|
Instrument Information |
|
| IDENTIFIER | urn:nasa:pds:context:instrument:lgrs-b.grail-b::1.0 |
| NAME |
LUNAR GRAVITY RANGING SYSTEM B |
| TYPE |
ATMOSPHERIC SCIENCES |
| DESCRIPTION |
Instrument Overview
===================
Radio science investigations utilize instrumentation with
elements both on a spacecraft and at ground stations -- in this
case, at the NASA Deep Space Network (DSN). 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
======================================
Instrument Id : LGRS-B
Instrument Host Id : GRAIL-B
PI PDS User Id : UNK
Instrument Name : LUNAR GRAVITY RANGING SYSTEM B
Instrument Type : RADIO SCIENCE
Build Date : UNK
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
Instrument Overview - Spacecraft
================================
The Lunar Gravity Ranging System (LGRS) instruments on board the
twin GRAIL spacecraft generate radio signals at Ka-band, X-band,
and S-band. The time and frequency of each signal is referenced
to its respective Ultra-Stable Oscillator (USO). The Ka-band
and S-band signals are captured by the other spacecraft, and
precise measurements of signal properties are recorded for later
transmission to Earth. The X-band link is received by stations
of the NASA Deep Space Network (DSN). Operations are continuous
and simultaneous on both spacecraft except that the X-Band
downlink to Earth is only used when a DSN station is available.
The sinusoidal Ka-band link is used to determine distance
(range) between the two spacecraft from the phase of the
received signal. The modulated S-band signal is for exchange of
Timing and Time Synchronization (TTS). The X-band link is a
one-way transmission to the DSN via the Radio Science Beacon
(RSB).
Except for mounting differences, LGRS-A and LGRS-B (on GRAIL-A
and GRAIL-B, respectively) are identical. Each is responsible
for working with its twin to send and receive the signals needed
to accurately and precisely measure the changes in range between
the two orbiters. Each LGRS consists of an Ultra-Stable
Oscillator (USO), Microwave Assembly (MWA), a Time-Transfer
Assembly (TTA), and the Gravity Recovery Processor Assembly
(GPA).
The USO provides a steady reference signal that is used by all
of the instrument subsystems. Within the LGRS, the USO provides
the reference frequency for the MWA and the TTA. The MWA
converts the USO reference signal to the Ka-band frequency,
which is transmitted to the other orbiter.
The function of the TTA is to provide a two-way time-transfer
link between the spacecraft both to synchronize and to measure
the clock offset between the two LGRS clocks. The TTA generates
an S-band signal from the USO reference frequency and sends a
GPS-like ranging code to the other spacecraft. The GPA combines
all the inputs received from the MWA and TTA to produce the
radiometric data that are downlinked to the ground.
Finally, each Radio Science Beacon (RSB) transmits an X-Band
signal to the ground based on its USO; the drift of the USO is
derived from the one-way Doppler data.
Science Objectives
==================
The inter-spacecraft radio links and the X-band radio link to
Earth are used to generate a high resolution gravitational field
of the Moon.
Operational Considerations - Spacecraft
=======================================
GRAIL Primary Mission (PM) & Extended Mission (XM) operational
considerations
The GRAIL PM started on March 01, 2012 and ended on May 29,
2012. The GRAIL XM started on August 29, 2012, and ended on
December 12, 2012, followed by decommissioning from December 12,
2012, to December 18, 2012. Spacecraft events for these phases
(for example, propulsive maneuvers, Ka boresight calibration
attitude maneuvers, telecommunication configuration changes and
the science Lunar Gravity Ranging System (LGRS) events) are
described below including their impact on science processing.
1)Propulsive Maneuvers
During PM, there were propulsive maneuvers for GRAIL-B but not
for GRAIL-A.
