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TDP-3 Vanguard: Verification of a New Communication System for CubeSats on BEXUS 22

Nicolas Appel1, Andreas Kimpe2, Karl Kraus1, Martin Langer1, Martin J. Losekamm3, Michael Milde3, Thomas
oschl3, Sebastian R¨
uckerl1, Felix Sch¨
afer1, Anke Stromsky2, and Korbinian W¨
1Technical University of Munich, Department of Mechanical Engineering, Germany
2DLR MORABA, Germany
3Technical University of Munich, Department of Physics, Germany
CubeSats are evolving from simple, low-cost satellites
built solely for education purposes to ever more pow-
erful platforms capable of supporting scientific experi-
ments. Among the technologies required for the opera-
tion of scientific instruments are communication systems
that can transmit all relevant data to its operators. We
have developed two such systems for the MOVE-II satel-
lite, a single-unit CubeSat being built at the Technical
University of Munich (TUM). Slated for launch in late
2017, MOVE-II shall demonstrate several new technolo-
gies supporting the operation of scientific instruments in
successive missions. We conducted the TDP-3 (Tech-
nology Demonstrator Platform 3) Vanguard experiment
aboard the BEXUS 22 stratospheric balloon to verify
the correct operation of the communication systems in
a near-space environment and at large distances between
the transceivers and the receiving ground station.
Key words: CubeSat, MOVE-II, communication, data
handling, REXUS/BEXUS.
TDP-3 Vanguard is a technology demonstration platform
that was built by students of the Technical University
of Munich (TUM) as part of the REXUS/BEXUS pro-
gram. The near-space environment during the flight of
the BEXUS 22 stratospheric balloon was used to verify
the communication and command & data handling sub-
systems of the MOVE-II nanosatellite. The said environ-
ment approximates two important aspects of the environ-
mental conditions of a satellite mission: A fairly long dis-
tance between the experiment and the ground station and
the reduced air pressure and temperatures in Earth orbit.
This allowed us to test and operate the satellite subsys-
tems under realistic conditions.
Initially, we planned to include a prototype of the Multi-
purpose Active-target Particle Telescope (MAPT) as sci-
entific payload (Losekamm et al., 2016). A first prototype
of MAPT was flown on BEXUS 18 in 2014 (Losekamm
et al., 2015). However, due to a mismatch in develop-
ment schedules, the MAPT prototype was replaced by a
payload simulator providing comparable scientific data as
expected during regular operations of the experiment.
We give an overview of the MOVE-II satellite in Sec. 2
and a detailed description of the TDP-3 mission in Sec. 3.
We summarize our findings and results in Sec. 4 be-
fore concluding with a summary of what we achieved in
Sec. 5.
The MOVE-II satellite is a single-unit (1U) CubeSat cur-
rently under development at the Technical University of
Munich (TUM). The MOVE (Munich Orbital Verifica-
tion Experiment) satellite program was initiated in 2006
with the objective of building a single-unit CubeSat veri-
fication platform called First-MOVE (Czech et al., 2010).
First-MOVE was launched in late 2013 and operated in
space for about a month.
Since then, the main purpose of the program has been the
hands-on education of undergraduate and graduate stu-
dents. Funded by the German Aerospace Center (DLR)
as an educational project, the objectives of MOVE-II are
to build and operate a 1U CubeSat capable of support-
ing a scientific payload, to enhance the subsystems that
were developed for First-MOVE, and to apply the lessons
learned from the First-MOVE project (Langer et al.,
2015b). The mission’s scientific objective is to measure
the current-voltage characteristics of novel multi-junction
solar cells in orbit (Rutzinger et al., 2016).
