|
Instrument Information |
|
| IDENTIFIER | urn:nasa:pds:context:instrument:mgs.rss::1.0 |
| NAME |
RADIO SCIENCE SUBSYSTEM |
| TYPE |
ATMOSPHERIC SCIENCES |
| DESCRIPTION |
Instrument Overview
===================
The Mars Global Surveyor (MGS) Radio Science investigations
utilized instrumentation with elements on the spacecraft and
at the NASA Deep Space Network (DSN). Much of this was
shared equipment, being used for routine telecommunications
as well as for Radio Science. The performance and
calibration of both the spacecraft and tracking stations
directly affected the radio science data accuracy, and they
played a major role in determining the quality of the
results. The spacecraft part of the radio science
instrument is described immediately below; that is followed
by a description of the DSN (ground) part of the instrument.
Instrument Specifications - Spacecraft
======================================
The Mars Global Surveyor spacecraft telecommunications
subsystem served as part of a radio science subsystem for
investigations of Mars. Many details of the subsystem are
unknown; its 'build date' is taken to be 1994-10-12, which
was during the Prelaunch Phase of the Mars Global Surveyor
mission.
Instrument Id : RSS
Instrument Host Id : MGS
Pi Pds User Id : UNK
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : 1994-10-12
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
Instrument Overview - Spacecraft
================================
The spacecraft radio system was constructed around a
redundant pair of X-band Mars Observer Transponders (MOT).
Other components included two redundant Low-Gain Receive
antennas (LGR); two redundant Low-Gain Transmit antennas
(LGT); two redundant Command Detector Units (CDU); two
redundant Traveling Wave Tube Amplifiers (TWTA); a single
high-gain antenna (HGA); a single UltraStable Oscillator
(USO); miscellaneous cables, connectors, waveguides, and
switches; and a Ka-band Link Experiment (KaBLE).
The X-band capability reduced plasma effects on radio
signals by a factor of 10 compared with previous S-band
systems, but absence of a dual-frequency capability (both
S- and X-band) meant that plasma effects could not be
estimated and removed from radio data.
The spacecraft was capable of X-band uplink commanding and
simultaneous X-band downlink telemetry. The MOT 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 MOT
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. The nominal coherent downlink frequency was
8417716050 Hz.
In the non-coherent mode, the downlink carrier frequency was
derived from one of the spacecraft's on-board crystal-
controlled oscillators. After warm-up, the 'auxiliary'
oscillator (AUX OSC) frequency was estimated to be
8417700000. Hz. A temperature-controlled UltraStable
Oscillator (USO) was used as the frequency reference during
one-way Radio Science observations. Representative USO
frequencies (at X-Band) are shown in the table below:
Earth Receive Date and Time Frequency (Hz) Drift (Hz/s)
--------------------------- -------------- -------------
1997-270T07:23:52 8423152969.720 +1.8560E-06
1998-049T02:19:38 8423152989.927 +1.5034E-06
1999-095T14:55:53 8423153024.367 +4.5321E-07
2000-001T05:54:53 8423153036.279 +3.7603E-07
2001-001T04:43:45 8423153045.552 +2.3561E-07
2003-001T05:25:58 8423153056.611 +1.1274E-07
2005-001T01:26:05 8423153062.908 +8.9172E-08
A Traveling Wave Tube Amplifier (TWTA), driven at
saturation, amplified the MOT output before the signals
were radiated via (nominally) the 1.5 m diameter parabolic
high gain antenna (HGA). During Inner Cruise, maneuvers,
and spacecraft anomalies the TWTA output was fed to a low-
gain transmitting antenna. Nominal Effective Isotropic
Radiated Power (EIRP) for both high- and low-gain antennas
is shown below:
Quantity Units HGA LGT
(Mapping) (Inner Cruise)
------------------------ ----- --------- --------------
RF Power Output dBm 44.23 44.23
Transmitter Circuit Loss dB -0.97 -1.37
Boresight Antenna Gain dBi 38.72 6.90
Antenna Pointing Loss dB -0.30 -4.60
----- -----
EIRP toward Earth dB 81.68 45.16
The strength of a spacecraft carrier signal, and thus the
quality of the radio science data, depends on its modulation
state. Mars Global Surveyor telemetry data were sent to
Earth at rates between 10 bits per second (bps) and 75
kilobits per second (kbps). Minimum Pt/No ratio (total
signal power to receiver noise in 1 Hz bandwidth) was 43 dB
during Inner Cruise with LGT1 transmitting to a 34-m HEF
on the ground; this would support a data rate of at least 8
kbps. For Outer Cruise Pt/No began at 76 dB and dropped
monotonically to 50 dB, the latter supporting a data rate
of 43 kbps. During Mapping, Pt/No varied between 47 dB and
64 dB, allowing data rates to 34-m HEF antennas of at least
21 kbps.
The HGA consisted of a 1.5-meter Cassegrain reflector system
with a dual-frequency (X- and Ka-band) feed horn.
