TshepisoSAT, six months on orbit
Leon Steenkamp, Francois Visser and Robert van Zyl
French South African Institute of Technology (F’SATI), Cape Peninsula University of Technology (CPUT),
Cape Town, South Africa.
http://www.cput.ac.za/fsati
Abstract — This paper will give a brief introduction to the
F’SATI programme, the constructed CubeSat and mission. An
outline of the milestones reached thus far with the Tshepiso
nano-satellite will be given, the outstanding activities that must
still be completed and challenges faced. Some of the images
captured by the satellite will also be presented.
I. INTRODUCTION
The mission – from concept to operation – span just over
two years allowing students to witness the full mission during
their studies. Because of the very tight time limit set on the
mission it was decided that some of the hardware would have
to be bought as commercial off the shelf hardware with the
remaining hardware developed in-house.
III. TSHEPISOSAT (ZACUBE-1)
The 21st of May 2014 marks TshepisoSAT’s sixth month
in space. Since its launch on 21 November 2013 it would have
circled the earth more than 2600 times, captured over twenty
images and have had two close encounters with space objects.
The process of extending its twelve meter long high-frequency
(HF) antenna is underway.
The space weather mission is performed by its HF beacon
transmitter payload. The produced HF signal is to be used in
ionospheric propagation studies. The transmitted HF signal
frequency was also chosen so that it could be used to
characterise the SuperDARN radar system operated in the
Antarctic by the SANSA.
The first six months of the mission is the on-going product
of more than two years of development work by a group of
students and lecturers at the French South African Institute of
Technology based at CPUT. The TshepisoSAT spacecraft is
South Africa’s third satellite and first launched CubeSat. It is
also the first CubeSat launched that was developed on the
African continent.
The ZACUBE-1 spacecraft is a one-unit form factor
CubeSat, which means that it is a ten centimetre cube. In
support of its HF and imaging payloads it carries a
communication, power and attitude determination and control
system. The spacecraft has body-mounted solar panels on five
of its six facets with the sixth containing openings for the
camera and deployable HF antenna. The sixth facet also
houses the satellite’s UHF and VHF antenna system. The
following message by Dr Sandile Malinga, CEO of SANSA, is
engraved on this panel: ‘The South African National Space
Agency (SANSA) is proud to be a part of this august scientific
journey of discovery and look forward in anticipation for the
results borne forth from the passion, dedication and expertise
of our local scientists, researchers, engineers and students.
This may be a small step for South Africa, but it is certain to
inspire a large transformation of our space technologies and
education.'
II. F’SATI PROGRAMME AND ZACUBE-1 MISSION
The roots of the F’SATI programme at CPUT can be
found in the Department of Science and Technology’s 10Year Innovation Plan. This plan outlines five grand challenges
in technology development and innovation, one of which is in
the area of Space Science.
The coursework and research at F’SATI is focused on
satellite systems and as part of this focus the decision was
made to start work on a CubeSat mission. Together with the
South African National Space Agency (SANSA) - Space
Science Directorate, the ZACUBE-1 mission was conceived.
The mission allowed students to get first-hand experience
in designing, constructing and operating the mission and
spacecraft. The mission would also allow students to further
refine their research projects into something that can fly in
space.
The ZACUBE-1 spacecraft has a number of mission
objectives, namely education and training, technology
demonstrator, catalyst for a national nano-satellite programme,
and space weather research.
The CubeSat structure, power system and onboard
computer were bought as commercial off the shelf
components, while the rest of the spacecraft was developed inhouse. The attitude determination and control system was
developed with inputs from the Stellenbosch University’s
Electronic Systems Laboratory. On-board and ground support
software for the mission was developed in-house.
The payload HF transmitter and deployable antenna
mechanism were developed at F’SATI along with the
satellite’s UHF/VHF communication transceiver, Figure 1.
This paper was presented at the SA AMSAT Space Symposium on 24 May 2014
at the Innovation Hub, Pretoria, South Africa.
http://www.amsatsa.org.za
Figure 1 - First generation UHF/VHF transceiver
Figure 3 - Satellite major components
The first generation UHF/VHF communication transceiver
also known as the Communication Major-Component (CMC)
used on ZACUBE-1 can be seen in Figure 1.
The developed HF beacon antenna deployment mechanism
housing the 12 meter wire antenna can be seen in Figure 2.
IV. MISSION PROGRESS
An internal document was drafted dividing the mission
into phases with the first phase listing very modest goals,
ranging from hearing the first beacon transmission after
launch to establishing positive contact with the satellite and
downloading the first logged data. This should be seen in the
light that often, even with previous mission experience, some
groups never hear from their satellites after launch.
For TshepisoSAT (ZACUBE-1) and its two companions in
the ISIPOD launch adapter, FUNcube-1 (AO-73) and
HINCube, the launch went off without a hitch. Signals from
TshepisoSAT and FUNcube-1 were heard within the first few
orbits after separation from the launch vehicle. It appears that
a signal has yet to be heard from HINCube [1].
The first few months of the mission have been a huge
learning experience for all participants. This involved
establishing the ground operations, operating the launched
satellite and dealing with close encounters with other space
objects.
