Instrument Overview
===================
Galileo Radio Science investigations utilized instrumentation with elements on the spacecraft and at the Deep Space Network (DSN). Much of this was shared equipment, being used for routine telecommunications as well as for Radio Science. The performance and calibration of both the spacecraft and tracking stations directly affected the radio science data accuracy, and they played a major role in determining the quality of the results. The spacecraft part of the radio science instrument is described immediately below; that is followed by adescription of the DSN (ground) part of the instrument.

Radio Science investigations were carried out by two teams.
The Celestial Mechanics Team, under Team Leader John Anderson, conducted experimental tests of general relativity (including searching for gravitational waves), made measurements to improve solar system ephemerides, and sought to improve gravitational models for Jupiter and its satellites [ANDERSONETAL1992]. The Radio Propagation Team, under Team Leader Tay Howard, investigated the solar corona and carried out various studies in the Jovian system primarily concerningatmospheres and ionospheres [HOWARDETAL1992].


Instrument Specifications - Spacecraft
======================================
The Galileo spacecraft telecommunications subsystem served as part of a radio science subsystem for investigations primarily of Jupiter and its satellites, but also including Venus, the Earth-Moon system, and the Sun. Many details of the subsystem are unknown; its 'build date' is taken to be 1989-01-01, which was during the prelaunch phase of theGalileo mission.

Instrument Id : RSS Instrument Host Id : GO Pi Pds User Id : UNK Instrument Name : RADIO SCIENCE SUBSYSTEM Instrument Type : RADIO SCIENCE Build Date : 1989-01-01 Instrument Mass : UNK Instrument Length : UNK Instrument Width : UNK Instrument Height : UNK Instrument Manufacturer Name : UNK

Instrument Overview - Spacecraft
================================
The spacecraft radio system was constructed around a redundant pair of transponders which received and transmitted at both S-band (2.3 GHz, 13 cm wavelength) and X-band (8.4 GHz, 3.6 cm wavelength) frequencies; the following combinations of uplink/downlink were supported bythe design: S/S, X/X, S/X and S.

The exact frequency transmitted from the spacecraft was controlled by the signal received from a ground station ('two-way' or 'coherent' mode) or by an on-board oscillator ('one-way' or 'non-coherent' mode). In some circumstances an uplink signal was transmitted from one ground station while two ground stations participated in reception; this was known as the 'three-way' mode. In the absence of an uplink signal, the spacecraft system switched automatically to the one-way mode. The on-board frequency reference could be either of two redundant 'auxiliary' crystal oscillators or a single ultra-stable oscillator (USO) provided specificallyto support radio science observations.

Each transponder included a receiver, command detector, exciter, and low-power amplifier. The transponders provided the usual uplink command and downlink data transmission capabilities. The following modulation states could be commanded: telemetry alone, ranging alone, telemetry andranging, or carrier only.

Each transponder could be operated through one of two low-gain antennas at S-band only; a furlable high-gain antenna (HGA) never deployed properly during Cruise, resulting in a serious degradation of radio science measurements, including loss of X-band capability. The HGA was aligned with the spin axis of the rotor part of the spacecraft. Low-Gain Antenna 1 (LGA-1) was located at theend of the HGA feed, so it is also aligned with the spin axis.
LGA-2 was at the end of a boom, 3.52 m from the spin axis.

When operating in the coherent mode, the transponder downlink frequency was related to the uplink frequency by the 'turn-around ratio' of 240/221 at S-band. At X-band it would have been 880/749. An X-band downlink controlled by an S-banduplink would have had a turn-around ratio of (240/221)*(11/3).


Science Objectives
==================
Two different types of radio science measurements were conducted with the Galileo Orbiter: radio tracking in which the magnitude and direction of gravitational forces could be derived from 'closed-loop' Doppler (and, sometimes, ranging) measurements, and radio propagation experiments in which modulation on the signal received at Earth stationscould be attributed to properties of the intervening medium.
The radio science measurements were analyzed by two investigation teams; the Celestial Mechanics Team was primarily interested in characterizing variations in gravitational forces, and the Radio Propagation Team was primarily interested in the atmospheres of the Sun, Jupiter,and Jupiter's satellites.

Gravity Measurements--------------------
Measurement of the gravity field provides significant constraints on inferences about interior structure of Jupiter and its satellites. Precise, detailed study of spacecraft motion in Jupiter orbit and during satellite flybys can yield a mass distribution of each body and higher-order field terms if the measurements are sensitive enough. Compared with determinations from previous missions, improvements in the gravity field of Jupiter itself were not expected from tracking the Galileo Orbiter, but second-order gravity harmonics were expected from flyby encounters with satellites. One equatorial and one polar flyby at Ganymede were sought to determine independently the rotational andtidal response of the body assuming hydrostatic equilibrium.
Departures from hydrostatic equilibrium were expected to confuse that issue at Europa, though the measurements were expected to be useful, while the relatively weak response to rotation and tides at Callisto made the experiment most marginal there [HUBBARD&ANDERSON1978]. Differences in principal moments of inertia to an accuracy of one percentor better were sought at Io [ANDERSONETAL1996].

