transmission of data to JPL (an Original Data Stream, or ODS)
may be possible in certain circumstances;
The DSP is operated through the LMC. Using the SPA-R
software, the DSP allows for real-time frequency and time
offsets (while in RUN mode) and, if necessary, snap tuning
between the two frequency ranges transmitted by the
spacecraft: coherent and non-coherent. The DSP receives
Radio Science frequency predicts from the CMC, allows for
multiple predict set archiving (up to 60 sets) at the SPA,
and allows for manual predict generation and editing. It
accepts configuration and control data from the LMC, provides
display data to the LMC, and transmits the signal spectra
from the SSI as well as status information to NOCC and the
Project Mission Support Area (MSA) via the GCF data lines.
The DSP records the digitized narrowband samples and the
supporting header information (i.e., time tags, POCA
frequencies, etc.) on 9-track magnetic tapes in 6250 or 1600
bpi GCR format.
Through the DSP-RIC interface the DSP controls the RIV filter
selection and attenuation levels. It also receives RIV
performance monitoring via the RIC. In case of failure of
the DSP-RIC interface, the RIV can be controlled manually
from the front panel.
All the RIV and DSP control parameters and configuration
directives are stored in the SPA in a macro-like file called
an 'experiment directive' table. A number of default
directives exist in the DSP for the major Radio Science
experiments. Operators can create their own table entries.
Items such as verification of the configuration of the prime
open-loop recording subsystem, the selection of the required
predict sets, and proper system performance prior to the
recording periods will be checked in real-time at JPL via the
NOCC displays using primarily the remote SSI display at NOCC
and the NRV displays. Because of this, transmission of the
DSP/SSI monitor information is enabled prior to the start of
recording. The specific run time and tape recording times
will be identified in the Sequence of Events (SOE) and/or DSN
Keyword File.
The DSP can be used to duplicate ODRs. It also has the
capability to play back a certain section of the recorded
data after conclusion of the recording periods.
DSCC Frequency and Timing Subsystem
-----------------------------------
The Frequency and Timing Subsystem (FTS) provides all
frequency and timing references required by the other DSCC
subsystems. It contains four frequency standards of which
one is prime and the other three are backups. Selection of
the prime standard is done via the CMC. Of these four
standards, two are hydrogen masers followed by clean-up loops
(CUL) and two are cesium standards. These four standards all
feed the Coherent Reference Generator (CRG) which provides
the frequency references used by the rest of the complex. It
also provides the frequency reference to the Master Clock
Assembly (MCA) which in turn provides time to the Time
Insertion and Distribution Assembly (TID) which provides UTC
and SIM-time to the complex.
JPL's ability to monitor the FTS at each DSCC is limited to
the MDA calculated Doppler pseudo-residuals, the Doppler
noise, the SSI, and to a system which uses the Global
Positioning System (GPS). GPS receivers at each DSCC receive
a one-pulse-per-second pulse from the station's (hydrogen
maser referenced) FTS and a pulse from a GPS satellite at
scheduled times. After compensating for the satellite signal
delay, the timing offset is reported to JPL where a database
is kept. The clock offsets stored in the JPL database are
given in microseconds; each entry is a mean reading of
measurements from several GPS satellites and a time tag
associated with the mean reading. The clock offsets provided
include those of SPC 10 relative to UTC (NIST), SPC 40
relative to SPC 10, etc.
