FEDSAT Information
Contents
FEDSAT and the CRCSS
FEDSAT is a Low Earth Orbit (LEO) micro-satellite built by the Australian Cooperative Research Centre for Satellite Systems (CRCSS). The satellite was launched from Tanegashima Space Centre on 14 December 2002 into a 10:30 Local Time sun-synchronous polar orbit at just over 800km altitude. Onboard the satellite carries a range of scientific and engineering payloads, one of which is the NEWMAG triaxial (vector) magnetometer.
The CRCSS was a joint venture of four Australian companies, six Universities and two government agencies. It was established 1 January 1998 under the Commonwealth' Cooperative Research Centres Program. The Centre carried out research and development, education, training, operations and commercial activities relating to space technologies, particularly in the field of low-cost satellite missions. FEDSAT was the CRC's first major project and was the first satellite built in Australia in over thirty years.
NEWMAG Magnetometer
The NEWMAG magnetometer experiment onboard FEDSAT consists of a very sensitive and rapid sampling triaxial fluxgate magnetometer mounted at the end of a 2.5 metre boom for measuring the strength of the Earth's magnetic field, as well as a star-camera for accurate attitude determination.
The Principle Investigator of the NEWMAG experiment is Professor Brian Fraser of the Centre for Space Physics, University of Newcastle, Australia.
NEWMAG measures the main geomagnetic field vector and the three components of the AC magnetic field in the Ultra Low Frequency (ULF) range, from 0.1 Hz to 50 Hz. The aim is to observe naturally occurring electromagnetic wave signatures and field-aligned currents in the ionospheric F-region and the exosphere. These include ULF waves propagating in the F2 region ionospheric waveguide, and turbulence and other signatures associated with field aligned currents at auroral latitudes and the equatorial electrojet. All these data contribute to Solar Terrestrial Physics research within the Space Physics Group of the University of Newcastle (Australia), global space weather studies and international solar terrestrial physics programs. Measurements of the geomagnetic field over Australia will contribute to mapping the geomagnetic reference field. NEWMAG is based on a space proven design from the University of California, Los Angeles (UCLA) which has been flown on the FAST mission. It comprises a three axis orthogonal fluxgate magnetometer and associated electronics. The magnetometer sensors have a dynamic field measuring range of 65536nT with a resolution of 8nT.
For further information on the NEWMAG payload onboard the FEDSAT satellite please visit the University of Newcastle Centre for Space Physics.
Blackjack GPS
The Blackjack GPS receiver onboard FEDSAT is used for precise orbit determination of the spacecraft, accurate real-time positioning, precision timing reference, and for study of the propagation characteristics of GPS signals through the earth's atmosphere and ionosphere, derivation of ionospheric Total Electron Content (TEC) and temperature and pressure profiles for the lower atmosphere. These parameters are invaluable for the study of space weather and terrestrial weather.
WDC Summary plots
Summary data plots of FEDSAT and NEWMAG data are available through the WDC FEDSAT summary plot page. For display purposes, the summary plots are degraded in time resolution by resampling to a time resolution of 10 seconds. NEWMAG data is nominally recorded at 10Hz (0.1s resolution) with high data rate burst intervals of 100Hz data (0.01s resolution). Processed NEWMAG data at 10Hz resolution is available by Data Request to the FEDSAT/NEWMAG experiment Principle Investigator via the WDC.
Also available in summary plot form on the FEDSAT summary plot page is FEDSAT ephemeris showing the Latitude/Longitude position of FEDSAT at any point in time. Altitude is not shown in the summary data. Due to the circular orbit of FEDSAT, the mean altitude of the FEDSAT orbit is 810 +/- 10km. The position summary plot shows only the location of FEDSAT for those time intervals when there exists Newmag magnetic field data.
Summary plots of data from the GPS or COMMS payloads onboard FEDSAT are not currently available through the FEDSAT summary plot facility.
WDC online summary plots of FEDSAT data are unchecked, degraded-resolution summary plots which are not suitable for publication.
