RSS: Radio Science Subsystem
The Radio Science Subsystem (RSS) uses the spacecraft X-band communication link, an S-band downlink and a Ka-band uplink and downlink to study compositions, pressures, and temperatures of atmospheres and ionospheres, radial structure and particle size distribution within rings, body and system masses, and gravitational waves.
Radio science experiments use the spacecraft radio system and ground antennas as the science instrument. These experiments measure the refractions, Doppler shifts, and other modifications to radio signals that occur when the spacecraft is occulted by planets, moons, atmospheres, and physical features such as planetary rings. From these measurements, scientists can derive information about the structures and compositions of the occulting bodies, atmospheres, and rings.
RSS Scientific Objectives
- To search for and characterise gravitational waves coming from beyond the solar system
- To study the solar corona and general relativity when Cassini passes behind the Sun
- To improve estimates of the masses and ephemerides of Saturn and its satellites
- To study the radial structure and particle size distribution within Saturn's rings
- To determine temperature and composition profiles within Saturn's/Titan's atmospheres
- To determine temperatures and electron densities within Saturn's/Titan's ionospheres
RSS Instrument Description
The RSS consists of a Ka-band traveling wave tube amplifier, a translator, an exciter; an S-band transmitter; and various microwave components.
The purpose of the Ka-band traveling wave tube amplifier (K-TWTA) subassembly is to amplify the signals going to the high-gain antenna to the power level necessary for them to be received by the Deep Space Network. The K-TWTA subassembly consists of the a traveling wave tube (TWT) and an electronic power conditioner (EPC). The non-redundant TWT is the signal amplifier. It can be commanded into a standby mode for low d.c. power consumption. The EPC converts d.c. power from the Power and Pyrotechnic Subsystem (PPS) to the voltages required to operate the TWT. It can power the TWT in the standby mode or power down the TWT in case of TWT or EPC fault detection. The EPC also supplies engineering telemetry to the RFS and provides direct-access signals.
The Ka-band translator (KAT) subassembly receives the 34 GHz uplink carrier from the high-gain antenna and translates it by a factor of 14/15 for retransmission back to the DSN. The phase and phase-shift of the signal are used for the actual science observations and measurements. The KAT contains a power converter that allows it to operate from the 30 Volt DC power bus. It also supplies engineering telemetry data to the RFS and provides for direct access.
The Ka-band exciter (KEX) generates a stable 32 GHz signal and provides an RF power combiner to combine the RF signal generated by the KAT with its own signal. It is powered by the 30 Volt spacecraft bus, and it supplies telemetry data to the RFS and provides direct access.
The S-band transmitter (SBT) receives a 115 MHz signal from the RFS, multiplies it by 20, amplifies it to 10 watts, and supplies the resultant signal at approximately 2290 MHz to the high-gain antenna. This carrier signal is used for radio science experiments. The transmitter contains a power converter to allow operation from the 30 volt power bus, and it supplies telemetry data to the RFS and provides direct access.
The microwave components consist of two band pass filters (BPFs) and waveguide components. BPFs are filters that allow only certain wavelengths of microwave energy to pass, with all other wavelengths being blocked. In this case, the BPFs permit reception and transmission of the Ka-band signals using different antenna feed polarizations and provide isolation between the transmit and receive frequencies. Waveguide is essentially tubing of precise dimensions that provides a path for microwave energy of a certain wavelength. In this subsystem it is used for all Ka-band microwave component interconnections.
Last Update: 25 February 2005