|
Instrument Information |
|
| IDENTIFIER | urn:nasa:pds:context:instrument:mgn.rss::1.0 |
| NAME |
RADIO SCIENCE SUBSYSTEM |
| TYPE |
ATMOSPHERIC SCIENCES |
| DESCRIPTION |
Instrument Overview
===================
The Magellan Radio Science investigations utilized
instrumentation with elements on the spacecraft and at the
DSN. Much of this is 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 affect the radio science data
accuracy, and they play 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.
Instrument Specifications - Spacecraft
======================================
The Magellan spacecraft telecommunications subsystem served
as part of a radio science subsystem for investigations of
Venus. 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 Magellan mission.
Instrument Id : RSS
Instrument Host Id : MGN
Pi Pds User Id : UNK
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : 1989-01-01
Instrument Mass : 102.2 KG
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 NASA S-band Standard Transponders (NSTs). In front of the S-band
transponders was a single cross-strapped X-band down-converter, which
allowed the NST to receive and transmit at both S-band (2.3 GHz,
13 cm wavelength) and X-band (8.4 GHz, 3.6 cm wavelength) frequencies.
The X-band capability reduced plasma effects on radio signals by a
factor of 10 and significantly improved the quality of radio tracking
data for gravity investigations. The exact transmitted frequency was
controlled by the signal received from a ground station or by an
on-board oscillator. 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 spacecraft was capable of either S- or X-band uplink
for commanding and simultaneous S- and X-band downlink for
telemetry. The NST generated a downlink signal in either a
'coherent' or a 'non-coherent' mode, also known as the 'two-
way' and 'one-way' modes, respectively. When operating
in the coherent mode, the NST behaved as a conventional
transponder; its transmitted carrier frequency was derived
coherently from the received uplink carrier frequency with a
'turn-around ratio' of 880/749 at X-band and 240/221 at
S-band. When the X-band downlink was controlled by an
S-band uplink, the turn-around ratio was (240/221)*(11/3).
In the non-coherent mode, the downlink carrier frequency was derived
from one of the spacecraft's on-board crystal-controlled oscillators.
After a 3-hour warm-up, the 'local' oscillator frequency was estimated
to be 8425.864 +/- 0.002 MHz at X-band; the S-band signal was lower
by a factor 3/11. Auxiliary Oscillator A was judged to have slightly
better stability. During bistatic radar experiments in May-June
1994 it served as the frequency reference. After a 1.5 hour warm-up
(first orbit, T=41C) its X-band frequency was estimated to be
8425.831 +/- 0.002 MHz; during subsequent orbits (T=43.3C) its
frequency was estimated to be 8425.827+/-0.002 MHz. These frequencies
depended primarily on the thermal environment, which could range
over 43C < T < 45C after initial warm-up. Sensitivity of Auxiliary
Oscillator A to thermal changes was -1.9 kHz per degree C.
The strength of a spacecraft carrier signal, and thus the
quality of the radio science data, depends on its modulation
state. Magellan radar data were sent to Earth at a nominal
rate of 268.8 kilobits per second at X-band; S-band was used
for transmission of engineering data at 1.2 kilobits per
second. Backup data rates of 115.2 kilobits for radar data
and 40 bits per second for engineering were available for
special contingencies and were required frequently during
later phases of the mission.
Traveling wave tube amplifiers, driven at saturation,
amplified the NST output before the signals were radiated
via (nominally) a 3.7 m diameter parabolic high gain antenna
(HGA). The same antenna was used for the on-board Synthetic
Aperture Radar (SAR) system. Medium-gain and low-gain
antennas (MGA and LGA, respectively) were also provided.
The S-band signal transmitted by the Magellan HGA was
linearly polarized. For radar operation, the nominal S-band
polarization was linear in the y-direction of the spacecraft
coordinate system (HH on the surface). For telecommunications
(and radio science) the S-band polarization was linear in the
x-direction. The X-band signal transmitted by the HGA was
circularly polarized, with the sense of polarization depending
on the transponder connected.