Reflector, subreflector, and struts were spares from the
Mars Observer mission. The feed horn was a new Lockheed
Martin Astronautics (LMA) design consisting of co-located
X- and Ka-band elements. A radome fabricated of reinforced
germanium-coated Kapton covered the entire HGA aperture to
protect the system from the predicted aerobraking thermal
environment. TWTAs and associated components were enclosed
and mounted on the back of the HGA structure.
The HGA structure was mounted at the end of a 2-meter boom
with two gimbals to control azimuth and elevation pointing.
Certain parts of the sky were not visible with the HGA, but
pointing toward Earth was possible from all parts of the
orbit (see important exceptions described in the section
'Operational Considerations - Spacecraft' below). The HGA
azimuth gimbal was used during Mapping to track the slowly
changing seasonal (apparent) motion of the Earth. The HGA
elevation gimbal rotated at orbital rate to track the Earth
and was rewound every orbit during Earth occultation. The
orbital rate was 0.051 deg/sec, and the rewind rate was
0.12 deg/sec. Stepper motors controlled both gimbals. Step
size was 0.009375 deg; the stepping rate of approximately
5 per second was visible as a 5 Hz modulation in open-loop
Radio Science data collected after HGA deployment.
HGA performance is defined in terms of gain and beamwidth.
The table below summarizes some of those data. Beamwidth is
half-power, full-width, one-way. Nominal polarization is
right-hand circular in all cases.
Quantity X-Band X-Band Ka-Band Downlink
Uplink Downlink
-------- ------ ------- ------ ------- --------
Frequency Reference N/A AUX OSC USO AUX OSC USO
or VCO
Frequency (MHz) 7164.6 8417.7 8423.1 31987.3 32008.0
Beamwidth (deg) 1.717 1.546 1.546 0.375 0.375
Axial Ratio (dB) 1.0 1.0 1.0 1.0 1.0
Measured Gain (dBi) 37.43 39.10 38.72 49.14 48.99
Low-gain antennas were light-weight, low-cost microstrip
patch antennas derived from earlier missile and spacecraft
programs. Their performance is summarized below. Axial
ratio is defined over +/- 85 degrees from boresight.
Beamwidth is half-power, full-width, one-way. Nominal
polarization is right-hand circular in all cases.
Quantity X-Band Uplink X-Band Downlink
-------- ------------- ---------------
Center Frequency (MHz) 7200 8400
Bandwidth (MHz) 45 50
Axial Ratio (dB) <8 <8
Beamwidth (deg) 80 80
Gain (dBi) 6.3 6.9
More information can be found in the MGS Telecommunications
System Operations Reference Handbook [JPLD-14027].
Science Objectives
==================
Two different types of radio science experiments were
conducted with Mars Global Surveyor: 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 Mars
and scattering from its surface. 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
Mars. Precise, detailed study of the spacecraft motion
in Mars orbit can yield the mass distribution of the
planet. Topographic data obtained by the Mars Orbiting
Laser Altimeter (MOLA) 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. An early
gravity model based on MGS data was presented by
[SMITHETAL1999]. Later versions were described in
[LEMOINEETAL2001] and [YUANETAL2001].
'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 300 to 1,000 km. Because of the relative simplicity
of the data analysis, results can be available very soon
after the data are collected.
A by-product of the gravity field analysis is information
on the density structure of the upper atmosphere
[TRACADISETAL2001].
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 Mars. These results are based on detailed
analysis of the radio signal received from MGS as it
entered and exited 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
scintillations in the signal, which provide information
on smaller scale variations -- e.g, turbulence.
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 was
obtained first from the MGS Navigation Team and later
from high quality orbits derived by the Team's own
gravity investigators. Initial solutions from MGS
occultations provided atmospheric structure -- temperature
and pressure vs. absolute radius -- to altitudes as high
as about 50 km from the surface [HINSONETAL1999].
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 a regular basis using a
polar orbit, there was extensive occultation coverage at
high northern and southern latitudes (e.g., beyond 60
degrees). Often several occultations were observed in
succession in each hemisphere at time spacings of less
than two hours. Later in the primary mission, as the
orbit appeared to drift from edge-on to nearly broadside
as viewed from Earth, occultation points moved toward the
equator and the entry/exit angle approached grazing.
For several months in 1999, there were no occultations at
all. More than 21000 neutral atmosphere profiles had
been derived from MGS radio occultations by the end of
the mission.
No scintillations which could be attributed to turbulence
were detected in the occultation data.
It is also possible to retrieve profiles of electron
density in the ionosphere from occultation data. When
the density is high enough, it reduces the refractive
index of the medium (where the neutral atmosphere
increases the refractive index) causing the radio wave
phase to be advanced. The methods for retrieval are
somewhat different since hydrostatic equilibrium cannot
be assumed in the plasma. 5600 electron density
profiles were derived from MGS data, mostly near the
terminator [BOUGHERETAL2001][BOUGHERETAL2004]
[WITHERSETAL2005].
Bistatic Surface Scattering Measurements
------------------------------------------
For a few seconds before and after geometrical occultation
the HGA illuminated a small strip of surface as well as
the atmosphere. Under some circumstances, an echo could be
observed from the surface. For smooth surfaces, the echo
properties (particular the strength) could be related to the
surface dielectric constant through the Fresnel reflection
equations. For rougher surfaces, diffraction and surface
wave phenomena may play a role. Surface echoes were
sought during most occultation events and several thousand
were studied in some detail [TYLERETAL2001].
