| DESCRIPTION |
Instrument Overview
===================
The gravity science instrument utilizes the X and Ka-band transponders
on-board the Juno spacecraft and Doppler tracking equipment at
the Deep Space Network to perform radio science investigations
to determine the gravitational field of celestial bodies.
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. For more
information about the Juno spacecraft and mission, see
[MATOUSEK2006].
Instrument Specifications - Spacecraft
======================================
Instrument Id : RSS
Instrument Host Id : JUNO
Pi Pds User Id : UNK
Instrument Name : GRAVITY SCIENCE INSTRUMENT
Instrument Type : RADIO SCIENCE
Build Date : UNK
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
Instrument Overview - Spacecraft
================================
The Juno telecommunications system operates at X-band and Ka-band
to support the gravity science investigation at Jupiter. The
X-band transponder onboard the spacecraft provides the primary
communications and telemetry with the ground station. The
Ka-band telemetry system is augmented with a Ka-band Translator
and downconverter enabling a two-way Ka-band radio science link
to the Deep Space Network. The X-band and Ka-band systems can be
operated simultaneously for dual X-up/X-down and Ka-up/Ka-down.
The ground station uplinks a carrier to the spacecraft which
the receiver acquires and tracks. The spacecraft then transmits
a signal that is coherent with the uplink signal received. When
no uplink signal is present, the downlink signal was
referenced to the auxiliary oscillator. Data that are
noncoherent contains too much Doppler noise to be useful
for gravity science.
Science Objectives
==================
The radio tracking data are used to improve knowledge of
the magnitude and direction of Jupiter's gravity field.
The analysis of the interplanetary tracking data (both
range data and VLBI) to Juno can be used to improve the
modeling of the orbit of Jupiter in future versions of the
solar system planetary ephemerides.
Gravity Measurements
--------------------
Measurement of the gravity field provides significant
constraints on inferences about the interior structure of
Jupiter. Precise, detailed study of the spacecraft motion
in Jovian orbit can yield the mass distribution of the
gas giant.
Studies of the gravity field emphasize both the global
field and local characteristics of the field. The first
task is to determine the global field. Doppler and range
tracking measurements yield accurate spacecraft trajectory
solutions. Simultaneously with reconstruction of the
spacecraft orbit, observation equations for field
coefficients and a small number of ancillary parameters
can be solved. This type of gravity field solution is
essential for characterizing tectonic phenomena and can
also be used to study localized features.
'Short-arc' line-of-sight Doppler tracking measurements
obtained when the Earth-to-spacecraft line-of-sight is
within a few degrees of the orbit plane provide the
highest resolution of local features. The results from
this type of observation typically are presented as
contoured acceleration profiles of specific features
(e.g., craters, volcanoes, etc.) or line-of-sight
acceleration maps of specific regions.
Operational Considerations - Spacecraft
=======================================
Ka-band measurements are only available when the onboard
Ka-band Translator is powered on. Ka-band uplink/downlink
is available when the spacecraft is being tracked by
the Deep Space Network's DSS-25 in Goldstone, CA because
it is the only station in the network with a Ka-band
transmitter. During Ka-band tracks not over DSS-25, only
non-coherent Ka-band or Ka-band referenced to the X-band
uplink is available.
During the capture orbit phase, Ka-band checkout passes
were conducted to ensure operational status of the Ka-band
equipment onboard the spacecraft.
Science phase perijoves are all conducted over the DSS-25
antenna in Goldstone, CA. Only X-band data are available
for MWR perijoves. Ka-band and X-band data are available
for GRAV perijoves. See the MISSION.CAT for details on
perijove types and dates.
Investigators
=============
Folkner, William (Juno Gravity Science Co-I)
Asmar, Sami
Anderson, John
Buccino, Dustin (Juno Gravity Science Instrument Ops)
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 Beam WaveGuide (BWG)], 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 see reports by [ASMAR and RENZETTI1993]
and [ASMARETAL1995]. For design
specifications on DSN subsystems see [DSN810-5].
Subsystems - DSN
================
The Deep Space Communications Complexes (DSCCs) are an integral
part of Radio Science instrumentation, along with 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 [ASMARETAL1995]; 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.
