Instrument Host Information
The majority of the text in this file was extracted from the Cassini 
Mission Plan Document, D. Seal, 2003. [JPLD-5564]

  Instrument Host Overview

For most Cassini Orbiter experiments, data were collected by instruments on 
the spacecraft then relayed via the orbiter telemetry system to stations of 
the NASA Deep Space Network (DSN).  Radio Science required the DSN for its 
data acquisition on the ground.  The following sections provide an 
overview, first of the orbiter, then the science instruments, and 
finally the DSN ground system.

  Instrument Host Overview - Spacecraft

Cassini was successfully launched on 15 October 1997 from Cape Canaveral, 
Florida, using a Titan IV/Centaur launch vehicle with Solid Rocket Motor 
Upgrade (SRMU) strap-ons and a Centaur upper stage.  The spacecraft flew a 
6.7-year Venus-Venus-Earth-Jupiter Gravity Assist (VVEJGA) trajectory to 
Saturn, during which cruise operations included checkout, characterization, 
calibration, and maintenance of the instruments and limited science 

Until they separated after Saturn orbit insertion, Cassini was a combined 
Saturn orbiter and Titan atmospheric probe.  It was a three-axis stabilized 
spacecraft equipped for 27 diverse science investigations with 12 orbiter 
and 6 Huygens probe instruments, one high gain (HGA) and two low gain 
antennas (LGAs), three Radioisotope Thermoelectric Generators (RTGs), main 
engines, attitude thrusters, and reaction wheels.  This description covers 
the orbiter portion of Cassini, which will frequently be called 'the 

   Orbiter Description

The Cassini orbiter was a three-axis-stabilized spacecraft.  The origin of 
the spacecraft coordinate system was located at the center of the plane at 
the bus/upper shell structure interface (i.e., base of the electronic bays 
on the upper equipment module).  The remote sensing pallet was mounted on 
the +X side of the spacecraft, the magnetometer boom extended in the +Y 
direction, and the +Z axis completed the orthogonal body axes in the 
direction of the main engine.  The primary remote sensing boresights viewed 
in the -Y direction, the probe was ejected in the -X direction, the HGA 
boresight was in the -Z direction, the main engine exhaust was in the +Z 
direction, and the main engine thrust was in the -Z direction.  The 
coordinates and some of the larger elements of the spacecraft are shown in 
the figure below.

                             \                                /
                              \                              /    HGA
                               \                            /
               MAG Boom          --------------------------
            ... =================|                        |
                                 |           h            |
                                  \          ^           /
                                   |         |          |
                                   |         |          |
                        Ysc -------|   v <---o          |
                                   |           b, Xsc   |
                                   |                    |
                                   |                    |
                                   |                    |
                                   |                    |
                                   |                    |
                                          /      \
                                         /        \  Main Rocket Engine
           where b and Xsc   point out of the screen or page.

The main body of the spacecraft was formed by a stack consisting of the 
lower equipment module, the propulsion module, the upper equipment module, 
and the HGA.  Attached to this stack were the remote sensing pallet, the 
fields and particles pallet, and the Huygens Probe system.  The Huygens 
Probe was built by the European Space Agency and was deployed into Titan's 
atmosphere by the Orbiter.  Some instruments such as RADAR and some 
instrument components such as those of RPWS were attached to the upper 
equipment module.  The two equipment modules were also used for external 
mounting of the magnetometer boom and the three radioisotope thermoelectric 
generators (RTGs) which supplied the spacecraft power.  The spacecraft 
electronics bus was part of the upper equipment module and carried the 
electronics to support the spacecraft data handling, including the command 
and data subsystem and the radio frequency subsystem.  Other electronics to 
support instruments and other spacecraft functions were also carried in the 
bus.  During the inner cruise, the HGA and two Low Gain Antennas (LGAs) 
were used to transmit data and receive commands.  One of the two LGAs was 
selected when operational constraints prevented pointing the HGA towards 
the Earth.

