OPS-SAT (Operations nanoSatellite)
OPS-SAT marks ESA's entry into the nanosatellite world - starting in 2012. This is a clear signal that this market segment has reached a certain maturity and this is good news for the blossoming European nanosatellite industry. The satellite will demonstrate a massive jump in capabilities for this class of spacecraft (communication rates, processor speeds, on-board memory, reconfigurable FPGAs etc). This will accelerate the rapid transition from supporting educational missions to supporting operational ones in this area. The project will also be a chance for real European cooperation. For example, the project drew interest from CNES and DLR on the hardware side, but the agencies also support experiments demonstrating new CCSDS standards. 1) 2) 3) 4) 5) 6)
• Develop a satellite specifically designed to allow constant experimentation with critical on-board and ground software using modern space to ground interfaces
• An operational perspective, the emphasis is to demonstrate innovation that is asked for by the operators rather than imposed on the operators.
• The nanosatellite should be: representative, cheap, and quick to launch.
2) The general OPS-SAT CDF (Concurrent Design Facility) mission requirements are:
• Must allow easy and complete replacement of on-board software in flight - i.e. an open experimental platform
• Software should be able to be updated quickly, easily and often – a complete reload of the entire software in less than 3 passes
• Allow the use of standard terrestrial CPU, OS and Java – aim for the equivalent of mobile phone performances
• The satellite should be no bigger than a 3U CubeSat (30 x 10 x 10 cm) and compatible for launch in a P-POD
• COTS units shall be used wherever possible (no new developments)
• Cost to be kept below 2 MEuro
• Time to launch between 1-2 years from kick off
• Single string implementation but reduce single point failures to a minimum
• Make the satellite safe by design (even without the processor running)
• Do not assume that any unit will work all the time
• Always ensure the ground can recover any unit.
3) The experiments – both software & hardware:
• CCSDS mission operations services
• File-based operations
• Autonomy operations and opportunistic science
• Housekeeping telemetry compression
• Potentially many more SW experiments
• Miniature X-band transmitter.
4) Mission operations are considered an experiment:
• OPS-SAT is a special ESA project because it is meant to drive innovation and experimentation in the spacecraft control domain. Therefore the ground segment(s) and operations are experiments!
• The CDF treated them as such assuming that they will be funded from other sources and that normal ESA standards will not be applied in the development.
• Use of low cost ground station alternatives (for instance the UHF/VHF/S band antenna in ESOC) were also assumed.
• OPS-SAT shall provide an in orbit platform that through reconfigurability shall allow experimenters to uplink and execute software experiments that will advance the state-of-the-art of mission operations and have a clear potential for use in future ESA missions.
• Experimenters are entities within ESA and within the European academic and industrial community that can deliver relevant software experiments compliant with the OPS-SAT capabilities. Software experiments shall have open access to all on-board resources and systems unless justified due to safety.
• The mission shall be realized as a nanosatellite mission levering CubeSat COTS components where possible, without compromising a minimum life-time target of two years.
• The spacecraft shall be power and thermally safe even if tumbling. The mission shall be robust against single event upsets, latching events or faulty experimental software. It shall be demonstrated that despite using COTS components a reconfigurable and yet re-liable platform can be delivered.
• The OPS-SAT payload shall deliver as a minimum; two processors running at 500+MHz with 500 MB of RAM, 10 GB solid storage and a reconfigurable FPGA.
• At least one configuration shall be representative of an ESA mission (including ground software and OBSW (On-Board Software).
• S-band uplink rates of at least 256 kbit/s and S-band downlink rates of 1 Mbit/s shall be supported. The high uplink data rate is due to the fact that this mission is focused on new software experiments. Therefore it is needed to upload the frequently changing software experiments in reasonable times.
• The spacecraft shall be recoverable and resettable by at least two independent communications routes in hardware and software. The spacecraft shall be able to communicate with the respective ground station in any orientation
ESA and its European industry partners generate every year many new and innovative ideas for advancing European space technology regarding mission operations but the majority of these innovations never make it to orbit. OPS-SAT emerged, providing a low cost in-orbit laboratory available for authorized experimenters to test, demonstrate and validate their development software experiments. OPS-SAT is the first CubeSat designed by ESA and is a safe experimental platform which shall fly in a low-earth sun synchronous orbit. OPS-SAT makes available a reconfigurable platform, at every layer from channel coding upwards, and it will be available for experimenters wishing to test and demonstrate new software and mission operation concepts.
OPS-SAT is a nanosatellite (3U form factor) designed by ESA CDF (Concurrent Design Facility) to provide a platform for in-orbit validation of these new concepts developed by ESOC (European Space Operations Center), Darmstadt, Germany. OPS-SAT is the first CubeSat designed by ESA, integrating state of the art components (such as a miniaturized X-band transmitter derived from the PROBA-V mission) allowing it to provide unmatched performances, up to several hundreds times better than any other CubeSat flown before. - Note that this transmitter is now flying first on the GOMX-3 mission supported by ESA. 10) 11) 12)
The CDF and the supporting concurrent engineering environment were able to adapt successfully to this new type of application, providing tools and methodologies to enhance performances and reliability through architectural trade-offs. Fast iterations of the design process, helped by an updated concurrent engineering data model and rapid prototyping techniques allowed ESA to achieve a mission design that meets all the requirements.
