PDS_VERSION_ID = PDS3 DATA_SET_ID = "GO-J_JSA_X_V_E_A_C_UPL_V1.0" RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2015-05-18 NOTE = "GOUP_0002_INFO.TXT was originally archived in the GOUP_0002 archive volume at the root level of the volume as info.txt" END_OBJECT = TEXT END This file contains a brief description of the sequences that occurred during the Galileo Extended Mission (GEM) encounter phase. The descriptions will contain the name of the sequence, the sequence ID along with the start and stop times in UTC, SCLK times and any comments that may accompany the sequence. SEQUENCE: E12A SEQ ID: E12ACL Sequence BEGIN: 97-349/08:00:00.000 Sequence END: 97-351/18:00:00.000 There were two anomalies during the E12 encounter. The gyro anomaly began at 97-349/23:27 when SEQID crashed and the AACS FM17 tripped at 97-350/00:21. Fifty minutes later, at 97-350/01:13, FM17 tripped again. Spacecraft attitude information at this time is suspect, but the sequence proceeded to execute nominally with the exception of 7 scan platform misslews. The uplink of an E11 Playback Table shown in the command log for E12A is real and was done as a precaution to halt playback until recovery from the gyro anomaly was complete. The EPD thermal anomaly (ISA 10819) began at 97-350/18:00 when all real time science data disappeared. By 97-350/22:27:40 the instrument LEMMS temperature had dropped to near the 3-210 limits and went into alarm. SEQUENCE: E12B SEQ ID: E12BGN, E12BF, E12BA Sequence BEGIN: 97-351/18:00:00.000 Sequence END: 98-040/06:00:00.000 E12B was extremely complex because there were 4 separate background sequences executing during this period. The original E12BGN was cancelled by real time command following the second gyro anomaly which occurred on 97-355 during OTM-39. E12BPC was a short, stripped-down sequence which was uplinked to provide backgound telemetry during the anomaly resolution period. E12BQD (Fred) followed E12BPC but had increasingly poor telecom performance as the s/c drifted farther off-earth since there had been no attitude updates following the anomaly. Finally E12BRC (Arnold) was uplinked which cancelled (terminated) Fred and provided updated telemetry information following the successful sun acquisition on 98-012. All AACS activities were removed from the background sequences and performed by a series of RBSs. In addition, The EPD instrument was turned off at the beginning of E12B in response to the E12A thermal anomaly. Later in Arnold, a real time checkout of the instrument was performed. This was the first part of a 3 part checkout which continued on into E12C. Playback did not start in E12A because the gyro anomaly disabled data compression and then because an old E11 PBT was purposely sent to keep playback paused. Playback finally started in E12B when Segment 1 was again radiated on 97-352. Playback was later terminated and then initiated on 97-364 because SSI data was undercompressing. A new Segment 1 was created to replace the original Segment 1. SEQUENCE: E12C SEQ ID: E12CHL Sequence BEGIN: 98-040/06:00:00.000 Sequence END: 98-087/13:00:00.000 There were several real time activities and reserved box sequences during this period. Both siturns, an RPM maintainence, and an inertial test were implemented by RBS. The only spacecraft anomaly in E12C was when Fault Monitor 12 tripped during the inertial test on 98-069. The gyro performance had further degraded after the E13 perijove pass resulting in too large a discrepancy between the gyro and the star based attitude estimates once SEQID was enabled. Real time commands were sent on 98-070 to re-enable AACS data compression and on 98-077 to clear the alarms. The final two parts of the EPD real time checkout, Phases B & C, were also performed in E12C. The checkouts were nominal and the final condition of EPD was that the instrument was turned on and configured for E14 encounter. The actual execution times of these two packages are within a minute of the times listed in the SEF. A series of 4 DACs to turn the INS gyro electronics off and on around E14 perijove were transmitted to the spacecraft on 98-087 during E12C; however, the execution of these commands was not until E14A. Those DACs are not found in this SEF although their transmission does appear in the Script File and MCT Log for E12C. SEQUENCE: E14A SEQ ID: E14AJE Sequence BEGIN: 98-087/13:00:00.000 Sequence END: 98-090/01:45:00.000 The Final E14A As-Run SEF is ready and released. There were 4 DACs which executed in E14A which