Tests of General Relativity---------------------------
There has been continuing interest in testing the theory of general relativity by bouncing radar signals from hard planetary surfaces and using two-way ranging data from spacecraft anchored to other planetary bodies. No hard surface exists at Jupiter and no previous spacecraft had orbited the planet, so Galileo represented a unique opportunity to investigate this question. Two years of ranging to Galileo were expected to fix the range to Jupiter to an accuracy of about 150 m, with the limit set by orbit determination error along the Earth-Jupiter line and not by limitations of the radio 'instrument'. In combination with results from the Pioneer and Voyager spacecraft, these measurements were expected to lead to an improved ephemerisfor Jupiter.

As Jupiter (and Galileo) appear to pass behind the Sun when viewed from Earth, solar gravity should retard the radio signal propagating between the spacecraft and Earth. One set of time delay measurements to/from the Viking Orbiters and Landers agreed to within 0.1 percent of the General Relativity prediction. Measurements with Galileo were expected to be a factor of 5 worse, but the next best measurements were only to 2 percent of the General Relativity prediction. Not only would another set of measurements at the sub-one percent level be good experimental practice, but Galileo measurements could also verify the agreementover a range of directions in inertial space [WILL1981].

The red shift of the signal in Jupiter's gravitational field could be measured to an accuracy of about +/-1 percent after radiation hardening of the USO crystal in Jupiter's chargedparticle environment.

Search for Gravitational Radiation----------------------------------
Matter undergoing asymmetrical motion (theoretically) radiatesgravitational waves which propagate at the velocity of light.
Observed acceleration of the mean orbital motion of binary pulsar PSR 1913+16 is consistent with predictions [TAYLOR&WEISBERG1989]; other evidence is more ambiguous, and gravity waves themselves had not been detected with certainty before Galileo. For several extended periods during Galileo's cruise to Jupiter, when other spacecraft activity was at a minimum and when the spacecraft was near opposition, its radio link with Earth was monitored carefully for signs of passing, cosmicly generated, long period gravitational waves. Similar observations were conducted simultaneously with the Mars Observer and Ulysses spacecraft so that detections could be confirmed and direction of propagation of the gravitationalwaves inferred from time differences along other paths.
Previous searches have been conducted using Viking, Voyager,and Pioneers 10 and 11 [ARMSTRONG1989].

Solar Corona Observations-------------------------
For several weeks around each of four superior conjunctionsGalileo's radio link passed through the solar corona.
Signals were scattered and refracted as they propagated through the turbulent plasma; the resulting modulation could be analyzed to obtain estimates of coronal structure and dynamics [WOO1993]. Specific objectives of the Galileo solar corona experiments included better understanding of: (1) three-dimensional electron density distribution and its relation to the photospheric magnetic field configuration, solar cycle, distance from the surface, and solar latitude; (2) structural differences among coronal 'holes', active regions, and the 'quiet' Sun; (3) characteristics of the acceleration regions of the solar wind in coronal holes, streamers, and other parts of the corona; (4) energy sources responsible for creation of coronal materials with temperatures over 1000000K; (5) resonant solar oscillations on the dynamical characteristics of the tenuous solar atmosphere; (6) excitation and propagation conditions for magnetoacoustic, Alfven, and other waves; and (7) form and evolution of disturbances near the Sun and their relationship to white light coronal massejections.

Jupiter Occultations--------------------
Radio occultation measurements can contribute to an improved understanding of structure, circulation, dynamics, and transport in the atmosphere of Jupiter. Results from Galileo were based on detailed analysis of the radio signal as it entered and exited occultation by the planet. Three phases of the atmospheric investigation may be defined. The first is to obtain vertical profiles of electron content in the ionosphere; second is to extract large scale structure in the neutral atmosphere; third is to detect and interpret fine scale structure in both the ionospheric and neutral atmosphere profiles and to measure absorption in the neutralatmosphere.

The Galileo tour permitted radio occultations on approximately half of the planned orbits at a number of latitudes. Pioneers 10 and 11 had earlier shown sharp, multiple, dense, low-lying ionospheric layers [FJELDBOETAL1976]. The vertical extent of the ionized layers, their time histories, and detailed structure were sought as keys to both the composition andchemistry of the upper atmosphere.

With precise pointing of the HGA, Galileo was expected to penetrate below the condensation level for ammonia in the neutral atmosphere, providing global measures of ammonia concentration in well-mixed regions where Voyager had produced only one [LINDALETAL1981]. Measurements between 15N and 15S latitudes were expected to provide snapshots of vertical structure of waves propagating in the atmosphere; ingress and egress measurements from the same occultation could provide strong constraints on zonal wavenumber and meridionalstructure [HINSON&MAGALHAES1991].

Satellite Occultations----------------------
Radio data acquired during occultation by a satellite could be used to determine its diameter to accuracies on the order of 1 km and, possibly, properties of any satellite atmosphere or ionosphere. In the case of Io a substantial ionosphere had been detected by Pioneer 10 [KLIOREETAL1975]; repeated occultations by Io were intended to improve understanding of spatial and temporal variability of the charged particlesand their interaction with Jupiter's magnetic field.
Occultations by the Io torus would provide a measure of the total number of free electrons along the propagation path,a useful constraint of the spatial structure of the torus.