In 2013 an Open Call for OPS-SAT experiment ideas was launched by ESA with more than 100 experiments being suggested, followed by a highly successful experimenters' day with an attendance of more than 150 participants. In July 2013 two parallel Phase A/B1 study contracts were awarded to TU Graz and GOMSPACE, respectively. The team led by the Institute of Communication Networks and Satellite Communications of TU Graz presented the results in January 2014. In February 2015 the Phase B2/C/D/E1 contract was kicked off. The team led by TU Graz is composed of GMV and the Space Research Center Warsaw (Poland). BST (Berlin Space Technologies) and MEW Aerospace (Germany), GOMSPACE (Denmark) as well as MAGNA STEYR Engineering and Unitel (Austria). 13) 14) 15) 16)
The final avionics design of OPS-SAT can be viewed as four interconnected parts: a CubeSat bus, an ESA communications module, a payload and a FDIR (Failure Detection, Isolation and Recovery ) system. The payload can be further broken down into a processing core, various peripherals (camera, GPS, advanced ADCS subsystem) and several payloads of opportunity.
OPS-SAT is a 3U CubeSat having a size of 10 x 10 x 30 cm and a mass of approximately 5.4 kg. Two double folded deployable solar array panels generate 30 W of electrical (peak) power. Key requirements of OPS-SAT are that at least one configuration must be representative of a standard ESA mission and that the spacecraft has to be inherently safe. Faulty software which experimenters may upload to the satellite cannot jeopardize the mission To achieve this, in the OPS-SAT design all potential single points of failures have been removed. The spacecraft will utilize a CCSDS-compatible S-band telemetry system. This is relatively new for CubeSats which normally rely on amateur packet radio technology and UHF/VHF telemetry.
OPS-SAT bus: Approximately 1U of the satellite accommodates the CubeSat COTS components, including: the UHF antenna deployment system (as well as the software defined radio receiver payload antenna, see later), a motherboard with the UHF transceiver, the NanoMind OBC (On-Board Computer), the BP4 battery pack with 4 battery cells, the EPS (Electical Power Subsystem), consisting of a motherboard accommodating two power input boards for the body mounted and deployable solar array strings, and two power output boards for power regulation and distribution and the Z axis magnetorquer integrated in a PCB (Printed Circuit Board). The double deployable solar arrays are provided by ClydeSpace whereas the remaining components are provided by GomSpace. Using a quasi-single provider keeps the integration costs and risks of the satellite bus low. GOMSpace also provide the ground terminal for the UHF communications. The one area where some development was required on the COTS components was the power conditioning subsystem. The mission sometimes generates over 30 W of peak power and is connected in 11 strings. To accommodate this GOMSpace proposed an architecture with two separate power conditioning and distribution boards, each connected to half of the solar arrays on the satellite.
Solar arrays cover the satellite except for the Z faces, as shown in Figure 1 (right). The deployable solar arrays have integrated sun sensors and magnetorquers. The bus also includes a GPS unit which is linked to the NanoMind OBC to provide GPS functionality to the ADCS system. The GPS antenna is integrated into the –X panel next to the umbilical connectors of the spacecraft. As the GPS will be integrated with the CubeSat bus and not directly to the processing platform, all data from the GPS can be made available over the I2C payload bus interface from the NanoMind to processing platform. In addition, the GPS will be used for timekeeping on the Nanomind OBC, which keeps the OBT (On-Board Time).
Figure 1: Illustration of the OPS-SAT nanosatellite configuration with solar arrays deployed; left: front view; right: rear view (image credit: ESA)
Figure 3 shows the block diagram of OPS-SAT. There are two sections, the satellite bus and the payload. The satellite bus consists of low-cost COTS subsystems developed for other CubeSat missions. A UHF/UHF telemetry provides a backup telecommand and control facility in addition to the CCSDS-compatible S-band. Other bus components include the OBC (On-Board Computer) with GPS receiver providing coarse attitude control, and the power unit with batteries and charge/discharge regulators. An FDIR (Fault Detection, Isolation and Recovery) computer is responsible for monitoring the status of the payload subsystems and for controlling the data buses (I2C, SPI, LVDS, serial RS 422) as well as the power buses allowing to interconnect, activate and deactivate the payload subsystems as needed.
Figure 2: As a flying laboratory, ESA's OPS-SAT will test and validate new techniques in mission control and on-board systems (image credit: ESA) 17)
EPS (Electrical Power Subsystem): The EPS includes the ability to selectively cut power to individual boards, controlled by I2C from the on-board computer. With two P31us power supplies in their default configuration, the OPS-SAT EPS will be able to provide sufficient power to all CubeSat Bus systems and payloads. The P31us power supplies will feed into a single power distribution board, which will provide at least 20 latch-up protected configurable power outputs. Each of these will provide a single switchable power line to each subsystem as needed. These outputs allow full control by the OBC to remotely reset systems in a failure state without affecting the rest of the satellite. Each switch can be independently configured to deliver any desired voltage to its source, and has a current range of 0.5-3.0 A.
A GomSpace BP-X battery pack with 8 cells will provide the power storage for OPS-SAT. By configuring the BP-X with multiple strings in parallel, the failure of an individual cell will not cut off the rest of the battery pack. By using 8 cells in the BP-X, OPS-SAT will have the same total battery capacity as 2 BP-4 packs, with easier mechanical and electrical integration. Additionally, by using a single battery instead of 2, failure of a single power supply will not degrade battery storage capacity.
