|
Instrument Information |
|
| IDENTIFIER | urn:nasa:pds:context:instrument:rsi.ro::1.0 |
| NAME |
ROSETTA RADIO SCIENCE INVESTIGATION |
| TYPE |
ATMOSPHERIC SCIENCES |
| DESCRIPTION |
Instrument Overview
===================
Rosetta (RO) Radio Science Investigations utilized
instrumentation with elements on both the spacecraft and ground
(Earth). Much of this was shared equipment, being used for
routine telecommunications as well as for Radio Science. Ground
systems were provided by the European Space Agency (ESA) at New
Norcia, Australia, and by the U.S.
National Aeronautics and Space Administration (NASA) Deep Space
Network (DSN) at sites in Australia, Spain, and the United
States.
Performance and calibration of both the spacecraft and ground
systems directly affected the radio science data accuracy and
played a major role in determining the quality of the results.
The spacecraft was able to receive and transmit signals at both
S-band (approximately 13 cm wavelength) and X-band
(approximately 3.5 cm). The spacecraft transmissions could use
either an onboard oscillator (for RSI the onboard ultra stable
Oscillator USO was used.) for the frequency reference ('one-way'
mode) or a signal transmitted from the ground ('two-way' mode);
in the latter case, either an S- or X-band signal from the
ground could be used as the reference.
Science Objectives
==================
Two different types of radio science measurements were carried
out with Rosetta:
Radiometric Measurements: 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 and/or to investigate gas and dust mass
flux from non-gravitational perturbations of the Rosetta S/C.
NB: Doppler measurements can be made in one-way with USO on
but are usually more accurate if carried out in two-way mode.
Radio Propagation Measurements: 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. Radio propagation measurements can
be conducted in either one-way or two-way mode.
These measurements were applied - separately and together - to
Rosetta science objectives such as determination of the gravity
field of Churyumov-Gerasimenko and Asteroids Steins and Lutetia,
mass of Churyumov-Gerasimenko and Asteroids Steins and Lutetia,
temperature and pressure of the plasma and dust environment of
the comet, electron density around the comet, scattering
properties of the surface, and structure of the solar wind.
Gravity Measurements
--------------------
Determination of the cometary mass and bulk density is a
fundamental objective required to assess the validity and
accuracy of various cometary models. Extensive simulation
studies, in preparation for the Near Earth Asteroid Rendezvous
(NEAR) mission to asteroid 433 Eros, demonstrate that orbiting
a small asteroid will require a gravity field extraction process
fundamentally different from previous gravity studies of the
planets or moons [SCHEERES1995], [MILLERETAL1995].
Upon arrival at the comet, the nucleus size, shape, mass,
activity and spin state will be poorly known and will most
likely be active during some portions of the gravity field
investigation campaign.
An initial flyby during the Rosetta approach phase should
enable a mass determination to an accuracy of 10%. Injection
into a bound high orbit allows iterative improvements of the
mass determination down to the 1% level. The orbit can then be
safely reduced to 20 - 30 cometary radii (depending on the
actual mass of the comet) and mass determination will reach an
accuracy of 0.1%.
The second order and degree gravity coefficients (C20 and C22)
can be estimated using the shape model (from imaging
observations) and assuming constant density. The result is a
constraint on the true gravity field. The most stable low orbits
for the spacecraft will be in equatorial, retrograde orbits
about the comet (no outgasing perturbations assumed). Beginning
with these orbits, the second-order gravity field can be solved
for in the orbit determination process.
Higher-order gravity coefficients might be determined from low
polar orbits. This strategy also assumes that cometary
outgassing does not induce significant accelerations upon the
spacecraft.
The shape gravity model (with constant density) and the true
gravity model (from spacecraft tracking) can then be compared to
yield information on the mass heterogeneity of the comet
nucleus.
Asteroid flyby
------------
During the Rosetta Mission two close flybys at asteroids
Lutetia and Steins will take place. RSI will be able to derive
the mass and density of the asteroids.
The spacecraft velocity is perturbed by the gravitational
field of asteroids during sufficiently close flybys. The
spacecraft is accelerated toward the asteroid along its flyby
trajectory. The analysis of the resultant velocity changes
ultimately yields a measure of its total mass or GM. The bulk
density is determined from the mass determination and the
volume estimate made by the camera experiment. Mass and bulk
density estimates of asteroids have thus far only been
obtained from the Galileo flyby at asteroid Ida and from the
NEAR flybys at asteroid Mathilde and Eros. Asteroid Ida was
too small to perturb the flyby trajectory of Galileo above the
threshold of detectability. The discovery of Ida moon Dactyl,
however, provided an unexpected opportunity to estimate Ida
mass and bulk density. Mathilde bulk density was found to be
surprisingly low.
Radio Occultation Measurements and Coma sounding
------------------------------------------------
Atmospheric measurements by the method of radio occultation
i.e coma sounding contribute to an improved understanding of
structure and compostion of the plasma and dust environment of
Churyumov-Gerasimenko.
These results are based on detailed analysis of the radio
signal phase as the ray path enters and exits occultation by
the comet, leading to profiles of pressure for neutral
particles and profiles of electron density for plasma. In
addition the exact size and shape of the shape of the comet
can be derived by determining at which time the occultations
start and end exactly.
Retrieval of such profiles requires coherent samples with a
sample rate of at least 10 per second of the radio signal
that has propagated through the atmosphere, plus accurate
knowledge of the spacecraft trajectory. The latter was
obtained from the ROS Flight Dynamics Team.
Spatial and temporal coverage in radio occultation
experiments are determined by the geometry of the spacecraft
orbit and the dates and times at which occultation data are
acquired.
Bistatic Surface Scattering Measurements
------------------------------------------
The spacecraft high-gain antenna (HGA) could also be pointed
toward the surface of the planet. The strength of the signal
scattered from the illuminated area could be measured and the
results interpreted in terms of the dielectric constant of the
surface material. The model for interpretation assumes Fresnel
reflection at the specular angle.
Under certain circumstances, the dispersion of the echo (its
spectral width) could be interpreted in terms of the surface
roughness on scales comparable to the wavelength. One such MGS
bistatic radar was conducted over the Mars Polar Lander/Deep
Space 2 site in May 2000 [SIMPSON&TYLER2001].
For a few seconds before and after geometrical occultation
the HGA illuminated a small strip of surface as well as the
atmosphere. In some cases, an echo could be observed from the
surface. The interpretation of these transient echoes is
more difficult than for the case above, possibly involving
diffraction and surface waves in addition to Fresnel
reflection.
Rosetta is the first spacecraft to use bistatic radar to
explore the properties of the comet's surface and its
interior. On Rosetta this operation will be done in ONED mode.
That is no uplink but with X- and S-Band downlink. The HGA
will be pointed towards the comet. Pointing will be inertial.
That is no slew was performed during the measurement.
Solar Scintillation and Faraday Rotation Experiments
----------------------------------------------------
Solar scintillation and Faraday rotation experiments were
conducted to improve understanding of the structure and
dynamics of the solar corona and wind. On its route to the
comet the Rosetta spacecraft will be behind the solar disk,
as seen from Earth. Radio waves propagating between RO and
Earth stations are refracted and scattered 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 S-band than X-band.
Measurements during solar conjunction should be typically
been done in TWOD-S configuration. That is in two-way mode
with S-Band uplink and coherent and simultanous in X- and
S-Band. However, due to problems to lock S-Band in the 2004
conjunction season. The TWOD-X configuration was used instead.
