PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 1977-12-01 NOTE = "INST.TXT contains the instrument description." END_OBJECT = TEXT END INSTRUMENT: PLASMA WAVE RECEIVER SPACECRAFT: VOYAGER 1 Instrument Overview =================== Instrument Id : PWS Instrument Host Id : VG1 Principal Investigator : DONALD A. GURNETT Pi Pds User Id : DGURNETT Instrument Name : PLASMA WAVE RECEIVER Instrument Type : PLASMA WAVE SPECTROMETER Build Date : UNK Instrument Mass : 1.400000 Instrument Length : 0.318000 Instrument Width : 0.185000 Instrument Height : 0.048000 Instrument Serial Number : SN002 Instrument Manufacturer Name : UNIVERSITY OF IOWA The Plasma Wave Receiver on Voyager consists of both a 16_channel spectrum analyzer covering the range of 10 Hertz to 56.2 kiloHertz and a wideband waveform receiver which returns the waveform of waves in the frequency range of 40 Hertz to 12 kiloHertz. The spectrum analyzer provides data on a continual basis with a maximum temporal resolution of one spectrum per 4 seconds. The waveform receiver returns 4- bit samples of the electric field measured at a rate of 28,800 samples per second. Because of the very high data rate, the waveform samples must be transmitted in the same manner as the Voyager imaging information. At Jupiter, some 10,000 48-second waveform frames were obtained. At Saturn, the number of frames obtained was very small due to the lower telemetry rates available at the greater distance of that planet. Science Objectives ================== The primary science objective of the Voyager plasma wave investigation is to make the first surveys of the plasma wave and low frequency radio wave spectra in the magnetospheres of the outer planets: Jupiter and Saturn. Plasma waves participate in a fundamental manner in the dynamics of planetary magnetospheres and in the interactions of that magnetosphere with the external solar wind and internal perturbations such as those induced by satellites interior to the magnetosphere. Plasma waves also provide diagnostic information about the plasma environment near the planets including such parameters as electron density and sometimes temperature. The instrument is also sensitive to low frequency radio emissions and, therefore, acts as a low frequency extension to the Planetary Radio Astronomy investigation. Radio waves are often the only means of remotely observing regions of plasma not accessible to the spacecraft and also lead to remote diagnostics of plasma conditions. The plasma wave receivers are also sensitive to the results of small dust particles impacting on various parts of the spacecraft at high velocities and, hence, provide a direct measure of the rate of impact, the density of the dust, and an estimate of the mass distribution of dust in the vicinity of the large planets, especially those with rings and otherwise dusty environments. Finally, the Plasma Wave Receiver will characterize the plasma wave and radio wave spectrum of the outer heliosphere and perhaps beyond, extending our understanding of solar wind plasma processes and wave-particle interactions to several tens of Astronomical Units. Operational Considerations ========================== The primary operational considerations of the PWS include maintaining the proper operating mode and obtaining waveform samples as often as the spacecraft tape recorder/downlink capabilities allow. The standard instrument mode is with Waveform Power On and Input Gain State Hi. For encounter periods, this corresponds to GS3GAINHI/WFMPWRON. Since there has never been a period when the signal levels were so high as to require the Low input gain state, and it is highly unlikely that such levels will ever be encountered, Low Input Gain State should never be selected. As long as there is power margin available, it is most straightforward to leave the Waveform Receiver Power on. The power consumption is less than 0.5 Watt for this section, hence, the power savings afforded by turning it off is not large. The most involved operational consideration is providing for the transmission of waveform data to the ground. At Jupiter, the majority of the waveform data could be sent directly to the ground via the 115200 bps downlink. This capability disappeared after Jupiter, however, because of the greater distance to the spacecraft, hence, lower telecon rates. Since operating the A/D converter at a rate less than 28800 Hertz would result in aliasing, it is necessary to record the data at the 115200 bps rate on the spacecraft tape recorder using the appropriate data mode and playback the recorded data at a lower rate, commensurate with the link capabilities. Again, a choice of the proper playback mode is required. Since the data modes available on the spacecraft are highly dependent on mission phase, these modes are not described here. Calibration Description ======================= The Voyager plasma wave receiver spectrum analyzers were calibrated by first establishing a relationship between input voltage (of a sine wave at the filter center frequency) and output voltage and second by measuring the effective bandwidth of the filter. The bandwidth is measured by applying a random noise signal of known spectral density and by measuring the output voltage which, by the first part of the calibration, is related to the rms voltage of a sine wave. Dividing the equivalent sine wave voltage squared by the input spectral density gives a bandwidth. This procedure is repeated for each of the frequency channels. 