Jupiter's Magnetic Field------------------------
Galileo was the first spacecraft equipped to measure both Faraday rotation of propagating waves and differential phase retardation between S- and X-band. Faraday rotation measurements were planned during each occultation by Jupiter and were to be used to investigate the characteristics of the magnetic field in the planet's ionosphere. Different models of the magnetic field yield differences in the predicted Faraday rotation on the order of 0.3 radians; the Faraday rotation experiment designed for Galileoexceeded this threshold by a factor of 10.

Bistatic Scattering from Icy Galilean Moons-------------------------------------------
Monostatic radar echoes from Europa, Ganymede, and Callisto were found to be anomalously diffuse, strong, and polarized [CAMPBELLETAL1978]. By using the Galileo spacecraft as a microwave signal source during encounters with each of these bodies, the bistatic scattering as a function of angle could be determined, providing constraints on both the models for the anomalous scattering process and also the properties ofthe ice that presumably is responsible.


Operational Considerations - Spacecraft
=======================================

Because the HGA never deployed and only right-circularly polarized signals at S-band were available from LGA-1, theFaraday and dual-frequency measurements were never realized.
For the Celestial Mechanics Team, the single frequency meant that signal dispersion resulting from passage through the solar wind, Earth's ionosphere, and other media could not be removed easily from data. For the Radio Propagation Team, the loss of antenna gain meant that only observations with the strongest signals could be made. Penetration below the ionosphere during Jupiter occultations and sensing charged and neutral particle environments of satellites became verydifficult, and the bistatic surface experiments were dropped.
Because Faraday Rotation experiments required linearly transmitted polarizations (available only from the HGA),those were also dropped.

Calibration Description - Spacecraft
====================================
No information available.


Platform Mounting Descriptions - Spacecraft
===========================================
The HGA and LGA-1 antennas were mounted facing in the negative Zr direction; see the GO_SPACECRAFT_DESC_INST.CAT file formore information.


Principal Investigators
=======================
The Team Leader for the Celestial Mechanics Team was John D.
Anderson of the Jet Propulsion Laboratory. Team members were (all from JPL): J.W. Armstrong J.K. Campbell F.B. Estabrook T.P. Krisher E.L. Lau The Team Leader for the Radio Propagation Team was H. Taylor Howard of Stanford University. Team members and affiliations were: V.R. Eshleman Stanford University D.P. Hinson Stanford University A.J. Kliore Jet Propulsion Laboratory G.F. Lindal Jet Propulsion Laboratory R. Woo Jet Propulsion Laboratory M.K. Bird University of Bonn, Germany H. Volland University of Bonn, Germany P. Edenhofer University of Bochum, Germany M. Paetzold DFLR, Germany H. Porsche DFLR, Germany Experiment Representative at JPL for both teams was RandyHerrera.


Instrument Section / Operating Mode Descriptions - Spacecraft
=============================================================
The Galileo radio system consisted of two sections, which could be operated in the following modes:
Section Mode-------------------------------------------
Oscillator two-way (coherent) one-way (non-coherent) RF output low-gain antenna (choice from two) high-gain antenna (failed to deploy properly)
Details for the radio system, as designed, are given in the table below:
Transmitting Parameters: Frequency (MHz) 8415 2295 Transmit Power (w) 12 or 21 9 or 27 HGA Gain (dBi) 50 38 HGA Half-Power Beamwidth (deg) 0.6 1.5 Polarization LCP or RCP Linear Axial Ratio (dB) 2 32
Receiving Parameters: Frequency (MHz) 7167 2115 HGA Gain (dBi) 46 36 Polarization LCP or RCP Linear Noise Temperature (K) 270 1000

Instrument Overview - DSN
=========================
Three Deep Space Communications Complexes (DSCCs) (near Barstow, CA; Canberra, Australia; and Madrid, Spain) comprise the DSN tracking network. Each complex is equipped with several antennas [including at least one each 70-m, 34-m High Efficiency (HEF), and 34-m standard (STD)], associated electronics, and operational systems. Primary activity at each complex is radiation of commands to and reception of telemetry data from active spacecraft. Transmission and reception is possible in several radio-frequency bands, the most common being S-band (nominally a frequency of 2100-2300 MHz or a wavelength of 14.2-13.0 cm) and X-band (7100-8500 MHz or 4.2- 3.5 cm). Transmitter output powers of up to 400 kw areavailable.

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 gravityfields of objects near the spacecraft.

Ground stations can record spacecraft signals that havepropagated through or been scattered from target media.
Measurements of signal parameters after wave interactions with surfaces, atmospheres, rings, and plasmas are used to inferphysical and electrical properties of the target.

