810-005, Rev. E
DSMS Telecommunications Link
Design Handbook

209
Open-Loop Radio Science
Effective November 30, 2000

Document Owner:              Approved by:

-----------------------      --------------------------
Massimo Tinto      Date      Massimo Tinto          Date
                             Radio Science Services
                             System Development Engineer

Prepared by:                 Released by:
                             [Signature on file in TMOD Library]
------------------------     ---------------------------
R.W. Sniffin        Date      TMOD Document Release  Date




Change Log
Rev           Issue Date               Affected Paragraphs       Change Summary
Initial       1/15/2001                All                       All



Note to Readers 
There are two sets of document histories in the 810-005 document, and these
histories are reflected in the header at the top of the page. First, the entire document is
periodically released as a revision when major changes affect a majority of the modules. For
example, this module is part of 810-005, Revision E. Second, the individual modules also
change, starting as an initial issue that has no revision letter. When a module is changed, a
change letter is appended to the module number on the second line of the header and a summary
of the changes is entered in the module's change log.

This module documents the new Radio Science Receivers that will become operational in the 
year 2001 and the Ka-band capability at DSS 25. The equipment that was previously documented 
in module RSS-10 of 810-005, Rev. D has been removed from the network.

Contents
Paragraph                                                                                             Page
1 Introduction ......................................................................................... 4
1.1 Purpose ............................................................................................ 4
1.2 Scope .............................................................................................. 4
2 General Information................................................................................... 4
2.1 Functions........................................................................................... 5
2.2 Hardware Configuration ............................................................................. 5
2.3 RSR Signal Processing .............................................................................. 7
2.4 RSR Signal Detection................................................................................ 7
2.5 RSR Operation ...................................................................................... 9
2.6 Data Delivery ..................................................................................... 11
2.6.1 Ancillary Data .................................................................................. 11
2.7 Performance ....................................................................................... 11
2.7.1 Frequency Stability.............................................................................. 11
2.7.2 Phase Noise...................................................................................... 13
2.7.3 Amplitude Stability ............................................................................. 14
2.8 Precision Telemetry Simulator...................................................................... 14
3 Proposed Capabilities................................................................................ 14
3.1 70-m X-band Uplink Implementation ................................................................. 14

Illustrations
Figure                                                                                                Page
1. Radio Science Receiving Equipment Configuration ..................................................... 6
2. Relationships Between RSR Processing Bands.......................................................... 10

Tables
Table                                                                                                 Page
1. Supported Bandwiths and Resolutions with Resulting Data Rate......................................... 8
2. Radio Science Receiver Characteristics ............................................................. 12
3. Uplink and Downlink Allan Deviation Requirements ................................................... 15
4. Uplink and Downlink Phase Noise Requirements........................................................ 16


1 Introduction


1.1 Purpose
This module describes the capabilities and performance of the Deep
Space Network (DSN) Open-loop Radio Science equipment used for supporting
radio science (RS) experiments.

1.2 Scope
          This module discusses the open-loop radio science receiving equipment
functions, architecture, operation, and performance. Although some RS
experiments require uplink support and closed-loop Doppler and ranging data,
this module emphasizes a description of the open-loop recording capability that
is used solely during radio science experiments. Details of the closed-loop
Doppler tracking system can be found in module 203, 34-m and 70-m Receiver
Doppler. Details of the uplink functions can be found in the 70-m, 34-m High
Efficiency (HEF), and 34-m Beam Waveguide (BWG) telecommunications interface
modules 101, 103, and 104.


2 General Information

          Radio science experiments involve measurements of small changes in the
phase, frequency, amplitude, and polarization of the radio signal propagating
from an interplanetary spacecraft to an Earth receiving station. By properly
analyzing these data, investigators can infer characteristic properties of the
atmosphere, ionosphere, and planetary rings of planets and satellites, measure
gravitational fields and ephemeredes of planets, monitor the solar plasma and
magnetic fields activities, and test aspects of the theory of general
relativity. Details of the Radio Science System applications may be found in the
JPL Publication 80-93, Rev. 1, written by S.W. Asmar and N.A. Renzetti, titled:
The Deep Space Network as an Instrument for Radio Science Research.
2.1 Functions

          The functions of the DSN with respect to conducting radio science
experiments can be summarized as follows:

-Providing an uplink carrier signal to the spacecraft with a pure spectrum, 
 including low phase noise and stable frequency.
-Acquisition, down conversion, digitization, and recording of the downlink carrier 
 with minimal degradation to its frequency, phase, and amplitude stability.
-Providing assurance that the expected signals are being acquired and
 recorded.