Figure 4: GomSpace NanoPower BP-X battery pack as a 6 cell system (image credit: GomSpace)
RF communications module:
A driving mission requirement is that a satellite configuration should exist that is indistinguishable to the ground from a typical ESA satellite. Among other things, this means that the spacecraft has to fly firmware and software that implement CCSDS protocols. The solution is to deploy the IP core of an ESA TM/TC encoder/decoder chip onto a commercially available FPGA. This unit is referred to as the CCSDS engine (Figure 17). This chain will be used for nominally communicating between the Nanomind OBC and the ESA ground control system. However it will be possible for the experimenters to bypass this unit and go directly between the S-band transponder and the SEEP (Satellite Experimental Processing Platform). This will allow configurations that use non-CCSDS protocols such as TCP/IP on the mission.
Since over 90% of the experimenters want to load large software images to the spacecraft as part of their experiment, it was decided that the mission had to allow the fast upload. The S-band receivers must therefore be able to accept an uplink signal at 256 kbit/s. For comparison the UHF transceiver on the Cubesat bus can only support data rates of 9.6 kbit/s. This is much higher than the highest uplink rate for normal ESA spacecraft which is 4 kbit/s rising to a maximum of 64 kbit/s in some rare cases. This requirement is already driving innovation on the ground as during ground prototype testing ;ESA realized its ground segment could not produce such a fast telecommand stream without major modifications. This presents the OPS-SAT project with a prime example of the nanosatellite world challenging long standing and accepted limitations in the world of big space. On-board the new EWC31 S-band TT&C transceiver from Syrlinks of Bruz, France has been selected to provide this high uplink and a variable downlink with data rates of up to 1 Mbit/s. It will be a follow-up of the transceivers used for the Myriade microsatellite program of CNES and the PROBA-V mission. This is the company that is developing the mini X-band transmitter on behalf of CNES. 18) 19) 20) 21)
The new S-band system of Syrlinks represents a 60% reduction in mass and volume for that unit compared to the preliminary design. This has been one of the main reasons that the consortia has been able to improve the design to be much safer and meet much more of the experimenter's requirements. The new unit will be able to sustain a data rate for the downlink of 1 Mbit/s and an uplink data rate of 256 kbit/s. CCSDS compatible modulation and demodulation will be supported.
The first elements of a functional X-band prototype transmitter which is able to modulate data up to 100 Mbit/s, using fully CCSDS compatible filtered OQPSK modulation and convolutional coding (k=7, R= ½+RS coding), deliver up to 2 W RF with no more than up to 10 W DC/DC consumption, and fit inside a 0.25 U form factor of a standard CubeSat. In the first half of 2014, an EQM has been developed and the final evaluation tests are on-going(see a description of Micro S-band transceiver and X-band transmitter under "Payloads/Experiments of opportunity").
The S-band telemetry system consists of the miniaturized S-band transceiver which supports a data rate of 1 Mbit/s in downlink and 256 kbit/s in uplink. The compatibility with the CCSDS/PUS/SCOS protocol stack is provided by an IP core made available by ESA and integrated in a radiation-hard FPGA. Bypassing of the IP core will be possible allowing to implement new protocols different from the CCSDS standard.
Figure 5: Block diagram of the communications module (image credit: ESA, TU Graz)
OBC (On-Board Computer): The GomSpace NanoMind A712D, currently on-orbit with several CubeSat missions, serves as the OBC of OPS-SAT. The NanoMind gathers telemetry from the various on-board systems including the payload systems, via the I2C bus which runs the CSP (CubeSat Space Protocol). Additionally, the NanoMind will have another I2C bus that will serve as a secondary data interface between the CubeSat Bus and the payload (Ref. 4).
Fine ADCS (Attitude Determination and Control Subsystem)
OPS-AT contains two ADCS systems. One is provided as part of the bus and is referred to as the coarse ADCS. The control algorithms are implemented on the Nanomind OBC and it relies on magnetotorquers as actuators and sun sensors and magnetometers as sensors. The other is implemented as part of the payload and is referred to as the fine-pointing ADCS or iADCS (integrated Attitude Determination and Control Subsystem). Experimenters can use this for carrying out attitude control experiments and to provide higher pointing accuracy for camera and optical data transmission experiments. Control algorithms can be placed directly on the iADCS FPGA or on the SEPP. The iADCS-100 by BST (Berlin Space Technologies) and Hyperion Technologies B.V. of Delft, The Netherlands (Figure 6) has been chosen allowing a pointing accuracy well below 1°. The iADCS provides a set of high performance sensors and actuators such as the ST-200 star tracker and miniature reaction wheels. In combination with the proven ADCS algorithms derived from the renowned TUBSAT satellites, the iADCS-100 offers a number of autonomous modes such as nadir pointing and target pointing that were before only available for larger spacecraft.
The evaluation of the experimenters' proposals showed that there is significant interest in camera experiments. Several experimenters will develop on-board processing algorithms for simple remote sensing applications.
Figure 6: Schematic view of the iADCS (image credit: ESA, BST, Hyperion Technologies)
The ADCS sensor inputs include sun sensors located on the exterior solar panels and a 3-axis Honeywell MC5843 magnetometer on the NanoMind. Additionally, a 3-axis gyro can be connected to the NanoMind to provide additional attitude determination capability. The NanoMind is a flight proven system capable of providing ADCS processing. The NanoMind controls magnetorquers embedded in the body solar panels. The GomSpace body panels can include air core magnetorquers in single 1U loops for each axis of rotation. Combined with the NanoMind A712D, these magnetorquers have the capability to provide a pointing accuracy of approximately 12º (Ref. 4).