Principal investigators vary from experiment to experiment.
See the corresponding section of the spacecraft instrumentdescription 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 theU.S. National Aeronautics and Space Administration.
Specifications include:
Instrument Id : RSS Instrument Host Id : DSN Pi Pds User Id : N/A Instrument Name : RADIO SCIENCE SUBSYSTEM Instrument Type : RADIO SCIENCE Build Date : N/A Instrument Mass : N/A Instrument Length : N/A Instrument Width : N/A Instrument Height : N/A Instrument Manufacturer Name : N/A
For more information on the Deep Space Network and its use in radio science investigations see the reports by [ASMAR&RENZETTI1993] and [ASMAR&HERRERA1993]. For design specifications on DSN subsystems see [DSN810-5]. For anexample of use of the DSN for Radio Science see [TYLERETAL1992].


Subsystems - DSN
================
The Deep Space Communications Complexes (DSCCs) are an integral part of the Radio Science instrument, along with other receiving stations and the spacecraft Radio Frequency Subsystem. Their system performance directly determines the degree of success of Radio Science investigations, and their system calibration determines the degree of accuracy in the results of the experiments. The following paragraphs describethe functions performed by the individual subsystems of a DSCC.
This material has been adapted from [ASMAR&HERRERA1993]; foradditional 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 individuallyinstrumented) are listed in the table.

-------- -------- -------- -------- --------
| DSS 12 | | DSS 18 | | DSS 14 | | DSS 15 | | DSS 16 |
|34-m STD| |34-m STD| | 70-m | |34-m HEF| | 26-m |-------- -------- -------- -------- --------
| | | | |
| v v | v| --------- | ---------
--------->|GOLDSTONE|<---------- |EARTH/ORB|
| SPC 10 |<-------------->| LINK |
--------- ---------
| SPC |<-------------->| 26-M |
| COMM | ------>| COMM |
--------- | ---------
| | |
v | v------ --------- | ---------
| NOCC |<--->| JPL |<------- | |
------ | CENTRAL | | GSFC |
------ | COMM | | NASCOM |
| MCCC |<--->| TERMINAL|<-------------->| |
------ --------- ---------
^ ^
| |
CANBERRA (SPC 40) <---------------- |
|
MADRID (SPC 60) <----------------------

GOLDSTONE CANBERRA MADRID
Antenna SPC 10 SPC 40 SPC 60-------- --------- -------- --------
26-m DSS 16 DSS 46 DSS 66 34-m STD DSS 12 DSS 42 DSS 61DSS 18 DSS 48 DSS 68
34-m HEF DSS 15 DSS 45 DSS 65 70-m DSS 14 DSS 43 DSS 63 Developmental DSS 13

Subsystem interconnections at each DSCC are shown in the diagram below, and they are described in the sections that follow. The Monitor and Control Subsystem is connected to allother 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, andarchiving functions necessary to operate a DSCC.
Communication between the various subsystems is done using a Local Area Network (LAN) hooked up to each subsystem via anetwork 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 inthe 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 ifnecessary.

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 RadioScience 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 passesthem on to the CMC.


DSCC Antenna Mechanical Subsystem---------------------------------
Multi-mission Radio Science activities require support from the 70-m, 34-m HEF, and 34-m STD antenna subnets. The antennas at each DSCC function as large-aperture collectors which, by double reflection, cause the incoming radio frequency (RF) energy to enter the feed horns. The large collecting surface of the antenna focuses the incoming energy onto a subreflector, which is adjustable in both axial and angular position. These adjustments are made to correct for gravitational deformation of the antenna as it moves between zenith and the horizon; the deformation can be as large as 5 cm. The subreflector adjustments optimize the channeling of energy from the primary reflector to the subreflector and then to the feed horns. The 70-m and 34-m HEF antennas have 'shaped' primary and secondary reflectors, with forms that are modified paraboloids. This customization allows more uniform illumination of one reflector by another. The 34-m STD primary reflectors are classical paraboloids, whilethe subreflectors are standard hyperboloids.

On the 70-m and 34-m STD antennas, the subreflector directs received energy from the antenna onto a dichroic plate, a device which reflects S-band energy to the S-band feed horn and passes X-band energy through to the X-band feed horn. In the 34-m HEF, there is one 'common aperture feed,' whichaccepts both frequencies without requiring a dichroic plate.
RF energy to be transmitted into space by the horns is focused by the reflectors into narrow cylindrical beams, pointed with high precision (either to the dichroic plate or directly to the subreflector) by a series of drive motors and gear trains that can rotate the movable components and theirsupport 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 theAPA 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 antennastatus 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 predeterminedSystematic Error Correction (SEC) model.

Independent of CONSCAN state, subreflector motion in at least the z-axis may introduce phase variations into the received Radio Science data. For that reason, during certain experiments, the subreflector in the 70-m and 34-m HEFs may be frozen in the z-axis at a position (often based on elevation angle) selected to minimize phase change and signal degradation. This can be done via Operator Control Inputs (OCIs) from the LMC to the Subreflector Controller (SRC) which resides in the alidade room of the antennas. The SRC passes the commands to motors that drive the subreflector to the desired position. Unlike the 70-m and 34-m HEFs which have azimuth-elevation (AZ-EL) drives, the 34-m STD antennas use (hour angle-declination) HA-DEC drives. The same positioning of the subreflector on the 34-m STD does notcreate the same effect as on the 70-m and 34-m HEFs.

