SOMP (Students' Oxygen Measurement Project)
SOMP is a CubeSat project of the TU (Technische Universität) Dresden (or Dresden University of Technology), Germany, organized by students in the students’ research group STARD (Spacecraft Engineering in Dresden). SOMP is an educational satellite project. Designing and developing SOMP will allow the students to practically apply their knowledge and gaining unique hands-on experience in many aspects of a space project. The mission objectives are: 1) 2)
• Prototype development of a satellite bus
• Verification of the satellite
• Launch of the satellite SOMP
• Establishment of first contact with SOMP
• Operation of the satellite to fulfill scientific mission objectives.
SOMP has two scientific objectives: the first objective is to measure the concentration of atomic oxygen in the upper atmosphere using an oxygen electrolyte sensor. The second goal is the testing of flexible TFSC (Thin Film Solar Cells), so far not tested in space.
The satellite was developed by students from various departments of the TU Dresden in the years 2008 – 2012. The project is funded by various companies who sponsored materials such as the solar cells and PCBs. The German Aerospace Center (DLR) has also contributed to the project. The project management is done by the Department of Space Systems and Utilization and is supported by the Department of High Frequency Technology and the UZLR (Universitätszentrum für Luft und Raumfahrt).
Figure 1: Artist's rendition of the deployed SOMP CubeSat in orbit (image credit: TU Dresden)
SOMP is based on the 1U Cubesat standard of size (10 cm x 10 cm x 10 cm) and a total mass of 1 kg. The spacecraft structure [SMS (Structure and Mechanical System)] consists of 4 side panels which are almost identical in construction, one upper face similar to the side panel and one payload face. The 4 fold-out antennas are arranged on the side panels, wound around the satellite and tucked in during the launch phase. Four circuit boards and one battery pack are seen inside the satellite. 3) 4)
EPS (Electrical Power Subsystem): Five of the outer panels and ½ of the payload side panel are covered with solar cells with a cumulative size of 0.03m2. Triple junction GaAs (Gallium Arsenide) cells from AzurSpace with 28% efficiency are used. These are the only energy source for the satellite with less than 2 W of electrical power available for satellite operations. Li-ion batteries are used to store electrical energy and provide power as needed during eclipse and peak load phases of the orbit.
• Power generation: 6 x solar panels with 2 x TJGA solar cells (AzurSpace 3G28) each, connected in series.
• Energy storage: 2 x CGA103450B Li-ion batteries (~7.4 V, 1950 mAh) BQ29312A and BQ20Z80 as protection circuits, Minco Kapton foil for heating (1 W max).
• Control: MSP430, an ultra-low power 16-bit microcontroller of TI (Texas Instruments).
• Voltages and converters:
- Raw bus voltage ~8 V
- Buck regulation to 3.3 V – TPS62111
- Buck regulation to 5 V – TPS62112
- Boost regulation to 12 V – MAX1771
- Battery charging voltage ~8 V.
Figure 2: Photo of the EPS (image credit: TU Dresden)
AOCS (Attitude and Orbit Control Subsystem): AOCS is a passive 3-axis stabilization system using a permanent magnet, magnetometers and sun sensors. Magnetorquers (passive coils) are used which interact with the Earth's magnetic field to provide a means for orientation and adequate detumbling after deployment of the CubeSat. Pointing accuracies of ±5º are obtained.
- 12 x S6560 sun sensors
- 3 x FLC100 analog magnetometers
- 3 x magnetorquer (80 mm x 83 mm, 0,16 mm copper wire, 188 twists, 200 mW)
- 3 x ADS7952/7953 ADC (1 MS, 12bit, 12 / 16 ch., SPI)
- ATtiny461 + 3 x BD6211F driver ICs for controlling the magnetorquers.
C&DH (Command and Data Handling) subsystem: The main computer (ARM9-based) performs various functions, such as payload control and data handling, attitude and position determination, as well as control of the SDR (Software Defined Radio) based communication system. with a 70 cm UHF-module, called CTRX. The key parameters are:
• ARM9 (AT91SAM9G20) @200MHz, 64 MB SDRAM, 2 x 512 kB MRAM, 1 GB SD Card
• RTC, CPU-Core voltage regulators, USB serial port, isolated SPI
• High Precision Frequency 20 MHz TCXO
• AD9861 TX DAC
• AD9874 IF digitizing subsystem
• Support of RF modules up to 200kHz bandwidth.