During the XM, weekly Eccentricity Correction Maneuvers (ECM)
were needed on both GRAIL spacecraft to correct rapid orbit
eccentricity changes due to large gravity variations at low
altitudes. The ECMs were between 5 and 15 m/sec and required
near radial thrusting which meant that the science measurements
were interrupted for about 15 minutes while the spacecraft
executed the ECMs. In the day following the ECMs a cleanup Orbit
Trim Maneuver (OTM) maneuver was executed if needed. The OTMs in
general were at the cm/sec level and science measurements were
not interrupted during an OTM.
The mass change history for both spacecraft can be found in the
MAS1A/B Level-1 products and the thruster on-times are available
in the THR1A/B level-1 products. LGRS measurements are taken
during the propulsive maneuvers but it is recommended to break
science data arcs at the propulsive maneuver event times, since
the velocity changes imparted on the spacecraft are not known
with sufficient accuracy for science processing.
PM GRAIL-B Propulsive Maneuvers
start time end time duration dV comment
(TDB) (TDB) (sec) (mm/sec)
2012-03-30 18:42:45.776 2012-03-30 18:44:19.651 93.875 28.0 OTM-B2
XM GRAIL-B Propulsive Maneuvers
start time end time duration dV comment
(TDB) (TDB) (sec) (mm/sec)
2012-09-10 15:16:20.626 2012-09-10 15:18:35.782 135.156 9680.0 ECM-B4
2012-09-17 16:53:01.102 2012-09-17 16:55:21.652 140.551 10590.0 ECM-B5
2012-09-24 11:18:37.600 2012-09-24 11:20:54.975 137.375 9780.0 ECM-B6
2012-10-01 14:27:34.071 2012-10-01 14:29:29.809 115.738 8050.0 ECM-B7
2012-10-08 15:42:50.548 2012-10-08 15:44:19.119 88.570 5940.0 ECM-B8
2012-10-15 15:37:34.030 2012-10-15 15:39:47.049 33.019 9460.0 ECM-B9
2012-10-22 09:56:15.529 2012-10-22 09:58:12.689 17.160 8510.0 ECM-B10
2012-10-29 12:59:13.000 2012-10-29 13:01:19.688 126.687 9110.0 ECM-B11
2012-11-05 16:08:33.472 2012-11-05 16:11:19.796 166.324 12170.0 ECM-B12
2012-11-12 16:16:36.952 2012-11-12 16:19:11.773 154.820 11120.0 ECM-B13
2012-11-19 19:41:10.423 2012-11-19 19:42:35.638 85.215 5680.0 ECM-B14
2012-11-29 17:27:03.689 2012-11-29 17:27:20.294 16.605 4.0 OTM-B5
2012-12-06 15:36:20.176 2012-12-06 15:38:00.777 100.601 6860.0 ECM-B15
2012-12-10 17:44:16.873 2012-12-10 17:46:55.552 158.680 11370.0 ECM-B16
2012-12-14 15:08:45.584 2012-12-14 15:09:55.885 70.301 4520.0 ECM-B17
2012-12-17 21:36:27.342 2012-12-17 21:41:48.748 321.406 25970.0 BTD-B
2) Angular momentum desaturation maneuvers
The GRAIL spacecraft attitude is maintained with angular
momentum wheels. The angular momentum wheels apply torques on
the spacecraft by spinning up or down to maintain attitude. The
angular momentum wheels are only allowed to operate within a
specified wheel speed range. If the wheel speeds exceed the
specified range then attitude control thrusters (desaturation
maneuver) are used to apply a torque on the spacecraft to slow
or speed up the wheels, such that the resulting wheel speed is
within the specified range. In general the wheel speeds are
predictable, the desaturation maneuvers are planned in
advance, and the burns occur over the lunar poles. Since the
attitude control thrusters are not perfectly balanced, a
velocity is imparted on the spacecraft for every maneuver. The
velocity changes in general are small (< 5 mm/sec). LGRS
measurements are taken during the desaturation maneuvers but it
is recommended to break science data arcs at the desaturation
maneuver event times, since the velocity changes imparted on the
spacecraft are not known with sufficient accuracy for science
processing. A table for all desaturation events is shown below
for each spacecraft. The time reported in the table is the
average for all thruster activations associated with one
desaturation event. For detailed thruster on time histories see
level-1 product THR1A/B. The spacecraft mass change is very
small at the level of a few grams per event. For the December
2012 and June 2013 deliveries, the spacecraft mass change is not
accounted for in the MAS1A/B products, but it will be in future
higher version of the level-1 products.