were actually transmitted to the spacecraft during E12C. The DACs were sent to turn the INS gyro electronics off for 12 hours around perijove in order to protect the gyros from further radiation degradation. The remaining real time commands in this sequence were routine instrument mode changes. SEQUENCE: E14B SEQ ID: E14BGD Sequence BEGIN: 98-090/02:15:00.000 Sequence END: 98-150/21:00:00.000 The Final E14B As-Run SEF is ready and released. The primary planned real time activity in E14B was a flight software change to the AACS Gyro Scale Factor code to compensate for the degradation in the gyro 1-X axis observed in the E12/13 orbits. The AACS FSW patch which executed on 98-123 contained new code to add an extra step in the calculation of the gyro output and new values for the gyro scale factors. Results from the real time Gyro Performance Test following the FSW patch indicated that there was an error in the ordering of the gyro delta values in the matrix. A second real time package executed on 98-133 to fix the order of these parameters. The final result was that the new code properly removed most of the gyro error. A residual error remained because the actual gyro performance had changed between the time the parameters had been determined and the time the patch had executed. The first anomaly (ISA 11039) in E14B occurred during the Siturn on 98-113. After the turn of about 2.5 deg was completed, a routine vernier correction was performed. Apparently the attitude control system had only locked on to two of the stars in its four star set, and had about a 6 mrad perceived attitude estimate error at the time the vernier correction began. The end result is that the final spacecraft attitude was about 5 mrad different than the target attitude. The second anomaly (ISA 11029) was the spacecraft safing which occurred during OTM-47 at 98-148/20:21:25.889. The spacecraft executed the majority of the maneuver before a sequence timing error created an AACS command constraint violation which caused the spacecraft to abort the on-board sequence and safe itself. The Science Virtual Machine was recovered on 98-149, and a mini-sequence, BSCIMA, was uplinked to turn on the science instruments and match the spacecraft states to the E15A sequence. SEQUENCE: E15A SEQ ID: E14AHB Sequence BEGIN: 98-150/21:00:00.000 Sequence END: 98-154/10:00:00.000 The Final E15A As-Run SEF is ready and released. The primary real time activity in E15A was recovery from the AACS Fault Monitor trips which occurred at approximately 98-152/08:56 SCET (ISA 11035) during the targetting for the SSI 15IISSRFMON01 observation. This observation had a large slew going into the polar region which when coupled with the bad gyro performance resulted in a large attitude estimate error. The scan platform commander tried to correct for the SBA position error by moving the SBA at a high rate. The high rate gyro fault protection was tripped which turned the INS and gyros off. Shortly after this, FM 28 sensed the gyro information was gone and aborted inertial mode leaving the spacecraft in cruise mode for the remainder of the E15 observations. Tripping the fault monitors also disabled data compression which interrupted PWS real time science. Real time commands were sent to restore data compression and to turn on the accelerometers. The remaining real time commands in this sequence were routine NIMS mode changes. SEQUENCE: E15B SEQ ID: E15BGE Sequence BEGIN: 98-154/10:00:00.000 Sequence END: 98-201/05:00:00.000 The Final E15B As-Run SEF is ready and released. The majority of the real time commands in E15B were DACs to overwrite the heater configuration from the background sequence. As a result of the AACS Fault Monitor Trip in E15A, the project decided to change the heater strategy for E15B. Going into E15A the Bay C/D heater was ON and the Bay B heater was OFF. After the FM Trip, fault protection turned OFF both heaters causing the temperature of the CDS electronics in Bay A to drop. At that point it was considered to be prudent to adopt the new strategy where the Bay B heater would be ON and the Bay C/D heater would be OFF. This was the thermal state planned to be adopted in E16B but not the state that was already sequenced in E15B. Three additional real time commands were sent to clear the AACS fault codes and inertial reference loss bits as final clean up from the E15A anomaly. An IAP was sent during the 98-181 gyro test in order to increase the engineering telemetry from 10 bps to 40 bps. The