More information can be found in the Magellan Spacecraft Final
Report [MGN-MA-011-1995].
Science Objectives
==================
Two different types of radio science experiments were
conducted with Magellan: radio tracking experiments in which
the magnitude and direction of the planet's gravity field
were derived from the Doppler (and, sometimes, ranging)
measurements, and radio propagation experiments in which
signal modulation detected on Earth could be
attributed to properties of the medium. Several variations
of the radio propagation experiments were carried out
including radio occultations by the atmosphere of Venus and
scattering from its surface. Polarization and
scintillation measurements were also obtained when the radio
wave passed through the solar corona.
Gravity Measurements
--------------------
Measurement of the gravity field provides significant
constraints on inferences about the interior structure of
Venus. Precise, detailed study of the spacecraft motion
in Venus orbit can yield constraints on the mass
distribution of the planet. Topographic data obtained by
the Magellan Altimeter (ALT) forms a critical adjunct to
these measurements since only after the gravitational
effects are adjusted for topography can the gravity
anomalies be interpreted geophysically.
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. The high spatial
resolution of these products makes them especially useful
to geophysicists for study of features in the size range
of 100 to 1,000 km. Because of the relative simplicity
of the data analysis, results can be available within a
few weeks after the data are collected.
The gravity investigation has been described in more detail
by [KONOPLIV&SJOGREN1996] and [KONOPLIVETAL1999].
Radio Occultation Measurements
------------------------------
Atmospheric measurements by the method of radio
occultation contribute to an improved understanding of
structure, circulation, dynamics, and transport in the
atmosphere of Venus. These results are based on detailed
analysis of the radio signal received from Magellan as it
enters and exits occultation by the planet. Two phases
of the atmospheric investigation may be defined. The
first is to obtain vertical profiles of atmospheric
structure with emphasis on investigation of large-scale
phenomena. The second is to concentrate on studies of
the absorption at various levels in the atmosphere
(absorption correlates with concentration of sulfuric
acid vapor).
Retrieval of atmospheric profiles requires coherent
samples of the radio signal that has propagated through
the atmosphere, plus accurate knowledge of the antenna
pointing and the spacecraft trajectory. The latter is
obtained from the Magellan Navigation Team. Initial
solutions from Magellan occultations provided atmospheric
structure -- temperature and pressure vs. absolute radius
-- to altitudes as low as about 35 km from the surface.
The atmosphere becomes critically refracting at levels
only a short distance lower, so these results represent
very nearly the maximum depth achievable using radio
occultation probing.
The spatial and temporal coverage in the radio occultation
experiments are determined by the geometry of the
spacecraft orbit and the dates and times at which
occultation data were acquired. Since radio occultation
experiments were conducted on an ad hoc basis, the
Magellan coverage is sparse.
Bistatic Surface Scattering Measurements
----------------------------------------
The spacecraft telecommunications antenna can also be
pointed toward the surface of the planet. The strength
of the scattered signal from the illuminated area may
then be interpreted in terms of the texture of the surface
at that point. In an experiment conducted on 6 October
1993, the Magellan high-gain antenna was aimed toward the
summit of Gula Mons and the scattered signal was measured
at DSN stations in California and Australia. On 9 November
1993, the high-gain antenna was aimed toward the (moving)
point on the surface which would give mirror-like
reflection toward Earth; those signals were received at
the DSN station in Spain. In May and June 1994 experiments
were conducted over Maxwell Montes; those data were
processed to give the polarization of the reflected signal,
which can lead to estimates of complex dielectric constant
of the surface material. Results were published by
[PETTENGILLETAL1996].
Solar Scintillation and Faraday Rotation Experiments
----------------------------------------------------
Solar scintillation and Faraday rotation experiments are conducted
to improve our understanding of the structure and dynamics of the
solar corona and wind. Because Venus orbits the Sun, spacecraft like
Magellan are transported behind the solar disk, as seen from Earth.
Radio waves propagating between Magellan and Earth stations are
refracted and scattered (scintillation) by the solar plasma [WOO1993].
