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Sun sensors are commonly used attitude determination equipment which measure a spacecraft’s attitude relative to the sun. Multiple types of low-cost sun sensors were developed for the SOURCE and EIVE CubeSats. The SOURCE sun sensors consist of single photodiodes which are placed in a one-sensor-per-face as well as a pyramid arrangement. EIVE employs digital vector sun sensors based on quad-pin photodiodes. The SOURCE sun sensors in the one-sensor-per-face arrangement archive an accuracy of

The scientific mission objectives of the Stuttgart Operated University Research CubeSat for Evaluation and Education are meteor observation, measurement of the lower Earth's atmosphere during re-entry as well as technology demonstrations. The meteor observation is done by pointing a camera towards Earth and continuously taking images during Eclipse. Since it is not possible to downlink all images, an on-board detection algorithm is necessary and mission critical. Therefore, this algorithm needs to be tested thoroughly. Realistic test data showing meteors from orbit is needed to properly develop and test the algorithm. Existing videos, provided by the Planetary Exploration Research Center, captured from the ISS are used as a baseline but are not sufficient to test the algorithm. The videos do not have the diversity of meteors needed and the meteor properties are not settable which makes it difficult to test the detection algorithm in as many scenarios as possible. Therefore, an artificial meteor program was developed to simulate meteors with given properties as perceived from a meteor observation system in a low Earth orbit. Here, we present the details of the artificial meteor program, its working principle and how we tested an algorithm for meteor detection. The user can choose between different background videos, the existing ISS videos from PERC or the self-generated videos. Each different background is used to test a different aspect of the meteor detection algorithm. The ISS videos from PERC provide more diverse backgrounds than the self-generated videos with e.g., clouds and lightning. For these self-generated videos, a program is developed to take image sections of NASA’s Black Marble and putting them frame by frame together into a video. These videos are more suitable for simulating satellite rotation and camera properties. Independent of the background video, settable meteor properties contain important characteristics of a meteor like the light curve, brightness, speed, direction and shape. Additionally, the user can choose the meteor position in the video frame, in which frame it appears and which distance it covers. Furthermore, distortion settings can be applied which contain airplanes with adjustable parameters and scalable noise. Only a properly working meteor detection algorithm leads to a success of a mission critical part of the SOURCE CubeSat. Therefore, the development of this artificial meteor generation program is crucial. Furthermore, this technology demonstration of developing and especially testing a meteor detection algorithm will enable future space-based missions for meteor observations

SOURCE (Stuttgart Operated University CubeSat for Evaluation and Education) is a 3U+ re-search CubeSat that is being developed by students at the University of Stuttgart in coopera-tion with the Institute for Space Systems and the Small Satellite Student Society KSat e.V.. The objectives include technology demonstrations, atmospheric research and the investigation of satellite demise while also serving as an educational program. SOURCE was selected by ESA's "Fly your Satellite" program and is currently in Phase D. The electrical power supply system combines commercial off-the-shelf parts with self-devel-oped units to meet the requirements of the payloads. The solar array configuration and Power Conditioning and Distribution Unit (PCDU) are self-developed, while the battery is a commer-cial product. A total of 56 solar cells provides up to 32W under ideal conditions, which can be stored in a 75Wh space-qualified lithium-ion battery. To maximise the power output of the solar cells, maximum power point tracking is performed by the PCDU. This is controlled by a radiation hardened microcontroller. The PCDU provides regulated 3.3V, 5V and unregulated battery voltage to the subsystems with 32 switchable outputs, 27 of which are latch-up current protected. The microcontroller controls these individual output channels and the switching between the various CubeSat modes as commanded by the on-board computer. Additionally, every output channel power consumption is monitored for overcurrents. The PCDU functions as a watchdog by checking the health of the on-board computer, rebooting it in case of a failure. High priority commands can be sent directly to the PCDU from the ground via the communication system, bypassing the on-board computer. These can reset either the communication subsystem, the on-board computer or the entire satellite. Four hybrid inhibits, using a combination of mechanical switches and FETs are integrated in the PCDU, replacing the usual fully mechanical design. Three are used to deactivate the satellite in the deployer configuration and the fourth is a remove-before-flight inhibit. An engineering model was manufactured during phase C and is being tested functionally, en-vironmentally and for performance. This paper presents the detailed design of the PCDU, the acquired test results and outlines issues encountered during the tests

Downlink measurement campaigns from the optical downlink terminal OSIRISv1 onboard the LEO satellite Flying Laptop were carried out with the French Observatoire de la Côte d’Azur and with two Optical Ground Stations of the German Aerospace Center. On/off keyed data at 39 Mb/s were modulated on the laser signal, and according telecom reception was performed by the ground stations. The pointing of the laser terminal was achieved by open-loop body pointing of the satellite orientation, with its star sensor as attitude control signal. We report here on the measurements and investigations of the downlink signal and the data transmission.