We had to enhance several subsystems of First-MOVE to
achieve the objectives of the MOVE-II project (Langer
et al., 2015a). The new attitude determination and con-
trol system (ADCS) uses magnetic actuators and allows
a pointing accuracy of better than ±10. An advanced
solar panel deployment mechanism uses shape memory
alloy technology, enabling repeated tests with the flight
Figure 1. The MOVE-II nanosatellite in launch (top) and
deployed configuration (bottom).
unit without compromising its performance (Figure 1
shows the satellite in its launch and deployed configu-
ration). A UHF/VHF transceiver ensures a reliable trans-
mission of telemetry and scientific data. An experimen-
tal S-band transceiver will provide a bandwidth of more
than 1 Mbit/s for a high-rate downlink of payload data.
Both transceivers use the TUM-developed Nanolink pro-
tocol (Appel et al., 2016). The launch of the satellite is
currently expected in early 2018.
The TDP-3 platform demonstrator experiment consists of
a flight segment and a ground segment. The ground seg-
ment simulates the ground station and mission operations
center of the MOVE-II mission. It provides the capabili-
ties to monitor and remote-control the flight segment via
the BEXUS E-Link communication system. The flight
segment is the demonstrator platform itself, comprising
the satellite subsystems to be tested and support systems
for power supply and monitoring purposes.
3.1. Flight Segment
The flight segment of TDP-3 consists of four main com-
ponents: The communications (COM) system compris-
ing the UHF/VHF and S-band transceivers, the command
& data handling (CDH) system, a scientific payload, and
support systems. As the MAPT detector was replaced by
a payload simulator, it is considered as part of the support
systems in this paper. Figure 2 shows the flight segment
shortly before installation into the BEXUS 22 gondola.
3.1.1. Command & Data Handling
The CDH system of TDP-3 is a development board based
on an Atmel SAMA5D2 system-on-a-chip, designed and
produced by Hyperion Technologies1for the MOVE-II
project. It is equipped with all the interfaces required
for the final MOVE-II CDH system, as well as a number
of additional interfaces only used for connections to the
TDP-3 support systems and for evaluation purposes. The
main interface of the CDH system is a board-to-board
SPI2connection to the communication system. An addi-
tional Ethernet interface is used for communications with
the support systems—including the payload simulator—
using the TCP/IP and UDP/IP protocols.
The software of the CDH system is running on a cus-
tom Linux distribution. This choice of operating sys-
tem enables us to use of a variety of software modules
available for standard Linux distributions. A custom SPI
driver is used to communicate with the COM system’s
transceivers. The CDH system is the bus master for all
SPI communications. As SPI slave devices cannot initiate
communications, the interface uses an additional inter-
rupt pin to signal a communication need from the COM
3.1.2. Communication
The COM system of TDP-3 consists of two radio
transceivers, one of them operating within the UHF/VHF
bands, the other within the S-band. These transceivers
were developed for the MOVE-II project in cooperation
with Multimedia Studio Rolf-Dieter Klein3. Table 1 lists
the basic properties and parameters of the transceivers.
Software-Defined Radio Transceivers Both COM
system transceivers are software-defined radios. A Xilinx
Spartan-6 field-programmable gate array (FPGA) is used
for data handling and baseband signal processing. The
generated baseband I/Q signal is converted to an analog
signal and fed to a quadrature mixer through a chain of
filters and amplifiers.
For the UHF/VHF transceiver, a similar approach is used
for the receiver. The received signal is amplified and fil-
tered, fed to a quadrature demodulator, and directly con-
verted to a digital representation. All further signal pro-
cessing is done on the FPGA. The receiver part of the S-
2Serial Peripheral Interface Bus
Figure 2. The TDP-3 flight segment.
Band transceiver was not used during the BEXUS flight.
Figures 3 and 4 show functional diagrams of the analog
signal processing chains of both transceivers.
Data Flow Data is transferred to and from the
transceivers using a SPI-based custom protocol. SPI is
a master-slave protocol in which only the master can ini-
tiate the communication, in our case the SPI bus master is
the CDH system. To avoid active polling an additional in-
terrupt line is used. The SPI-based protocol itself was de-
signed to reduce the risk of errors due to erroneous com-
munication. Checksums are used to detect these errors,
and a simple acknowledge mechanism informs the com-
munication partner. This reduces the risk of invalid states
due to single event upsets or other disturbances.
