Papers by Hannu Leppinen
In this paper we will describe briefly Finnish Aalto-1 CubeSat mission and summarize the mission ... more In this paper we will describe briefly Finnish Aalto-1 CubeSat mission and summarize the mission results achieved during first five months of the mission. The Aalto-1 is the first nanosatellite built in Finland and launched by Finnish consortium. The satellite project started in 2010 as a Aalto University student project, supported by consortium of Universities and institutes. The satellite main mission is education and technology demonstration, as most of the subsystems and payloads are purpose made for this satellite and operated in space for the first time. Main payload of the satellite is a miniature spectral imager AaSI (Aalto-1 Spectral Imager) designed for Earth Observation by VTT Technical Research Centre of Finland. The instrument is based on a Piezo-actuated tunable Fabry-Perot interferometer and is the first such instrument for EO in space. The secondary payload is a radiation monitor, RADMON, which can detect and identify incident particles and their corresponding total energy at 15-second time resolution. The payload is developed by the University of Turku and the University of Helsinki. [4] The third payload is an experimental e-sail technology based deorbiting device, called Plasma Brake, developed and constructed by Finnish Meteorological Institute. Additionally, the satellite has three axis attitude system, on board computer system, several sensor systems and two purpose built-communication systems, tested first time in space. The satellite was finalized and tested for launch inspring 2016 and it was launched to space on 23.6.2017 by Indian PSLV rocket. By now, the satellite has been in space for five months and has already delivered substantial amount of data about its subsystems and achieving many mission goals. The spectral imager AaSI is calibrated in orbit and it has delivered several test images. Also the RADMON instrument has been calibrated in orbit and it has operated over several weeks, providing electron and proton spectrum measurements for several solar storms in autumn 2017. The deorbiting experiment has not been initiated yet. The mission team works currently with attitude stabilization and data collection with two main instruments.
In this paper, we will describe the Finnish Aalto-1 CubeSat satellite mission, the satellite stat... more In this paper, we will describe the Finnish Aalto-1 CubeSat satellite mission, the satellite status and the first in-orbit observations. The Aalto-1 satellite is designed by students is built by a consortium of universities and institutes. It is the first Finnish nanosatellite project and also the first satellite registered to Finland. The mission has primary goals in education, technology demonstration and science. The mission has initiated several New Space companies and initiatives in Finland and brought the nation to the circle of space faring nations. The satellite platform was mainly developed by Aalto University students while the payloads were developed by consortium partners. The satellite was successfully launched in June 2017. By the end of July, all instruments on-board of the satellite were commissioned and first scientific measurements were performed with spectral camera and radiation measurement instrument. Also, data was collected about all other sensors and subsystems, such as solar cells with conductive cover, novel sun sensors and redundant Linux-based onboard computer.
In this paper we present a hardware-in-loop (HIL) test setup and usage designed for high performa... more In this paper we present a hardware-in-loop (HIL) test setup and usage designed for high performance Attitude Determination and Control System (ADCS) end-to end testing and validation for multi-payload Cubesat missions. The Aalto-1 mission requires accurate pointing of a miniature radiation monitor and a hyperspectral imager, and a 200 °/s spin-stabilized operation mode for an electric solar wind sail based plasma brake experiment. The satellite's ADCS, iADCS-100 provided by Berlin Space Technologies (BST), contains sensors and actuators typically only seen in larger satellites: star tracker, gyroscopes, a magnetometer, magnetorquers and reaction wheels. In addition, six digital sun sensors and a GPS receiver are integrated to the system. To verify correct operation of the ADCS before launch, and to assure compatibility with the satellite's scientific mission, a thorough testing campaign is currently being performed. BST conducts environmental qualification, functional testing and control algorithm testing, whereas end-to-end mission tests and acceptance tests are performed in Aalto University. The mission tests are carried out using a HIL test setup running an attitude and orbit dynamics simulator in Simulink xPC Target. The simulation provides real-time sensor data to the ADCS through an I 2 C interface according to simulated sensor and actuator models, mission operations and disturbances. By connecting the HIL setup to the ADCS while integrated to the rest of the satellite subsystems, even the most complex mission operations can be tested and validated end-to-end in a closely flight representative configuration.