The spacecraft stood 6.8 meters (22.3 ft) high.  Its maximum diameter, the 
diameter of the HGA, was 4 meters (13.1 ft).  Therefore, the HGA could 
fully shield the rest of the spacecraft (except the deployed MAG boom and 
RPWS antennas) from sunlight when the HGA was pointed within 2.5 degrees of 
the Sun.  The dry mass of the spacecraft was 2523 kg, including the Huygens 
Probe system and the science instruments.  The best estimate of the actual 
spacecraft mass at separation from the Centaur was 5573.8 kg.  Future 
estimates of spacecraft mass were maintained by the Spacecraft Operations 
team (SCO).  


The spacecraft comprised several subsystems, which are described briefly 
below. For more detailed information, see JPLD-5564.

Structure Subsystem

The Structure Subsystem (STRU) provided mechanical support and alignment 
for all flight equipment including the Huygens Probe. It also served as a 
local thermal reservoir and provided an equipotential container, an 
electrical grounding reference, RFI shielding, and protection from 
radiation and meteoroids.  The STRU consisted of the Upper Equipment Module 
(UEM) which contained the 12-bay electronics bus assembly, the instrument 
pallets, and the MAG boom, and the Lower Equipment Module (LEM), plus all 
the brackets and structure for integrating the Huygens Probe, the HGA, 
LGAs, RTGs, reaction wheels, the main rocket engines, the four RCS thruster 
clusters, and other equipment.  The STRU also included an adapter which 
supported the spacecraft on the Centaur during launch.

Radio Frequency Subsystem

The Radio Frequency Subsystem (RFS) provided the telecommunications 
facilities for the spacecraft and was used as part of the radio science 
instrument.  For telecommunications, it produced an X-band carrier at 8.4 
GHz, modulated it with data received from the CDS, amplified the X-band 
carrier power to produce 20 W from the Traveling Wave Tube Amplifiers 
(TWTA), and delivered it to the Antenna Subsystem (ANT).  From ANT, RFS 
accepted X-band ground command/data signals at 7.2 GHz, demodulated them, 
and delivered the commands/data to CDS for storage and/or execution.

The Ultra Stable Oscillator (USO), the Deep Space Transponder (DST), the X-
band Traveling Wave Tube Amplifier (TWTA), and the X-band Diplexer were 
elements of the RFS which were used as part of the radio science 
instrument.  The DST could phase-lock to an X-band uplink and generate a 
coherent downlink carrier with a frequency translation adequate for 
transmission at X-, S-, or Ka-band.  The DST had the capability of 
detecting ranging modulation and of modulating the X-band downlink carrier 
with the detected ranging modulation.  Differenced one-way ranging (DOR) 
tones could also be modulated onto the downlink.  The DST could also accept 
the reference signal from the USO and generate a non-coherent downlink 

Propulsion Module Subsystem

The Propulsion Module Subsystem (PMS) provided thrust and torque to the 
spacecraft. Under command from AACS, the thrust and torque established the 
spacecraft attitude, pointing, and the amount of velocity vector change.  

For attitude control, the PMS had a Reaction Control Subsystem (RCS) 
consisting of four thruster clusters mounted off the PMS core structure 
adjacent to the LEM at the base of the spacecraft. Each of the clusters 
contained 4 hydrazine thrusters. The thrusters are oriented to provide 
thrust along the spacecraft +/-Y and -Z axes. RCS thrusters also provide DV 
for small maneuvers.

For larger DVs, the PMS had a primary and redundant pressure-regulated main 
rocket engine.  Each engine was capable of a thrust of approximately 445 N 
when regulated. The bipropellant main engines burned nitrogen tetroxide 
(N2O4) and monomethylhydrazine (N2H3CH3) producing an expected specific 
impulse of up to 308s. These engines were gimbaled so when under AACS 
control during burns the thrust vector could be maintained through the 
shifting center of mass of the spacecraft. AACS-provided valve drivers for 
all the engines/thrusters operated in response to commands received from 
AACS via the CDS data bus. 

Power and Pyrotechnics Subsystem

 The Power and Pyrotechnics Subsystem (PPS) provided regulated electrical 
 power from three RTGs on command from CDS to spacecraft users at 30 Volts 
 DC, distributed over a power bus.  In addition, PPS provided power to the 
 various pyrotechnic devices on command from CDS.  PPS disposed of excess 
 power by heat radiation to space via a resistance shunt radiator. 
 Measurements of the output of the radioisotope thermoelectric generators 
 indicated a beginning-of- life power of 876 +/- 6 Watts, 740 Watts at SOI, 
 and 692 Watts at end of mission.  These estimates were at least 30 Watts 
 above pre-launch predictions.  