GOLDSTONE CANBERRA MADRID
Antenna SPC 10 SPC 40 SPC 60
-------- --------- -------- --------
34-m HEF DSS-15 DSS-45 DSS-65
34-m BWG DSS-24 DSS-34 DSS-54
DSS-25 DSS-35 DSS-55
DSS-26 DSS-36
34-m HSB DSS-27
DSS-28
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 among the various subsystems is done using a
Local Area Network (LAN) hooked up to each subsystem via a
network interface unit (NIU).
DSCC Antenna Mechanical Subsystem
---------------------------------
Multi-mission Radio Science activities require support from
the 70-m, 34-m HEF, and 34-m BWG 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
BWG reflector shape is ellipsoidal.
On the 70-m 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.
In the 34-m BWG, a series of small mirrors (approximately 2.5
meters in diameter) directs microwave energy from the
subreflector region to a collection area at the base of
the antenna -- typically in a pedestal room. A retractable
dichroic reflector separates S- and X-band on some BWG
antennas or X- and Ka-band on others. 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.
Pointing angles for all 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. The LMC operator then downloads the
antenna predict points to the antenna-mounted ACS computer
along with a selected SEC model. The pointing predicts
consist of time-tagged AZ-EL 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.
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 and 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 HEF 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.
34-m BWG Antennas: These antennas use feeds and low-noise
amplifiers (LNA) in the pedestal room, which can be switched
in and out as needed. Typically the following modes are
available:
1. downlink non-diplexed path (RCP or LCP) to LNA-1, with
uplink in the opposite circular polarization;
2. downlink non-diplexed path (RCP or LCP) to LNA-2, with
uplink in the opposite circular polarization
3. downlink diplexed path (RCP or LCP) to LNA-1, with
uplink in the same circular polarization
4. downlink diplexed path (RCP or LCP) to LNA-2, with
uplink in the same circular polarization
For BWG antennas with dual-band capabilities (e.g., DSS 25)
and dual LNAs, each of the above four modes can be used in a
single-frequency or dual-frequency configuration. Thus, for
antennas with the most complete capabilities, there are
sixteen possible ways to receive at a single frequency
(2 polarizations, 2 waveguide path choices, 2 LNAs, and 2
bands).
DSCC Receiver-Exciter Subsystem
-------------------------------
The Receiver-Exciter Subsystem is composed of two groups of
equipment: the closed-loop receiver group and the open-loop
receiver 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 V 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 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 (OLR): The OLR utilized a fixed first
Local Oscillator (LO) frequency and a tunable second LO
frequency to minimize phase noise and improve frequency
stability. The OLR consisted of an RF-to-IF downconverter
located at the feed , an IF selection switch (IFS), and a
Radio Science Receiver (RSR). The RF-IF downconverters
in the 70-m antennas were equipped for four IF channels:
S-RCP, S-LCP, X-RCP, and X-LCP. The 34-m HEF stations
were equipped with a two-channel RF-IF: S-band and X-band.
The IFS switched the IF input among the antennas.
DSCC Transmitter Subsystem
--------------------------
The Transmitter Subsystem accepts the S-band frequency
exciter signal from the 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, however, 80 kW transmitters are being installed
at the 34-m stations.
The Ka-band Transmitter at DSS-25 transmits at 300 W using
two combined Traveling Wave Tube Amplifiers (TWTAs).
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 a Tracking and Navigation Service File (TNF),
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 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.
Detectors - DSN
===============
Nominal carrier tracking loop threshold noise bandwidth at
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
For the open-loop subsystem, signal detection is done in
software.
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.
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 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 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 880/749. 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.
Location - DSN
==============
Station locations are documented in [DSN810-5]. Geocentric
coordinates are summarized here.