A high-speed data downlink system provides many challenges for a CubeSat design. Two major aspect are an adequate power management as well as the thermal implications of the dissipated power. The goal of the 6U CubeSat EIVE is to prove the feasibility of an E-band link at 71-76 GHz and explore the influence of different atmospheric conditions on the link quality. The requirements of the E-band transmitter in terms of mass, volume, power and pointing accuracy outline the specific constraints imposed on the design of the satellite bus. The major design drivers of the system are the peak power demand of 60 W for the payload itself and the required pointing accuracy of less than 1◦. To cope with these demands, general design considerations, the choice of the orbit and the operation of the satellite are discussed. A special focus is the power generation and consumptions by means of a dynamic attitude and power simulation. The thermal simulation is verified by building a detailed structural and thermal replica of the satellite to investigate the heat dissipation. An overview of the current EIVE CubeSat platform design concludes this paper.

The term operating system refers to a software component, which traditionally controls the resources and the processes of a computer, and by providing the appropriate interfaces allows for the implementation of custom user applications. This is a common definition, working very well for ordinary computer systems. Yet, what if the operating system and a corresponding application are physically separated, because the computer is within a satellite in space, while the user program is executed on ground? Then, capabilities must be created to connect both, which is of course complicated by the natural boundaries in satellite communication, for example the limited satellite contact times. Over the past decades, several systems have been developed, which are capable of managing satellite resources and the mission schedule from ground. Although this covers quite well the purpose of an operating system, other terms have evolved in this domain: operations system, ground system, mission control system, ground data handling, etc. The problem though is, those systems primarily focus on the exchange of data and satellite TM/TC, rather than the actual control process. This creates an artificial barrier between ground and space, which harms the development capabilities for ground based satellite applications. This paper introduces a novel approach for an operations system architecture, which can be considered as a ground extension of the satellite’s operating system. This approach shall not break with the existing conventions and definitions, especially in terms of operating systems, but shall introduce a new view on satellite operations. In a layered, functional software architecture, the operating system is the lowest layer between the hardware and the application. Through the definition of the appropriate interfaces in the ground system, a software architecture can be created that actively supports outsourcing parts of the satellite control process to ground. The proposed approach has great potential for various applications in satellite operations. It supports the implementation of automatic system control processes, the implementation of custom payload applications, and the integration of respective activities into the satellite schedule. As applications and operators interact with a verified schedule, and operations is thus no longer limited to low-level commanding, the approach further reduces the risk of the mission being jeopardized by human mistake.

The Institute of Space Systems (IRS) of the University of Stuttgart and the TU Berlin are planning a mission to observe meteors and dust particles using a formation of two small satellites. In this paper, we analyse the formation and satellite parameters to optimize the scientific output of the meteor observation. The stereoscopic observation of meteors allows calculating the corresponding meteor trajectory. The potential output of a meteor observation strongly depends on the configuration of the satellite formation (orbit, satellite distance) and the satellite bus parameters (knowledge of satellite position and attitude). Therefore, a simulation, based on the trajectory algorithm of the Meteor Orbit and Trajectory Determination Software (MOTS), is conducted, in order to calculate the accuracy of the meteor trajectory depending on those parameters. Furthermore, different meteor properties are taken into account to evaluate the influence on the accuracy of the calculated trajectory. According to our simulations, the satellite attitude knowledge has a huge influence on the trajectory accuracy, while the position knowledge is less relevant. Furthermore, the simulation allows calculating the ideal satellite distance with a minimal trajectory error for a specific orbit. The trajectory error is ~200 m, when typical errors on satellite position and attitude knowledge (7”) are used.