That is in two-way mode with X-Band uplink and coherent and
simultanous in X- and S-Band
Investigators and Other Key Personnel
=====================================
Martin Paetzold University of Cologne Principal
Investigator;
solar physics
Bernd Hausler Universitaet der Bundeswehr Experiment
Munich Manager
Richard Simpson Stanford University Data Manager;
surface
scattering
Silvia Tellmann University of Cologne Operations
Manager
Sami Asmar Jet Propulsion Laboratory JPL/DSN
operations
G. Leonard Tyler Stanford University radio
propagation
David Hinson Stanford University atmosphere,
ionosphere,
radio
occultation
Jean-Pierre Barriot Centre National d'Etudes gravity
Spatiale
Toulouse
Veronique Dehant Observatoire Royale gravity
Brussels
Instrument Specification - Spacecraft
=====================================
The Rosetta spacecraft telecommunications subsystem served as
part of a radio science subsystem for investigations of Comet
Churyumov-Gerasimenko. Many details of the subsystem are
unknown; but they are not of importance for understanding the
science.
Instrument Id : RSI
Instrument Host Id : RO
Pi Pds User Id : MPAETZOLD
Instrument Name : ROSETTA RADIO SCIENCE
INVESTIGATIONS
Instrument Type : RADIO SCIENCE
Build Date : 2003-06-01
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
Subsystems
----------
SWITCH TRANSPONDER 1
-------- ------ ----- --------------------
\ | |---| TWTA |---|\ /|<--------| X-Band Transmitter |
\ | | ------ | \ / | | |
HGA >--| | | X | ------| S-Band Transmitter |
/ | | ------ | / \ | | | |
/ | RFDU |---| TWTA |---|/ \| | --->| X-band Receiver |
| | ------ ----- | | | |
\ | | | | | |
MGA >---| |<---------------------- | ->| S-Band Receiver |
/ | | | | --------------------
| | | | ^
| |------------------------- | |
| | | -----
| | | | USO |
| | | -----
| | | |
| | | v
| |---------------------------| TRANSPONDER 2
| | --------------------
LGA >--| |---< LGA (rear) <---| X-Band Transmitter |
(front) -------- | |
<---| S-Band Transmitter |
TRANSPONDERS 1 and 2 were | |
connected to provide fully --->| X-band Receiver |
redundant, switchable | |
functions. --->| S-band Receiver |
--------------------
The Rosetta radio subsystem comprised several components
(shown above), configured to provide redundant functions
should any single
component fail (except the high-gain antenna).
The high-gain antenna (HGA) was a body-fixed 1.60 m diameter
parabolic dish which allowed transmission and reception at
both S- and X-band.
The HGA boresight was in the -X direction of the spacecraft
coordinate system, offset 5 degrees in the +Z direction.
Its gain was 29.56 dB and 41.43 dB at S- and X-band,
respectively. Two low-gain antennas (LGA) were mounted on the
front and rear of the spacecraft; they operated only at
S-band. The HGA was the main antenna for receiving
telecommands from and transmitting telemetry signals to the
ground.
The LGAs were used during the commissioning phase after
launch and for emergency operations.
The Radio Frequency Distribution Unit (RFDU) switched the
onboard radio frequency hardware among the three antennas.
Switchable Traveling Wave Tube Amplifiers (TWTA) provided 60
watts of X-band transmitter power to the RFDU; their inputs
could come from either Transponder 1 or Transponder 2.
The S-band transmitter power was 5 watts, which was generated
within the transponder units.
The S-band uplink was received via the LGA or HGA. In the
coherent two-way mode the received frequency was used to
derive the downlink frequencies by using the constant
transponder ratios 880/221 and 240/221 for X-band and S-band
downlink, respectively.
The X-band uplink was received via the HGA only. In the
coherent two-way mode the received frequency was used to
derive the downlink
frequencies by using the constant transponder ratios 880/749
and 240/749 for X-band and S-band downlink, respectively. An
X-band uplink generally enhanced the performance of the radio
link because X-band is less sensitive to the interplanetary
plasma along the propagation path.
The X-band and S-band frequencies were related by a factor of
11/3. If an uplink existed, the downlinks were also coherent
with the uplink by their respective transponding ratios.
The dual-frequency downlink allowed separation of the
classical Doppler shift, due to relative motion of the
spacecraft and the ground station, from the dispersive media
effects, due to the propagation of the radio waves through the
ionosphere and interplanetary medium.
In one-way mode, the downlink transmitter frequency was
derived from either an onboard Temperature Controlled Crystal
Oscillator (TCXO) or an Ultrastable oscillator (USO). The
one-way mode could be selected by command from the ground. If
the spacecraft receiver could not detect an uplink signal from
the ground, the TCXO was selected by default. TCXO stability
was several orders of magnitude less than the uplink
reference.
Radio Science in one-way link mode (ONES, ONED) are either
conducted during bistatic radar experiments or during an
occultation of the spacecraft by the nucleus as seen from
Earth. This enables radio sounding of the immediate vicinity
of the nucleus and perhaps even the nucleus itself, should the
solid cometary body prove to be penetrable by microwaves.
These one-way occultation experiments require an Ultra-Stable
Oscillator (USO) added to the radio subsystem. The prime
purpose of the USO is to serve as a phase-coherent frequency
reference for the simultaneous one-way downlink transmissions
at S-band and X-band. The required stability (Allan variance)
of the USO is about (Delta)f /f = 1E-13 at 10-1000 seconds
integration time. The one-way radio link can be transmitted
either while receiving a noncoherent uplink or without any
uplink contact at all. This radio subsystem design makes
Rosetta one of the best equipped spacecraft (besides Galileo
and Cassini) for radio science experiments.
The redundant transponders each consisted of an S-band and
X-band receiver and transmitter. The spacecraft was capable
of receiving one uplink signal at S-band (2100 MHz) via the
LGAs, or at either X-band (7100 MHz) or S-band via the HGA or
MGA. The spacecraft could transmit a downlink signal at
S-band (2300 MHz) and (simultaneously) a downlink signal at
X-band (8400 MHz) using the HGA; or it could transmit one
downlink signal at S-band via the LGAs.
Operational Considerations
--------------------------
Due to the fact that the HGA antenna can be directed within
certain limits independent of the spacecraft, Radio Science
observations are not so severely constrained due to spacecraft
constraints, telecommunications, and requirements for other
instruments as on other space missions (MEX/VEX).
Calibration
-----------
For many experiments, calibration data were collected in
conjunction with the scientific observations. For example,
carrier power and frequency could be determined before and/or
after bistatic radar and radio occultation experiments when
the antenna was pointed toward Earth.
The gain, beam patterns, and pointing of the HGA were
calibrated during post-launch tests. The half-power points
were about 2.6 and 0.8 degrees from the boresight at S- and
X-band, respectively.
For radio tracking data, error sources in two-way mode are
shown below, where the tabulated error values are given in
terms of equivalent spacecraft velocity error. These values
were based on pre-launch tests.
|======================================================|
| Error Source | Equivalent Velocity |
| | Error (mm/s) |
| |---------------------|
| | S-band | X-Band |
|================================+==========+==========|
|Total phase error (thermal and | 1.0 | 0.3 |
|ground station contributions) | | |
|--------------------------------+----------+----------|
|Transponder quantization error | 0.4 | 0.1 |
|in frequency | | |
|--------------------------------+----------+----------|
|Transponder quantization error | 0.01 | 0.004 |
|in phase | | |
|================================+==========+==========|
|Total error (coherent mode) | 1.1 | 0.32 |
|======================================================|
Platform Mounting
-----------------
The ROS High Gain Antenna was attached to the +X side of the
spacecraft bus and is flexible. The ROS HGA frame
(ROS_HGA) was defined as a fixed offset frame with its
orientation given relative to the ROS_SPACECRAFT frame.
For details please refer to INSTHOST.CAT also located in this
folder.