Acta Astronautica, 2016
This paper proposes a method for deploying a nanosatellite constellation to several orbital plane... more This paper proposes a method for deploying a nanosatellite constellation to several orbital planes from a single launch vehicle. The method is based on commercially available deorbit devices that are used to lower the initial orbit, and that are discarded after the correct altitude has been reached. Nodal precession of the right ascension of the ascending node at different altitudes results in spreading the orbital planes of the satellites. Maneuvering all satellites to a similar final altitude freezes the relative separation of the orbital planes. Calculations and simulations of the method are presented, and the results indicate that with a launch of 6 satellites to an initial 800 km sun-synchronous orbit, orbital plane separation of approximately 30 degrees between each satellite can be achieved within 5 years, with each satellite in its own final 600 km orbital plane. Such a constellation could provide continuous global coverage, while requiring only one launch vehicle. Due to the timescales required by the method, it is best suited for nanosatellite missions designed for long lifetimes. Possible applications of such constellations are also discussed.
OpenSimKit is a free and open source system simulation software distributed under the GNU Public ... more OpenSimKit is a free and open source system simulation software distributed under the GNU Public License. It provides the functionality to simulate systems based on their numerical properties, fully reflecting the system topology. OpenSimKit is scalable in the time as well as in the complexity domain and features a clean cut interface between simulator kernel and models. The scalability in these domains makes OpenSimKit a tool suitable for crossphase systems engineering. This means that OpenSimKit can be used for mission design and feasibility studies as well as for hardware in the loop system integration tests, on-board software verification campaigns or operations training. By providing these capabilities in a single tool it is possible to incrementally refine the system simulation as the system is developed. The OpenSimKit simulator kernel distinguishes between physical transport from model to model through ports and the so called provider-subscriber architecture. An example of the connection through ports is the exchange of material transport such as fluids or electrical signal lines. An example for the latter are forces, thermal radiation or the location and speed of an object. OpenSimKit additionally provides connections to the visualization tool Celestia and the CPU emulator QEMU. Celestia offers real-time visualization of the space-craft attitude while QEMU offers integration of the on-board computer in the simulation and allows early software development and testing. Finally a new graphical user interface called "OpenSatDK" has been developed in order to provide an integrated systems engineering framework for space-craft development. The requirements engineering tool ProR has been integrated into the Eclipse RCP platform. In this paper it is described how the aforementioned tools are applied to a satellite mission. First requirements are defined and basic simulations of the system budgets and contact times are performed. The mission which is used for this purpose is a demonstration mission, because the purpose of this paper is only to demonstrate how to use the "OpenSatDK" in the systems engineering process.
Proceedings of the Small Satellites Systems and Services - The 4S Symposium 2014, May 27, 2014
After a decade of experimental nanosatellite projects, the past few years have seen a growing tre... more After a decade of experimental nanosatellite projects, the past few years have seen a growing trend of utilizing nanosatellites in more complex scientific and commercial missions. More complex nanosatellite missions typically involve longer target lifetimes, sophisticated instruments and complex ground operations. These missions can achieve lower costs than traditional satellites by using commercial off-the-shelf (COTS) components where possible. However, COTS components may not function reliably in space for extended periods of time, and more ambitious missions with longer lifetimes require more reliability than experimental nanosatellites. Components developed by the traditional space industry are known to be reliable and robust, but they are usually too expensive and bulky compared to the requirements of nanosatellites. Using components designed for terrestrial safety-critical applications, such as automotive use, could provide cost savings while maintaining reliability compared to space-grade components. This paper considers the Texas Instruments Hercules TMS570 microcontroller family for the on-board data handling (OBDH) system of a nanosatellite mission in development at Aalto University. Several parties, including NASA, already plan to use Hercules in space applications. The proposed on-board computer (OBC) design is based on a Texas Instruments TMS570LS3137 Hercules Safety Microcontroller with built-in fault tolerance, including two processors running in lockstep and error correction codes (ECC) implemented in internal memories. Other components in the OBC are selected from automotive and other high-grade catalogs. The proposed OBC design is compared to LEON-based traditional OBCs and some CubeSat designs, and the built-in fault-tolerant lockstep architecture is compared to some previous fault-tolerant methods used in nanosatellites. Using microcontrollers with built-in fault tolerance for nanosatellite OBDH provides more reliability while speeding up mission development.