'PWS ANTENNA' Detector ====================== Detector Type : DIPOLE ANTENNA Nominal Operating Temperature : 298.000000 The PWS uses a pair of 10 meter antenna elements as a balanced dipole antenna. The two elements are extended from the spacecraft at right angles to each other. (The elements are shared with the Planetary Radio Astronomy instrument, which uses them as a pair of monopoles so that measurements of the degree of right and left hand circular polarization can be made.) The PWS measures the voltage difference between the two elements which, when coupled with the effective length of the antenna system (7.07 m) yields an electric field strength in units of volt/meter. The antenna system has the usual dipole antenna pattern which yields nearly 4*pi steradians in its field of view, although there is a range of fields of view where the detector response drops dramatically as one expects from a dipole pattern. The PWS antenna, used as a balanced dipole with an effective length of 7.07 meters gives a sensitivity to fluctuating (wave) electric fields down to the range of 5.E-6 volt/meter. Even though the antenna elements are extended orthogonally to each other, the antenna pattern is still a dipole since the elements are short with respect to the wavelengths of the waves. The presence of the various parts of the spacecraft in close proximity to the antenna can result in a distorted pattern, but this has not been studied in the frequency range of the PWS. Electronics =========== The PWS electronics system consists of three basic sections. The first is the power supply system which regulates and filters the 28 volt, 2400 Hertz spacecraft power supply and provides DC voltages to the remainder of the instrument electronics. The second section is the spectrum analyzer which consists of two banks of 8 narrowband filters, and two logarithmic detectors, each of which provides an analog voltage proportional to the log of the signal strength delivered to the detector from any of the eight filters it services. The analog outputs from these two compressors, as they are called, are sent to the Flight Data System of the spacecraft for conversion to an 8-bit digital value. The spacecraft steps the inputs to the two compressors periodically (once per 0.5 seconds in GS3 or encounter mode) so that signal strengths in each of the 16 channels is measured over a 4-second interval. The third section consists of a single broadband filter of 40 Hertz to 12 kiloHertz, an automatic gain controlled amplifier, and a 4-bit A/D converter. This section digitizes the electric field waveform at a 28800 Hertz rate. The output amplitude is controlled by the automatic gain control in order to keep the signals within the useful range provided by the 4-bit digitization. Section 'SA' ------------ Total Fovs : 1 Data Rate : 32.000000 Scan Mode Id : 4.0 Sample Bits : 8 'SA' Detectors -------------- PWS ANTENNAS 'SA' Section FOV Shape 'DIPOLE' ------------------------------- Section Id : SA Fovs : 1 Horizontal Fov : 360.000000 Vertical Fov : 180.000000 'SA' Section Parameter 'WAVE ELECTRIC FIELD INTENSITY' ------------------------------------------------------ A measured parameter equaling the electric field strength in a specific frequency passband (in MKS unit: VOLTS/METER) measured in a single sensor or antenna. Instrument Parameter Name : WAVE ELECTRIC FIELD INTENSITY Sampling Parameter Name : TIME Instrument Parameter Unit : VOLT/METER Minimum Instrument Parameter : 0.000005 Maximum Instrument Parameter : 0.500000 Minimum Sampling Parameter : 197709051420.000000 Noise Level : 0.000005 Sampling Parameter Interval : 4.000000 Sampling Parameter Resolution: 4.000000 Sampling Parameter Unit : SECOND Section 'WFRM' -------------- Total Fovs : 1 Data Rate : 115200.000000 Scan Mode Id : .055 Sample Bits : 4 'WFRM' Detectors ---------------- PWS ANTENNA 'WFRM' Section FOV Shape 'DIPOLE' --------------------------------- Section Id : WFRM Fovs : 1 Horizontal Fov : 360.000000 Vertical Fov : 180.000000 'WFRM' Section Parameter 'ELECTRIC FIELD COMPONENT' --------------------------------------------------- A measured parameter equaling the electric field strength (e.g. in milli-Volts per meter) along a particular axis direction. Instrument Parameter Name : ELECTRIC FIELD COMPONENT Sampling Parameter Name : TIME Instrument Parameter Unit : VOLT/METER Minimum Instrument Parameter : 0.000005 Maximum Instrument Parameter : 0.500000 Minimum Sampling Parameter : 19771213021723132.000000 Noise Level : 0.000005 Sampling Parameter Interval : 0.000035 Sampling Parameter Resolution: 0.000035 Sampling Parameter Unit : SECOND Operating Modes 'GS3GAINHI/WFMPWRON' ==================================== Data Path Type : REALTIME Gain Mode Id : HIGH Instrument Power Consumption : 1.600000 The PWS instrument gain is high and the waveform receiver power is on. This is the normal encounter operating mode of the instrument and places it in its most sensitive input gain state with the waveform receiver section turned on. The fact that the waveform receiver power is on does not guarantee that waveform data is available. The spacecraft is in the GS-3 data mode which cycles the plasma wave spectrum analyzer so that a complete spectrum is obtained every 4 seconds. Mounted On Platform 'SPACECRAFT BUS' ==================================== Cone Offset Angle : UNK Cross Cone Offset Angle : UNK Twist Offset Angle : UNK The PWS is mounted on top of the Planetary Radio Astronomy experiment on top of spacecraft bus bays 8 and 9. The two orthogonal antenna elements are attached to the Planetary radio astronomy package.