Modeling Drag

• 1976 Standard. A table look-up model based on the satellite's altitude. Valid range is 86 km to 1000 km.

• CIRA 1972. Empirical model of atmospheric temperature and densities as recommended by the Committee on Space Research (COSPAR). Similar to the Jacchia 1971 model but uses numeric integration rather than interpolating polynomials for some quantities. Lower altitude boundary is 90 km.

• DTM 2012. The Drag Temperature Model (DTM), 2012 version, is a semi-empirical model which computes the temperature, density, and composition of the thermosphere. Developed at CNES. Valid range is 120 km to 1500 km.

• Harris-Priester. Takes into account a 10.7 cm solar flux level and diurnal bulge. Valid range is 0 km to 1000 km.

• Jacchia 1960. An earlier model by Jacchia that uses the solar cycle to predict a value for the F10.7 cm flux and accounts for the effects of the dirunal bulge. Lower altitude boundary is 0 km.

• Jacchia 1970. The predecessor to the Jacchia 1971 model. Valid range is 90 km to 2500 km.

• Jacchia 1971. Computes atmospheric density based on the composition of the atmosphere, which depends on the satellite's altitude as well as a divisional and seasonal variation. Valid range is 100 km to 2500 km.

• Jacchia-Roberts. Similar to Jacchia 1971 but uses analytical methods to improve performance. Lower altitude boundary is 90 km.

• Mars GRAM models. MarsGRAM 3.7, MarsGRAM 2000, MarsGRAM 2001, MarsGRAM 2005, MarsGRAM 2010. (see below)

• MSIS models. MSIS 1986, MSISE 1990, NRLMSISE 2000. (see below)

Only atmosphere models that are valid to the ground can be used for missile objects. These are: Harris-Priester, NRLMSISE 2000, MSISE 1990, and Jacchia 1960.

• Enter Manually. Enter one or more of the values below, depending on the Atmospheric Density Model selected (above).
• Use File. Enter or browse to the path and name of a flux file. A flux file contains flux data (ap, kp, f10.7, and avg f10.7) for each date. The geomagnetic flux data (ap/kp) includes a daily value and eight values measured at three-hour intervals for each date. STK reads both the ap and kp data from a file, and each density model uses the appropriate data natively.

  The file may follow the format of CSSI predicts (.dat) files, SpaceWeather (.txt) files, or the stkFluxGeoMag (.fxm) files. For more information about the format of these file types, see the Solar Flux Files page of this help system.

  When reading the flux file, the observation time for F10.7 data is 20:00 UTC (the time at which the value begins to apply for each day listed in the file) and when using F10.7 values from the flux file, the value of F10.7 at any given time is found using linear interpolation of the table of data.

  When reading fxm flux files, which contain only adjusted F10.7 values, the values listed in the file are corrected by the Sun-Earth distance to obtain observed F10.7 values.

  All three files can be reported using the Geo Mag Flux Tool under Scenario Tools.

• Daily. Updates using the daily ap/kp value for the entire day.
• 3-Hourly. Updates using the eight values measured at three-hour intervals.
• 3-Hourly Interp. Updates by interpolating the three-hour values. The interpolation uses a spline between data points, the average value of which - over a three hour window - is made equal to the ap/kp value for that three-hour value.
• 3-Hourly Cubic Spline. Updates by interpolating the 3-hourly data using natural cubic splines.

If you select the 3-Hourly or 3-Hourly Interp update rate when using MSIS models, a special setting of the MSIS model, (SW[9]=-1), is set for the use of present and past ap values when computing density. In addition, STK does not use interpolation with MSIS models; selecting the 3-Hourly Interp update rate for an MSIS model will produce the same result as selecting the 3-Hourly rate.

Empirical density model developed by the US Naval Research Laboratory based on satellite data. Finds the total density by accounting for the contribution of N, N2, O, O2, He, Ar and H. Includes anomalous oxygen. 2000 version, valid range is 0 to 1000 km.

This implementation always calls the gtd7d routine (in contrast to switching between it and gtd7) per the recommendation of Mike Picone, one of the code authors.