Command and Data Subsystem

The Command and Data Subsystem (CDS) received the uplink command stream via 
the RFS and decoded it.  The stream included timing (immediate or 
sequence), routing, action, and parameter information.  The CDS then 
distributed commands designated for other subsystems or instruments, 
executed those commands which were decoded as CDS commands, and stored 
sequence commands for later execution.  

The Cassini spacecraft included two identical Solid State Recorders (SSRs). 
Each CDS (A & B) was attached to the two SSRs such that each CDS could 
communicate (read, write) with only one SSR at any one time. The Mission 
and Science Operations Office had the capability to control how the SSR 
attachments were configured via immediate command or a stored sequence. 
Under fault response conditions flight software (FSW) could switch an SSR 
attachment from CDS A to CDS B.  

The CDS received data from other on-board subsystems via the data bus, then 
processed and formatted them for telemetry and delivered them to RFS for 
transmission to Earth.  Each subsystem interfaced with the data bus through 
a standard Bus Interface Unit (BIU) or a Remote Engineering Unit (REU). 
Data were collected in 8800 bit frames, and Reed-Solomon Encoded on 
downlink.  A 32 framesync marker along with the encoding increased these 
frames to 10,112 bits.

CDS software contained algorithms that provided protection for the 
spacecraft and the mission in the event of a fault.  Fault protection 
software ensured that, in the case of a serious fault, the spacecraft would 
be placed into a safe, stable, commandable state (without ground 
intervention) for a period of at least two weeks to give the mission 
operations team time to solve the problem and send the spacecraft a new 
command sequence.  It was also capable of autonomously responding to a 
predefined set of faults needing immediate action.

Attitude and Articulation Control Subsystem

The Attitude and Articulation Control Subsystem (AACS) provided dynamic 
control of the spacecraft in rotation and translation. It provided fixed-
target staring for HGA and remote sensing pointing and performed target 
relative pointing using inertial vector propagation as well as repetitive 
subroutines such as scans and mosaics. AACS also controlled actuators for 
the main rocket engine gimbals. Rotational motion during the Saturn tour 
that required high pointing stability was normally controlled by the three 
main Reaction Wheel Assemblies (RWAs), although modes requiring faster 
rates or accelerations may have used thrusters. The additional fourth 
reaction wheel could articulate to replace any single failed wheel.

AACS contained a suite of sensors that included redundant Sun Sensor 
Assemblies (SSA), redundant Stellar Reference Units (SRU, also called star 
trackers), a Z-axis accelerometer, and two 3-axis gyro Inertial Reference 
Units (IRU).  Each IRU consisted of four gyros, three orthogonal to each 
other and the fourth skewed equidistant to the other three. 

Temperature Control Subsystem

The TEMPerature control subsystem (TEMP) allowed operations over the 
expected solar ranges (0.61 to 10.1 AU) with some operational constraints. 
Temperatures of the various parts of the spacecraft were kept within 
allowable limits by a large number of local TEMP thermal control 
techniques, many of which were passive.  The 12-bay electronics bus had 
automatically positioned reflective louvers.  Radio Isotope Heater Units 
(RHU) were used where constant heat input rates were needed and where 
radiation was not a problem.  Multilayer insulation blankets covered much 
of the spacecraft and its equipment.

Electric heaters were used in different locations and operated by CDS and 
instruments.  Temperature sensors were located at many sites on the 
spacecraft, and their measurements were used by CDS to command the TEMP 
heaters.  Shading was executed by pointing the HGA (-Z axis) towards the 
sun; the HGA was large enough to provide shade for the entire spacecraft 
body including the Huygens Probe.