The data received via SPI is embedded in Nanolink
frames. Nanolink is a versatile data link layer protocol
for radio links with low bandwidth-delay product. Nano-
link utilizes type-I hybrid ARQ, and provides eight vir-
tual channels for qualitiy of service. Additional protocol
features can be used by means of extension headers. All
these features are designed with low overhead for effi-
cient use of the communication link (Appel et al., 2016).
Nanolink frames are serialized and embedded in larger
blocks of data with a preceding sync marker. The sync
marker is used to align the bit stream at byte boundaries
at the receiver side.
The whole data, including the sync marker, is encoded
with a forward error correction code. The resulting bit
stream is modulated and filtered in the baseband, before
converting it to an analog signal. The setup allows recep-
tion and decoding of the code blocks by CCSDS com-
patible receivers. Thus, the transceiver downlink can be
decoded by virtually any satellite telemetry station oper-
ating within the S-band.
The receivers’ structure is quite similar regarding the data
flow. The digital baseband signal is filtered, its frequency
error is corrected and the symbols are recovered. These
symbols are decoded and the resulting bit stream is byte-
aligned. Nanolink frames are extracted from the resulting
byte stream and are subsequently decoded. The payload
data itself is then transmitted to the CDH system via the
SPI interface.
Antennas The flight segment antenna of the UHF/VHF
transceiver is a radial-free monopole antenna. Other than
for the MOVE-II satellite, only a single dual-band an-
tenna with additional diplexer to remove the transmitted
signal from the receiver and vice versa is used. A ground
plane is used for S-band transmissions. As the S-band
transceiver was used as transmitter only during the TDP-3
mission, no diplexer or additional antenna was needed in
Frequency 144 MHz 2323 MHz
Power <30 dBm <30 dBm
Modulation DBPSK OQPSK
FEC - Viterbi
RX Frequency 435 MHz -
Modulation DBPSK -
Table 1. Properties and parameters of the UHF/VHF and
S-band transceivers.
I/Q Demo d.
Band-pas s Low-pass
Band-pas s
Modul ator
144 MHz
435 MHz
Figure 3. Functional diagram of the UHF/VHF transceiver.
Band-pass Low-pass
Band-pas s
I/Q Mod./ Demod.
Figure 4. Functional diagram of the S-band transceiver.
Rx 144 MHz
Tx 435 MHz
Figure 5. Functional diagram of the UHF/VHF ground station.
Figure 6. Antennas mounted to the gondola. The longer
one is the UHF/VHF antenna, the shorter one is the case
of the S-band ground plane antenna.
this case. Figure 6 shows how the antennas were mounted
to the gondola.
3.1.3. Support Systems
The support systems of TDP-3 are responsible for the
power and network interface of the experiment, the pay-
load data simulation, and the supporting structure to
mount the experiment to the gondola.
Power Supply Module The power supply module pro-
vides power to all other systems of the TDP-3 flight seg-
ment. It converts the 28V supplied by the BEXUS bat-
tery system to the voltages required by each system. We
us commercially available DC-DC converters that have
been proven to operate reliably during previous balloon
flights (Losekamm et al., 2015). Each power bus is
monitored by the module’s central microcontroller and is
switched off in case of out-of-limits sensor readings. The
controller is connected to the BEXUS E-Link system via
the flight segment’s network E-Link interface and can be
accessed and controlled from the ground segment using
the TCP/IP protocol.
Network Interface The network interface is a standard
100-Mbit network switch that is connected to the BEXUS
E-Link communication system via an Ethernet connec-
tion. The flight segment’s systems are connected to the
switch using industrial M12 Ethernet connectors. The E-
Link system supports the TCP/IP and UDP/IP protocols.
Payload Simulator The payload simulator consists of
a Raspberry Pi single-board computer running a standard
Linux distribution. It is directly connected to the net-
work interface and communicates with the CDH system
via UDP/IP. The data stream generated by the simulator
closely resembles the one generated by the MAPT pay-
load and can thus be used to assess the CDH system’s
performance and stability when operating as the interme-
diary between a payload and the COM system. The pay-
load simulator can be accessed and controlled from the
ground segment through the E-Link system.