Operating Modes
---------------
A two-way dual-frequency radio link was used for
occultations, gravity observations, and solar corona
investigations. Such a radio link benefited from the superior
frequency stability of the ground station. The dual-frequency
downlink at X-band and S-band was used to separate classical
and dispersive Doppler shifts, allowing correction of the
observed frequency shift by any plasma contribution. For some
observations (e.g., solar corona) an S-band uplink was used to
increase sensitivity to plasma effects along the path.
In the above experiments, operation was usually preferred
with full power in the carrier (no telemetry or other
modulation on the downlink) to maximize signal-to-noise ratio.
The dual-frequency one-way radio link at S- and X-band was
used for bistatic radar experiments. In these experiments,
the HGA will be pointed toward the Comet and could not be used
to capture an uplink signal, receive commands, or transmit
telemetry.
The dual-frequency USO driven one-way radio link will also
used for occultation experiments where there is no time to
establish a two-way link. Stability of the one-way link is
sufficient to allow scientifically useful probing of the
neutral atmosphere; the ionospheric analysis can be carried
out using the differential phase/frequency effects at S- and
X-band which were proportional to each other.
Instrument Specification - New Norcia
=====================================
ESA completed construction of a 35 m ground station at its
complex near New Norcia, Australia, in the year before launch of
Mars Express. The station provided uplink at either S- or
X-band and simultaneous dual-frequency downlink at both bands.
Specifications are given below. the 'build date' is taken
arbitrarily to be 1 January 2003.
Instrument Id : RSS
Instrument Host Id : NNO
Pi Pds User Id : MPAETZOLD
Instrument Name : UNK
Instrument Type : RADIO SCIENCE
Build Date : 2003-01-01
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
The IFMS (Intermediate Frequency Modulation System) at NNO is a
piece of equipment which mainly provides:
- generation of the uplink IF carrier, possibly modulated with
a TC signal (from an extrernal source) and a Ranging signal
(internally generated)
- reception of the downlink IF signal
- diversity combination estimation
- demodulation (remnant and suppressed carrier demodulators and
Ranging demodulator) and generation of bit stream for the
telemetry decoding system
- collection of Doppler, Meteo and Ranging measurements into
data sets, later available for local display and remote
retrieval via DDS
- telemetry decoding is provided by the integrated TCDS
(Telemetry Channel Decoding System) functional unit (the
presence of the TCDS may be optional)
System overview
---------------
Antenna
o
\ /|\ /
\ / | \ /
--v--
/ \
/ \
/ \
|----------------------------------------------------|
| Front-End |
|----------------------------------------------------|
^ ------- |
| |Meteo | |
| |sensors| |
| ------- |
| | |
| v |
|----| |------|-------------------------|------------| |---|
| TC | |IFMS | v | |TM |
| | | v |-------------------------| | | |
| | | |---------| | Common Front End/ | | | |
| |---------->| Up-link | .>| Diversity Combiner | | | |
| | | |Modulator| . |-------------------------| | | |
| |<--------->|---------| . | | | | | |
| | Uplink | ^ . v v v | | |
| |handshake| . . ----- ------- -------- | | |
| | | . . | OLP | |RG Dmod| |R/S carr|--->| |
|----| | . . ----- ------- | Demod || | |
| . . ^ ^ -------- | | |
| . . . . | | | |
| . . . . v | | |
| . . . . ------- | | |
| . . . . | TCDS |---->| |
| . . . . ------- | | |
| . . . . ^ | |---|
| . . . . . |
| . . . . . |
| v v v v v |
| |----------------------------------------| |
| | System Monitoring & Control | |
| | (UCPU software) | |
| |----------------------------------------| |
|---------------------------------------------|
| | |
----- ------ -----
| DCP | |STC II| | OCC |
----- ------ -----
IFMS software
-------------
The IFMS software is mainly in charge of the following
functions:
- handle the Digital Signal Processing (DSP) units (Uplink
Modulator, Common Front End, Diversity Combiner, Ranging
Demodulator, Remnant Carrier Demodulator, Suppressed Carrier
Demodulator, Meteo system and TCDS)
- execute data acquisition requests and collect independently
Doppler, AGC, Meteorological, Ranging and Open-Loop data
- allow the Control Centre to retrieve the collected data
- provide Monitoring & Control access to the Station Computer
(STC)
- provide Monitoring & Control access to an operator via the
Development Control Position (DCP) for both local control
and engineering purpose
Subsystems
----------
Of primary interest to radio science are the three
Intermediate Frequency and Modem Systems (IFMS) at New Norcia
which controlled both the uplink and downlink.
The IFMS baseband processor operated on a 17.5 Msps 24-bit
complex sample stream (12 bit words each for the I and Q
channels) which resulted from filtering and decimating the 280
Msps 8-bit stream output by the Common Front End (CFE)
analog-to-digital converter. These channels were provided for
both the right circular and left-circular polarizations (RCP
and LCP, respectively).
The Radio Science raw data could be directly transferred to a
mass storage device and/or processed by a Fast Fourier
routine. Data transfer rates from the digital signal processor
to data storage (disk) were limited to 10 samples/s. Data
transfer to the European Space Operations Center (ESOC) could
be done at a rate of 2 ksps.
Subsystems overview
-------------------
The IFMS is constituted of a 48.26 cm (19') crate containing
the UNIX CPU (UCPU), the Time Code Reader (TCR) and the DSP
units (Uplink Modulator (ULM), CFE units, General DSP units
(GDSP), except the Meteo unit which is external to the
system).
- Internal network and IP Processor (IPP):
The Internet Protocol suite is used to interface most of
the IFMS elements on an internal IP network. For this the
GDSP units are equipped with an IPP (IP Processor), in
charge of mamaging data communication with the UNIX-CPU
(based on IP) and the DSP board controller (based on serial
interface).
- The Time Code Reader (TCR) receives:
- the Time Reference (IRIG-B on 1 kHz or 5 MHz carrier)
- the Frequency Reference (5 MHz or 10 MHz)
It distributes Time to the other units to be used for
measurement time-tagging.
- Meteo Unit:
The Meteo Unit includes outdoor sensors providing analogue
data for humidity, pressure, temperature and indoor
electronic equipment (located in fact outside of the IFMS
rack). It provides ASCII formatted numerical measurement of
humidity, pressure and temperature to the IFMS management
processor.
- Uplink Modulator (ULM):
The ULM unit generates internally the ranging signal (Tone
and Code) in digital form. It receives the telecommand
signal in either digital or analogue form from external
equipment. It outputs an IF signal (230 MHz or 70 MHz)
modulated by the uplink ranging signal and/or the
telecommand signal.
- Common Front End Unit:
The CFE unit receives (from the down-converters) the 70 MHz
down-link IF signals modulated by telemetry and possibly
ranging signals and digitises them for further processing.
The digital data is propagated on the rack back-plane.
Note: A second CFE can be present in the IFMS.
- Diversity combiner:
The DCE unit makes estimates of:
- the depolarisation angle between the LH and RH channels
- the phase error between the LH and the RH channels
It then provides qualification information on the rack
back-plane for further use by the demodulators.
- Ranging receiver and demodulator:
The RGD unit receives, from the Common Front End and
Diversity Combiner units, the digital demodulated 70 MHz
signal and qualification information. It demodulates the
down-link signal and extracts Doppler measurement. It
generates a replica Ranging signal and performs the Tone PLL
and the Ambiguity Resolution in order to measure signal
round-trip delay, modulo the maximum code length. It
provides Doppler and Ranging measurement.
- Remnant and Suppress Carrier demodulators:
The RCD and SCD units receive, from the Common Front End
and Diversity Combiner units, the digital demodulated 70 MHz
signal and qualifier. They provide demodulated telemetry
data and Doppler measurement.
