PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM LABEL_REVISION_NOTE = "2000-06-29 RS:simpson Revision; 2001-02-21 RS:simpson Revision; 2001-12-06 RS:simpson Revision; 2002-01-25 RS:simpson Revision; 2002-02-25 RS:simpson Add RSR; 2002-07-09 RS:simpson Fix typos; 2003-05-24 RS:simpson Fix RSR; 2005-07-22 RS:simpson Update DSS 65 location; 2007-07-19 RS:simpson Updates, corrections at EOM" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "MGS" INSTRUMENT_ID = "RSS" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "RADIO SCIENCE SUBSYSTEM" INSTRUMENT_TYPE = "RADIO SCIENCE" INSTRUMENT_DESC = " Instrument Overview =================== The Mars Global Surveyor (MGS) Radio Science investigations utilized instrumentation with elements on the spacecraft and at the NASA Deep Space Network (DSN). Much of this was shared equipment, being used for routine telecommunications as well as for Radio Science. The performance and calibration of both the spacecraft and tracking stations directly affected the radio science data accuracy, and they played a major role in determining the quality of the results. The spacecraft part of the radio science instrument is described immediately below; that is followed by a description of the DSN (ground) part of the instrument. Instrument Specifications - Spacecraft ====================================== The Mars Global Surveyor spacecraft telecommunications subsystem served as part of a radio science subsystem for investigations of Mars. Many details of the subsystem are unknown; its 'build date' is taken to be 1994-10-12, which was during the Prelaunch Phase of the Mars Global Surveyor mission. Instrument Id : RSS Instrument Host Id : MGS Pi Pds User Id : UNK Instrument Name : RADIO SCIENCE SUBSYSTEM Instrument Type : RADIO SCIENCE Build Date : 1994-10-12 Instrument Mass : UNK Instrument Length : UNK Instrument Width : UNK Instrument Height : UNK Instrument Manufacturer Name : UNK Instrument Overview - Spacecraft ================================ The spacecraft radio system was constructed around a redundant pair of X-band Mars Observer Transponders (MOT). Other components included two redundant Low-Gain Receive antennas (LGR); two redundant Low-Gain Transmit antennas (LGT); two redundant Command Detector Units (CDU); two redundant Traveling Wave Tube Amplifiers (TWTA); a single high-gain antenna (HGA); a single UltraStable Oscillator (USO); miscellaneous cables, connectors, waveguides, and switches; and a Ka-band Link Experiment (KaBLE). The X-band capability reduced plasma effects on radio signals by a factor of 10 compared with previous S-band systems, but absence of a dual-frequency capability (both S- and X-band) meant that plasma effects could not be estimated and removed from radio data. The spacecraft was capable of X-band uplink commanding and simultaneous X-band downlink telemetry. The MOT generated a downlink signal in either a 'coherent' or a 'non-coherent' mode, also known as the 'two-way' and 'one-way' modes, respectively. When operating in the coherent mode, the MOT behaved as a conventional transponder; its transmitted carrier frequency was derived coherently from the received uplink carrier frequency with a 'turn-around ratio' of 880/749. The nominal coherent downlink frequency was 8417716050 Hz. In the non-coherent mode, the downlink carrier frequency was derived from one of the spacecraft's on-board crystal- controlled oscillators. After warm-up, the 'auxiliary' oscillator (AUX OSC) frequency was estimated to be 8417700000. Hz. A temperature-controlled UltraStable Oscillator (USO) was used as the frequency reference during one-way Radio Science observations. Representative USO frequencies (at X-Band) are shown in the table below: Earth Receive Date and Time Frequency (Hz) Drift (Hz/s) --------------------------- -------------- ------------- 1997-270T07:23:52 8423152969.720 +1.8560E-06 1998-049T02:19:38 8423152989.927 +1.5034E-06 1999-095T14:55:53 8423153024.367 +4.5321E-07 2000-001T05:54:53 8423153036.279 +3.7603E-07 2001-001T04:43:45 8423153045.552 +2.3561E-07 2003-001T05:25:58 8423153056.611 +1.1274E-07 2005-001T01:26:05 8423153062.908 +8.9172E-08 A Traveling Wave Tube Amplifier (TWTA), driven at saturation, amplified the MOT output before the signals were radiated via (nominally) the 1.5 m diameter parabolic high gain antenna (HGA). During Inner Cruise, maneuvers, and spacecraft anomalies the TWTA output was fed to a low- gain transmitting antenna. Nominal Effective Isotropic Radiated Power (EIRP) for both high- and low-gain antennas is shown below: Quantity Units HGA LGT (Mapping) (Inner Cruise) ------------------------ ----- --------- -------------- RF Power Output dBm 44.23 44.23 Transmitter Circuit Loss dB -0.97 -1.37 Boresight Antenna Gain dBi 38.72 6.90 Antenna Pointing Loss dB -0.30 -4.60 ----- ----- EIRP toward Earth dB 81.68 45.16 The strength of a spacecraft carrier signal, and thus the quality of the radio science data, depends on its modulation state. Mars Global Surveyor telemetry data were sent to Earth at rates between 10 bits per second (bps) and 75 kilobits per second (kbps). Minimum Pt/No ratio (total signal power to receiver noise in 1 Hz bandwidth) was 43 dB during Inner Cruise with LGT1 transmitting to a 34-m HEF on the ground; this would support a data rate of at least 8 kbps. For Outer Cruise Pt/No began at 76 dB and dropped monotonically to 50 dB, the latter supporting a data rate of 43 kbps. During Mapping, Pt/No varied between 47 dB and 64 dB, allowing data rates to 34-m HEF antennas of at least 21 kbps. The HGA consisted of a 1.5-meter Cassegrain reflector system with a dual-frequency (X- and Ka-band) feed horn. Reflector, subreflector, and struts were spares from the Mars Observer mission. The feed horn was a new Lockheed Martin Astronautics (LMA) design consisting of co-located X- and Ka-band elements. A radome fabricated of reinforced germanium-coated Kapton covered the entire HGA aperture to protect the system from the predicted aerobraking thermal environment. TWTAs and associated components were enclosed and mounted on the back of the HGA structure. The HGA structure was mounted at the end of a 2-meter boom with two gimbals to control azimuth and elevation pointing. Certain parts of the sky were not visible with the HGA, but pointing toward Earth was possible from all parts of the orbit (see important exceptions described in the section 'Operational Considerations - Spacecraft' below). The HGA azimuth gimbal was used during Mapping to track the slowly changing seasonal (apparent) motion of the Earth. The HGA elevation gimbal rotated at orbital rate to track the Earth and was rewound every orbit during Earth occultation. The orbital rate was 0.051 deg/sec, and the rewind rate was 0.12 deg/sec. Stepper motors controlled both gimbals. Step size was 0.009375 deg; the stepping rate of approximately 5 per second was visible as a 5 Hz modulation in open-loop Radio Science data collected after HGA deployment. HGA performance is defined in terms of gain and beamwidth. The table below summarizes some of those data. Beamwidth is half-power, full-width, one-way. Nominal polarization is right-hand circular in all cases. Quantity X-Band X-Band Ka-Band Downlink Uplink Downlink -------- ------ ------- ------ ------- -------- Frequency Reference N/A AUX OSC USO AUX OSC USO or VCO Frequency (MHz) 7164.6 8417.7 8423.1 31987.3 32008.0 Beamwidth (deg) 1.717 1.546 1.546 0.375 0.375 Axial Ratio (dB) 1.0 1.0 1.0 1.0 1.0 Measured Gain (dBi) 37.43 39.10 38.72 49.14 48.99 Low-gain antennas were light-weight, low-cost microstrip patch antennas derived from earlier missile and spacecraft programs. Their performance is summarized below. Axial ratio is defined over +/- 85 degrees from boresight. Beamwidth is half-power, full-width, one-way. Nominal polarization is right-hand circular in all cases. Quantity X-Band Uplink X-Band Downlink -------- ------------- --------------- Center Frequency (MHz) 7200 8400 Bandwidth (MHz) 45 50 Axial Ratio (dB) <8 <8 Beamwidth (deg) 80 80 Gain (dBi) 6.3 6.9 More information can be found in the MGS Telecommunications System Operations Reference Handbook [JPLD-14027]. Science Objectives ================== Two different types of radio science experiments were conducted with Mars Global Surveyor: radio tracking experiments in which the magnitude and direction of the planet's gravity field were derived from the Doppler (and, sometimes, ranging) measurements, and radio propagation experiments in which signal modulation detected on Earth could be attributed to properties of the medium. Several variations of the radio propagation experiments were carried out including radio occultations by the atmosphere of Mars and scattering from its surface. Measurements were also obtained when the radio wave passed through the solar corona. Gravity Measurements -------------------- Measurement of the gravity field provides significant constraints on inferences about the interior structure of Mars. Precise, detailed study of the spacecraft motion in Mars orbit can yield the mass distribution of the planet. Topographic data obtained by the Mars Orbiting Laser Altimeter (MOLA) forms a critical adjunct to these measurements since only after the gravitational effects are adjusted for topography can the gravity anomalies be interpreted geophysically. Studies of the gravity field emphasize both the global field and local characteristics of the field. The first task is to determine the global field. Doppler and range tracking measurements yield accurate spacecraft trajectory solutions. Simultaneously with reconstruction of the spacecraft orbit, observation equations for field coefficients and a small number of ancillary parameters can be solved. This type of gravity field solution is essential for characterizing tectonic phenomena and can also be used to study localized features. An early gravity model based on MGS data was presented by [SMITHETAL1999]. Later versions were described in [LEMOINEETAL2001] and [YUANETAL2001]. 