2.2 Hardware Configuration

          All radio science experiments require use of the antenna, microwave,
antenna-mounted receiving, and frequency and timing equipment at the stations.
They also require the Ground Communications Facility (GCF) to deliver the data
from the stations to users and the Advanced Multi-mission Operations System
(AMMOS) at JPL, where experiments are monitored. DSN stations are designed to
meet radio science requirements for stability. However, one of the beam
waveguide stations at the Goldstone Deep Space Communications Complex (DSCC),
DSS 24, is not equipped with a high-quality frequency distribution system and is
not recommended for radio science applications. A block diagram of the open-loop
radio science receiving capability is shown in Figure 1.

     The receiving equipment on each DSN antenna produces one or more
intermediate frequency (IF) signals with a nominal center frequency of 300 MHz
and a bandwidth that depends on the microwave and low noise amplifier equipment
on the antenna as described in modules 101, 103, and 104. These IF signals are
routed to a distribution amplifier (not shown in Figure 1) that provides
multiple copies of each signal for use by the Radio-science Receivers (RSRs),
the telemetry and tracking receivers, and other equipment in the signal
processing center (SPC). One copy of each signal is provided to the RSR IF
Switch that further divides and amplifies it with the result being that any of
the RSR channels can be connected to any antenna IF signal.

          There are two dedicated RSRs at the Goldstone Deep Space
Communications Complex (DSCC) and one at the Canberra and Madrid DSCCs. Each
complex also has an online spare that is shared with other functions including
very-long baseline Interferometry (VLBI). Each RSR contains two channels however
the design of the system software is such that, from the user's viewpoint, each
RSR channel can be considered to be an independent open-loop receiver.

Figure 1. Radio Science Receiving Equipment Configuration
(Figure omitted in text-only document)


2.3 RSR Signal Processing

          The IF signal selected by the RSR IF Switch is fed to the Digitizer
(DIG) where it is filtered to limit its bandwidth to the range of 265-375 MHz
centered at 320 MHz. This corresponds to a received frequency range of
2,265-2,375 MHz at S-band, 8,365-8,475 MHz at X-band, and 31,965-32,075 MHz at
Ka-band. However, the actual received frequency range will depend on the
characteristics of the equipment on the selected antenna. The filtered signal is
downconverted to a center frequency of 64 MHz and digitized at 256 MHz with an 8-
bit resolution. The resultant data are fed to the Digital Downconverter (DDC)
that selects any 16-MHz bandwidth from the original bandpass with a resolution
of 1 MHz and downconverts it to baseband in the form of a 16-Ms/s, 8-bit,
complex data stream.

          Baseband processing provides up to four subchannel filters to select
frequency bands of interest for recording. The number of available filters
depends on the selected bandwidths that can be broadly categorized as
Narrowband, Medium Band, or Wideband. The following selection of filters is
available:

-4 Narrowband
-2 Narrowband and 1 Medium Band
-2 Medium Band
-1 Wideband

The filters are specified by their bandwidths, the desired resolution
(bits/sample) and an offset from the predicted sky frequency predict file. This
frequency predict file is created by the DSN network support function and
contains the spacecraft frequency altered by spacecraft trajectory and Earth-
rotation. Table 1 lists the supported filter bandwidths and resolutions and
gives the resultant data rate for each combination. Figure 2 shows the
relationship between the frequency bands within the RSR.

2.4 RSR Signal Detection
          Because the RSR is an open-loop receiver, it does not have a
mechanism to align its passband to (establish lock with, or track) the received
signal. Instead, it relies on predicts to position its passband. This creates a
risk that a predict error might result in the wrong portion of the received
spectrum being processed. To assist in recognizing this, the RSR analyzes the
data in each subchannel and provides a detected signal indication on the main
display for that subchannel

          In addition to the detected signal indication, the RSR provides a
frequency-domain representation of the bandpass being recorded in each RSR
subchannel using a Fast-Fourier Transform (FFT). Characteristics of the FFT
such as number of points, averaging, and update rate are under user control.


