! File: 3972C.PROP ! Database: PEPDB ! Date: 20-FEB-1994:02:10:10 coverpage: title_1: PSEA RMGA DRIFT BIAS CALIBRATION - PART 2 proposal_for: ENG/AST cont_id: 3972 pi_fname: WILLIAM pi_lname: OCHS pi_inst: CODE 441 pi_country: USA num_pri: 1 ! end of coverpage abstract: line_1: This proposal will acquire engineering data to be used line_2: to compute a bias estimate of PSEA Retrieval Mode Gyro line_3: Assembly (RMGA) by putting the PSEA into test mode. line_4: The results will be uplinked to the PSEA Configuration line_5: Memory. ! ! end of abstract general_form_proposers: lname: OCHS fname: WM. inst: GFSC/CODE 441 country: USA esa: X ! ! end of general_form_proposers block general_form_text: question: 2 section: 1 line_1: The Pointing and Safemode Electronics Assembly (PSEA) line_2: provides the backup attitude control function in the event line_3: of a serious problem with the DF-224 flight computer. The line_4: PSEA uses sun sensors, rate gyro assembly (RGA), and, line_5: if required, the retrieval mode gyro assembly (RMGA) as line_6: inputs and produces commands to the reaction wheels and line_7: magnetic torquers. ! question: 2 section: 2 line_1: The Fixed Head Star Trackers are used in map mode to obtain line_2: an attitude reference and PSEA test mode will be used to line_3: enable the safemode computer (SMC). The PASS system will line_4: process the RMGA data and produce vehicle-frame RMGA line_5: biases that will then be uplinked to the PSEA Configuration line_6: Memory. ! question: 2 section: 3 line_1: The biases are important to ensure proper attitude control line_2: should gyro (RGA) failures force the PSEA to use the line_3: the RMGA. This is particularly important in the case of line_4: gravity gradient mode, which is sensitive to bias errors. ! question: 3 section: 1 line_1: Format P is required for this test. line_11: There is no particular vehicle attitude required for this line_12: test, although vehicle attitude must remain constant while line_13: the data take occurs. The RMGA will be powered up by line_14: realtime commands (RTCs) and allowed to warm up for a line_15: minimum of 5 mins. Safemode Computer A will be selected. line_16: A minimum of 5 mins. after entry into orbit day, the STOCC line_17: will begin issuing soft-keep alive disable commands to the line_18: PSEA to prevent entry into hardware sunpoint if the DF-224 line_19: keep alives are stopped while the PSEA is inthe test mode. line_20: These commands are automatically issued every 30secs by the line_21: online system. PSEA test mode will be commanded by the RTC. line_22: Two FHST's will be placed in map mode for a 25 min. period line_23: via MOC Merge. ! question: 3 section: 2 line_1: Test mode will then be commanded by RTC for a 20 line_2: min. period to obtain bias drift informatiom for the RMGA line_3: calibration. At the completion of the 20 min. period, line_4: test mode and soft keep-alive disable commands will be line_5: terminated. line_7: The vehicle attitude must remain constant throughout this line_8: period. line_9: CONSTRAINT 1: Continuous forward link is required whenever line_10: the PSEA is in test mode. This is necessary to keep the soft line_11: keep-alive disable commands and the test mode initiate line_12: commands going. line_13: CONSTRAINT 2: The HST must be in full sunlight whenever test line_14: mode is active. Test mode is active for 73 secs following the line_15: test mode initiate command. This is required to prevent the line_16: PSEA from closing the aperture door when test mode is line_17: initiated. line_18: After completion of test mode the RMGA will be powered off. ! question: 5 section: 1 line_1: The 20 min. period requested for RMGA calibraton is a line_2: tradeoff between obtaining adequate data for a drift bias line_3: estimation and the orbital and communication constraints. line_4: The test can be scheduled as an interleaved activity. At line_5: least 30 minutes of uninterrupted forward link is required line_6: while the PSEA is in test mode. Also this forward link line_7: must begin no earlier than 5 minutes after Enter Orbit line_8: Day and end no later than 5 minutes prior to Enter Orbit line_9: Night. ! question: 6 section: 1 line_1: Continuous forward link required whenever the PSEA is in line_2: test mode is required to keep it in test mode. The PSEA line_3: will automatically exit out of the test mode, 73 secs. line_4: after the test mode initiate command is received. line_5: The PSTOL proc issues this command every 73 secs. ! question: 7 section: 1 line_1: Data will be processed by the PASS system to provide line_2: uplinkable values for the RMGA drift bias estimate. ! !end of general form text general_form_address: lname: OCHS fname: WM. category: PI inst: GFSC/CODE 441 ! ! end of general_form_address records ! No fixed target records found ! No solar system records found ! No generic target records found exposure_logsheet: linenum: 2.000 sequence_1: DEFINE sequence_2: OBS targname: DARK config: S/C opmode: DATA aperture: NONE num_exp: 1 time_per_exp: 30M fluxnum_1: 1 priority: 1 req_1: CYCLE 2; req_2: RT ANALYSIS; req_3: REQ UPLINK; comment_1: FORWARD LINK MUST BE UN- comment_2: INTERRUPTED AND BEGIN NO comment_3: SOONER THAN EOD +5MIN, AND comment_4: END NO LATER THAN EON -5MIN comment_5: PSEA WILL BE IN TEST MODE, comment_6: NO SLEWS, SIPS, ETC. ! linenum: 3.000 sequence_1: USE sequence_2: OBS ! linenum: 4.000 sequence_1: USE sequence_2: OBS req_1: AFTER 3 BY 60D +/- 7D; ! linenum: 5.000 sequence_1: USE sequence_2: OBS req_1: AFTER 4 BY 60D +/- 7D; ! linenum: 6.000 sequence_1: USE sequence_2: OBS req_1: AFTER 5 BY 180D +/- 14D; ! ! end of exposure logsheet ! No scan data records found