Data availability
Following the launch of FEDSAT on 14 December 2002, and a subsquent period of in-orbit comissioning, data from the various payloads is available from 15 January 2003. FEDSAT is still in operation and apart from the Star Camera which failed in January 2005, all payloads are functioning normally.
Throughout the FEDSAT data archive there are intervals of missing data due to operational reasons, telemetry drop-outs, attitude instability or missing attitude information. The table on the WDC FEDSAT data availability page provides a broad overview of the availability of FEDSAT and FEDSAT payload data in the WDC, however to check on the availability and quality of various data sets over specific intervals, please use the online FEDSAT summary plot facility to view summary plots of the data over the interval of interest.
NEWMAG: In its initial configuration, NEWMAG was operated for half-orbit intervals from 15 January 2003 - 21 July 2003. From 21 July 2003, NEWMAG has been operated continuously. Intervals of 10Hz NEWMAG data are available through the WDC.
GPS: Data from the GPS payload onboard FEDSAT are not currently available through the WDC.
COMMS: Data from the COMMS and COMPUTING payloads onboard FEDSAT are not currently available through the WDC.
Data reference frames
The FEDSAT orbital frame has components defined as follows:
- X - Normal to the orbital plane, completes the R.H orthognal set
- Y - Parallel to the satellite velocity vector, perpendicular to Z, in the satellite orbital plane
- Z - Parallel to the vector connecting the satellite and the Earth centre, Postitive away from Earth
FEDSAT position data {r, theta, phi} is recorded in an Earth-Centred Spherical Geographic (ESG/ECEF) Reference Frame in units of {km,deg,deg}. This reference frame has components defined as follows:
- r - radial distance from Earth centre (R=0 at centre of Earth)
- theta - Co-latitude, angle from North Pole (theta=0 at North Pole)
- phi - Longitude, angle from Greenwich meridian (phi=0 at Greenwich meridian)
NEWMAG vector magnetic field data {Br, Btheta, Bphi} is recorded in a Local Spherical Geographic (LSG) Reference Frame in units of nT. This is an orthogonal reference frame centred on the satellite, with components defined as follows:
- Br - Parallel to the vector connecting the satellite and the Earth centre. Positive away from Earth.
- Btheta - Perpendicular to Br, in the local meridian plane. Positive South.
- Bphi - Completes orthogonal set of axes, perpendicular to local meridian plane. Positive East.
Timing, position and attitude accuracy
Timing
Unless otherwise indicated (in the timing quality flag), the accuracy of the timestamp is 0.005s.
Position
FEDSAT position data included in the NEWMAG CDF data files is calculated using the NORAD SGP4 orbital model, with the appropriate Two-Line-Element (TLE) from NORAD. NORAD publishes new element sets for FEDSAT on average once every 1-2 days. FEDSAT has a Blackjack GPS receiver onboard which can provide precise positioning, however this data is not currently available through the WDC.
Spacecraft Attitude
Standard FEDSAT data products requiring attitude information (eg NEWMAG) in general rely on the
onboard Attitude Control System (ACS) for their attitude information. The accuracy of the ACS however is thought to be no
greater than 5 degrees, especially at times of large and rapid variations in spacecraft orientation. Note, however that the
estimation of (for example) Field Aligned Current (FAC) magnitudes relies on the differential of the magnetic field component
perpendicular to the main field as the satellite passes through the FAC region which is not sensitive to the comparatively slow
variations introduced by inaccuracies in satellite attitude.
For those intervals where ACS attitude data is not available, the 'ideal' (designed orbit) attitude is assumed to hold true. Those data
points are flagged with a value of ' 1 ' in the data quality flag 'rfFlag'
(see NEWMAG Data Quality Flags), which otherwise contains a value of ' 0 '.
NOTE: For those intervals, the vector magnetic field data must be treated with caution as deviations from the 'ideal'
pointing may have occurred.
