Instrument Overview
===================
The Near-Earth Asteroid Rendezvous (NEAR) 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 Near-Earth Asteroid Rendezvous spacecraft telecommunications
subsystem served as part of a radio science subsystem for
investigations of asteroids 253 Mathilde and 433 Eros. Many
details of the subsystem are unknown; its 'build date' is taken to
be 1995-02-01, the date on which acceptance testing began at
Motorola.
Instrument Id : RSS
Instrument Host Id : NEAR
Pi Pds User Id : UNK
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : 1995-02-01
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : Motorola
Instrument Overview - Spacecraft
================================
The spacecraft radio system was constructed around a
redundant pair of X-band Cassini Transponders.
Other components included two redundant power amplifiers,
two redundant diplexers, two redundant microstrip patch low-gain
antennas (LGA), one microstrip patch medium-gain antenna (MGA)
providing a fan beam and one high-gain antenna (HGA) dish with
a diameter of 1.5 m.
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 transponder
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 transponder 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 and
noncoherent downlink frequencies were 8438.1 MHz and 8435 MHz
respectively.
The HGA was a 1.5 m diameter dish of a Cassegrain design that was
directed in the spacecraft's +Z direction. The gain was 40 dBic
at 8.4 GHz (on Z axis). The 3 dB beamwith was 1.7 degrees. The
MGA had a maximum gain of 18 dBic at 8.4 GHz (on Z axis) with a 3
dB beamwith of 8 x 40 degrees. The two LGAs were mounted forward
and aft with their axes pointing in the +Z and -Z directions
respectively. These LGAs had a gain of +5 to -10 dBic at 8.4 GHz
over the hemispheric field of view. The MGA had a single
polarization while the HGA and the two LGAs had dual, selectable,
circular polarizations.
NEAR telemetry data were sent to Earth at rates between
9 bits per second (bps) and 26.5 kilobits per second (kbps).
Uplink data rates were either 7 or 125 bps.
Science Objectives
==================
The science objectives of this investigation were to determine the
mass of Eros to better than 0.1%, to determine the bulk density of
Eros to an accuracy level commensurate with the accuracy of the
volume determination (~1%), and to investigate the interior
homogeneity of the asteroid by determining high order gravity
fields from the shape models and comparing these models with those
determined directly from the spacecraft tracking data. Additional
science objectives included the determination of the asteroid's
moment of inertia matrix and its rotation state, placing upper
limits upon any outgassing that may have occurred during its 100-
year observational history, and determining the masses and orbits
of any satellites discovered in orbit about Eros.
During the 1997 June 27 NEAR spacecraft flyby of asteroid 253
Mathilde, the Doppler and range tracking data was used to solve
for the mass of this asteroid. In combination with the volume
estimate provided by the imaging team, the asteroid's bulk density
(1.3 g/cm3) was determined [YEOMANSETAL1997].
The radio science objectives of this mission were more extensive
than traditional gravity science for large solar system bodies and
there were additional challenges to be overcome to meet
those objectives. For example, the figure of Eros was
very irregular and traditional spherical harmonics were no
longer the obvious choice for gravity field analyses. In
addition, the rotation state of the asteroid was not well known
prior to the spacecraft's arrival and the spacecraft orbits about
the asteroid were often near the plane-of-sky as seen from the
Earth, thus limiting the power of the Doppler data to define the
gravity field of Eros. Because of these technical challenges
and additional ones dictated by the short lead time before launch
and the modest budget associated with Discovery class missions,
the NEAR radio science team relied upon experienced personnel
who had already been tasked with navigating the NEAR spacecraft
during the approach and orbiting phases of the mission. The
success with which the NEAR Radio Science Team met its
objectives depended upon a very close cooperative effort with the
JPL Navigation Team.
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.
Their performance also depends upon factors which were not
always under the control of the NEAR Project.
Calibration Description - Spacecraft
====================================
No information available.
Platform Mounting Descriptions - Spacecraft
===========================================
The spacecraft +Z axis vector was aligned with the HGA boresight
perpendicular to the top surface of the spacecraft. The +Y
axis vector ran through the power switching electronics box
and the +X axis completed the orthogonal, right-handed,
rectangular coordinate system.
The axes of the two low gain antennas were in the +Z and -Z
directions. The MGA boresight was along the +Z axis.
Investigators
=============
Team Leader for the NEAR Radio Science Team was D.K. Yeomans
of the Jet Propulsion Laboratory (JPL). Members of the Team
included Jon D. Giorgini (JPL), Alex Konopliv (JPL) and
Jean-Pierre Barriot (CNES, France). Addition collaborative
efforts were provided by members of the JPL navigation team
including B.G. Williams, J.K. Miller, P. Antreasian, C. Helfrich,
J.D. Giorgini and mission design personnel from the Johns Hopkins
University's Applied Physics Laboratory (R. Farquhar, D. Dunham,
and J. McAdams).