PM GRAIL-B angular momentum desaturation maneuvers
time (TDB) dV (mm/sec)
01-MAR-2012 16:15:48 1.77506
02-MAR-2012 15:06:32 0.54055
06-MAR-2012 23:40:06 7.12499
07-MAR-2012 21:35:39 2.02239
10-MAR-2012 13:55:41 4.84207
13-MAR-2012 15:44:19 5.72732
16-MAR-2012 23:13:12 6.18764
20-MAR-2012 10:28:58 6.35047
23-MAR-2012 21:45:14 6.23994
27-MAR-2012 19:50:32 9.11779
28-MAR-2012 02:03:09 0.43297
30-MAR-2012 07:02:26 3.66186
01-APR-2012 12:01:31 3.78817
03-APR-2012 13:13:07 3.49518
06-APR-2012 13:08:15 4.89412
12-APR-2012 07:17:43 7.67245
22-APR-2012 01:57:33 7.56332
24-APR-2012 06:56:14 2.75304
26-APR-2012 13:48:50 3.06747
28-APR-2012 22:34:54 4.05138
30-APR-2012 23:46:35 4.03603
03-MAY-2012 00:58:53 4.37953
05-MAY-2012 19:13:36 6.62569
08-MAY-2012 21:02:03 7.11001
11-MAY-2012 17:09:16 6.52837
14-MAY-2012 13:16:36 6.64819
17-MAY-2012 07:30:46 6.67855
19-MAY-2012 21:58:12 6.27396
22-MAY-2012 14:19:05 6.35658
25-MAY-2012 04:45:27 6.14663
27-MAY-2012 19:11:59 5.97279
29-MAY-2012 16:36:48 4.29327
XM GRAIL-B Angular momentum desaturation maneuvers
Time(TDB) dV (mm/sec)
30-AUG-2012 16:17:05 3.64928
02-SEP-2012 01:48:40 2.63681
04-SEP-2012 10:56:05 2.84093
06-SEP-2012 12:41:03 2.52960
08-SEP-2012 14:25:59 2.58691
12-SEP-2012 23:26:27 3.25711
15-SEP-2012 08:32:49 2.98007
20-SEP-2012 00:56:54 2.89469
22-SEP-2012 10:03:54 3.05824
26-SEP-2012 19:04:37 2.86992
29-SEP-2012 04:10:45 2.63358
03-OCT-2012 22:25:32 2.29323
06-OCT-2012 07:32:41 2.30012
17-OCT-2012 23:35:03 1.82512
20-OCT-2012 08:41:50 1.90001
24-OCT-2012 17:42:30 2.85745
27-OCT-2012 02:48:58 3.69902
31-OCT-2012 21:03:56 4.61761
03-NOV-2012 06:10:48 4.27835
08-NOV-2012 00:23:56 4.64773
10-NOV-2012 09:31:04 5.12199
15-NOV-2012 01:54:53 5.42636
17-NOV-2012 11:01:27 5.34206
22-NOV-2012 05:03:38 5.50408
24-NOV-2012 13:59:55 5.38920
26-NOV-2012 22:56:19 5.29400
29-NOV-2012 09:42:23 5.18747
01-DEC-2012 20:28:01 5.58101
04-DEC-2012 07:13:52 5.04374
08-DEC-2012 15:33:25 4.23834
12-DEC-2012 18:03:29 3.53912
3) GPA reboots
During PM and XM the LGRS Gravity Processor Assemby (GPA)
rebooted several times resulting in the loss of Ka range and the
Time Transfer System (TTS) observables for about 1.5 minutes.