'Short-arc' line-of-sight Doppler tracking measurements obtained when the Earth-to-spacecraft line-of-sight is within a few degrees of the orbit plane provide the highest resolution of local features. The results from this type of observation typically are presented as contoured acceleration profiles of specific features (e.g., craters, volcanoes, etc.) or line-of-sight acceleration maps of specific regions. The high spatial resolution of these products makes them especially useful to geophysicists for study of features in the size range of 300 to 1,000 km. Because of the relative simplicity of the data analysis, results can be available very soon after the data are collected. A by-product of the gravity field analysis is information on the density structure of the upper atmosphere [TRACADISETAL2001]. Radio Occultation Measurements ------------------------------ Atmospheric measurements by the method of radio occultation contribute to an improved understanding of structure, circulation, dynamics, and transport in the atmosphere of Mars. These results are based on detailed analysis of the radio signal received from MGS as it entered and exited occultation by the planet. Two phases of the atmospheric investigation may be defined. The first is to obtain vertical profiles of atmospheric structure with emphasis on investigation of large-scale phenomena. The second is to concentrate on studies of scintillations in the signal, which provide information on smaller scale variations -- e.g, turbulence. Retrieval of atmospheric profiles requires coherent samples of the radio signal that has propagated through the atmosphere, plus accurate knowledge of the antenna pointing and the spacecraft trajectory. The latter was obtained first from the MGS Navigation Team and later from high quality orbits derived by the Team's own gravity investigators. Initial solutions from MGS occultations provided atmospheric structure -- temperature and pressure vs. absolute radius -- to altitudes as high as about 50 km from the surface [HINSONETAL1999]. The spatial and temporal coverage in the radio occultation experiments are determined by the geometry of the spacecraft orbit and the dates and times at which occultation data were acquired. Since radio occultation experiments were conducted on a regular basis using a polar orbit, there was extensive occultation coverage at high northern and southern latitudes (e.g., beyond 60 degrees). Often several occultations were observed in succession in each hemisphere at time spacings of less than two hours. Later in the primary mission, as the orbit appeared to drift from edge-on to nearly broadside as viewed from Earth, occultation points moved toward the equator and the entry/exit angle approached grazing. For several months in 1999, there were no occultations at all. More than 21000 neutral atmosphere profiles had been derived from MGS radio occultations by the end of the mission. No scintillations which could be attributed to turbulence were detected in the occultation data. It is also possible to retrieve profiles of electron density in the ionosphere from occultation data. When the density is high enough, it reduces the refractive index of the medium (where the neutral atmosphere increases the refractive index) causing the radio wave phase to be advanced. The methods for retrieval are somewhat different since hydrostatic equilibrium cannot be assumed in the plasma. Several thousand electron density profiles were derived from MGS data, mostly near the terminator [WITHERSETAL2005]. Bistatic Surface Scattering Measurements ------------------------------------------ For a few seconds before and after geometrical occultation the HGA illuminated a small strip of surface as well as the atmosphere. Under some circumstances, an echo could be observed from the surface. For smooth surfaces, the echo properties (particular the strength) could be related to the surface dielectric constant through the Fresnel reflection equations. For rougher surfaces, diffraction and surface wave phenomena may play a role. Surface echoes were sought during most occultation events and several thousand were studied in some detail [TYLERETAL2001]. The spacecraft telecommunications antenna could also be pointed toward the surface of the planet. The strength of the scattered signal from the illuminated area could then be interpreted in terms of the dielectric constant of the surface through the Fresnel equations; the frequency dispersion of the signal could be related to the texture of the surface at the reflecting point. One such experiment was conducted over the Mars Polar Lander/Deep Space 2 site in May 2000 [SIMPSON&TYLER2001]. For some surface materials, the Fresnel equations do not apply; most of the signal penetrates the surface and is scattered by the volume below. Clean water ice is known to have these properties, and has been postulated as the cause of anomalous scattering from the Galilean satellites of Jupiter and from polar deposits on both Mercury and Mars. Interpreting such observations quantitatively is not straightforward, but Mars Global Surveyor had the potential for collecting such data in a bistatic geometry, providing additional insight on the surface structure and properties. Although such observations were sought, none were ever scheduled. Search for Gravitational Waves ------------------------------ During the MGS Cruise Phase, nearly continuous radio tracking of the spacecraft was conducted. At the same time an effort was made to keep on-board spacecraft activity to a minimum. The objective during this period was to search for evidence that gravitational waves were passing through the solar system while the spacecraft was at maximum separation from known massive bodies. A gravitational wave was expected to change the position and motion of the spacecraft, the Earth, or both. Two-way tracking was used; both closed-loop and open-loop data were collected, the latter being more sensitive but also more voluminous. Sources of gravitational waves have been postulated outside the solar system [ANDERSONETAL1993][ESTABROOKETAL1995], but no unambiguous detection of such radiation has ever been made. Solar Scintillation and Faraday Rotation Experiments ---------------------------------------------------- Solar scintillation and Faraday rotation experiments are conducted to improve our understanding of the structure and dynamics of the solar corona and wind. Because Mars orbits the Sun, spacecraft like MGS are transported behind the solar disk, as seen from Earth. Radio waves propagating between MGS and Earth stations are refracted and scattered (scintillation) by the solar plasma [WOO1993]. Intensity fluctuations can be related to fluctuations in electron density along the path, while Doppler or phase scintillations can be related to both electron density fluctuations and also the speed of the solar wind. Many plasma effects decrease as the square of the radio frequency; scintillations are about an order of magnitude stronger at X-band than Ka-band. The first solar conjunction observed with MGS was on 12 May 1998; more data were collected and archived two years later [BARBINIS2001]. Operational Considerations - Spacecraft ======================================= Descriptions given above are for nominal performance. The spacecraft transponder system comprised redundant units, each with slightly different characteristics. As transponder units age, their performance changes slightly. More importantly, the performance for radio science depended on operational factors such as the modulation state for the transmitters, which cannot be predicted in advance. The performance also depended on factors which were not always under the control of the Mars Global Surveyor Project. Early in the Mapping phase, the HGA assembly encountered an obstruction. Two gimbals allowed the HGA to point toward Earth; the elevation gimbal rotated the HGA in the orbit plane, and the azimuth gimbal pointed the HGA out of the orbit plane at the Earth 'beta' angle. The obstruction prevented the azimuth gimbal from pointing at any beta angle less than 41.5 deg. After the anomaly (1999-04-15) and until the beta angle exceeded 41.5 deg (1999-05-06), the spacecraft was operated in the Fixed High Gain Antenna (FHGA) configuration. The Earth beta angle dropped below 41.5 deg again in February 2000 and remained there until June 2001, during which the spacecraft was operated in the 'Beta Supplement' mode. In Beta Supplement the spacecraft was oriented so that the azimuth gimbal could be set to the supplement of the beta angle; the elevation gimbal was flipped. The supplement to the beta angle ranged from 139 to 183 deg during the second year of Mapping. But there was physical interference between the HGA and its boom; and HGA rewinds, which normally occurred while the spacecraft was occulted, now took place on the 'front' side of the planet. The boom interference precluded collection of occultation egress measurements during most of Mapping; the HGA rewind reduced the amount of nearside radio tracking that could be captured. During normal operations, the spacecraft sensed solar eclipses; a pre-programmed timing offset initiated onboard radio occultation activities so that orbit prediction errors would not affect collection of occultation data. During Beta Supplement, all occultation times were derived from the MGS Navigation Team Orbit Propagation and Timing Geometry file; when the OPTG predicted occultation time was in error by more than about 40 s, occultation data were lost (for example on 2001-02-06 and 2001-02-07). The HGA azimuth obstruction mysteriously disappeared during a 'safe' mode event which ended on 2005-09-28. After testing, the spacecraft was allowed to fly in its normal (non-Beta Supplement) configuration for the remainder of the mission. And, when other restrictions were not imposed, occultations at both ingress and egress were recorded. Calibration Description - Spacecraft ==================================== No information available. Platform Mounting Descriptions - Spacecraft =========================================== Origin of the spacecraft reference frame was located at the intersection of the spacecraft/launch vehicle interface plane and the spacecraft central axis -- that is, at the bottom of the propulsion unit nozzle. The spacecraft +Z axis was along the spacecraft central axis and normal to the nadir equipment deck; the main engine was aimed in the -Z direction. The +X axis vector was in the direction of the velocity vector during Mapping. +X was also in the direction of the HGA boresight during Cruise, and the HGA boom was mounted to the +X panel of the propulsion module. The +Y axis completed an orthogonal rectangular coordinate system. The +/-Y axes defined generally the deployment directions of the solar panels. The solar cells themselves were on the -Z sides of the panels. The primary LGT was mounted on the TWTA enclosure, which was mounted on the rim of the HGA reflector; its boresight was aligned with the HGA boresight, which was in the +X direction until HGA deployment. The backup (LGT2) was also mounted on the TWTA enclosure; its boresight was aligned at a cant angle approximately 160 degrees away from the shared boresights of the HGA and LGT1. This angle was chosen to minimize the consequences of a gimbal failure once HGA articulation began after deployment of the HGA boom in the mapping orbit. LGT2 was not used prior to HGA deployment because its orientation and proximity to the nadir payload deck would lead to irradiation of the payload instruments while the HGA was in its stowed position. One LGR was mounted on the -X panel of the equipment module; the other was on the +X side of the propulsion module. The five MGS antennas -- HGA, primary and backup low-gain transmitting antennas (LGT1 and LGT2, respectively) and low-gain antennas for receiving on the +X and -X sides of the spacecraft (LGR1 and LGR2, respectively) are shown below in their stowed (pre-HGA deployment) configuration. Note that dimensions are given in inches; one inch (1 in) equals 0.0254 meters. -Y Side View: ^ S/C +Z Axis | | | +39.318 in |<----------->| | | | +39.318 in | |<--------->| | | | | | +20.72 in | | |<-->| | | -25.81 in| |<----->| LGT2 __LGT1 | | @=| |=@ ---------------- | | | | __ ^ | | |__|/ | | | +-----------+ / | | | | | / | |+81.46 in | | | / | | | | || | | LGR2 | | || HGA | ------ | ----- @=| || | ^ | ^ |-----------| \ | | | | | | \ | | | | | \ | | | | | +31.75 in \__| | | | | |<----->| | | | | | | LGR1 |+66.15 | | | |=@ --- | in | | +----+-+----+ ^ | | |+49.94 / | \ |+17.56 | | | in / | \ | in | | v / | \ v v v -------- +----o----+ ------------------------> | S/C Frame S/C +X Axis | Origin Top View: ^ S/C +Y Axis | | __ LGR1 / | | +-----------+ / | v | | |=@/ ------------ 0 in| | S/C Frame | / | |+5.29 in v | Origin || HGA | | ---- @=| o ||__ | ------------ ---> ^ LGR2 || | | ^ ^ ^ S/C +X Axis | | || | | | | | || | | |-28.18 | +----+-+----+| | | | in |-30.05 in | |\__| v | | |=@ --- v @=|__| --------------------- LGT2 LGT1 The geometrical center of the HGA (coordinates given below) is taken to be the geometric center of the HGA reflector rim. This is not the phase center of the HGA. The geometric and phase centers of the low-gain antennas are taken to be at the centers of the 1.45 x 1.45 in square-shaped active elements of each antenna. MGS Antenna Center Locations (inches) (meters) X Y Z X Y Z ------ ------ ------ ------ ------ ------ HGA 39.318 0.00 66.15 0.999 0.000 1.680 LGT1 39.318 -28.18 81.46 0.999 -0.716 2.069 LGT2 20.72 -30.05 81.56 0.526 -0.763 2.072 LGR1 31.75 5.29 17.56 0.806 0.134 0.446 LGR2 -25.81 0.00 49.94 -0.655 0.000 1.268 Investigators ============= Team Leader for the MGS Radio Science Team was G. Leonard Tyler of Stanford University. Members of the Team conducting atmospheric investigations were David P. Hinson and Richard Woo. Members conducting gravity investigations were Georges Balmino, William L. Sjogren, and David E. Smith. John Armstrong (gravitational waves), Michael Flasar (atmospheres), and Richard Simpson (surface scattering) were selected as Participating Scientists. Instrument Section / Operating Mode Descriptions - Spacecraft ============================================================= Redundant components (LGR, LGT, MOT, CDU, and TWTA) could be configured as desired. Each configuration had slightly different performance, but the quantitative differences are unknown. Each Mars Observer Transponder (MOT) responded to the the following commands: Command Function ------- -------- USO Enable If MOT is in two-way noncoherent mode, selects USO as downlink frequency reference; If MOT is in two-way coherent mode, implements automatic transfer from VCO to USO whenever on-board receiver loses phase lock on uplink signal. USO Inhibit If MOT is in two-way noncoherent mode, selects AUX OSC as downlink frequency reference; If MOT is in two-way coherent mode, implements automatic transfer from VCO to AUX OSC whenever on-board receiver loses phase lock on uplink signal. Ranging ON Enables the ranging signal path to the X-band phase demodulator Ranging OFF Disables the ranging signal path to the X-band phase demodulator DOR ON Enables DOR generator, using downlink frequency source to derive DOR tones DOR OFF Disables DOR generator TWNC ON Forces downlink frequency source to be non-coherent (AUX OSC or USO), independent of receiver lock status TWNC OFF If on-board receiver is phase-locked to uplink signal, forces downlink to be generated from uplink If on-board receiver is NOT phase-locked to uplink, provides automatic transfer to selected downlink frequency source (AUX OSC or USO) TLM ON Enables telemetry signal path to X-band phase demodulator TLM OFF Disables telemetry signal path to X-band phase demodulator Instrument Overview - DSN ========================= Three Deep Space Communications Complexes (DSCCs) (near Barstow, CA; Canberra, Australia; and Madrid, Spain) comprise the DSN tracking network. Each complex is equipped with several antennas [including at least one each 70-m, 34-m High Efficiency (HEF), and 34-m Beam WaveGuide (BWG)], associated electronics, and operational systems. Primary activity at each complex is radiation of commands to and reception of telemetry data from active spacecraft. Transmission and reception is possible in several radio-frequency bands, the most common being S-band (nominally a frequency of 2100-2300 MHz or a wavelength of 14.2-13.0 cm) and X-band (7100-8500 MHz or 4.2-3.5 cm). Transmitter output powers of up to 400 kW are available. Ground stations have the ability to transmit coded and uncoded waveforms which can be echoed by distant spacecraft. Analysis of the received coding allows navigators to determine the distance to the spacecraft; analysis of Doppler shift on the carrier signal allows estimation of the line-of-sight spacecraft velocity. Range and Doppler measurements are used to calculate the spacecraft trajectory and to infer gravity fields of objects near the spacecraft. Very Long Baseline Interferometry (VLBI) techniques can be applied to determine the position of the spacecraft in the plane of the sky. Use of VLBI became more common, especially for pre-encounter navigation, after loss of the Mars Climate Orbiter on 23 September 1999. Ground stations can record spacecraft signals that have propagated through or been scattered from target media. Measurements of signal parameters after wave interactions with surfaces, atmospheres, rings, and plasmas are used to infer physical and electrical properties of the target. Principal investigators vary from experiment to experiment. See the corresponding section of the spacecraft instrument description or the data set description for specifics. The Deep Space Network is managed by the Jet Propulsion Laboratory of the California Institute of Technology for the U.S. National Aeronautics and Space Administration. Specifications include: Instrument Id : RSS Instrument Host Id : DSN Pi Pds User Id : N/A Instrument Name : RADIO SCIENCE SUBSYSTEM Instrument Type : RADIO SCIENCE Build Date : N/A Instrument Mass : N/A Instrument Length : N/A Instrument Width : N/A Instrument Height : N/A Instrument Manufacturer Name : N/A The DSN and its subsystems evolved over the 10+ year lifetime of the MGS mission. Electronic (real-time) distribution of data superseded use of magnetic tape, and most subsystems were at least upgraded if not entirely replaced. Changes critical to understanding collection and handling of radio science data are reflected in this document. The reader should be aware, however, that details may be missing and that subsystems not central to radio science activities may be described more as they existed in the late 1990's rather than as they were at the end of science data collection in 2006. For more information on the Deep Space Network and its use in radio science see reports by [ASMAR&RENZETTI1993], [ASMAR&HERRERA1993], and [ASMARETAL1995]. For design specifications on DSN subsystems see [DSN810-5]. For DSN use with MGS Radio Science see [TYLERETAL1992], [TYLERETAL2001], and [JPLD-14027]. Subsystems - DSN ================ The Deep Space Communications Complexes (DSCCs) are an integral part of Radio Science instrumentation, along with the spacecraft Radio Frequency Subsystem. Their system performance directly determines the degree of success of Radio Science investigations, and their system calibration determines the degree of accuracy in the results of the experiments. The following paragraphs describe the functions performed by the individual subsystems of a DSCC. This material has been adapted from [ASMAR&HERRERA1993] and [JPLD-14027]; for additional information, consult [DSN810-5]. Each DSCC includes a set of antennas, a Signal Processing Center (SPC), and communication links to the Jet Propulsion Laboratory (JPL). The general configuration is illustrated below; antennas (Deep Space Stations, or DSS -- a term carried over from earlier times when antennas were individually instrumented) are listed in the table. -------- -------- -------- -------- -------- | DSS 25 | | DSS 27 | | DSS 14 | | DSS 15 | | DSS 16 | |34-m BWG| |34-m HSB| | 70-m | |34-m HEF| | 26-m | -------- -------- -------- -------- -------- | | | | | | v v | v | --------- | --------- --------->|GOLDSTONE|<---------- |EARTH/ORB| | SPC 10 |<-------------->| LINK | --------- --------- | SPC |<-------------->| 26-M | | COMM | ------>| COMM | --------- | --------- | | | v | v ------ --------- | --------- | NOCC |<--->| JPL |<------- | | ------ | CENTRAL | | GSFC | ------ | COMM | | NASCOMM | | MCCC |<--->| TERMINAL|<-------------->| | ------ --------- --------- ^ ^ | | CANBERRA (SPC 40) <---------------- | | MADRID (SPC 60) <---------------------- GOLDSTONE CANBERRA MADRID Antenna SPC 10 SPC 40 SPC 60 -------- --------- -------- -------- 26-m DSS 16 DSS 46 DSS 66 34-m HEF DSS 15 DSS 45 DSS 65 34-m BWG DSS 24 DSS 34 DSS 54 DSS 25 DSS 26 34-m HSB DSS 27 DSS 28 70-m DSS 14 DSS 43 DSS 63 Developmental DSS 13 Subsystem interconnections at each DSCC are shown in the diagram below, and they are described in the sections that follow. The Monitor and Control Subsystem is connected to all other subsystems; the Test Support Subsystem can be. ----------- ------------------ --------- --------- |TRANSMITTER| | | | TRACKING| | COMMAND | | SUBSYSTEM |-| RECEIVER/EXCITER |-|SUBSYSTEM|-|SUBSYSTEM|- ----------- | | --------- --------- | | | SUBSYSTEM | | | | ----------- | | --------------------- | | MICROWAVE | | | | TELEMETRY | | | SUBSYSTEM |-| |-| SUBSYSTEM |- ----------- ------------------ --------------------- | | | ----------- ----------- --------- -------------- | | ANTENNA | | MONITOR | | TEST | | DIGITAL | | | SUBSYSTEM | |AND CONTROL| | SUPPORT | |COMMUNICATIONS|- ----------- | SUBSYSTEM | |SUBSYSTEM| | SUBSYSTEM | ----------- --------- -------------- DSCC Monitor and Control Subsystem ---------------------------------- The DSCC Monitor and Control Subsystem (DMC) is part of the Monitor and Control System (MON) which also includes the ground communications Central Communications Terminal and the Network Operations Control Center (NOCC) Monitor and Control Subsystem. The DMC is the center of activity at a DSCC. The DMC receives and archives most of the information from the NOCC needed by the various DSCC subsystems during their operation. Control of most of the DSCC subsystems, as well as the handling and displaying of any responses to control directives and configuration and status information received from each of the subsystems, is done through the DMC. The effect of this is to centralize the control, display, and archiving