SGP4 to useful coordinate systems

[shentonfreude]

From: Matney, Mark (JSC-KX111) at nasa.gov

The SGP software only gives information in Earth Centered Inertial (ECI) coordinates, so you will need to solve for the Earth orientation with time as well.

See:

http://en.wikipedia.org/wiki/Earth-centered_inertial http://celestrak.com/columns/v02n01/ http://www.mathworks.com/help/toolbox/aeroblks/f3-22568.html Hard math: http://onlinelibrary.wiley.com/doi/10.1002/0471200719.app0c/pdf

Check the Miura code stack and see if there are PREDICT integrations.

Check various 'predict' implementations and see if they use SGP4.

[shentonfreude]

Can we get Vallado's tome "Fundamentals of Astrodynamics and Applications" from HQ's Library?

http://www.amazon.com/Fundamentals-Astrodynamics-Applications-David-Vallado/dp/1881883140/ref=cm_cr_pr_product_top

[shentonfreude]

testmat:

%%% From Miura's paper:
%%% For each satellite, there are 7-13 columns of data (columns 8- 13
%%% are date and time data which is not calculated for catalog mode):
%%% 01. Minutes from Epoch
%%% 02. X-Position
%%% 03. Y-Position
%%% 04. Z-Position
%%% 05. X-Velocity
%%% 06. Y-Velocity
%%% 07. Z-Velocity
%%% 08. Year
%%% 09. Month
%%% 10. Day
%%% 11. Hour
%%% 12. Minute
%%% 13. Second
%%%
% **Note, the position vector is based in ECI coordinate frame.**

rv2coe: this function finds the classical orbital elements given the geocentric % equatorial position and velocity vectors. % arglat - argument of latitude (ci) 0.0 to 2pi rad % truelon - true longitude (ce) 0.0 to 2pi rad % lonper - longitude of periapsis (ee) 0.0 to 2pi rad

[shentonfreude]

C++ code which uses SGP4 as a library and then has SatTrack to calc lat/lon/alt as well as position from observer on earth. http://www.danrw.com/sgp4-satellite.php

Celestrak article, and the subsequent ones (hack the URL), show how to tranform from ECI TEME coordinate frame into other references: lat/lon/alt.

The ECI frame used for the NORAD two-line elements is sometimes called true equator, mean equinox (TEME) although it does not use the conventional mean equinox.

Celestrak discusses how to answer questions like "where do I look" and "what's the lat, lon, alt of a satellite", and how to find angle between Greenwich Meridian and vernal equinox -- position of Earth w.r.t. ECI. Uses local sidereal time vs. mean solar time.

[shentonfreude]

Rotate into time-based ECF (Earth Centered Fixed) with

billboards.modelMatrix = Cesium.Matrix4.fromRotationTranslation(Cesium.Transforms.computeTemeToPseudoFixedMatrix(now),
                                                                            Cesium.Cartesian3.ZERO);