The server provides both RTN coordinates and spacecraft coordinates. RTN is defined with R from the center of the Sun to STEREO. T is along the cross product of the Sun's rotation axis and the R direction so that T is roughly in the direction of planetary motion. N is along the R cross T direction, roughly northward so that the R-N plane contains the Sun's rotation axis. Spacecraft coordinates are defined with X toward the Sun (opposite R of RTN). Y and Z are along the spacecraft Y and Z directions which are oriented to optimize Earth communication and hence the coordinates systems may be oriented in quite different directions on the two observatories.
Three data resolutions are provided in the level 1 Server: 1second, 8 Hz, and 32 Hz burst mode. The 1s data are created from the 125ms data by overlapped averages. The averaged total field is also averaged from the high resolution total field and not from the averaged components.The 32 Hz data is not continuous.
Plots can be drawn in any of the three time resolutions, in either coordinate system and for either spacecraft. The plots can be made to the screen or made in .gif and .ps format to saved digitally.
The magnetic field can be listed in RTN and S/C coordinates, at either of the three time resolutions, in either of the two coordinate systems and for either spacecraft.
A separate web page provides access to GSM coordinates for the Earth Orbit Phase.
All date are diaplayed in UTC and selection is performed in UTC. Underlying the program is a timing convention (single binary word) that keeps track of leap seconds.
Data are available in spacecraft and RTN coordinates beginning November 7, 2006 Since data must be first consolidated during a one month interval and processing is performed one month at a time, data availability is normally two to three months behind real time. If data are needed more rapidly, please use the beacon data that come to Earth and made available in real time.
Correlative solar wind and IMF data from Wind and ACE magnetometers are also available for comparative analysis.
Magnetometer Description Figure 1 shows the IMPACT magnetometer, MAG. MAG is a triaxial fluxgate Magnetometer built at Goddard Space Flight Center to measure the vector magnetic field in two ranges up to 65,536 nT and up to 500 nT with 0.1 nT accuracy. It is a high-heritage instrument, with updated features based on the Messenger magnetometer design (Acuna et al., 2006). The location of the magnetometer near the end of the ~5.8 m IMPACT boom minimizes the contribution of any spacecraft fields to the measurements. In addition, a magnetics cleanliness program was enforced from the beginning of the project in order to provide a minimum cost, intrinsically clean spacecraft from a magnetics perspective. This was achieved by sensitizing instrument and spacecraft providers to materials uses and design and construction practices, by screening particularly troublesome parts such as reaction wheels, and by magnetically “sniffing” the instruments from all investigations prior to their delivery as well as the spacecraft and the integrated system. In addition, magnetic field data were obtained during integration and test phases to keep track of and characterize unavoidable signatures in the MAG data from permanent instrument and spacecraft features, and during spacecraft and instrument commissioning operations. The MAG design, calibration and operation is described in detail in a companion paper by Acuna et al. (in preparation, 2006). Figure 1. Photograph of an IMPACT MAG flight unit on its boom tray. The digital resolution of the 500 nT range of the IMPACT MAG is 16 pT. Signals from the fluxgate sensor are processed by the analog electronics and then fed to the IDPU for interfacing to the spacecraft. These magnetometer raw data are low pass filtered, digitized, averaged, and then formatted into a MAG telemetry packet. The magnetometer has sufficient sensitivity and dynamic range to study the magnetic fields associated with all the phases and regions of interest in the mission. For example, the lower sensitivity range permits MAG operation in the Earth's field without special shields or field cancellation equipment. The limitation of the measurements is the amount of magnetic noise introduced by the spacecraft and its instruments. The nominal accuracy of ±0.1 nT is adequate to achieve the STEREO mission science objectives for the magnetometer. The nominal time resolution of the MAG data is 8 vectors/s, though 32 Hz (~.03 s) vector data are available during the IMPACT burst mode periods described below. Planned spacecraft rolls throughout the mission allow checks on the MAG sensor offsets and calibrations. No regular commanding is needed for MAG.
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Last updated: December 9, 2008