Instrument Information
IDENTIFIER urn:esa:psa:context:instrument:rl.consert::1.1
NAME COMET NUCLEUS SOUNDING EXPERIMENT BY RADIOWAVE TRANSMISSION
TYPE
DESCRIPTION INSTRUMENT OVERVIEW =================== THE COMPLETE CONSERT EXPERIMENT IS COMPOSED OF: - ONE ORBITER PART (ELECTRONICS, ANTENNA, HARNESS) - ONE LANDER PART (ELECTRONICS, ANTENNAS,HARNESS) SCIENTIFIC OBJECTIVES ===================== Our experiment concerns the rough tomography of the comet nucleus performed by the CONSERT instrument. It works as a time domain transponder between one module landed on the comet surface (Lander) and another flying around the comet (Orbiter). The CONSERT signal consists in a 90 MHz sinusoidal waveform which is phase modulated by a pseudorandom code or PSK (phase shift keying) coding. Such frequency, in the radio range, is expected to minimize the losses during the propagation inside the comet material and the generated pulse code maximizes the signal to noise ratio. In these experimental conditions CONSERT will perform a measurement of the mean dielectric properties and on the detection of large size embedded structures or small irregularities within the comet nucleus. CALIBRATION =========== Due to the design of the instrument, there is no special calibration operation mode. The science data are composed of the signal characterising the propagation channel of the comet nucleus as a function of time: - The propagation time is the main data to be inverted and its accuracy is waranted by the Consert clock absolute accuracy and stability. - The signal amplitude can also provide information about the nucleus structure but there is no internal calibration channel to increase the link budget accuracy. OPERATIONAL CONSIDERATIONS ========================== The Lander makes a coherent addition and a detection of the position (delay) of the correlation principal peak. A clean coded signal is finally back emitted to the Orbiter with the found delay. The orbiter accumulates the received signal and sends it to the Earth (via the satellite interface). OPERATIONAL MODES ================= Each scientific measurement sequence (called scanning sequence) involves the Orbiter part and the Lander. The duration of this scan sequence is related to the duration of the orbit of the Rosetta spacecraft relatively to the Lander on the rotating comet nucleus. This duration is typically of the order of 10 hours during one revolution around the nucleus. The individual duration of each sounding is less than one second. This duration of scanning sequence should correspond to the time when the Lander and the Orbiter are separated by the comet. During the direct line of sight periods, where Philae and Rosetta are in visibility of each others, the synchronization occurs. This mandatory and preliminary phase is also called the CONSERT 'tuning'. This means that the duration of the data recording does not correspond to the total time of one revolution, but only for the part where Philae and Rosetta are in occultation by the comet nucleus. The number of samples which theoretically should be taken is given by the following formula: 2 * pi * radius of comet / ( lambda / 2 ) where lambda is wavelength. During the scanning sequence for a hypothetical circular comet with a 750 m radius, about 3000 individual measurements, called soundings should be taken. The general structure of the Consert operational scenario does not depend on the comet type that is explored during the Rosetta mission, however a certain amount of the parameters depends on the shape and size of the comet nucleus and on the orbit of the spacecraft and nucleus rotation. MEASURED PARAMETERS =================== While acquiring the signal which propagates through the comet nucleus, the CONSERT intrument measures the following physical parameters: - Propagation time of one to three peaks (in case of multi-path propagation). - Attenuation of these signal peaks along the propagation channel.
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NAIF INSTRUMENT IDENTIFIER
SERIAL NUMBER not applicable
REFERENCES Kofman, W. et al., The Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT): A Short Description of the Instrument and of the Commissioning Stages, Space Science Reviews, 128(1-4), 431-432, Feb 2007.