Интерфейсный документ GPS (1014597), страница 9
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The following three operational intervals have been defined. These labelswill be used to refer to differences in the interface definition as time progresses from SV acceptance of the lastnavigation data upload.6.2.3.1 Normal Operations. The SV is undergoing normal operations whenever the fit interval flag (referenceparagraph 20.3.3.4.3.1) is zero.6.2.3.2 Short-term Extended Operations.
The SV is undergoing short-term extended operations whenever the fitinterval flag is one and the IODE (reference paragraph 20.3.4.4) is less than 240.6.2.3.3 Long-term Extended Operations. The SV is undergoing long-term extended operations whenever the fitinterval flag is one and the IODE is in the range 240-255.IS-GPS-200D7 Dec 2004526.2.4 GPS Week Number. The GPS week numbering system is established with week number zero (0) beingdefined as that week which started with the X1 epoch occurring at midnight UTC(USNO) on the night of January 5,1980/ morning of January 6, 1980. The GPS week number continuously increments by one (1) at each end/start ofweek epoch without ever resetting to zero. Users must recognize that the week number information contained in theNav Message may not necessarily reflect the current full GPS week number (see paragraphs 20.3.3.3.1.1,20.3.3.5.1.5, 20.3.3.5.2.4, and 30.3.3.1.1.1).6.2.5 L5 Civil Signal.
L5 is the GPS downlink signal at a nominal carrier frequency of 1176.45 MHz. The L5signal is only available on Block IIF and subsequent blocks of SVs and the signal is specified/described in a separateand different interface control document.6.3 Supporting Material6.3.1 Received Signals.
The guaranteed minimum user-received signal levels are defined in paragraph 3.3.1.6.As additional supporting material, Figure 6-1 illustrates an example variation in the minimum received power of thenear-ground user-received L1 and L2 signals from Block II/IIA/IIR SVs as a function of SV elevation angle.Higher received signals levels can be caused by such factors as SV attitude errors, mechanical antenna alignmenterrors, transmitter power output variations due to temperature variations, voltage variations and power amplifiervariations, and due to a variability in link atmospheric path loss.
For Block II/IIA and IIR SVs, the maximumreceived signal levels as a result of these factors is not expected to exceed -155.5 dBW and -153.0 dBW,respectively, for the P(Y) and C/A components of the L1 channel, nor -158.0 dBW for either signal on the L2channel. For Block IIR-M and IIF SVs, the maximum received signal levels as a result of these factors is notexpected to exceed -155.5 dBW and -153.0 dBW, respectively, for the P(Y) and C/A components of the L1 channeland L2 channel.
In addition, due to programmable power output capabilities of Block IIR-M and IIF SVs, undercertain operational scenarios, individual signal components of Block IIR-M/IIF SVs may exceed the previouslystated maximum but are not expected to exceed -150 dBW.IS-GPS-200D7 Dec 200453RECEIVED POWER AT 3dBi LINEARLY POLARIZED ANTENNA (dBW)-155.5C/A - L1-158.5P - L1-161.5P - L2 or-164.5C/A - L20o 5o20o40o60o80o90o100oUSER ELEVATION ANGLE (DEG)Figure 6-1.User Received Minimum Signal Level Variations (Example, Block II/IIA/IIR)IS-GPS-200D7 Dec 2004546.3.2 Extended Navigation Mode (Block II/IIA). The Block II and IIA SVs are capable of being uploaded by theCS with a minimum of 60 days of navigation data to support a 60 day positioning service.
Due to memoryretention limitations, the Block II SVs may not transmit correct data for the entire 60 days but are guaranteed totransmit correct data for at least 14 days to support short-term extended operations. Under normal conditions the CSwill provide daily uploads to each SV, which will allow the SV to maintain normal operations as defined inparagraph 6.2.3.1 and described within this IS. During normal operations, the SVs will have a user range error thatis at or below a level required to support a positioning accuracy of 16 meters spherical error probable (SEP).
Inaddition, the almanac data, UTC parameters and ionospheric data will be maintained current to meet the accuracyspecified in this IS.If the CS is unable to upload the SVs (the CS is unavailable or the SV is unable to accept and process the upload),each SV will individually transition to short-term extended operations and eventually to long-term extendedoperations (based on time from each SV's last upload) as defined in paragraphs 6.2.3.2 and 6.2.3.3, and as furtherdescribed throughout this IS.
As time from upload continues through these three operational intervals, the userrange error of the SV will increase, causing a positioning service accuracy degradation. The rate of accuracydegradation is slow over the short-term extended operations interval, such that at the end of this interval(approximately 14 days after upload) the US will be able to achieve a positioning accuracy of 425 meters SEP.
Therate of accuracy degradation increases in the long-term extended interval, such that by the 180th day after the lastupload, the positioning errors will have grown to 10 kilometers SEP. During these intervals the URA will continueto provide the proper estimate of the user range errors.During short-term and long-term extended operations (approximately day 2 through day 62 after an upload), thealmanac data, UTC parameters and ionospheric data will not be maintained current and will degrade in accuracyfrom the time of last upload.IS-GPS-200D7 Dec 2004556.3.3 Block IIA Mode (Block IIR/IIR-M). The Block IIR/IIR-M SVs, when operating in the Block IIA mode, willperform similarly to the Block IIA SVs and have the capability of storing at least 60 days of navigation data, withcurrent memory margins, to provide positioning service without contact from the CS for that period (throughshort-term and long-term extended operations). (Contractual requirements for these SVs specify transmission ofcorrect data for only 14 days to support short-term extended operations while in IIA mode.) Under normalconditions, the CS will provide daily uploads to each SV, which will allow the SV to maintain normal operations asdefined in paragraph 6.2.3.1 and described within this IS.If the CS is unable to upload the SVs (the CS is unavailable or the SV is unable to accept and process the upload),each SV will individually transition to short-term extended operations and eventually to long-term extendedoperations (based on time from each SV’s last upload) as defined in paragraph 6.2.3.2 and 6.2.3.3, and as furtherdescribed throughout this IS.