Geocentric Geocentric Geocentric
Station Radius (km) Latitude (N) Longitude (E)
------------------- ------------ ------------ -------------
Goldstone
DSS 13 (34-m R and D) 6372125.096 35.0660180 243.2055410
DSS 14 (70-m) 6371993.267 35.2443523 243.1104618
DSS 15 (34-m HEF) 6371966.511 35.2403129 243.1128049
DSS 24 (34-m BWG) 6371973.601 35.1585346 243.1252056
DSS 25 (34-m BWG) 6371982.537 35.1562591 243.1246368
DSS 26 (34-m BWG) 6371992.264 35.1543409 243.1269835
Canberra
DSS 34 (34-m BWG) 6371693.538 -35.2169824 148.9819644
DSS 35 (34-m BWG) 6371697.350 -35.2143052 148.9814558
DSS 43 (70-m) 6371688.998 -35.2209189 148.9812673
DSS 45 (34-m HEF) 6371675.873 -35.2169608 148.9776856
Madrid
DSS 54 (34-m BWG) 6370025.490 40.2357726 355.7459032
DSS 55 (34-m BWG) 6370007.988 40.2344478 355.7473667
DSS 63 (70-m) 6370051.198 40.2413554 355.7519915
DSS 65 (34-m HEF) 6370021.709 40.2373555 355.7493011
Measurement Parameters - DSN
============================
Closed-loop data are recorded in Tracking and Navigation Service
Files (TNFs), as well as certain other products such as the
Orbit Data File (ODF). The TNFs are comprised of SFDUs that
have variable-length, variable-format records with mixed typing
(i.e., can contain ASCII, integer, and floating-point items in
a single record). These files all contain entries that include
measurements of Doppler, Range, and signal strength, along with
status and uplink frequency information.
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
AUX Auxiliary
AZ Azimuth
BPF Band Pass Filter
bps bits per second
BWG Beam WaveGuide (antenna)
CDU Command Detector Unit
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
DDC Digital Down Converter
DEC Declination
deg degree
DIG RSR Digitizer
DMC DSCC Monitor and Control Subsystem
DOR Differential One-way Ranging
DP Data Processor
DSCC Deep Space Communications Complex
DSN Deep Space Network
DSP DSCC Spectrum Processing Subsystem
DSS Deep Space Station
DTK DSCC Tracking Subsystem
E east
EIRP Effective Isotropic Radiated Power
EL Elevation
FET Field Effect Transistor
FFT Fast Fourier Transform
FIR Finite impulse Response
FTS Frequency and Timing Subsystem
GCF Ground Communications Facility
GHz Gigahertz
GPS Global Positioning System
HA Hour Angle
HEF High-Efficiency (as in 34-m HEF antennas)
HEMT High Electron Mobility Transistor (amplifier)
HGA High-Gain Antenna
HSB High-Speed BWG
IF Intermediate Frequency
IFS IF Selector Switch
IVC IF Selection Switch
JPL Jet Propulsion Laboratory
K Kelvin
Ka-Band approximately 32 GHz
KaBLE Ka-Band Link Experiment
kbps kilobits per second
kHz kilohertz
km kilometer
kW kilowatt
LAN Local Area Network
LCP Left-Circularly Polarized
LGR Low-Gain Receive (antenna)
LGT Low-Gain Transmit (antenna)
LMA Lockheed Martin Astronautics
LMC Link Monitor and Control
LNA Low-Noise Amplifier
LO Local Oscillator
LPF Low Pass Filter
m meters
MCA Master Clock Assembly
MCCC Mission Control and Computing Center
MDA Metric Data Assembly
MHz Megahertz
MON Monitor and Control System
MSA Mission Support Area
N north
NAR Noise Adding Radiometer
NBOC Narrow-Band Occultation Converter
NCO Numerically Controlled Oscillator
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
OSC Oscillator
PDS Planetary Data System
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
RMS Root Mean Square
RSR Radio Science Receiver
RSS Radio Science Subsystem
RT Real-Time (control computer)
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
sps samples per second
SRA Sequential Ranging Assembly
SRC Sub-Reflector Controller
SSI Spectral Signal Indicator
TID Time Insertion and Distribution Assembly
TLM Telemetry
TNF Tracking and Navigation File
TSF Tracking Synthesizer Frequency
TWM Traveling Wave Maser
TWNC Two-Way Non-Coherent
TWTA Traveling Wave Tube Amplifier
UNK unknown
USO UltraStable Oscillator
UTC Universal Coordinated Time
VCO Voltage-Controlled Oscillator
VDP VME Data Processor
VF Video Frequency
X-band approximately 7800-8500 MHz
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