| Date: | 2001-02-02 16:20:00 | |
| Sender: | Mike Pearlman <Mike Pearlman <mpearlman@cfa.harvard.edu>> | |
| Subject: | [SLR-Mail] No. 730: (Fwd) SUNSAT | |
| Author: | Mike Pearlman | |
| Content: | ******************************************************************************** SLR Electronic Mail 2001-02-02 16:20:00 UTC Message No. 730 ******************************************************************************** Author: Mike Pearlman Subject: (Fwd) SUNSAT Dear Colleagues: We have received the following messsge from the SUNSAT Project at the University of Stellenbosch. Contact with the satellite has been lost and no further SLR activity is contemplated. In its short lifetime, the SUNSAT satellite has had considerable success as summarized below. We wish congratulate the University of Stellenbosch and all of those who worked on the project. Regards, Mike Pearlman Secretary, ILRS Central Bureau **** SUNSAT Press Release 1 February 2001 The End of SUNSAT´s Functional Life in Orbit We regret to announce that the last communication with SUNSAT from our ground station at the Electronic Systems Laboratory at Stellenbosch University took place on Friday, 19 January 2001 at 15:22:37 UTC. We are certain, after having performed several tests since the last contact, that an irreversible, probably physical, failure has occurred on the satellite. It is therefore unlikely that we will have any further contact with SUNSAT, apart from the occasional visual sighting by telescope! Summary of achievements: We are nevertheless very satisfied with SUNSAT´s achievements in orbit during the period of nearly 2 years since launch. The programme has exceeded all its original goals, namely: * to co-operate as OSCAR-35 with the amateur radio and amateur satellite communities worldwide, contributing new standards in the field. * to demonstrate high resolution imaging not before considered possible with a satellite this size and costs. * to stimulate challenging research and technology development at graduate student level * to foster valued international ties in the science and engineering community and * to promote science, engineering and technology among the school children of South Africa. Some statistics to underscore this statement are: Operational life: 969 days between launch on 10:29:55 UTC 23 February 1999 last contact: 15:22:37 UTC on 19 February 2001 giving 10027 orbits, or nearly 500 million kilometers 51 high resolution photos taken at places all over the globe, in 3 spectral bands and 15 m pixel sizes on ground 937 command dairies uploaded in operating SUNSAT 241700 telecommands executed successfully 161.144 Mbytes of whole orbit data (WOD) downloaded 94868 GPS data points downloaded in support of JPL 3.144 Mbytes APRS digilogs leading to a new activity 1.656 Mbytes of Magnetometer data 888 Kbytes international school experimental data 7.052 Mbytes of data for the star camera experiment Several hours of PAL videotape data of Southern Africa It was indeed a privilege to be part of this successful post graduate student satellite research programme! The SUNSAT management team wants to use this opportunity to thank everyone the world over for all the enthusiasm and the long extra hours they have invested in the design, building and operation of SUNSAT. The pride of having participated therein shall be treasured by all. More details on achievements on web-page: Two years after SUNSAT´s launch, on 23 February 2001, we will publish a full tribute to the first launched South African satellite on the website http://WWW.SUNSAT.EE.SUN.AC.ZA. The following items will be displayed: 1. A full disclosure of the involvement of the Faculty of Engineering at the University of Stellenbosch in space matters - from SPUTNIK to SUNSAT. 2. A processed graphical database of the most important telemetry data of SUNSAT as well as the school experiments (one for a Malaysian school experiment). 3. A collection of commendations for SUNSAT received from the international amateur radio community, highlighting its pioneering of new technology for radio amateurs, the large variety of amateur radio services it offered and the high signal quality achieved. 4. The PAL video images and high-resolution photos taken with SUNSAT. 5. A summary of the other scientific missions such as the GPS experiment for JPL Attempts that were made to recover SUNSAT: 1. During the first year of SUNSAT´s operations, the orbit provided ideal lighting conditions for imaging, and eclipse periods during every orbit to cool down the satellite. The various functions of the satellite were commissioned and operated, such as the high resolution camera, the PAL video camera, the amateur radio communications systems, the attitude control system, the science experiments and the school experiments. 