3.2. Ground Segment
The ground segment of TDP-3 simulated the ground
station of the future MOVE-II satellite mission and
supported the operations of the experiment during the
BEXUS 22 flight. The ground segment consists of three
main components: a UHF/VHF ground station, a S-band
ground station, and a control and data storage server.
3.2.1. UHF/VHF ground station
Figure 5 shows a functional diagram of the UHF/VHF
ground station. It consists of widely available amateur ra-
dio components. The antenna is a dual band ground plane
and the digital signal processing was done with GNU-
Radio. It included the modulation and demodulation of
the signal, handling of the blocks to synchronize the bit
stream, and the Nanolink frame handling. The resulting
byte stream was then forwarded to the control and storage
3.2.2. S-band ground station
The S-band ground station service was provided by the
MORABA telemetry station at Esrange Space Center.
It is capable of tracking signals automatically, decoding
them, correcting bit errors with forward error correction,
and synchronizing the bit stream. These tasks were per-
formed by a Cortex RTR-XL radio telemetry receiver.
The byte stream output of the Cortex modem was for-
warded to the control and storage server. The byte stream
contained the Nanolink frames, which were decoded by
the central control server.
3.2.3. Control & Storage Server
The central control and storage server collected all impor-
tant data generated by the UHF/VHF and S-band ground
stations. It also interpreted the Nanolink frames of the S-
band transmissions and visualized the status of the COM
system. This visualization was combined with the con-
trol interface to switch the system into different states of
operation and to control the flight segment’s CDH com-
ponents remotely.
3.3. Verification Strategy
The high floating altitude of the BEXUS 22 balloon gave
us the unique opportunity to test the MOVE-II communi-
cations hardware with a moving, long-range transmission
path. Although the balloon appears stationary when com-
pared to the velocity of a satellite, other aspects of the
radio link are quite similar to an orbital link. The most
important common features are the high slant range and
decreasing elevation angle. They are also encountered in
the last minutes of a pass, when the satellite approaches
the horizon. During that time, the worst signal conditions
of a pass are experienced. Moreover, since the balloon is
moving, signal conditions change rapidly and deep fad-
ing can be observed. A characterization of these features
is important for a satellite mission. The BEXUS 22 flight
gave us a good opportunity to test the capabilities of the
COM system under worst-case conditions.
The BEXUS 22 balloon was launched on 05 Octo-
ber 2016 at 13:34 UTC from Esrange Space Center in
northern Sweden. The COM system’s transceivers were
switched on 30 minutes before release of the balloon. The
VHF baseband signal and the extracted data frames from
both links were recorded.
The balloon reached its floating altitude of about 32.5 km
110 minutes after launch. The gondola was separated
from the balloon at 17:41 UTC, resulting in a floating
phase of about 2 hours. From launch until touchdown,
the balloon traveled a ground distance of 270km. The
recording stopped after 301 minutes, when the radio con-
nection to the gondola was lost.
4.1. VHF Flight Results
The user data rate of the VHF downlink can be derived
from the VHF frames recorded by the ground segment.
Figure 7 shows the VHF data rate over the duration of the
flight. Values are averaged over a window of 60seconds.
The green horizontal line marks the maximum possible
total data rate of 1562.5 bits per second (bit/s).
The data rate graph is complemented by Figure 8, which
illustrates the signal-to-noise ratio (Eb/N0, SNR) of the
baseband signal. The x axis is given in samples, since
restarts of the GNURadio software rendered a tempo-
ral assignment imprecise. We used GNURadio’s built-in
MPSK SNR Estimator block and the 2nd and 4th Moment
method for the Eb/N0measurement. The green line in
Figure 8 marks the signal level that corresponds to a bit
error rate (BER) of 106.
