BEESAT-2 and 3
BEESAT-2 and -3 (Berlin Experimental and Educational Satellite-2 and -3)
BEESAT-2 is a follow-up mission of BEESAT-1 of TU Berlin with the objective to improve the validation of reaction wheels (RW-1) and targets 3-axis stabilization using sun sensors, magnetic field sensors, magnetic coils and reaction wheels. The reaction wheels were developed in cooperation with Astro- und Feinwerktechnik Adlershof GmbH (AstroFein). BEESAT-2 and BEESAT-3 are scheduled to be launched on the Bion M-1 satellite mission of Russia in April 2013. 1)
ADCS (Attitude Determination and Control Subsystem): A 3-axis stabilization is implemented on BEESAT-2.
• Attitude control rate: 2 Hz
• Sensors: Sun sensors, Earth magnetic field sensors, gyros
• Actuators: reaction wheels, magnetic coils
• ADCS software implemented as state machine:
- After switch-on ADCS is in suspend mode – attitude is determined, but not controlled
- With a TC a control core can be activated or a wheel test can be conducted
Figure 1: Software concept of BEESAT-2 (image credit: TU Berlin)
Figure 2: Schematic of ADCS pointing implementation (image credit: TU Berlin)
Figure 3: Photo of the reaction wheels (image credit: TU Berlin, AstroFein)
Table 1: Parameters of the RW-1 (Reaction Wheel-1)
Figure 4: Fault-tolerant design of BEESAT-2 (image credit: TU Berlin)
Table 2: Overview of technology implementations in the BEESAT series CubeSats (Ref. 1)
BEESAT-3, a picosatellite complying with the 1U CubeSat design specification in size and mass, is the most recent development within the BEESAT CubeSat series of the Department of Aeronautics and Astronautics at TU (Technische Universität) Berlin, Germany. The project is supported by DLR (German Aerospace Center).
The primary objective of the BEESAT-3 mission is to enrich the space engineering education at TU Berlin with hands-on spacecraft design experience. Therefore, the satellite was developed from scratch by students of TU Berlin. The secondary mission objective is the on-orbit validation of HiSPiCO (Highly Integrated S-band transmitter for Pico and Nanosatellites), which was developed in a previous research project at TU Berlin in cooperation with IQ wireless GmbH. The goal of HiSPiCO is to answer the need for high downlink data rates of CubeSat payloads. 2) 3)
The BEESAT-3 bus structure is a custom made, three parts aluminum structure coated with an electroless nickel layer to improve its thermal properties and surface hardness. The top panel, square tube and base plate are assembled to form the satellite structure. Two rail pairs are part of the base and the top plate, which minimizes the launch stresses at the structure connection points. Inside the structure mainboard, battery and hysteresis plate are stacked on the four bolts that connect base and top plate.
To maximize the mass and space available for the payload, all satellite bus electronics, except for the transceiver module are integrated in a single PCB (Printed Circuit Board). Figure 5shows the BEESAT-3 mainboard, which accommodates the on-board data handling, the EPS (Electrical Power Subsystem), the attitude sensors (except for the sun sensors, which are accommodated on the solar panels), the modem and the payload data handling.
Figure 5: Illustration of the BEESAT-3 mainboard (image credit: TU Berlin)
A block diagram of BEESAT-3, depicting the electronic components of each subsystem as well as the data and energy flow between these components, is shown in Figure 7. The EPS of the satellite is based on a 3.3 V and a 5 V power bus and an additional, unregulated power line is provided for the HiSPiCO transmitter. The on-board computer provides a SPI (Serial Peripheral Interface) bus and an I2C (Inter-Integrated Circuit) bus for the communication with sensors, subsystems, and payload controller.
Figure 6: Photo of the BEESAT-3 flight model in the cleanroom (image credit: TU Berlin)
Figure 7: Block diagram of the BEESAT-3 (image credit: TU Berlin)
ADCS (Attitude Determination and Control Subsystem): Although not required for the mission, the satellite is equipped with an ADCS consisting of six sun sensors and three MEMS gyros. The gained data will be used to verify the satellites attitude during S-band transmissions and to generate data for refining the BEESAT-3 attitude simulations.
A passive attitude control system was selected for BEESAT-3, since it provides sufficient pointing accuracy for the patch antenna, without requiring energy or computing power from the satellite bus. The BEESAT-3 passive attitude control system consists of a permanent magnet that aligns the satellite to the magnetic field lines and a hysteresis plate, which damps the nutation of the satellite. The position of the permanent magnet and the hysteresis plate within the structure is shown in Figure 8.
Figure 8: Accommodation of the hysteresis plate and permanent magnet within the BEESAT-3 structure (image credit: TU Berlin)
Since only one side of the satellite is equipped with a patch antenna, the passive attitude control system needs to be designed such that a correct pointing of the patch antenna is guaranteed when the satellite passes over the ground station. Due to the IGRF (International Geomagnetic Reference Field) model, the angle between the magnetic field lines and the orbital altitude of 575 km at the ground station in Berlin (52°30’54’’N, 13°19’25’’E) is 67.13º. To direct the patch antenna to the ground station, the permanent magnet is aligned with the satellite's x-axis, which results in an angle of 22.83º between patch antenna and ground, when the satellite passes the ground station.
Figure 4 shows how the magnetic field of the permanent magnet aligns to Earth’s magnetic field when BEESAT-3 passes the TU Berlin ground station. The hysteresis plate is aligned to the satellite's y-z plane so that rotations around the y- and z-axis are damped, whereas rotations around the satellite's x-axis remain undamped.