 Table 1. Supported Bandwiths and Resolutions with Resulting Data Rate 
                                        
     Category          Bandwidth     Resolution           Data Rate (b/s)
                                     (b/sample)
    Narrowband           1 kHz               16                    32,000
                         2 kHz               16                    64,000
                         4 kHz               16                    128,000
                         8 kHz               16                    256,000
                        16 kHz               16                    512,000
                        25 kHz               16                    800,000
                        50 kHz               16                   1,600,000
                        100 kHz              16                   3,200,000
                         1 kHz                8                    16,000
                         2 kHz                8                    32,000
                         4 kHz                8                    64,000
                         8 kHz                8                    128,000
                        16 kHz                8                    256,000
                        25 kHz                8                    400,000
                        50 kHz                8                    800,000
                        100 kHz               8                   1,600,000
   Medium Band          250 kHz              16                   8,000,000
                        500 kHz              16                  16,000,000
                        250 kHz               8                   4,000,000
                        500 kHz               8                   8,000,000
                         1 MHz                8                  16,000,000
                        250 kHz               4                   2,000,000
                        500 kHz               4                   4,000,000
                         1 MHz                4                   8,000,000
                         2 MHz                4                  16,000,000


Table 1. Supported Bandwiths and Resolutions with Resulting Data Rate (Continued)

    Category          Bandwidth      Resolution           Data Rate (b/s)
                                     (b/sample)
Medium Band            250 kHz                2                   1,000,000
(Continued)
                       500 kHz                2                   2,000,000
                        1 MHz                 2                   4,000,000
                        2 MHz                 2                   8,000,000
                        4 MHz                 2                  16,000,000
                       250 kHz                1                    500,000
                       500 kHz                1                   1,000,000
                        1 MHz                 1                   2,000,000
                        2 MHz                 1                   4,000,000
                        4 MHz                 1                   8,000,000
    Wideband            8 MHz                 2                  32,000,000
                        8 MHz                 1                  16,000,000
                        16 MHz                1                  32,000,000

2.5 RSR Operation
          The radio science equipment operates in both a link-assigned and a
stand-alone mode. In the link-assigned mode, the Network Monitor and Control
(NMC) function receives monitor data from the RSR for incorporation into the
data set for tracking support and provides a workstation from which the RSR can
be operated. RSRs that are not assigned to a link may be operated in a stand-
alone mode without interference to any activities in process at the complex.
Monitor data is not forwarded to the NMC by RSRs operating in the stand-alone
mode.

          The RSR employs a client-server architecture where each RSR channel
acts as a server capable of accepting connections from up to five users
operating the radio science client software at any time. In the link-assigned
mode, one of these five clients is the NMC workstation. The RSR does not
recognize any client as being superior to the others so it is up to the user to
assign responsibility for control to one client with the other clients operating
in a passive mode. One RSR client is required for each RSR channel being
controlled or observed. Thus, a complex radio science experiment involving four
RSR channels would require four RSR clients at the control point.


Figure 2. Relationships Between RSR Processing Bands
(Figure omitted in text-only document)

All functions of the RSR may be performed from the RSR client in real
time. Of special interest to the RS experimenter are the ability to adjust
(slew) the predicted frequency profile, to slew the individual subchannel
frequencies, to adjust FFT parameters, and to enable or disable recording for
each subchannel.

2.6 Data Delivery
          When recording is enabled, baseband samples and ancillary
information, discussed below, are formatted into a file of data blocks and
stored on disk drives for delivery to JPL or other users. A separate data file
is created for each subchannel. Data delivery is normally via the Reliable
Network System (RNS). Data also may be obtained via File Transfer Protocol
(FTP) or Digital Linear Tape (DLT) cartridges. The format is the same
independent of the method of delivery.

2.6.1 Ancillary Data
          The following ancillary data are included as a header for each data
block. A detailed description of the data blocks is contained in TMOD Document
820-013, module 0159.

-Data record version
-Subchannel identification
-Time tag for first sample in block
-Station and pass identification
-Spacecraft identification
-Receiver configuration

2.7 Performance
          The principal characteristics of the RSRs are summarized in Table 2.
In addition, radio science experiments are influenced by the overall stability
of equipment at the stations. The following sections provide information on the
techniques used to validate RS equipment stability.

