PDS_VERSION_ID = PDS3 RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 80 OBJECT = TEXT PUBLICATION_DATE = 2000-09-12 NOTE = "Description of GEODYN SPK Files" END_OBJECT = TEXT END GEODYN SPK files (data type GDN) are QUICK LOOK orbits produced by the MOLA POD (Precise Orbit Determination) team. They are used for preliminary analysis of the MOLA data, and have been made available to other MGS project participants. They are produced on a best efforts basis, as time and resources permit. Each file is in SPK format, compatible with readers in the SPICE toolkit (see companion files TK_FTP.TXT, TK_DESCR.TXT, and TK_INSTL.TXT in this DOCUMENT directory for more information on the SPICE toolkit and files). The data were originally written out by GEODYN (the orbit processor) at five or ten second intervals. They were converted from the original true of date (IAU of date) coordinates to J2000, and then were written in an SPK-format (type 8, discrete states, evenly spaced, Lagrange Interpolation). A TOPEX-like/POE (ASCII) format is available upon request from the MOLA POD Team. File names have the format gdn_qlnn.ymmddhhmm.ymmddhhmm.tsp where the components refer to: gdn derived from analysis using the GEODYN orbit processor; ql quick-look; nn version number; yymmddhhmm start and stop times tsp suffix designating an SPK transfer file Files can also be obtained via anonymous ftp from geodesy.gsfc.nasa.gov (node number 128.183.201.91). Change directories (Unix command "cd") to directory /dist/MGS/quick-look-orbits/ and retrieve the data of interest. Version 02 orbits are produced from a preliminary analysis of the Doppler and range data supplied by the DSN. They are preliminary, because certain ancillary information may be missing at the time these orbits are reconstructed, for instance the dates and times of momentum dumps, weather data (used for Earth troposphere refraction corrections), finalized Earth orientation (polar motion) values. The a priori modelling includes the GMM-1 gravity field, the 1991 IAU model, the Stewart (1987) drag model, and the DE403 ephemeris. Each arc adjusts the state vector, a drag coefficient, pass-by-pass range biases, and empirical parameters at regular intervals to absorb orbit error and other mismodeling. Version 04 orbits are derived from a reanalysis of the tracking data using an improved gravity model to 70x70 (MGM0827E) that includes the MGS tracking data from SPO-1, orbit insertion, and the hiatus (october, november 1997). Other than the improvement in the gravity model, the parameterization remains the same as the Version 02 orbits. The orbits will be refined on a schedule yet to be determined. Greg Neumann of the MOLA team has evaluated the orbits using the MOLA altimetry. For the MGM0827E orbits, the standard deviation of the crossovers in SPO-1 is 60 m; Using the square-root of two rule of thumb, the radial orbit error for the SPO-1 orbits would then be about 42 to 43 meters. For SPO-2, the crossover standard deviation is higher (168 m or a radial orbit error of 119 m via the square-root of two rule of thumb), reflecting the fact that the apriori gravity model (mgm0827e) does not yet include SPO-2 tracking. Hiatus vs SPO-1 crossovers are 60 m in the standard deviation. Version 06 orbits are released beginning on November 2, 1998. ============================================================= These orbits are based on an updated preliminary gravity model, mgm0883, a 70x70 model that includes the historical tracking (mariner 9, viking orbiter), and the tracking of MGS for both SPO-1 and SPO-2. No other changes to the processing were made, other than updating the gravity model. Version 09 orbits are