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 S-Band Characteristics
64-m 70-m 34-m 34-m
Transmit STD HEF
-------- ----- ----- ----- -----
Frequency (MHz) 2110- 2110- 2025- N/A
2120 2120 2120
Wavelength (m) 0.142 0.142 0.142 N/A
Ant Gain (dBi) 62.7 55.2 N/A
Beamwidth (deg) 0.119 0.31 N/A
Polarization L or R L or R N/A
Tx Power (kW) 20-400 20 N/A
Receive
-------
Frequency (MHz) 2270- 2270- 2270- 2200-
2300 2300 2300 2300
Wavelength (m) 0.131 0.131 0.131 0.131
Ant Gain (dBi) 61.6 63.3 56.2 56.0
Beamwidth (deg) 0.108 0.27 0.24
Polarization L & R L & R L or R L or R
System Temp (K) 22 20 22 38
DSS X-Band Characteristics (N/A for Galileo)
64-m 70-m 34-m 34-m
Transmit STD HEF
-------- ----- ----- ----- -----
Frequency (MHz) 8495 8495 N/A 7145-
7190
Wavelength (m) 0.035 0.035 N/A 0.042
Ant Gain (dBi) 74.2 N/A 67
Beamwidth (deg) N/A 0.074
Polarization L or R L or R N/A L or R
Tx Power (kW) 360 360 N/A 20
Receive
-------
Frequency (MHz) 8400- 8400- 8400- 8400-
8500 8500 8500 8500
Wavelength (m) 0.036 0.036 0.036 0.036
Ant Gain (dBi) 71.7 74.2 66.2 68.3
Beamwidth (deg) 0.031 0.075 0.063
Polarization L & R L & R L & R L & R
System Temp (K) 27 20 25 20
Electronics - DSN
=================
DSCC Open-Loop Receiver
-----------------------
The open loop receiver block diagram shown below is for 70-m
and 34-m High-Efficiency (HEF) antenna sites. Based on a
tuning prediction file, the POCA controls the DANA
synthesizer the output of which (after multiplication) mixes
input signals at both S- and X-band to fixed intermediate
frequencies for amplification. These signals in turn are
down converted and passed through additional filters until
they yield baseband output of up to 25 kHz in width. The
baseband output is digitally sampled by the DSP and either
written to magnetic tape or electronically transferred for
further analysis.
S-Band X-Band
2295 MHz 8415 MHz
Input Input
| |
v v
--- --- --- ---
| X |<--|x20|<--100 MHz 100 MHz-->|x81|-->| X |
--- --- --- ---
| |
295| |315
MHz| |MHz
v v
--- -- 33.1818 --- ---
| X |<--|x3|<------ MHz ------>|x11|-->| X |
--- -- |115 | --- ---
| |MHz | |
| | | |
50| 71.8181 --- --- |50
MHz| MHz->| X | | X |<-10 MHz |MHz
v --- --- v
--- ^ ^ ---
| X |<--60 MHz | | 60 MHz-->| X |
--- | | ---
| 9.9 | 43.1818 MHz | 9.9 |
| MHz ------------- MHz |
| | ^ | |
10| v | v |10
MHz| --- ---------- --- |MHz
|------>| X | | DANA | | X |<------|
| --- |Synthesizr| --- |
| | ---------- | |
v v ^ v v
------- ------- | ------- -------
|Filters| |Filters| ---------- |Filters| |Filters|
|3,4,5,6| | 1,2 | | POCA | | 1,2 | |3,4,5,6|
------- ------- |Controller| ------- -------
| | ---------- | |
10| |0.1 0.1| |10
MHz| |MHz MHz| |MHz
v v v v
--- --- --- ---
| X |- -| X | | X |- -| X |
--- | | --- --- | | ---
^ | | ^ ^ | | ^
| | | | | | | |
10 | | 0.1 0.1 | | 10
MHz | | MHz MHz | | MHz
| | | |
v v v v
Baseband Baseband
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.
Radio Science IF-VF (RIV) Converter Assembly at 70-m and 34-m
High-Efficiency (HEF) antennas:
FSant=3*[POCA+(790/11)*10^6] + 1.95*10^9 - Fsamp - Frec
FXant=11*[POCA-10^7] + 8.050*10^9 - 3*Fsamp + Frec
Multi-Mission Receivers at 34-m Standard antennas (DSS 42 and
61; the diagram above does not apply):
FSant=48*POCA + 3*10^8 - 0.75*Fsamp + Frec
FXant = (11/3)*[48*POCA + 3*10^8 - 0.75*Fsamp] + Frec
where
FSant = S-band antenna frequency
FXant = X-band antenna frequency
POCA = POCA frequency
Fsamp = sampling frequency
Frec = frequency of recorded signal
Filters - DSN
=============
DSCC Open-Loop Receiver
-----------------------
Nominal filter center frequencies and bandwidths for the
Open-Loop Receivers are shown in the table below.
