Low Cost Control and Simulation Environment for the Flying Laptop, a University Microsatellite

Transcription

1 SpaceOps 200 Conference<br><b><i>Delivering on the Dream</b></i><br><i>Hosted by NASA Mars April 200, Huntsville, Alabama AIAA Low Cost Control and Simulation Environment for the Flying Laptop, a University Microsatellite Michael Fritz and Hans-Peter Roeser2 Institute of Space Systems, University of Stuttgart, 70569, Germany Jens Eickhoff3 EADS Astrium, Friedrichshafen, 88039, Germany Simon Reid4 Rhea System S.A., Louvain-La-Neuve, 348, Belgium The Institute of Space Systems at the University of Stuttgart is preparing the Flying Laptop, a microsatellite for technology evaluation and Earth observation. The university environment mandates low cost, which rules out engineering models. Thus a model-based development approach is used to verify concepts during the development phase and to support on-board software tests. The applied simulation infrastructure should use professional software to train students on an appropriate environment. However, the software has also to be intuitive and easy to learn in order that students can be quickly productive in the limited time that they have available during their theses. The solution was to combine established industry toolsets, supplied at low cost. The system simulation infrastructure Model-based Development and Verification Environment (MDVE) was developed by Astrium as real time simulator and is commanded via an ESA SCOS-2000 mission control system. The spacecraft can be visualized by connecting the real-time 3D visualization software Celestia to the simulator. Efficient commanding is ensured by the procedure editor and execution engine Manufacturing and Operations Information System (MOIS) which replaces the operator and enables automated tests. U I. Introduction NIVERSITY satellite projects are usually equipped with very low budgets. They have educational purposes, students should gain experience in spacecraft development. Thus there are hardly any customers who fund these projects. Industrial projects may be better equipped but in the last decade their budgets decreased. So both, university and industry have to build their satellites at low costs. As engineering models of satellites come at high prices, their abandonment is necessary. In order to keep the risk of mission failure nevertheless at a low level, the Model-Based Development and Verification Environment (MDVE) has been established. By the use of a simulation infrastructure real hardware is replaced by software models enabling operational test scenarios and on-board software testing. This technique has initially been realized by EADS Astrium and been used for the development of several satellites. The Institute of Space Systems (IRS) at the University of Stuttgart also uses this approach for the development of the microsatellite Flying Laptop depicted in Figure.2 Institute of Space Systems, Pfaffenwaldring 3, Stuttgart, Germany, fritz@irs.uni-stuttgart.de Institute Director, Institute of Space Systems 3 EADS Astrium, Friedrichshafen, 88039, Germany 4 Chief Engineer, Rhea System S.A, s.reid@rheagroup.com 2 Copyright 200 by Institute of Space Systems, University of Stuttgart. Published by the, Inc., with permission.

2 Figure. The microsatellite Flying Laptop, IRS The Flying Laptop has a mass of about 20 kg and a size of 60 x 70 x 80 cm 3. The primary mission objective is to demonstrate and qualify new small-satellite technologies, although along with this multiple scientific experiments are planned. High-speed Ka-band communication, a high accurate attitude control system, a new kind of release mechanism and the space-use of components like state-of-the-art fiber optic gyroscopes and solar cells are the technologies to be demonstrated. Precipitation measurement, search for Near Earth Objects, multi-spectral and multi-angular Earth observation are the plans on the scientific side. The Flying Laptop is the first University satellite in Europe completely commanded by industry standards. There is a close cooperation with many companies in order to realize this intention. Test infrastructure like the simulation infrastructure described below has been built up. Figure 2 Simulation infrastructure at the Institute of Space Systems, IRS A university institute has neither the manpower nor the financial capabilities to build up its own model-based simulation environment. Students should furthermore be trained on industrial tools to leave university well prepared for their jobs. Thus the Institute of Space Systems cooperates with EADS Astrium and uses simulation infrastructure For example the ESA Packet Utilization Standard 2