extra engineering data was requested to provide greater visibility of the power excursions during the gyro test. OTM 50 was not necessary so it was cancelled. A real time command was sent to resume playback during the OTM window. SEQUENCE: E16A SEQ ID: E16AKE Sequence BEGIN: 98-201/05:00:00.000 Sequence END: 98-209/00:00:00.000 The Final E16A As-Run SEF is ready and released. The E16A sequence was terminated prior to the Europa fly-by when the spacecraft entered safing at 17:35:46 SCET on July 20, 1998. Safing was called as a result of the CDS A string being taken down by a hardware bus parity error (ISA 11033), shortly after entering the high radiation region of the perijove passage. The root cause of a despun bus reset is debris generated in the slip rings that transfer power and signals between the spun portion of the spacecraft and the despun portion. Debris in this area can cause shorts in a line which normally indicates to the CDS despun section that the CDS subsystem has experienced a power on reset. In that circumstance the despun section performs a reset and prepares for recovery. In the case of this erroneous reset, the rest of the CDS notes the despun section reset, and calls the on-board safing algorithm. Real time recovery of the spacecraft was completed by July 24 and a state matching reserved box sequence was sent to reconfigure the science instruments and prepare for the start of E16BŐ. The EPD instrument experienced another temperature anomaly following the spacecraft safing (ISA 11034) and was turned off by real time commands. The NIMS DACs which were transmitted to the spacecraft at the beginning of E16A did no execute as a result of the spacecraft safing. SEQUENCE: E16B SEQ ID: E16BPC Sequence BEGIN: 98-209/00:00:00.000 Sequence END: 98-268/04:00:00.000 The Final E16B As-Run SEF is ready and released. This sequence is technically E16B Prime since the front end was truncated in order to allow time to recover from the spacecraft safing in E16A. The most extensive real time activity in the E16B period was the reserved box sequence, BDSNAD which executed from 98-245 through 98-264. Since most of the recorded science data was lost in E16 from the anomaly, the science teams did not require the same level of tracking coverage in E16 cruise as it would have in the nominal plan. Therefore, a large number of DSN passes were released to other projects. Since the E16B sequence was uplinked prior to the station negotiations, the reserve box sequence was used to pause and resume playback around the missing stations to preserve the E15 and E16 playback data. The Magnetospheric Working Group (MWG) was also given the opportunity to collect long intervals of real time science data during cruise and this was incorporated into the RBS. Other MWG real time science was collected using real time commands. There were two real time command packages to recover the EPD instrument from the anomaly that occurred in E16A. These packages were very similar to those used in E12 although the cause of the EPD anomaly was different. In the case of E16 the EPD instrument experienced a Power On Reset (POR) while the CDS A-string was down. SEQUENCE: E17A SEQ ID: E17AFC Sequence BEGIN: 98-268/04:00:00.000 Sequence END: 98-271/02:00:00.000 The Final E17A As-Run SEF is ready and released. Six seconds into the first scan platform slew in E17A fault monitor 28 (no gyro data in inertial mode) tripped (ISA 11045). This implies a gyro high rate fault tripped first. The INS and accelerometers were turned off and the spacecraft switched from inertial to cruise mode. These are the same faults that were seen in E15A, however, the scan platform was not near the cone pole region. The reason for the faults was never determined, but the remainder of the sequence executed nominally with the exception of degraded scan platform performance. Real time commanding in this sequence was for diagnostic purposes and to re-enable data compression and clean up after the fault. SEQUENCE: E17B SEQ ID: E17BFB Sequence BEGIN: 98-271/02:00:00.000 Sequence END: 98-325/12:00:00.000 The Final E17B As-Run SEF is ready and released. There were no anomalies in this sequence, however, there were several major real time activities. The first real time activity was change to the AACS telemetry in map 3 to increase visibility into gyro behavior for the purposes of calibration and gyro related anomaly characterization. Channels E-1457 and E-1459 were added to monitor the raw gyro data on the 1X and 2X