After a GPA reboot the LGRS clock is synched with the LGRS clock
on the non-rebooting spacecraft using the TTS system. GPA
reboots will cause a gap in the inter-satellite range data
products (KBR1B, SBR1B) of about 2 minutes. In the tables below
all GPA reboots are listed. The reboot times are approximate and
can be off as much as 30 seconds.
PM GRAIL-B GPA reboots table
time (UTC) data gap (sec)
08-MAR-2012 03:48:55 100.0
18-ARR-2012 00:00:59 80.0
19-APR-2012 05:53:49 80.0
22-MAY-2012 19:02:41 80.0
XM GRAIL-B GPA reboots table
time (UTC) data gap (sec)
15-OCT-2012 06:10:54.000 90.0
02-NOV-2012 08:18:23.000 90.0
11-NOV-2012 21:36:03.000 80.0
4) S-band phase resets
On GRAIL-B the TTS phase measurement is reset to zero due to a
software bug in the LGRS software. The TTS ranging measurement
is not affected, but the relative LGRS clock reconstruction
analysis needs to be restarted at a phase reset. In the table
below all S-band phase resets during PM are listed. There were
no S-band phase resets in XM. The S-band reset times are
approximate and can be off as much as 30 seconds.
GRAIL-B S-band phase resets
Time (UTC)
01-Mar-2012 21:02:49
04-Mar-2012 21:18:19
04-Mar-2012 23:40:09
05-Mar-2012 02:28:19
12-Mar-2012 03:57:59
17-Mar-2012 00:10:19
22-Mar-2012 10:06:29
23-Mar-2012 15:29:49
25-Mar-2012 04:15:29
31-Mar-2012 15:27:29
01-Apr-2012 18:11:59
13-Apr-2012 07:05:29
24-Apr-2012 22:07:29
27-Apr-2012 22:13:39
30-Apr-2012 15:31:29
30-Apr-2012 23:38:59
04-May-2012 21:36:49
05-May-2012 15:11:19
08-May-2012 16:36:49
08-May-2012 18:58:29
18-May-2012 08:51:19
19-May-2012 16:45:49
27-May-2012 05:02:49
5) X-band and S-band antenna switching
Due to orbital viewing geometry the GRAIL spacecraft are
changing between the +X and -X S-band and X-band (Radio Science
Beacon) antennas approximately every 14 days. The complete
history for the antenna change are listed in the VGS1B product
(S-band) and VGX1B product (X-band).
6) Ka boresight vector calibrations
During the primary and extended missions, the GRAIL spacecraft
were in nominal science attitude called orbiter point attitude
mode. For this mode the solar arrays of the spacecraft are
parallel to the orbital plane and the Ka boresight vectors (2.1
degrees off the -Z axis in the YZ spacecraft frame) are pointed
in the direction of line of sight toward the other spacecraft.
The GRAIL spacecraft remained in orbit point attitude mode
except during Ka boresight vector calibration maneuvers when the
spacecraft performed two orthogonal slews of 3 deg about the
line of sight vector between the two spacecraft. The tables
below are showing all the Ka boresight calibration maneuvers for
each spacecraft. LGRS measurements are taken during the
maneuvers but should not be used in the science processing
because the measured range change is the sum of orbit geometry,
lunar gravity, and range change induced by spacecraft attitude
variation. Ka boresight vector data contain range corrections
for the phase center to center of mass offset during the
maneuvers but these corrections are not reliable and should not
be used.