Figure 7: Photo of the iADCS with star sensor and 3 reaction wheels (image credit: ESA, TU Graz)
Development status and some project background:
• April 27, 2017: This week, he engineering model of OPS-SAT, was for the first time connected to its control system. Both spacecraft and the ground system are using innovative new protocols to inter-communicate and both will now undergo an extensive testing and validation campaign. OPS-SAT contains an experimental computer, that is ten times more powerful than any current ESA spacecraft. 22)
Figure 8: Photo of the OPS-SAT engineering model on a test bench gets connected to an innovative ground control system at ESA/ESOC for the first time (image credit: ESA, CC BY-SA 3.0 IGO)
• The OPS-SAT project is in Phase C (Ref. 5).
• OPS-SAT is an ESA nanosatellite mission designed exclusively to demonstrate ground-breaking satellite and ground control software under real flight conditions. The project is being led by ESOC (European Space Operations Center) in Darmstadt, Germany. Following a successful ESA Concurrent Design Facility (CDF) study early in 2012, the project kicked off with two parallel Phase AB1 studies in July 2013. These were led by TU Graz of Austria and GomSpace of Denmark, respectively. Phase B/C/D/E started officially in February 2015 and the satellite will be ready to launch in 2018. TU-Graz is now leading a consortium for Phase B/C/D/E. Core avionics will be delivered by GomSpace (Ref. 23).
• One of the major requirements of the mission is that at least one configuration shall be representative of an ESA mission (including ground to space interfaces). In simple terms, OPS-SAT has to look like a real ESA satellite to the ground and be compatible with the ESTRACK ground station network. During the CDF , this requirement was identified as a major challenge due to the lack of a CubeSat sized CCSDS compatible S-band transceiver on the market. The solution proposed was to mechanically modify an existing S-band transceiver to try to squeeze it into the CubeSat form factor. The solution was declared feasible but with a diplexer it took up around half of the available volume of the satellite. The CDF declared that "All the requirements can be matched with presented design but two options have been identified with the intention of reducing onboard resources requested by the communication subsystem and are as follows:
1) Development of a dedicated miniaturized Transponder/Transceiver with low power consumption RX as driver.
2) Development of a miniaturized Diplexer: solution based on dual port antenna can be of interest.
- The identification of the new EWC31 S-band transceiver from Syrlinks by the TU Graz led team in Phase A/B1 has led to significant advantages for the mission as a whole. The 60% reduction in volume and power usage achieved in the new design has been exploited to remove the single point failures in the CDF design and to drastically improve the capabilities of the payload. In turn this has allowed significantly more of the proposed experiments for the mission to be accepted.
- Another fundamental OPS-SAT mission requirement is to be able to change the complete on-board software on a daily basis. This has led to the system requirement that uplink rates of a minimum 256 kbit/s are required. This is way above the highest uplink rate for normal ESA spacecraft which is 4 kbit/s rising to a maximum of 64 kbit/s in some rare cases. This requirement is already driving innovation on the ESA ground segment and presents us with a prime example of the nanosatellite world challenging long standing and accepted limitations in the world of big space. This high uplink date rate is supported by the transceiver.
- Finally, the mission requires that the ground can communicate with the satellite via S-band in any attitude. In fact, to minimize the amount of critical software, when OPS-SAT enters safe mode then the fine pointing attitude control system is switched off. The spacecraft relies on solar panels being placed on most faces and a robust, passive thermal design to survive rather than going to any particular set attitude. Hence it is clear that the EWC31 S-band transceiver must serve two receive/transmit antennas (one on each side of the spacecraft) to provide the necessary quasi omni-directional coverage.
- While the EWC31 S-band transceiver was important in the latter parts of the core mission, the miniature EWC27 X-band HDR-TM (High Data Rate -Telemetry) transmitter was highly relevant in defining the OPS-SAT mission in the first place. CNES contacted ESA/ESOC with the idea of flying such a transmitter on-board a CubeSat in 2011. Further discussions led to the conclusion that the required technology to fly a CCSDS compatible transponders on nanosatellites (even given the constraints on mass, power and volume) was on the verge of being available. This directly led to the concept of OPS-SAT being studied in the CDF and the EWC27 X band transmitter experiment was used to generate requirements for the platform design.
- In Phase AB1 the HDR-TM was included as a payload of opportunity i.e. to be considered once the margins left for such payloads were clear. It was subsequently selected to fly because it has a great deal of synergy with the other experiments (some want to download large amounts of data e.g. video). This would only be possible via a X-band or higher frequency transmitter.
- OPS-SAT will be a "laboratory in the sky". The core is a system on-chip module (Altera Cyclone-V) with dual ARM-9 processors and an FPGA allowing software and hardware reconfigurability for the experimenters. During an Open Call by ESA in 2013, more than 100 experiments were proposed, the majority being software experiments. 91 % of the experiments are feasible on OPS-SAT. To allow the fast upload of software images, the S-band transmitters must be able to uplink at 256 kbit/s. The UHF transceiver on the CubeSat bus can only support data rates of 9.6 kbit/s and is not suitable for the transfer of large software images. On the other hand, some experiments will generate substantial data volumes, e.g. when high-resolution images are taken. In this case the relatively high data rate of the S-band transmitter is beneficial.