3 developed by them. As each spacecraft has its own characteristics, all component models of the microsatellite Flying Laptop used in the MDVE have been created at the institute.2 The complete setup consists of five elements, a procedure editor and execution engine, a mission control system, a real-time simulator and a 3D visualization engine. The corresponding screens can be seen upon Figure 2. The last element is hidden by the acting operator of the simulation setup in this figure. It is a handful of FPGA development boards which can be connected to this environment in order to test on-board control algorithms with the use of MDVE, see also Figure 4 further below. This setup is in extensive use now. The next enhancement will be the connection of the real on-board computer in order to test the on-board software later in the development process.3-5 Students can test on-board algorithms developed by them with this infrastructure. The real-time simulator itself is a powerful tool, but has some restrictions. Neither comfortable live monitoring and control nor easy test procedure handling is available. However, students developing control algorithms are in need of such tools. They do not have the time to get deeply involved in the real-time simulator during their theses which typically last six months. Therefore further industrial tools have been integrated into the environment. One is the ESA mission control system SCOS-2000 enabling easy control and comfortable live monitoring. However, students have to act as an operator to make use of this system. In order to enable automated tests with SCOS-2000 and comfortable test procedure handling, the procedure editor and execution engine Manufacturing and Operations Information System (MOIS) has been integrated. This software tool has been sponsored by Rhea, the company which developed MOIS. Furthermore a 3D live visualization for simulation results was developed. This upgrade is based on the open-source software Celestia and makes it easier to evaluate simulation runs which is also an advantage for students.3,5,6 II. Control and simulation infrastructure Heart of the environment is the real-time simulator developed by EADS Astrium. It has to run in real-time in order to allow hardware-in-the-loop setups. The simulator consists of two big parts. The first is the simulator core which comprises simulator kernel, several propagators and mathematical functions. This part has completely been delivered by EADS Astrium. The second one comprises the applied component models and their data and power links. That part has been developed at the institute using UML models. By the use of a script which generates code from UML the raw C++ code can easily be created and has to be filled with algorithms representing component behaviour. This process is outlined in Figure 3. Figure 3 Code Generation from a UML diagram All Flying Laptop components have been modeled up to now. The models have been verified both by unit tests checking the internal correctness of single component models and by comparing simulation results with other simulation environments like Simulink and ESATAN. Several FPGA development boards have been connected to the simulator up to now. They can be connected both via serial connection using RS-422 and via ethernet connection using sockets. A driver has been written to connect the boards with the simulator models. Figure 4 shows one of the boards which have been connected to MDVE. Attitude control algorithms running on an FPGA development board have been verified with this setup.4 3

4 The simulator can be controlled with a command line interface. Certain commands like simulator and propagator start are used very often. Thus a command line is very inefficient. Though the simulator provides the visualization of results in graph, it is only a very basic concept. For these reasons the ESA mission control system SCOS-2000 has been integrated targeting on these issues. Another advantage is to command the development boards from SCOS2000. A proxy has been created enabling the communication between SCOS-2000 and the simulator as well as the development boards. SCOS-2000 can be configured to projects needs by the Mission Information Base (MIB). For example telemetry and telecommand packets as well as graphical and alphanumerical displays can be configured here. Figure 6 shows the SCOS-2000 Telemetry Desktop visualizing the rotational rates around the body axes. The tested algorithm is the detumbling mode which shall decrease the rotational rates.6,7 Figure 4. FPGA development board IRS Figure 5. SCOS-2000 Telemetry Desktop 4