PM GRAIL-B Ka boresight maneuvers
start time (UTC) end time (UTC)
02-MAR-2012 19:00 02-MAR-2012 19:15
08-MAR-2012 19:45 08-MAR-2012 20:00
08-MAR-2012 20:45 08-MAR-2012 21:00
08-MAR-2012 16:34 08-MAR-2012 16:49
08-MAR-2012 17:35 08-MAR-2012 17:50
03-APR-2012 19:10 03-APR-2012 19:25
03-APR-2012 20:10 03-APR-2012 20:25
02-MAY-2012 16:20 02-MAY-2012 16:35
02-MAY-2012 17:20 02-MAY-2012 17:35
29-MAY-2012 09:41 29-MAY-2012 09:56
29-MAY-2012 11:35 29-MAY-2012 11:50
XM GRAIL-B Ka boresight maneuvers table
start time (UTC) end time (UTC)
05-SEP-2012 10:20 05-SEP-2012 10:35
05-SEP-2012 11:20 05-SEP-2012 11:35
12-SEP-2012 10:20 12-SEP-2012 10:35
12-SEP-2012 11:20 12-SEP-2012 11:35
19-SEP-2012 10:20 19-SEP-2012 10:35
19-SEP-2012 11:20 19-SEP-2012 11:35
26-SEP-2012 10:20 26-SEP-2012 10:35
26-SEP-2012 11:20 26-SEP-2012 11:35
03-OCT-2012 10:20 03-OCT-2012 10:35
03-OCT-2012 11:20 03-OCT-2012 11:35
10-OCT-2012 10:20 10-OCT-2012 10:35
10-OCT-2012 11:20 10-OCT-2012 11:35
17-OCT-2012 10:20 17-OCT-2012 10:35
17-OCT-2012 11:20 17-OCT-2012 11:35
24-OCT-2012 10:20 24-OCT-2012 10:35
24-OCT-2012 11:20 24-OCT-2012 11:35
31-OCT-2012 10:20 31-OCT-2012 10:35
31-OCT-2012 11:20 31-OCT-2012 11:35
07-NOV-2012 10:20 07-NOV-2012 10:35
07-NOV-2012 11:20 07-NOV-2012 11:35
14-NOV-2012 10:20 14-NOV-2012 10:35
14-NOV-2012 11:20 14-NOV-2012 11:35
21-NOV-2012 10:20 21-NOV-2012 10:35
21-NOV-2012 11:20 21-NOV-2012 11:35
28-NOV-2012 10:20 28-NOV-2012 10:35
28-NOV-2012 11:20 28-NOV-2012 11:35
08-DEC-2012 10:20 08-DEC-2012 10:35
08-DEC-2012 11:20 08-DEC-2012 11:35
11-DEC-2012 22:20 11-DEC-2012 22:35
11-DEC-2012 23:20 11-DEC-2012 23:35
Calibration Description - Spacecraft
====================================
Performance calibrations were done on the ground and the
requirements for a measurement were met if science instrument
temperatures were used to calibrate the science measurements.
During the Prime Mission, other error sources dominated the
gravity field determination, but with the inclusion of the
Extended Mission, the temperature-correlated science
measurements will be applied.
Platform Mounting Descriptions - Spacecraft
===========================================
Platform mounting is part of the instrument design. The
following antennas are mounted to each spacecraft:
- 2 S-band transponder antennas to communicate with Earth
(LGA1 & LGA2)
- 2 X-band beacon antennas for Doppler ranging measurements from
Earth of the Moon's near side (RSB1 & RSB2)
- S-band time-transfer system (TTS) antenna, which sends a
time-synchronization code back and forth between the spacecraft
- Ka-band ranging antenna for precision distance measurement
between the spacecraft
The spacecraft frame is defined such that the -Y axis of GRAIL-A
and the +Y axis of GRAIL-B point to nadir. The solar panels are
on the -X side of each spacecraft. The +/-Z axes of the
spacecraft are along the direction of flight.
The two S-Band transponder antennas are on opposite faces of the
spacecraft to provide full sky coverage. The LGA1 boresight is
along the -X axis of the spacecraft, facing in the direction of
the solar panels. LGA2 is on the opposite side, facing the +X
direction.
