| Date: | 1998-09-06 14:00:00 | |
| Sender: | Roger Wood and Andrew Sinclair <rw@gxvf.rgo.ac.uk (Roger Wood, SLR Herstmonceux)> | |
| Subject: | [SLR-Mail] No. 151: Daily GLONASS IRVs for IGEX-98 | |
| Author: | Roger Wood and Andrew Sinclair | |
| Content: | ******************************************************************************** SLR Electronic Mail 1998-09-06 14:00:00 UTC Message No. 151 ******************************************************************************** Author: Roger Wood and Andrew Sinclair Subject: Daily GLONASS IRVs for IGEX-98 Daily GLONASS IRVs for IGEX-98 1. Introduction This message announces an extension, to include all active GLONASS satellites, to the scheme for daily computation and distribution of IRVs for GPS 35 and 36 described by Andrew Sinclair in SLRMAIL 36. The GPS predictions are derived from the precise orbits computed daily at the Centre for Orbit Determination (CODE) at the University of Berne. The GLONASS predictions are of lower precision since they are formed from positional data derived by CODE from the satellites´ broadcast ephemerides. But in both cases the predictions require no timebias corrections and allow the use of much narrower range gates, typically +/-50 ns or better. It is hoped that the availability of these new predictions for GLONASS satellites will greatly increase the quantity of SLR data obtained during the forthcoming IGEX-98 campaign, in particular for daylight passes. (A request for SLR tracking will be issued soon by the IGEX-98 steering committee). The new predictions have undergone a short period of evaluation at Herstmonceux and are being made available to the community. The IRVs for each satellite will be produced and distributed in two forms: at 6 hourly intervals, the same as the GPS IRVs; and at the ´standard´ interval of 24 hours. Format and file naming are described in the sections which follow - previous users of the 6 hourly IRVs for GPS should note changes to filenames. 2. IRV format The IRV files sent out each day covers 72 hours so as to guard against network failures on any one day. The header line for each day gives information on the origin of the IRVs, the date of formation, the identity of the satellite and the multiplicity (number of IRV sets per day - see SLRMAIL 36 for a more detailed description) of the IRVs which follow. Thus: COD09732 GLO71 4 indicates that the IRVs for GLONASS 71 were formed from the CODE orbit for day 2 of GPS week 973 and that there are 4 sets of IRVs per day, one for each interval of 6 hours. The header: COD09732 GLO71 1 introduces the more familiar IRVs for the same day but with one set covering the whole 24 hours. 3. Distribution The IRV files for GPS and GLONASS are formed at Herstmonceux as soon as the relevant CODE files are available by FTP. This is usually between 10:00 and 12:00 UT but can on occasion be much later. The files are then deposited at the European Data Centre (EDC) in subdirectory: pub/laser/predictions/RGO_PRED and at RGO in subdirectory: pub/slrirv/current from where they are available by anonymous FTP. The files can also be mailed directly to stations on request. It will only be possible to finalise the EDC distribution arrangements after September 10, but files are available at the RGO FTP site now. 4. File naming To make it easier to distinguish GPS from GLONASS files the naming convention (defined in SLRMAIL 36) has been amended to identify the satellites explicitly and to indicate both the origin of the orbits and the multiplicity, as well as the date. Examples of two files formed on 1998 September 1 are: glo67_cod4_9809.01 - GLONASS 67 with 6 hourly IRVs, glo71_cod1_9809.01 - GLONASS 71 with 24 hourly IRVS. The same naming convention will also be applied to GPS files. 