During the flight, the ground station software had to be
restarted seven times. Restarts of the ground station
software and the resulting communication dropouts are
marked in Figure 7 as red vertical lines. Please note that
due to the time needed to restart the ground station soft-
ware there is some discrepancy in time between the two
graphs in Figures 7 and 8.
The data rate remained high and stable for the most part
of the flight. From the beginning of the recording up to
minute 39 it was stable at about 1065 bit/s, with only one
small dropout happening after about 30 minutes. The
reason for this lower but stable value was an incorrect
setting in the frame synchronizer, which resulted in the
loss of a part of every transmitted block. We detected
this issue after about 39 minutes and restarted the ground
station. An analysis of the baseband data with an up-
dated GNURadio flow graph revealed a steady transmis-
sion with an average data rate of 1490bit/s.
Short-term increases in data rate above this value were
likely caused by the storage software, since timestamps
were generated when the data was stored, not when it was
received. At minute 56, frames with a repetitive pattern
with a size of 990 bit were transmitted for 240 seconds.
At the same time, we observed a sharp decline in the data
rate (see mark 1 in Figure 7). This may have been due to
a lack of bit transitions in the transmitted pattern, which
caused the receiver’s timing recovery to fall out of lock.
Sharp declines in the SNR in minutes 89 and 96 resulted
in frame losses, which in turn caused drops in the data
rate (see marks 2 and 3 in Figure 7). It is likely that these
were caused by interference from nearby hand-held radio
devices. We observed these devices to significantly in-
crease the noise level at the receiver and thus deteriorate
the SNR.
At events 4 and 5, frames with a size of 1000 bit were
transmitted for 100 seconds each, leading to a local
increase in the data rate with a global maximum of
1545 bit/s. This increase reflects the increase in efficiency
of larger payload data compared to the shorter telemetry
frames sent otherwise.
A noteworthy feature of the SNR graph in Figure 8 is the
high fluctuation which can be observed between samples
2000 and 4000. The magnitude of the fluctuation is up
to 5 dB. This fast fading stems from a multi-path propa-
gation of the transmitted signal. It travels along different
paths and is received at the ground station with a phase
difference, resulting in destructive or constructive inter-
ference. This effect is expected and its magnitude is an
important parameter for the MOVE-II mission.
The link remained very stable until minute 168, but
the SNR graph reveals a gradual decrease of the signal
quality. Afterwards, the signal continued to deteriorate
strongly as a result of the increasing distance between the
flight and ground segments. Objects in the vicinity of
the ground station began to block the signal as they ob-
structed the line of sight. As a remedy, we relocated the
receiver antenna, which improved reception for a short
period of time and kept the data rate at a tolerable level
of more than 1000 bit/s.
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Time (min)
Data Rate (Bps)
Figure 7. VHF data rate during the BEXUS 22 flight.
0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000
Sample Number
Figure 8. VHF signal-to-noise ratio during the BEXUS 22 flight.
Altitude (km)
050 100 150 200 250 300
Time (min)
Temperature (C)
Figure 9. Temperature of the UHF/VHF transceiver during the BEXUS flight.
At this period, the GNURadio software could not recover
from low signal levels and loss of synchronization. These
cases required a restart of the entire ground station soft-
ware to resume operation. In minute 218, the ground sta-
tion was restarted due to loss of synchronization. When
the signal was lost a second time, we manually elevated
the antenna to about 2 m above the ground. This im-
proved the SNR by about 10dB for roughly 10 minutes.
Figure 7 reveals the sharp increase in data rate as a result
of this action.
At minute 276, the gondola was separated from the bal-
loon. As the balloon approached the horizon, effects
of signal scattering and multi-path transmission increase.
No more frames could be decoded after minute 289 and
the experiment was concluded.
Another interesting aspect of the experiment was the ob-
servation of the transceiver temperature during the flight.
