BEOSAT (Braunschweig's Earth Observation Satellite)
BEOSAT is a low-budget student microsatellite project at the Technical University of Braunschweig (in English, the city is also known as Brunswick), Germany which started in 2003. The project is organized and managed by ERIG e.V. (Experimental-Raumfahrt-Interessen-Gemeinschaft), or simply "Experimental-Space-Interest-Community," a student body organization and its partners and sponsors (two institutes of the university act as sponsors). The ERIG organization itself was founded in 1999. More than 40 students have been working on the project. The current (2005) BEOSAT team includes about 20 students.
BEOSAT is designed as a multifunctional Earth observation platform equipped with a microspectrometer and a debris sensor. The objectives are to analyze gases in Earth's atmosphere and to detect the distribution of space debris in a 600-650 km sun-synchronous orbit. Other possible monitoring functions of BEOSAT are the detection of environmental pollution and the detection of light pollution to find new possible sites for Earth-based telescope locations that are not disturbed by the lights of nearby civilization. As of 2005, the project is in phase B. 1) 2) 3) 4) 5) 6)
BEOSAT employs an Earth-pointed multifunctional platform with three-axis stabilization. The spacecraft bus has a box shape (a cube) with an edge length of 40 cm and a mass of about 40 kg (max). The platform structure design is called FIBS (Functional Integrated Primary Structure). FIPS uses an Al baseplate. The panels are set up with honeycomb and CFRP (Carbon Fiber Reinforced Plastic) plates. All S/C components are chosen to provide a satellite design life of two years.
The ADCS (Attitude Determination Control Subsystem) employs a CESS (Coarse Earth Sun Sensor), a three-axis magnetometer, a fine-sun-sensor, three gyros, and a GPS receiver. Three reaction wheels and magneto-torquers are being used as actuators. The combination of sensors and actuators allows a pointing accuracy of 0.7º. The microsatellite is nadir-pointed during observations S/C operations, and sun-pointed for charging purposes (no measurements). The ADCS operations are controlled by a microprocessor.
Figure 1: Main elements of OBC architecture (image credit: ERIG)
Electric power of up to 100 W (max, 32 W average) is being provided by two fixed solar panels with a total number of 132 triple-junction solar cells (26% efficiency). In addition, the PCDU (Power Control and Data Unit) employs a lithium-ion type battery of 130 Wh (space qualification) for eclipse operations. The design makes use of fixed solar panels to avoid the provision of a complex deployment mechanism. The main solar panel is mounted on the zenith side of the S/C. A secondary smaller panel is being fixed in the anti-flight direction. The main panel is protruding over the bus structure, this has two effects: 1) to gain more panel area, and 2) to provide shadowing for the radiator. The peak energy consumption for the S/C is estimated to be 48 W.
The OBDH (Onboard Data Handling) system employs FPGA-based multiple redundant processing units. Onboard communication is provided by RS-422 serial lines. The OBC (Onboard Computer) features a dual hot redundant architecture employing two XILINX Virtex II per FPGA which feature two Power PC cores each. These processing units are configured and booted by a radiation tolerant ACTEL FPGA. The telemetry subsystem employs an on-chip-radio, i.e. the baseband downlink signal is generated and up-converted to an intermediate frequency (IF) using programmable logic. The demodulation and baseband processing of the uplink signal are also carried out in programmable logic.
RF communication: Use of S-band uplink and downlink with a downlink rate of 270 kbit/s using adaptive code sampling. The uplink is 3.2 kbit/s. A ground station with a 3 m parabolic dish is being installed at the University of Braunschweig providing all functions for spacecraft monitoring and control.
Figure 2: Illustration of the BEOSAT spacecraft (image credit: ERIG)
Orbit: Sun-synchronous orbit, altitude = 650 km, inclination = 98º, with an LTAN (Local Time on Ascending Node) at 10:00 hours.
A launch of BEOSAT is planned for 2008/9 (most likely on a Dnepr launch vehicle from Baikonur, Kazakhstan, but several other piggy-back solutions are still possible and under consideration).
Figure 3: View into the interior of the spacecraft (image credit: ERIG)
Sensor complement: (µSCIA, AIDA, µMAG)
All payload data processing is completely performed in the payload instruments. A DPU (Data Processing Unit) controls each instrument and stores the payload data in its 512 MB SDRAM mass memory.
µSCIA (Micro SCIAMACHY) of SCIAMACHY heritage, flown on Envisat of ESA. The instrument µSCIA is a low-cost project of IEP (Institute of Environmental Physics) of the University of Bremen, Germany, and ERIG EEV. COTS components are used whenever possible. The instrument consists of a microspectrometer and a telescope. The aim is to measure trace gases of the atmosphere with a ground resolution of 20 km x 20 km (normal observation mode) - this represents an improvement by a factor of 4.5 over the SCIAMACHY measurements on Envisat, the latter with a ground resolution of 60 km x 30 km. In fine observation mode, the ground pixel can be reduced to 12 km x 4 km. However, due to the enormous increase of the data rate, this mode will only be used occasionally. The instrument data can be compressed onboard to reduce the amount of data for the transfer. The µSCIA instrument is a box of size 130 mm x 80 mm x 50 mm, the power consumption is 4 W, the mass is 6 kg.
The science objective is to monitor nitrogen dioxide (NO2), an indicator of air pollution. The trace gas NO2 is emitted in many types of combustion processes, in particular in such fields as public/private transportation (automobiles, aircraft, etc.) as well as in households and in industry. NO2 is the agent causing acid rain and is responsible for supporting the production of troposhperic ozone. Its main observation area onboard BEOSAT is Europe, but other industrial countries or disaster areas can be observed as well.
