{"id":4404,"date":"2013-03-01T09:00:08","date_gmt":"2013-03-01T14:00:08","guid":{"rendered":"https:\/\/blogs.mathworks.com\/pick\/?p=4404"},"modified":"2013-02-28T18:33:36","modified_gmt":"2013-02-28T23:33:36","slug":"a-matlab-script-for-calculating-greenwich-sidereal-time-with-novas","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/pick\/2013\/03\/01\/a-matlab-script-for-calculating-greenwich-sidereal-time-with-novas\/","title":{"rendered":"A MATLAB Script for Calculating Greenwich Sidereal Time with NOVAS"},"content":{"rendered":"<a href=\"https:\/\/www.mathworks.com\/matlabcentral\/fileexchange\/authors\/76890\">Will<\/a>'s pick this week is <a href=\"https:\/\/www.mathworks.com\/matlabcentral\/fileexchange\/39846-a-matlab-script-for-calculating-greenwich-sidereal-time-with-novas\">A MATLAB Script for Calculating Greenwich Sidereal Time with NOVAS<\/a> by <a href=\"https:\/\/www.mathworks.com\/matlabcentral\/fileexchange\/authors\/30927\">David Eagle<\/a>.\r\n<br><br>\r\nAnyone who's taken an orbital dynamics class knows that you need to understand a fair amount of astronomy to perform any meaningful satellite analysis. For spacecraft orbiting the Earth, it is typically most convenient to calculate their trajectories in an Earth-Centered Inertial (ECI) frame. The axes of this frame are fixed relative to the stars.\r\n<br><br>\r\nOf course the Earth merrily spins about relative to the stars. In order to keep track of items on the ground, it is convenient to use a coordinate system whose axes are fixed on the surface. We call this the Earth-Centered Earth-Fixed (ECEF) frame. Since their origins and Z axis are identical, the ECEF and ECI coordinate systems only differ by some rotational angle in the XY plane. The angle rotates 360 degrees roughly every 24 hours.\r\n<br><br>\r\nIf you know this angle, then you can perform the coordinate transformation between ECI and ECEF. If you can do that, then you can determine where a satellite is relative to any point on the Earth's surface. This is a necessary first step for tracking and communication. One recurring challenge is predicting this angle as accurately as possible over as wide a range of time as possible. \r\n<br><br>\r\nDavid's submission achieves just that. It's but one example of a whole slew of goodies that he's uploaded to the File Exchange. He provides the <a title=\"http:\/\/www.usno.navy.mil\/USNO\/astronomical-applications\/software-products\/novas (link no longer works)\">Naval Observatory Vector Astrometry Software<\/a> (NOVAS) in MATLAB form. There are all kinds of wonderful utilities that are provided in this package. I picked Greenwich Sidereal Time because I recall that being a particularly important detail in my grad student days. But there are all sorts of other functions in there that are just as valuable to an aerospace engineer.\r\n<br><br>\r\n<strong>Comments<\/strong><br>\r\nLet us know what you think <a href=\"https:\/\/blogs.mathworks.com\/pick\/?p=4404#respond\">here<\/a> or leave a <a href=\"https:\/\/www.mathworks.com\/matlabcentral\/fileexchange\/39846-a-matlab-script-for-calculating-greenwich-sidereal-time-with-novas#comments\">comment<\/a> for David.","protected":false},"excerpt":{"rendered":"<p>Will's pick this week is A MATLAB Script for Calculating Greenwich Sidereal Time with NOVAS by David Eagle.\r\n\r\nAnyone who's taken an orbital dynamics class knows that you need to understand a fair... <a class=\"read-more\" href=\"https:\/\/blogs.mathworks.com\/pick\/2013\/03\/01\/a-matlab-script-for-calculating-greenwich-sidereal-time-with-novas\/\">read more >><\/a><\/p>","protected":false},"author":45,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[16],"tags":[],"_links":{"self":[{"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/posts\/4404"}],"collection":[{"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/users\/45"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/comments?post=4404"}],"version-history":[{"count":5,"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/posts\/4404\/revisions"}],"predecessor-version":[{"id":4409,"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/posts\/4404\/revisions\/4409"}],"wp:attachment":[{"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/media?parent=4404"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/categories?post=4404"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/pick\/wp-json\/wp\/v2\/tags?post=4404"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}