- Telemetry Channel Decoder System:
The TCDS unit receives, from the demodulator units, the
telemetry bit stream and performs Viterbi and Reed-Solomon
decoding and frame synchronisation. It provides decoded and
synchronised telemetry data emitted via a UDP/IP protocol.
- Open-Loop Processor:
The OLP unit receives, from the Common Front End and
Diversity Combiner units, the digital demodulated 70 MHz
signal and qualifier. It provides Open-Loop measurements.
Operational Considerations
--------------------------
By agreement between the Rosetta Radio Science (RSI) Team
and the European Space Operations Centre (ESOC), the three
IFMS units at New Norcia were configured as follows:
IFMS 1: Controlled uplink, including choice of band (usually
X-band, but S-band for solar conjunction). Two
channels of closed-loop downlink were possible; these
could be any two of the four X-RCP, X-LCP, S-RCP, and
S-LCP combinations. If X-RCP and X-LCP were selected,
then the IFMS computed polarization.
IFMS 2: Backup for IFMS 1; RSI could specify its
configuration if it was not assigned otherwise.
IFMS 3: RSI could always specify the configuration
Platform Mounting
-----------------
In the IRTF2000 reference system at epoch 2002-07-24 12:00:00,
the cartesian coordinates of the intersection of the azimuth
and elevation axes of the New Norcia antenna were (meters):
X = -2414067.051
Y = 4907869.387
Z = -3270605.276
Using the WGS84 reference ellipsoid with equatorial radius
6378137 m and inverse flattening 298.257223563, the geodetic
latitude, longitude, and height were
geodetic latitude = -31.04822306 degrees north
longitude = 116.19150227 degrees east
height = 252.224 meters
Calibration
-----------
See Calibration section for spacecraft.
Modes
-----
See Modes section for spacecraft. In addition, there were
two mode choices on the ground.
Closed-loop data acquisition was done with a phase-locked
loop receiver at the ground station. The downlink signal
arriving at the station could be either one-way or two-way.
Two-way Doppler shifts were extracted by comparing each
measurement of the downlink carrier frequency from the
phase-locked loop with a reference from the ground station
frequency reference source -- e.g., a hydrogen maser with a
frequency stability on the order of 1E-15 to 1E-16. Because
this frequency reference source was also used for generation
of the uplink carrier, the accuracy of the frequency
determination was as good as the reference source. The
Doppler integration time needed to achieve a certain signal to
noise ratio determined the time between successive frequency
determinations. The amplitude of the radio signal was
estimated by the Automatic Gain Control (AGC).
Open-loop data recording was done by filtering and
down-converting the received radio carrier signal to baseband
where it was digitally sampled and stored for subsequent
analysis. The open-loop receiver was tuned by a local
oscillator. The frequency of the local oscillator was given
by the best available estimate of the carrier frequency
transmitted by the spacecraft and applying Doppler
corrections due to the relative spacecraft-to-Earth motion.
Measurement Parameters
----------------------
Each IFMS generated up to four types of data records:
Doppler, gain, range, and/or meteorology. Each included a
header with the following information:
station identifier;
spacecraft identifier;
time tag of the first and last samples;
sample period;
total number of samples; and
several flags or other markers to identify the data.
Doppler samples could be taken at 1000, 100, 10, 1, or 0.1
per second; the data records contain:
sample number and time;
unwrapped phase and
accumulated phase with respect to a reference.
Gain records contain:
sample number and time;
carrier level and
polarization angle.
Range data could be taken every 1-120 seconds (in user
selectable increments of 1 second); range records contain:
sample number and time;
round trip delay modulo the ranging code;
current code number and
several flags and status words.
Meteorological records contain:
sample number and time;
humidity;
pressure and
temperature.
Instrument Specification - DSN
==============================
Three Deep Space Communications Complexes (DSCCs) (near
Barstow, CA; Canberra, Australia; and Madrid, Spain) comprised
the DSN tracking network. Each complex was 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 was radiation of commands to and reception of telemetry
from active spacecraft.
Transmission and reception was 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 were available.
The Deep Space Network was managed by the Jet Propulsion
Laboratory of the California Institute of Technology for the
U.S. National Aeronautics and Space Administration.
Specifications included:
Instrument Id : RSS
Instrument Host Id : DSN
Pi Pds User Id : MPAETZOLD
Instrument Name : RADIO SCIENCE SUBSYSTEM
Instrument Type : RADIO SCIENCE
Build Date : UNK
Instrument Mass : UNK
Instrument Length : UNK
Instrument Width : UNK
Instrument Height : UNK
Instrument Manufacturer Name : UNK
So far as radio science was concerned, the DSN was an evolving
'instrument;' the paragraphs which follow describe its
capabilities during the first year of Rosetta orbital
operations. 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 [TYLERETAL1992A], [TYLERETAL2001],
and [JPLD-14027].
Subsystems - DSN
----------------
The Deep Space Communications Complexes (DSCCs) were an integral
part of Radio Science instrumentation. Their system performance
directly determined the degree of success of Radio Science
investigations, and their system calibration determined 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 [DSN871-049-041]; for additional
information, consult [DSN810-5], [DSN821-110], and [DSN821-104].
Each DSCC included a set of antennas, a Signal Processing
Center (SPC), and communication links to the Jet Propulsion
Laboratory (JPL). The general configuration is illustrated
below; not all antennas are shown.
-------- -------- -------- -------- --------
| 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 |
|AMMOS |<--->| TERMINAL|<-------------->| |
------ --------- ---------
^ ^
| |
CANBERRA (SPC 40) <---------------- |
|
MADRID (SPC 60) <----------------------
The following table lists the DSN antennas (Deep Space Stations,
or DSS's -- a term carried over from earlier times when antennas
were individually instrumented) available for Rosetta. Not
all antennas were actually used for ROS; their capabilities
varied and some were more suitable for ROS Radio Science than
others.
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 55
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 are described in the sections that follow.
The Monitor and Control Subsystem was connected to all other
subsystems; and the Test Support Subsystem could have been.
----------- ------------------ ---------------------
|TRANSMITTER|_| UPLINK |_| COMMAND |_
| SUBSYSTEM | | SUBSYSTEM | | SUBSYSTEM | |
----------- ------------------ --------------------- |
| |
----------- ------------------ --------------------- |
| MICROWAVE |_| DOWNLINK |_| TELEMETRY |_|
| SUBSYSTEM | | 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) was part of the
Monitor and Control System (MON) which also included the
ground communications Central Communications Terminal (CCT)
and the Network Operations Control Center (NOCC) Monitor and
Control Subsystem. The DMC was the center of activity at a
DSCC. The DMC received and archived 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, was done through the
DMC. The effect of this was to centralize the control,
display, and short-term archiving functions necessary to
operate a DSCC. Communication among the various subsystems
was done using a Local Area Network (LAN) hooked up to each
subsystem via a network interface unit (NIU).
DMC operations were divided into two separate areas: the
Complex Monitor and Control (CMC) and the Network Monitor and
Control (NMC). The primary purpose of the CMC processor for
Radio Science support was to receive and store all predict
sets transmitted from NOCC -- such as 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 could be stored in the CMC
for a maximum of three days under normal conditions. The CMC
also received, processed, and displayed event/alarm messages,
and maintained an operator log. Assignment and configuration
of the NMCs was done through the CMC; to a limited degree the
CMC could perform some of the functions performed by the NMC.
There were two CMCs (one on-line and one backup) and three
NMCs at each DSCC. The backup CMC could function as an
additional NMC if necessary.