Pointing angles for all three antenna types are computed by the NOCC Support System (NSS) from an ephemeris provided by the flight project. These predicts are received and archived by the CMC. Before each track, they are transferred to the APA, which transforms the direction cosines of the predicts into AZ-EL coordinates for the 70-m and 34-m HEFs or into HA-DEC coordinates for the 34-m STD antennas. The LMC operator then downloads the antenna AZ-EL or HA-DEC predict points to the antenna-mounted ACS computer along with a selected SEC model. The pointing predicts consist of time-tagged AZ-EL or HA-DEC points at selected time intervals along with polynomial coefficients for interpolation betweenpoints.

The ACS automatically interpolates the predict points, corrects the pointing predicts for refraction and subreflector position, and adds the proper systematic error correction and any manually entered antenna offsets. The ACS then sends angular position commands for each axis at the rate of one per second. In the 70-m and 34-m HEF, rate commands are generated from the position commands at the servo controller and are subsequently used to steer the antenna. In the 34-m STD antennas motors, rather than servos, are used to steer the antenna; there is no feedbackonce the 34-m STD has been told where to point.

When not using binary predicts (the routine mode for spacecraft tracking), the antennas can be pointed using 'planetary mode' -- a simpler mode which uses right ascension (RA) and declination (DEC) values. These change very slowly with respect to the celestial frame. Values are provided to the station in text form for manual entry. The ACS quadratically interpolates among three RA and DEC pointswhich are on one-day centers.

A third pointing mode -- sidereal -- is available for tracking radio sources fixed with respect to the celestialframe.

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 bymoving 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 theirbeamwidths are twice as large as on the 70-m antennas.


DSCC Antenna Microwave Subsystem--------------------------------
70-m Antennas: Each 70-m antenna has three feed conesinstalled 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 toR&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 theamplifiers are Block IIA TWMs.

34-m STD Antennas: These antennas have two feed horns, one for S-band signals and one for X-band. The horns are mounted on a cone which is fixed in relation to the subreflector. A dichroic plate mounted above the horns directs energy fromthe subreflector into the proper horn.

The AMS directs the received S- and X-band signals through polarizer plates and on to amplification. There are twoBlock III S-band TWMs and two Block I X-band TWMs.

34-m HEF Antennas: Unlike the other antennas, the 34-m HEF uses a single feed for both S- and X-band. Simultaneous S- and X-band receive as well as X-band transmit is possible thanks to the presence of an S/X 'combiner' which acts as a diplexer. For S-band, RCP or LCP is user selected through a switch so neither a polarizer nor an orthomode transducer is needed. X-band amplification options include two Block II TWMs or an HEMT Low Noise Amplifier (LNA). S-bandamplification is provided by an FET LNA.


DSCC Receiver-Exciter Subsystem-------------------------------
The Receiver-Exciter Subsystem is composed of three groups of equipment: the closed-loop receiver group, the open-loop receiver group, and the RF monitor group. This subsystem is controlled by the Receiver-Exciter Controller (REC) which communicates directly with the DMC for predicts and OCIreception 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) whichreceives 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 thereceiver system.

Closed Loop Receivers: The Block IV receiver-exciter at the 70-m stations allows for two receiver channels, each capable of L-Band (e.g., 1668 MHz frequency or 18 cm wavelength), S-band, or X-band reception, and an S-band exciter for generation of uplink signals through the low-power or high-power transmitter. The Block III receiver-exciter at the 34-m STD stations allows for two receiver channels, each capable of S-band or X-band reception and an exciter used togenerate an uplink signal through the low-power transmitter.
The receiver-exciter at the 34-m HEF stations allows for onechannel only.

The closed-loop receivers provide the capability for rapid acquisition of a spacecraft signal and telemetry lockup. In order to accomplish acquisition within a short time, the receivers are predict driven to search for, acquire, and track the downlink automatically. Rapid acquisition precludes manual tuning though that remains as a backup capability. The subsystem utilizes FFT analyzers for rapid acquisition. The predicts are NSS generated, transmitted to the CMC which sends them to the Receiver-Exciter Subsystem where two sets can be stored. The receiver starts acquisition at uplink time plus one round-trip-light-time or at operator specified times. The receivers may also be operated from the LMC without a local operator attending them. The receivers send performance and status data,displays, and event messages to the LMC.

Either the exciter synthesizer signal or the simulation (SIM) synthesizer signal is used as the reference for the Doppler extractor in the closed-loop receiver systems, depending on the spacecraft being tracked (and Project guidelines). The SIM synthesizer is not ramped; instead it uses one constant frequency, the Track Synthesizer Frequency(TSF), which is an average frequency for the entire pass.

The closed-loop receiver AGC loop can be configured to one of three settings: narrow, medium, or wide. It will be configured such that the expected amplitude changes are accommodated with minimum distortion. The loop bandwidth (2BLo) will be configured such that the expected phase changes can be accommodated while maintaining the bestpossible 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 tothe DSCC Spectrum Processing Subsystem (DSP).