Mechanical Devices Subsystem

The mechanical devices subsystem provided a pyrotechnic separation device 
used to separate the spacecraft from the launch vehicle adapter.  Springs 
provided the impulse to separate the spacecraft from the adapter.  The 
mechanical devices subsystem also provided a self-deploying 10.5 meter 
coiled longeron mast stored in a canister for the two magnetometers, 
electrostatic discharge covers over inflight separation connectors, an 
articulation system for the backup reaction wheel assembly, a 'pinpuller' 
for the RPWS Langmuir Probe, and louvers and variable RHUs for temperature 

Electronic Packaging Subsystem

The Electronic Packaging Subsystem (EPS) consisted of the electronics 
packaging for most of the spacecraft in the form of the 12-bay electronics 
bus.  The bus was made up of bays containing standardized, dual-shear plate 
electronics modules.

Solid State Recorder Subsystem 

Cassini's two Solid State Recorders (SSRs) were the primary memory storage 
and retrieval devices used on the orbiter.  Each SSR contained 128 
submodules, of which 8 were used for flight software and 120 were used for 
telemetry.  Each submodule could hold 16,777,200 bits for data, so the 
total data storage for telemetry on each SSR was 2.013 Gbits.  Expressed in 
terms of 8800-bit telemetry frames, this was 228,780 frames per SSR. 

Spacecraft telemetry and AACS, CDS, and instrument memory loads were stored 
in separate files called partitions.  All data recorded to and played back 
from the SSR was handled by the CDS. There were three different SSR 
functional modes: Read-Write to End, Circular FIFO, and Ring Buffer.  There 
was also a record pointer and a playback pointer, which marked the memory 
addresses at which the SSR could write or read.  In Read-Write to End, 
there was a logical beginning and end to the SSR.  Recording began at this 
logical beginning and continued until either the SSR was reset (the record 
and playback pointers were returned to the logical beginning) or until the 
record pointer reached the end.  If the record pointer did not reach the 
end, recording was halted until the SSR was reset.  In Circular FIFO, there 
was no logical end to the SSR.  The data was continuously recorded until 
the record pointer reached the playback pointer.  The Ring Buffer mode 
behavior was similar to the Circular FIFO except that recording did not 
stop if the record pointer reached the playback pointer.

Antenna Subsystem  

The ANTenna subsystem (ANT) provided a directional high gain antenna (HGA) 
with X-, Ka-, S and Ku-band for transmitting and receiving on all four 
bands.  Because of its narrow halfpower beam width of 0.14 deg for Ka-band, 
it had to be accurately pointed.  The HGA, and the low gain antenna 1 
(LGA1) located on the HGA feed structure, were provided by the Italian 
Space Agency.  Another LGA (LGA2) was located below the Probe pointing in 
the -X direction.  During the inner solar system cruise, the HGA was Sun-
pointed to provide shade for the spacecraft.  ANT provided two LGAs which 
allowed one or the other to receive/transmit X-band from/to the Earth when 
the spacecraft was Sun-pointed.  The LGAs also provided an emergency 
uplink/downlink capability while Cassini was at Saturn.  The HGA downlink 
gain at X-band was 47dBi and the LGA1 peak downlink gain was 8.9 dBi.  The 
X-band TWTA power was 20 watts.


 There were 12 science instrument subsystems on the Cassini spacecraft, 
 listed immediately below with their acronyms, then described in more 
 detail in the following paragraphs.  Three of the instruments (CAPS, CDA, 
 and MIMI/LEMMS) were capable of commanded articulation relative to the 

          Cassini Plasma Spectrometer               CAPS
          Cosmic Dust Analyzer                      CDA
          Composite Infrared Spectrometer           CIRS
          Ion and Neutral Mass Spectrometer         INMS
          Imaging Science Subsystem                 ISS
          Magnetometer                              MAG
          Magnetospheric Imaging Instrument         MIMI
          Cassini RADAR                             RADAR
          Radio and Plasma Wave Science             RPWS
          Radio Science Subsystem                   RSS
          Ultraviolet Imaging Spectrograph          UVIS
          Visible and Infrared Mapping Spectrometer VIMS

Cassini Plasma Spectrometer (CAPS): The CAPS instrument was designed to 
perform an in-situ study of plasma within and near Saturn's magnetosphere.  
Specific science and measurement objectives were:

