Degenerate Conic

Atmosphere Models

The drag force magnitude on a spacecraft can be computed using the following equation:

Which can be easily implemented in the following Fortran function:

pure function drag(density, v, area, cd)

    use iso_fortran_env, only: wp => real64

    implicit none

    real(wp) :: drag !! drag force magnitude (N)
    real(wp), intent(in) :: density !! atmospheric density (kg/m^3)
    real(wp), intent(in) :: v       !! relative velocity magnitude (m/s)
    real(wp), intent(in) :: area    !! spacecraft cross-sectional area (m^2)
    real(wp), intent(in) :: cd      !! spacecraft drag coefficient

    drag = 0.5_wp * density * v**2 * area * cd

end function drag

The density \(\rho\) is computed using an atmosphere model. Here is a listing of some atmosphere model codes available in Fortran:

• 1976 Standard Atmosphere
• INPE-atmosphere-models -- My archive of models originally from this page (which now seems to be gone). Includes five models:
  • Jacchia 70
  • Jacchia-Roberts
  • Jacchia 77
  • LaFontaine-Hughes
  • Jacchia-Lineberry
• MSIS86
• MSISE90
• NRLMSISE00
• NRLMSIS 2.0
• Earth Global Reference Atmospheric Model 2010 (Earth GRAM 2010)

See also

• Fox & Mcdonald, "Introduction To Fluid Mechanics", Wiley
• Drag Coefficient [Wikipedia]
• U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976.
• ModelWeb Catalogue and Archive [NASA GSFC]
• W. W. Vaughan, "Guide to Reference and Standard Atmospheric Models", AIAA G-003C-2010, January 2010