The spacecraft telecommunications antenna could also be
pointed toward the surface of the planet. The strength
of the scattered signal from the illuminated area could
then be interpreted in terms of the dielectric constant
of the surface through the Fresnel equations; the
frequency dispersion of the signal could be related to the
texture of the surface at the reflecting point. One such
experiment was conducted over the Mars Polar Lander/Deep
Space 2 site in May 2000 [SIMPSON&TYLER2001].
For some surface materials, the Fresnel equations do not
apply; most of the signal penetrates the surface and is
scattered by the volume below. Clean water ice is known
to have these properties, and has been postulated as the
cause of anomalous scattering from the Galilean satellites
of Jupiter and from polar deposits on both Mercury and
Mars. Interpreting such observations quantitatively is not
straightforward, but Mars Global Surveyor had the
potential for collecting such data in a bistatic geometry,
providing additional insight on the surface structure
and properties. Although such observations were sought,
none were ever scheduled.
Search for Gravitational Waves
------------------------------
During the MGS Cruise Phase, nearly continuous radio
tracking of the spacecraft was conducted. At the same time
an effort was made to keep on-board spacecraft activity to
a minimum. The objective during this period was to search
for evidence that gravitational waves were passing through
the solar system while the spacecraft was at maximum
separation from known massive bodies. A gravitational wave
was expected to change the position and motion of the
spacecraft, the Earth, or both. Two-way tracking was used;
both closed-loop and open-loop data were collected, the
latter being more sensitive but also more voluminous. Sources
of gravitational waves have been postulated outside the solar
system [ANDERSONETAL1993][ESTABROOKETAL1995], but no
unambiguous detection of such radiation has ever been made.
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 Mars
orbits the Sun, spacecraft like MGS are transported behind
the solar disk, as seen from Earth. Radio waves
propagating between MGS 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. Many plasma effects decrease as the
square of the radio frequency; scintillations are about an
order of magnitude stronger at X-band than Ka-band.
The first solar conjunction observed with MGS was on
12 May 1998; more data were collected and archived two
years later [BARBINIS2001].
Operational Considerations - Spacecraft
=======================================
Descriptions given above 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 Mars Global Surveyor Project.
Early in the Mapping phase, the HGA assembly encountered an
obstruction. Two gimbals allowed the HGA to point toward
Earth; the elevation gimbal rotated the HGA in the orbit
plane, and the azimuth gimbal pointed the HGA out of the orbit
plane at the Earth 'beta' angle. The obstruction prevented
the azimuth gimbal from pointing at any beta angle less than
41.5 deg. After the anomaly (1999-04-15) and until the beta
angle exceeded 41.5 deg (1999-05-06), the spacecraft was
operated in the Fixed High Gain Antenna (FHGA) configuration.
The Earth beta angle dropped below 41.5 deg again in February
2000 and remained there until June 2001, during which the
spacecraft was operated in the 'Beta Supplement' mode.
In Beta Supplement the spacecraft was oriented so that the
azimuth gimbal could be set to the supplement of the beta angle;
the elevation gimbal was flipped. The supplement to the beta
angle ranged from 139 to 183 deg during the second year of
Mapping. But there was physical interference between the HGA
and its boom; and HGA rewinds, which normally occurred while
the spacecraft was occulted, now took place on the 'front'
side of the planet. The boom interference precluded collection
of occultation egress measurements during most of Mapping; the
HGA rewind reduced the amount of nearside radio tracking that
could be captured.
During normal operations, the spacecraft sensed solar
eclipses; a pre-programmed timing offset initiated onboard
radio occultation activities so that orbit prediction errors
would not affect collection of occultation data. During Beta
Supplement, all occultation times were derived from the MGS
Navigation Team Orbit Propagation and Timing Geometry file;
when the OPTG predicted occultation time was in error by more
than about 40 s, occultation data were lost (for example on
2001-02-06 and 2001-02-07).
The HGA azimuth obstruction mysteriously disappeared during a
'safe' mode event which ended on 2005-09-28. After testing,
the spacecraft was allowed to fly in its normal (non-Beta
Supplement) configuration for the remainder of the mission.
And, when other restrictions were not imposed, occultations
at both ingress and egress were recorded.
Calibration Description - Spacecraft
====================================
No information available.
Platform Mounting Descriptions - Spacecraft
===========================================
Origin of the spacecraft reference frame was located at the
intersection of the spacecraft/launch vehicle interface
plane and the spacecraft central axis -- that is, at the
bottom of the propulsion unit nozzle. The spacecraft +Z axis
was along the spacecraft central axis and normal to the
nadir equipment deck; the main engine was aimed in the -Z
direction. The +X axis vector was in the direction of the
velocity vector during Mapping. +X was also in the
direction of the HGA boresight during Cruise, and the HGA
boom was mounted to the +X panel of the propulsion module.
The +Y axis completed an orthogonal rectangular coordinate
system. The +/-Y axes defined generally the deployment
directions of the solar panels. The solar cells themselves
were on the -Z sides of the panels.