The operating system is based on eCos, an open source package, which has been modified for SOMP.
RF communication subsystem: The 70 cm HF-module has the following parameters:
• Frequency range: 430– 440 MHz (UHF)
• Output power: up to 27 dBm
• Differential RF output ports
• On-Board LO (Local Oscillator) generation
• Channel bandwidth: 25 kHz (up to 100 kHz in experimental mode)
• Data rate: 23 kbit/s Netto (BPSK modulation) , up to 180 kbit/s in experimental mode with QPSK modulation.
Additionally SOMP has a backup communication subsystem, namely the SDR. The SMR (SOMP Radio Module) is a transceiver and modem which receives the digital data from a PC and generates a HF signal for transmission or vice versa. The SMR consists of a MSP430 microcontroller board and a slave board with the Si4420 single transceiver chip as shown in Figure 3.
• Frequency range: 430 – 440 MHz
• Channel bandwidth: 50 kHz
• BFSK for the 9.6 kbit/s channel.
The satellite transmits a CW beacon signal. The signal is always transmitted, exceptions are when:
- the satellite is in silent mode or payload operation mode
- the battery charge level is below 30%.
Figure 3: Photo of the SMR (image credit: TU Dresden)
Figure 4 gives an overview of the electrical/electronic components of the CubeSat. The key operational functions of the satellite are divided between the EPS (Electrical Power Subsystem) and the C&DH (Command and Data Handling) subsystem. The EPS oversees the electric power supply; its functions including but not restricted to power conditioning of the energy generated by the solar cells, battery control and its safety, collection of information from various parts of the power system etc. In addition, the EPS also has control of the backup communication system which takes over the communication should something go wrong with the main CS (Communication Subsystem).
Figure 4: Block diagram of the SOMP spacecraft (image credit: TU Dresden)
Figure 5: Photo of the SOMP CubeSat (image credit: TU Dresden)
Launch: The SOMP CubeSat was launched as a secondary payload on April 19, 2013 on a Soyuz-2-1b vehicle from the Baikonur launch facility in Kazakhstan. The primary spacecraft on this flight was Bion-M 1 of Roskosmos, carrying a biological payload into LEO (international payload of live animals, plants and other life sciences experiments for exposure to microgravity). 5)
Orbit: Initial elliptical orbit with an altitude of ~300 km x 575 km, inclination = 64.9º. After separation from the launch vehicle, the Bion-M1 spacecraft circularizes its orbit to the altitude of 575 km. The secondary payloads will be deployed from Bion-M1 after the target orbit is reached (~2 days after launch).
Figure 6: Illustration of the Bion-M1 spacecraft (image credit: TsSKB Progress) 6)
The Bion capsule will parachute back to Earth after a one-month mission. The Bion-M1 spacecraft has a launch mass of ~6,840 kg.
The secondary payloads on this flight are:
• SOMP, a 1U CubeSat of the TU Dresden, Germany.
• OSSI-1 (Open Source Satellite Initiative-1), a 1U CubeSat of Korea. The project was initiated by the Korean artist Song Hojun. OSSI-1 has a 12 WPM (Words Per Minute) CW Morse code beacon on 145.980 MHz, a data communications transceiver on 437.525 MHz and carries a 44 W LED optical beacon to flash Morse code messages to observers on Earth.
• BEESat-2 (Berlin Experimental and Educational Satellite-2) and BEESat-3, 1U CubeSats of TU (Technische Universität) Berlin, Germany.
• Dove-2, a nanosatellite (3U CubeSat) technology demonstration mission of Cosmogia Inc. (Sunnyvale, CA, USA).
• AIST-2 is a Russian microsatellite project, a technology demonstration, developed and designed by students, postgraduates and scientists of the Samara Aerospace University in cooperation with TsSKB Progress of Samara, Russia. The microsatellite with a mass of 39 kg will perform a 3 year mission dedicated to measurements of the geomagnetic field and to test methods to compensate low-frequency microaccelerations. Also, the spacecraft will study high-speed mechanical particles of natural and artificial origin.