Proceedings of the 2nd IAA Conference On University Satellite Missions And Cubesat Workshop, Feb 7, 2013
GPS receivers are increasingly used in nanosatellite applications to provide the means for autono... more GPS receivers are increasingly used in nanosatellite applications to provide the means for autonomous and accurate navigation in orbit. However, many of the available nanosatellite GPS receivers consume a large amount of power compared to the available power budget. This can be a problem when the main science instruments have high power requirements and GPS is only used to support the science mission. This paper presents the design and proposed integration and qualification of a GPS subsystem that uses commercial, low-power GPS components to support the science mission of the 3U CubeSat-based Aalto-1 nanosatellite. Aalto-1 has three science payloads which require accurate positioning: a Fabry-Pérot imaging spectrometer used for remote sensing, a radiation monitor used for studying the near-Earth radiation environment and an electrostatic plasma brake used for deorbiting the satellite at the end of the mission. Ground-based tracking with only one ground station or NORAD-provided two-line element sets cannot position the satellite accurately enough for the science payloads, and it was concluded that GPS navigation is the best option. The GPS receiver and antenna have a combined power budget of 160 mW. Navigation accuracy of less than 100 meters is needed by the scientific instruments of Aalto-1. Effects of antenna placement on GPS navigation performance are considered, as the antenna on Aalto-1 will have a limited view of the sky. The preliminary functional tests and simulations with a GPS signal simulator indicate that the subsystem is capable of navigating in orbit and providing the Aalto-1 mission with the required navigation capability.
Thesis Chapters by Hannu Leppinen
M.Sc. (Tech.) thesis
GPS is increasingly used for spacecraft navigation in low Earth orbit. Equipping a satellite with... more GPS is increasingly used for spacecraft navigation in low Earth orbit. Equipping a satellite with a GPS receiver enables it to determine position, velocity and time autonomously, without the need for ground-based tracking stations. Using commercial off-the-shelf GPS components enables autonomous positioning even for low-cost nanosatellites. However, the components need to be selected and qualified carefully. This thesis presents the design of a GPS subsystem and a plan for its integration into the Aalto-1 nanosatellite. Although the flight model of the satellite won’t be ready by the completion of the thesis, the plan can be used in the integration of the final satellite system. The thesis also evaluates the feasibility of using this kind of commercial components in a satellite application.
The thesis begins by introducing the Aalto-1 satellite project, basics of the Global Positioning System, and satellite tracking with GPS. After this necessary background information, the design for the GPS subsystem is presented, as are its mechanical, electrical and software interfaces. A verification plan is outlined that aims to ensure that the subsystem will operate correctly in space. Some initial steps of the verification plan are done as a part of the thesis and are also described, most importantly GPS signal simulations, PCB prototype tests and antenna performance tests. Finally, conclusions about the spaceworthiness of the GPS subsystem are given, as are suggestions for the final integration of the subsystem into the satellite.
B.Sc. (Tech.) thesis in Finnish on methods for nanosatellite attitude control
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Papers by Hannu Leppinen
Thesis Chapters by Hannu Leppinen
The thesis begins by introducing the Aalto-1 satellite project, basics of the Global Positioning System, and satellite tracking with GPS. After this necessary background information, the design for the GPS subsystem is presented, as are its mechanical, electrical and software interfaces. A verification plan is outlined that aims to ensure that the subsystem will operate correctly in space. Some initial steps of the verification plan are done as a part of the thesis and are also described, most importantly GPS signal simulations, PCB prototype tests and antenna performance tests. Finally, conclusions about the spaceworthiness of the GPS subsystem are given, as are suggestions for the final integration of the subsystem into the satellite.
The thesis begins by introducing the Aalto-1 satellite project, basics of the Global Positioning System, and satellite tracking with GPS. After this necessary background information, the design for the GPS subsystem is presented, as are its mechanical, electrical and software interfaces. A verification plan is outlined that aims to ensure that the subsystem will operate correctly in space. Some initial steps of the verification plan are done as a part of the thesis and are also described, most importantly GPS signal simulations, PCB prototype tests and antenna performance tests. Finally, conclusions about the spaceworthiness of the GPS subsystem are given, as are suggestions for the final integration of the subsystem into the satellite.