{ "Spase": { "xmlns:xsi": "http://www.w3.org/2001/XMLSchema-instance", "xmlns": "http://www.spase-group.org/data/schema", "xsi:schemaLocation": "http://www.spase-group.org/data/schema http://www.spase-group.org/data/schema/spase-2_2_1.xsd", "Version": "2.2.1", "Instrument": { "ResourceID": "spase://SMWG/Instrument/Voyager2/PRA", "ResourceHeader": { "ResourceName": "Voyager 2 Planetary Radio Astronomy (PRA) experiment", "AlternateName": "Voyager 2 PRA", "ReleaseDate": "2019-05-05T12:34:56Z", "Description": "\n The Planetary Radio Astronomy (PRA) experiments' primary \n objective is to locate and explain kilometric, hectometric, and \n decametric radio emissions from the planets, to measure plasma \n resonances near the giant planets, and to detect lightning on \n the giant planets. They have also been successful at observing \n solar radio emissions from the perspective of the outer solar \n system. \n \n The Voyager Planetary Radio Astronomy experiment is designed to \n investigate naturally-occurring radio emissions from the outer \n planets and Sun. Radio emissions from Jupiter have been known \n from Earth-based measurements since 1955 (Burke, B. F., and K. L. Franklin,\n Observations of a variable radio source associated with planet\n Jupiter, J. Geophys. Res., 60, 213–217, 1955.); PRA represents the \n first attempt to survey those emissions, and to perform near- \n encounter searches for radio emissions from the other gas \n planets. \n \n Radio emissions can be used to determine the rate of rotation \n of the inner core of a planet; to determine the existence of a \n magnetic field and search for magnetic anomalies. Radio \n emissions are often the only remote diagnostic for interactions \n occurring in the portions of magnetospheres through which a \n spacecraft does not pass. This is particularly true for the \n inner magnetosphere, which usually goes unsampled. \n \n PRA is also sensitive to impacts on the spacecraft by micron- \n sized dust particles. Particularly in its high data rate modes, \n the information obtained therefrom produces insights into the \n processes which occur under such situations. \n\n Instrument Description \n ====================== \n There were two receivers on each spacecraft, for the\n lower and higher frequency ranges, respectively. The low-band\n receiver had 70 channels of 1.0 kHz bandwidth each, with center\n frequencies spaced at 19.2 kHz intervals from 1.2 kHz to 1326kHz.\n The high-band receiver consisted of 128 channels of 200 kHz\n bandwidth each, with center frequencies spaced at 307.2 kHz\n intervals from 1.2 MHz to 40.4 MHz. The high-band receiver was\n designed especially for the observation of Jovian decametric radio\n emissions.\n \n The PRA receivers were driven by two orthogonal antennas mounted \n on the spacecraft body. Each antenna element is made of BeCu \n hollow tubes 0.5 inches in diameter and is 10 meters in \n length. By combining the signals from the two antennas in a \n 90 degree hybrid, the PRA instrument can distinguish between \n the opposing states, left hand and right hand, of circular \n polarization of an incoming wave. \n \n The Planetary Radio Astronomy (PRA) receivers were calibrated \n under environmentally-controlled conditions and over the \n entire frequency and dynamic range of the instruments. This \n calibration consisted in application of a known narrow-band \n signal across the inputs and recording the receiver outputs. \n \n The laboratory calibrations provided power levels for each \n data number (DN) and each frequency in terms of known inputs \n across the antenna terminals of each of the experiment's two \n monopoles. Calibrations were carried out over a range of \n receiver temperatures, but in practice the stability of the \n receiver as a function of temperature and the stability of the \n temperature of the receiver as a function of mission phase and \n the status of the overall spacecraft were such that a single \n calibration for each DN at each frequency could be used. \n \n Receiver output levels were quantized. The minimum value for \n the wave flux density was frequency dependent varying from \n 5.E-20 W M**-2 Hz**-1 at frequencies below 1.5 MHz to 5.E-19 \n at frequencies above 1.5 MHz. The maximum wave flux density \n was typically 50 dB above the minimum value. The instrument \n noise level also was frequency dependent. It was about 1.E-19 \n W M**-2 Hz**-1 below 1.5 MHz. The noise at 10 MHz was still \n about 1E-19 W M**-2 Hz**-1, increased to about 1.E-17 W M**-2 \n Hz**-1 at 25 MHz, and then decreased to an intermediate value \n at 40 MHz. \n \n The low-band and high-band operation of the receiver differ. \n In low-band the receiver operated with a sharply tuned filter \n only 1 kHz broad at the 3 dB points and in high-band, with a \n 200 kHz filter. The gain of the receivers was designed in such \n a way that the output increased discontinuously by 23 dB \n (corresponding to the 200:1 bandwidth ratio) between the \n lowest frequency of high-band and the highest frequency of \n low-band. This caused the instrument output to remain \n constant across the high-band to low-band transition point if \n its input was broadband noise. \n \n If unpolarized radiation fell orthogonally on each monopole, \n the total unpolarized flux density for signals below about 5 \n MHz could be roughly estimated to be \n \n S = So (10**(m/1000)), \n \n where m was the channel reading in millibels and So is \n \n So = 1.5E-21 (W/Hz m**2). \n \n No reliable method for estimating the flux density exists for \n frequencies above 5 MHz due to the increasing effect of \n antenna resonances. \n \n Although the PRA instrument had 14 possible operating modes, \n in practice the mode called POLLO was used more than 95% of \n the time. In POLLO, the receiver swept through all 198 \n channels in sequence from the highest frequency to the lowest. \n At each frequency step, data were produced every 30 msec, \n consisting of 25 msec of integration and 5 msec of switching \n and settling time. Thus, a full sweep through all 200 channels \n took 6 sec (including 60 msec for two status words). Between \n steps the 90 degree hybrid was switched such that the receiver \n was sensitive to the alternate sense of circular polarization. \n This toggling between left hand and right hand polarization \n itself alternated with each 6 sec receiver sweep. Thus, for a \n given frequency, a pair of left hand and right hand \n measurements were 6 sec apart. \n\n For further details on the PRA instrument see\n Warwick, J.W. et al., Planetary Radio Astronomy Experiment for\n Voyager Missions, Space Science Reviews, 21, 309-327, 1977 and,\n\n Lang, G.J. and Peltzer, R.G., Planetary Astronomy Receiver,\n IEEE Transactions on Aerospace and Elecronics Systems, AES-13, 466-472, 1977.\n \n For further details on calibration see Wang, L. and Carr, T.D.,\n Recalibration of the Voyager PRA antenna for polarization sense\n measurement, Astron. Astrophys., 281, 945-954, 1994. and references therein.\n \n", "Contact": [ { "PersonID": "spase://SMWG/Person/James.W.Warwick", "Role": "PrincipalInvestigator" }, { "PersonID": "spase://SMWG/Person/Joseph.K.Alexander.Jr", "Role": "DeputyPI" }, { "PersonID": "spase://SMWG/Person/Andre.C.Boischot", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Walter.E.Brown.Jr", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Thomas.D.Carr", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Samuel.L.Gulkis", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Fred.T.Haddock", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Christopher.C.Harvey", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Michael.L.Kaiser", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Yolande.Leblanc", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/R.G.Peltzer", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Roger.J.Phillips", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/Anthony.C.Riddle", "Role": "CoInvestigator" }, { "PersonID": "spase://SMWG/Person/David.H.Staelin", "Role": "CoInvestigator" } ], "InformationURL": [ { "Name": "NSSDC's Master Catalog", "URL": "https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1977-076A-10", "Description": "Information about the Planetary Radio Astronomy (PRA) instrument on the Voyager 2 mission." }, { "Name": "PPI/PDS PRA Instrument catalog file PRAINST.CAT", "URL": "https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VG_1601/CATALOG/PRAINST.CAT", "Description": "Information about the PRA instrument on the Voyager mission including operational mode descriptions.\n" }, { "Name": "PPI/PDS PRA Instrument file INST.TXT", "URL": "https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/VG_1501/DATA/PRA/INST.TXT", "Description": "Information about the PRA instrument on the Voyager spacecraft." } ] }, "InstrumentType": [ "SpectralPowerReceiver", "Antenna", "LongWire" ], "InvestigationName": "Planetary Radio Astronomy (PRA) instrument on Voyager 2", "ObservatoryID": "spase://SMWG/Observatory/Voyager2" } } }