The µSCIA monitoring concept is nadir-oriented providing information about the total column amount (there is no height-dependent information). The µSCIA source data are planned to be posted onto the Internet so that all parties of interest may take a look at their local air pollution situation.
Figure 4: Illustration of the µSCIA instrument (image credit: ERIG)
AIDA (Advanced Impact Detector Assembly). The overall objective is to improve the knowledge of Earth's space debris and meteorite environment by in-situ monitoring. The AIDA instrument concept realizes a new detection method/technology (calorimetric impact detection) to measure the impact vector and energy of impinging particles or small space debris. The sensor development is partly being sponsored by PTB (Physikalisch Technische Bundesanstalt) Braunschweig within the ESA/ESTEC study "Assessment of In-Situ Impact Detectors", while Eta_Max Space GmbH of Braunschweig is the instrument manufacturer and prime contractor of this study with PTB acting as a sub-contractor of Eta_Max Space GmbH.
AIDA consists of a solid baseplate (target sensor) whose surface is covered with a fine grid of conductive thermal detectors -i.e., a thermopile array of 256 sensitive elements (each of 3.6 mm x 3.6 mm). An absorber array (each element of size 3.55 mm x 3.55 mm) is glued onto the thermopile array, while each absorber is glued to the center of the corresponding thermopile with a 20 µm adhesive layer. During an impact the space debris particle or the micro-meteoroid will be captured by the absorber. To a certain degree kinetic energy will be converted into heat. This heat is then conducted to the center of the thermopile which generates a voltage increase due to the temperature increase. The sensor electronics read out the generated voltage and assess the particle's impact energy based on the sensor calibration. Another position sensitive sensor is placed on top of each calorimetric stage.
Figure 5: Illustration of an AIDA sensor unit or block array (image credit: ERIG)
The particle impact vector is measured optically by means of three parallel laser curtains (or light fences) positioned in front of the baseplate, this device is referred to as "Ariel." The curtains are placed in successive planes about 20 cm ahead of the baseplate. Whenever an incoming particle impacts the sensor (baseplate), it's flight path is first detected by the 3 laser curtains. So, whenever a particle hits a curtain, a flash (strobe) is generated. These flashes are registered by optical cameras which provide also a time signal for storage of the flash location. The same concept applies to the other curtains. Ariel is a position sensitive impact plasma detector using three grids (measuring, ground, plasma protection). With Ariel and AIDA_cal data, two different measuring principles for a particles' impact energy are implemented. Hence, it is possible to assess a particles' mass and velocity.
This successive detection/monitoring technique allows a deduction about each particle's direction and velocity.
The measured impact energy correlates with the impact plasma production. Because of the two physically different types of impact energy assessment, an estimation of the particle's mass and velocity will be possible. 7)
AIDA consists of 16 sensor units (block arrays) with a cumulative sensitive sensor area of 576 cm2 (see Figure 7). Each sensor unit measures 76 mm x 70 mm x 36 mm with a sensitive area of 60 x 60 mm2. The total AIDA instrument mass is estimated to be 5 kg, the power consumption is about 4 W. The 16 AIDA sensor units are integrated into the load-carrying structure of the S/C whose surface is pointed into the flight direction (representing a duty cycle of 1 which means continuous observations). The new sensor has the potential to improve estimations of particle distributions and their dynamics in its orbit path.
Figure 6: Schematic of the AIDA impact concept (image credit: ERIG)
Figure 7: AIDA sensor unit mounting is integrated into the S/C structure (image credit: ERIG)
µMAG (Micro Magnetometer). The instrument is a fluxgate magnetometer of IMT (Institute of Microtechnology) at the University of Braunschweig. The objective is space qualification of µMAG, a tiny device of 20 mm side length.
Figure 8: 3D array of the µMAG (image credit: IMT)
1) B. Rievers, L. Guicking, H. Thamm, S. Schröder, "BEOSAT: (Brunswick's Earth-Observation-Satellite)," STEC (Space Technology Education Conference) 2005, April 6-8, 2005, Aalborg University, Aalborg, Denmark
2) J. Pfingstgräff, R. Kluge, S. Grotjan, C. Zapf, "BEOSAT (Braunschweig's Earth Observation Satellite," Proceedings of IAC 2004, Vancouver, Canada, Oct. 4-8, 2004, IAC-04-IAA.4.11.P.03
4) R. Kluge, J. Pfingstgräff, M. Berger, D. Kubus, "BEOSAT (Brunswick-Earth-Observation Satellite)," Proceedings of the 5th IAA Symposium on Small Satellites for Earth Observation, April 4-8, 2005, Berlin, Germany
5) Information was provided by Mareike Krause of ERIG e.V., Braunschweig
6) A. Sauer, J. Pfingstgräff, D. Kubus, "The BEOSAT-Project (Student Built Microsatellite)," Proceedings of the 56th IAC 2005, Fukuoda, Japan, Oct. 17-21, 2005, IAC-05-B5.6.A.06
7) K. D. Bunte, M. Kobusch, J. Hollandt, J. Illemann, F. Jäger, M. Gläser, S. Sarge, "AIDA - An Advanced Impact Detector Assembly," 54th International Astronautical Congress (IAC) of the International Astronautical Federation, the International Academy of Astronautics, and the International Institute of Space Law, Sept. 29 - Oct. 3, 2003, Bremen, Germany, IAC-03-IAA.5.P.02
This description was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" - comments and corrections to this article are welcomed by the author.