The primary LGT was mounted on the TWTA enclosure, which
was mounted on the rim of the HGA reflector; its boresight
was aligned with the HGA boresight, which was in the +X
direction until HGA deployment. The backup (LGT2) was also
mounted on the TWTA enclosure; its boresight was aligned at
a cant angle approximately 160 degrees away from the shared
boresights of the HGA and LGT1. This angle was chosen to
minimize the consequences of a gimbal failure once HGA
articulation began after deployment of the HGA boom in the
mapping orbit. LGT2 was not used prior to HGA deployment
because its orientation and proximity to the nadir payload
deck would lead to irradiation of the payload instruments
while the HGA was in its stowed position. One LGR was
mounted on the -X panel of the equipment module; the other
was on the +X side of the propulsion module.
The five MGS antennas -- HGA, primary and backup low-gain
transmitting antennas (LGT1 and LGT2, respectively) and
low-gain antennas for receiving on the +X and -X sides of
the spacecraft (LGR1 and LGR2, respectively) are shown
below in their stowed (pre-HGA deployment) configuration.
Note that dimensions are given in inches; one inch (1 in)
equals 0.0254 meters.
-Y Side View:
^ S/C +Z Axis
|
|
| +39.318 in
|<----------->|
| |
| +39.318 in |
|<--------->| |
| | |
| +20.72 in | |
|<-->| | |
-25.81 in|
|<----->| LGT2 __LGT1
| | @=| |=@ ----------------
| | | | __ ^
| | |__|/ | |
| +-----------+ / | |
| | | / | |+81.46 in
| | | / | |
| | || | |
LGR2 | | || HGA | ------ |
----- @=| || | ^ |
^ |-----------| \ | | |
| | | \ | | |
| | \ | | |
| | +31.75 in \__| | |
| | |<----->| | |
| | | | LGR1 |+66.15 |
| | |=@ --- | in |
| +----+-+----+ ^ | |
|+49.94 / | \ |+17.56 | |
| in / | \ | in | |
v / | \ v v v
-------- +----o----+ ------------------------>
| S/C Frame S/C +X Axis
| Origin
Top View:
^ S/C +Y Axis
|
| __
LGR1 / | |
+-----------+ / | v
| | |=@/ ------------
0 in| | S/C Frame | / | |+5.29 in
v | Origin || HGA | |
---- @=| o ||__ | ------------ --->
^ LGR2 || | | ^ ^ ^ S/C +X Axis
| | || | | | |
| || | | |-28.18 |
+----+-+----+| | | | in |-30.05 in
| |\__| v |
| |=@ --- v
@=|__| ---------------------
LGT2 LGT1
The geometrical center of the HGA (coordinates given below)
is taken to be the geometric center of the HGA reflector rim.
This is not the phase center of the HGA.
The geometric and phase centers of the low-gain antennas are
taken to be at the centers of the 1.45 x 1.45 in square-shaped
active elements of each antenna.
MGS Antenna Center Locations
(inches) (meters)
X Y Z X Y Z
------ ------ ------ ------ ------ ------
HGA 39.318 0.00 66.15 0.999 0.000 1.680
LGT1 39.318 -28.18 81.46 0.999 -0.716 2.069
LGT2 20.72 -30.05 81.56 0.526 -0.763 2.072
LGR1 31.75 5.29 17.56 0.806 0.134 0.446
LGR2 -25.81 0.00 49.94 -0.655 0.000 1.268
Investigators
=============
Team Leader for the MGS Radio Science Team was G. Leonard
Tyler of Stanford University. Members of the Team
conducting atmospheric investigations were David P. Hinson
and Richard Woo. Members conducting gravity investigations
were Georges Balmino, William L. Sjogren, and David E.
Smith. John Armstrong (gravitational waves), Michael Flasar
(atmospheres), and Richard Simpson (surface scattering) were
selected as Participating Scientists.
Instrument Section / Operating Mode Descriptions - Spacecraft
=============================================================
Redundant components (LGR, LGT, MOT, CDU, and TWTA) could
be configured as desired. Each configuration had slightly
different performance, but the quantitative differences are
unknown.
Each Mars Observer Transponder (MOT) responded to the
the following commands:
Command Function
------- --------
USO Enable If MOT is in two-way noncoherent mode,
selects USO as downlink frequency
reference;
If MOT is in two-way coherent mode,
implements automatic transfer from VCO
to USO whenever on-board receiver loses
phase lock on uplink signal.
USO Inhibit If MOT is in two-way noncoherent mode,
selects AUX OSC as downlink frequency
reference;
If MOT is in two-way coherent mode,
implements automatic transfer from VCO
to AUX OSC whenever on-board receiver
loses phase lock on uplink signal.