- OPS-SAT will also carry a camera with an estimated ground resolution of approximately 60 m. On-board image processing has been proposed This camera will support both still image and streaming video modes. In the latter case, a high downlink data rate is required. Such camera experiments will require substantial downlink data rates for which the EWC27 X-band transmitter will be needed, particularly when bearing in mind real-time applications and the short contact times (typically 10 minutes for a ground station pass).
- The S-band and X-band antennas for OPS-SAT were designed by TU Graz. The engineering models are currently (2015) undergoing subsystem tests.
- OPS_SAT mission statement: OPS-SAT is a safe, hard/software laboratory, flying in a LEO orbit, reconfigurable at every layer from channel coding upwards, available for authorized experimenters to demonstrate innovative new mission operation concepts (Ref. 12).
Launch: A launch of OPS-SAT as a secondary payload of ESA is expected in 2018.
Orbit: Sun-synchronous LEO orbit with an altitude of ~600 km.
ESOC will operate the satellite through its Small Mission Infrastructure Laboratory Environment facilities. These include reconfigurable baseband equipment based on FPGA/Software Defined Radios, a small UHF/S-band ground station, computer hardware and the entire ground software control chain. ESOC also intends to deliver the on-board image and corresponding ground software to enable the CFDP (CCSDS File Delivery Protocol) to run on OPS-SAT.
Payloads/Experiments of opportunity:
SEPP (Satellite Experimental Processing Platform): SEPP is the heart of the OPS-SAT payload. It is a powerful ALTERA Cyclone V system-on-chip module with sufficient on-board memory in order to carry out advanced software and hardware experiments. It is the reconfigurable platform required on OPS-SAT on which all major experiments will be processed. The Altera Cyclone V SX System-on-Chip (SoC) digital core logic device provides with a 800 MHz CPU clock and 1GB DDR3 RAM a powerful processing capability. All Altera SoC SX devices consist of an internal HPS (Hard Processing System) and a FPGA (Field Programmable Gate Array) portion. The Altera Cyclone V SX SoC HPS is a fully functional computer and contains a dual core ARM CPU with several built-in hardware blocks and device interfaces. It also has built-in ECC (Error Correction Coding) features.
The system offers the possibility to use DDR2, LPDDR2 or DDR3 RAM. The ARM CPU is connected to a large number of HPS hardware blocks. Bridges enable high speed data exchange between FPGA and HPS portions. Linux is used as default operation system (OS) for the SoC. All HPS blocks can be accessed from the installed OS application software. The HPS portion has to be configured at system startup. The SoC configuration data is part of the SEPP software image stored in the external memory. The image is based on the Altera reference Yocto Linux and U-Boot boot loader software.
Figure 9: Photo of the MitySOM-5CSX SoM (System on Module), image credit: ESA, Critical Link
The system level solution is to deploy four MitySOM-5CSX SoMs on a CubeSat-sized mother board. They would operate in cold redundancy along four 1 GB microSD cards for mass memory storage. These powerful units can output a significant amount of heat, especially if the FPGA fabric is highly clocked. The solution is to thermally couple the units to a surrounding mechanical aluminum structure which will allow the temperature to be passively managed. This solution also has the advantage that it will provide extra radiation shielding as these are non-radiation hard components. Another benefit, compared to other SoM platforms, is the availability of an ECC RAM system (in built SEU mitigation).
• SEPP (Satellite Experimenters Processing Platform)
• Four systems in cold redundancy. Altera Cyclone V SX SoC.
- Dual Core ARM Cortex-A9
- Running up to 800 MHz
- FPGA Fabric
• Memory: 1 GB DDR3 RAM (+ ECC!)
• External Mass Memory: 8 GB
• ~5W power consumption (Linux).
The baseline for the OPS-SAT optical camera is the BST IMS-100 instrument. This is a small space camera developed by Berlin Space Technologies based on the ST-200 star tracker. The ST-200 has been developed and tested for the Earth Video Camera project for the International Space Station. Sensor and MCU have been tested with proton irradiation of 130 MeV for a TID of 10 krad. It can provide still images as well as video, whereby image processing will be performed on the processor core (SEPP). For video download, the X-band transmitter will be used. The camera performance is provided in Table 1.
Table 1: IMS-100 camera performance
Micro S-band transceiver and X-band transmitter:
CNES and ESA are interested in a micro S-band TTC transceiver, and in a micro X-band transmitter, both designed for CubeSats. The goal is to provide considerable higher data rates for CubeSats and nanosatellites. This is especially important for experiments that want to record and transmit video to the ground. ESA decided to design the OPS-SAT triple CubeSat to test new space operation control concepts using EES (Earth Exploration Satellite) S- and X-bands (Ref. 21). 23) 24) 25)
The micro S-band TTC transceiver, the EWC31 of Syrlinks,takes some results from a multi-annual CNES R&D program related to low cost basebricks for TTC, in terms of flexible power amplifiers (with a 1 to 10 W output power in S-band, and a optimized efficiency at the different RF powers), high performance synthesizer and modem, and high integration of the TTC functions. The system architecture of this new product is generic. It was tested and fully validated on a first breadboard. All the key base-band functions are implemented in an FPGA. So this platform can be also easily adapted and provides the possibility to cover specific needs for new missions.
Table 2: Key S-band micro TTC transceiver parameters of the EWC31 device of Syrlinks
Some optimizations were made to provide a highly integrated solution with the following external dimensions (without diplexer) of: 96 x 90 x 24 mm3.