Intensity fluctuations can be related to fluctuations in electron
density along the path, while Doppler or phase scintillations can
be related to both electron density fluctuations and also the
speed of the solar wind. The plane of linearly polarized waves can
be rotated if there is an accompanying magnetic field (Faraday
rotation). Many plasma effects decrease as the square of the radio
frequency; scintillations are about an order of magnitude stronger
at S-band than X-band. But only Magellan's S-band radio system
used linear polarization; the circularly polarized X-band system
was essentially immune to Faraday rotation.
Operational Considerations - Spacecraft
=======================================
Descriptions given here are for nominal performance. The
spacecraft transponder system comprised redundant units,
each with slightly different characteristics. As
transponder units age, their performance changes slightly.
More importantly, the performance for radio science depended
on operational factors such as the modulation state for the
transmitters, which cannot be predicted in advance. The
performance also depended on factors which were not always
under the control of the Magellan Project. The sample
design control table below is adapted from [BUROW1986] for
the X-band link carrying 268.8 kbps telemetry. Mean and
variance denote expectations after accounting for best and
worst case variations on design values.
Parameter Design Mean Variance
Value
-----------------------------------------------------------
Transmit Parameters:
Total transmit power (dBm) 43.42 43.26 0.0139
Transmit circuit loss (dB) -0.80 -0.85 0.0176
Transmit antenna gain (dB) 48.75 48.75 0.0104
Transmit antenna pointing (dB) 1.03* -0.65* 0.1484
Path Parameters:
Space loss (dB) -279.09 -279.09 --
Atmospheric loss (dB) -0.31 -0.31 0.0000
Receive Parameters:
Polarization loss (dB) -0.04 -0.04 0.0005
Receive antenna gain (dB) 73.42 73.42 0.1200
Receive antenna pointing (dB) -0.10 -0.07 0.0006
Receive circuit loss (dB) 0.00 0.00 0.0000
Total Power Summary:
Net loss (dB) -158.84 0.2975
Total receiver power (dBm) -115.58 0.3114
Receiver noise (dBm/Hz) -179.64 -179.76 0.0416
Carrier Performance:
Carrier modulation loss (dB) -13.83 -14.32 2.1302
Polarization loss (dB) 0.00 0.00 0.0000
Receiver carrier power (dBm) -129.90 2.4416
Carrier noise bandwidth (dB/Hz) 20.00 19.98 0.2111
Carrier threshold SNR (dB) 10.00 10.00 0.0000
Carrier threshold power (dBm) -149.78 0.0627
Performance margin (dB) 19.98 2.5042
* Archivist's Note: The sign difference between design value
and mean is carried forward from the original [BUROW1986].
We were unable to contact the author and confirm his intent.
A plausible explanation is that the design value should be
-1.03, reflecting performance loss from antenna pointing
errors, while the -0.65 mean represents a more favorable
expectation after further design study. The specific values
are not crucial to interpretation of these radio science data.
On 4 January 1992 at 15:39 UTC, after a star calibration on
orbit 3880, the X-band telemetry and high-rate science data
did not reappear in the Magellan downlink. After several
configuration changes and diagnostic tests, the Spacecraft
Team reached the preliminary conclusion that a summing
amplifier in Transponder-A had failed. This summing
amplifier combined the X-band engineering and science
telemetry signals before phase-modulation, amplification,
and transmission of the signal to Earth via the High-Gain
Antenna. As part of the testing on 4 January,
Transponder-B was turned on and substituted for
Transponder-A for about 25 minutes. Transponder-B had been
turned off on 13 March 1991 when it developed a spurious
sideband that masked the data subcarriers. The spurious
signal appeared several MHz above the carrier frequency at
X-band, sometimes containing more power than the carrier.
During the short test on 4 January, Transponder-B started
out at 28-deg C and transmitted good data to Earth. Later
it warmed to 34-deg C and the downlink signal degraded.