The readings of a temperature sensor placed below the
transceiver’s power amplifier was transmitted as part of
the telemetry packages. The readings are shown in Fig-
ure 9. Before launch, there was a steep increase in tem-
perature with a maximum of 48 C reached shortly af-
ter launch. During ascent, the temperature gradually de-
creases to a minimum of 15 C at about 80 minutes into
the flight. Afterwards, the it slowly increases again to
a maximum of 30 C at 173 minutes. Subsequently, the
temperature begins to fall again with very constant rate
of about 0.08 C
/min. After cutoff, the temperature drops
rapidly with about 0.16 C
/min, most likely due to an in-
creased air flow during the free fall.
4.2. S-Band Flight Results
Regrettably, the data from the S-band transceiver received
by the ground station was lost and could not be recovered
after the flight. An analysis of the S-band telemetry was
therefore not possible.
Figure 10 shows the SNR of the S-band signal as re-
ceived by the MORABA ground station. The measure-
ment was performed at the automatic gain control (AGC)
of the ground station. The figure shows the calculated
signal strength according to the link budget. This calcu-
lation was performed using the data from the balloon’s
GPS tracking device. The green line at the bottom of the
graph indicates the approximate SNR required for a BER
of 106. The first observation that can be made from the
figure is an extreme variation of the signal quality in the
first 30 minutes prior to launch. There are several causes
of this. First, the attenuation is partly due to partial or to-
tal occlusion of the line of sight by nearby trees. Second,
the antenna did not point at the gondola the entire time,
so that the signal may been received through a side lobe
of the antenna. Lastly, the movement of the balloon by
the launch vehicle may have also introduced some signal
level variance.
Another observation is a signal variance of about 10dB
during the ascent phase. The signal becomes more sta-
ble as the balloon enters the floating phase. The same
observation has already been made from the VHF signal,
therefore it can be assumed that there is a common source
which causes this effect.
During the flight, a defective contact in the CDH system
disabled the SPI slave-select line. At 170 minutes into the
flight, the S-band transmitter was restarted in an attempt
to resolve this issue. This can be seen in the SNR graph as
short spike. As the attempt was unsuccessful, no further
experiments were conducted with the transmitter.
The SNR graph reveals a steep decline of the SNR at
about 275 to 280 minutes after launch. At this time, the
gondola was in free fall, resulting in a very low eleva-
tion angle. The automatic pointing mechanism directed
the antenna to a negative elevation, which was corrected
manually. This showed an improvement of the signal
quality. However, as the graph shows, the signal began
to quickly fade soon after. Since the gondola’s altitude
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
Time (min)
SNR (dB)
AGC Measurement
Link Budget Prediction
Figure 10. Signal-to-noise ratio of the S-band transmission during the BEXUS flight.
decreased quickly, it is very likely that the signal did not
travel via line of sight but rather by diffraction at the hori-
zon. Moreover, occlusion by foliage and trees around the
location very likely amplified this effect. The signal was
lost entirely when the gondola was at a height of less than
3 km above the ground. At this point, all other commu-
nication systems on the gondola had already lost connec-
When comparing the measured and calculated SNR
graphs in Figure 10, it can be seen that apart from the
smaller variations, the calculation yields a good approxi-
mation of the actual signal levels. Therefore, these results
can be transferred to the satellite model. At the farthest
point in an overpass of MOVE-II, the satellite is about
2800 km away from the ground station. This is about ten
times more than the maximum distance of the BEXUS
22 balloon to the MORABA ground station. By the in-
verse square law, this results in 20 dB higher free-space
path loss. The ground station at TUM that will be used
for MOVE-II has a gain of approximately 30.6dBi and
the satellite antenna has a gain of 5 dBi. Also, a stronger
LDPC 1/2 code will be used instead of the convolutional
code, resulting in a coding gain of about 2.7dB. In total
the additional attenuation of the MOVE-II setup is about
22.7dB. This leaves only a very thin link margin of about
3dB for the system. However, this margin increases dur-
ing an overpass.