1) Orbital Tour Observing Objectives:
   a)   Near continuous survey.
   b)   MAPS Campaigns.
   c)   SOI, targeted Titan and icy satellite observations.
   d)   CAPS Magnetospheric Survey.
2) Solar Wind/Aurora Campaign Objectives:
   a)   Measure solar wind while ORS observed aurora.
   b)   Unambiguous measurements of unperturbed solar wind, correlation 
        with Earth based and RPW auroral data.
3) Study microphysical and rapidly varying processes near the bow shock and
4) Observe particle acceleration, particle injection, and dynamical events
   (e.g.  substorms) in the magnetotail.
5) Measure vertical (field aligned) structure of plasma in the inner 
6) Observe the dynamics and microphysics of the auroral and Saturn 
   Kilometric Radiation (SKR) source regions.
7) Study the Titan plasma torus and distant signatures of Titan's 
   interaction with the magnetosphere.
8) Study the distant signatures of satellites and ring interactions with 
   the magnetosphere.

Cosmic Dust Analyzer (CDA): The CDA instrument was designed to perform an 
in- situ study of dust grains in the Saturn system.  Specific science and 
measurement objectives were: 

1) Study interplanetary and interstellar dust at Saturn.
2) Saturn Rings Objectives:
    a)    Map size distribution.
    b)    Search for particles in the 'clear zone' (F/G ring).
    c)    Determine orbits of particles to identify their possible parents.
    d)    Study the interaction between E ring and Saturn's magnetosphere.
    e)    Distinguish temporal and spatial effects.
    f)    Analyze eccentricity and inclination of dust orbits 
3) Icy Satellites Objectives:
    a)    Interaction with the ring system.
    b)    Role of satellites as a source and sink for ring particles.
    c)    Chemical composition of satellites (dust atmospheres).

Composite Infrared Spectrometer (CIRS): The CIRS instrument was designed to 
perform spectral mapping to study temperature and composition of surfaces, 
atmospheres, and rings within the Saturn system.  Specific science and 
measurement objectives were: 

1) Thermal Structure Objectives:
   a)   Vertical profiles of atmospheric temperature.
   b)   Maps of atmospheric and surface temperatures.
   c)   Aerosol opacities.
   d)   Thermal inertia of surfaces.
   e)   Subsurface regolith structure.
   f)   Ring particle sizes.
   g)   Ring thermal structure.
2) Composition Objectives:
   a)   Spatial distribution of atmospheric gases.
   b)   Surfaces.
   c)   Ring material.
3) Atmosphere Objectives:
   a)   Circulation:  Zonal jets, Meridional motion, vortices, wave,
   b)   Composition:  Dis-equilibrium species, elemental and isotope
        abundances and distribution, ortho/para ratio, condensable 
        gases, external sources (e.g., rings).
   c)   Clouds/Aerosols:  Composition, microphysical properties, spatial
        and temporal distribution.
   d)   Atmospheric.  Structure:  Temperature, pressure, density, vertical
        distribution of major constituents.
   e)   Internal Structure:  He abundance, internal heat, gravity.
   f)   Aurora, lighting, airglow:  Spatial and temporal distribution, 
        special properties.
   g)   Titan:  Aerosols and clouds, Titan winds.
4) Rings Objectives:
   a)   Vertical structure and thermal gradient.
   b)   Vertical Dynamics.
   c)   Particle Surface Properties.
   d)   Particle Composition.
   e)   Radial Structure.
5) Non-Targeted Icy Satellites Objectives:
   a)   Determine surface composition.
   b)   Determine vertical thermal structure (Greenhouse).
   c)   Determine thermophysical properties (Thermal Inertia).
   d)   Search for active thermal sources (space and time).

Ion and Neutral Mass Spectrometer (INMS): The INMS instrument was designed 
to perform an in-situ study of the compositions of neutral and charged 
particles within the Saturn magnetosphere.  Specific science and 
measurement objectives were:

1) Outer Magnetosphere: Science Objectives:
   a)   Neutral and ion composition of the magnetosphere.
   b)   Composition of the Titan plasma torus.
   c)   Additional low energy ion distribution function information to
        complement CAPS.
2) Inner Magnetosphere: Science Objectives:
   a)   Studies of solar system formation.  Plasma sources derived from 
        the rings and icy satellites - composition and isotopic ratio.
   b)   Studies of plasma transport.  Determination of plasma transport 
        velocities and determination of momentum transfer from charge 
        exchange chemistry - water products.