The probable failure mechanism of Transponder-B was
determined to be a cracked, failed capacitor. Informal
Spacecraft Team contacts with Motorola on 6 January
indicated that Transponder-B might be returned to use if it
were operated with little or no thermal cycling. That
strategy was adopted for most of the remainder of the
mission. Use of the 115.2 kbs science data rate allowed
reception of radar data on Earth through most of that time
despite presence of the spur, but the mapping time on each
orbit was reduced commensurate with the playback
capabilities. Both Transponder-A and -B could support
gravity observations in their degraded states. Both
transponders had strong X-band carriers in spite of their
failures. The existence of the spur also affected radio
propagation observations to the extent that carrier power
was reduced to between a tenth and a half of its nominal level when
Transponder-B was in use. Over time periods of an orbit,
the frequency and strength of the spur did not change
appreciably; so a calibration of carrier level at one point
in the orbit was sufficient to establish carrier level
during other parts of the orbit.
For the bistatic surface scattering observations in October and
November 1993, estimates of transmitted power and spur parameters were
derived from spacecraft engineering telemetry and ground measurements.
The total power at S-band was 4.188+/-0.025 watts; the total
power at X-band was 17.298+/-0.100 watts. The X-band spur
was approximately 9.3 MHz above and at least 0.5 dB stronger than the
carrier. For experiments conducted in May and June of 1994,
Transponder-A was used so that full power was available in each
carrier (no X-band spur).
Calibration Description - Spacecraft
====================================
No information available.
Platform Mounting Descriptions - Spacecraft
===========================================
The spacecraft +Z axis vector was in the nominal direction
of the HGA boresight. The +X axis vector was parallel to
the nominal rotation axis of the solar panels. The +Y axis
vector formed a right-handed coordinate system and was in
the nominal direction of the star scanner boresight. The
spacecraft velocity vector was in approximately the -Y
direction when the spacecraft was oriented for left-looking
SAR operation. The nominal HGA S-band polarization for radar
operation was linear in the y-direction; the nominal HGA S-band
polarization for telecommunications (and radio science) was
linear in the x-direction. The nominal X-band polarization
was circular, with the sense depending on the transmitter
attached.
Cone Offset Angle : 0.00
Cross Cone Offset Angle : 0.00
Twist Offset Angle : 0.00
The medium gain antenna boresight was 70 degrees from the +Z
direction and 20 degrees from the -Y direction. The low
gain antenna was mounted on the back of the HGA feed; its
boresight was in the +Z direction and it had a hemispherical
radiation pattern.
Principal Investigators
=======================
The Principal Investigators for the gravity investigations
were William L. Sjogren, Michel Lefebvre, and Georges
Balmino. The Principal Investigator for the radio
occultation experiments was G. Leonard Tyler. The
Principal Investigator for the surface bistatic radar
experiments was Gordon H. Pettengill. Investigators for the
solar scintillation and Faraday rotation observations were
Richard Woo and Michael Bird, respectively.
Instrument Section / Operating Mode Descriptions - Spacecraft
=============================================================
The Magellan radio system consisted of two sections, which
could be operated in the following modes:
Section Mode
-------------------------------------------
Oscillator two-way (coherent)
one-way (non-coherent)
RF output low-gain antenna (no information available)
medium-gain antenna
high-gain antenna
Selected parameters describing NST performance are listed
below:
Oscillator Parameters: S-Band X-Band
Two-Way Transponder Turnaround Ratio 880/749 880/749
One-Way Transmit Frequency (MHz) 2297.963 8425.864
Frequency Uncertainty (+/- MHz) 0.0005 0.002
Nominal Wavelength (cm) 12.97 3.54
RF Output parameters: S-Band X-Band
RF Power Output (w) 5.6 17.8
Medium-Gain Antenna:
Half-Power Half Beamwidth (deg) 9.2
Gain (dBi) 19.
EIRP (dBm) 56.5
Polarization Circular
High-Gain Antenna:
Half-Power Half-Beamwidth (deg) 1.1 0.32
Gain (dBi) 35.9 48.3
EIRP (dBm) 71.4 90.5
Polarization Linear Circular
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],
[ASMAR&HERRERA1993], and [ASMARETAL1995]. For design
specifications on DSN subsystems see [DSN810-5]. For an
example of use of the DSN for Radio Science see [TYLERETAL1992].
