In  the  TBUS  bulletin  Part  IV,  all  information necessary to calculate a satellite’s orbit and variations in the orbit is provided. This information includes an epoch orbit number, two forms of an epoch date, position  and  velocity  coordinates,  the  nodal  period, and anomaly values used to determine the change in position of the satellite over any period of time. SAT MOD Ephemeris Updates Like  the  TESS,  the  SAT  MOD  may  update ephemeris  information  by  reading  a  TBUS  message file. If the appropriate TBUS bulletin is not available directly from a disk file, the system may be updated with manual entries by using information in the TBUS bulletins. Only certain elements from each TBUS bulletin are required for each satellite in the SAT MOD. The resulting ephemeris files need only be updated every 2 weeks. Instructions  for  imputing TBUS bulletin data is contained in the IMOSS user’s guide. TESS Ephemeris Updates TESS  allows  satellite  ephemeris  data  files  to  be updated manually by entering selected data via the keyboard.  TESS,  interfaced  with  a  communications system, may be directed to read a saved TBUS message file  to  automatically  update  ephemeris  information. TESS may only use each particular TBUS bulletin during a 7-day valid period following the prediction date; in this case January 05 to January 12. Since predict bulletins are sent out daily, TESS may store more than one file of ephemeris information for each satellite, and prediction periods may overlap. AN/SMQ-11 Ephemeris Updates The AN/SMQ-11 does not have the capability to interpret  imported  TBUS  messages  to  update  its ephemeris files. Various parameters from the TBUS bulletin Part IV may be manually entered. The SMQ- 11 requires the epoch calendar date-time-group be entered  vice  the  epoch  decimal  date-time-group. NASA TWO-LINE DATA Another predict message is the NASA Two-Line Orbital   Elements   (TLE)   bulletin.   This   bulletin contains orbital information very similar to Part IV of the TBUS bulletin. The message is divided into 16 elements and can be input into the SAT MOD and AN/SMQ-11 in lieu of TBUS data. Keep in mind that while similarly named elements appear in both the NASA Two-Line and TBUS bulletins, the values are NOT interchangeable between systems to compute satellite tracks. Table 1-4 is an example of a NASA Two-line bulletin and table 1-5 is a description of the information. NAVSPASURCEN ORBITAL DATA The   Naval   Space   Surveillance   Center (NAVSPASURCEN)  in  Dahlgren,  Virginia,  tracks  all U.S.  and  foreign-operated  satellites  and  space  debris. Navy and Marine Corps satellite-receiver system users may request message support for satellite tracking information.  The  AN/SMQ-11  contains  software designed to use and interpet separate messages of data known as Satellite Equator Crossings. TESS uses a product known as C-Element Orbital Data to calculate orbits for the AN/SMQ-11. A  Satellite  Equator  Crossings  message  contains information similar to TBUS Part I. The AN/SMQ-11 needs to be updated frequently (about every 2 days) by using the information from this product. The message contains information on all U.S. and foreign-operated environmental satellites. Table 1-6 contains a portion of   a   Satellite   Equator   Crossings   message   with explanations  of  the  elements  required  to  update  the AN/SMQ-11.  The  underlined  elements  are  required input. C-Element orbital data also contains information similar to Part IV of the TBUS bulletin. See table 1-7 for an example of a typical message containing C- element orbital data and table 1-8 for an explanation of the data. In the C-element orbital data message, each line of data is repeated three times.  This is done so that Table 1-4.—Sample NASA Two-line bulletin 1-34