axes. A real time scan platform slew test was performed on 98-311 to recreate the slew in E17A which caused fault monitor 28 to trip. The fault was successfully recreated. Playback was paused from 98-316 to 98-317 because of an unplanned DSN station loss to the Voyager Project. A reserve box sequence was uplinked to the spacecraft in order to protect playback data from the anticipated loss of additional DSN 43 passes to Voyager, however, the passes were released by Voyager so a command was sent to cancel the RBS. SEQUENCE: E18A SEQ ID: E18AFE Sequence BEGIN: 98-325/12:00:00.000 Sequence END: 98-328/01:00:00.000 The Final E18A As-Run SEF is ready and released. Several anomalies occurred in this sequence. At 98-325/18:42:46.533 SCET the Gyro 1x High Rate Fault monitor was tripped (ISA 11049). The s/c switched into cruise mode and safed the scan platform. Real time commands were sent to re-enable data compression, clear the AACS fault code, inertial reference loss bits, and fault max counter array. Inertial mode was restored by the background sequence. The following day at 98-326/05:24:13.102 the s/c entered safing from a CDS despun bus reset (ISA 11050). During the real time recovery commanding there was a second CDS despun bus reset at approximately 98-327/01:38 (ISA 11051). The second safing occurred between the MRO of the missing message list (98E281) and the CAP to set the chaining variable and clear system fault protection variables and CDS entry presence (98E282). However, all of the radiated commands were received and executed by the s/c, including the restart of the science virtual machine. The timing of the second safing is not known precisely since the commands to clear the time of the first safing were received by the s/c after the second safing had occurred. SEQUENCE: E18B SEQ ID: E18BFE Sequence BEGIN: 98-328/01:00:00.000 Sequence END: 99-031/02:00:00.000 The Final E18B As-Run SEF is ready and released. There were no anomalies in this sequence, however, the original onboard cruise sequence was replaced by E18B Prime. E18B Prime was created to protect science data from being lost over DSN passes that were released after E18 bus reset anomaly and the loss of the encounter data. Replacing the E18B sequence happened in two phases. First an RBS was sent to cancel E18BFE in order to release sequence memory for the uplink of E18BQK. The Cancel RBS contained several days worth of the original E18BFE to provide flexibility in timing for the uplink of E18BQK. E18BQK then cancelled the Cancel RBS once it began executing. Because extra telemtry capability was available following the loss of the recorded E18 encounter data, E18B Prime contained additional recorded science observations for the MWG, SSI and NIMS. Real time commands were also sent to collect 3 days of Real Time Science data for the fields and particles instruments. Other real time activities in E18B included a real time MRO of the alert and power code buffers which was sent on 98-348 to get more information on the second E18A safing. MROs were sent on 98-351 to return information from the star intensity buffer to characterize the radiation degradation of the star scanner. There was a real time update of the AACS gyro parameters on 99-018 and two real time auto gyro drift cals on 99-028 to insure proper performance of the two large SITURNS planned for E19A. SEQUENCE: E19A SEQ ID: E19AHC Sequence BEGIN: 99-031/02:00:00.000 Sequence END: 99-042/16:00:00.000 The Final E19A As-Run SEF is ready and released. The E19A sequence was terminated by onboard fault protection software about four hours after Europa closest approach. The spacecraft entered safing at 99-032/5:41:33 SCET on February 1, 1999, as a result of an incomplete sun acquisition turn designed to bring it back to the nominal Earth point attitude (ISA# 11055). In the nominal encounter sequence, it was necessary to turn the spacecraft to an off-earth angle of approximately 60 degrees to eliminate boom obscuration and substantially increase science viewing geometry. During the sun acquisition turn back to earth point, the spacecraft failed to detect the sun as it passed through an angle of approximately 45 degrees. The sun acquisition was used in this encounter to minimize dependence on the gyros. Two small siturn RBS products were uplinked to return the spacecraft to nominal earth point, followed by a state matching sequence to reconfigure the science instruments and prepare for the start of E19B Prime. SEQUENCE: E19B SEQ ID: E19BDH Sequence BEGIN: 99-042/16:00:00.000 Sequence END: 99-081/05:00:00.000 The Final E19B As-Run SEF is ready and released. There were no anomalies in this sequence, however, E19B Prime was sent in place of the originally planned E19B sequence, due to recovery time needed from the E19A safing. OTM-60 was cancelled. SEQUENCE: E19C SEQ ID: E19CDD Sequence BEGIN: 99-081/05:00:00.000 Sequence END: 99-122/17:00:00.000 The Final E19C As-Run SEF is ready and released. There were no anomalies in this sequence. E19C spans the solar conjunction period, which began on March 22, 1999 and ended May 01, 1999. Real-time commands were uplinked to install a new flight software patch (BURP) to prevent Despun Bus Reset PORs from calling safing. SSF Version E19CDD was created for SEQTRAN because of new MEMFILE/SYMFILE from MN61AA, and also to modify the uplink window and to add single setters to change HLM B box sizes to make room for the BURP patch if needed. SEQUENCE: C20A SEQ ID: C20AJD Sequence BEGIN: 99-122/17:00:00.000 Sequence END: 99-127/12:00:00.000 The Final C20A As-Run SEF is ready and released. The C20A encounter sequence was five days long, began on May 2, 1999, 17:00 UTC and ended on May 7, 1999, 12:00 UTC. This encounter marked the beginning of the second phase of GEM, the Perijove Reduction Campaign. On Monday, 5/3/99, between 123/17:57 and 18:51 (SCET), telemetry indicates that the spacecraft had survived a bus reset and that the bus reset patch had executed as expected- meaning the sequence was NOT cancelled and we did NOT go through safing. Subsequently, at around 124/02:00 (SCET) the spacecraft experienced a second reset. Again, the protection worked as planned. There was an AACS anomaly - a gyro high rate trip early in the sequence (at 99-124/12:34:58 SCET), which had only minimal impact as there were no immediate NIMS observations. After returning to inertial mode for the beginning of the Callisto observations, the spacecraft tripped out of inertial again (at 99-125/14:08 SCET). This was due to a gyro Y axis mismatch. The spacecraft has fully redundant gyro capability in the Y axis, and the Attitude Control System has fault protection checks that both of the Y axis gyros are reporting consistent values. Subsequent Gyro tests have indicated that the -1Y gyro axis error increased during the perijove pass to almost 10%. With the -2Y axis still hanging in at almost no mismatch, this would almost guarantee a fault trip. After this trip we remained in cruise mode for the duration of the encounter. SEQUENCE: C20B SEQ ID: C20BFE Sequence BEGIN: 99-127/12:00:00.000 Sequence END: 99-180/07:00:00.000 The Final C20B As-Run SEF is ready and released. There were no anomalies in this sequence. C20B included OTM-63, OTM-64, and OTM-65. An RBS was sent for an AACS gyro test, a realtime gyro scale factor update was uplinked, and realtime commands were sent in an attempt to fix a failing UVS grating. SEQUENCE: C21A SEQ ID: C21AQG Sequence BEGIN: 99-180/07:00:00.000 Sequence END: 99-184/11:00:00.000 The Final C21A As-Run SEF is ready and released. The C21A encounter sequence was four days long, began on June 29, 1999, 07:00 UTC and ended on July 3, 1999, 11:00 UTC. Three minor anomalies occurred during the perijove pass through the high radiation environment, all believed to be radiation related. At about 5:17 p.m. PDT on 7/1, the radiation appears to have caused the star scanner to mis-identify stars sufficient to erroneously cause a discrete jump in the spacecraft attitude. The Attitude Control Subsystem then reacted to the sudden jump by assuming the spin bearing assembly was misbehaving and swapped autonomously to the backup SBA. No remote sensing data was lost as a result of this swap, and the spacecraft continued to record the planned observations. The Attitude Control Subsystem disabled it's data compression function, impacting Plasma Wave Subsystem science gathering until a real time command re-enabled the compression. At about 11:29 p.m. PDT on 7/1, the radiation appears to have cause a second fault similar to the above incident but this time in the Scan Actuator Subsystem in the Attitude Control Subsystem. A bus reset occurred at about 3:27 a.m. PDT on 7/2. The software handled it as planned, and the sequence continued unaffected. A heating cycle was performed on the Photopolarimeter/Radiometer (PPR) instrument to attempt to recover the radiometry channels, and was successful. The Energetic Particle Detector (EPD) utilized its "chicken mode" scanning