Ranging ON Enables the ranging signal path to the
X-band phase demodulator
Ranging OFF Disables the ranging signal path to the
X-band phase demodulator
DOR ON Enables DOR generator, using downlink
frequency source to derive DOR tones
DOR OFF Disables DOR generator
TWNC ON Forces downlink frequency source to be
non-coherent (AUX OSC or USO),
independent of receiver lock status
TWNC OFF If on-board receiver is phase-locked to
uplink signal, forces downlink to be
generated from uplink
If on-board receiver is NOT phase-locked
to uplink, provides automatic transfer
to selected downlink frequency source
(AUX OSC or USO)
TLM ON Enables telemetry signal path to X-band
phase demodulator
TLM OFF Disables telemetry signal path to X-band
phase demodulator
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. Very Long Baseline
Interferometry (VLBI) techniques can be applied to determine
the position of the spacecraft in the plane of the sky. Use
of VLBI became more common, especially for pre-encounter
navigation, after loss of the Mars Climate Orbiter on
23 September 1999.
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
The DSN and its subsystems evolved over the 10+ year lifetime
of the MGS mission. Electronic (real-time) distribution of
data superseded use of magnetic tape, and most subsystems were
at least upgraded if not entirely replaced. Changes critical
to understanding collection and handling of radio science data
are reflected in this document. The reader should be aware,
however, that details may be missing and that subsystems not
central to radio science activities may be described more as
they existed in the late 1990's rather than as they were at
the end of science data collection in 2006.
For more information on the Deep Space Network and its use in
radio science see reports by [ASMAR&RENZETTI1993],
[ASMAR&HERRERA1993], and [ASMARETAL1995]. For design
specifications on DSN subsystems see [DSN810-5]. For DSN use
with MGS Radio Science see [TYLERETAL1992], [TYLERETAL2001],
and [JPLD-14027].
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 [ASMAR&HERRERA1993] and [JPLD-14027]; 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 25 | | DSS 27 | | DSS 14 | | DSS 15 | | DSS 16 |
|34-m BWG| |34-m HSB| | 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 HEF DSS 15 DSS 45 DSS 65
34-m BWG DSS 24 DSS 34 DSS 54
DSS 25
DSS 26
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).
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 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&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 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 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: Prior to December 2001 the Radio Science
Open-Loop Receiver (OLR) was a dedicated four channel,
narrow-band receiver which provided amplified and
downconverted video band signals to the DSCC Spectrum
Processing Subsystem (DSP); it sometimes was known as the
'RIV'. Beginning in mid-2001 for tests and starting in
December 2001 for routine operations, open loop data were
acquired using a new digital system -- the Radio Science
Receiver (RSR) -- which is described below under
'Electronics - DSN.'
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 (IVC), and a Radio Science IF-VF
downconverter (RIV) located in the SPC. 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 34-m BWG stations varied in their capabilities.
The IVC switched the IF input among the antennas.
The RIV contained the tunable second LO, a set of video
bandpass filters, IF attenuators, and a controller (RIC).
The LO tuning was done via DSP control of the POCA/PLO
combination based on a predict set. The POCA was a
Programmable Oscillator Control Assembly and the PLO was a
Programmable Local Oscillator (commonly called the DANA
synthesizer). The bandpass filters were selectable via the
DSP. The RIC provided an interface between the DSP and the
RIV. It was controlled from the LMC via the DSP. The RIC
selected the filter and attenuator settings and provided
monitor data to the DSP. The RIC could also be manually
controlled from the front panel in case the electronic
interface to the DSP was lost.
RF Monitor -- SSI and PPM: The RF monitor group of the
Receiver-Exciter Subsystem provided 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 provided a local display of the received signal
spectrum at a dedicated terminal at the DSCC and routed these
same data to the DSP which routed them to NOCC for remote
display at JPL for real-time monitoring and RIV/DSP
configuration verification. These displays were used to
validate Radio Science Subsystem data at the DSS, NOCC, and
Mission Support Areas. The SSI configuration was controlled
by the DSP and a duplicate of the SSI spectrum appeared on
the LMC via the DSP. During real-time operations the SSI
data also served as a quick-look science data type for Radio
Science experiments.
The PPM measured system noise temperatures (SNT) using a
Noise Adding Radiometer (NAR) and downlink signal levels
using the Signal Level Estimator (SLE). The PPM accepted its
input from the closed-loop receiver. The SNT was 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 was 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 allowed direct calculation of
SNT. Signal level was measured by calculating an FFT to
estimate the SNR between the signal level and the receiver
noise floor where the power was known from the SNT
measurements.
There was one PPM controller at the SPC which was used to
control all SNT measurements. The SNT integration time
could be selected to represent the time required for a
measurement of 30K to have a one-sigma uncertainty of 0.3K
or 1%.
When the DSP was replaced by the RSR in late 2001, many of
the SSI and PPM functions were absorbed into the RSR. SNT
calibration because part of the DSN Monitor function.
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.
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 form of these products for later
analysis.
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)
----------------------------------------
Until it was decommissioned in early 2002 the DSCC Spectrum
Processing Subsystem (DSP) located at the SPC digitized and
recorded the narrowband output data from the RIV. It
consisted of a Narrow Band Occultation Converter
(NBOC) containing 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 were known as Original
Data Records (ODRs). Electronic near real-time data
transmission (known as an Original Data Stream, or ODS) was
the default for Mars Global Surveyor.
The DSP was originally operated through the LMC. During
1996-97 a remote operations capability was developed by the
JPL Radio Science Systems Group so that the DSP could be
operated from JPL.