The two RSB antennas are oriented similarly, with RSB1 on the -X
side and RSB2 on the +X side. During the mission, transmissions
switch between the two in sync with the S-Band transponder
antennas.
The Ka-Band Antenna Assembly and the TTS are oriented along the
-Z axis of the spacecraft. Since these antennas point at each
other to form a communications link, one is always pointed in
the direction of flight while the other is pointed away. During
the prime mission, the direction of flight is along GRAIL-A's -Z
axis and GRAIL-B's +Z axis. During extended mission, they are
reversed. In addition, the antennae on each spacecraft are
rotated 45 degrees around their boresight, so that in the flight
configuration they form mirror images of each other. This allows
orthogonal polarizations to separate the transmit and receive
channels in the antenna.
For more specific information, see
lib_10_grail_coord_trans_rev1.pdf in the document directory.
Instrument Overview - DSN
=========================
Three Deep Space Communications Complexes (DSCCs) (near Barstow,
CA; Canberra, Australia; and Madrid, Spain) comprise the DSN
tracking network. Each complex is equipped with several
antennas [including at least one each 70-m, 34-m High Efficiency
(HEF), and 34-m Beam WaveGuide (BWG)], associated electronics,
and operational systems. Primary activity at each complex is
radiation of commands to and reception of telemetry data from
active spacecraft. Transmission and reception is possible in
several radio-frequency bands, the most common being S-band
(nominally a frequency of 2100-2300 MHz or a wavelength of
14.2-13.0 cm) and X-band (7100-8500 MHz or 4.2-3.5 cm).
Transmitter output powers of up to 400 kW are available.
Ground stations have the ability to transmit coded and uncoded
waveforms which can be echoed by distant spacecraft. Analysis
of the received coding allows navigators to determine the
distance to the spacecraft; analysis of Doppler shift on the
carrier signal allows estimation of the line-of-sight spacecraft
velocity. Range and Doppler measurements are used to calculate
the spacecraft trajectory and to infer gravity fields of objects
near the spacecraft.
Ground stations can record spacecraft signals that have
propagated through or been scattered from target media.
Measurements of signal parameters after wave interactions with
surfaces, atmospheres, rings, and plasmas are used to infer
physical and electrical properties of the target.
Principal investigators vary from experiment to experiment. See
the corresponding section of the spacecraft instrument
description or the data set description for specifics.
The Deep Space Network is managed by the Jet Propulsion
Laboratory of the California Institute of Technology for the
U.S. National Aeronautics and Space Administration.
Specifications include:
Instrument Id : RSS
Instrument Host Id : DSN
Pi Pds User Id : N/A
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : N/A
Instrument Mass : N/A
Instrument Length : N/A
Instrument Width : N/A
Instrument Height : N/A
Instrument Manufacturer Name : N/A
For more information on the Deep Space Network and its use in
radio science see reports by [ASMAR&RENZETTI1993] and
[ASMARETAL1995]. For design specifications on DSN subsystems
see [DSN810-5].
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 [ASMARETAL1995] 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).
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 two groups of
equipment: the closed-loop receiver group and the open-loop
receiver 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 (OLR): 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 (IFS), and a
Radio Science Receiver (RSR). 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 IFS switched the IF input among the antennas.
DSCC Transmitter Subsystem
--------------------------
The Transmitter Subsystem accepts the S-band frequency
exciter signal from the Receiver-Exciter Subsystem exciter
and amplifies it to the required transmit output level. The
amplified signal is routed via the diplexer through the feed
horn to the antenna and then focused and beamed to the
spacecraft.
The Transmitter Subsystem power capabilities range from 18 kW
to 400 kW. Power levels above 18 kW are available only at
70-m stations.
DSCC Tracking Subsystem
-----------------------
The Tracking Subsystem primary functions are to acquire and
maintain communications with the spacecraft and to generate
and format radiometric data containing Doppler and range.