Imaging Science Subsystem (ISS): The ISS instrument was designed to perform 
multispectral imaging of Saturn, Titan, rings, and icy satellites to 
observe their properties.  Specific science and measurement objectives 

1) Motions and Dynamics:
   a)   Basic flow regime (Titan).
   b)   Poleward flux of momentum (u'v').
   c)   Poleward flux of heat (with CIRS).
   d)   Life cycles and small-scale dynamics of eddies.
   e)   Radiative heating for dynamical studies.
2) Clouds and Aerosols:
   a)   Could and haze stratigraphy (strongly couples with wind studies).
   b)   Particle optical properties.
   c)   Particle physical properties.
   d)   Auroral processes and particle formation.
   e)   Haze microphysical models.
3) Lightning (related to water clouds on Saturn, don't know what to expect 
   for Titan).
4) Auroras (H and H2 emissions on Saturn, N and N2 emissions on Titan).
5) ISS High Priority Rings Goals:
   a)   Ring Architecture/Evolution:  Azimuthal, radial, temporal 
        variations across tour.
   b)   New satellites: orbits, masses/densities, effects on rings; 
        complete inventory of Saturn's inner moons.
   c)   Search and characterize material potentially hazardous to Cassini:
        diffuse rings, arcs, Hill's sphere material, etc.
   d)   Orbit refinement of known satellites; temporal variations; 
        resonant effects.
   e)   Particle/Disk properties: vertical disk structure; particle 
        physical properties and size distribution; variations across disk.
   f)   Spokes: Formation timescales/process; periodic variations.
   g)   Diffuse Rings (E, G): Structure, characterize particle properties.

Magnetometer (MAG): The MAG instrument was designed to study Saturn's 
magnetic field and interactions with the solar wind.  Specific science and 
measurement objectives were:

1) Intrinsic magnetic fields of Saturn and its moons:
   a)   Determine the multiple moments of Saturn's dynamo-driven 
        magnetic field.
   b)   Determine weather Titan has an internal field due to dynamo action,
        electromagnetic induction or even remnant magnetization in a 'dirty
        ice' crust.
   c)   Search for possible evidence of ancient dynamos and crustal 
        remnants in the icy satellites.
2) Derive a 3-D global model of the magnetospheric magnetic field.
3) Establish the relative contributions to electromagnetic and mechanical
   stress balance.
4) Identify the energy source for dynamical processes (rotationally driven,
   solar wind driven, or other).
5) Characterize the phenomena of the distant dayside/flank planetary
6) Survey satellite/dust/ring/torus electromagnetic interactions.
7) Determine tail structure and dynamic processes therein.
8) Establish nature and source of all ULF wave sources.
9) Magnetosphere/ionosphere coupling.
10) Titan:
    a)   Determine the internal magnetic field sources of Titan as well as
         the sources external to I I - thereby determining the interaction
    b)   Determine all Titan-plasma flow interactions (magnetosphere,
         magnetosheath, solar wind).
    c)   Determine the variation of the Titan-magnetosphere interaction 
         with respect to Titan orbital phase.
    d)   Determine the nature of the low frequency wave (ion
         cyclotron/hydromagnetic) spectrum of the near-Titan plasma
11) Icy Satellites:
    a)   Search for possible evidence of ancient dynamos and crustal 
         remanence in the icy satellites
    b)   Investigate icy satellite plasma environments.

Magnetospheric Imaging Instrument (MIMI): MIMI was designed for global 
magnetospheric imaging and in-situ measurements of Saturn's magnetosphere 
and solar wind interactions.  Specific science and measurement objectives 

1) MIMI Survey:
   a)   What is the source of energetic particles in Saturn's magnetosphere
        and how are they energized?
   b)   To what extent does the solar wind and rotation regulate the size,
        shape and dynamics of Saturn's magnetosphere; are there Earth-like
        storms and substorms?
   c)   How does the interaction between the magnetospheric particle 
        population and Saturn cause the aurora, and affect magnetospheric 
        and upper atmospheric processes?
   d)   How does the distribution of satellites affect global 
        magnetospheric morphology and processes?
2) MIMI Campaigns:
   a)   How do satellites and their exospheres affect local magnetospheric
        plasma flow and contribute to energetic particle populations?
   b)   What particles (species, energy) cause Saturnian aurora; what
        processes accelerate them and what is the exospheric response?
   c)   What unique role do Saturn's rings play in controlling the 
        structure, composition, and transport of the inner magnetosphere?