released beginning on February 4, 1999 ============================================================ These orbits are based on an updated gravity model, mgm0890, a 70x70 model. The changes from the previous model, mgm0883, are the following: (1) The remaining SPO-2 tracking data from Sept. 1, to Sept. 17 1998 were included; (2) All the one-way Doppler data in SPO-1 and SPO-2 were rigorously reanalyzed and scrutinized on a pass-by-pass basis, and the Low Gain Antenna (LGA) measurement offset correction was systematically applied (in conjunction with the spacecraft quaternions which orient the spacecraft as a function of time) in the reduction of these data. Previously, in the mgm0827e and mgm0883 solutions the one-way Doppler data had not included the measurement offset correction; (3) The one-way Doppler data were upweighted in the OD solutions from 1 Hz (3.57 mm/s), to 0.2 Hz (0.71 mm/s). Greg Neumann has evaluated the SPO-1 and SPO-2 altimeter crossovers using the gdn_ql06* orbits, and the new gdn_ql09* orbits by computing the L2 and L2 norms (L1 and L2? - Simpson, 2000-09-12) Remember, so far the altimeter data are an independent data type. The new mgm0890 orbits show a major improvement, especially for SPO-2. His report follows: ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Wed, 3 Feb 1999 19:05:19 -0500 (EST) From: Greg Neumann To: flemoine@ares.gsfc.nasa.gov The crossovers for SPO-1/SPO-1 and SPO2/SPO-2 show slight improvement in SPO-1 and major improvement in SPO-2. In both cases, attitude kernels were set to Dave's preferred values. Observation timing bias was set to 115.2 ms. I see a small component of drift in both groups, this bias could be upped to 116 or 117 but it is not a major factor. orbits: gdn_ql06 (0885) gdn_ql09 (0890) --------------- --------------- SPO-1/SPO-1 L2 63.94 61.57 L1 10.14 9.50 N 1188 1189 SPO-2/SPO-2 L2 141.86 70.87 L1 38.83 13.86 N 5879 5875 (slight difference due to in-plane changes) +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Direct questions to F. G. Lemoine (flemoine@olympus.gsfc.nasa.gov) or D.E. Smith (dsmith@tharsis.gsfc.nasa.gov) Version 15(gdn_ql15*) orbits are released starting February 8, 2000 =================================================================== Eventually, all orbits will be redone with this model. These orbits use a new gravity model (mgm0989a). The mgm0989a model is still complete to 70x70, but includes more MGS mapping orbit tracking data from May-June, Sept-Oct, and Nov-December 1999. Orbit fits on five to six day arcs are now typically 0.15 mm/s, compared to 0.35 mm/s with mgm0964c20. The new data definitely strengthen the gravity solution, and improve the orbit modelling. more information on version 15 (gdn_ql15* orbits) 2/29/2000 The orbits include the following changes over the previous generations of orbits (gdn_ql13* and gdn_ql14) (1) New gravity model (mgm0989a) to 70x70 that includes five months of tracking data after HGA deployment, specifically, May-June 1999; Sept-Dec 1999. The gdn_ql13 and gdn_ql14 used the mgm0964c20 gravity model (70x70) that only included MGS low altitude data from Feb and March 1999. (2) Proper application of the Earth troposphere correction for arcs from August 99 to October 1999. A format change on the DSN weather data files meant that DSN station meteorological data was not being used and rather mean climatological data was used to compute the Earth tropo corrections in the tracking data. This error has been corrected for the reprocessing and the new gdn_ql15* orbits. (3) Here and there, some other miscellaneous anomalies were detected for instance momentum dump information was missing on some arcs; some tracking data on some