Using the SPA-Radioscience (SPA-R) software, the DSP allowed
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 received Radio Science frequency
predicts from the CMC, allowed for multiple predict set
archiving (up to 60 sets) at the SPA, and allowed for manual
predict generation and editing. It accepted configuration and
control data from the LMC (or remote operations console),
provided display data to the LMC (or remote operations
console), and transmitted 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 recorded
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 and/or
on a local disk for later transmission to JPL.
Through the DSP-RIC interface the DSP controlled the RIV
filter selection and attenuation levels. It also received
RIV performance monitoring via the RIC. In case of failure
of the DSP-RIC interface, the RIV could be controlled
manually from the front panel.
All the RIV and DSP control parameters and configuration
directives were stored in the SPA in a macro-like file called
an 'experiment directive' table. A number of default
directives existed in the DSP for the major Radio Science
experiments. Operators could 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 were 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 was enabled prior to the start of
recording. The specific run time and tape recording times
were identified in the Sequence of Events (SOE) and/or DSN
Keyword File.
The DSP could be used to duplicate ODRs. It also had 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. 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
70-m 34-m 34-m
Transmit BWG HEF
-------- ----- ----- -----
Frequency (MHz) 2110- 2025- N/A
2120 2120
Wavelength (m) 0.142 0.142 N/A
Ant Gain (dBi) 62.7 56.1 N/A
Beamwidth (deg) 0.119 N/A N/A
Polarization L or R L or R N/A
Tx Power (kW) 20-400 20 N/A
Receive
-------
Frequency (MHz) 2270- 2270- 2200-
2300 2300 2300
Wavelength (m) 0.131 0.131 0.131
Ant Gain (dBi) 63.3 56.7 56.0
Beamwidth (deg) 0.108 N/A 0.24
Polarization L & R L or R L or R
System Temp (K) 20 31 38
DSS X-Band Characteristics
70-m 34-m 34-m
Transmit BWG HEF
-------- ----- ----- -----
Frequency (MHz) 8495 7145- 7145-
7190 7190
Wavelength (m) 0.035 0.042 0.042
Ant Gain (dBi) 74.2 66.9 67
Beamwidth (deg) N/A 0.074
Polarization L or R L or R L or R
Tx Power (kW) 360 20 20
Receive
-------
Frequency (MHz) 8400- 8400- 8400-
8500 8500 8500
Wavelength (m) 0.036 0.036 0.036
Ant Gain (dBi) 74.2 68.1 68.3
Beamwidth (deg) 0.031 N/A 0.063
Polarization L & R L & R L & R
System Temp (K) 20 30 20
NB: X-band 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) (valid until late 2001)
-----------------------------------------------------
The open loop receiver block diagram shown below was for the
RIV system at 70-m and 34-m HEF and BWG antenna sites until
late in 2001, when it was superseded by the Radio Science
Receiver (RSR) (see below). Input signals at both S- and
X-band were mixed to approximately 300 MHz by fixed-frequency
local oscillators near the antenna feed. Based on a tuning
prediction file, the POCA controlled the DANA synthesizer,
the output of which (after multiplication) mixed the 300 MHz
IF to 50 MHz for amplification. These signals in turn were
down converted and passed through additional filters until
they yielded output with bandwidths up to 45 kHz. The Output
was 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 could 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.
Radio Science Receiver (RSR) (used after mid-2001)
--------------------------------------------------
The Radio Science Receiver (RSR) was tested for Mars Global
Surveyor starting in mid-2001 and then used routinely for MGS
open loop data collection beginning in December 2001. For
more information, see [JPLD-16765].
A radio frequency (RF) spacecraft signal at S-band, X-band,
or Ka-band is captured by a receiving antenna on Earth, down
converted to an intermediate frequency (IF) near 300 MHz and
then fed via a distribution network to one input of an IF
Selector Switch (IFS). The IFS allows each RSR to select any
of the available input signals for its RSR Digitizer (DIG).
Within the RSR the digitized signal is then passed to the
Digital Down Converter (DDC), VME Data Processor (VDP), and
Data Processor (DP).
\ ----------- ------ ----- ----- -----
\ | RF TO IF | | |----| | | | | |
|----| DOWN |----| |----| |----| DIG | | DP |
/ | CONVERTER | | |----| | | | | |
/ ----------- | IF |----| IFS | ----- -----
ANTENNA --| DIST |----| | | |
300 MHz IF --| | .. | | ----- -----
FROM OTHER --| |----| | | | | |
ANTENNAS --| | ----- | DDC | | VDP |
------ | | | |
----- -----
| |
-------
In the DIG the IF signal is passed through a programmable
attenuator, adjusted to provide the proper level to the Analog
to Digital Converter (ADC). The attenuated signal is then
passed through a Band Pass Filter (BPF) which selects a
frequency band in the range 265-375 MHz. The filtered output
from the BPF is then mixed with a 256 MHz Local Oscillator
(LO), low pass filtered (LPF), and sampled by the ADC. The
output of the ADC is a stream of 8-bit real samples at 256
Msamples/second (Msps). DIG timing is derived from the
station FTS 5 MHz clock and 1 pulse per second (1PPS)
reference; the DIG generates a 256 MHz clock signal for later
processing. The 1 PPS signal marks the data sample taken at
the start of each second.