The NMC processor provided 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 one or more Radio Science Receivers (RSRs), the DSCC
Uplink Subsystem (UPL), and one or more DSCC Downlink Tracking
and Telemetry Subsystems (DTTs). The NMC also maintained an
operator log which included all operator directives and
subsystem responses. One important Radio Science-specific
function that the NMC performed was receipt and transmission
of the system temperature and signal level data from the PPM,
for display at the NMC console, and for inclusion in Monitor
blocks. These blocks were recorded on magnetic tape as well
as appearing in the NOCC displays. The NMC was required to
operate without interruption for the duration of the Radio
Science data acquisition period.
The Area Routing Assembly (ARA), which was part of the Digital
Communications Subsystem, controlled all data communication
between the stations and JPL. The ARA received all required
data and status messages from the NMC/CMC, and could record
them to tape as well as transmit them to JPL via data lines.
The ARA also received predicts and other data from JPL, and
passed them on to the CMC.
DSCC Antenna Mechanical Subsystem
---------------------------------
Radio Science activities generally required support from
the 70-m, 34-m HEF, and 34-m BWG antenna subnets. The
antennas at each DSCC functioned as large-aperture collectors
which, by double reflection, caused the incoming radio
frequency (RF) energy to enter the feed horns. The large
collecting surface of the antenna focused the incoming energy
onto a subreflector, which was adjustable in both axial and
angular position. These adjustments were made to correct for
gravitational deformation of the antenna as it moved between
zenith and the horizon; the deformation could be as large as
7 cm. The subreflector adjustments optimizde 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
had 'shaped' primary and secondary reflectors, with forms
that were modified paraboloids. This customization allowed
more uniform illumination of one reflector by another. The
BWG reflector shape was ellipsoidal.
On the 70-m antennas, the subreflector directed
received energy from the antenna onto a dichroic plate, a
device which reflected S-band energy to the S-band feed horn
and passed X-band energy through to the X-band feed horn. In
the 34-m HEF, there was one 'common aperture feed,' which
accepted both frequencies without requiring a dichroic plate.
In the 34-m BWG, a series of small mirrors (approximately 2.5
meters in diameter) directed 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 separated the S and X bands on some BWG
antennas, or the X and Ka bands on others. RF energy to be
transmitted into space by the horns was 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 could rotate the movable components and their support
structures.
The different antennas could be pointed by several means. Two
pointing modes commonly used during tracking passes were
CONSCAN and 'blind pointing.' With CONSCAN enabled and a
closed-loop receiver locked to a spacecraft signal, the
system tracked the radio source by conically scanning around
its position in the sky. Pointing angle adjustments were
computed from signal strength information (feedback) supplied
by the receiver. In this mode the Antenna Pointing Assembly
(APA) generated a circular scan pattern which was sent to the
Antenna Control System (ACS). The ACS added the scan pattern
to the corrected pointing angle predicts. Software in the
receiver-exciter controller computed the received signal
level and sent it to the APA. The correlation of scan
position with the received signal level variations allowed the
APA to compute offset changes which were sent to the ACS.
Thus, within the capability of the closed-loop control
system, the scan center was pointed precisely at the apparent
direction of the spacecraft signal source. An additional
function of the APA was 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 sent 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 were expected (e.g., during an
occultation experiment), CONSCAN could not be used. Under
these conditions, blind pointing (CONSCAN OFF) was used, and
pointing angle adjustments were based on a predetermined
Systematic Error Correction (SEC) model.
Independent of CONSCAN state, subreflector motion in at least
the z-axis could 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 was
frozen in the z-axis at a position (often based on
elevation angle) selected to minimize phase change and signal
degradation. This could be done via Operator Control Inputs
(OCIs) from the NMC to the Subreflector Controller (SRC)
which resided in the alidade room of the antennas. The SRC
passed the commands to motors that drove the subreflector to
the desired position.
Pointing angles for all antenna types were computed by
the NOCC Support System (NSS) from an ephemeris provided by
the flight project. These predicts were received and archived
by the CMC. Before each track, they were transferred to the
APA, which transformed the direction cosines of the predicts
into AZ-EL coordinates. The LMC operator then downloaded the
antenna predict points to the antenna-mounted ACS computer
along with a selected SEC model. The pointing predicts
consisted of time-tagged AZ-EL points at selected time
intervals along with polynomial coefficients for interpolation
between points.
The ACS automatically interpolated the predict points,
corrected the pointing predicts for refraction and
subreflector position, and added the proper systematic error
correction and any manually entered antenna offsets. The ACS
then sent angular position commands for each axis at the
rate of one per second. In the 70-m and 34-m HEF, rate
commands were generated from the position commands at the
servo controller and were subsequently used to steer the
antenna.
When not using binary predicts (the routine mode for
spacecraft tracking), the antennas could be pointed using
'planetary' mode -- a simpler mode which used right ascension
(RA) and declination (DEC) values. These changed very slowly
with respect to the celestial frame. Values were provided to
the station in text form for manual entry. The ACS
quadratically interpolated among three RA and DEC points
which were on one-day centers.
A third pointing mode -- sidereal -- was available for
tracking radio sources fixed with respect to the celestial
frame.
Regardless of the pointing mode being used, a 70-m antenna
had a special high-accuracy pointing capability called
'precision' mode. A pointing control loop derived the
main AZ-EL pointing servo drive error signals from a two-
axis autocollimator mounted on the Intermediate Reference
Structure. The autocollimator projected a light beam to a
precision mirror mounted on the Master Equatorial drive
system, a much smaller structure, independent of the main
antenna, which was exactly positioned in HA and DEC with shaft
encoders. The autocollimator detected elevation/cross-
elevation errors between the two reference surfaces by
measuring the angular displacement of the reflected light
beam. This error was 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) were
possible in 'precision' mode. The 'precision' mode was not
available on 34-m antennas -- nor was it needed, since their
beamwidths were twice as large as on the 70-m antennas.
DSCC Antenna Microwave Subsystem
--------------------------------
70-m Antennas: Each 70-m antenna had three feed cones
installed in a structure at the center of the main reflector.
The feeds were positioned 120 degrees apart on a circle.
Selection of the feed was made by rotation of the
subreflector. A dichroic mirror assembly, half on the S-band
cone and half on the X-band cone, permitted simultaneous use
of the S- and X-band frequencies. The third cone was devoted
to R&D and more specialized work.
The Antenna Microwave Subsystem (AMS) accepted the received S-
and X-band signals at the feed horn and transmitted them
through polarizer plates to an orthomode transducer. The
polarizer plates were adjusted so that the signals were
directed to a pair of redundant amplifiers for each frequency,
thus facilitating the simultaneous reception of signals in two
orthogonal polarizations. For S-band these were two Block IVA
S-band Traveling Wave Masers (TWMs); for X-band the amplifiers
were Block IIA TWMs.
34-m HEF Antennas: The 34-m HEF used a single feed for both
S- and X-band. Simultaneous S- and X-band receive as well as
X-band transmit was possible thanks to the presence of an S/X
'combiner' which acted as a diplexer. For S-band, RCP or LCP
was user selected through a switch, so neither a polarizer nor
an orthomode transducer was needed. The X-band amplification
options included two Block II TWMs or a High Electron Mobility
Transistor (HEMT) Low Noise Amplifier (LNA), while the S-band
amplification was provided by a Field Effect Transistor (FET)
LNA.
34-m BWG Antennas: These antennas used feeds and low-noise
amplifiers (LNA) in the pedestal room, which could be switched
in and out as needed. Typically the following modes were
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 and dual LNAs,
each of the above four modes could be used in a single- or
dual-frequency configuration. Thus, for antennas with the
most complete capabilities, there were sixteen possible ways
to receive (2 polarizations, 2 waveguide path choices, 2
LNAs, and 2 bands).