days went missing or was never downloaded. (4) In particular for the arcs in July-August 1999, the start and stop times were scrutinized to ensure that the arcs always started and ended with a few hours of tracking. This avoids "extrapolation" which hurts some of the orbit overlaps for the gdn_ql13* series. (5) A change was made in the method used to estimate empirical accelerations to accommodate momentum desaturations. In the OD solutions for the gdn_ql13* series, these empirical accels. were too tightly constrained- loosening up on the sigmas for these accels has improved the orbit solutions (confirmed by Greg Neumann who looked at this by comparing the gdn_ql13* and gdn_ql14* orbits). (6) For completeness orbits are also made available for the period of the HGA anomaly. Some anomalies persist: (a) The orbits in mid-October 1999 do not seem well behaved - for no apparent reason the residual fits are higher and the overlaps are slightly worse. (b) We cannot fix periods where there was simply sparse tracking for example- between the 990729-990805 and the 990803-990809 arcs. The use of crossovers in the OD later on might improve these. (c) No knowledge of the time of momentum desat maneuvers is available from 990414 0615 to the start of the HGA anomaly on 990416 04:30. This information was probably lost when the spacecraft went into safe mode. The orbits will be degraded over this two day period prior to the HGA anomaly. Overall, the gdn_ql15* orbits are a substantial improvement over the previous generation of orbits. gdn_ql13*orbit overlaps with mgm0964c20 --------------------------------------- RMS (rad, cross-tr, along-tr) MGS orbit overlaps in apr-dec 1999 with mgm0964c20 for arc set orbit6d.articulate (all units are meters) 990402.990409.990408.990416. RMS 8.5478871 8.5738000 24.361220 990428.990505.990504.990507. RMS 12.794992 5.2559646 37.305254 990507.990511.990510.990517. RMS 4.7353123 3.9718403 12.134107 990510.990517.990516.990522. RMS 2.8457408 1.4603881 6.0618437 990516.990522.990521.990527. RMS 3.2613190 6.2501872 19.900643 990521.990527.990526.990601. RMS 1.0217967 1.7342791 3.9580685 990531.990606.990604.990610. RMS 5.9566392 37.905730 77.826173 990610.990616.990614.990621. RMS 2.7152193 3.5597722 16.562606 990614.990621.990619.990626. RMS 3.6610427 44.202035 113.45547 990619.990626.990624.990701. RMS 13.690489 13.603720 33.505998 990624.990701.990629.990706. RMS 3.3027734 30.224560 78.488887 990629.990706.990704.990711. RMS 4.5630410 7.2827163 36.078289 990704.990711.990709.990716. RMS 5.8833224 19.539573 80.431233 990709.990716.990714.990721. RMS 36.444519 20.672090 1850.7563 990714.990721.990719.990726. RMS 3.5793738 105.70277 294.01707 990719.990726.990724.990731. RMS 8.2439697 29.935881 103.55589 990724.990731.990729.990805. RMS 18.016063 26.836933 1666.8873 990729.990805.990803.990809. RMS 6.5096780 29.347110 82.188620 990811.990819.990817.990824. RMS 7.4809164 56.606029 207.82842 990817.990824.990822.990829. RMS 4.2204799 12.532611 50.083650 990822.990829.990827.990903. RMS 6.4114722 15.986730 67.892548 990827.990903.990901.990908. RMS 8.7635897 31.498692 137.65659 990901.990908.990906.990913. RMS 16.346757 21.794102 123.66222 990906.990913.990911.990918. RMS 9.4722347 33.771217 166.28677 990911.990918.990916.990923. RMS 4.3821741 6.3620710 33.081496 990916.990923.990921.990928. RMS 5.4271513 3.3433700 22.681609 990921.990928.990926.991003. RMS 6.4846701 7.7355377 59.225652 990926.991003.991001.991008. RMS 2.7186806 1.3313987 8.5170878 new gdn_ql15* orbits with mgm0989a ============================== RMS (rad, cross-tr, along-tr) MGS orbit overlaps in apr-dec 1999 with mgm0989a for arc set orbit6e.articulate (all