2.7.1 Frequency Stability
          Long-term frequency stability tests are conducted with the exciter/
transmitter equipment and the Radio Science open-loop receiving equipment. An
uplink signal generated by the exciter is translated at the antenna to a
downlink frequency. The downlink signal is passed through the RF-IF
downconverter at the antenna and into the RSR. In doing this test, however,
instability in the frequency and timing equipment and the mechanical vibrations
of the antenna are not included. This is because frequency and timing
instability is cancelled out, while the mechanical vibrations of the antenna are
not present in these data. Measurements of these items can however be obtained
via other means, making it possible to provide an estimate of the
 Table 2. Radio Science Receiver Characteristics Table 2. Radio Science Receiver
                           Characteristics (Continued)
                                        
       Parameter                Value                      Remarks
Number of Channels                           Note: Any channel may be connected
                                             to any received spectrum
Goldstone                         4          2 additional channels are available
                                             shared with other applications
Canberra and Madrid               2          2 additional channels are available
                                             shared with other applications
Frequency Ranges Covered                     
At RSR Input (MHz)            265 - 375      
Referenced to L-band        1,645 -1,755     L-band receive capability at 70-m
(MHz)                                        subnet is 1,628-1,708 MHz
Referenced to S-band        2,265 - 2,375    S-band downlink allocation is
(MHz)                                        2,200-2,290 MHz for Earth orbiter
                                             application and 2,290-2,300 MHz for
                                             deep space applications
Referenced to X-band        8,365 - 8,475    X-band downlink allocation is
(MHz)                                        8,400-8,450 MHz for deep space
                                             application and 8,450-8,500 MHz for
                                             Earth orbiter applications
IF Attenuation                               
Range (dB)                    0 - 31.5       
Resolution (dB)                  0.5         
Doppler Compensation                         
Maximum Doppler Shift            30          At all downlink frequencies
(km/s)
Maximum Doppler Rate             17          At all downlink frequencies
(m/s2)
Maximum Doppler                  0.3         At all downlink frequencies
Acceleration (m/s3)
Maximum Tuning Error             0.5         At all downlink frequencies
(Hz)
Manual Offset (MHz)         -8.0 to +8.0     
Baseband Bandwidth (MHz)         16          

       Parameter                 Value                     Remarks
Baseband Resolution                1           Positioning of baseband within
(MHz)                                          IF or RF bandwidth
Number of Subchannels            1 - 4         Configuration depends on data
Available for each RSR                         volume.
Subchannel Tuning                              
Tuning (MHz)                      +/-8           From center of baseband
Resolution (Hz)                   <1           
Recording Bandwidths                           See Table 2 for exact values.
Narrowband (NB), kHz            1 - 100        1 - 4-subchannels
 Medium Band (MB), kHz        250 - 4,000      2 or 1 with 2 NB subchannels
Wideband (WB), MHz              8 or 16        NB and MB subchannels are not
                                               available
Resolutions                     16 - 1         Depends on selected bandwidth.
(bits/sample)                                  See Table 2 for available
                                               resolutions.
Time Tagging                                   
Resolution (10^-6 s)               1           
Accuracy (10^-6 s)                 1           With respect to station clock
Signal Detection Display                       1 for each subchannel being
                                               recorded
Number of points in FFT       100 - 4096       Default is 1000
Spectra Averaging               1 - 100        Default is 10
FFT Interval (s)              1 - 10,000       Default is 10

overall frequency stability of the stations. The long-term frequency stability
is presented in terms of the Allan deviation over a specified integration time.
Table 3 shows uplink and downlink Allan deviation requirements for the 34-m HEF,
34-m BWG, and 70-m antennas. Repeated testing has always produced estimates
better than these requirements.

2.7.2 Phase Noise
Phase stability (Spectral Purity) testing characterizes stability
over very short integration times. The region of the frequency band where phase
noise measurements are performed can be as far as 10 kHz off the carrier
frequency. Such measurements are reported in dB relative to the carrier (dBc),
in a 1-Hz band at a specified distance from the carrier. Table 4 contains the
required phase noise levels, at specified offsets, for the 34-m HEF, 34-m BWG,
and 70-m subnets. As is the case with frequency stability measurements,
repeated testing ensures these requirements are not exceeded.

2.7.3 Amplitude Stability
Amplitude stability tests measure the amplitude fluctuations produced
by the open-loop receiving system relative to a constant (mean) amplitude input
signal. The amplitude stability performance is specified in terms of a threshold
on the amplitude fluctuations relative to the mean amplitude, and the
corresponding probability that such fluctuations will not exceed such a
threshold. An analysis indicates that 99.7% of the time, the amplitude stability
at the 70-m, 34-m HEF, and 34-m BWG stations at S- and X-bands is less than 0.2
dB including the gain variation due to antenna pointing errors.