strategy to protect the detectors from the high radiation environment. SEQUENCE: C21B SEQ ID: C21BQG Sequence BEGIN: 99-184/11:00:00.000 Sequence END: 99-223/14:00:00.000 The Final C21B As-Run SEF is ready and released. There were no anomalies in this sequence. C21B ran from July 3, 1999 to August 11, 1999, and included OTM-66, OTM-67, and OTM-68. Encounter cleanup items and parameter updates were sent via realtime commands for AACS, as well as a gyro speed trap test. SEQUENCE: C22A SEQ ID: C22AJD Sequence BEGIN: 99-223/14:00:00.000 Sequence END: 99-226/22:00:00.000 The Final C22A As-Run SEF is ready and released. The C22A encounter sequence was three days long, began on August 11, 1999, 14:00 UTC and ended on August 14, 1999, 22:00 UTC. The spacecraft flew within 7.3 Jupiter radii of the planet's center at 03:59 am PDT. The flyby of Jupiter's moon Callisto occurred on August 14, at 1:31 a.m. PDT, at a distance of 2296 kilometers (1427 miles). The radiation environment during this flyby appears to have been exceptionally severe. Background radiation (as measured in real time by our star scanner) peaked at a 1400 pulse count level during the plasma sheet crossing two hours before Jupiter close approach. Four minor anomalies occurred during the perijove pass through the high radiation environment, all believed to be radiation related. At 6:07 a.m. PDT on 8/12, the radiation environment near Jupiter close approach appears to have caused a despun bus reset. The bus reset protection software succeeded in keeping the encounter going, but the tape recorder truncated the recording of an observation. On board algorithms in the CDS continued the recording sequence, but had to skip recording several other observations to get back on track. This error resulted in the truncation of 10% of a fields and particles recording, the loss of two Near Infrared Mapping Spectrometer observations, and the loss of another fields and particles observation. At 8:21 a.m. PDT on 8/12, the radiation environment appears to have also caused a backup spin source to experience a hardware error. The spin detector is monitored by on board fault protection, which disabled the spin detector and data compression of the Plasma Wave instrument. Data compression was re-enabled at 5:00 PM on 8/12. The bus reset protection software again proved its value, as another 2 bus resets occurred at about 10:29 a.m. PDT on 8/12 and again at 5:00 p.m. PDT on 8/12. The software handled both as planned, and the sequence continued unaffected. Playback of recorded data began at 1:17 p.m. PDT on 8/13. SEQUENCE: C22B SEQ ID: C22BFD Sequence BEGIN: 99-226/22:00:00.000 Sequence END: 99-256/20:00:00.000 The Final C22B As-Run SEF is ready and released. The C22B sequence was thirty days long, began on August 14, 1999, 22:00 UTC and ended on September 13, 20:00 UTC, and included OTM-69 and OTM-70. Playback of C22 encounter data began in the C22A sequence. EPD HV was powered off and recovered on DOY 245/246 due to an anomaly (ISA #11104). Additional realtime commands were sent for encounter cleanup from bus resets, and for spin detector checkouts and AACS parameter updates. Finally, a CDS patch was uplinked on DOY 254 to protect against another spurious DMS ready mode command. SEQUENCE: C23A SEQ ID: C23ANG Sequence BEGIN: 99-256/20:00:00.000 Sequence END: 99-283/04:00:00.000 The Final C23A As-Run SEF is ready and released. The C23A encounter and cruise sequences were combined into a single load, lasting 27 days. Encounter began on September 13, 20:00 UTC and cruise ended on October 10, 04:00 UTC. The spacecraft flew within 6.5 Jupiter radii (Rj or 523,000 kilometers, 325,000 miles) of the planet's center at 03:59 am PDT. The flyby of Jupiter's moon Callisto occurred on September 16, at 11:02 a.m. PDT, at a distance of 1,052 kilometers (654 miles). The radiation environment during this flyby appears to have been much lower than the previous encounter. No anomalies occurred during the C23A encounter. This sequence contains OTM-72 and OTM-73. At 3:39 p.m. PDT on 9/14, the radiation environment near our Jupiter close approach appears to have caused a despun bus reset. The bus reset protection software again proved its value, as the software handled the reset as planned, and the sequence continued unaffected. Playback of recorded data began at 10:05 a.m. PDT on 9/15. The UVS instrument grating was not operating properly in this encounter, and a set of 4 cold start grating tests and 4 backup grating tests