units are meters) 990402.990409.990408.990411. RMS .26602135E-01 2.4404452 1.4042684 990408.990411.990411.990414. RMS .29289153E-01 6.7990012 4.2292421 990411.990414.990411.990416. RMS 24.077367 82.814325 110.72312 (hga anomaly from 990416 to 990428; No altimeter data) *990415.990420.990419.990423. RMS 14.454085 9.3382247 42.541879 *990415.990420.990419.990426. RMS 11.674179 6.3528254 32.141780 *990419.990423.990422.990426. RMS 21.072293 89.873746 131.32076 *990419.990426.990425.990501. RMS 8.0518707 24.730370 29.729717 *990422.990426.990425.990501. RMS 4.6003099 3.6321188 11.814762 *990425.990501.990428.990505. RMS 2.6916475 10.626004 13.769183 990428.990505.990504.990507. RMS .84071776 34.533468 18.501459 990507.990511.990510.990517. RMS .24521696E-01 2.0211352 2.8601187 990510.990517.990516.990522. RMS .49648244E-01 .88977530 1.4557974 990516.990522.990521.990527. RMS 2.9528288 .80504988 10.893720 990521.990527.990526.990601. RMS .38449218E-01 .37721692 .72345897 990526.990601.990531.990606. RMS .18497435 .24879138 .50628277 990531.990606.990604.990610. RMS .63623884E-01 .22038774 .44333733 990610.990616.990614.990621. RMS 2.1634424 2.2480613 9.6529723 990614.990621.990619.990626. RMS 6.8218056 1.4469060 23.742182 990619.990626.990624.990701. RMS .54199988 4.0350169 9.7199520 990624.990701.990629.990706. RMS .16052960 9.4176705 24.621438 990629.990706.990704.990711. RMS .30156572 5.3912208 14.077718 990704.990711.990709.990716. RMS .71588654 2.1618235 5.5462150 990709.990716.990714.990721. RMS .94041900E-01 6.2990846 18.010297 990714.990721.990719.990726. RMS .33386605 3.8534201 5.5626211 990719.990726.990724.990731. RMS .78712504 5.8201727 13.907414 990724.990731.990729.990805. RMS 1.5823004 11.965775 30.310286 990729.990805.990803.990809. RMS 14.131301 5.9630139 212.28963 990811.990819.990817.990824. RMS .90449172E-01 2.3428405 8.8396513 990817.990824.990822.990829. RMS .16992664 1.2400101 5.1104635 990822.990829.990827.990903. RMS .20966876 5.1924582 17.327613 990827.990903.990901.990908. RMS .35475273 1.4930652 6.2033409 990901.990908.990906.990913. RMS 8.0199503 4.9526030 40.132398 990906.990913.990911.990918. RMS .11370534 3.7912814 18.465808 990911.990918.990916.990923. RMS .18685024 3.2714266 15.842628 990916.990923.990921.990928. RMS .10304025 .48309406 2.6081617 990921.990928.990926.991003. RMS .19243874 1.6035864 7.3462898 990926.991003.991001.991008. RMS .10754712 1.0211810 5.0971979 991001.991008.991006.991013. RMS .20792834 1.7547535 10.752814 991006.991013.991011.991018. RMS .54476433 .78449885 4.5002087 991011.991018.991016.991019. RMS 4.4054786 2.2028631 18.451957 991016.991019.991018.991023. RMS 4.0726221 3.0879400 18.165049 991018.991023.991021.991028. RMS .40279883 1.0066467 5.6460455 991021.991028.991026.991102. RMS 4.2030643 1.0935689 11.913583 991026.991102.991031.991107. RMS .13361002 1.2423392 5.8855735 991031.991107.991105.991112. RMS .30888231 1.8341067 8.2318803 991105.991112.991110.991117. RMS .43889269E-01 .89193060E-02 .10903352 991115.991122.991120.991127. RMS .60652997 .33676538 1.0746306 991120.991127.991125.991202. RMS .93427901E-01 .65779294E-01 .16940613 991125.991202.991130.991207. RMS .60820069E-01 .22333015 .66485832 991130.991207.991205.991212. RMS .86599260 2.0757641 5.9896479 991205.991212.991210.991217. RMS .17525641 1.4979084 3.6591614 991210.991217.991215.991222. RMS .60770565 .82068836 4.7495095 991215.991222.991220.991227. RMS .34836829E-01 .30641639 .73703826 Direct questions to F. G. Lemoine (flemoine@ares.gsfc.nasa.gov) or D.E. Smith (dsmith@tharsis.gsfc.nasa.gov) ============================================================= This README file last modified February 29, 2000: 15:34 UTC