Figure 2 - HF antenna deployment mechanism
A breakdown of the various major components used in the
satellite can be seen in Figure 3. The PUMPKIN structure was
modified to house a deployable magnetometer. The satellite
makes use of an ISIS deployable VHF/UHF antenna, Clyde
Space electronic power system and on-board computer (OBC)
from PUMPKIN. The OBC software was written in C using
PUMPKIN’s Salvo Real Time Operating System.
As part of the mission a school’s competition was run by
the South African Agency for Science and Technology
Advancement (SAASTA) to choose a new name for the
satellite. From all the submissions the name “Tshepiso” was
chosen, meaning “promise” in Sesotho. The name was
announced at the launch event for the satellite.
The first close approach notification arrived the morning
of 25 February 2014 from the United States Joint Space
Operations Center (JSpOC) through the South African
National Space Agency (SANSA). A close approach
notification is generated by the JSpOC to warn spacecraft
operators when their spacecraft will come in close proximity
to another object. The warning was for a close approach with
the Russian built COSMOS 2151 launched in 1991. The
second close approach warning arrived a few days after the
first warning. The second object was a piece of debris from a
METEOR 2-5 satellite. As TshepisoSAT has no propulsion or
means to change its orbit the only action was to monitor the
situation very closely. Both events occurred not long after the
satellite passed over the CPUT ground station which meant
that the status of the satellite could be confirmed before these
events. On very short notice the ground station at the
California Polytechnic State University in San Luis Obispo,
California, confirmed that it would be able to assist in
confirming the satellite status after the events. The University
of Florida also assisted with the second close approach event.
After both events the operational status of the satellite could
be confirmed less than two hours after each event occurred
and communicated to SANSA, the South African Council for
Space Affairs (SACSA), and the Department of Science and
Technology (DST).
After six months on orbit the status of the major
components of the satellite still indicates nominal operation.
The adequate charging of the battery under various operational
conditions has also been verified. More than 20 images have
been captured and downloaded and over 40 log files created
with sensor readings over one or multiple orbits.
Because the satellite is not stabilised in three axes its
orientation with respect to the earth is constantly changing.
This makes capturing images very interesting because the only
indication of the contents of the image is the file size
generated. Figure 4, 5 and 6 shows some of the images
captured by TshepisoSAT.
Figure 6 - TshepisoSAT images, sun and earth
Various logs were generated to confirm parameters like
battery voltage and internal temperature when the satellite was
not over the ground station at CPUT. The first logs were
generated over a single orbit. Figure 7 shows the battery
voltage, internal OBC temperature and UHF/VHF antenna
temperature. The antenna temperature sensor is mounted
closer to the outside of the satellite than the OBC sensor. This
can be seen from the larger temperature fluctuations and the
fact that the antenna temperature reaches the maximum and
minimum temperatures first.
Figure 4 - TshepisoSAT images, west coast of Africa
Figure 7 - Temperature and battery voltage, single orbit
Figure 5 - TshepisoSAT images, ocean with clouds
Temperature and battery voltage logs were also generated
for multiple orbits. Figure 8 shows the battery voltage for a
twelve hour period after a pass used to download log files and
upload new settings. It can be seen that it took three orbits for
the satellite’s batteries to reach its full charge of 8.2 volt.
decided to try and find a configuration in which the satellite
could continue to beacon at a regular interval in both UHF and
HF but also maintain a steady battery charge through eclipse.
A few configurations have been tested and are currently being
fine tuned.
Commands to burn the release wires holding down the tip
mass of the HF antenna and ring containing the HF antenna
wire have been sent and confirmed as received. Commands to
deploy the first few increments of the HF antenna have also
been sent and confirmed as received.
Figure 8 - Battery voltage
Figure 9 shows the internal OBC temperature for a 24 hour
period.
Information on the configuration of the HF beacon and
whether the HF beacon is transmitting can be found on the
TshepisoSAT (ZACUBE-1) webpage [2]. It is important to
note that the full deployment the antenna could take a few
weeks and that it is likely that a signal from the beacon will
only be heard once the antenna has been deployed to an
appropriate length (10 – 12 meters).
V. CONCLUSION
The last six months have been the product of over two
years of active development work, late nights, lots of coffee
and travelling to distant countries. The students and staff
involved at CPUT and F’SATI have definitely learned a
tremendous amount from the experience and also forged
relationships with other institutions and organisations that
might not have come about otherwise. ZACUBE-1 also
provides a solid foundation for the second national CubeSat
mission, ZACUBE-2, for which funding from the DST has
been acquired. It is the intention to broaden participation in
the ZACUBE-2 mission to more universities.
The ZACUBE-1 mission is, however, not yet over and
work still remains to be done.
Figure 9 - Internal temperature
Over the last few weeks work has begun on the
configuration of the HF beacon transmitter. The initial idea
was to switch over from the existing UHF beacon to the HF
beacon, but this would effectively leave the satellite quiet
while the HF antenna is deployed to an efficient length. It was
[1]
Uknown author, “HINCube” http://hincube.cubesat.no/wp/ - Last visited 19 May
2014.
[2]
Uknown author, “ZACUBE-1” http://www.cput.ac.za/blogs/fsati/zacube-1 - Last
visited 19 May 2014.