karn@mouton.UUCP (08/22/84)
Posted: Tue Aug 21, 1984 12:35 PM GMT Msg: DGIE-1880-3641 From: MSWEETING To: DOCS Subj: Uo-9 bulletin 88 **** UoSAT Bulletin-88 17th August 1984 **** ** UoSAT-Oscar-9 Schedule ** The daily operations of UoSAT-1 will continue to be disrupted next week, and this Bulletin will be transmitted, together with 1200 bd telemetry and Digitalker, until Wednesday - to be followed by check-summed telemetry. The preparation of the Bulletin is being re-organised to spread the workload - please bear with us! Items of relevant interest for the Bulletin are always welcome - the weekly deadline is 10.30 local time each Friday - and should be sent to the UoSAT Team in writing. The 2.4 GHz Beacon will be in use this week. ** General News ** Martin (G3YJO), Roger (G8NEF) and Tony (G8ONO) visited ESTEC (ESA) on Monday, Tuesday & Wednesday this week to give presentations on the UOSAT Programme and to discuss possible future collaboration and use of their facilities. The meeting was most profitable and interesting. A Masters Degree in 'Satellite Communications Engineering', based heavily around the experience gained through the UoSAT Projects, will commence at the University of Surrey this October - although welcome, this adds, however, to the already overloaded UoSAT Team! Details avaliable from G3YJO. Future UoSAT Missions are being proposed and studied, varying in scope from UO-9 & UO-11 orbits to Phase 111 and Geosynchronous orbits. We would be very interested to hear of any (reasonable!) suggestions or areas of interest that you may have - again please direct to G3YJO. Three Active Magnetospheric Particle Tracer Expt. (AMPTE) spacecraft were launched successfully by NASA DELTA from Cape Canaveral on Thursday 16th August - after three aborted launch attempts following ground station computer malfunctions and the discovery of debris in the vehicle. A small UK spacecraft, contributed by the UK SERC, was mounted between the two large US & DL spacecraft - UoSAT contributed to the Particle Wave Experiment on this s/c. ** UoSAT-Oscar-11 Operations ** Harold Price, NK6K, has continued his efforts to commission the Digital Communications Experiment (DCE). Whole-orbit data gathering has continued, interspersed with telemetry, to support analysis of the GG lock and libration. The frequent dumps of data from the ODATA whole-orbit telemetry recording program indicate that the gravity-gradient lock is stable, and analysis now indicates that the libration (oscillation about the ideal downward-pointing direction) is currently contained within a 20 degree cone and with a very long period - of the order of hours. The simulations carried out at UoS before GG boom deployment indicated that we might expect about 38 to 42 degrees of libration, so this result is particularly pleasing. Work is now under way to consider spinning the spacecraft slowly (once every 5-10 mins) in order to improve the temperatures and also to develop de-libration algorithms to improve further the earth pointing. 'Thermal spin' manoeuvres are planned to commence next week. A number of CCD Imager tests have been carried out (Thurs & Fri) - results will take some time to process, but will be announced a.s.a.p.! ** UOSAT-OSCAR-11 Gravity Gradient Boom Deployment ** Following several days final preparation and rehearsals, the UO-11 gravity gradient boom was deployed under on-board 1802 computer control at 10:35 gmt during orbit 2113 on 24th July. The automatic magnetorquing manoeuvres, continuously executed by the 1802 OBC over the previous few weeks, had aligned the spacecraft closely to the geomagnetic field vector and reduced residual motions (wobble) to a very low value. Following final confirmation of auspicious deployment conditions at AOS at Surrey on orbit 2113, the OBC was given instructions to terminate the magnetorquing routines and deploy the boom for 15 minutes taking the spacecraft out of range of UoS. The OBC simultaneously recorded X,Y,Z, +5V current and boom & computer status channels automatically throughout the operation whilst the boom was being deployed and during the following orbit, to monitor gravity gradient capture and spacecraft operations. The stored data was dumped at UoS on the next orbit (2114) and examination confirmed the correct operation of the deployment routine and preliminary analysis of the stored Navigation Magnetometer data indicated successful gravity gradient capture. Data gathered regularly since then has confirmed that the spacecraft has maintained successful gravity gradient stabilisation and showed no evidence of severe libration. Residual energy before boom deployment translated itself into libration following GG-lock - which has been monitored and will be minimised using magnetorquing routines similar to those used during initial attitude control manoeuvres. The spacecraft will soon be spun very slowly around the Z-axis in order to improve the internal temperatures - currently running somewhat cool. Introducing a very slow Z-spin does, of course, interact with the GG stabilising forces but