The DSCC Tracking Subsystem (DTK) receives the carrier
signals and ranging spectra from the Receiver-Exciter
Subsystem. The Doppler cycle counts are counted, formatted,
and transmitted to JPL in real time. Ranging data are also
transmitted to JPL in real time. Also contained in these
blocks is the AGC information from the Receiver-Exciter
Subsystem. The Radio Metric Data Conditioning Team (RMDCT)
at JPL produces an Archival Tracking Data File (ATDF) which
contains Doppler and ranging data.
In addition, the Tracking Subsystem receives from the CMC
frequency predicts (used to compute frequency residuals and
noise estimates), receiver tuning predicts (used to tune the
closed-loop receivers), and uplink tuning predicts (used to
tune the exciter). From the LMC, it receives configuration
and control directives as well as configuration and status
information on the transmitter, microwave, and frequency and
timing subsystems.
The Metric Data Assembly (MDA) controls all of the DTK
functions supporting the uplink and downlink activities. The
MDA receives uplink predicts and controls the uplink tuning
by commanding the DCO. The MDA also controls the Sequential
Ranging Assembly (SRA). It formats the Doppler and range
measurements and provides them to the GCF for transmission to
NOCC.
The Sequential Ranging Assembly (SRA) measures the round trip
light time (RTLT) of a radio signal traveling from a ground
tracking station to a spacecraft and back. From the RTLT,
phase, and Doppler data, the spacecraft range can be
determined. A coded signal is modulated on an uplink carrier
and transmitted to the spacecraft where it is detected and
transponded back to the ground station. As a result, the
signal received at the tracking station is delayed by its
round trip through space and shifted in frequency by the
Doppler effect due to the relative motion between the
spacecraft and the tracking station on Earth.
DSCC 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.
Radio Science Receiver (RSR)
----------------------------
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
Digitial Down Converter (DDC), VME Data Processor (VDP), and
Data Processor (DP) [JPLD-16765].
\ ----------- ------ ----- ----- -----
\ | 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 1PPS 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 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 +
reside_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
Detectors - DSN
===============
Nominal carrier tracking loop threshold noise bandwidth at
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
For the open-loop subsystem, signal detection is done in
software.
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.
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 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 880/749. 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.
Location - DSN
==============
Station locations are documented in [DSN810-005-301H]. Geocentric
coordinates are summarized here. All antennas are AZ-EL type unless
otherwise specified.
Antenna Geocentric Coordinates
------------------------------
Name Description Latitude Longitude Geocentric Radius
(deg) (deg) (m)
---------------------------------------------------------------------
Goldstone
DSS 13 34-m R & D 35.0660180 243.2055410 6372125.096
DSS 14 70-m 35.2443523 243.1104618 6371993.267
DSS 15 34-m HEF 35.2403129 243.1128049 6371966.511
DSS 24 34-m BWG 35.1585346 243.1252056 6371973.601
DSS 25 34-m BWG 35.1562591 243.1246368 6371982.537
DSS 26 34-m BWG 35.1543409 243.1269835 6371992.264
DSS 27 34-m HSB 35.0571452 243.2233496 6372110.240
Canberra
DSS 34 34-m BWG -35.2169824 148.9819644 6371693.538
DSS 43 70-m -35.2209189 148.9812673 6371688.998
DSS 45 34-m HEF -35.2169608 148.9776856 6371675.873
Madrid
DSS 54 34-m BWG 40.2357726 355.7459032 6370025.490
DSS 55 34-m BWG 40.2344478 355.7473667 6370007.988
DSS 63 70-m 40.2413554 355.7519915 6370051.198
DSS 65 34-m HEF 40.2373555 355.7493011 6370021.709
Measurement Parameters - DSN
============================
Closed-loop data are recorded in Archival Tracking Data Files
(ATDFs), as well as certain secondary products such as the
Orbit Data File (ODF). The ATDF Tracking Logical Record
contains 150 entries including status information and
measurements of ranging, Doppler, and signal strength.