functions necessary to operate a DSCC. Communication among the various subsystems is done using a Local Area Network (LAN) hooked up to each subsystem via a network interface unit (NIU). DMC operations are divided into two separate areas: the Complex Monitor and Control (CMC) and the Link Monitor and Control (LMC). The primary purpose of the CMC processor for Radio Science support is to receive and store all predict sets transmitted from NOCC such as Radio Science, antenna pointing, tracking, receiver, and uplink predict sets and then, at a later time, to distribute them to the appropriate subsystems via the LAN. Those predict sets can be stored in the CMC for a maximum of three days under normal conditions. The CMC also receives, processes, and displays event/alarm messages; maintains an operator log; and produces tape labels for the DSP. Assignment and configuration of the LMCs is done through the CMC; to a limited degree the CMC can perform some of the functions performed by the LMC. There are two CMCs (one on-line and one backup) and three LMCs at each DSCC The backup CMC can function as an additional LMC if necessary. The LMC processor provides the operator interface for monitor and control of a link -- a group of equipment required to support a spacecraft pass. For Radio Science, a link might include the DSCC Spectrum Processing Subsystem (DSP) (which, in turn, can control the SSI), or the Tracking Subsystem. The LMC also maintains an operator log which includes operator directives and subsystem responses. One important Radio Science specific function that the LMC performs is receipt and transmission of the system temperature and signal level data from the PPM for display at the LMC console and for inclusion in Monitor blocks. These blocks are recorded on magnetic tape as well as appearing in the Mission Control and Computing Center (MCCC) displays. The LMC is required to operate without interruption for the duration of the Radio Science data acquisition period. The Area Routing Assembly (ARA), which is part of the Digital Communications Subsystem, controls all data communication between the stations and JPL. The ARA receives all required data and status messages from the LMC/CMC and can record them to tape as well as transmit them to JPL via data lines. The ARA also receives predicts and other data from JPL and passes them on to the CMC. DSCC Antenna Mechanical Subsystem --------------------------------- Multi-mission Radio Science activities require support from the 70-m, 34-m HEF, and 34-m BWG antenna subnets. The antennas at each DSCC function as large-aperture collectors which, by double reflection, cause the incoming radio frequency (RF) energy to enter the feed horns. The large collecting surface of the antenna focuses the incoming energy onto a subreflector, which is adjustable in both axial and angular position. These adjustments are made to correct for gravitational deformation of the antenna as it moves between zenith and the horizon; the deformation can be as large as 5 cm. The subreflector adjustments optimize the channeling of energy from the primary reflector to the subreflector and then to the feed horns. The 70-m and 34-m HEF antennas have 'shaped' primary and secondary reflectors, with forms that are modified paraboloids. This customization allows more uniform illumination of one reflector by another. The BWG reflector shape is ellipsoidal. On the 70-m antennas, the subreflector directs received energy from the antenna onto a dichroic plate, a device which reflects S-band energy to the S-band feed horn and passes X-band energy through to the X-band feed horn. In the 34-m HEF, there is one 'common aperture feed,' which accepts both frequencies without requiring a dichroic plate. In the 34-m BWG, a series of small mirrors (approximately 2.5 meters in diameter) directs microwave energy from the subreflector region to a collection area at the base of the antenna -- typically in a pedestal room. A retractable dichroic reflector separates S- and X-band on some BWG antennas or X- and Ka-band on others. RF energy to be transmitted into space by the horns is focused by the reflectors into narrow cylindrical beams, pointed with high precision (either to the dichroic plate or directly to the subreflector) by a series of drive motors and gear trains that can rotate the movable components and their support structures. The different antennas can be pointed by several means. Two pointing modes commonly used during tracking passes are CONSCAN and 'blind pointing.' With CONSCAN enabled and a closed loop receiver locked to a spacecraft signal, the system tracks the radio source by conically scanning around its position in the sky. Pointing angle adjustments are computed from signal strength information (feedback) supplied by the receiver. In this mode the Antenna Pointing Assembly (APA) generates a circular scan pattern which is sent to the Antenna Control System (ACS). The ACS adds the scan pattern to the corrected pointing angle predicts. Software in the receiver-exciter controller computes the received signal level and sends it to the APA. The correlation of scan position with the received signal level variations allows the APA to compute offset changes which are sent to the ACS. Thus, within the capability of the closed-loop control system, the scan center is pointed precisely at the apparent direction of the spacecraft signal source. An additional function of the APA is to provide antenna position angles and residuals, antenna control mode/status information, and predict-correction parameters to the Area Routing Assembly (ARA) via the LAN, which then sends this information to JPL via the Ground Communications Facility (GCF) for antenna status monitoring. During periods when excessive signal level dynamics or low received signal levels are expected (e.g., during an occultation experiment), CONSCAN should not be used. Under these conditions, blind pointing (CONSCAN OFF) is used, and pointing angle adjustments are based on a predetermined Systematic Error Correction (SEC) model. Independent of CONSCAN state, subreflector motion in at least the z-axis may introduce phase variations into the received Radio Science data. For that reason, during certain experiments, the subreflector in the 70-m and 34-m HEFs may be frozen in the z-axis at a position (often based on elevation angle) selected to minimize phase change and signal degradation. This can be done via Operator Control Inputs (OCIs) from the LMC to the Subreflector Controller (SRC) which resides in the alidade room of the antennas. The SRC passes the commands to motors that drive the subreflector to the desired position. Pointing angles for all antenna types are computed by the NOCC Support System (NSS) from an ephemeris provided by the flight project. These predicts are received and archived by the CMC. Before each track, they are transferred to the APA, which transforms the direction cosines of the predicts into AZ-EL coordinates. The LMC operator then downloads the antenna predict points to the antenna-mounted ACS computer along with a selected SEC model. The pointing predicts consist of time-tagged AZ-EL points at selected time intervals along with polynomial coefficients for interpolation between points. The ACS automatically interpolates the predict points, corrects the pointing predicts for refraction and subreflector position, and adds the proper systematic error correction and any manually entered antenna offsets. The ACS then sends angular position commands for each axis at the rate of one per second. In the 70-m and 34-m HEF, rate commands are generated from the position commands at the servo controller and are subsequently used to steer the antenna. When not using binary predicts (the routine mode for spacecraft tracking), the antennas can be pointed using 'planetary mode' -- a simpler mode which uses right ascension (RA) and declination (DEC) values. These change very slowly with respect to the celestial frame. Values are provided to the station in text form for manual entry. The ACS quadratically interpolates among three RA and DEC points which are on one-day centers. A third pointing mode -- sidereal -- is available for tracking radio sources fixed with respect to the celestial frame. Regardless of the pointing mode being used, a 70-m antenna has a special high-accuracy pointing capability called 'precision' mode. A pointing control loop derives the main AZ-EL pointing servo drive error signals from a two- axis autocollimator mounted on the Intermediate Reference Structure. The autocollimator projects a light beam to a precision mirror mounted on the Master Equatorial drive system, a much smaller structure, independent of the main antenna, which is exactly positioned in HA and DEC with shaft encoders. The autocollimator detects elevation/cross- elevation errors between the two reference surfaces by measuring the angular displacement of the reflected light beam. This error is compensated for in the antenna servo by moving the antenna in the appropriate AZ-EL direction. Pointing accuracies of 0.004 degrees (15 arc seconds) are possible in 'precision' mode. The 'precision' mode is not available on 34-m antennas -- nor is it needed, since their beamwidths are twice as large as on the 70-m antennas. DSCC Antenna Microwave Subsystem -------------------------------- 70-m Antennas: Each 70-m antenna has three feed cones installed in a structure at the center of the main reflector. The feeds are positioned 120 degrees apart on a circle. Selection of the feed is made by rotation of the subreflector. A dichroic mirror assembly, half on the S-band cone and half on the X-band cone, permits simultaneous use of the S- and X-band frequencies. The third cone is devoted to R&D and more specialized work. The Antenna Microwave Subsystem (AMS) accepts the received S- and X-band signals at the feed horn and transmits them through polarizer plates to an orthomode transducer. The polarizer plates are adjusted so that the signals are directed to a pair of redundant amplifiers for each frequency, thus allowing simultaneous reception of signals in two orthogonal polarizations. For S-band these are two Block IVA S-band Traveling Wave Masers (TWMs); for X-band the amplifiers are Block IIA TWMs. 34-m HEF Antennas: The 34-m HEF uses a single feed for both S- and X-band. Simultaneous S- and X-band receive as well as X-band transmit is possible thanks to the presence of an S/X 'combiner' which acts as a diplexer. For S-band, RCP or LCP is user selected through a switch so neither a polarizer nor an orthomode transducer is needed. X-band amplification options include two Block II TWMs or an HEMT Low Noise Amplifier (LNA). S-band amplification is provided by an FET LNA. 34-m BWG Antennas: These antennas use feeds and low-noise amplifiers (LNA) in the pedestal room, which can be switched in and out as needed. Typically