Figure 10: EWC31 S-band TT&C/ISL with the first diplexer configuration and integrated coupler (image credit: Syrlinks, CNES, ESA)
Another key subsystem is highly critical in this TTC function, the diplexer. A system analysis was made to balance the transceiver's performances (TX and RX) with the diplexer's size. Moreover, the specifics using one or two antennas on the CubeSat platform was addressed and optimized solutions are available for these two configurations (Figure 11).
The coherent transponder option is currently in development for the microsatellite S-band TT&C equipment of Syrlinks, thanks to activities of ESA and CNES, the functionalities enabling ground stations to perform coherent Doppler and/or ranging measurements could be implemented in EWC31 advanced TT&C S-band equipment.
Figure 11: EWC31 S-band TT&C/ISL with a second diplexer configuration and integrated coupler (image credit: Syrlinks, CNES, ESA)
Micro X-band transmitter: The CNES funded micro X-band transmitter from Syrlinks, referred to as EWC27 X-band HDR-TM transmitter, is capable of transmitting up to 50 Mbit/s. The objective is to produce synergies with many of the experiments, since the mission data download capability is greatly increased.
The on-board camera will support both still image and streaming video modes and many experiments intend to exploit this. Such camera experiments will require substantial downlink data rates for which the EWC27 X-band transmitter will be needed, particularly when bearing in mind real-time applications and the short contact times (typically 10 minutes for a ground station pass, four times a day). In fact the EWC27 has already flown as part of the ESA/GOMSpace mission GOMX-3 which was released from ISS on August 19th 2015. The unit has already been tested successfully at its maximum limit of 3 Mbit/s (due to ITU regulations).
The key specifications of this product are :
- Useful data rate from 2.8 up to 50 Mbit/s (up to 100 Mbit/s in constant bit rate)
- Configurable data rate (in flight up to 50 Mbit/s)
- Convolutive data coding: Puncturing rate ½, constraint length 7, polynomial generators 171 and 133
- Offset-QPSK modulation
- High-efficiency power amplifier
- Flexible RF output power between 27 – 33 dBm, with 1-dB step
- Power consumption: <7 W for 1 W RF output power; < 10 W for 2 W RF output power.
Figure 12: Photo of the EWC27 X-band HDR-TM transmitter (image credit: Syrlinks, CNES, ESA)
The micro X-band transmitter has a size of 96 x 90 x 24 mm3, its mass is < 400 g. The micro X-band transmitter can provide up to 50 Mbit/s using VBR (Variable Bit Rate), or up to 100 Mbit/s using CBR/CCM (Constant Bit Rate/Constant Coding Modulation). Syrlinks and CNES are currently studying a version of the EWC27 X-band HDR-TM compatible with some mod-cods of the CCSDS DVB-S2 telemetry standard.
This optical communications experiment supports an optical uplink for the first time on a nanosatellite. It provides a transmission rate of 16 kbit/s using a small optical receiver which fits into OPS-SAT. A photon counting module with a built-in multi-pixel photon counter is the heart of this system. An avalanche detector array of 400 photodiodes is used. A prototype of the receiver was tested on ground and it was demonstrated that transmissions with the specified data rate can be carried out. For the uplink, the Satellite Laser Ranging Station operated by TU Graz and the Space Research Institute of the Austrian Academy of Sciences at the Lustbühel Observatory shall be used.
Table 3: Optical link budget
The optical receiver will be connected to the SEEP so that uplink data can be received and processed by on-board experimental software. The laser ranging station at TU Graz will be used as the ground segment for the experiment. The laser ranging station at TU Graz will be used as the ground segment for the experiment. Optical retro-reflectors on the surfaces of the nanosatellite will provide the means to locate and track the spacecraft by laser tracking & ranging stations, assisted by an on-board GPS which is integrated in the core avionics.
An interesting aspect of the experiment is that this will be the first time a nanosatellite has been communicated with via an optical channel. Also the application will allow the secure uplink of one-time pad encryption keys. These can be used on the RF downlink making the broadcast extremely secure. Such an experiment has never been done before.
Figure 13: Front-end of the optical receiver (image credit: TU Graz)
Figure 14: Photo of the Lustbühel Observatory serving as the TU the TU Graz laser station (image credit: TU Graz)
SDR (Software Defined Radio) front-end:
This is a very small radio front-end consisting of a tuner, down-converter and ADC (Analog to Digital Converter). Complex signal samples are delivered to the SoMs where signal processing (e.g. demodulation and decoding) can be performed. This allows the monitoring and demodulation of radio signals for a wide frequency range.
Core of the SDR payload is an RF front-end consisting of a tuner (covering the frequency range from 300 MHz – 3.8 GHz), down-converter and A/D converter. This unit interfaces with the processing platform. Complex signal samples are delivered to the processor core, where signal processing (e.g. demodulation and decoding) can be performed. This facilitates the monitoring and demodulation of radio signals over a wide frequency range. Possible radio signal monitoring experiments include:
• ADS-B (Automatic Dependent Surveillance-Broadcast) for aircraft
• Interference level identification in different frequency bands and geographical areas.
RF front-end: The Myriad–RF 1 board was identified as a suitable candidate which is a multi-band, multi-standard RF module, based on the state-of-the art LMS6002D transceiver IC by Lime Microsystems.
The Myriad-RF has one RF broadband output, one RF broadband input with digital baseband interface, established via standard connector. The board also provides the user with pin headers for power supply, reference clock, analog I/Q input/output and SPI interface connections. It can be easily connected to baseband chipsets, FPGAs or to run in standalone mode. The module is shown in Figure 3.