Cassini RADAR (RADAR): The RADAR instrument was designed for synthetic 
aperture RADAR (SAR) imaging, altimetry, and radiometry of Titan's surface.  
Specific science objectives for the Cassini mission are as follows.

1) Rings:
   a)   Determine scattering properties of rings.
   b)   Determine ring global properties.
   c)   Determine additional thermal and compositional properties of rings.  
   d)   Extended ring global properties: low-elevation measurements.
   e)   Radial scans through optically thin rings (E, F and G).
   f)   Identify thermal component.  
2) Catalog of each satellite's base radar/radiometric properties and their
   degree of global variation.

Radio and Plasma Wave Science (RPWS): The RPWS instrument was designed to 
study plasma waves, radio emissions, and dust in the Saturn system. 
Specific science and measurement objectives were:

1) Aurora and SKR: Obtain radio and plasma wave data which provide 
   information on the SKR source and plasma waves on auroral field lines.
2) Satellite and ring interactions: Measure dust flux, look for effects of 
   selective absorption of electrons and ions near rings (thermal 
   anisotropy), multi-ion wave particle interactions, satellite torii.
3) Inner Magnetosphere: Wave particle interactions via ULF waves; Stability
   of trapped electrons and relation to whistler-mode emissions; 
   ECH (N+ 1/2)fce waves trapped near the equatorial region and heating of 
   cool electrons.
4) Titan Interactions: Multi-ion species wave-particle interactions; 
   Evidence of Titan plumes/detached plasma blobs.
5) Magnetospheric Boundaries: Nature of the Saturnian Bow shock: Look for 
   the signatures of waves accelerating electrons.
6) What is the nature of Saturn's magnetotail?  Are there substorms or 
   other dynamical processes there?
7) Observe lightning via SED and whistlers from Saturn's atmosphere and
   possible Titan's.
8) Determine the equatorial dust flux and scale height as a function of 
   radial distance.
9) Provides for mapping and synoptic measurements required for the RPWS
   portion of the magnetospheric survey.
10) Search for electromagnetic phenomena which may be triggers of ring 

Radio Science Subsystem (RSS): The RSS was designed to study atmospheres 
and ionospheres of Saturn, Titan, rings, and gravity fields of Saturn and 
its satellites (also, search for gravitational waves during cruise). 
Specific science and measurement objectives were:

1) Ring Occultations:
   a)   To profile radial ring structure with resolution <= 100m; 
        characterize structure variability with azimuth, wavelength, 
        ring-opening-angle, and time.
   b)   To determine the physical particle properties (size distribution, 
        bulk density, surface density, thickness, viscosity).
   c)   To study ring kinematics and dynamics (morphology, interaction with
        embedded and exterior satellites), and to investigate ring origin 
        and evolution.
2) Atmospheric Occultations:
   a)   To determine the global fields of temperature, pressure, and zonal
        winds in the stratosphere and troposphere of Saturn.
   b)   To determine the small scale structure due to eddies and waves.
   c)   To determine the latitudinal variations of NH3 abundance in 
        Saturn's atmosphere.
   d)   To improve the knowledge of H2/He ratio in Saturn's troposphere
3) Ionospheric Occultations:
   a)   To determine the vertical profiles of the electron density in 
        Saturn's terminator ionosphere, and its variability with latitude.
   b)   To investigate interaction of the ionosphere with Saturn's
        magnetosphere and Saturn's rings.
4) Gravity Field of Saturn:
   a)   To determine the mass of Saturn and zonal harmonic coefficients of 
        its gravity field to at least degree 6 (J2, J4, J6).
   b)   To constrain models of Saturn's interior based on the results
5) Gravity Field and Occultation of Untargeted Satellites:
   a)   To determine the masses of Mimas, Tethys, Dione, Hyperion, and 
   b)   To search for a possible tenuous ionosphere around any occulted
        satellites (a la Europa and Callisto).