Subsystems - DSN
================
The Deep Space Communications Complexes (DSCCs) are an integral
part of the Radio Science instrument, along with other
receiving stations and the spacecraft Radio Frequency
Subsystem. Their system performance directly determines the
degree of success of Radio Science investigations, and their
system calibration determines the degree of accuracy in the
results of the experiments. The following paragraphs describe
the functions performed by the individual subsystems of a DSCC.
This material has been adapted from [ASMAR&HERRERA1993]; for
additional information, consult [DSN810-5].
Each DSCC includes a set of antennas, 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 | | NASCOMM |
| 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 among 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: There are two types of Radio Science Open-Loop
Receivers (OLR) in use. At 70-m and 34-m HEF stations the OLR is a
a dedicated four channel, narrow-band receiver which provides
amplified and downconverted video band signals to the DSCC Spectrum
Processing Subsystem (DSP); it sometimes goes by the designation
'RIV'. At 34-m STD stations (DSS 42 and DSS 61) the OLR is an
older system, the Multi-Mission Receiver (MMR), which provides two
channels of narrow-band receiver output. Both OLR systems are
described in detail below under 'Electronics - DSN'; here the
overview continues only for the RIV system.
The 70-m and 34-m HEF 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) 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 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 several magnetic tape drives. Magnetic tapes containing
DSP output are known as Original Data Records (ODRs). Electronic
near real-time data transmission (known as an Original Data Stream,
or ODS) may be possible in certain circumstances.
The DSP is operated through the LMC. Using the SPA-Radioscience
(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
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
NB: X-band 64-m and 70-m transmitting parameters are given
at 8495 MHz, the frequency used by the Goldstone
planetary radar system. For telecommunications, the
transmitting frequency would be in the range 7145-7190
MHz, the power would typically be 20 kW, and the gain
would be about 72.6 dB (70-m antenna). When ground
transmitters are used in spacecraft radio science
experiments, the details of transmitter and antenna
performance rarely impact the results.
Electronics - DSN
=================
DSCC Open-Loop Receiver (RIV)
-----------------------------
The open loop receiver block diagram shown below is for the RIV
system at 70-m and 34-m High-Efficiency (HEF) antenna sites.
Input signals at both S- and X-band are mixed to approximately
300 MHz by fixed-frequency local oscillators near the antenna feed.
Based on a tuning prediction file, the POCA controls the DANA
synthesizer, the output of which (after multiplication) mixes
the 300 MHz IF to 50 MHz for amplification. These signals in turn
are down converted and passed through additional filters until they
yield Output with bandwidths up to 45 kHz. The Output is digitally
sampled 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 |<-10MHz |MHz
v --- --- v
--- ^ ^ ---
| X |<--60 MHz | | 60 MHz-->| X |
--- | approx | ---
| 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
--- --- --- ---
10 MHz -->| X | | X |<------ 0.1 MHz ------->| X | | X |<-- 10 MHz
--- --- --- ---
| | | |
v v v v
Output Output 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. Filters are defined below.
FSant=3*SYN+1.95*10^9+3*(790/11)*10^6+Frec (Filter 4)
=3*SYN+1.95*10^9+3*(790/11)*10^6-Fsamp+Frec (Filters 1-3,5,6)
FXant=11*SYN + 7.940*10^9 + Fsamp - Frec (Filter 4)
=11*SYN + 7.940*10^9 - 3*Fsamp + Frec (Filters 1,2,3,6)
where
FSant,FXant are the antenna frequencies of the incoming
signals at S and X bands, respectively,
SYN is the output frequency of the DANA synthesizer,
commonly labeled the readback POCA frequency on
data tapes,
Fsamp is the effective sampling rate of the digital
samples, and
Frec is the apparent signal frequency in a spectrum
reconstructed from the digital samples.