The DDC selects one 16 MHz subchannel from the possible 128
MHz bandwidth available from the DIG by using Finite Impulse
Response (FIR) filters with revolving banks of filter
coefficients. The sample stream from the DIG is separated
into eight decimated streams, each of which is fed into two
sets of FIR filters. One set of filters produces in-phase (I)
8-bit data while the other produces quadrature-phase (Q) 8-bit
data. The center frequency of the desired 16 MHz channel is
adjustable in 1 MHz steps and is usually chosen to be near the
spacecraft carrier frequency. After combining the I and Q
sample streams, the DDC feeds the samples to the VDP. The DDC
also converts the 256 MHz data clock and 1PPS signals into a
msec time code, which is also passed to the VDP.
The VDP contains a quadruply-redundant set of custom boards
which are controlled by a real-time control computer (RT).
Each set of boards comprises a numerically controlled
oscillator (NCO), a complex multiplier, a decimating FIR
filter, and a data packer. The 16 Msps complex samples
from the DDC are digitally mixed with the NCO signal in the
complex multiplier. The NCO phase and frequency are updated
every millisecond by the RT and are selected so that the
center frequency of the desired portion of the 16 MHz channel
is down-converted to 0 Hz. The RT uses polynomials derived
from frequency predictions. The output of the complex
multiplier is sent to the decimating FIR filter where its
bandwidth and sample rate are reduced (see table below). The
decimating FIR filter also allows adjustment of the
sub-channel gain to take full advantage of the dynamic range
available in the hardware. The data packer truncates samples
to 1, 2, 4, 8, or 16 bits by dropping the least significant
bits and packs them into 32-bit data words. Q-samples are
packed into the first 16 bits of the word, and I-samples into
the least significant 16 bits (see below). In 'narrow band'
operation all four sets of custom boards can be
supported simultaneously. In 'medium band' operation no more
than two channels can be supported simultaneously. In
'wide band' operation, only one sub-channel can be recorded.
|============================================================|
| RSR Sample Rates and Sample Sizes Supported |
|================+=======+======+=================+==========|
| Category | Rate | Size | Data Rate |Rec Length|
| | (ksps)|(bits)|(bytes/s) (rec/s)| (bytes) |
|================+=======+======+=========+=======+==========|
|Narrow Band (NB)| 1 | 8 | 2000 | 1 | 2000 |
| | 2 | 8 | 4000 | 1 | 4000 |
| | 4 | 8 | 8000 | 1 | 8000 |
| | 8 | 8 | 16000 | 1 | 16000 |
| | 16 | 8 | 32000 | 2 | 16000 |
| | 25 | 8 | 50000 | 2 | 25000 |
| | 50 | 8 | 100000 | 4 | 25000 |
| | 100 | 8 | 200000 | 10 | 20000 |
| | 1 | 16 | 4000 | 1 | 4000 |
| | 2 | 16 | 8000 | 1 | 8000 |
| | 4 | 16 | 16000 | 1 | 16000 |
| | 8 | 16 | 32000 | 2 | 16000 |
| | 16 | 16 | 64000 | 4 | 16000 |
| | 25 | 16 | 100000 | 4 | 25000 |
| | 50 | 16 | 200000 | 10 | 20000 |
| | 100 | 16 | 400000 | 20 | 20000 |
|Medium Band (MB)| 250 | 1 | 62500 | 5 | 12500 |
| | 500 | 1 | 125000 | 5 | 25000 |
| | 1000 | 1 | 250000 | 10 | 25000 |
| | 2000 | 1 | 500000 | 20 | 25000 |
| | 4000 | 1 | 1000000 | 40 | 25000 |
| | 250 | 2 | 125000 | 5 | 25000 |
| | 500 | 2 | 250000 | 10 | 25000 |
| | 1000 | 2 | 500000 | 20 | 25000 |
| | 2000 | 2 | 1000000 | 40 | 25000 |
| | 4000 | 2 | 2000000 | 100 | 20000 |
| | 250 | 4 | 250000 | 10 | 25000 |
| | 500 | 4 | 500000 | 20 | 25000 |
| | 1000 | 4 | 1000000 | 40 | 25000 |
| | 2000 | 4 | 2000000 | 100 | 20000 |
| | 250 | 8 | 500000 | 20 | 25000 |
| | 500 | 8 | 1000000 | 40 | 25000 |
| | 1000 | 8 | 2000000 | 100 | 20000 |
|Wide Band (WB) | 8000 | 1 | 2000000 | 100 | 20000 |
| | 16000 | 1 | 4000000 | 200 | 20000 |
| | 8000 | 2 | 4000000 | 200 | 20000 |
|============================================================|
|============================================================|
| Sample Packing |
|=================+==========================================|
| Bits per Sample | Contents of 32-bit Packed Data Register |
|=================+==========================================|
| 16 | (Q1),(I1) |
| 8 | (Q2,Q1),(I2,I1) |
| 4 | (Q4,Q3,Q2,Q1),(I4,I3,I2,I1) |
| 2 | (Q8,Q7,...Q1),(I8,I7,...I1) |
| 1 | (Q16,Q15,...Q1),(I16,I15,...I1) |
|============================================================|
Once per second the RT sends the accumulated data records from
each sub-channel to the Data Processor (DP) over a 100 Mbit/s
ethernet connection. In addition to the samples, each data
record includes header information such as time tags and NCO
frequency and phase that are necessary for analysis. The DP
processes the data records to provide monitor data, such as
power spectra. If recording has been enabled, the records are
stored by the DP.