only to impart a small forward or backward 'tilt' of a few degrees dependent on spin rate. Gravity gradient stabilisation of UO-11 is the culmination of many months of preparation and many weeks of spacecraft activities - most of which has not been visible to the outside world! It has been very demanding and has necessitated the use of considerable facilities and required a particular, dedicated effort from the UOSAT Team - particularly Stephen (Attitude, Stabilisation & Navigation Analysis), Roger G8NEF (Spacecraft Software) and Neville G8NOB (Ground Station Software). Deployment 'highlights' follow: Saturday 21/7/84 TORQUEH (the 1802 program which actively controls the magnetorquers in conjunction with reading the navigation magnetometer, records and replays whole orbit data and runs command timing loops) was further exercised as well as re-initialising its ODATA function at 21:29:40. Monday 23/7/84 Morning - tests of final ground "deployment decision" software were made by switching the magnetometer on permanently and watching the fields changing. Residual oscillations of under 10 degrees were encouraging. Evening - A full rehearsal of the boom deployment operation was run over 3 passes. The boom deployment commands were substituted by commands which were equally visible on the telemetry status points but otherwise harmless! After the ODATA was dumped, active magnetorquing was re-enabled. Tuesday 24/7/84 - Boom deployment Orbit 2112 - While holding the telemetry system in dwell mode (which prevents ODATA from recording since all channels are not found), the TORQUEH ODATA segment was reset, and active magnetorquing resumed. The spacecraft was left until LOS transmitting dwell telemetry to the ground analysis software. Orbit 2113 - Sending one command told the 1802 to turn the z-magnetorquer on continuously, to allow the ground software to take a precise fix of the spacecraft attitude. After about 3 minutes of data, Stephen finally confirmed a suitable attitude, and the telemetry system was switched out of dwell mode to enable ODATA recording to start at 10:35:00 (approx). The channels recorded were 1,2,3,41,61,67. The last two record hexadecimal numbers - sorry if your ODATA program expired at this new facility! At 10:35:20, a command to the 1802 turned the boom motor on for a 15.0 minute deployment and we watched the telemetry anxiously. An anomaly on the 5v current sensor prevented us seeing the true current, but the 14v bus was as expected and the motor was left running as the spececraft disappeared below our horizon. Orbit 2114 - Telemetry at AOS looked good, with the boom motor off and a good battery voltage. After taking the stored ODATA dump, the magnetorquers were disarmed and ODATA was reset at 12:19:23 to record channels 1,2,3 and 52. The real-time dump of the ODATA looked most encouraging. By the evening, the next ODATA dump to be analysed confirmed a stable gravity gradient lock. More rapid dumps (always using channels 1,2,3,52) were made after resets at 18:37:53 and 20:09:45. Friday 27/7/84 The 2.4GHz beacon was tested and found to be much improved in the new attitude. This downlink should prove to be very useful for engineering and high speed data for ground stations which are well-equipped with good receiving and decoding equipment. ** UO-11 Mission Plan ** Gravity gradient stabilisation marks the end of the major spacecraft commissioning phase of UO-11 and now allows us to progress with the commissioning of the experiments. This will commence with evaluation of the DCE and CCD Camera, however a more detailed Plan will be available shortly. ** NOAA Spacecraft Status Update ** * NOAA-8, the first in a series of Advanced TIROS-N spacecraft, began exhibiting problems on June 12 when it experienced a 'clock interrupt' that caused the spacecraft's gyros to loose synchronism. Continued clock perturbations interfered with the meteorological instruments on June 13th. Over the weekend of June 30/July 1, the situation deteriorated to the extent that the spacecraft's attitude control systems were affected and NOAA-8 began tumbling. The spacecraft has no nitrogen attitude control fuel left after remedial manoeuvres following launch on March 28, 1983 aboard an ATLAS-E launcher. NOAA-8 weighes 3,775 lbs and carries six environmental monitoring instruments and a search-and-rescue experiment. Although the search-and-rescue facility will be lost if NOAA-8 cannot be recovered, much of the environmental monitoring is being conducted by NOAA-6, still operational since launch on 27 June 1979. Engineers are working to resolve the problem before the launch of NOAA-F, currently scheduled for 23 October 1984. * NOAA-7 will complete its planned operational lifetime this summer, but is continuing to perform well. ** Thanks for Reports & Questionnaire Returns ** PE1HLB, VK2ZYE, I2KBD, VK2RX, VK2XPW, VK2AVH, ON4HW. W2RS, M.D.Oslender, G8DGR, WB9ANQ, G8KTM, G4PSO, G6TRR, G8JUB. ON4AWV, OZ1IWS, G4ILN, G4SAQ, ON5EX, GM4CUX, G4MAB, G8AVH, I2KBD, G6FPX This week: G3MBN, VK5HI, ON6RL, G1BUY, G5TU, G3SLI, Steve Hodson.