DSCC Uplink Subsystem
---------------------
The Uplink Subsystem (UPL) comprised the Exciter, the Command
Modulation, Uplink Controller, and Uplink Ranging assemblies.
The UPL was based around the Block V Exciter (BVE) equipment.
The BVEs generated uplink carrier and uplink range phase data,
and delivered these data directly to the Project.
The exciter generated a sky-level signal which was provided to
the Transmitter Subsystem for the spacecraft uplink signal.
Based on predicts from the CMC, the BVE provided a sky-level
uplink signal to either the low-power or the high-power
transmitter. It was tunable under command of the DCO
(Digitally Controlled Oscillator).
The diplexer in the signal path between the transmitter and
the feed horn for all antenna types (used for simultaneous
transmission and reception) could be configured such that it
was 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.
DSCC Downlink Subsystem
-----------------------
The Downlink Subsystem consisted of three groups of equipment:
the closed-loop receiver group, the open-loop receiver group,
and the RF monitor group.
Closed-Loop Receivers: The current closed-loop group, called
the Downlink Tracking and Telemetry Subsystem (DTK), consisted
of the Downlink Controller, the Receiver and Ranging Processor
(RRP), and the Telemetry Processor (TLP) assemblies. The DTT
was currently based around the Block V Receiver (BVR)
equipment. The BVRs generated downlink carrier and downlink
range phase data (not Doppler counts and ranging units, as had
been the case before early 2003), and delivered these (phase)
data directly to the Project.
The DTT could simultaneously support as many downlink channels
as could be assigned by the NMC, up to the total number of
RRPs available at a given complex (allowing for the reception
of several different frequencies/wavelengths/bands, or
different polarizations of the same downlink band). The only
other constraint was that any selected downlink band/bands had
to be supported by that antenna.
The closed-loop receivers provided the capability for rapid
acquisition of a spacecraft signal, and telemetry lock-up. In
order to accomplish signal acquisition within a short time,
the receivers were predict driven to search for, acquire, and
track the downlink automatically. Rapid acquisition precluded
manual tuning, though that remained as a backup capability.
The BVRs utilized FFT analyzers for rapid lock-up. The
downlink predicts were generated by the NSS and then
transmitted to the CMC, which sent them to the Receiver
Subsystem where two sets could be stored. The receiver
started acquisition at the beginning of a track (pass), or at
an operator-specified time. The BVRs could also be operated
from the NMC without local operators attending them. The
receivers also sent performance and status data, displays,
and event messages to the NMC.
With the BVRs, the simulation (SIM) synthesizer signal was
used as the reference for the Doppler extractor. The
synthesizer was adjusted before the beginning of the pass to a
frequency that was appropriate for the channel (i.e., within
the band) of the incoming signal; and would generally remain
constant during the pass.
The closed-loop receiver AGC loop could be configured to one
of three settings: narrow, medium, or wide. It was configured
such that the expected amplitude changes were accommodated
with minimum distortion. The loop bandwidth (2BLo) was
configured such that the expected phase changes could be
accommodated while maintaining the best possible loop SNR.
Open-Loop Receivers: The open-loop Radio Science Receiver
(RSR) was a dedicated receiver that got a downconverted signal
(about 300 MHz), filtered the signal to limit its bandwidth
(to 265-375 MHz, centered at 320 MHz), and then further
downconverted (to a center frequency of 64 MHz) and digitized
the signal. The RSR filters were specified by their
bandwidths, desired resolution, and offset from the predicted
sky frequency.
The open-loop receivers operated in both a link-assigned and a
stand-alone mode. In the link-assigned mode, the NMC received
monitor data from the RSR for incorporation into the data set
for tracking support, and provided a workstation from which
the RSR could be operated. RSRs that were not assigned to a
link could be operated in a stand-alone mode without
interference to any activities in progress at the complex.
Monitor data were not sent to the NMC by RSRs operating in
the stand-alone mode.
DSCC Transmitter Subsystem
--------------------------
The Transmitter (TXR) Subsystem accepted a sky-level frequency
exciter signal from the Uplink (Exciter) Subsystem exciter.
This signal was routed via the diplexer through the feed horn
to the antenna, where it was then focused and beamed to the
spacecraft.
The Transmitter Subsystem power capabilities ranged from 18 kW
to 400 kW, for S- and X-band uplink. Power levels above 20 kW
were available only at 70-m stations.
DSCC Tracking Subsystem
-----------------------
Beginning in early 2003, all the Tracking Subsystem functions
were incorporated within the Uplink Subsystem (UPL) and the
Downlink Tracking and Telemetry Subsystem (DTT) -- the DTK was
eliminated.
DSCC Frequency and Timing Subsystem
-----------------------------------
The Frequency and Timing Subsystem (FTS) provided all of the
frequency and timing references required by the other DSCC
subsystems. It contained four frequency standards, of which
one was prime and the other three were backups. Selection of
the prime standard was done via the CMC. Of these four
standards, two were hydrogen masers followed by clean-up loops
(CUL) and two were cesium standards. These four standards all
fed the Coherent Reference Generator (CRG), which provided
the frequency references used by the rest of the complex. FTS
also provided the frequency reference to the Master Clock
Assembly (MCA), which in turn provided time to the Time
Insertion and Distribution Assembly (TID), which provided UTC
and SIM-time to the complex.
JPL's ability to monitor the FTS at each DSCC was limited to
the station-calculated Doppler pseudo-residuals, the Doppler
noise, the RSR, the SSI, and to a system that used the Global
Positioning System (GPS). GPS receivers at each DSCC received
a one-pulse-per-second signal 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 was reported to JPL, where a database
was kept. The clock offsets stored in the JPL database were
given in microseconds; each entry was a mean reading of the
measurements from several GPS satellites, and a time tag
associated with the mean reading. The clock offsets that were
provided included those of SPC 10 relative to UTC (NIST), SPC
40 relative to SPC 10, etc.
Optics - DSN
============
Performance of the DSN ground stations depended primarily on
the size of the antenna and capabilities of the 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) 20-100 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) 20 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: The 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 was 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 were used in spacecraft radio science
experiments, the details of transmitter and antenna
performance rarely impacted the results.
Calibration - DSN
=================
Calibrations of hardware systems were carried out periodically
by DSN personnel; these ensured that systems operated at
required performance levels -- for example, that antenna
patterns, receiver gain, propagation delays, and Doppler
uncertainties met specifications. No information on specific
calibration activities was 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 performed a
series of calibrations to ensure that systems met specifications
for that operational period. Included in these calibrations was
measurement of receiver system temperature in the configuration
to be employed during the pass. Results of these calibrations
were recorded in (hard copy) Controller's Logs for each pass.
Operational Considerations - DSN
================================
The DSN was a complex and dynamic 'instrument.' Its performance
for Radio Science depended 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 could be carried out in several
ways. For details see the subsection 'DSCC Antenna Mechanical
Subsystem' in the 'Subsystem' section. Binary pointing was
the preferred mode for tracking spacecraft; pointing
predicts were provided, and the antenna simply followed those.
With CONSCAN, the antenna scanned conically about the optimum
pointing direction, using closed-loop receiver signal
strength estimates as feedback. In planetary mode, the
system interpolated from three (slowly changing) RA-DEC
target coordinates; this was 'blind' pointing since there was
no feedback from a detected signal. In sidereal mode, the
antenna tracked a fixed point on the celestial sphere. In
'precision' mode, the antenna pointing was adjusted using an
optical feedback system. In addition, it was possible on
most antennas to freeze the z-axis motion of the subreflector
to minimize phase changes in the received signal.
