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PROCEDURE: morbit
PURPOSE:
Given the orbit size and shape (based on 2 of 5 orbital parameters),
calculates the orbital position and velocity of a satellite around a
planet as a function of time. This routine is very fast when the
orbital eccentricity is less than 0.95, but labors when it is very
close to unity. This routine will not work at all for parabolic and
hyperbolic orbits.
Calculations assume a spherical central body with a spherically
symmetric mass distribution, and that the mass of the central body
dominates in the region of interest.
You can also specify an orientation for the orbit and then create a
'fly-through' in cartesian coordinates.
USAGE:
morbit, param, dt=dt, result=dat
INPUTS:
PARAM: Orbit parameter structure, which has two of the
following tags:
period : orbital period (hours)
sma : semi-major axis (km)
palt : periapsis altitude (km)
aalt : apoapsis altitude (km)
ecc : eccentricity
The two parameters you specify must define the
size and shape of the orbit. Any two will work,
except for period and sma, which both define the
orbit size. The remaining parameters are
calculated from the two you specify.
KEYWORDS:
ORIENT: A structure specifying the orientation of the
orbit with three tags:
lon : longitude of periapsis (deg)
lat : latitude of periapsis (deg)
incl : orbital inclination (deg)
Lon and lat can be arrays, resulting in a grid of
calculations. Incl must be a scalar.
Note that abs(lat) <= abs(incl) is required.
Default = {lon:0, lat:0, incl:90}
Normally, the longitude, latitude, and inclination
are specified in planetocentric coordinates (i.e.,
relative to the planet's spin axis); however, any
coordinate system can be assumed, so long as all
three parameters are in the SAME coordinate system.
FLYTHRU: The name for a text output file containing the
cartesian coordinates of the satellite vs. time
for the orbit orientation specified in ORIENT.
The columns for this table are:
1 -> time (sec after apoapsis)
2 -> X (km)
3 -> Y (km)
4 -> Z (km)
5 -> orbital velocity (km/s)
If you don't specify this keyword, then the
fly-through is still calculated and saved in
RESULT.
PLANET: This can be a string to select one of the eight
planets. The following are also recognized: Moon,
Sun, Pluto, Charon, Eris, and Ceres. It can also
be a structure with the following tags:
Mass : mass (g)
Radius : radius (km)
Name : 'name' [optional]
Default = 'Mars'. If PLANET is unrecognized, you
will be prompted for mass and radius. This routine
is not expected to give good results for the Pluto-
Charon system, because they have masses within a
factor of 10 of each other.
SHOCK: If PLANET = 'Mars' or 'Earth', then setting this
keyword will show the nominal shock location on the
orbit plots (see keyword OPLOT). Default = no.
DT: Time resolution (sec). Default = PARAM.period/1000.
NORBIT: Number of orbits for calculating the solution.
Default = 1.
NMAX: Maximum number of iterations for the orbit solver.
Default = 400. Larger numbers might be needed if
the orbital eccentricity is greater than 0.95.
OERR: Maximum error in orbit solution, which translates
roughly into fractional error in the position.
Default = 1.e-6. Increase this only if you want a
quicker solution at the expense of accuracy.
RESULT: A structure containing the satellite altitude and
true anomaly versus time. The true anomaly is the
angle in the plane of the orbit about the center
of the planet, with zero degrees at periapsis.
The orbital velocity, and the orbit size and shape
parameters are also given.
OPLOT: The number of an IDL window for plotting the orbit
with three orthogonal views. Default = none.
TPLOT: The number of an IDL window for a time series plot
of altitude and orbital velocity. Default = none.
WSCALE: Window size scale factor. Default = 1.
XYPLANE: Plot the orbit in the XY plane only. Only works if
OPLOT is set.
XYRANGE: Axis plot ranges in planetary radii. Default is to
fit the orbit on the plot.
NODOT: Do not plot a symbol for periapsis.
PS: Postscript plots are produced for OPLOT and TPLOT.
SILENT: If set, then suppress output.
SEGMENTS: Divide the orbit up into segments for color coding.
This keyword should contain the time in minutes
relative to apoapsis of each segment boundary.
The first segment extends from APO to SEGMENTS[0].
The last segment extends from SEGMENTS[N-1] to APO,
where N is the number of segments.
SCOLORS: Color for each segment. Must have the same number of
elements as SEGMENTS.
$LastChangedBy: dmitchell $
$LastChangedDate: 2019-12-20 11:02:44 -0800 (Fri, 20 Dec 2019) $
$LastChangedRevision: 28133 $
$URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/spdsoft/tags/spedas_4_0/projects/maven/morbit.pro $
CREATED BY: David L. Mitchell
(See projects/maven/morbit.pro)
Function: mvn_spc_met_to_unixtime Purpose: Convert MET (mission Elapsed Time) to Unix Time (which is almost equivalent to UTC) see also: "mvn_spc_unixtime_to_met" for the reverse conversion This routine is in the process of being modified to use SPICE Kernels to correct for clock drift as needed. Author: Davin Larson $LastChangedBy: davin-mac $ $LastChangedDate: 2015-10-21 11:55:01 -0700 (Wed, 21 Oct 2015) $ $LastChangedRevision: 19123 $ $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/spdsoft/tags/spedas_4_0/projects/maven/mvn_spc_met_to_unixtime.pro $
(See projects/maven/mvn_spc_met_to_unixtime.pro)