2. However, the non-ideal drifting orbit plane eventually exposed SUNSAT to continuous sunlight. This particular orbit was determined by the requirements of the Danish Orsted satellite, together with which SUNSAT was a secondary (and free) payload on the launch vehicle. When the satellite became exposed to full sun continuously, the SUNSAT operations team started taking measures to alleviate serious problems of high operating temperature and overcharging of the batteries, by continuously re-orientating the satellite. Amateur radio services were still provided by SUNSAT during this phase and science and control systems experiments were conducted. However, imaging was discontinued due to poor lighting conditions. This non- eclipting situation continued for 5 months before the orbit plane again started to cause sun eclipses. 3. When the eclipses restarted, it was clear that battery capacities were low (fast voltage drop under load), as evidenced by some of the on-board processors resetting during eclipses. The assumption of a typical NiCd memory problem due to overcharging led to procedures that reconditioned the battery cells via a number of forced fast discharges. This exercise was successful to the extent that the resultant improvement of battery capacity enabled SUNSAT to once again function throughout full eclipses without processor resets. 4. Operations were back to normal when, after the communications pass of Friday, 19 January 2001, radio contact ceased altogether. It is unlikely that battery failure is the cause, since there was no evidence of gradual power failure from the telemetry of the last few orbits of normal operations, and even during direct sunlit passes, SUNSAT is not reacting. It is also unlikely to be a solar cell malfunction, since this would also have been evident from the solar cell current measurements and a lack of battery charging over a number of orbits. 5. The functionality of the ground station was also verified through communications with other amateur satellites, up- and downlinking via both UHF and VHF frequency bands. 6. All possible combinations of the RF-Modem-Telecommand- subsystems were attempted unsuccessfully. All other communication paths to and from SUNSAT were thereafter investigated systematically, but without success. This includes efforts to use telecommands directly on a command- for-command basis (open loop) to place the subsystems in recognisable states. Probable causes for the failure: >From the tests conducted, the possible failure scenarios in order of likelihood, are: (a) A possible failure cause would be simultaneous multi-point failures. However, the access experiments listed above tested all possible single point failures through previously used redundant routes. The probability of a simultaneous multi-point failure is consequently rather low. (b) A battery cell or main power diode could have burst and caused physical mechanical damage in the power supply system, since limited communication would have been possible with either battery or solar power. (c) An external object in space could have caused major physical damage to SUNSAT. Acknowledgements: The history and achievements of SUNSAT, a post graduate student designed and built satellite, proves what can be achieved through perseverance, enthusiasm and innovation even in the face of severe manpower and funding restrictions. We are grateful for the zeal of the whole SUNSAT team comprising industry, students, academics and support staff. SUNSAT has been completed through friends and colleagues in many organisations. The following organisations (in alphabetical order) have supplied funds, components, facilities, engineering support, etc.: Altech-Alcatel ECS First National Bank (Technology Division) Grintek Houwteq Irdeto Malaysian Airlines MTN NASA NRF Orbicom Plessey Reumech SA Radio League SA AMSAT Siemens Somchem Telkom University of Stellenbosch Vodacom We give honour to God, who through this project has shown us once again how wonderful His creation is; this universe that we may explore with admiration. Prof Jan du Plessis: jjdp@ing.sun.ac.za. Tel (021) 808 4011 Prof Arnold Schoonwinkel: schoonwi@ing.sun.ac.za. Tel (021) 808 4936 Prof Jan J. du Plessis Jan J. du Plessis Computer and Control Systems Prof: Rekenaar en Beheerstelsels Electrical+Electronic Engineering Departement E+E Ingenieurswese University of Stellenbosch Universiteit van Stellenbosch STELLENBOSCH 7600 STELLENBOSCH 7600 Republic of South Africa Republiek van Suid Afrika jjdp@ing.sun.ac.za JJDP@ING.SUN.AC.ZA Tel (+27 21) 808 4023 Fax (+27 21) 808 4981 WWW oor ons SUNSAT mikro satelliet by http://www.sunsat.ee.sun.ac.za Besoek ook die Universiteit se SunSpace-filiaal http://www.sunspace.co.za WWW on our SUNSAT micro satellite at http://www.sunsat.ee.sun.ac.za Also visit the University´s SunSpace-filiate http://www.sunspace.co.za ------- End of forwarded message ------- Dr. Michael R. Pearlman Harvard-Smithsonian Center for Astrophysics 60 Garden St. Cambridge MA 02138 tel. (617) 495-7481 fax. (617) 495-7105 e-mail. mpearlman@cfa.harvard.edu From: ”Mike Pearlman” ******************************************************************************** |