the following modes are available: 1. downlink non-diplexed path (RCP or LCP) to LNA-1, with uplink in the opposite circular polarization; 2. downlink non-diplexed path (RCP or LCP) to LNA-2, with uplink in the opposite circular polarization 3. downlink diplexed path (RCP or LCP) to LNA-1, with uplink in the same circular polarization 4. downlink diplexed path (RCP or LCP) to LNA-2, with uplink in the same circular polarization For BWG antennas with dual-band capabilities (e.g., DSS 25) and dual LNAs, each of the above four modes can be used in a single-frequency or dual-frequency configuration. Thus, for antennas with the most complete capabilities, there are sixteen possible ways to receive at a single frequency (2 polarizations, 2 waveguide path choices, 2 LNAs, and 2 bands). DSCC Receiver-Exciter Subsystem ------------------------------- The Receiver-Exciter Subsystem is composed of three groups of equipment: the closed-loop receiver group, the open-loop receiver group, and the RF monitor group. This subsystem is controlled by the Receiver-Exciter Controller (REC) which communicates directly with the DMC for predicts and OCI reception and status reporting. The exciter generates the S-band signal (or X-band for the 34-m HEF only) which is provided to the Transmitter Subsystem for the spacecraft uplink signal. It is tunable under command of the Digitally Controlled Oscillator (DCO) which receives predicts from the Metric Data Assembly (MDA). The diplexer in the signal path between the transmitter and the feed horn for all three antennas (used for simultaneous transmission and reception) may be configured such that it is out of the received signal path (in listen-only or bypass mode) in order to improve the signal-to-noise ratio in the receiver system. Closed Loop Receivers: The Block V receiver-exciter at the 70-m stations allows for two receiver channels, each capable of L-Band (e.g., 1668 MHz frequency or 18 cm wavelength), S-band, or X-band reception, and an S-band exciter for generation of uplink signals through the low-power or high-power transmitter. The closed-loop receivers provide the capability for rapid acquisition of a spacecraft signal and telemetry lockup. In order to accomplish acquisition within a short time, the receivers are predict driven to search for, acquire, and track the downlink automatically. Rapid acquisition precludes manual tuning though that remains as a backup capability. The subsystem utilizes FFT analyzers for rapid acquisition. The predicts are NSS generated, transmitted to the CMC which sends them to the Receiver-Exciter Subsystem where two sets can be stored. The receiver starts acquisition at uplink time plus one round-trip-light-time or at operator specified times. The receivers may also be operated from the LMC without a local operator attending them. The receivers send performance and status data, displays, and event messages to the LMC. Either the exciter synthesizer signal or the simulation (SIM) synthesizer signal is used as the reference for the Doppler extractor in the closed-loop receiver systems, depending on the spacecraft being tracked (and Project guidelines). The SIM synthesizer is not ramped; instead it uses one constant frequency, the Track Synthesizer Frequency (TSF), which is an average frequency for the entire pass. The closed-loop receiver AGC loop can be configured to one of three settings: narrow, medium, or wide. It will be configured such that the expected amplitude changes are accommodated with minimum distortion. The loop bandwidth (2BLo) will be configured such that the expected phase changes can be accommodated while maintaining the best possible loop SNR. Open-Loop Receivers: Prior to December 2001 the Radio Science Open-Loop Receiver (OLR) was a dedicated four channel, narrow-band receiver which provided amplified and downconverted video band signals to the DSCC Spectrum Processing Subsystem (DSP); it sometimes was known as the 'RIV'. Beginning in mid-2001 for tests and starting in December 2001 for routine operations, open loop data were acquired using a new digital system -- the Radio Science Receiver (RSR) -- which is described below under 'Electronics - DSN.' The OLR utilized a fixed first Local Oscillator (LO) frequency and a tunable second LO frequency to minimize phase noise and improve frequency stability. The OLR consisted of an RF-to-IF downconverter located at the feed , an IF selection switch (IVC), and a Radio Science IF-VF downconverter (RIV) located in the SPC. The RF-IF downconverters in the 70-m antennas were equipped for four IF channels: S-RCP, S-LCP, X-RCP, and X-LCP. The 34-m HEF stations were equipped with a two-channel RF-IF: S-band and X-band. The 34-m BWG stations varied in their capabilities. The IVC switched the IF input among the antennas. The RIV contained the tunable second LO, a set of video bandpass filters, IF attenuators, and a controller (RIC). The LO tuning was done via DSP control of the POCA/PLO combination based on a predict set. The POCA was a Programmable Oscillator Control Assembly and the PLO was a Programmable Local Oscillator (commonly called the DANA synthesizer). The bandpass filters were selectable via the DSP. The RIC provided an interface between the DSP and the RIV. It was controlled from the LMC via the DSP. The RIC selected the filter and attenuator settings and provided monitor data to the DSP. The RIC could also be manually controlled from the front panel in case the electronic interface to the DSP was lost. RF Monitor -- SSI and PPM: The RF monitor group of the Receiver-Exciter Subsystem provided spectral measurements using the Spectral Signal Indicator (SSI) and measurements of the received channel system temperature and spacecraft signal level using the Precision Power Monitor (PPM). The SSI provided a local display of the received signal spectrum at a dedicated terminal at the DSCC and routed these same data to the DSP which routed them to NOCC for remote display at JPL for real-time monitoring and RIV/DSP configuration verification. These displays were used to validate Radio Science Subsystem data at the DSS, NOCC, and Mission Support Areas. The SSI configuration was controlled by the DSP and a duplicate of the SSI spectrum appeared on the LMC via the DSP. During real-time operations the SSI data also served as a quick-look science data type for Radio Science experiments. The PPM measured system noise temperatures (SNT) using a Noise Adding Radiometer (NAR) and downlink signal levels using the Signal Level Estimator (SLE). The PPM accepted its input from the closed-loop receiver. The SNT was measured by injecting known amounts of noise power into the signal path and comparing the total power with the noise injection 'on' against the total power with the noise injection 'off.' That operation was based on the fact that receiver noise power is directly proportional to temperature; thus measuring the relative increase in noise power due to the presence of a calibrated thermal noise source allowed direct calculation of SNT. Signal level was measured by calculating an FFT to estimate the SNR between the signal level and the receiver noise floor where the power was known from the SNT measurements. There was one PPM controller at the SPC which was used to control all SNT measurements. The SNT integration time could be selected to represent the time required for a measurement of 30K to have a one-sigma uncertainty of 0.3K or 1%. When the DSP was replaced by the RSR in late 2001, many of the SSI and PPM functions were absorbed into the RSR. SNT calibration because part of the DSN Monitor function. DSCC Transmitter Subsystem -------------------------- The Transmitter Subsystem accepts the S-band frequency exciter signal from the Receiver-Exciter Subsystem exciter and amplifies it to the required transmit output level. The amplified signal is routed via the diplexer through the feed horn to the antenna and then focused and beamed to the spacecraft. The Transmitter Subsystem power capabilities range from 18 kW to 400 kW. Power levels above 18 kW are available only at 70-m stations. DSCC Tracking Subsystem ----------------------- The Tracking Subsystem primary functions are to acquire and maintain communications with the spacecraft and to generate and format radiometric data containing Doppler and range. The DSCC Tracking Subsystem (DTK) receives the carrier signals and ranging spectra from the Receiver-Exciter Subsystem. The Doppler cycle counts are counted, formatted, and transmitted to JPL in real time. Ranging data are also transmitted to JPL in real time. Also contained in these blocks is the AGC information from the Receiver-Exciter Subsystem. The Radio Metric Data Conditioning Team (RMDCT) at JPL produces an archival form of these products for later analysis. In addition, the Tracking Subsystem receives from the CMC frequency predicts (used to compute frequency residuals and noise estimates), receiver tuning predicts (used to tune the closed-loop receivers), and uplink tuning predicts (used to tune the exciter). From the LMC, it receives configuration and control directives as well as configuration and status information on the transmitter, microwave, and frequency and timing subsystems. The Metric Data Assembly (MDA) controls all of the DTK functions supporting the uplink and downlink activities. The MDA receives uplink predicts and controls the uplink tuning by commanding the DCO. The MDA also controls the Sequential Ranging Assembly (SRA). It formats the Doppler and range measurements and provides them to the GCF for transmission to NOCC. The Sequential Ranging Assembly (SRA) measures the round trip light time (RTLT) of a radio signal traveling from a ground tracking station to a spacecraft and back. From the RTLT, phase, and Doppler data, the spacecraft range can be determined. A coded signal is modulated on an uplink carrier and transmitted to the spacecraft where it is detected and transponded back to the ground station. As a result, the signal received at the tracking station is delayed by its round trip through space and shifted in frequency by the Doppler effect due to the relative motion between the spacecraft and the tracking station on Earth. DSCC Spectrum Processing Subsystem (DSP) ---------------------------------------- Until it was decommissioned in early 2002 the DSCC Spectrum Processing Subsystem (DSP) located at the SPC digitized and recorded the narrowband output data from the RIV. It consisted of a Narrow Band Occultation Converter (NBOC) containing Analog-to-Digital Converters (ADCs), a ModComp CLASSIC computer processor called the Spectrum Processing Assembly (SPA), and several magnetic tape drives. Magnetic tapes containing DSP output were known as Original Data Records (ODRs). Electronic near real-time data transmission (known as an Original Data Stream, or ODS) was the default for Mars Global Surveyor. The