The small satellite Flying Laptop, launched in July 2017, was developed and built by graduate and undergraduate students at the Institute of Space Systems of the University of Stuttgart with support by space industry and research institutions. The mission goals are technology demonstration, earth observation, and serving as an educational satellite. At a mass of 110 kg, it features three-axis stabilized attitude control and several payloads, including an AIS receiver, a multi spectral camera system, a wide angle camera, and an optical communication terminal. The pointing requirement for the optical communication is an accuracy of less than 150 arcseconds during a target overflight. To fulfill this requirement, several measures are needed. A major part of them is the characterization of the attitude control system (ACS). Since there is no optical receiver onboard, it is not possible to perform closed loop tracking of the satellite attitude. Therefore, the absolute performance and the characteristic noise levels of the attitude control system, can only be determined with other payloads. In this case the multi-spectral camera system was used, providing a ground resolution of 25 m. To use the images from the satellite to improve the ACS, three steps have to be taken. As a first action, the images have to be georeferenced to know the position of each pixel in the WGS84 coordinate system. With this information, the deviation of the image center from the desired target is measured. This second step includes the calculation of the deviation matrix. To avoid a corruption of the attitude control of the satellite, the matrix is checked for unrealistic values in a third and final step. These three actions can be repeated as needed without human interaction. By updating the ACS model onboard the satellite, the results of the image processing are used to correct the off-pointing. This deviation is time invariant and is caused by an insufficient alignment of the satellite axes and the cameras on ground. In contrast to that, characterizing noise as a time variant factor, the ACS is tested over a long period of time. This is achieved by analyzing images from one, as well as from multiple target overflights. This conquers the issue of a very low image rate while observing high frequency attitude changes. Using this mechanism, the proposed process can be used to continuously monitor the pointing quality. As a first approach the described processing is done manually by comparing the target position on Earth with the center of the taken image. The method successfully showed an improvement of the pointing in the pictures, paving the way for their automation. This paper gives an overview of the needed image processing and tools to automatically use cameras on board the satellite to validate and improve the ACS periodically. First results of the long term characteristics and pointing improvements are shown.

A first step towards realization, a small satellite study for OSAS (Oxygen Spectrometer for Atmospheric Science) has been performed based on Concurrent Engineering methods.

Precise attitude control is a key factor of many payloads with high ground resolutions, small fields of view or narrow beams such as an optical data downlink. The small satellite Flying Laptop (FLP), launched in July 2017, was developed by graduate and undergraduate students at the Institute of Space Systems of the University of Stuttgart with support by the space industry and research institutions. The satellite is three-axis stabilized with reaction wheels as main actuators. FLP is equipped with the OSIRIS optical data downlink which was built by the German Aerospace Center (DLR). As this instrument is body mounted on an optical bench, the attitude determination and control system (ACS) is required to point the whole satellite in the direction of the ground station with a high pointing accuracy of 150 arcseconds. At the time of launch the ACS did not reach this precision. This paper describes how the attitude determination and control were improved to achieve the required performance. The improvements can be divided into two parts. The first part includes the enhancement of on-board sensor processing and attitude control. In the second part, in-orbit data were utilized to increase the accuracy of parameters which are used to control the spacecraft. The first part includes the addition of a Kalman filter, an improved position propagation, and the introduction of adaptive gains to the on-board ACS. The FLP simulation test bed was used to verify the changes. The test bed was also used to find adequate initial values for the Kalman filter and to find inaccuracies in the sensor processing. In the second part, the adaptive gains and the Kalman initial values were validated in-orbit after the upload of the new sensor processing. Moreover, the on-board component orientation settings were corrected for the star trackers, the multi-spectral camera system, and the OSIRIS instrument on FLP. As a result, the satellite fulfills the pointing requirement of less than 150 arcsecond deviation from the target attitude for a sufficient period of time during a pass over the target. Successful links with the optical data downlink were demonstrated with the DLR ground station in Oberpfaffenhofen.

Since mid-2014, the fully integrated small satellite Flying Laptop is in the system testing phase at the Institute of Space Systems located at the University of Stuttgart in Germany. The satellite’s mass is 120 kg and it is designed to conduct multi-spectral earth observation as well as to demonstrate new technologies. A part of the acceptance tests prior to launch is the environmental testing in order to verify spacecraft functionality under environmental conditions during launch and in orbit. The following three main environmental tests were successfully conducted: Tests of Electromagnetic Compatibility (EMC): The EMC test of the Flying Laptop covered the verification of electromagnetic compatibility as well as interference of the various electromagnetic signals generated on-board. Vibration test: For the structural acceptance of the spacecraft sine and random vibration tests were performed for each satellite axis. Thermal Balance / Thermal Vacuum test: The thermal vacuum test was conducted to verify the functionality of the entire satellite at hot and cold temperatures. A similar test setup was used to perform the thermal balance test that allowed the validation of the thermal model. The environmental test campaign was completed successfully in December 2014. All system requirements were met according to the defined specifications.