DSCC Downlink Tracking and Telemetry Subsystem
----------------------------------------------
The diplexer in the signal path between the transmitter and
the feed horns on all antennas could be configured so that it
was out of the received signal path in order to improve the
signal-to-noise ratio in the receiver system. This was known
as the 'listen-only' or 'bypass' mode.
Closed-Loop vs. Open-Loop Reception
-----------------------------------
Radio Science data could be collected in two modes: closed-
loop, in which a phase-locked loop receiver tracked the
spacecraft signal, or open-loop, in which a receiver sampled
and recorded a band within which the desired signal presumably
resided. Closed-loop data were collected using Closed-Loop
Receivers, and open-loop data were collected using Open-Loop
Receivers in conjunction with the Full Spectrum Processing
Subsystem (FSP). See the Subsystems section for further
information.
Closed-Loop Receiver AGC Loop
-----------------------------
The closed-loop receiver AGC loop could be configured to one
of three settings: narrow, medium, or wide. In general, it
was configured so that expected signal amplitude changes were
accommodated with minimum distortion. The loop bandwidth was
typically configured so that expected phase changes could be
accommodated while maintaining the best possible loop SNR.
Coherent vs. Non-Coherent Operation
-----------------------------------
The frequency of the signal transmitted from the spacecraft
could 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 were known as the coherent (or
'two-way') and non-coherent ('one-way') modes, respectively.
Mode selection was made at the spacecraft, based on commands
received from the ground. When operating in the coherent
mode, the transponder carrier frequency was derived from the
received uplink carrier frequency with a 'turn-around ratio'
as expressed in the table below:
Uplink Downlink Turn-Around
Band Band Ratio
---------------------------------
X X 880/749
X S 240/749
In the non-coherent mode, the downlink carrier frequency was
derived from the spacecraft's on-board, crystal-controlled
oscillator. Either closed-loop or open-loop receivers (or
both) could be used with either spacecraft frequency reference
mode. Closed-loop reception in the two-way mode was usually
preferred for routine tracking/navigation. Occasionally the
spacecraft operated coherently such that one ground station
did the transmitting, and a second/different ground station
received the 'downlink' signal -- this was referred to as the
'three-way' mode.
Media Calibration System
------------------------
The Earth's atmosphere contributes phase and amplitude noise
to the spacecraft radio signal received at a ground station.
Each DSCC had a GPS receiver subsystem to calibrate for both
the ionosphere and troposphere (both wet and dry components),
along the zenith direction. This subsystem also measured the
temperature, pressure, humidity, wind speed and direction, and
Faraday rotation.
Location - DSN
==============
Accurate spacecraft navigation using radio metric data required
knowledge of the locations of the DSN tracking stations. The
coordinate system in which the locations of the tracking
stations were expressed needed to be consistent with the
reference frame definitions used to provide Earth orientation
calibrations.
The International Earth Rotation Service (IERS) had established
a terrestrial reference frame for use with Earth orientation
measurements. The IERS issued a new realization of the
terrestrial reference frame each year. The definition of the
coordinate system changed slowly as the data improved, and as
ideas about how best to define the coordinate system developed.
The overall changes from year to year were at the level of as
few centimeters. The 1993 version of the IERS Terrestrial
Reference Frame (IRTF1993) was most used for DSN station
locations.
The DSN station locations were determined by use of VLBI
measurements, and by conventional and GPS surveying. Tables of
station locations were available in either Cartesian or geodetic
coordinates. The geodetic coordinates were referred to a geoid
with an equatorial radius of 6378136.3 m, and a flattening
factor f=298.257, as described in IERS Technical Note 13.
The DSN Station Locations in ITRF1993 Cartesian reference frame
at epoch 1993.0 (assuming subreflector-fixed configuration) were
as follows:
Antenna x(m) y(m) z(m)
------------------------------------------------
DSS 12 -2350443.812 -4651980.837 +3665630.988
DSS 13 -2351112.491 -4655530.714 +3660912.787
DSS 14 -2353621.251 -4641341.542 +3677052.370
DSS 15 -2353538.790 -4641649.507 +3676670.043
DSS 16 -2354763.158 -4646787.462 +3669387.069
DSS 17 -2354730.357 -4646751.776 +3669440.659
DSS 23 -2354757.567 -4646934.675 +3669207.824
DSS 24 -2354906.528 -4646840.114 +3669242.295
DSS 25 -2355021.795 -4646953.325 +3669040.628
DSS 26 -2354890.967 -4647166.925 +3668872.212
DSS 27 -2349915.260 -4656756.484 +3660096.529
DSS 28 -2350101.849 -4656673.447 +3660103.577
DSS 33 -4461083.514 +2682281.745 -3674570.392
DSS 34 -4461146.720 +2682439.296 -3674393.517
DSS 42 -4460981.016 +2682413.525 -3674582.072
DSS 43 -4460894.585 +2682361.554 -3674748.580
DSS 45 -4460935.250 +2682765.710 -3674381.402
DSS 46 -4460828.619 +2682129.556 -3674975.508
DSS 49 -4554231.843 +2816758.983 -3454036.065 (Parkes)
DSS 53 +4849330.129 -0360338.092 +4114758.766
DSS 54 +4849434.496 -0360724.062 +4114618.570
DSS 55 +4849525.318 -0360606.299 +4114494.905
DSS 61 +4849245.211 -0360278.166 +4114884.445
DSS 63 +4849092.647 -0360180.569 +4115109.113
DSS 65 +4849336.730 -0360488.859 +4114748.775
DSS 66 +4849148.543 -0360474.842 +4114995.021
The DSN Station Locations in ITRF1993 Geodetic reference frame
at epoch 1993.0 (assuming subreflector-fixed configuration) were
as follows:
latitude longitude height
Antenna deg min sec deg min sec (m)
----------------------------------------------------------
DSS 12 35 17 59.77577 243 11 40.24697 962.87517
DSS 13 35 14 49.79342 243 12 19.95493 1071.17855
DSS 14 35 25 33.24518 243 6 37.66967 1002.11430
DSS 15 35 25 18.67390 243 6 46.10495 973.94523
DSS 16 35 20 29.54391 243 7 34.86823 944.71108
DSS 17 35 20 31.83778 243 7 35.38803 937.65000
DSS 23 35 20 22.38335 243 7 37.70043 946.08556
DSS 24 35 20 23.61492 243 7 30.74701 952.14515
DSS 25 35 20 15.40494 243 7 28.70236 960.38138
DSS 26 35 20 8.48213 243 7 37.14557 970.15911
DSS 27 35 14 17.78052 243 13 24.06569 1053.20312
DSS 28 35 14 17.78136 243 13 15.99911 1065.38171
DSS 33 -35 24 1.76138 148 58 59.12204 684.83864
DSS 34 -35 23 54.53984 148 58 55.06236 692.71119
DSS 42 -35 24 2.44494 148 58 52.55396 675.35557
DSS 43 -35 24 8.74388 148 58 52.55394 689.60780
DSS 45 -35 23 54.46400 148 58 39.65992 675.08630
DSS 46 -35 24 18.05462 148 58 59.08571 677.55141
DSS 49 -32 59 54.25297 148 15 48.64683 415.52885
DSS 53 40 25 38.48036 355 45 1.24307 827.50081
DSS 54 40 25 32.23152 355 44 45.24459 837.60097
DSS 55 40 25 27.45965 355 44 50.51161 819.70966
DSS 61 40 25 43.45508 355 45 3.51113 841.15897
DSS 63 40 25 52.34908 355 45 7.16030 865.54412
DSS 65 40 25 37.86055 355 44 54.88622 834.53926
DSS 66 40 25 47.90367 355 44 54.88739 850.58213
Measurement Parameters - DSN
============================
Open-Loop System
----------------
Output from the Open-Loop Receivers (OLRs), as sampled and
recorded by the Radio Science Receiver (RSR), was a stream of
1-, 2-, 4-, 8-, or 16-bit I (In-Phase) and Q
(Quadrature-Phase) samples. The spacecraft transmitted an RF
signal to an antenna, where the signal was downconverted to
IF. The RSR selected an IF signal for a particular frequency
band and passed it through a digitizer (where it was
attenuated and then mixed with timing information). The
signal was then decimated, filtered (to I&Q samples), and then
multiplied by the signal from a numerically controlled
oscillator. Finally, the RSR reduced the bandwidth
and sample rate of the samples, and truncated the results
(thus creating an offset of -0.5 in the output data). The
samples of data were packed into SFDU blocks (nominally
containing a single second's worth of data), and a header was
attached to provide the following associated data for the
record:
- time tag for the first sample in the data block
- data source identification (DSS, RSR, and sub-channel), and
frequency band
- data sample resolution (bits per sample) and rate (samples
per second)
- filter gain, ADC RMS amplitude, and attenuation
- frequency and phase polynomial coefficients
Closed-Loop System
------------------
Since mid 2003, closed-loop data were recorded and provided in
Tracking and Navigation Files (TNFs). The TNFs were comprised
of SFDUs that had variable-length, variable-format records
with mixed typing (i.e., can contain ASCII, integer, and
floating-point items in a single record). These files all
contained entries that included measurements of Doppler,
range, and signal strength, along with status and uplink
frequency information.