From the analysis of the VHF transmission, we can see
that the TDP-3 setup was sensitive to bad signal con-
ditions. This is a result of the uncoded transmission:
Single-bit errors void the checksum of a frame, which
leads to high data losses. When the SNR fell below
10 db, severe frame losses occured and the data rate de-
graded quickly. This may be a result of a suboptimal im-
plementation in GNURadio. When the SNR was above
10 dB, the performance was very high, with an efficiency
of 95%.
We observed that the transceiver is able to dissipate ex-
cess heat well despite the lack of air for convection. It re-
mained comparatively cool and far from the limits of the
operating temperature of its commercially available com-
ponents, which typically lies between -40 C and +85 C.
The experiment showed the S-band link to be very stable.
The transmitter hardware and software operated flaw-
lessly in near vacuum for more than four hours. The ob-
served margin for signal fading of about 5dB is reason-
able for future satellite missions. The long duration of
continuous transmission proves that the thermal design
of the system is sufficient. When translating the results
of the SNR measurement to the MOVE-II mission, it be-
comes clear that the link may not operate optimally at low
elevations at the beginning of a pass, but should be stable
through most of it.
The REXUS/BEXUS program is realized under a bilat-
eral agency agreement between the German Aerospace
Center (DLR) and the Swedish National Space Board
(SNSB). The Swedish share of the payload has been
made available to students from other European countries
through a collaboration with the European Space Agency
This research was supported by the DFG Cluster of Ex-
cellence Origin and Structure of the Universe. The
authors acknowledge the funding of MOVE-II by the
Federal Ministry of Economics and Energy, following
a decision of the German Bundestag, via the German
Aerospace Center (DLR) with funding grant number
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... During this mission the communication link was tested in the stratosphere over a distance of 270 km. 13 Payload As its scientific goal, the MOVE-II CubeSat will be used for the verification of novel 4-junction solar cells under space conditions. On top of the CubeSat one full size solar cell (8x4 cm 2 ) and four corresponding isotope cells (2x2 cm 2 ) are located . ...
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MOVE-II (Munich Orbital Verification Experiment II) is a 1 Unit CubeSat currently under development at the Technical University of Munich (TUM). This paper reports on the technical as well as the organizational advancements of the project. With overall more than 130 students involved so far, the project is currently in Phase D, with the launch of the satellite scheduled for early 2018. For communication purposes, MOVE-II will utilize a novel robust and efficient radio protocol for small satellite radio links, called Nanolink, both on an UHF/VHF transceiver and an S-Band transceiver. The usual power restrictions of the 1U envelope are overcome by four deployable solar panels, which are held down and released by a reusable shape memory mechanism. This allows repeated tests of the mechanism and true test-as-your-fly philosophy. As its scientific goal, the MOVE-II CubeSat will be used for the verification of novel 4-junction solar cells. With a footprint of 10x10 cm, the payload consists of one full size solar cell (8x4 cm) and five positions (each 2x2 cm) for the corresponding isotype solar cells. As opposed to its predecessor mission, MOVE-II will be the first CubeSat of TUM utilizing a magnetorquer based, active attitude determination and control system (ADCS). The system consists of five Printed-Circuit-Boards with directly integrated magnetic coils, forming the outer shell of the spacecraft, and one so-called ADCS Mainboard, located in the board stack of the satellite. Each Sidepanel has its own microcontroller and is connected to the ADCS Mainboard with one of two redundant SPI buses. From an organizational point of view, we tried to increase the reliability of MOVE-II by fast prototyping and releases as well as enhanced hardware-in-the loop tests. We will present the application of agile software development in the project as well as methods that we applied to assure reliability on system level. For that purpose a Reliability Growth Model, based on our CubeSat Failure Database, was adapted for the project.
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We present Nanolink, a data link layer protocol for CubeSats and other spaceborne assets with similar bandwidth and hardware resources. The protocol is designed to operate with high efficiency and high reliability over links with a small bandwidth-delay product and moderate to weak signal quality. A type-I hybrid automatic repeat request (ARQ) scheme and an extensible header structure reduce the overhead added by unused protocol features, thus minimizing the overhead added on the return channel by the ARQ. Simulations show a good performance of the protocol, despite high bit error rate on the channel. Furthermore, the return channel bandwith efficiency of the protocol allows its use on asymmetric links.
