Magnetic field experiment on Vega - 1 and 2 spacecraft.

     A unique opportunity to combine missions to Venus and Comet Halley was available in 1985-1986. This mission was being conducted by the USSR with the cooperation of a number of other countries. Two spacecrafts, Vega-1 and Vega-2 have been launched aboard Proton rockets from Baykonour on 15 and 21 December 1984, respectively. Full description of Vega mission is available here

   The prime objective of the magnetometer experiment MISCHA (Magnetic field in Interplanetary Space during Comet Halley's Approach) carried by Vega - 1 and Vega - 2 was to determine the role of the magnetic field in the interaction between the solar wind and the comet and to identify the characteristic boundaries of the cometary environment (bow shock, contact surface, etc.). For magnetic field measurement two-sensor fluxgate system was used. . The advantage of this dual-sensor fluxgate system is possibility to determine the spacecraft's stray magnetic field. Ttriaxial sensor was mounted on a boom at the end of the solar panel and one axial sensor mounted on meter closer it to the spacecraft (spin) axis. The instrument had a dynamic range of ± 100 nT and a sensitivity of 0.05 nT. It measured magnetic field vector with a sampling frequency of 10 vectors per second.

   Magnetometers operated in three data rate modes. Trassa-1 mode: the measured components were averaged during 2.5 minutes and transmitted to telemetry; Trassa-2 mode: the measured components were averaged during 1 minute and transmitted to telemetry; DT-65 mode: direct transmission mode, the measured components without averaging were transmitted to telemetry.
During the cruise phase from Earth to Venus both Vega-1 and Vega-2 spacecrafts had one-axis orientation i.e. Bx of magnetometer was directed to the Sun, By and Bz axes were rotated around Bx-axis. The rotation of the spacecrafts along X axes was not controlled, therefore the directions of By and Bz components are unknown. Magnetometer data for this period are presented in spacecraft coordinate system Br (directed radially from spacecraft  to the Sun) which almost coincides with X axes of the spacecraft-centered solar ecliptic coordinate  system , Bysc, Bzsc. It is proposed to use for analysis of interplanetary magnetic field during this period  Br - component, and total Bt = sqrt((Br^2+Bysc^2+Bzsc^2). Bysc and Bzsc components also included in data, but put in mind that orientation of these axes is unknown. The orientation of these axes can be considered as fixed during periods up to a few hours, so data can be used to look for IMF discontinues and  IMF orientation variations.

    After flyby Venus (June 1986) up to comet Halley and to the end of mission Vega-1 and Vega-2 had three-axes stabilized orientation. For analysis of IMF during this period, magnetic field measurements are presented in in spacecraft-centered solar ecliptic coordinate system as Br, Bzse, Byse, B, where Br is directed from the spacecraft to the Sun, Bzse is directed along Bz axes of the Solar Ecliptic system (to ecliptic pole), Byse completes the right handed set and B=sqrt(Br^2+By^2+Bz^2).

   Spacecraft position data are presented in HGI  and SE systems. Before Halley comet flyby and flyby data are presented in CSE system.
 

Vega-1 magnetic data for 1984

Vega-1 position data for 1984

#

Vega-1 magnetic data for 1985

Vega-1 position data for 1985

Vega-2 magnetic data for 1985

Vega-2 position data for 1985

#

Vega-1 magnetic data for 1986

Vega-1 position data for 1986

Vega-2 magnetic data for 1986

Vega-2 position data for 1986