DSP was originally operated through the LMC. During 1996-97 a remote operations capability was developed by the JPL Radio Science Systems Group so that the DSP could be operated from JPL. Using the SPA-Radioscience (SPA-R) software, the DSP allowed for real-time frequency and time offsets (while in RUN mode) and, if necessary, snap tuning between the two frequency ranges transmitted by the spacecraft: coherent and non-coherent. The DSP received Radio Science frequency predicts from the CMC, allowed for multiple predict set archiving (up to 60 sets) at the SPA, and allowed for manual predict generation and editing. It accepted configuration and control data from the LMC (or remote operations console), provided display data to the LMC (or remote operations console), and transmitted the signal spectra from the SSI as well as status information to NOCC and the Project Mission Support Area (MSA) via the GCF data lines. The DSP recorded the digitized narrowband samples and the supporting header information (i.e., time tags, POCA frequencies, etc.) on 9-track magnetic tapes in 6250 or 1600 bpi GCR format and/or on a local disk for later transmission to JPL. Through the DSP-RIC interface the DSP controlled the RIV filter selection and attenuation levels. It also received RIV performance monitoring via the RIC. In case of failure of the DSP-RIC interface, the RIV could be controlled manually from the front panel. All the RIV and DSP control parameters and configuration directives were stored in the SPA in a macro-like file called an 'experiment directive' table. A number of default directives existed in the DSP for the major Radio Science experiments. Operators could create their own table entries. Items such as verification of the configuration of the prime open-loop recording subsystem, the selection of the required predict sets, and proper system performance prior to the recording periods were checked in real-time at JPL via the NOCC displays using primarily the remote SSI display at NOCC and the NRV displays. Because of this, transmission of the DSP/SSI monitor information was enabled prior to the start of recording. The specific run time and tape recording times were identified in the Sequence of Events (SOE) and/or DSN Keyword File. The DSP could be used to duplicate ODRs. It also had the capability to play back a certain section of the recorded data after conclusion of the recording periods. DSCC Frequency and Timing Subsystem ----------------------------------- The Frequency and Timing Subsystem (FTS) provides all frequency and timing references required by the other DSCC subsystems. It contains four frequency standards of which one is prime and the other three are backups. Selection of the prime standard is done via the CMC. Of these four standards, two are hydrogen masers followed by clean-up loops (CUL) and two are cesium standards. These four standards all feed the Coherent Reference Generator (CRG) which provides the frequency references used by the rest of the complex. It also provides the frequency reference to the Master Clock Assembly (MCA) which in turn provides time to the Time Insertion and Distribution Assembly (TID) which provides UTC and SIM-time to the complex. JPL's ability to monitor the FTS at each DSCC is limited to the MDA calculated Doppler pseudo-residuals, the Doppler noise, the SSI, and to a system which uses the Global Positioning System (GPS). GPS receivers at each DSCC receive a one-pulse-per-second pulse from the station's (hydrogen maser referenced) FTS and a pulse from a GPS satellite at scheduled times. After compensating for the satellite signal delay, the timing offset is reported to JPL where a database is kept. The clock offsets stored in the JPL database are given in microseconds; each entry is a mean reading of measurements from several GPS satellites and a time tag associated with the mean reading. The clock offsets provided include those of SPC 10 relative to UTC (NIST), SPC 40 relative to SPC 10, etc. Optics - DSN ============ Performance of DSN ground stations depends primarily on size of the antenna and capabilities of electronics. These are summarized in the following set of tables. Beamwidth is half-power full angular width. Polarization is circular; L denotes left circular polarization (LCP), and R denotes right circular polarization (RCP). DSS S-Band Characteristics 70-m 34-m 34-m Transmit BWG HEF -------- ----- ----- ----- Frequency (MHz) 2110- 2025- N/A 2120 2120 Wavelength (m) 0.142 0.142 N/A Ant Gain (dBi) 62.7 56.1 N/A Beamwidth (deg) 0.119 N/A N/A Polarization L or R L or R N/A Tx Power (kW) 20-400 20 N/A Receive ------- Frequency (MHz) 2270- 2270- 2200- 2300 2300 2300 Wavelength (m) 0.131 0.131 0.131 Ant Gain (dBi) 63.3 56.7 56.0 Beamwidth (deg) 0.108 N/A 0.24 Polarization L & R L or R L or R System Temp (K) 20 31 38 DSS X-Band Characteristics 70-m 34-m 34-m Transmit BWG HEF -------- ----- ----- ----- Frequency (MHz) 8495 7145- 7145- 7190 7190 Wavelength (m) 0.035 0.042 0.042 Ant Gain (dBi) 74.2 66.9 67 Beamwidth (deg) N/A 0.074 Polarization L or R L or R L or R Tx Power (kW) 360 20 20 Receive ------- Frequency (MHz) 8400- 8400- 8400- 8500 8500 8500 Wavelength (m) 0.036 0.036 0.036 Ant Gain (dBi) 74.2 68.1 68.3 Beamwidth (deg) 0.031 N/A 0.063 Polarization L & R L & R L & R System Temp (K) 20 30 20 NB: X-band 70-m transmitting parameters are given at 8495 MHz, the frequency used by the Goldstone planetary radar system. For telecommunications, the transmitting frequency would be in the range 7145-7190 MHz, the power would typically be 20 kW, and the gain would be about 72.6 dB (70-m antenna). When ground transmitters are used in spacecraft radio science experiments, the details of transmitter and antenna performance rarely impact the results. Electronics - DSN ================= DSCC Open-Loop Receiver (RIV) (valid until late 2001) ----------------------------------------------------- The open loop receiver block diagram shown below was for the RIV system at 70-m and 34-m HEF and BWG antenna sites until late in 2001, when it was superseded by the Radio Science Receiver (RSR) (see below). Input signals at both S- and X-band were mixed to approximately 300 MHz by fixed-frequency local oscillators near the antenna feed. Based on a tuning prediction file, the POCA controlled the DANA synthesizer, the output of which (after multiplication) mixed the 300 MHz IF to 50 MHz for amplification. These signals in turn were down converted and passed through additional filters until they yielded output with bandwidths up to 45 kHz. The Output was digitally sampled and either written to magnetic tape or electronically transferred for further analysis. S-Band X-Band 2295 MHz 8415 MHz Input Input | | v v --- --- --- --- | X |<--|x20|<--100 MHz 100 MHz-->|x81|-->| X | --- --- --- --- | | 295| |315 MHz| |MHz v v --- -- 33.1818 --- --- | X |<--|x3|<------ MHz ------>|x11|-->| X | --- -- |115 | --- --- | |MHz | | | | | | 50| 71.8181 --- --- |50 MHz| MHz->| X | | X |<-10MHz |MHz v --- --- v --- ^ ^ --- | X |<--60 MHz | | 60 MHz-->| X | --- | approx | --- | 9.9 | 43.1818 MHz | 9.9 | | MHz ------------- MHz | | | ^ | | 10| v | v |10 MHz| --- ---------- --- |MHz |------>| X | | DANA | | X |<------| | --- |Synthesizr| --- | | | ---------- | | v v ^ v v ------- ------- | ------- ------- |Filters| |Filters| ---------- |Filters| |Filters| |3,4,5,6| | 1,2 | | POCA | | 1,2 | |3,4,5,6| ------- ------- |Controller| ------- ------- | | ---------- | | 10| |0.1 0.1| |10 MHz| |MHz MHz| |MHz v v v v --- --- --- --- 10 MHz -->| X | | X |<------ 0.1 MHz ------->| X | | X |<-- --- --- --- --- | | | | | 10 MHz v v v v Output Output Output Output Reconstruction of the antenna frequency from the frequency of the signal in the recorded data could be achieved through use of one of the following formulas. Filters are defined below. FSant=3*SYN+1.95*10^9+3*(790/11)*10^6+Frec (Filter 4) =3*SYN+1.95*10^9+3*(790/11)*10^6-Fsamp+Frec (Filters 1-3,5,6) FXant=11*SYN + 7.940*10^9 + Fsamp - Frec (Filter 4) =11*SYN + 7.940*10^9 - 3*Fsamp + Frec (Filters 1,2,3,6) where FSant,FXant are the antenna frequencies of the incoming signals at S and X bands, respectively, SYN is the output frequency of the DANA synthesizer, commonly labeled the readback POCA frequency on data tapes, Fsamp is the effective sampling rate of the digital samples, and Frec is the apparent signal frequency in a spectrum reconstructed from the digital samples. NB: For many of the filter choices (see below) the Output is that of a bandpass filter. The sampling rates in the table below are sufficient for the bandwidth but not the absolute maximum frequency, and aliasing results. The reconstruction expressions above are appropriate ONLY when the sample rate shown in the tables below is used. Radio Science Receiver (RSR) (used after mid-2001) -------------------------------------------------- The Radio Science Receiver (RSR) was tested for Mars Global Surveyor starting in mid-2001 and then used routinely for MGS open loop data collection beginning in December 2001. For more information, see [JPLD-16765]. A radio frequency (RF) spacecraft signal at S-band, X-band, or Ka-band is captured by a receiving antenna on Earth, down converted to an intermediate frequency (IF) near 300 MHz and then fed via a distribution network to one input of an IF Selector Switch (IFS). The IFS allows each RSR to select any of the available input signals for its RSR Digitizer (DIG). Within the RSR the digitized signal is then passed to the Digital Down Converter (DDC), VME Data Processor (VDP), and Data Processor (DP). \ ----------- ------ ----- ----- ----- \ | RF TO IF | | |----| | | | | | |----| DOWN |----| |----| |----| DIG | | DP | / | CONVERTER | | |----| | | | | | / ----------- | IF |----| IFS | ----- ----- ANTENNA --| DIST |----| | | | 300 MHz IF --| | .. | | ----- ----- FROM OTHER --| |----| | | | | | ANTENNAS --| | ----- | DDC | | VDP | ------ | | | | ----- ----- | | ------- In the DIG the IF signal is passed through a programmable attenuator, adjusted to provide the proper level to the Analog to Digital Converter (ADC). The attenuated signal is then passed through a Band Pass Filter (BPF) which selects a frequency band in the range 265-375 MHz. The filtered output from the BPF is then mixed with a 256 MHz Local Oscillator (LO), low pass filtered (LPF), and sampled by the ADC. The output of the ADC is a stream of 8-bit real samples at 256 Msamples/second (Msps). DIG timing is derived from the station FTS 5 MHz clock and 1 pulse per second (1PPS) reference; the DIG generates a 256 MHz clock signal for later processing. The 1 PPS signal marks the data sample taken at the start of each second. The DDC selects one 16 MHz subchannel from the possible 128 MHz bandwidth available from the DIG by using Finite Impulse Response (FIR) filters with revolving banks of filter coefficients. The sample stream from the DIG is