NB: For many of the filter choices (see below) the Output
is that of a bandpass filter. The sampling rates
in the table below are sufficient for the bandwidth
but not the absolute maximum frequency, and aliasing
results. The reconstruction expressions above are
appropriate ONLY when the sample rate shown in the
tables below is used.
DSCC Open-Loop Receiver (MMR at DSS 5 and 61)
---------------------------------------------
The open loop receiver block diagram shown below is for MMR systems
at the 34-m Standard (STD) DSS 61 antenna site and at the
DSS 5 JPL DSN facility. 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 Output with bandwidths up to 45 kHz. The Output is digitally
sampled 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 |<------------- -------------->| X |
--- 1995| |8115 ---
| MHz| |MHz |
| | | |
| | --- |
| | | X |<--800 MHz |
| | --- |
| | | |
300| | | |300
MHz| --- ---- |MHz
| |x48| |x176| |
v --- ---- v
--- ^ ^ ---
| X |<--290 MHz | | 290 MHz-->| X |
--- | approx | ---
| 9.9 | 41.56 MHz | 9.9 |
| MHz ------------- MHz |
| | ^ | |
10| v | v |10
MHz| --- ---------- --- |MHz
|------>| X | | DANA | | X |<------|
| --- |Synthesizr| --- |
| | ---------- | |
v v ^ v v
------- ------- | ------- -------
|Filters| |Filters| ---------- |Filters| |Filters|
| 4-8 | | 1-3 | | POCA | | 1-3 | | 4-8 |
------- ------- |Controller| ------- -------
| | ---------- | |
10| |0.1 0.1| |10
MHz| |MHz MHz| |MHz
v v v v
--- --- --- ---
10 MHz -->| X | | X |<------ 0.1 MHz ------->| X | | X |<-- 10 MHz
--- --- --- ---
| | | |
v v v v
Output Output 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. Filters are defined below.
FSant = 48*SYN + 300*10^6 - Fsamp + Frec (Filters 1,2,3,8)
= 48*SYN + 300*10^6 + Frec (Filters 4,5,6,7)
FXant = 176*SYN + 1100*10^6 - 3*Fsamp + Frec (Filters 1,2,3,8)
= 176*SYN + 1100*10^6 + Frec (Filters 4,5,6,7)
where the definition of terms and 'NB' are the same as for the RIV
system (above).
DSCC Open-Loop Receiver (MMR at DSS 7 and 42)
---------------------------------------------
The open loop receiver block diagram shown below is for the MMR
system at the 34-m Standard (STD) DSS 42 antenna site and the DSS 7
DSN facility at JPL. 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 Output with bandwidths up to 45 kHz. The Output is digitally
sampled and either written to magnetic tape or electronically
transferred for further analysis.
S-Band X-Band
2295 MHz 8415 MHz
Input 800 MHz Input
| | |
v v 8115 v
--- 1995 MHz --- MHz ---
| X |<------------- | X |------------>| X |
--- | --- ---
| | | |
| --- --- |
| |x 3| |x11| |
| --- approx --- |
| | 665 MHz | |
| ------------- |
300| | |300
MHz| --- |MHz
| | X |<--600 MHz |
v --- v
--- ^ ---
| X |<--290 MHz | 290 MHz-->| X |
--- ----- ---
| 9.9 |x 1.5| 9.9 |
| MHz ----- MHz |
| | ^ | |
10| v | v |10
MHz| --- ---------- --- |MHz
|------>| X | | DANA | | X |<------|
| --- |Synthesizr| --- |
| | ---------- | |
v v ^ v v
------- ------- | ------- -------
|Filters| |Filters| ---------- |Filters| |Filters|
| 4-8 | | 1-3 | | POCA | | 1-3 | | 4-8 |
------- ------- |Controller| ------- -------
| | ---------- | |
10| |0.1 0.1| |10
MHz| |MHz MHz| |MHz
v v v v
--- --- --- ---
10 MHz -->| X | | X |<------ 0.1 MHz ------->| X | | X |<-- 10 MHz
--- --- --- ---
| | | |
v v v v
Output Output 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. Filters are defined below.