Instrument Section / Operating Mode Descriptions - Spacecraft
=============================================================
The NEAR radio system consisted of two sections, which
could be operated in the following modes:
Section Mode
-------------------------------------------
Oscillator two-way (coherent)
one-way (non-coherent)
RF output low-gain antenna (choice from two)
medium-gain antenna
high-gain antenna
Instrument Overview - DSN
=========================
Three Deep Space Communications Complexes (DSCCs) (near
Barstow, CA; Canberra, Australia; and Madrid, Spain) comprise
the DSN tracking network. Each complex is equipped with
several antennas [including at least one each 70-m, 34-m High
Efficiency (HEF), and 34-m Beam WaveGuide (BWG)], associated
electronics, and operational systems. Primary activity
at each complex is radiation of commands to and reception of
telemetry data from active spacecraft. Transmission and
reception is possible in several radio-frequency bands, the
most common being S-band (nominally a frequency of 2100-2300 MHz
or a wavelength of 14.2-13.0 cm) and X-band (7100-8500 MHz or
4.2-3.5 cm). Transmitter output powers of up to 400 kW are
available.
Ground stations have the ability to transmit coded and uncoded
waveforms which can be echoed by distant spacecraft. Analysis
of the received coding allows navigators to determine the
distance to the spacecraft; analysis of Doppler shift on the
carrier signal allows estimation of the line-of-sight
spacecraft velocity. Range and Doppler measurements are used
to calculate the spacecraft trajectory and to infer gravity
fields of objects near the spacecraft.
Ground stations can record spacecraft signals that have
propagated through or been scattered from target media.
Measurements of signal parameters after wave interactions with
surfaces, atmospheres, rings, and plasmas are used to infer
physical and electrical properties of the target.
Principal investigators vary from experiment to experiment.
See the corresponding section of the spacecraft instrument
description or the data set description for specifics.
The Deep Space Network is managed by the Jet Propulsion
Laboratory of the California Institute of Technology for the
U.S. National Aeronautics and Space Administration.
Specifications include:
Instrument Id : RSS
Instrument Host Id : DSN
Pi Pds User Id : N/A
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : N/A
Instrument Mass : N/A
Instrument Length : N/A
Instrument Width : N/A
Instrument Height : N/A
Instrument Manufacturer Name : N/A
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.
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: The Radio Science Open-Loop Receiver
(OLR) is a dedicated four channel, narrow-band receiver which
provides amplified and downconverted video band signals to
the DSCC Spectrum Processing Subsystem (DSP); it sometimes
goes by the designation 'RIV'.
The OLR utilizes a fixed first Local Oscillator (LO) frequency
and a tunable second LO frequency to minimize phase
noise and improve frequency stability. The OLR consists of
an RF-to-IF downconverter located 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 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 34-m BWG stations vary in their capabilities.
The IVC switches the IF input among the 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 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 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).
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 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 (or remote operations console),
provides display data to the LMC (or remote operations
console), 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 and/or
on a local disk for later transmission to JPL.
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
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)
-----------------------------
The open loop receiver block diagram shown below is for the
RIV system at 70-m and 34-m HEF and BWG 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.
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 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 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) 6370.021697 40.2373325 355.7485795
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 150 entries including status information and
measurements of ranging, Doppler, and signal strength.
ACRONYMS AND ABBREVIATIONS - DSN
================================
ACS Antenna Control System
ADC Analog-to-Digital Converter
AGC Automatic Gain Control
AMS Antenna Microwave System
APA Antenna Pointing Assembly
ARA Area Routing Assembly
ATDF Archival Tracking Data File
AUX Auxiliary
AZ Azimuth
bps bits per second
BWG Beam WaveGuide (antenna)
CDU Command Detector Unit
CMC Complex Monitor and Control
CNES Centre National d'Etudes Spatiales
CONSCAN Conical Scanning (antenna pointing mode)
CRG Coherent Reference Generator
CUL Clean-up Loop
DANA a type of frequency synthesizer
dB deciBel
dBic dB relative to isotropic, circularly polarized radiator
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
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
LGA Low-Gain Antenna
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
MGA Medium Gain Antenna
MHz Megahertz
MON Monitor and Control System
MSA Mission Support Area
N north
NAR Noise Adding Radiometer
NBOC Narrow-Band Occultation Converter
NEAR Near-Earth Asteroid Rendezvous
NIST SPC 10 time relative to UTC
NIU Network Interface Unit
NOCC Network Operations and Control System
NRV NOCC Radio Science/VLBI Display Subsystem
NSS NOCC Support System
OCI Operator Control Input
ODF Orbit Data File
ODR Original Data Record
ODS Original Data Stream
OLR Open Loop Receiver
OSC Oscillator
PDS Planetary Data System
POCA Programmable Oscillator Control Assembly
PPM Precision Power Monitor
RA Right Ascension
REC Receiver-Exciter Controller
RCP Right-Circularly Polarized
RF Radio Frequency
RIC RIV Controller
RIV Radio Science IF-VF Converter Assembly
RMDCT Radio Metric Data Conditioning Team
RMS Root Mean Square
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
TSF Tracking Synthesizer Frequency
TWM Traveling Wave Maser
TWNC Two-Way Non-Coherent
TWTA Traveling Wave Tube Amplifier
UNK unknown
USO UltraStable Oscillator
UTC Universal Coordinated Time
VCO Voltage-Controlled Oscillator
VF Video Frequency
X-band approximately 7800-8500 MHz