separated into eight decimated streams, each of which is fed into two sets of FIR filters. One set of filters produces in-phase (I) 8-bit data while the other produces quadrature-phase (Q) 8-bit data. The center frequency of the desired 16 MHz channel is adjustable in 1 MHz steps and is usually chosen to be near the spacecraft carrier frequency. After combining the I and Q sample streams, the DDC feeds the samples to the VDP. The DDC also converts the 256 MHz data clock and 1PPS signals into a msec time code, which is also passed to the VDP. The VDP contains a quadruply-redundant set of custom boards which are controlled by a real-time control computer (RT). Each set of boards comprises a numerically controlled oscillator (NCO), a complex multiplier, a decimating FIR filter, and a data packer. The 16 Msps complex samples from the DDC are digitally mixed with the NCO signal in the complex multiplier. The NCO phase and frequency are updated every millisecond by the RT and are selected so that the center frequency of the desired portion of the 16 MHz channel is down-converted to 0 Hz. The RT uses polynomials derived from frequency predictions. The output of the complex multiplier is sent to the decimating FIR filter where its bandwidth and sample rate are reduced (see table below). The decimating FIR filter also allows adjustment of the sub-channel gain to take full advantage of the dynamic range available in the hardware. The data packer truncates samples to 1, 2, 4, 8, or 16 bits by dropping the least significant bits and packs them into 32-bit data words. Q-samples are packed into the first 16 bits of the word, and I-samples into the least significant 16 bits (see below). In 'narrow band' operation all four sets of custom boards can be supported simultaneously. In 'medium band' operation no more than two channels can be supported simultaneously. In 'wide band' operation, only one sub-channel can be recorded. |============================================================| | RSR Sample Rates and Sample Sizes Supported | |================+=======+======+=================+==========| | Category | Rate | Size | Data Rate |Rec Length| | | (ksps)|(bits)|(bytes/s) (rec/s)| (bytes) | |================+=======+======+=========+=======+==========| |Narrow Band (NB)| 1 | 8 | 2000 | 1 | 2000 | | | 2 | 8 | 4000 | 1 | 4000 | | | 4 | 8 | 8000 | 1 | 8000 | | | 8 | 8 | 16000 | 1 | 16000 | | | 16 | 8 | 32000 | 2 | 16000 | | | 25 | 8 | 50000 | 2 | 25000 | | | 50 | 8 | 100000 | 4 | 25000 | | | 100 | 8 | 200000 | 10 | 20000 | | | 1 | 16 | 4000 | 1 | 4000 | | | 2 | 16 | 8000 | 1 | 8000 | | | 4 | 16 | 16000 | 1 | 16000 | | | 8 | 16 | 32000 | 2 | 16000 | | | 16 | 16 | 64000 | 4 | 16000 | | | 25 | 16 | 100000 | 4 | 25000 | | | 50 | 16 | 200000 | 10 | 20000 | | | 100 | 16 | 400000 | 20 | 20000 | |Medium Band (MB)| 250 | 1 | 62500 | 5 | 12500 | | | 500 | 1 | 125000 | 5 | 25000 | | | 1000 | 1 | 250000 | 10 | 25000 | | | 2000 | 1 | 500000 | 20 | 25000 | | | 4000 | 1 | 1000000 | 40 | 25000 | | | 250 | 2 | 125000 | 5 | 25000 | | | 500 | 2 | 250000 | 10 | 25000 | | | 1000 | 2 | 500000 | 20 | 25000 | | | 2000 | 2 | 1000000 | 40 | 25000 | | | 4000 | 2 | 2000000 | 100 | 20000 | | | 250 | 4 | 250000 | 10 | 25000 | | | 500 | 4 | 500000 | 20 | 25000 | | | 1000 | 4 | 1000000 | 40 | 25000 | | | 2000 | 4 | 2000000 | 100 | 20000 | | | 250 | 8 | 500000 | 20 | 25000 | | | 500 | 8 | 1000000 | 40 | 25000 | | | 1000 | 8 | 2000000 | 100 | 20000 | |Wide Band (WB) | 8000 | 1 | 2000000 | 100 | 20000 | | | 16000 | 1 | 4000000 | 200 | 20000 | | | 8000 | 2 | 4000000 | 200 | 20000 | |============================================================| |============================================================| | Sample Packing | |=================+==========================================| | Bits per Sample | Contents of 32-bit Packed Data Register | |=================+==========================================| | 16 | (Q1),(I1) | | 8 | (Q2,Q1),(I2,I1) | | 4 | (Q4,Q3,Q2,Q1),(I4,I3,I2,I1) | | 2 | (Q8,Q7,...Q1),(I8,I7,...I1) | | 1 | (Q16,Q15,...Q1),(I16,I15,...I1) | |============================================================| Once per second the RT sends the accumulated data records from each sub-channel to the Data Processor (DP) over a 100 Mbit/s ethernet connection. In addition to the samples, each data record includes header information such as time tags and NCO frequency and phase that are necessary for analysis. The DP processes the data records to provide monitor data, such as power spectra. If recording has been enabled, the records are stored by the DP. NCO Phase and Frequency ----------------------- At the start of each DSN pass, the RSR is provided with a file containing a list of predicted frequencies. Using these points, the RT computes expected sky frequencies at the beginning, middle, and end of each one second time interval. Based on the local oscillator frequencies selected and any offsets entered, the RT computes the coefficients of a frequency polynomial fitted to the DDC channel frequencies at these three times. The RT also computes a phase polynomial by integrating the frequency polynomial and matching phases at the one second boundaries. The phase and frequency of the VDP NCO's are computed every millisecond (000-999) from the polynomial coefficients as follows: nco_phase(msec) = phase_coef_1 + phase_coef_2 * (msec/1000) + phase_coef_3 * (msec/1000)**2 + phase_coef_4 * (msec/1000)**3 nco_freq(msec) = freq_coef_1 + freq_coef_2 * ((msec + 0.5)/1000) + freq_coef_3 * ((msec + 0.5)/1000)**2 The sky frequency may be reconstructed using sky_freq = RF_to_IF_LO + DDC_LO - nco_freq + resid_freq where RF_to_IF_LO is the down conversion from the microwave frequency to IF (bytes 42-43 in the data record header) DDC_LO is the down-conversion applied in the DIG and DDC (bytes 40-41 in the data record header) resid_Freq is the frequency of the signal in the VDP output Filters - DSN ============= DSCC Open-Loop Receiver (RIV) ----------------------------- Nominal filter center frequencies and bandwidths for the RIV Receivers are shown in the table below. Recommended sampling rates are also given. S-Band X-Band ------------------------ ------------------------- Output 3 dB Sampling Output 3 dB Sampling Filter Center Band Rate Center Band Rate Freq Width Freq Width (Hz) (Hz) (sps) (Hz) (Hz) (sps) ------ ------ ------ -------- ------ ------ -------- 1 150 82 200 550 82 200 2 750 415 1000 2750 415 1000 3 3750 2000 5000 13750 2000 5000 4 1023 1700 5000 3750 6250 15000 5 75000 45000 100000 275000 45000 100000 6 37500 20000 50000 137500 20000 50000 Detectors - DSN =============== DSCC Open-Loop Receivers ------------------------ Open-loop receiver output is detected in software by the radio science investigator. DSCC Closed-Loop Receivers -------------------------- Nominal carrier tracking loop threshold noise bandwidth at both S- and X-band is 10 Hz. Coherent (two-way) closed-loop system stability is shown in the table below: integration time Doppler uncertainty (secs) (one sigma, microns/sec) ------ ------------------------ 10 50 60 20 1000 4 Calibration - DSN ================= Calibrations of hardware systems are carried out periodically by DSN personnel; these ensure that systems operate at required performance levels -- for example, that antenna patterns, receiver gain, propagation delays, and Doppler uncertainties meet specifications. No information on specific calibration activities is available. Nominal performance specifications are shown in the tables above. Additional information may be available in [DSN810-5]. Prior to each tracking pass, station operators perform a series of calibrations to ensure that systems meet specifications for that operational period. Included in these calibrations is measurement of receiver system temperature in the configuration to be employed during the pass. Results of these calibrations are recorded in (hard copy) Controller's Logs for each pass. The nominal procedure for initializing open-loop receiver attenuator settings is described below. In cases where widely varying signal levels are expected, the procedure may be modified in advance or real-time adjustments may be made to attenuator settings. Open-Loop Receiver Attenuation Calibration ------------------------------------------ The open-loop receiver attenuator calibrations are performed to establish the output of the open-loop receivers at a level that will not saturate the analog-to-digital converters. To achieve this, the calibration is done using a test signal generated by the exciter/translator that is set to the peak predicted signal level for the upcoming pass. Then the output level of the receiver's video band spectrum envelope is adjusted to the level determined by equation (3) below (to five-sigma). Note that the SNR in equation (2) is in dB while the SNR in equation (3) is linear. Pn = -198.6 + 10*log(SNT) + 10*log(1.2*Fbw) (1) SNR = Ps - Pn (SNR in dB) (2) Vrms = sqrt(SNR + 1)/[1 + 0.283*sqrt(SNR)] (SNR linear) (3) where Fbw = receiver filter bandwidth (Hz) Pn = receiver noise power (dBm) Ps = signal power (dBm) SNT = system noise temperature (K) SNR = predicted signal-to-noise ratio Operational Considerations - DSN ================================ The DSN is a complex and dynamic 'instrument.' Its performance for Radio Science depends on a number of factors from equipment configuration to meteorological conditions. No specific information on 'operational considerations' can be given here. Operational Modes - DSN ======================= DSCC Antenna Mechanical Subsystem --------------------------------- Pointing of DSCC antennas may be carried out in several ways. For details see the subsection 'DSCC Antenna Mechanical Subsystem' in the 'Subsystem' section. Binary pointing is the preferred mode for tracking spacecraft; pointing predicts are provided, and the antenna simply follows those. With CONSCAN, the antenna scans conically about the optimum pointing direction, using closed-loop receiver signal strength estimates as feedback. In planetary mode, the system interpolates from three (slowly changing) RA-DEC target coordinates; this is 'blind' pointing since there is no feedback from a detected signal. In sidereal mode, the antenna tracks a fixed point on the celestial sphere. In 'precision' mode, the antenna pointing is adjusted using an optical feedback system. It is possible on most antennas to freeze z-axis motion of the subreflector to minimize phase changes in the received signal. DSCC Receiver-Exciter Subsystem ------------------------------- The diplexer in the signal path between the transmitter and the feed horns on all antennas may be configured so that it is out of the received signal path in order to improve the signal-to-noise ratio in the receiver system. This is known as the 'listen-only' or 'bypass' mode. Closed-Loop vs. Open-Loop Reception ----------------------------------- Radio Science