The RF front-end interfaces with the Cyclone V processor core where demodulation and signal processing takes place. The RF module delivers complex I/Q samples. Control of the board (e.g. of synthesizer center frequencies etc.) is carried out by the processor core. Commands are sent via the I2C bus. A (shortened) deployable dipole antenna will be integrated in the top panel of the spacecraft perpendicular to the UHF antenna dipole. Interference is not possible as the UHF transmitter will be inactive during SDR experiments.
Table 4: Specification of the RF front-end
Figure 15: Photo of the Myriad RF board (image credit: ESA)
SDR experiments: An interesting experiment will be the measurement of interference level measurement from Space. This experiment was triggered by the experience of TU Graz during the BRITE astero-seismological nanosatellite mission. Since October 2013, spacecraft operating in the 430-440 MHz amateur radio band experience significant ground interference over large parts of Europe. Having a "spectrum analyzer" in the sky offers valuable opportunities of potentially localizing and identifying the nature of the interferer. Since (unfortunately) in many officially coordinated bands unidentified interferers impair other missions and systems, the OPS-SAT mission may help to assist organizations such as the ITU (International Telecommunications Union).
For this experiment algorithms are under development implementing classical spectrum analyzer functions. The center frequency, span, sweep time and resolution bandwidth can be selected via ground control.
It is also planned to implement synchronization algorithms on the processor core for automatic carrier tracking.
Another experiment which can be easily accommodated is an ADS-B receiver. Demodulation of the MSK signal and retrieval of the ADS-B datagrams will be carried out by the processor core. Since datagrams will certainly collide in high-density traffic regions, reconstruction of the datagrams can be done on board on the Cyclone V, or on ground.
Optical Retro-Reflectors on Panels for Attitude Determination:
This passive experiment will allow attitude monitoring and precise tracking using laser stations on the ground. There is an interest, especially among the space debris community to investigate the spacecraft dynamics of asymmetric objects such as OPS-SAT when uncontrolled. This can be done on this mission by simply disabling the actuation for periods when the mission is running and after mission termination using the laser reflections to determine attitude sate and evolution as it slowly descends.
Mission Operations Concept
A major improvement in design in the Phase AB1 has been the establishment of a robust but low cost mission operations concept. The idea is to exploit the robustness of the satellite to allow experimenters to load their own complete images to the processing core on a daily basis without extensive checking by ESA. Experimenters will also be able to update the corresponding ground system. This will allow them to change the end to end control chain from a CCSDS ground-space control interface to a TCP-IP/web-based interface during a single ten minute pass.
The concept relies on file exchange as the primary mode of changing configurations. On the ground, this will be done by allowing the experimenters connect realtime TM and TC streams at different access points in the ground control chain. To change the configuration on the spacecraft, the experimenters will provide bootable memory images for the SoM as input. These images will be tested on a flatsat at ESOC to check they meet the basic safety requirements and then uploaded to the spacecraft's memory, using a state of the art protocol called CFDP (CCSDS File Delivery Protocol). This same protocol will be used to download experimenter's data once it has been compressed into a single file on-board. CFDP is targeted to be flown first on EUCLID (scheduled for launch in 2017). Hence OPS-SAT would be the first flight of this protocol. In order to reduce the sizes of the image uploads the mission will provide pre-loaded standard images with exit points. Experimenters can load new images which contain an identifier , indicating from which preloaded image and exit point it should start from (Figure 16).
Figure 16: OPS-SAT file based experiment concept (image credit: ESA)
CCSDS MO (Mission Operations) Framework: 26)
A CCSDS Mission Operations On-Board Software Development Framework for Nanosatellites (NanoSat MO Framework) implementation is being developed by TU Graz in partnership with ESA (European Space Agency). The NanoSat MO Framework is based on the CCSDS Mission Operations concept and it is intended to be implemented and used by experiments on the future ESA OPS-SAT mission.
The SM&C (Spacecraft Monitoring & Control) Working Group of the CCSDS has defined a service-oriented architecture for space mission operations. The goal of the Working Group is to define a set of standardized, interoperable mission operation services, which allow rapid and efficient construction of cooperating space systems (Ground Segment, but also part of the Space Segment). For this purpose the Working Group has defined a layered service framework, which allows mission operation services to be specified in an implementation and communication agnostic manner. OPS-SAT will be the first in-orbit demonstration of a spacecraft with fully MO-based on-board software and ground implementations. 27) 28)
Figure 17: CCSDS MO Framework (image credit: CCSDS)
The main design characteristic of the NanoSat MO Framework software architecture is the introduction of independence between the application layer (app) and the underlying platform. In order to create this independence, a set of services shall be made available which can be used by the app both for interfacing with the peripherals and for communicating with ground. These services will be based on the CCSDS Mission Operations framework and can be divided in two main sets, the MO Standardized services (STD services) which are already defined by the CCSDS and the Peripheral services which will have to be defined. In the set of the STD services, it shall provide two sets of standardized MO services: COM (Common Object Model) services, M&C (Monitor and Control) services. In the set of the Peripheral services, it shall provide services such as: Camera service, ADCS service, GPS service, SDR (Software-defined Radio) service, and ODR (Optical Data Receiver Service).