As time from upload continues through these three operational intervals, the userrange error (URE) of the SV will increase, causing a positioning service accuracy degradation.6.3.4 Autonomous Navigation Mode. The Block IIR/IIR-M and Block IIF SV, in conjunction with a sufficientnumber of other Block IIR/IIR-M or Block IIF SVs, operates in an Autonav mode when commanded by the CS.Each Block IIR/IIR-M/IIF SV in the constellation determines its own ephemeris and clock correction parameters viaSV-to-SV ranging, communication of data, and on-board data processing which updates data uploaded by the CS.In the Autonav mode the Block IIR/IIR-M/IIF SV will maintain normal operations as defined in paragraph 6.2.3.1and as further described within this IS, and will have a URE of no larger than 6 meters, one sigma for Block IIR/IIRM.
URE of 6 meters, one sigma, is expected to support 16 meter SEP accuracy under a nominal position dilution ofprecision. If the CS is unable to upload the SVs, the Block IIR/IIR-M/IIF SVs will maintain normal operations forperiod of at least 60 days after the last upload.In the Autonav mode, the almanac data, UTC parameters and ionospheric data are still calculated and maintainedcurrent by the CS and uploaded to the SV as required. If the CS is unable to upload the SVs, the almanac data,UTC parameters and ionospheric data will not be maintained current and will degrade in accuracy from the time ofthe last upload.IS-GPS-200D7 Dec 20045610. APPENDIX I.
LETTERS OF EXCEPTION10.1 Scope. Approval of this document, as well as approval of any subsequent changes to the document, can becontingent upon a "letter of exception". This appendix depicts such "letters of exception" when authorized by theGPS JPO.10.2 Applicable Documents. The documents listed in Section 2.0 shall be applicable to this appendix.10.3 Letters of Exception. Any letter of exception which is in force for the revision of the IS is depicted in Figure10-1.IS-GPS-200D7 Dec 200457(This page intentionally left blank.)IS-GPS-200D7 Dec 200458Lockheed Martin Space Systems CompanySpace & Strategic MissilesValley Forge OperationsP.O. Box 8555 Philadelphia, PA 1910126 May 2003GPS IIR-CM-MOD-147SMC/CZK2420 VELA WAY, SUITE 1467LOS ANGELES AFB CA 90245-4659Attention:Mr.
David SmithSubject:GPS Block IIR Modernization Contract F04701-00-C-0006Review and approval of ICD-GPS-PIRN-200C-007B, dated 08 November 2003, post 9April 2003 CCB (L2C = -160).Reference:1)PCOL# 03-012, dated 22 May 03; F04701-00-C-0006; REQUEST FOR IMPACTSDUE TO IMPLEMENTING PROPOSED CHANGES TO PIRN-200C-007REVISION BDear Mr. Smith:Lockheed Martin Space Systems Company has been asked to review and comment on changes made toICD-GPS-PIRN-200C-007B at the JPO CCB boarded on or about 09 April 2003. It is our understandingthat the ONLY change made to the 08 November 2002 of the subject ICD is L2C for IIR-M SVs changedfrom –161.4 dBW to –160.0 dBW.Based on that change, Lockheed Martin takes exception to IIR-M L2 C signal power specified in Table 3III.
Per Lockheed Martin contract requirements as specified in SS-SS-500, Rev. A, dated 14 May 2001,LMSSC calculates links using:• 0-dBi circularly polarized user receiving antenna (located) near ground when the SV is above a 5°elevation angle• Atmospheric loss of 0.5 dB at edge of earth• Assumes SV antenna gains are averaged about azimuthUsing the assumptions as specified in paragraph 3.3.1.6 of PIRN-200C-007B, the GPS IIRM SVs providea minimum receive signal of -161.4 dBW for L2 C signal. Lockheed Martin therefore takes exception to 160 dBW for L2C of PIRN-200c-007B. Formal request for cost and schedule impacts should comethrough the JPO Contracting Officer.To change from -161.4 dBW to -160.0 dBW would have to be analyzed and coordinated betweenLockheed Martin and ITT.
If such a change were technically possible, there would be impacts to L-Bandlevel testing, SV level testing, test scripts, Specs, OOH, and various ICDs. These impacts would be inboth cost and schedule.Figure 10-1. Letters of Exception.IS-GPS-200D7 Dec 200459GPS IIR-CM-MOD-147Page 2Currently, there is an ongoing effort between Lockheed Martin, Boeing, Arinc, Aerospace, and the JPOconcerning signal flexibility under the ConOps study. Lockheed Martin recommends, based on theoutcome and direction of this effort, that an impact to the ICD-200 change be included in the resultingrequest for ROMs for Flex Power implementation.Note that if Lockheed Martin has taken earlier exception to a change in any requirements in a previousrevision of this document, Lockheed Martin continues to take exception to that change. A letter explicitlystating that the exception is no longer valid will accomplish the retraction of an exception.Should you have any questions, please contact Martin O’Connor at (610) 354-7866 for technicalconcerns, or the undersigned at (610) 354-7989 for contractual matters.Very truly yours,LOCKHEED MARTIN CORPORATIONSignature on fileBrent B.
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