The OLR utilizes a fixed first Local Oscillator (LO) frequency and a tunable second LO frequency to minimize phase noise and improve frequency stability. The OLR consists of an RF-to-IF downconverter located in the antenna, an IF selection switch (IVC), and a Radio Science IF-VF downconverter (RIV) located in the SPC. The RF-IF downconverters in the 70-m antennas are equipped for four IF channels: S-RCP, S-LCP, X-RCP, and X-LCP. The 34-m HEF stations are equipped with a two-channel RF-IF: S-band and X-band. The IVC switches the IF input between the 70-m and34-m HEF antennas.

The RIV contains the tunable second LO, a set of videobandpass 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 electronicinterface 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 signallevel 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 RadioScience 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 SNTmeasurements.

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 measurementof 30K to have a one-sigma uncertainty of 0.3K or 1%.


DSCC Transmitter Subsystem--------------------------
The Transmitter Subsystem accepts the S-band frequency exciter signal from the Block III or Block IV Receiver- Exciter Subsystem exciter and amplifies it to the required transmit output level. The amplified signal is routed via the diplexer through the feed horn to the antenna and thenfocused 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 at70-m stations.


DSCC Tracking Subsystem-----------------------
The Tracking Subsystem primary functions are to acquire and maintain communications with the spacecraft and to generateand 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) tapewhich 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 andtiming 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 toNOCC.

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 thespacecraft and the tracking station on Earth.


DSCC Spectrum Processing Subsystem (DSP)----------------------------------------
The DSCC Spectrum Processing Subsystem (DSP) located at the SPC digitizes and records on magnetic tapes the narrowband output data from the RIV. It consists of a Narrow Band Occultation Converter (NBOC) containing four Analog-to- Digital Converters (ADCs), a ModComp CLASSIC computer processor called the Spectrum Processing Assembly (SPA), and two to six magnetic tape drives. Magnetic tapes are known as Original Data Records (ODRs). Electronic near real-time transmission of data to JPL (an Original Data Stream, or ODS) may be possible in certain circumstances;
The DSP is operated through the LMC. Using the SPA-R software, the DSP allows for real-time frequency and time offsets (while in RUN mode) and, if necessary, snap tuning between the two frequency ranges transmitted by the spacecraft: coherent and non-coherent. The DSP receives Radio Science frequency predicts from the CMC, allows for multiple predict set archiving (up to 60 sets) at the SPA, and allows for manual predict generation and editing. It accepts configuration and control data from the LMC, provides display data to the LMC, and transmits the signal spectra from the SSI as well as status information to NOCC and theProject 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 1600bpi GCR format.

Through the DSP-RIC interface the DSP controls the RIV filter selection and attenuation levels. It also receives RIV performance monitoring via the RIC. In case of failure of the DSP-RIC interface, the RIV can be controlled manuallyfrom 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 Scienceexperiments. 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 DSNKeyword File.

The DSP can be used to duplicate ODRs. It also has the capability to play back a certain section of the recordeddata 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 UTCand 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 40relative 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-mantennas 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 Rdenotes right circular polarization (RCP).

DSS S-Band Characteristics
64-m 70-m 34-m 34-m Transmit STD HEF-------- ----- ----- ----- -----
Frequency (MHz) 2110- 2110- 2025- N/A2120 2120 2120
Wavelength (m) 0.142 0.142 0.142 N/A Ant Gain (dBi) 62.7 55.2 N/A Beamwidth (deg) 0.119 0.31 N/A Polarization L or R L or R N/A Tx Power (kW) 20-400 20 N/A
Receive-------
Frequency (MHz) 2270- 2270- 2270- 2200-2300 2300 2300 2300
Wavelength (m) 0.131 0.131 0.131 0.131 Ant Gain (dBi) 61.6 63.3 56.2 56.0 Beamwidth (deg) 0.108 0.27 0.24 Polarization L & R L & R L or R L or R System Temp (K) 22 20 22 38
DSS X-Band Characteristics (N/A for Galileo)
64-m 70-m 34-m 34-m Transmit STD HEF-------- ----- ----- ----- -----
Frequency (MHz) 8495 8495 N/A 7145-7190
Wavelength (m) 0.035 0.035 N/A 0.042 Ant Gain (dBi) 74.2 N/A 67 Beamwidth (deg) N/A 0.074 Polarization L or R L or R N/A L or R Tx Power (kW) 360 360 N/A 20
Receive-------
Frequency (MHz) 8400- 8400- 8400- 8400-8500 8500 8500 8500
Wavelength (m) 0.036 0.036 0.036 0.036 Ant Gain (dBi) 71.7 74.2 66.2 68.3 Beamwidth (deg) 0.031 0.075 0.063 Polarization L & R L & R L & R L & R System Temp (K) 27 20 25 20

Electronics - DSN
=================

DSCC Open-Loop Receiver-----------------------
The open loop receiver block diagram shown below is for 70-m and 34-m High-Efficiency (HEF) antenna sites. Based on a tuning prediction file, the POCA controls the DANA synthesizer the output of which (after multiplication) mixes input signals at both S- and X-band to fixed intermediate frequencies for amplification. These signals in turn are down converted and passed through additional filters until they yield baseband output of up to 25 kHz in width. The baseband output is digitally sampled by the DSP and either written to magnetic tape or electronically transferred forfurther analysis.