5. GLONASS satellite identification In order to minimise any possible confusion concerning the names of GLONASS satellites the following paragraphs provide a detailed description of the naming scheme adopted here, a list cross-referencing the main identifiers and the sources from which the information was taken. The cross-reference list is available in the EDC and RGO FTP directories with the name: glo_identifiers.lst the present version of which appears below. The SLR community uses a 2-digit GLONASS number for each satellite as the principal identifier, e.g., GLONASS 71. This 2-digit number is used in the header line of each set of IRVs, and is also used to form the 4-digit SIC number that appears in each IRV data message by adding 9000, e.g., 9071 for GLONASS 71. The satellite identifier used in the SLR normal point data format is the COSPAR 7-digit number, e.g., for GLONASS 71, 9500901. The identifier used in the navigational data broadcast by the GLONASS satellites themselves is the slot number which gives the location in the orbit plane. The orbital position data supplied by the Swiss use this identifier, and it is likely that the IGS community will use it too. Hence this is also included in the cross-reference list. The Russians use the slot number as an identifier, and also assign a Cosmos number and a 3-digit GLONASS number of their own. These are not the same as the GLONASS numbers used by the SLR community, and bear no simple relationship to them. A list of the Russian identifiers plus up-to-date status information, can be found in: http://www.rssi.ru/SFCSIC/NAGU.TXT. The Cosmos number and 3-digit GLONASS number are not included in the cross-reference list. The source used for cross-referencing the SLR GLONASS numbers against COSPAR ID and Russian GLONASS numbers is SpaceWarn Bulletin No. 513 (1996 July), which is available at: http://nssdc.gsfc.nasa.gov/spacewarn/spacewarn.html. Later bulletins do not give the GLONASS numbers, and it seems to be a dying numbering system. It is likely that the SLR community will have to assign these numbers themselves for any future launches. The COSPAR numbers are the identifiers in the NORAD two-line orbital elements. These elements can be used to determine the position of a satellite, and hence its slot number. Unfortunately there are some contradictions in relating COSPAR number to slot number by this route, compared with using the SpaceWarn Bulletins and the Russian NAGU notices. Where there is a contradiction we have chosen the identification that gives agreement in orbital position. In the cross-reference list the satellites for which the GLONASS number is questionable in this sense are GLONASS 71, 72, 77 and 79. 6. Acknowledgements Thanks are due to Tim Springer of CODE for depositing the daily orbit files for the GLONASS satellites in addition to those for GPS, to Werner Gurtner of EuroLas for helpful comments on early drafts and to Wolfgang Seemueller of EDC for providing database facilities for these new files. ------------- glo_identifiers.lst as at 1998 September 1 -------------- ! ! List of GLONASS satellite identifiers as used in RGO/CODE IRVs ! See SLRMAIL 163 for an explanation of the use of this file ! Slot occupation may change from time to time ! ! Col 1 = Glonass slot number ! 2 = 2-digit Glonass identifier ! 3 = COSPAR number ! 4 = Glonass plane ! 5 = Currently active (Y = Yes; N = No) ! 6 = Notes (* = currently tracked by SLR network) ! (? = cross-referencing of number has been questioned - ! see discussion in SLRMAIL 163) ! ! +-------------------------+ ! | Last updated 1998 Sep 1 | ! +-----------+-------------+ ! V ! 1 2 3 4 5 6 !-! ---------! ------! ! ! ------------------------! 3 Glonass 68 9407601 1 Y SLR candidate for IGEX-98 4 Glonass 70 9407603 1 Y SLR candidate for IGEX-98 6 Glonass 69 9407602 1 Y SLR candidate for IGEX-98 9 Glonass 79 9506803 2 Y SLR candidate for IGEX-98 ? 10 Glonass 75 9503702 2 Y 11 Glonass 76 9503703 2 Y 12 Glonass 65 9405001 2 Y SLR candidate for IGEX-98 * 13 Glonass 77 9506801 2 Y ? 14 Glonass 67 9405003 2 N * 15 Glonass 74 9503701 2 Y 16 Glonass 66 9405002 2 Y SLR candidate for IGEX-98 * 17 Glonass 62 9402101 3 Y SLR candidate for IGEX-98 18 Glonass 64 9402103 3 Y 20 Glonass 71 9500901 3 Y SLR candidate for IGEX-98 * ? 22 Glonass 72 9500902 3 Y SLR candidate for IGEX-98 ? --------------------- End of glo_identifiers.lst ---------------------- ======================================================================= Roger Wood, NERC Satellite Laser Ranger Facility, Herstmonceux Castle Hailsham, East Sussex, UK BN27 1RP Tel: +44 (01323) 833888 Fax: +44 (01323) 833929 Email: rw@gxvf.rgo.ac.uk ======================================================================= From: rw@gxvf.rgo.ac.uk (Roger Wood, SLR Herstmonceux) ******************************************************************************** |