02-03-2001, 12:29 AM
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 cost,
* 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.
Statistics from SUNSAT's operational life to underscore this statement:
* 696 days between launch at 10:29:55 UTC on 23 February 1999 and the
last contact at 15:22:37 UTC on 19 January 2001, giving 10027 orbits,
or nearly 500 million kilometers
* 51 high-resolution images captured 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
* 161144 kB of whole orbit data (WOD) downloaded
* 94868 kB of GPS-data downloaded in support of JPL
* 7052 kB of data for the star camera experiment
* 3144 kB of APRS digilogs, renewing interest in APRS via satellite
* 1656 kB of Magnetometer data
* 888 kB of international school experimental data
* 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 WEBSITE
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 SUNSAT
website at http://sunsat.ee.sun.ac.za/. The following information will
be available:
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 exceptional signal quality achieved.
4 A selection of the PAL video footage and high-resolution images,
captured by SUNSAT.
5 A summary of the other scientific missions such as the GPS experiment
for JPL.
ATTEMPTS 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 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. The non-eclipsing situation lasted
for 5 months.
3 When eclipses resumed, it was clear that battery capacities were low
(fast voltage drop under load), as evidenced by some of the on-board
processors resetting during eclipse. The assumption of a typical NiCd
memory problem due to overcharging led to procedures to recondition 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 is 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 have been evident from 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 on
the VHF and UHF frequency bands.
6 All possible combinations of the RF-Modem-Telecommand-subsystems were
attempted unsuccessfully. All other communications paths to and from
SUNSAT were thereafter investigated systematically, also 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
increasing likelihood, are:
1 Simultaneous multi-point failures due to internal effects. The access
tests listed above eliminated all possible single point failures by
utilisation of previously used redundant routes. The probability of a
simultaneous multi-point failure is considered to be low.
2 A ruptured battery cell or main power diode may have caused physical
(mechanical) damage to the power supply bus. With a single-point
failure in the battery or solar power system, limited communications
would still have been possible for a while, at least.
3 Collision with an external object, causing major physical damage,
leading to multi-point failures.
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 with the help of 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, +27 21 808 4011.
Prof. Arnold Schoonwinkel: schoonwi@ing.sun.ac.za, +27 21 808 4936.
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 cost,
* 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.
Statistics from SUNSAT's operational life to underscore this statement:
* 696 days between launch at 10:29:55 UTC on 23 February 1999 and the
last contact at 15:22:37 UTC on 19 January 2001, giving 10027 orbits,
or nearly 500 million kilometers
* 51 high-resolution images captured 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
* 161144 kB of whole orbit data (WOD) downloaded
* 94868 kB of GPS-data downloaded in support of JPL
* 7052 kB of data for the star camera experiment
* 3144 kB of APRS digilogs, renewing interest in APRS via satellite
* 1656 kB of Magnetometer data
* 888 kB of international school experimental data
* 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 WEBSITE
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 SUNSAT
website at http://sunsat.ee.sun.ac.za/. The following information will
be available:
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 exceptional signal quality achieved.
4 A selection of the PAL video footage and high-resolution images,
captured by SUNSAT.
5 A summary of the other scientific missions such as the GPS experiment
for JPL.
ATTEMPTS 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 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. The non-eclipsing situation lasted
for 5 months.
3 When eclipses resumed, it was clear that battery capacities were low
(fast voltage drop under load), as evidenced by some of the on-board
processors resetting during eclipse. The assumption of a typical NiCd
memory problem due to overcharging led to procedures to recondition 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 is 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 have been evident from 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 on
the VHF and UHF frequency bands.
6 All possible combinations of the RF-Modem-Telecommand-subsystems were
attempted unsuccessfully. All other communications paths to and from
SUNSAT were thereafter investigated systematically, also 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
increasing likelihood, are:
1 Simultaneous multi-point failures due to internal effects. The access
tests listed above eliminated all possible single point failures by
utilisation of previously used redundant routes. The probability of a
simultaneous multi-point failure is considered to be low.
2 A ruptured battery cell or main power diode may have caused physical
(mechanical) damage to the power supply bus. With a single-point
failure in the battery or solar power system, limited communications
would still have been possible for a while, at least.
3 Collision with an external object, causing major physical damage,
leading to multi-point failures.
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 with the help of 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, +27 21 808 4011.
Prof. Arnold Schoonwinkel: schoonwi@ing.sun.ac.za, +27 21 808 4936.