Filter Center Frequency 3 dB Bandwidth
------ ---------------- --------------
1 0.1 MHz 90 Hz
2 0.1 MHz 450 Hz
3 10.0 MHz 2000 Hz
4 10.0 MHz 1700 Hz (S-band)
6250 Hz (X-band)
5 10.0 MHz 45000 Hz
6 10.0 MHz 21000 Hz
MMR filters (DSS 42 and 61) include the following:
Filter Center Frequency 3 dB Bandwidth
------ ---------------- --------------
5 Unknown 2045 Hz (S-band)
7500 Hz (X-band)
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 bandwidth at
both S- and X-band is 10 Hz. Coherent (two-way) closed-loop
system stability is shown in the table below:
integration time Doppler uncertainty
(secs) (one sigma, microns/sec)
------ ------------------------
10 50
60 20
1000 4
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.
The nominal procedure for initializing open-loop receiver
attenuator settings is described below. In cases where widely
varying signal levels are expected, the procedure may be
modified in advance or real-time adjustments may be made to
attenuator settings.
Open-Loop Receiver Attenuation Calibration
------------------------------------------
The open-loop receiver attenuator calibrations are performed
to establish the output of the open-loop receivers at a level
that will not saturate the analog-to-digital converters. To
achieve this, the calibration is done using a test signal
generated by the exciter/translator that is set to the peak
predicted signal level for the upcoming pass. Then the
output level of the receiver's video band spectrum envelope
is adjusted to the level determined by equation (3) below (to
five-sigma). Note that the SNR in the equation (2) is in dB
while the SNR in equation (3) is linear.
Pn = -198.6 + 10*log(SNT) + 10*log(1.2*Fbw) (1)
SNR = Ps - Pn (SNR in dB) (2)
Vrms = sqrt(SNR + 1)/[1 + 0.283*sqrt(SNR)] (SNR linear)(3)
where Fbw = receiver filter bandwidth (Hz)
Pn = receiver noise power (dBm)
Ps = signal power (dBm)
SNT = system noise temperature (K)
SNR = predicted signal-to-noise ratio
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
=======================
DSCC Antenna Mechanical Subsystem
---------------------------------
Pointing of DSCC antennas may be carried out in several ways.
For details see the subsection 'DSCC Antenna Mechanical
Subsystem' in the 'Subsystem' section. Binary pointing is
the preferred mode for tracking spacecraft; pointing
predicts are provided, and the antenna simply follows those.
With CONSCAN, the antenna scans conically about the optimum
pointing direction, using closed-loop receiver signal
strength estimates as feedback. In planetary mode, the
system interpolates from three (slowly changing) RA-DEC
target coordinates; this is 'blind' pointing since there is
no feedback from a detected signal. In sidereal mode, the
antenna tracks a fixed point on the celestial sphere. In
'precision' mode, the antenna pointing is adjusted using an
optical feedback system. It is possible on most antennas to
freeze z-axis motion of the subreflector to minimize phase
changes in the received signal.
DSCC Receiver-Exciter Subsystem
-------------------------------
The diplexer in the signal path between the transmitter and
the feed horns on all three antennas may be configured so
that it is out of the received signal path in order to
improve the signal-to-noise ratio in the receiver system.
This is known as the 'listen-only' or 'bypass' mode.
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.