Figure 7: Photo of the AIST-2 microsatellite (image credit: TsSKB Progress)
Sensor complement: (FIPEX, TFSC)
FIPEX (Flux (Phi, Φ) Probe Experiment):
FIPEX is a microsensor system developed for measurements of atomic and molecular oxygen. As a payload on-board SOMP, it allows a time-resolved measurement series of the atomic oxygen concentration in LEO, while the altitude of the satellite decreases during its life cycle. Since atomic oxygen shows significant interactions with spacecraft structures and surfaces, the acquired data is crucial for future spacecraft missions in LEO, since it will help to develop more precise estimations of its distribution. 7) 8)
The measurement of the time resolved behavior of atomic & molecular oxygen in LEO (Low Earth Orbit) provides:
- time resolved data for correlation of atmosphere models
- time resolved data for prediction of AO (Atomic Oxygen) during a mission.
- FIPEX has been tested during ballistic flights on TEXUS sounding rockets from 1996 onwards, VS30, TEAMSAT (Ariane 502), 2 x IRDT (Inflatable Reentry and Descent Technology) probe flown on Soyuz/Fregat.
- 572 days of successful operation on the ISS (International Space Station). The FIPEX system was part of EuTEF (European Technology Exposure Facility), which was flown to the ISS on STS-122 on Feb. 7, 2008.
FIPEX sensor working principle: 9)
• Solid electrolyte sensors based on amperometric combined with the potentiometric-Nernst principle for polarization control
• Manufactured by screen printing technologies (thick-film) and thin-film technologies (up to 24 layers) and well-defined sinter cycles to 1500°C —> simple reproducible series production
• Based on noble metals, ceramic materials, and sensitive additives.
Sensor for atomic oxygen:
- Non-dissoziative adsorption
- Detection of AO (Atomic Oxygen)
- Cathode reaction (simplified).
Figure 8: Schematic view of the FIPEX working principle (image credit: TU Dresden)
Figure 9: Photo of FIPEX on SOMP (image credit: TU Dresden)
Figure 10: Illustration of the FIPEX components (image credit: TU Dresden) 10)
TFSC (Thin Film Solar Cells):
TFSC is a technology demonstration experiment.
2) S. Fasoulas, A. Deckert, C. Nitzschke, P. Voigt, A. Weber, “Das CubeSat Projekt an der TU Dresden: Students' Oxygen Measurement Project- SOMP,” Deutscher Luft- und Raumfahrtkongress der DGLR, Aachen, Germany, Sept. 8-10, 2009
3) “SOMP Operation Guide,” TU Dresden, March 5, 2013, URL: http://phpweb.tu-dresden.de/stard/SOMP/wp-content/uploads/2013/03/SOMP-SYS_Operation.pdf
4) S. Fasoulas, A. Deckert, C. Nitzschke, P. Voigt, A. Weber, “Das CubeSat Project an der TU Dresden: Students' Oxygen Measurement Project - SOMP,” Konferenzband der DGLR Jahrestagung 2009, September 8-9, 2009, Aachen
5) Patrick Blau, “Soyuz Launch Success - Bion-M1 & various Passengers safely in Orbit,” Spaceflight 101, April 19, 2013, URL: http://www.spaceflight101.com/bion-m1-mission-updates.html
6) A. N. Kirilin, R.N. Akhmetov, S. I. Tkachenko, “SRP SC “TsSKB-Progress”: Trends and Future Prospects,” 2011, URL: http://www.google.de/url?sa=t&rct=j&q=tsskb%20progress%20of%20samara%2C%20russia&source=web&cd=5re4QS-_IGoDw&usg=AFQjCNFA4ELDIyJShKf7c4CbUVdnNl4lxg&bvm=bv.45512109,d.Yms&cad=rja
7) Students' Research Group, “Student's Oxygen Measurement Project,” University of Dresden,Annual Spring CubeSat Developer's Workshop, Cal Poly State University, San Luis Obispo, CA, USA, April 9-11, 2008, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2008/SOMP.pdf
9) Tino Schmiel, Stefanos Fasoulas, “FIPEX sensor working principle,” SSWG (Sensor Selection Working Group), 2nd QB50 Workshop, von Karman Institute, Brussels, Belgium, July 27-28, 2011, URL: http://nohka.planet.ee/kool/keskkonnafyysika/kosmosetehnoloogia%20alused/Schmiel_FIPEX2011.pdf
10) T. Schmiel, S. Fasoulas, A. Weber, “Flux-Φ-Probe Experiment – FIPEX,” QB50 5th Workshop, VKI (Von Karman Institute), Brussels, Belgium, January 29, 2013, URL: URL: https://www.qb50.eu/download/workshop/workshop5th/5_5thQB50WS-ScienceUnits_and_Sensors.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.