FSant = (9/2)*SYN + 2100*10^6 - Fsamp + Frec (Filters 1,2,3,8)
= (9/2)*SYN + 2100*10^6 + Frec (Filters 4,5,6,7)
FXant = (33/2)*SYN + 7700*10^6 - 3*Fsamp + Frec (Filters 1,2,3,8)
= (33/2)*SYN + 7700*10^6 + Frec (Filters 4,5,6,7)
where the definition of terms and 'NB' are the same as for the RIV
system (above).
Filters - DSN
=============
DSCC Open-Loop Receiver (RIV)
-----------------------------
Nominal filter center frequencies and bandwidths for the RIV
Receivers are shown in the table below. Recommended sampling
rates are also given.
S-Band X-Band
------------------------ -------------------------
Output 3 dB Sampling Output 3 dB Sampling
Filter Center Band Rate Center Band Rate
Freq Width Freq Width
(Hz) (Hz) (sps) (Hz) (Hz) (sps)
------ ------ ------ -------- ------ ------ --------
1 150 82 200 550 82 200
2 750 415 1000 2750 415 1000
3 3750 2000 5000 13750 2000 5000
4 1023 1700 5000 3750 6250 15000
5 75000 45000 100000 275000 45000 100000
6 37500 20000 50000 137500 20000 50000
DSCC Open-Loop Receiver (MMR)
-----------------------------
MMR filters (DSS 5, 7, 42, and 61) and recommended sampling
rates include the following:
S-Band X-Band
------------------------ -------------------------
Output 3 dB Recommended Output 3 dB Recommended
Filter Center Band Sampling Center Band Sampling
Freq Width Rate* Freq Width Rate*
(Hz) (Hz) (sps) (Hz) (Hz) (sps)
------ ------ ------ -------- ------ ------ --------
1 150 100 200 550 100 200
2 750 500 1000 2750 500 1000
3 1500 1000 2000 5500 1000 2000
4 409 818 2000 1500 3000 6000
5 1023 2045 5000 3750 7500 15000
6 2045 4091 10000 7500 15000 30000
7 4091 8182 20000 15000 30000 60000
8 37500 20000 50000 137500 20000 50000
* Sampling rates depend on resolution of samples and number
of analog-to-digital converters assigned to each channel --
see discussion of modes under 'DSCC Spectrum Processing
Subsystem' below. The rates at which single A/D converters
can operate with the MMR include:
8-bit samples: 12-bit samples: 16-bit samples:
200 200 1250
250 1000
400 1250
500 2000
1000 5000
1250 10000
2000
2500
3125
4000
5000
6250
10000
12500
15625
20000
25000
31250
50000
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
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
AMS Antenna Microwave System
APA Antenna Pointing Assembly
ARA Area Routing Assembly
ATDF Archival Tracking Data File
AZ Azimuth
CMC Complex Monitor and Control
CONSCAN Conical Scanning (antenna pointing mode)
CRG Coherent Reference Generator
CUL Clean-up Loop
DANA a type of frequency synthesizer
dB deciBel
dBi dB relative to isotropic
dBm dB relative to one milliwatt
DCO Digitally Controlled Oscillator
DEC Declination
deg degree
DMC DSCC Monitor and Control Subsystem
DSCC Deep Space Communications Complex
DSN Deep Space Network
DSP DSCC Spectrum Processing Subsystem
DSS Deep Space Station
DTK DSCC Tracking Subsystem
E east
EL Elevation
FTS Frequency and Timing Subsystem
GCF Ground Communications Facility
GPS Global Positioning System
HA Hour Angle
HEF High-Efficiency (as in 34-m HEF antennas)
IF Intermediate Frequency
IVC IF Selection Switch
JPL Jet Propulsion Laboratory
K Kelvin
km kilometer
kW kilowatt
L-band approximately 1668 MHz
LAN Local Area Network
LCP Left-Circularly Polarized
LMC Link Monitor and Control
LNA Low-Noise Amplifier
LO Local Oscillator
m meters
MCA Master Clock Assembly