DSCC Spectrum Processing Subsystem (DSP)
----------------------------------------
The DSP can operate in four sampling modes with from 1 to 4
input signals. Input channels are assigned to ADC inputs
during DSP configuration. Modes and sampling rates 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
8-bit Samples 12-bit Samples
Sampling Rates Sampling Rates
(samples/sec per ADC) (samples/sec per ADC)
--------------------- ---------------------
50000
31250
25000
15625
12500
10000 10000
6250
5000 5000
4000
3125
2500
2000
1250
1000 1000
500
400
250
200 200
Input to each ADC is identified in header records by a Signal
Channel Number (J1 - J4). Nominal channel assignments are
shown below.
Signal Channel Number Receiver
(70-m or HEF) (34-m STD)
--------------------- ------------- ----------
J1 X-RCP not used
J2 S-RCP not used
J3 X-LCP X-RCP
J4 S-LCP S-RCP
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 (34-m STD) 6371.997815 35.1186672 243.1945048
DSS 13 (develop) 6372.117062 35.0665485 243.2051077
DSS 14 (70-m) 6371.992867 35.2443514 243.1104584
DSS 15 (34-m HEF) 6371.9463 35.2402863 243.1128186
DSS 16 (26-m) 6371.9608 35.1601436 243.1264200
DSS 18 (34-m STD) UNK UNK UNK
Canberra
DSS 42 (34-m STD) 6371.675607 -35.2191850 148.9812546
DSS 43 (70-m) 6371.688953 -35.2209308 148.9812540
DSS 45 (34-m HEF) 6371.692 -35.21709 148.97757
DSS 46 (26-m) 6371.675 -35.22360 148.98297
DSS 48 (34-m STD) UNK UNK UNK
Madrid
DSS 61 (34-m STD) 6370.027734 40.2388805 355.7509634
DSS 63 (70-m) 6370.051015 40.2413495 355.7519776
DSS 65 (34-m HEF) 6370.021370 40.2372843 355.7485968
DSS 66 (26-m) 6370.036 40.2400714 355.7485976
DSS 48 (34-m STD) UNK UNK UNK
Measurement Parameters - DSN
============================
Open-Loop System
----------------
Output from the Open-Loop Receivers (OLRs), as sampled and
recorded by the DSCC Spectrum Processing Subsystem (DSP), is
a stream of 8- or 12-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 DSP record; a header
record (presently 83 16-bit words) contains ancillary
information such as:
time tag for the first sample in the data block
RMS values of receiver signal levels and ADC outputs
POCA frequency and drift rate
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 117 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
AGC Automatic Gain Control
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
DCO Digitally Controlled Oscillator
DEC Declination
deg degree
DFLR Deutsche Forschungsanstalt fur Luft- und Raumfahrt
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
FET Field Effect Transistor
FFT Fast Fourier Transform
FTS Frequency and Timing Subsystem
GCF Ground Communications Facility
GCR Group Coded Recording
GHz gigahertz
GPS Global Positioning System
GSFC Goddard Space Flight Center
HA Hour Angle
HEF High-Efficiency (as in 34-m HEF antennas)
HEMT
HGA High Gain Antenna
IF Intermediate Frequency
IVC IF Selection Switch
JPL Jet Propulsion Laboratory
K Kelvin
km kilometer
kW kilowatt
L-band approximately 1668 MHz
LAN Local Area Network
LCP Left-Circularly Polarized
LGA Low Gain Antenna
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 Radio (Science)
MON Monitor and Control System
MSA Mission Support Area
N north
NAR Noise Adding Radiometer
NASA National Aeronautics and Space Administration
NASCOM NASA Communications
NBOC Narrow-Band Occultation Converter
NIST SPC 10 time relative to UTC
NIU Network Interface Unit
NOCC Network Operations and Control System
NRV NOCC Radio Science/VLBI Display Subsystem
NSS NOCC Support System
OCI Operator Control Input
ODF Orbit Data File
ODR Original Data Record
ODS Original Data Stream
OLR Open Loop Receiver
PLO Programmable Local Oscillator
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
Tx Transmitter
UNK unknown
UTC Universal Coordinated Time
VF Video Frequency
X-band approximately 7800-8500 MHz"
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