Any app willing to use the NanoSat MO Framework shall be able to easily use the provided interface for both communicating with ground and to interact with the satellite peripherals. This abstraction, allows an easier and faster development of software untied from any particular satellite implementation. The initial design was motivated by the operability of OPS-SAT (reference implementation) therefore the design is focused on the available peripherals in OPS-SAT, but this does not prevent its usage in other nanosatellites. This could open the door for future software portability among different nanosatellites and also facilitate testing of new software.
The NanoSat MO Framework will be freely available for download and it will provide a "ready to be used" implementation of all the up-to-date MO Standardized services and the defined Peripheral services.
Figure 18: NanoSat MO Framework diagram (image credit: TU Graz, ESA)
The separation of the services from the specific experiment code not only allows an easier embedding of standard MO services with the different experiments but also avoids the need to keep track of the specific MO service requirements by the experimenter. Moreover, the experimenter will be able to integrate these services in their experiment even if these services are in reviewing phase (at the moment, the M&C and Common). To get the latest version update, the experimenter will only have to do a "pull request" from the server.
Three java interfaces were defined to link the app to the STD services. These interfaces are for: Action invocations, Alert notifications, and Parameter status.
For the Peripheral services, the app can connect directly using the exposed MO service interfaces of those services. Between the Peripheral services and the satellite peripherals, java interfaces shall be defined to allow the implementation on a specific platform to allow re-usage of code. OPS-SAT peripherals will be used as a reference implementation.
Default parameters and actions shall be defined between the STD services and the Peripheral services to allow the interaction with the peripherals from the STD services. If an OPS-SAT experimenter intends to use the NanoSat MO Framework, its experiment will be in the application layer (app) of the diagram in Figure 18. The process of integrating the experiment was designed to be easy and simple.
For the COM services, the experimenter will be able select and use the services directly without any need for further modifications in the code.
For the M&C services, the experimenter will need to:
1) Select the desired services to be used from the NanoSat MO Framework
2) Implement the java interfaces for actions, alerts and parameters
3) Add default definition objects in the Archive service (if desired).
For the Peripheral services, the experiment can directly connect and exchange data with the peripherals or optionally use the STD services with the default parameters and actions.
Figure 19: NanoSat MO Framework diagram for OPS-SAT (image credit: TU Graz, ESA)
The green arrows of Figure 19 show the necessary modifications to be made by the experimenter: in the left it shall be necessary to implement the STD services interfaces to the particular experiment; in the right is presented the connection f the experiment to the Peripheral services which allows sending and receiving data from the peripherals on-board of OPS-SAT (which can also be optionally used through the default parameters and actions defined in the STD services).
A development environment is intended to be provided to all OPS-SAT experimenters in order to facilitate the development of experiments. In this development environment, experiment demos will show how to use and integrate the NanoSat MO Framework correctly with an experiment. A tutorial guide is also intended to be provided.
TU Graz in partnership with the European Space Agency and subcontractors from Austria, Denmark, Austria, Germany and Poland is currently developing the NanoSat MO Framework which can be used by experiments on-board of OPS-SAT.
Experimenters shall be able to use all the services or select, à la carte, from the NanoSat MO Framework the services which they desire to use for their experiments without having to write additional code related with the specific requirements from the MO standards. This almost effortless procedure will sharply decrease the difficulty of developing an experiment using MO services and, simultaneously, will increase the acceptance of MO services from the space community.
One special aspect of OPS-SAT is that the project allows the experimenters to communicate directly with their experiment running on-board, even in real-time. From the experimental processor they can operate the camera, GPS unit, fine ADCS (including reaction wheels, star tracker magnetorquers, magnetometers, sun sensors, gyros) and they can also process data arriving from the software defined radio, GPS unit and core avionics. The project offers six different possibilities for the experimenters to access the OPS-SAT network and then communicate with the satellite or the testing facilities (Ref. 5):
1) They can exchange files via SFTP (Secure File Transfer Protocol) with a data relay server at ESOC which serves as the interface between the OPS-SAT LAN and the Internet. Files which contain the down-loaded telemetry of the experiments will be stored there. In the other direction they can load their own software images which will then be uplinked to the experimental processor by the flight control team.
2) They can use the Mission Operations Services standards to monitor and control experiments running on the processing platform of the spacecraft. The raw MO messages are transferred between the user and the data relay server using TCP/IP over the Internet. These are then forwarded to the spacecraft and back automatically by the OPS-SAT ground segment.
3) Experimenters that don't want to write their own MO-based M&C software can use Web-EUD for that purpose. Web-EUD is accessible through a web browser and connects to the experiment through MO. It provides the user with tools to monitor their experiment software and they also can send basic commands to their software.
4) They can use the Space Packet Protocol to monitor and control experiments running on the processing platform of the spacecraft, also via TCP/IP over the Internet. These are then forwarded to the spacecraft and back automatically by the OPS-SAT ground segment.
5) For experimenters wanting to communicate with their experiments over a non CCSDS protocol then the OPS-SAT ground segment will offer a direct connection at ground station baseband level i.e. just before modulation.
6) For experimenters that use CCSDS standards and are interested in real-time data but do not want to process it themselves we offer a web based monitoring solution using an ESOC developed solution called WebMUST. The experimenters can access advanced display, store and retrieval functions with a web browser.
Figure 20: Experimenter access to test facilities (image credit: ESA)
Legend to Figure 20: SCOS-2000 (Spacecraft Control & Operation System-2000) is the generic mission control system software of ESA.
Figure 21: OPS-SAT Ground Segment showing experimenter access (image credit: ESA)
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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 (firstname.lastname@example.org).