PROCEDURE: maven_orbit_update PURPOSE: Updates the "current" spacecraft ephemeris using SPICE. USAGE: maven_orbit_update INPUTS: KEYWORDS: TSTEP: Ephemeris time step (sec). Default = 60 sec. $LastChangedBy: dmitchell $ $LastChangedDate: 2014-10-13 12:29:59 -0700 (Mon, 13 Oct 2014) $ $LastChangedRevision: 15983 $ $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/spdsoft/trunk/projects/maven/maven_orbit_tplot/maven_orbit_update.pro $ CREATED BY: David L. Mitchell 2014-10-13