data can be collected in two modes: closed- loop, in which a phase-locked loop receiver tracks the spacecraft signal, or open-loop, in which a receiver samples and records a band within which the desired signal presumably resides. Closed-loop data are collected using Closed-Loop Receivers, and open-loop data are collected using Open-Loop Receivers in conjunction with the DSCC Spectrum Processing Subsystem (DSP). See the Subsystems section for further information. Closed-Loop Receiver AGC Loop ----------------------------- The closed-loop receiver AGC loop can be configured to one of three settings: narrow, medium, or wide. Ordinarily it is configured so that expected signal amplitude changes are accommodated with minimum distortion. The loop bandwidth is ordinarily configured so that expected phase changes can be accommodated while maintaining the best possible loop SNR. Coherent vs. Non-Coherent Operation ----------------------------------- The frequency of the signal transmitted from the spacecraft can generally be controlled in two ways -- by locking to a signal received from a ground station or by locking to an on-board oscillator. These are known as the coherent (or 'two-way') and non-coherent ('one-way') modes, respectively. Mode selection is made at the spacecraft, based on commands received from the ground. When operating in the coherent mode, the transponder carrier frequency is derived from the received uplink carrier frequency with a 'turn-around ratio' typically of 240/221. In the non-coherent mode, the downlink carrier frequency is derived from the spacecraft on-board crystal-controlled oscillator. Either closed-loop or open-loop receivers (or both) can be used with either spacecraft frequency reference mode. Closed-loop reception in two-way mode is usually preferred for routine tracking. Occasionally the spacecraft operates coherently while two ground stations receive the 'downlink' signal; this is sometimes known as the 'three-way' mode. DSCC Spectrum Processing Subsystem (DSP) ---------------------------------------- The DSP can operate in four sampling modes with from 1 to 4 input signals. Input channels are assigned to ADC inputs during DSP configuration. Modes and sampling rates are summarized in the tables below: Mode Analog-to-Digital Operation ---- ---------------------------- 1 4 signals, each sampled by a single ADC 2 1 signal, sampled sequentially by 4 ADCs 3 2 signals, each sampled sequentially by 2 ADCs 4 2 signals, the first sampled by ADC #1 and the second sampled sequentially at 3 times the rate by ADCs #2-4 8-bit Samples 12-bit Samples Sampling Rates Sampling Rates (samples/sec per ADC) (samples/sec per ADC) --------------------- --------------------- 50000 31250 25000 15625 12500 10000 10000 6250 5000 5000 4000 3125 2500 2000 1250 1000 1000 500 400 250 200 200 Input to each ADC is identified in header records by a Signal Channel Number (J1 - J4). Nominal channel assignments are shown below. Signal Channel Number Receiver Channel --------------------- ------------- J1 X-RCP J2 S-RCP J3 X-LCP J4 S-LCP Location - DSN ============== Station locations are documented in [GEO-10REVD]. Geocentric coordinates are summarized here. Geocentric Geocentric Geocentric Station Radius (km) Latitude (N) Longitude (E) --------- ----------- ------------ ------------- Goldstone DSS 13 (34-m R&D) 6372.125125 35.0660185 243.2055430 DSS 14 (70-m) 6371.993286 35.2443527 243.1104638 DSS 15 (34-m HEF) 6371.966540 35.2403133 243.1128069 DSS 24 (34-m BWG) 6371.973553 35.1585349 243.1252079 DSS 25 (34-m BWG) 6371.983060 35.1562594 243.1246384 DSS 26 (34-m BWG) 6371.993032 35.1543411 243.1269849 Canberra DSS 34 (34-m BWG) 6371.693561 -35.2169868 148.9819620 DSS 43 (70-m) 6371.689033 -35.2209234 148.9812650 DSS 45 (34-m HEF) 6371.675906 -35.2169652 148.9776833 Madrid DSS 45 (34-m BWG) 6370.025429 40.2357708 355.7459008 DSS 63 (70-m) 6370.051221 40.2413537 355.7519890 DSS 65 (34-m HEF) (see next paragraph) The coordinates for DSS 65 until 1 February 2005 were 6370.021697 40.2373325 355.7485795 In cartesian coordinates (x, y, z) this was (+4849336.6176, -0360488.6349, +4114748.9218) Between February and September 2005, the antenna was physically moved to (+4849339.6448, -0360427.6560, +4114750.7428) Measurement Parameters - DSN ============================ Open-Loop System ---------------- Output from the Open-Loop Receivers (OLRs), as sampled and recorded for later analysis, is a stream of 8- to 16-bit quantized voltage samples. The nominal input to the Analog-to-Digital Converters (ADCs) is +/-10 volts, but the precise scaling between input voltages and output digitized samples is usually irrelevant for analysis; the digital data are generally referenced to a known noise or signal level within the data stream itself -- for example, the thermal noise output of the radio receivers which has a known system noise temperature (SNT). Raw samples comprise the data block in each output record; a header record contains ancillary information such as: time tag for the first sample in the data block RMS values of receiver signal levels and ADC outputs local oscillator (e.g., POCA) frequency and drift rate Closed-Loop System ------------------ Through early 2003 closed-loop data were recorded in Archival Tracking Data Files (ATDFs), as well as certain secondary products such as the Orbit Data File (ODF). The ATDF Tracking Logical Record contained 150 entries including status information and measurements of ranging, Doppler, and signal strength. Starting in December 2002 the Network Simplification Plan (NSP) brought in a new phase-based closed-loop system with both higher precision and higher accuracy. Nearly 20 different record formats were defined under the umbrella of the new Tracking and Navigation File (TNF). Ground stations were converted one at a time so that ATDF production ended with one pass and TNF production began on the next. ACRONYMS AND ABBREVIATIONS - DSN ================================ ACS Antenna Control System ADC Analog-to-Digital Converter AGC Automatic Gain Control AMS Antenna Microwave System APA Antenna Pointing Assembly ARA Area Routing Assembly ATDF Archival Tracking Data File AUX Auxiliary AZ Azimuth bps bits per second BWG Beam WaveGuide (antenna) CDU Command Detector Unit CMC Complex Monitor and Control CONSCAN Conical Scanning (antenna pointing mode) CRG Coherent Reference Generator CUL Clean-up Loop DANA a type of frequency synthesizer dB deciBel dBi dB relative to isotropic dBm dB relative to one milliwatt DCO Digitally Controlled Oscillator DEC Declination deg degree DMC DSCC Monitor and Control Subsystem DOR Differential One-way Ranging DSCC Deep Space Communications Complex DSN Deep Space Network DSP DSCC Spectrum Processing Subsystem DSS Deep Space Station DTK DSCC Tracking Subsystem E east EIRP Effective Isotropic Radiated Power EL Elevation FET Field Effect Transistor FFT Fast Fourier Transform FIR Finite Impulse Response FTS Frequency and Timing Subsystem GCF Ground Communications Facility GHz Gigahertz GPS Global Positioning System HA Hour Angle HEF High-Efficiency (as in 34-m HEF antennas) HEMT High Electron Mobility Transistor (amplifier) HGA High-Gain Antenna HSB High-Speed BWG IF Intermediate Frequency IVC IF Selection Switch JPL Jet Propulsion Laboratory K Kelvin Ka-Band approximately 32 GHz KaBLE Ka-Band Link Experiment kbps kilobits per second kHz kilohertz km kilometer kW kilowatt LAN Local Area Network LCP Left-Circularly Polarized LGR Low-Gain Receive (antenna) LGT Low-Gain Transmit (antenna) LMA Lockheed Martin Astronautics LMC Link Monitor and Control LNA Low-Noise Amplifier LO Local Oscillator m meters MCA Master Clock Assembly MCCC Mission Control and Computing Center MDA Metric Data Assembly MGS Mars Global Surveyor MHz Megahertz MOLA Mars Orbiting Laser Altimeter MON Monitor and Control System MOT Mars Observer Transponder MSA Mission Support Area N north NAR Noise Adding Radiometer NBOC Narrow-Band Occultation Converter NIST SPC 10 time relative to UTC NIU Network Interface Unit NOCC Network Operations and Control System NRV NOCC Radio Science/VLBI Display Subsystem NSP Network Simplification Plan NSS NOCC Support System OCI Operator Control Input ODF Orbit Data File ODR Original Data Record ODS Original Data Stream OLR Open Loop Receiver OSC Oscillator PDS Planetary Data System POCA Programmable Oscillator Control Assembly PPM Precision Power Monitor RA Right Ascension REC Receiver-Exciter Controller RCP Right-Circularly Polarized RF Radio Frequency RIC RIV Controller RIV Radio Science IF-VF Converter Assembly RMDCT Radio Metric Data Conditioning Team RMS Root Mean Square RSR Radio Science Receiver RSS Radio Science Subsystem RTLT Round-Trip Light Time S-band approximately 2100-2300 MHz sec second SEC System Error Correction SIM Simulation SLE Signal Level Estimator SNR Signal-to-Noise Ratio SNT System Noise Temperature SOE Sequence of Events SPA Spectrum Processing Assembly SPC Signal Processing Center sps samples per second SRA Sequential Ranging Assembly SRC Sub-Reflector Controller SSI Spectral Signal Indicator TID Time Insertion and Distribution Assembly TLM Telemetry TNF Tracking and Navigation File TSF Tracking Synthesizer Frequency TWM Traveling Wave Maser TWNC Two-Way Non-Coherent TWTA Traveling Wave Tube Amplifier UNK unknown USO UltraStable Oscillator UTC Universal Coordinated Time VLBI Very Long Baseline Interferometry VCO Voltage-Controlled Oscillator VF Video Frequency X-band approximately 7800-8500 MHz" END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "ANDERSONETAL1993" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "ASMAR&HERRERA1993" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "ASMAR&RENZETTI1993" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "ASMARETAL1995" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "BARBINIS2001" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "DSN810-5" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "ESTABROOKETAL1995" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "GEO-10REVD" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "HINSONETAL1999" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "JPLD-14027" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "JPLD-16765" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "LEMOINEETAL2001" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "SIMPSON&TYLER2001" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "SMITHETAL1999" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "TRACADISETAL2001" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "TYLERETAL1992" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "TYLERETAL2001" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "WITHERSETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "WOO1993" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "YUANETAL2001" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END