On 2006 May 24 NOAA's Geostationary Operational Environmental Satellite (GOES) 13 satellite was launched with the
next generation Solar X-ray Imager (SXI) aboard. This instrument represents a significant step forward in performance
over the previous SXI flown on GOES-12, even before that instrument suffered serious degradation. Like the previous
instrument, the new instrument uses a grazing incidence optical design, but with a new detector and other improvements,
it has about 10 times the sensitivity, twice the spatial resolution, and greatly reduced wide-angle scattering compared to
the GOES-12 SXI. The GOES-13 SXI completed its 6 month checkout period in December 2006. Performance tests
included dark current, flat-field, spatial response, scattered light, pointing stability and jitter. We present initial analyses
and results of these tests as well as comparisons to ground test results. In addition, GOES-13 solar observations are
compared to solar observations by other instruments. When it enters operations, the GOES-13 SXI will provide
continuous, real-time observations of the X-ray Sun at 1-minute cadence.
A jitter compensation system is incorporated in the Solar X-ray Imager
(SXI) that will be mounted to the solar array wing of the GOES N
spacecraft, the next in the series of NOAA weather satellites. The SXI obtains images in a back-thinned CCD with 5 arcsec pixels. The SXI incorporates a pointing aspect sensor manufactured by the Adcole
Corporation that is used in a semi-closed loop system with the SXI
flight computer to shift the detected image during an exposure along the readout columns of the CCD in order to compensate for jitter in one dimension. Simulations of the predicted motions caused by the GOES spacecraft and self-induced by the SXI filter wheels indicate that the jitter as experienced by the SXI instrument will be primarily along one axis, parallel to the east-west direction, with amplitudes in the tens of arcseconds and with dominant frequencies less than approximately 10 Hz. The SXI CCD columns are aligned along this direction in order to make possible on-chip compensation. The SXI motion compensation system has been evaluated with realistic models for the expected spacecraft jitter and assuming a performance algorithm for the SXI instrument. Our analysis indicates that the X-ray spatial imaging performance will be improved when the jitter compensation system is used. We discuss the design and analysis predictions.
The X-ray calibration of the GOES Solar X-ray Imagers (SXI) was accomplished at the component level and at the instrument level. The CCD and thin film filters were characterized in the facilities at the Lockheed Martin Solar and Astrophysics Laboratory. The grazing incidence telescope mirrors and the completed instruments were calibrated at the X-ray Calibration Facility (XRCF) at NASA’s Marshall Space Flight Center. The XRCF consists of an X-ray source at one end of a 518 m long evacuated tube and a large vacuum chamber at the opposite end. The X-ray source has a variety of interchangeable anodes and filters to provide filtered characteristic K- and L-shell line emission in the range from 0.109 to 8.6 keV. The absolute Photometric calibration of the SXI telescopes is very important for analysis and interpretation of their data, and to monitor the long-term solar variations at X-ray wavelengths. This paper describes the results of these calibrations.
A new Solar X-ray Imager (SXI) using back-illuminated, anti-blooming
CCD technology will become part of the instrument complement on
NOAA's GOES (Geosynchronous Orbiting Environmental Satellite) N and
O spacecraft, with probable launch dates beginning in the 2004-2005
time frame. SXI N and O were developed under a NASA contract by the
Solar and Astrophysics Laboratory at the Lockheed Martin Advanced
Technology Center, and are currently being integrated into their
respective spacecrafts by Boeing Space Systems. SXI N and O will
each provide full disk images of the Sun from 0.2 to 1.2 keV (10-60
Å) through the combination of a grazing incidence telescope,
bandpass filters, and an X-ray imaging CCD. The custom designed,
back-illuminated CCDs were fabricated and initially tested by
Marconi Technologies (formerly EEV Ltd, now e2v technologies),
screened in visible light by the Mullard Space Science Laboratory,
and fully characterized in both visible light and X-rays at LMSAL.
By minimizing the field-free region within the CCD, the spatial
resolution at low X-ray energies was significantly improved. The SXI
CCDs also exhibit only very modest response changes as a result of
solar X-ray exposure, based upon extended life tests. The flight
CCDs meet or surpass all specifications for quantum efficiency (QE),
spatial uniformity, defects, charge transfer efficiency, QE
stability in vacuum, read noise, linearity, full well and dark
current. A QE model based on earlier work with ion-implanted,
laser-annealed CCDs provides a consistent picture of the CCD
response from soft X-rays through far UV wavelengths.
We have measured the x-ray imaging performance of a grazing incidence telescope mirror, the HT #17, employing a hyperboloid-hyperboloid design. This design provides improved wide-field imaging compared to an optimally defocused Wolter Type I mirror. This improvement will be advantageous for future Geostationary Operational Environmental Satellite (GOES) missions that will provide full disk images of the sun with the Solar X-ray Imager (SXI). The x-ray measurements were made in the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center and the results are presented here.
Beginning in 2002, a new Solar X-ray Imager (SXI) will become part of the instrument complement on NOAA's GOES N and O spacecraft. The SXI is being developed under a NASA contract by the Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) within the LM Advanced Technology Center. The SXI will provide full disk images of the Sun from 0.2 to 2 keV through a combination of a grazing incidence telescope, bandpass filters, and a back-illuminated CCD. The CCDs are begin fabricated by EEV Ltd., screened by the Mullard Space Science Laboratory, and tested in x-rays by LMSAL. Early evaluation of test devices will be crucial in selecting the optimum backside treatment process for the flight CCDs, specifically with regard to quantum efficiency, spatial resolution, and the high dose of solar x-rays that the detector will experience over the course of SXI's 5 year mission life. In this paper, we describe results from an initial series of such test and the implications for the SXI mission.
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