Acronyms and Abbreviations
==========================
1PPS One Pulse per Second
ACS Antenna Control System
ADEV Allan Deviation
AGC Automatic Gain Control
APA Antenna Pointing Assembly
BPF Band Pass Filter
BWG Beam Wave Guide
CFE Common Front End
CONSCAN Connical Scanning
D/L downlink
dBi decibel relative to isotropic
DCP Development Control Position
DDC Digital Down Converter
DDS Data Distribution System
DSCC Deep Space Communications Complex
DSN Deep Space Network
DSP Digital Signal Processing
DSS Deep Space Network Station
ESA European Space Agency
ESOC European Space Operations Centre
FTS Frequency and Timing subsystem
HEF High Efficiency
HGA High Gain Antenna
HSB High-Speed BWG
IFMS Intermediate Frequency Modulation System
IVC Intermediate Frequency Selection Switch
JPL Jet Propulsion Laboratory
LCP Left Circular Polarization
LGA Low Gain Antenna
LNA Low Noise Amplifier
LPF Low Pass filter
MB Medium band
Mbit Mega bit
MOLA Mars Orbiting Laser Altimeter
N/A not applicable
NASA National Aeronautics and Space Administration
NMC Network Monitor and Control
NNO New Norcia
OCC Operation Control Centre
ODF Orbit Data File
OLR Open Loop Receiver
PDS Planetary Data System
PI Principal Investigator
pwr power
rcvrs receivers
RCP Right Circular Polarization
RF Radio Frequency
RFDU Radio Frequency Distribution Unit
RIV Radio Science IF-VF Downconverter
rms root mean square
RO Rosetta Orbiter
RSI Rosetta Radio Science Investigations
RSR Radio- Science Receiver
RSS Radio Science Subsystem
SIM Simulation
SNR Signal-Noise-Ratio
SNT System Noise Temperature
SPC Signal Processing Center
STC Station Computer
sps samples per second
STAT Science Time Analysis Tool
TCDS Telemetry Channel Decoding System
TCXO Temperature Controlled Crystal Oscillator
TID Time Insertion and Distribution Assembly
TNF Tracking and Navigation File
TWOD Two-way dual-frequency mode
TWOS Two-way single-frequency mode
TWTA Traveling wave tube amplifier
Tx Transmitter
U/L uplink
UNK unknown
UTC Coordinated Universal Time
USO Ultra stable Oscillator
VDP VME Data Processor
VF Video Frequency
VME Versa Module Eurocard (standard bus)
w watt
|
| MODEL IDENTIFIER | |
| NAIF INSTRUMENT IDENTIFIER |
not applicable |
| SERIAL NUMBER |
not applicable |
| REFERENCES |
Asmar, S.W., and R.G. Herrera, Radio Science Handbook, JPL D-7938, Volume 4,
Jet Propulsion Laboratory, Pasadena, CA, 22 January 1993. 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. Deep Space Network / Flight Project Interface Design Book, Document 810-5, Jet Propulsion Laboratory, Pasadena, CA. Deep Space Mission Systems, Tracking and Navigation Service, Requirements and Design, DSMS No. 821-104, Rev. B, JPL D-17235, Jet Propulsion Laboratory, Pasadena, CA, 2003. Deep Space Mission Systems, Radio Science Service, Requirements and Design, DSMS No. 821-110, Rev. A, JPL D-17241, Jet Propulsion Laboratory, Pasadena, CA, 2001. Deep Space Mission Systems, Mars Express (MEX) Project, Network Operations Plan, DSMS No. 871-049-041, JPL D-25808, Jet Propulsion Laboratory, Pasadena, CA, 2003. 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. Lemoine, F.G., D.E. Smith, D.D. Rowlands, M.T. Zuber, G.A. Neumann, D.S. Chinn, and D.E. Pavlis, An Improved Solution for the Gravity Field of Mars (GMM-2B) from Mars Global Surveyor, Journal of Geophysical Research, 106, 23359-23376, 2001. Miller, J.K., Williams, B.G., Bollman, W.E., Davis, R.P., Helfrich, C.E., Scheeres, D.J., Synnott, S.P., Wang, T.C. and Yeomans, D.K., Navigation analysis for Eros rendezvous and orbital phases, J. Astronaut. Sci., 43, 453-476, 1995. Scheeres, D.J., Analysis of orbital motion around 433 Eros, J. Astronaut. Sci., 43, 427-452, 1995. Simpson, R.A., and G.L. Tyler, Mars Global Surveyor bistatic radar probing of the MPL/DS2 target area, Icarus, 152, 70-74, 2001. Sjogren, W.L., Mars Gravity: High-resolution results from Viking Orbiter 2, Science, 203, 1006-1010, 1979. Tracadis, P.W., M.T. Zuber, D.E. Smith, and F.G. Lemoine, Density Structure of the Upper Thermosphere of Mars from Measurements of Air Drag on the Mars Global Surveyor Spacecraft, J. Geophys. Res., 106, 23349-23357, 2001. Tyler, G.L., G. Balmino, D.P. Hinson, W.L. Sjogren, D.E. Smith, R. Woo, S.W. Asmar, M.J. Connally, C.L. Hamilton, and R.A. Simpson, Radio Science Investigations with Mars Observer, J. Geophys. Res., 97, 7759-7779, 1992. Tyler, G.L., G. Balmino, D.P. Hinson, W.L. Sjogren, D.E. Smith, R.A. Simpson, S.W. Asmar, P. Priest, and J.D. Twicken, Radio science observations with Mars Global Surveyor: Orbit insertion through one Mars year in mapping orbit, Journal of Geophysical Research, 106, 23327-23348, 2001. Woo, R., Spacecraft Radio Scintillation and Solar System Exploration, Wave Propagation in Random Media (Scintillation), Society of Photo-Optical Instrumentation Engineers, Bellingham, WA, 1993. Yuan, D.N., W.L. Sjogren, A.S. Konopliv, and A.B. Kucinskas, Gravity Field of Mars: A 75th Degree and Order Model, Journal of Geophysical Research, 106, 23377-23401, 2001. Zuber, M.T., and D.E. Smith, Rotational dynamics and time-variable gravity of Mars and implications for volatile cycling and atmospheric structure, Lunar and Planetary Science Conference XXXIII, Paper 1925.pdf, Houston, 2002. |
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