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This paper presents the on-orbit results and the lessons learned from First-MOVE (Munich Orbital Verification Experiment), the first CubeSat mission of the Institute of Astronautics (LRT) at the Technische Universität München (TUM). The development of the satellite started as a student project in 2006. First-MOVE was launched on November 21st 2013. The student-designed and built satellite was operated for almost a month. On December 19th 2013 a major malfunction occurred, presumably due to an anomaly in the on-board data handling system (OBDH), which left the satellite in a mode where it is only transmitting continuous wave (CW) beacons. Although the short mission duration prevented several mission objectives from being achieved, the overall program can be considered a success, as it permitted more than 70 students hands-on experience and led to major in-house technology and spaceflight processing developments. The main aspects of a university-led satellite development, the results of the mission and both technical as well as educational lessons learned are described, including the management and planning of student projects as well as motivational and system engineering aspects. These aspects include planning the project around student's schedules rather than in a traditional, linear fashion, the careful selection and distribution of team members to subsystem teams and the deviation from traditional systems engineering process flows in order to retain student motivation. The importance of large milestone reviews and kick-off events as short term goals and as a means to recruit new team members are highlighted. Academic outreach programs included a one week summer school held in 2011 to recruit and train new students in a time-efficient setting in relevant technical aspects. The paper explains in more detail the technical lessons learned from the major satellite subsystems, both self-developed and purchased. The self-developed systems include, among others, the design of the solar-panel release mechanism, the unique CMOS latch-up protection system, the hard-command unit and the OBDH system. Although we can report a flawless function of all the purchased subsystems in-orbit, the detailed in-house system-level testing of these components is a major lessons learned of First-MOVE from the prospective of student education and system knowledge. Despite the existence of documentation, the time and knowledge needed for designing a test bed for the electric power system (EPS) and the subsequent testing was underestimated. Furthermore, from a testing prospective, the importance of integrated system-level testing and the need for longer, continuous operations test of the satellite are emphasized. On-orbit flight data, as well as educational lessons learned for efficient student involvement during mission operations are highlighted. An outlook to MOVE II, the follow-up satellite project of LRT, outlines how the lessons learned of the last generation students can be carried over and how they will influence future (student) satellite developments and spaceflight development processes at LRT.
Conference Paper
The Antiproton Flux in Space (AFIS) mission will measure the flux of low-energy antiprotons trapped in Earth’s magnetic field. We have developed a new active-target detector concept and have constructed and tested two prototypes. The instrument’s innovative, simple design relies on the stopping of particles in matter due to ionization. It can detect charged particles and identify ions with low kinetic energies. To identify antiprotons, the characteristics of their annihilation process are exploited as well. It is ideal for applications on nanosatellites. We present the results of a beam test of a prototype detector with a reduced number of channels undertaken at the Paul Scherrer Institute in 2013. In particular, we discuss the successful tracking of pions and protons and the reconstruction of beam energy characteristics. We also present the construction and testing of a full prototype detector that was selected to fly aboard the BEXUS 18 stratospheric research balloon.
MOVE (Munich Orbital Verification Experiment) is a program of the Institute of Astronautics (LRT) at the Technische Universität München (TUM), which aims on building pico-satellites with university students mainly for educational purposes. First-MOVE shall create a robust platform as a starting point for sophisticated satellite missions of the institute in the future. In the paper, the state of development is described, but emphasis is on the requirements for high reliability of the First-MOVE satellite and how robustness drives the actual design of the satellite.
On-orbit verification of space solar cells on the Cube-Sat MOVE-II
  • M Rutzinger
  • L Krempel
  • M Salzberger
Rutzinger, M., Krempel, L., Salzberger, M., et al. (2016). On-orbit verification of space solar cells on the Cube-Sat MOVE-II. In Photovoltaic Specialists Conference (PVSC), 2016 IEEE 43rd, pages 2605-2609. IEEE.