MCCC Mission Control and Computing Center
MDA Metric Data Assembly
MHz Megahertz
MMR Multi-Mission Receiver
MON Monitor and Control System
MSA Mission Support Area
N north
NAR Noise Adding Radiometer
NBOC Narrow-Band Occultation Converter
NIST SPC 10 time relative to UTC
NIU Network Interface Unit
NOCC Network Operations and Control System
NSS NOCC Support System
OCI Operator Control Input
ODF Orbit Data File
ODR Original Data Record
ODS Original Data Stream
OLR Open Loop Receiver
POCA Programmable Oscillator Control Assembly
PPM Precision Power Monitor
RA Right Ascension
REC Receiver-Exciter Controller
RCP Right-Circularly Polarized
RF Radio Frequency
RIC RIV Controller
RIV Radio Science IF-VF Converter Assembly
RMDCT Radio Metric Data Conditioning Team
RTLT Round-Trip Light Time
S-band approximately 2100-2300 MHz
sec second
SEC System Error Correction
SIM Simulation
SLE Signal Level Estimator
SNR Signal-to-Noise Ratio
SNT System Noise Temperature
SOE Sequence of Events
SPA Spectrum Processing Assembly
SPC Signal Processing Center
SRA Sequential Ranging Assembly
SRC Sub-Reflector Controller
SSI Spectral Signal Indicator
STD Standard (as in 34-m STD antennas)
TID Time Insertion and Distribution Assembly
TSF Tracking Synthesizer Frequency
TWM Traveling Wave Maser
UNK unknown
UTC Universal Coordinated Time
VF Video Frequency
X-band approximately 7800-8500 MHz
|
| MODEL IDENTIFIER | |
| NAIF INSTRUMENT IDENTIFIER |
not applicable |
| SERIAL NUMBER |
not applicable |
| REFERENCES |
Asmar, S.W., and R.G. Herrera, Radio Science Handbook, JPL D-7938, Volume 4,
Jet Propulsion Laboratory, Pasadena, CA, 22 January 1993. Asmar, S. W., N. A. Renzetti, The Deep Space Network as an instrument for radio science research, NASA Technical Reports Server, 1993STIN...9521456A, 1993. Asmar, S.W., R.G. Herrera, and T. Priest, Radio Science Handbook, JPL D-7938, Volume 6, Jet Propulsion Laboratory, Pasadena, CA, 1995. Burow, N.A., Magellan -- Communicating with a Spacecraft at Venus, 33rd Annual Meeting American Astronautical Society, Boulder, CO, 26-29 October 1986 Deep Space Network / Flight Project Interface Design Book, Document 810-5, Jet Propulsion Laboratory, Pasadena, CA. DSN Geometry and Spacecraft Visibility, Document 810-5, Rev. D, Vol. 1, DSN/Flight Project Interface Design, Jet Propulsion Laboratory, Pasadena, CA, 1987. Konopliv, A.S., and W.L. Sjogren, Venus Gravity Handbook, Jet Propulsion Laboratory Publication 96-2, January 1996. Konopliv, A.S., W.B. Banerdt, W.L. Sjogren, Venus Gravity: 180th degree and order model, Icarus, 139, 3-18, 1999. Magellan Spacecraft Final Report, JPL Contract 956700 MGN-MA-011, Martin Marietta Technologies Inc., Flight Systems, Denver, CO, 1995. Pettengill, G.H., P.G. Ford, and R.A. Simpson, Electrical properties of the Venus surface from bistatic radar observations, Science, 272, 1628-1631, 1996. Tyler, G.L., G. Balmino, D.P. Hinson, W.L. Sjogren, D.E. Smith, R. Woo, S.W. Asmar, M.J. Connally, C.L. Hamilton, and R.A. Simpson, Radio Science Investigations with Mars Observer, Journal of Geophysical Research, 97, 7759-7779, 1992. Woo, R., Spacecraft Radio Scintillation and Solar System Exploration, Wave Propagation in Random Media (Scintillation), Society of Photo-Optical Instrumentation Engineers, Bellingham, WA, 1993. |
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