2.8 Precision Telemetry Simulator
The Precision Telemetry Simulator (PTS) is an external device that
provides IF test signals for performance verification of the radio science
equipment. Its signals are generated in the digital domain and subsequently
converted to analog, with signal conditions driven from predicts. At least two
simulated signals can be generated, each having its own characteristics in terms
of Doppler and signal level, etc. The PTS signals are injected into the RSR via
the RSR IF Switch.


3 Proposed Capabilities

          The following paragraphs discuss capabilities that have not yet been
implemented by the DSN but have adequate maturity to be considered for
spacecraft mission and equipment design. Telecommunications engineers are
advised that any capabilities discussed in this section cannot be committed to
except by negotiation with the Telecommunications and Mission Operations
Directorate (TMOD) Plans and Commitments Program Office.

3.1 70-m X-band Uplink Implementation
          The 70-m X-band uplink implementation that has been completed at DSS
14 and DSS 43 will be extended to DSS 63. As a result, all 70-m stations will
have the same capabilities and performance as described for DSS 14 and 43 in
Tables 2, 3, and 4.

  Table 3. Uplink and Downlink Allan Deviation Requirements Table 4. Uplink and
                        Downlink Phase Noise Requirements
                                        
   Averaging Time, s                      Allan Deviation     
                               1          10          100          1000
Station and Band                                              
34-m HEF                                                      
X-band U/L                  1.0x10^-12   1.1x10^-13   4.5x10^-15   4.3x10^-15
S-band D/L                  4.1x10^-13   7.2x10^-14   9.1x10^-15   5.3x10^-15
X-band D/L                  4.0x10^-13   4.9x10^-14   5.3x10^-15   4.7x10^-15
34-m BWG    
S-band U/L(DSS 24,34,54)    1.0x10^-12   1.1x10^-13   4.5x10^-15   4.3x10^-15
X-band U/L(DSS 25,26,34,54) 1.0x10^-12   1.1x10^-13   4.5x10^-15   4.3x10^-15
S-band D/L(DSS 34,54)       4.1x10^-13   7.2x10^-14   9.1x10^-15   5.3x10^-15
X-band D/L(DSS 25,26,34,54) 4.0x10^-13   4.9x10^-14   5.3x10^-15   4.7x10^-15
Ka-band U/L (DSS 25)        No Rqmt.     No Rqmt.     1.1x10^-14   2.1x10^-15
Ka-band D/L (DSS 25)        1.3x10^-13   7.5x10^-14   6.8x10^-15   2.2x10^-15
70-m                                                          
S-band U/L                  1.5x10^-12   2.3x10^-13   1.1x10^-14   1.1x10^-14
X-band U/L (DSS 14, 43)     1.5x10^-12   2.3x10^-13   1.1x10^-14   1.1x10^-14
S-band D/L                  4.1x10^-13   7.2x10^-14   9.1x10^-15   5.3x10^-15
X-band D/L                  4.0x10^-13   4.9x10^-14   5.3x10^-15   4.7x10^-15

Offset from Carrier, Hz                 Phase Noise, dBc    
                             1           10         100           10 k
Station and Band                                         
34-m HEF                                                    
X-band U/L                 -52.3        -61.8      -65.9          -65.9
S-band D/L                 -62.8        -72.2      -76.7          -76.7
X-band D/L                 -51.5        -60.9      -65.5          -65.5
34-m BWG                                                    
S-band U/L (DSS 24, 34,    -63.5        -72.5      -77.1          -77.1
54)
X-band U/L (DSS 25, 26,    -52.3        -61.8      -65.9          -65.9
34, 54)
S-band D/L (DSS 34, 54)    -62.8        -72.2      -76.8          -76.8
X-band D/L (DSS 25, 26,    -51.6        -61.0      -65.5          -65.5
34, 54)
X-band D/L (DSS 25)        -59.7        -65.6      -66.0          -66.0
Ka-band D/L (DSS 25)       -55.2        -63.7      -64.0          -64.0
70-m                                                        
S-band U/L                 -63.5        -72.5      -77.1          -77.1
X-band U/L (DSS 14, 43)    -52.3        -61.8      -65.9          -65.9
S-band D/L                 -62.8        -72.2      -76.7          -76.7
X-band D/L                 -51.5        -60.9      -65.5          -65.5