NCO Phase and Frequency
-----------------------
At the start of each DSN pass, the RSR is provided with a
file containing a list of predicted frequencies. Using these
points, the RT computes expected sky frequencies at the
beginning, middle, and end of each one second time interval.
Based on the local oscillator frequencies selected and any
offsets entered, the RT computes the coefficients of a
frequency polynomial fitted to the DDC channel frequencies
at these three times. The RT also computes a phase
polynomial by integrating the frequency polynomial and
matching phases at the one second boundaries.
The phase and frequency of the VDP NCO's are computed every
millisecond (000-999) from the polynomial coefficients as
follows:
nco_phase(msec) = phase_coef_1 +
phase_coef_2 * (msec/1000) +
phase_coef_3 * (msec/1000)**2 +
phase_coef_4 * (msec/1000)**3
nco_freq(msec) = freq_coef_1 +
freq_coef_2 * ((msec + 0.5)/1000) +
freq_coef_3 * ((msec + 0.5)/1000)**2
The sky frequency may be reconstructed using
sky_freq = RF_to_IF_LO +
DDC_LO -
nco_freq +
resid_freq
where RF_to_IF_LO is the down conversion from the
microwave frequency to IF (bytes 42-43
in the data record header)
DDC_LO is the down-conversion applied in the
DIG and DDC (bytes 40-41 in the data
record header)
resid_Freq is the frequency of the signal in the
VDP output
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
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 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 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
Channel
--------------------- -------------
J1 X-RCP
J2 S-RCP
J3 X-LCP
J4 S-LCP
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 13 (34-m R&D) 6372.125125 35.0660185 243.2055430
DSS 14 (70-m) 6371.993286 35.2443527 243.1104638
DSS 15 (34-m HEF) 6371.966540 35.2403133 243.1128069
DSS 24 (34-m BWG) 6371.973553 35.1585349 243.1252079
DSS 25 (34-m BWG) 6371.983060 35.1562594 243.1246384
DSS 26 (34-m BWG) 6371.993032 35.1543411 243.1269849
Canberra
DSS 34 (34-m BWG) 6371.693561 -35.2169868 148.9819620
DSS 43 (70-m) 6371.689033 -35.2209234 148.9812650
DSS 45 (34-m HEF) 6371.675906 -35.2169652 148.9776833
Madrid
DSS 45 (34-m BWG) 6370.025429 40.2357708 355.7459008
DSS 63 (70-m) 6370.051221 40.2413537 355.7519890
DSS 65 (34-m HEF) (see next paragraph)
The coordinates for DSS 65 until 1 February 2005 were
6370.021697 40.2373325 355.7485795
In cartesian coordinates (x, y, z) this was
(+4849336.6176, -0360488.6349, +4114748.9218)
Between February and September 2005, the antenna was
physically moved to
(+4849339.6448, -0360427.6560, +4114750.7428)
Measurement Parameters - DSN
============================
Open-Loop System
----------------
Output from the Open-Loop Receivers (OLRs), as sampled and
recorded for later analysis, is a stream of 8- to 16-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 output record; a header
record contains ancillary information such as:
time tag for the first sample in the data block
RMS values of receiver signal levels and ADC outputs
local oscillator (e.g., POCA) frequency and drift rate
Closed-Loop System
------------------
Through early 2003 closed-loop data were 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 contained 150 entries including status
information and measurements of ranging, Doppler, and signal
strength. Starting in December 2002 the Network
Simplification Plan (NSP) brought in a new phase-based
closed-loop system with both higher precision and higher
accuracy. Nearly 20 different record formats were defined
under the umbrella of the new Tracking and Navigation File
(TNF). Ground stations were converted one at a time so that
ATDF production ended with one pass and TNF production began
on the next.
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
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
DEC Declination
deg degree
DMC DSCC Monitor and Control Subsystem
DOR Differential One-way Ranging
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
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
m meters
MCA Master Clock Assembly
MCCC Mission Control and Computing Center
MDA Metric Data Assembly
MGS Mars Global Surveyor
MHz Megahertz
MOLA Mars Orbiting Laser Altimeter
MON Monitor and Control System
MOT Mars Observer Transponder
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
NRV NOCC Radio Science/VLBI Display Subsystem
NSP Network Simplification Plan
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
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
VLBI Very Long Baseline Interferometry
VCO Voltage-Controlled Oscillator
VF Video Frequency
X-band approximately 7800-8500 MHz
|
| MODEL IDENTIFIER | |
| NAIF INSTRUMENT IDENTIFIER |
not applicable |
| SERIAL NUMBER |
not applicable |
| REFERENCES |
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