Ultraviolet Imaging Spectrograph (UVIS): The UVIS instrument was designed 
to produce spatial UV maps, map ring radial structure, and to determine 
hydrogen/deuterium ratios.  Specific science and measurement objectives 

1) Saturn System Scans:
   a)   EUV and FUV low resolution spectra of magnetosphere neutral and ion
   b)   System scans at every apoapsis.
2) Satellites: 
   a)   Latitude, longitude and phase coverage coordinated through SSWG.
   b)   Distant stellar occultations to determine satellite orbits and 
        Saturn reference frame.
3) Atmosphere:
   a)   Vertical profiles of H, H2, hydrocarbons, temp in exo, 
   b)   Long integrations map of hydrocarbons, airglow.
   c)   Map emissions with highest resolution at the limb.
   d)   Auroral Map:  H and H2 emissions over several rotations.
4) Ring Stellar Occultation Objectives:
   a)   Highest Radial resolution (20m) structure of rings
   b)   Discovery and precise characterization of dynamical features 
        generated by ring-satellite interactions.
             - Density waves and bending waves.
             - Edge waves and ring shepherding.
             - Embedded moonlets and discovery of new moons from 
               dynamical response in rings.
   c)   Discovery and precise characterization of azimuthal structure in
             - Eccentric rings.
             - Density waves and edge waves.
             - Small-scale self-gravitational clumping in rings.
   d)   Measure temporal variability in ring structure.
   e)   Simultaneously measure UV reflectance spectrum of rings.
             - Determine microstructure on particle surfaces.
             - Compositional information on ring particles.
   f)   Measure size distribution of large particles through occultation
   g)   Measure dust abundance in diffraction aureole.
   h)   Simultaneously search for flashes from 0.1 m - 1.0 m meteoroid

Visible and Infrared Mapping Spectrometer (VIMS): The VIMS instrument was 
designed to produce spectral maps to study the composition and structure of 
surfaces, atmospheres, and rings.  Specific science and measurement 
objectives were:

1) Ring Observation: 
   a)   Determine ring composition and its spatial variations.
   b)   Determine light scattering behavior of rings as a function of I, e,
        and alpha.
   c)   Constrain sizes and surface textures of ring particles.
   d)   Establish optical depth profile of rings as a function of 
        wavelength, incidence angle, and longitude.
   e)   Characterize variable features such as non-circular ringlets, 
        F ring, spokes, etc., and their evolution.
   f)   Ring moon compositions.
2) Icy Satellite Observation:
   a)   Measure UV and NIR spectra to:
               - Identify and map surface materials at the highest spatial
               - Determine microphysical surface properties.
               - Provide data on energy balance.

  Instrument Host Overview - DSN
Radio Science investigations utilized instrumentation with
elements both on the spacecraft and at the NASA Deep Space Network
(DSN).  Much of this was shared equipment, being used for routine
telecommunications as well as for Radio Science.
The Deep Space Network was a telecommunications facility managed by
the Jet Propulsion Laboratory of the California Institute of
Technology for the U.S.  National Aeronautics and Space
The primary function of the DSN was to provide two-way communications
between the Earth and spacecraft exploring the solar system.  To carry
out this function the DSN was equipped with high-power transmitters,
low-noise amplifiers and receivers, and appropriate monitoring and
control systems.
The DSN consisted of three complexes situated at approximately equally
spaced longitudinal intervals around the globe at Goldstone (near
Barstow, California), Robledo (near Madrid, Spain), and Tidbinbilla
(near Canberra, Australia).  Two of the complexes were located in the
northern hemisphere while the third was in the southern hemisphere.
The network comprised four subnets, each of which included one antenna
at each complex.  The four subnets were defined according to the
properties of their respective antennas: 70-m diameter, standard 34-m
diameter, high-efficiency 34-m diameter, and 26-m diameter.
These DSN complexes, in conjunction with telecommunications subsystems
onboard planetary spacecraft, constituted the major elements of
instrumentation for radio science investigations.
    For more information see [ASMAR&RENZETTI1993]