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
