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37.9 Instrument and Spacecraft Errors

All HST science observations are first received on the ground at White Sands, New Mexico, and are then relayed by satellite to the DCF (Data Capture Facility, after January 1996, PACCOR), Goddard Space Flight Center, Maryland. The DCF staff perform a check of the transmission using a Reed-Solomon error checking routine. When Reed-Solomon is used, the data are encrypted into a cyclic pattern. The down-linked data are then decrypted and the Reed-Solomon code will verify the pattern and corrects, if possible, those words that are not as expected. If any packets are missing, DCF will wait for the next STR (space tape recorder) dump to verify no more data packets are forthcoming. Missing data packets and the results of the Reed-Solomon check are written to the data quality accounting capsule (QAC). The data packets and QAC are transmitted to the pipeline.

Each GHRS observation set was processed through the pipeline as far as generic conversion. The output of generic conversion is what users refers to as the raw uncalibrated dataset. Furthermore, the pipeline automatically ran the calhrs software to calibrate science files, such as ACCUMs, RAPIDs, and SPYBALs. Any ACQuisition files, IMAGEs, and DEFCALs are not calibrated.

Each science data file (.d0h), extracted data file (.x0h), and target acquisition (.d1h) have a corresponding data quality file containing flags or fill values for bad data. These quality files (.q0h,.xqh,.q1h) were created during pipeline processing and contain information extracted from the QAC or were filled during the data evaluation process. For each data point in the .d0h, .x0h, or .d1h file, there is a corresponding data point in the quality file. For each good data value, the corresponding point in the quality file is zero. If there are missing data (data-dropout), due to tape recorder flips, down link problems, or data loss due to unforeseen problems, the pipeline will pad the corresponding data file with fill data; the corresponding data point in the quality file was set to 16. If the data failed the Reed-Solomon error check, the corresponding data point in the quality file was set to one. Data that fails the Reed-Solomon check were classified as suspect, and may not be bad data.



Quality Value

Description

0

Good data point

1

Reed-Solomon error

16

Fill data

Pipeline Data Quality Values



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