were commanded to try to restart grating motion. These did not have any effect on the instrument grating, and it remains stuck. UVS was commanded off at the end of this sequence. SEQUENCE: I24A SEQ ID: I24AQE Sequence BEGIN: 99-283/04:00:00.000 Sequence END: 99-287/03:00:00.000 The Final I24A As-Run SEF is ready and released. Encounter began on October 10, 04:00 UTC and cruise ended on October 14, 03:00 UTC. Closest approach to Io was on October 11, 1999 at 04:33 UTC at an altitude of 612 km. At 3:09 a.m. PDT ground receipt time (19 hours prior to the Io 24 close approach) on 10/10, a memory error caused a spacecraft safing. The spacecraft was returned to normal operations, and a revised encounter sequence was transmitted to the spacecraft to avoid the use of the suspect memory area. This was accomplished in time to resume normal encounter operations at 8:00 p.m. ground receipt time on 10/10. All observations for Io close approach were made as planned, but some pre-encounter PPR observations and a fields and particles Io torus recording was not accomplished due to the memory anomaly. Playback of the Io 24 data began on 10/11, but the initial playback was done without playback of SSI data. The bad memory location is in a buffer area used for recording three types of data (PPR Burst data and two types of NIMS), and is also used for the playback of imaging data. Memory testing continued beyond this sequence. The UVS instrument grating was still not operating properly in this encounter, and UVS remained off in this sequence. NIMS experienced a stuck grating sometime prior to the I24 observations, but were still able to collect valuable science data in this and subsequent encounters. SEQUENCE: I24B SEQ ID: I24BFC Sequence BEGIN: 99-287/03:00:00.000 Sequence END: 99-329/04:00:00.000 The Final I24B As-Run SEF is ready and released. The I24B sequence lasted 42 days, began on October 14, 1999 03:00 UTC and ended on November 25, 1999 03:00 UTC. This sequence includes OTM-75 and OTM-76A Memory testing continued during this sequence to trouble shoot the pre-encounter anomaly in I24A. NIMS grating tests were done in this sequence to attempt to recovery grating operation, but were unsuccessful. UVS was turned on after the Io 24 close approach, and the post encounter pre-planned observations were used to assist in troubleshooting of the instrument's anomaly. Data returned from these tests show that the backup grating drive electronics were successfully commanded, that the instrument's microprocessor was accepting commands, but that the grating was still not moving. Imaging playback began on DOY 291, after part of the memory anomaly was resolved. More memory patches were also done, working to provide PPR and NIMS the ability to record certain data formats. SEQUENCE: I25A SEQ ID: I25ADX Sequence BEGIN: 99-329/04:00:00.000 Sequence END: 99-348/08:00:00.000 The Final I25A As-Run SEF is ready and released. Encounter began on November 25, 1999 04:00 UTC and cruise ended on December 14, 1999 08:00 UTC. Closest approach to Io (5.9 Rj) was on November 26, 1999 at 04:05 UTC at an altitude of 300 km. Perijove passage was at 5.7 Rj, about 2 hours prior to Io closest approach. About four hours prior to Io closest approach on Thanksgiving Day, the spacecraft entered safing due to a memory addressing anomaly. The spacecraft was recovered in less than four hours, the tape recorder was repositioned, and a modified science contingency sequence was executed, salvaging one of two remaining tracks of tape planned for recording. A second sequence was generated to follow up with the next two weeks of activities, until I25B was scheduled to take over. This sequence also included OTM-78, as well as a large number of realtime recovery packages post-safing, including a NIMS software reload and an EPD recovery from a memory upset. Playback was initiated on DOY 330 by realtime command. SEQUENCE: I25B SEQ ID: I25BDE Sequence BEGIN: 99-348/08:00:00.000 Sequence END: 00-001/23:30:00.000 The Final I25B As-Run SEF is ready and released. The sequence runs from December 14, 1999 08:00 UTC to January 1, 2000 23:30 UTC. Also included in the baseline sequence are OTM­79, OTM-80 and OTM­81. EPD continued with realtime recovery commanding from the memory upset in I25A, and NIMS recovery commanding continued as well. Playback entered limited search on DOY 360, and was recovered by realtime command and new playback tables on DOY 364 (ISA #11121). This completes the Galileo Extended Mission data set.