For specific periods between January 2003 and January 2005 there exists in addition to ACS attitude information, data from a Star Camera mounted on the body of the satellite. This enables determination of satellite attitude to an accuracy of ~ 1 degree. However at this stage Star Camera data is not routinely used in the processing of NEWMAG data, and is not currently available through the WDC.
Current work on the NEWMAG payload is addressing the issue of quantifying more accurately the precision of the ACS using data from the onboard Star-Camera.
NEWMAG Data file naming convention
CDF-format FEDSAT/NEWMAG data files use the following file naming convention:
FS[L,H]yymmddpp.CDF
where:
- FS = FedSat
- [L,H] = Either L for Low (standard) time resolution NEWMAG data files - sampling rate of nominally 10Hz, or H for High time resolution NEWMAG data files containing intervals of data recorded at the burst sample rate of 100Hz.
- yy = 2 digit Year
- mm = 2 digit Month
- dd = 2 digit Day Of Month
For example, the filename of the low resolution Fedsat/NEWMAG CDF data file for 12 October 2003 would be FSL031012pp.CDF.
NEWMAG Data file format
NEWMAG data is stored in Common Data Format (CDF). CDF is a widely-used data format designed by the National Space Science Data Center (NSSDC) at NASA/GSFC. For a detailed description of this format please see the CDF homepage at http://cdf.gsfc.nasa.gov/. Read programs specific for NEWMAG CDF data are available on request. These read programs are written as functions in the Interactive Data Language (IDL). A description of the NEWMAG CDF data structure and its variables is shown below.
Each NEWMAG CDF-format data file contains the following variables:
| CDF Variable | Description | Units | Data Type |
|---|---|---|---|
| Year | Year | ARRAY of BYTE | |
| DOY | Day of Year | ARRAY of UINT | |
| UT time | Universal timestamp in milliseconds of day | ms since 00 UTC | ARRAY of ULONGINT |
| Br | NEWMAG Magnetic Field component 1 * | nT | ARRAY of FLOAT |
| Btheta | NEWMAG Magnetic Field component 2 * | nT | ARRAY of FLOAT |
| Bphi | NEWMAG Magnetic Field component 3 * | nT | ARRAY of FLOAT |
| r | FEDSAT Range * | km | ARRAY of FLOAT |
| theta | FEDSAT Co-latitude * | degrees | ARRAY of FLOAT |
| phi | FEDSAT Longitude * | degrees | ARRAY of FLOAT |
| timeFlag | [flag not implemented] | ARRAY of UINT | |
| dataFlag | [flag not implemented] | ARRAY of UINT | |
| posFlag | ACS Pointing error flag | ARRAY of UINT | |
| rfFlag | Reference frame transform flag | ARRAY of UINT |
* See Data Reference Frames.
NEWMAG Data quality flags
The following data quality flags are included in NEWMAG CDF-format data files. Each flag is a binary array, taking a value of 0 or 1 for each data point:
| Data Flag | Description | Details |
|---|---|---|
| timeFlag | Timing quality flag | (not implemented) |
| dataFlag | Magnetic field data quality flag | (not implemented) |
| posFlag | Pointing/Attitude accuracy | 0 if the Attitude Control System (ACS) indicates the attitude/pointing-direction is within 1 degree of the designed orbit. 1 if the ACS indicates the attitude/pointing-direction deviates more than 1 degree from the designed orbit. Note: this is NOT an accurate monitor of the pointing accuracy, but is included as a guide. |
| rfFlag | Model attitude or ACS attitude? |
0 for those magnetic field data values that have been rotated into the LSG reference frame using ACS-derived quaternions. 1 for those magnetic field data values that have been rotated using a model of the spacecraft pointing (designed orbit). Note: caution must be exercised when using vector magnetic field data with rfFlag=1 as deviations from the 'ideal' pointing may have occurred. |
FEDSAT Data policy (Rules-of-the-road)
FEDSAT data may be used for scientific purposes in line with a set of data usage Rules of the Road (or PDF).
WDC online summary plots of FEDSAT and NEWMAG data are unchecked, degraded-resolution summary plots, not suitable for publication.
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