NSSDCA ID: 1978-051A-12
Mission Name: Pioneer Venus OrbiterThis experiment used a triaxial fluxgate magnetometer with two ring-core sensors at the end of a magnetometer boom and one ring-core sensor, at 45 degrees to the spin axis, partway down the boom. The drive and electronics design had been used on the Apollo 15 and 16 subsatellites. The objectives of this investigation were to: (1) determine any planetary and remnant magnetic fields; (2) deduce the location and strength of the ionospheric current system; (3) determine the energy and mass balance in the upper atmosphere of Venus; (4) examine the nature of the solar wind interaction with Venus; and, (5) study the near-wake region of Venus and the structure of the Venusian bow shock. Additional objectives for interplanetary (solar wind) studies were to determine the perturbation of the near-planet region by Venus and to compare the properties of the average field at 0.7 and 1.0 AU.
The magnetometer consists of three basic units, the electronics unit mounted inside the main spacecraft bus, an inboard sensor assembly mounted about one-third of the way from the end of a 4.7 meter boom, and an outboard assembly mounted on the end of the boom. The electronics box is magnesium, 15 x 22 x 15 cm in size, and has a mass of 1,7 kg. It includes a 12-bit analog to digital converter. the inboard sensor is 6 x 7 x 6 cm, with a mass of 110 g. It holds a single magnetometer oriented at 45 degrees to the orbiter spin axis. The outboard sensor is 8 x 5 x 4.5 cm, with a mass of 170 g. It comprises two magnetometers, one parallel to the spin axis and one perpendicular. Total mass including wiring is 2 kg, and the system uses 2.2 W at 27 V DC.
The magentometers are triaxial fluxgate type with large loop gain and feedback. The core of the magnetometer is a ring wrapped with permeable metal. The core is surrounded by drive, sense, and feedback coils. A sinusoidal drive voltage with a 7.25 kHz frequency is used, 4 V peak-to-peak and 150 mA. The sense circuit detects the second harmonic of the drive frequency, which is a function of the external magnetic field along the sense axis of the magnetometer ring core. The feedback circuit acts to conceal the field and the output is the measured input to the feedback circuit required to cancel the field. The range of the instrument is 128 gamma, which remains constant, but the resolution can change from 1/16 gamma to 1/2 gamma. The sampling rate can vary by more than two orders of magnitude. The signals flow to the data handling assembly, where it is digitized to 12 bits for each of the three sensors. The 36 bits are compressed to a single 32 bit word by conversion to floating point words.
The instrument was intended to, in the worst case of low-bit and low-sample rates, measure one vector per 32 s. While in Venus orbit, when the spacecraft was coasting through the interplanetary region in the apoapsis mode, the sample rate was one vector per 8 s. While the spacecraft was passing through Venus' ionosphere in the periapsis mode, the sample rate was four vectors per second.
The last full orbit of three-axis data was 3602, which ended on 16 Oct. 1988 at 14:30 UT. After this time, only one-axis data were available.
Mass: 1.8 kg
Power (avg): 2 W
Questions and comments about this experiment can be directed to: Dr. Edwin V. Bell, II
Name | Role | Original Affiliation | |
---|---|---|---|
Prof. Charles F. Kennel | Co-Investigator | University of California, Los Angeles | kennel@uclaph.ucla.edu |
Prof. Paul J. Coleman, Jr. | Co-Investigator | University of California, Los Angeles | |
Prof. George L. Siscoe | Co-Investigator | University of California, Los Angeles | siscoe@buasta.bu.edu |
Prof. Robert L. McPherron | Co-Investigator | University of California, Los Angeles | rmcpherron@igpp.ucla.edu |
Dr. Janet G. Luhmann | Co-Investigator | University of California, Los Angeles | jgluhman@ssl.berkeley.edu |
Dr. Richard C. Elphic | Co-Investigator | University of California, Los Angeles | richard.c.elphic@nasa.gov |