S-Band X-Band 2295 MHz 8415 MHz Input Input| |
v v--- --- --- ---
| X |<--|x20|<--100 MHz 100 MHz-->|x81|-->| X |--- --- --- ---
| |
295| |315
MHz| |MHz v v--- -- 33.1818 --- ---
| X |<--|x3|<------ MHz ------>|x11|-->| X |--- -- |115 | --- ---
| |MHz | || | | |
50| 71.8181 --- --- |50
MHz| MHz->| X | | X |<-10 MHz |MHz v --- --- v--- ^ ^ ---
| X |<--60 MHz | | 60 MHz-->| X |--- | | ---
| 9.9 | 43.1818 MHz | 9.9 | | MHz ------------- MHz || | ^ | |
10| v | v |10 MHz| --- ---------- --- |MHz|------>| X | | DANA | | X |<------|
| --- |Synthesizr| --- || | ---------- | |
v v ^ v v------- ------- | ------- -------
|Filters| |Filters| ---------- |Filters| |Filters||3,4,5,6| | 1,2 | | POCA | | 1,2 | |3,4,5,6|
------- ------- |Controller| ------- -------
| | ---------- | |
10| |0.1 0.1| |10
MHz| |MHz MHz| |MHz v v v v--- --- --- ---
| X |- -| X | | X |- -| X |
--- | | --- --- | | ---
^ | | ^ ^ | | ^
| | | | | | | |
10 | | 0.1 0.1 | | 10
MHz | | MHz MHz | | MHz| | | |
v v v v Baseband Baseband Output Output

Reconstruction of the antenna frequency from the frequency of the signal in the recorded data can be achieved through useof one of the following formulas.

Radio Science IF-VF (RIV) Converter Assembly at 70-m and 34-m High-Efficiency (HEF) antennas:
FSant=3*[POCA+(790/11)*10^6] + 1.95*10^9 - Fsamp - Frec
FXant=11*[POCA-10^7] + 8.050*10^9 - 3*Fsamp + Frec
Multi-Mission Receivers at 34-m Standard antennas (DSS 42 and 61; the diagram above does not apply):
FSant=48*POCA + 3*10^8 - 0.75*Fsamp + Frec
FXant = (11/3)*[48*POCA + 3*10^8 - 0.75*Fsamp] + Frec
where FSant = S-band antenna frequency FXant = X-band antenna frequency POCA = POCA frequency Fsamp = sampling frequency Frec = frequency of recorded signal

Filters - DSN
=============

DSCC Open-Loop Receiver-----------------------
Nominal filter center frequencies and bandwidths for theOpen-Loop Receivers are shown in the table below.

Filter Center Frequency 3 dB Bandwidth------ ---------------- --------------
1 0.1 MHz 90 Hz 2 0.1 MHz 450 Hz 3 10.0 MHz 2000 Hz 4 10.0 MHz 1700 Hz (S-band) 6250 Hz (X-band) 5 10.0 MHz 45000 Hz 6 10.0 MHz 21000 Hz
MMR filters (DSS 42 and 61) include the following:
Filter Center Frequency 3 dB Bandwidth------ ---------------- --------------
5 Unknown 2045 Hz (S-band) 7500 Hz (X-band)
Detectors - DSN
===============

DSCC Open-Loop Receivers------------------------
Open-loop receiver output is detected in software by theradio 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 beavailable 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 calibrationsare 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 toattenuator 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 dBwhile 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 specificinformation 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; pointingpredicts 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 phasechanges in the received signal.


DSCC Receiver-Exciter Subsystem-------------------------------
The diplexer in the signal path between the transmitter and the feed horns on all three antennas may be configured so that it is out of the received signal path in order toimprove 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 furtherinformation.


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 beaccommodated 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 receptionin two-way mode is usually preferred for routine tracking.
Occasionally the spacecraft operates coherently while two ground stations receive the 'downlink' signal; this issometimes 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 areshown below.

Signal Channel Number Receiver (70-m or HEF) (34-m STD)--------------------- ------------- ----------
J1 X-RCP not used J2 S-RCP not usedJ3 X-LCP X-RCP
J4 S-LCP S-RCP


Location - DSN
==============
Station locations are documented in [GEO-10REVD]. Geocentriccoordinates are summarized here.