ACRONYMS AND ABBREVIATIONS - DSN
================================
ACS Antenna Control System
ADC Analog-to-Digital Converter
AGC Automatic Gain Control
AMS Antenna Microwave System
APA Antenna Pointing Assembly
ARA Area Routing Assembly
ATDF Archival Tracking Data File
AUX Auxiliary
AZ Azimuth
BPF Band Pass Filter
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
DDC Digital Down Converter
DEC Declination
deg degree
DIG RSR Digitizer
DMC DSCC Monitor and Control Subsystem
DOR Differential One-way Ranging
DP Data Processor
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
IFS IF Selector Switch
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
LPF Low Pass Filter
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
NCO Numerically Controlled Oscillator
NIST SPC 10 time relative to UTC
NIU Network Interface Unit
NOCC Network Operations and Control System
NRV NOCC Radio Science/VLBI Display Subsystem
NSS NOCC Support System
OCI Operator Control Input
ODF Orbit Data File
ODR Original Data Record
ODS Original Data Stream
OLR Open Loop Receiver
OSC Oscillator
PDS Planetary Data System
POCA Programmable Oscillator Control Assembly
PPM Precision Power Monitor
RA Right Ascension
REC Receiver-Exciter Controller
RCP Right-Circularly Polarized
RF Radio Frequency
RIC RIV Controller
RIV Radio Science IF-VF Converter Assembly
RMDCT Radio Metric Data Conditioning Team
RMS Root Mean Square
RSR Radio Science Receiver
RSS Radio Science Subsystem
RT Real-Time (control computer)
RTLT Round-Trip Light Time
S-band approximately 2100-2300 MHz
sec second
SEC System Error Correction
SIM Simulation
SLE Signal Level Estimator
SNR Signal-to-Noise Ratio
SNT System Noise Temperature
SOE Sequence of Events
SPA Spectrum Processing Assembly
SPC Signal Processing Center
sps samples per second
SRA Sequential Ranging Assembly
SRC Sub-Reflector Controller
SSI Spectral Signal Indicator
TID Time Insertion and Distribution Assembly
TLM Telemetry
TSF Tracking Synthesizer Frequency
TWM Traveling Wave Maser
TWNC Two-Way Non-Coherent
TWTA Traveling Wave Tube Amplifier
UNK unknown
USO UltraStable Oscillator
UTC Universal Coordinated Time
VCO Voltage-Controlled Oscillator
VDP VME Data Processor
VF Video Frequency
X-band approximately 7800-8500 MHz
|
| MODEL IDENTIFIER | |
| NAIF INSTRUMENT IDENTIFIER |
not applicable |
| SERIAL NUMBER |
not applicable |
| REFERENCES |
Asmar, S. W., N. A. Renzetti, The Deep Space Network as an instrument for radio
science research, NASA Technical Reports Server, 1993STIN...9521456A, 1993. Asmar, S.W., R.G. Herrera, and T. Priest, Radio Science Handbook, JPL D-7938, Volume 6, Jet Propulsion Laboratory, Pasadena, CA, 1995. DSN Telecommunications Link Design Handbook, 301, Rev. H Coverage and Geometry, Rev Oct 17, Jet Propulsion Laboratory, Pasadena, CA. Deep Space Network / Flight Project Interface Design Book, Document 810-5, Jet Propulsion Laboratory, Pasadena, CA. DSN Geometry and Spacecraft Visibility, Document 810-5, Rev. D, Vol. 1, DSN/Flight Project Interface Design, Jet Propulsion Laboratory, Pasadena, CA, 1987. Mars Global Surveyor Project, Telecommunications System Operations Reference Handbook, Version 2.1 (MGS 542-257), JPL Document D-14027, Jet Propulsion Laboratory, Pasadena, CA, 1996. Deep Space Mission System (DSMS) External Interface Specification (820-013, JPL D-16765), Radio Science Receiver Standard Formatted Data Unit (SFDU), Jet Propulsion Laboratory, Pasadena, CA, 2001. |
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