User-Created Atmospheric Drag File or ASCII JR File
For FreeFlyer users that wish to generate their own atmospheric drag data for use in Jacchia-Roberts or MSIS models, an ASCII form of the data file can be supplied. Detection of a files content for binary versus ASCII is automatic. The ASCII formats of the file are collectively referred to as ASCII JR.
The data within the ASCII JR can be represented in several ways. Exospheric temperatures can be expressed directly as either exospheric temperature or as F10.7 values. Geomagnetic indices can be expressed as Kp on three hour centers or Ap on daily centers. All four possible combinations are supported. If the file provides F10.7 and/or Ap, the ingestion process will convert these values into exospheric temperature and Kp, respectively for use internally in the atmospheric density and drag computations. Since conversion of F10.7 to Exospheric temperature requires an 81 day average of F10.7 centered on the day in question, conversions for the first 40 days shall use the value given for the first day for all days prior, and likewise the value given for the last day for all days post.
The ASCII JR format requires two header lines. The first required line is the designation "JR File". The second required line begins with either the keyword "Temperature" or "F10.7", and following this will be either the keyword ‘Kp’ or ‘Ap’. Following the header lines are the data lines organized with a line per day. The data lines begin with a date followed by a set of floating point numbers. Fixed floating-point representation is supported with optional decimal point for whole numbers. All items must be delimited by white space (space or tab). The dates are represented as UTC calendar dates in the MMM D YYYY format (reference EpochScan event). Note the data within the file must be from first day to last day with every day specified. Breaks in the data will cause execution error when drag calculations need to be processed on or beyond the missing day. Following the date is the first floating point number that represents either the Exospheric Temperature or F10.7 value as specified in the header. If Kp values have been specified then the next eight floating point numbers specify the Kp values at 3-hour centers throughout the day starting at 00:00 UTC. If Ap values have been specified then the next single floating point number specifies the Ap value centered on the day.
Leading white space is permitted on all lines. Trailing characters following the required data are permitted on all lines and are ignored during the file ingest process. These are to accommodate trailing comments. Blank lines are permitted and ignored. Lines with the first non-white space character pattern of "//" are also ignored. These are to accommodate comment lines.
Two examples of the ASCII JR file are included with FreeFlyer: JR_ASCII_sample_Flux_Kp.dat and JR_ASCII_sample_Temp_Ap.dat.