5 This setup seems to be very comfortable. However, an operator is needed to react to telemetry events which is essential for many test cases. Thus a software is needed enabling automated tests. There are several of such software tools available on the market. They provide different stages of comfort, from easy script handling up to graphical procedure handling and execution. A very comfortable tool is MOIS which comprises the following functionalities:8 Data can be imported from the SCOS-2000 MIB. Procedures can be filled by choosing the imported data from a dropdown menu. This does not only make the creation of procedures very comfortable, but also prevents typing errors and guarantees data consistency between the mission control system and the procedure editor and execution engine. The logic of a procedure can be created and edited in graphical flowcharts. The text-based logic is generated from the corresponding graphic. This simplifies procedure generation and enables their clear illustration. Procedures can be executed using another graphical illustration called MOIS Validator. This enables tracking the current state of a procedure run. An example is shown in Figure 6. MOIS furthermore provides the possibility to import and export scripts from and into any utilized operations language, for example Pluto and Tcl. Procedures can be exchanged with organizations which use a more basic engine. The intuitive use is appropriate for students who now can quickly create test procedures. Rhea kindly sponsored the Institute of Space Systems with an academic license for MOIS.3 Figure 6. MOIS Validator Rhea A complete command chain has been built up, enabling automated algorithm tests and soon on-board software tests, too. The other satellites which will be developed after the Flying Laptop can make use of this infrastructure which is outlined with its internal connections in Figure 7. Both students and the industry profit from this setup. Students are trained on industrial tools which increases their qualification. This is an advantage for the industry, too.9 5

6 Figure 7. Outline of simulation infrastructure IRS III. Conclusion The established simulation infrastructure opens up the following possibilities: Operational scenarios for the Flying Laptop and the subsequent missions can be tested and evaluated in terms of complete satellite behaviour, including power budget. On-board control algorithms and on-board software can be tested before real component hardware is available. This is necessary when the number of engineering models is significantly reduced. Otherwise the risk of mission failure would increase and the development time would be extended. This concept considerably reduces the development costs. By the use of MOIS, students can easily create and execute test procedures without getting deeply involved in simulator handling. So they can test on-board control algorithms and on-board software written by them. The exchange of procedures with organizations using another procedure execution engine is possible due to the import and export function provided by MOIS. Students are trained on industrial tools and finish their studies well educated. IV.Outlook The infrastructure has been built up and can now be used for extensive tests, the following ones serving as examples: Improved attitude control algorithms will be tested upon this environment. The results can be compared to the ones delivered by Simulink. The algorithm changes can then be evaluated. Failure detection, isolation and recovery functions will be extensively tested in the next months. The next enhancement of the infrastructure will be the integration of the simulator to a real-time linux system and the installation and configuration of an interface card. These steps prepare the integration of the real on-board computer. It will be also tested using the established environment. References Eickhoff, J., Simulating Spacecraft Systems, st ed., Springer Verlag, Heidelberg, Germany, Brandt, A., Kossev, I., Falke, A., Eickhoff, J., Roeser, H.-P., Preliminary System Simulation Environment of the University Microsatellite Flying Laptop, 6th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April Fritz, M., Simulated operations of the Microsatellite Flying Laptop with a Mission Operation System, IRS-08-S37, Institute 6

7 of Space Systems, Stuttgart, Germany, October Ziemke, C., Model-based development and verification of an on-board control algorithm architecture for the Microsatellite Flying Laptop, IRS-08-S6, Institute of Space Systems, Stuttgart, Germany, May Witt, R., Selection and configuration of a 3D tool for visualization purposes and realization of a real-time connection to the simulator, IRS-09-S20, Institute of Space Systems, Stuttgart, Germany, June Brandt, A., Development of Functional Models for Communication and Thermal Hardware and a Thermal Model for the Flying Laptop Microsatellite Simulation, IRS-07-S02, Institute of Space Systems, Stuttgart, Germany, February SCOS-2000 Team, SCOS-2000 Database Import ICD, European Space Agency, Rhea System, MOIS help, Louvain-La-Neuve, Belgium, March Fritz, M., Falke, A., Kuwahara, T., Roeser, H.-P., Pearson, S., Witts, A., Eickhoff, J., A commercial procedure execution engine completing the command chain of a university satellite simulation infrastructure, Academy Transactions Note, Acta Astronautica 66 (2009) , 200 7