Geocentric Geocentric Geocentric Station Radius (km) Latitude (N) Longitude (E)--------- ----------- ------------ -------------
Goldstone DSS 12 (34-m STD) 6371.997815 35.1186672 243.1945048 DSS 13 (develop) 6372.117062 35.0665485 243.2051077 DSS 14 (70-m) 6371.992867 35.2443514 243.1104584 DSS 15 (34-m HEF) 6371.9463 35.2402863 243.1128186 DSS 16 (26-m) 6371.9608 35.1601436 243.1264200 DSS 18 (34-m STD) UNK UNK UNK
Canberra DSS 42 (34-m STD) 6371.675607 -35.2191850 148.9812546 DSS 43 (70-m) 6371.688953 -35.2209308 148.9812540 DSS 45 (34-m HEF) 6371.692 -35.21709 148.97757 DSS 46 (26-m) 6371.675 -35.22360 148.98297 DSS 48 (34-m STD) UNK UNK UNK
Madrid DSS 61 (34-m STD) 6370.027734 40.2388805 355.7509634 DSS 63 (70-m) 6370.051015 40.2413495 355.7519776 DSS 65 (34-m HEF) 6370.021370 40.2372843 355.7485968 DSS 66 (26-m) 6370.036 40.2400714 355.7485976 DSS 48 (34-m STD) UNK UNK UNK

Measurement Parameters - DSN
============================

Open-Loop System----------------
Output from the Open-Loop Receivers (OLRs), as sampled and recorded by the DSCC Spectrum Processing Subsystem (DSP), is a stream of 8- or 12-bit quantized voltage samples. The nominal input to the Analog-to-Digital Converters (ADCs) is +/-10 volts, but the precise scaling between input voltages and output digitized samples is usually irrelevant for analysis; the digital data are generally referenced to a known noise or signal level within the data stream itself -- for example, the thermal noise output of the radio receivers which has a known system noise temperature (SNT). Raw samples comprise the data block in each DSP record; a header record (presently 83 16-bit words) contains ancillary information such as:
time tag for the first sample in the data block RMS values of receiver signal levels and ADC outputs POCA frequency and drift rate

Closed-Loop System------------------
Closed-loop data are recorded in Archival Tracking Data Files (ATDFs), as well as certain secondary products such as the Orbit Data File (ODF). The ATDF Tracking Logical Record contains 117 entries including status information andmeasurements of ranging, Doppler, and signal strength.


ACRONYMS AND ABBREVIATIONS - DSN

================================
ACS Antenna Control System ADC Analog-to-Digital Converter AGC Automatic Gain Control AMS Antenna Microwave System APA Antenna Pointing Assembly ARA Area Routing Assembly ATDF Archival Tracking Data File AZ Azimuth CMC Complex Monitor and Control CONSCAN Conical Scanning (antenna pointing mode) CRG Coherent Reference Generator CUL Clean-up Loop DANA a type of frequency synthesizer dB deciBel dBi dB relative to isotropic DCO Digitally Controlled Oscillator DEC Declination deg degree DFLR Deutsche Forschungsanstalt fur Luft- und Raumfahrt DMC DSCC Monitor and Control Subsystem DSCC Deep Space Communications Complex DSN Deep Space Network DSP DSCC Spectrum Processing Subsystem DSS Deep Space Station DTK DSCC Tracking Subsystem E east EL Elevation FET Field Effect Transistor FFT Fast Fourier Transform FTS Frequency and Timing Subsystem GCF Ground Communications Facility GCR Group Coded Recording GHz gigahertz GPS Global Positioning System GSFC Goddard Space Flight Center HA Hour Angle HEF High-Efficiency (as in 34-m HEF antennas)HEMT
HGA High Gain Antenna IF Intermediate Frequency IVC IF Selection Switch JPL Jet Propulsion Laboratory K Kelvin km kilometer kW kilowatt L-band approximately 1668 MHz LAN Local Area Network LCP Left-Circularly Polarized LGA Low Gain Antenna LMC Link Monitor and Control LNA Low-Noise Amplifier LO Local Oscillator m meters MCA Master Clock Assembly MCCC Mission Control and Computing Center MDA Metric Data Assembly MHz Megahertz MMR Multi-Mission Radio (Science) MON Monitor and Control System MSA Mission Support Area N north NAR Noise Adding Radiometer NASA National Aeronautics and Space Administration NASCOM NASA Communications NBOC Narrow-Band Occultation Converter NIST SPC 10 time relative to UTC NIU Network Interface Unit NOCC Network Operations and Control System NRV NOCC Radio Science/VLBI Display Subsystem NSS NOCC Support System OCI Operator Control Input ODF Orbit Data File ODR Original Data Record ODS Original Data Stream OLR Open Loop Receiver PLO Programmable Local Oscillator POCA Programmable Oscillator Control Assembly PPM Precision Power Monitor RA Right Ascension REC Receiver-Exciter Controller RCP Right-Circularly Polarized RF Radio Frequency RIC RIV Controller RIV Radio Science IF-VF Converter Assembly RMDCT Radio Metric Data Conditioning Team RTLT Round-Trip Light Time S-band approximately 2100-2300 MHz sec second SEC System Error Correction SIM Simulation SLE Signal Level Estimator SNR Signal-to-Noise Ratio SNT System Noise Temperature SOE Sequence of Events SPA Spectrum Processing Assembly SPC Signal Processing Center SRA Sequential Ranging Assembly SRC Sub-Reflector Controller SSI Spectral Signal Indicator STD Standard (as in 34-m STD antennas) TID Time Insertion and Distribution Assembly TSF Tracking Synthesizer Frequency TWM Traveling Wave Maser Tx Transmitter UNK unknown UTC Universal Coordinated Time VF Video Frequency X-band approximately 7800-8500 MHz