00readme.txt The magnetometers on Vega 1 and Vega 2 (PI: Prof. Willi Riedler) were designed to measure the magnetic field and its low-frequency fluctuations in the cometary and solar wind interaction zone and in interplanetary space. The instrument on each spacecraft consisted of two fluxgate sensor units (one axial and triaxial) mounted 1 m apart on a 2-m boom. The axial unit was oriented along the spacecraft symmetry (X) axis, which was perpendicular to the solar panels and pointed toward the Sun. Each sensor had a dynamic range of ± 100 nT and a sensitivity of 0.05 nT. Magnetic field vectors were measured with a sampling frequency of 10 vectors per second. The magnetometers operated in three data rate modes: 1) the measured components were averaged during 2.5 minutes and transmitted to telemetry; 2) the measured components were averaged during 1 minute and transmitted to telemetry; 3) direct transmission mode, the measured components were transmitted to telemetry without averaging. Cruise phase data were mostly taken in the 2.5-min averaging mode. During the cruise phase from Earth to Venus (12/84-06/85) both Vega-1 and Vega-2 spacecraft had one-axis orientation i.e. the spacecraft X axis was maintained sunward-pointing, while the spacecraft Y and Z axes rotated about the X axis. The spin phase of this rotation was not known, therefore the directions of By and Bz components are unknown. Magnetometer data for this period are presented in spacecraft coordinates as Br (directed radially from spacecraft to the Sun), Bysc, Bzsc. From the providers: "It is proposed to use for analysis of the interplanetary magnetic field during this period the Br component and the total B=sqrt(Bxsc^2+Bysc^2+Bzsc^2). Bysc and Bzsc components are included in the data, but keep in mind that the orientation of these axes is unknown. It can be considered as fixed during periods up to a few hours, so the data can be used to look for IMF discontinues and IMF orientation variations. " After Venus flybys (June, 11-15, 1985) up to Comet Halley (March, 6 and 9, 1986) and sometimes later Vega-1 and Vega-2 had three-axis stabilized orientations. After-Venus magnetic field data are presented in spacecraft-centered solar ecliptic (SE) 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 HelioGraphic Inertial (HGI) system. For a description of this system, see http://nssdc.gsfc.nasa.gov/space/helios/plan_des.html The contents of each of the 2.5-min records - WORD FORMAT MEANING UNITS/COMMENTS 1 I4 Year 1984,1985, etc. 2 I3 Month 1,...,12 3 I3 Day 1...,31 4 I3 Hour 0,...,23 5 I3 Minute 0,...,59 6 I3 Second 0,...,59 7 F7.1 Magnetic field radial (+ to Sun) component, nT 8 F7.1 Magnetic Field Bysc or Byse component, nT 9 F7.1 Magnetic field Bzsc or Bzse component, nT 10 F7.1 Total magnetic field B, nT 11 F7.2 Spacecraft radial distance from Sun, au 12 F7.1 HGI Spacecraft position azimuth, degrees 13 F7.1 HGI Spacecraft position elevation, degrees 14 I2 Flag=1 -magnetic data in SE, =0 - in spacecraft system ------------------------------------------------------------------ Mean hour data are presented in RTN system, spacecraft position in HelioGraphic Inertial (HGI) system. The contents of each of the mean hour records - WORD FORMAT MEANING UNITS/COMMENTS 1 I4 Year 1984,1985, etc. 2 I3 Month 1,...,12 3 I3 Day 1...,31 4 I3 Hour 0,...,23 5 F7.1 Magnetic field radial Br (+ from Sun) component, nT 6 F7.1 Magnetic Field Bt component, nT (9999.9 if no data) 7 F7.1 Magnetic field Bn component, nT (9999.9 if no data) 8 F7.1 Average value of total magnetic field |B|, nT 9 F7.3 Spacecraft radial distance from Sun, au 10 F7.1 HGI Spacecraft position azimuth, degrees 11 F7.1 HGI Spacecraft position elevation, degrees The RTN system is fixed at a spacecraft (or the planet). The R axis is directed radially away from the Sun, the T axis is the cross product of the solar rotation axis and the R axis, and the N axis is the cross product of R and T. At zero Heliographic Latitude when the spacecraft is in the solar equatorial plane the N and solar rotation axes are parallel. ------------------------------------------------------------------ VEGA MAGNETIC FIELD FLYBY PHASE DATA The FLYBY_1M (one minute) and FLYBY_HR (high resolution) files of the magnetic field data contains data for intervals of the closest approach of the VEGA spacecrafts to Halley comet. Files contains the following data: magnetic field data in SE coordinate system (for FLYBY_1M) or in cometocentric (solar) ecliptic coordinates, CSE (for FLYBY_HR) and the position of the spacecraft in CSE. CSE (CometoCentric ecliptic coordinate system) for the SC position: origin at comet position, x-axis from comet to the Sun, z-axis to ecliptic northpole, (x,y)-plane is parallel to the ecliptic plane. CSE coordinate system for the magnetic field data: axes are parallel to the CSE system for the position. This coord. system is valid only for VERY SHORT TIME, about 4 hours around the closest approach of the SC to the Comet, since for a larger angular distance of the SC from the Comet, the direction to the Sun from both objects will be different. The contents of each of before flyby and flyby record - WORD FORMAT MEANING UNITS/COMMENTS 1 I4 Year 1984,1985, etc. 2 I3 Month 1,...,12 3 I3 Day 1...,31 4 I3 Hour 0,...,23 5 I3 Minute 0,...,59 6 F7.1 Second 0,...,59.999 7 F7.1 Magnetic Bx component (SE or CSE), nT 8 F7.1 Magnetic Field By (SE or CSE), nT 9 F7.1 Magnetic field Bz (SE or CSE), nT 10 F7.1 Total magnetic field B, nT 11 F7.2 X spacecraft position, CSE system, km 12 F7.1 Y spasecraft position, CSE system, km 13 F7.1 Z spacerarft position, CSE system, km 14 F7.1 Distance between spacecraft and Halley comet, km ------------------------------------------------------------------ Data were reprocessed in IZMIRAN, contact person: Dr. V.Styazhkin (sva@izmiran.ru) V. Petrov, Sep 2004