Figure 9: Satellite orientation over the ground station (image credit: TU Berlin)
RF communications: The communications subsystem consists of a GMSK modem and a transceiver BK77 of the company: STE sas Elettronica Telecomunicazioni , Milan, Italy. This transceiver was already successfully used for the BEESAT-1 mission and supports half-duplex UHF communications.
Universal TC/TM system characteristics implemented:
• Event-based protocol approach
• Half-duplex communication in UHF
• Address oriented messages
• Messages are acknowledged – transmission errors result in retransmission of single data packets
• Satellites and ground station are network nodes
• A node can forward messages → swarm capable protocol
• Terminal node controller (TNC) will be open source hardware to build up a compatible ground station with listen-only mode
• TM organized similar to CCSDS
• Ground segment configurable to several missions using a database.
Table 3: Parameters of the RF communication subsystem
Figure 10: BEESAT-3 with HISPICO and patch antenna (image credit: TU Berlin)
Figure 11: Image of the BEESAT-3 CubeSat and its components (image credit: TU Berlin) 4)
Launch: The BEESAT-2 and BEESAT-3 CubeSats were launched on April 19, 2013 as secondary payloads on the primary spacecraft Bion-M1 (with biological and medical payloads of Russia and an international community) with a Soyuz-2.1b rocket. The launch site was the Baikonur launch facility, Kazakhstan. 5)
Orbit: Initial elliptical orbit with an altitude of ~300 km x 575 km, inclination = 64.9º. After separation from the launch vehicle, the Bion-M1 spacecraft circularizes its orbit to the altitude of 575 km. The secondary payloads will be deployed from Bion-M1 after the target orbit is reached (~2 days after launch).
Figure 12: Illustration of the Bion-M1 spacecraft (image credit: TsSKB Progress) 6)
The Bion capsule will parachute back to Earth after a one-month mission. The Bion-M1 spacecraft has a launch mass of ~6,840 kg.
The secondary payloads on Bion M-1 spacecraft are:
• BEESAT-2, a 1U CubeSat of TU Berlin
• BEESAT-3, a 1U CubeSat of TU Berlin
• SOMP (Students' Oxygen Measurement Project) of TU (Technische Universität) Dresden, or Dresden University of Technology, Germany.
• OSSI-1 (Open Source Satellite Initiative), an amateur radio CubeSat initiated by the Korean artist Song Hojun. The satellite will carry a 145 Mhz beacon as well as a data communications transceiver in the 435 MHz (UHF) band. It will also carry a 44 W LED (Light-Emitting Diode) array to flash Morse code messages to observers on Earth.
• Dove-2 , a nanosatellite (3U CubeSat, ~ 5.8 kg) technology demonstration mission of Cosmogia Inc. (Sunnyvale, CA, USA).
• AIST-2 is a Russian microsatellite project, a technology demonstration, developed and designed by students, postgraduates and scientists of the Samara Aerospace University in cooperation with TsSKB Progress of Samara, Russia. The microsatellite with a mass of 39 kg will perform a 3 year mission dedicated to measurements of the geomagnetic field and to test methods to compensate low-frequency microaccelerations. Also, the spacecraft will study high-speed mechanical particles of natural and artificial origin.
Figure 13: Photo of the AIST-2 microsatellite (image credit: TsSKB Progress)
Sensor/experiment complement: (HiSPiCO, Camera)
HiSPiCO (Highly Integrated S-band transmitter for Pico and Nanosatellites):
HiSPiCO is the primary payload on BEESAT-3. The device was developed in cooperation with IQ wireless GmbH and funded by DLR.
Several verification steps have been defined for the HiSPiCO on-orbit verification process:
• Successful synchronization of the HiSPiCO transmitter with the TU Berlin ground station.
• On-board generated test data are transmitted. This data is used to assess the link quality and to calculate the bit error rate.
• Pictures taken by the camera module are downlinked to Earth in order to demonstrate the transmitter’s ability to send real payload data.
• Downlinks with experimental user data rates of 0.68 Mbit/s and 1.39 Mbit/s are demonstrated and the link quality is assessed.
Table 4 shows an overview of the CubeSat missions with S-band transmission capabilities launched to date. So far only two transmitter models have been successfully demonstrated on orbit, both of them offering significantly lower data rates than HiSPiCO. Furthermore, S-Band transmission was not demonstrated with a single-unit CubeSat on orbit.
Table 4: Overview of CubeSat missions with S-band transmitting capabilities
Table 5 shows S-band transmitters/ transceivers suited for CubeSats that were already demonstrated on orbit or are offered for sale. It is obvious that S-band transmission data rates as high as offered by HiSPiCO have not been demonstrated from a CubeSat to date.
Table 5: S-band transmitters for CubeSats
Table 6: Parameters of the HiSPiCO S-band transmitter
The secondary payload of BEESAT-3 is a C-328 camera module that generates pictures with a resolution of 640 x 480 pixels.
1) F. Baumann, S. Trowitzsch, K. Briess, C. Nitzschke, “BEESAT – A CubeSat Series Demonstrates Novel Picosatellite Technologies,” 4th European CubeSat Symposium, Brussels, Belgium, Jan. 30- Feb. 1, 2012
2) Merlin F. Barschke, Frank Baumann, Klaus Briess, Christian Nitzschke, “BEESAT-3: Passive Attitude Control for Directed Radio Transmission on a Single-Unit CubeSat,” Proceedings of the UN/Japan Workshop and The 4th Nanosatellite Symposium (NSS), Nagoya, Japan, Oct. 10-13, 2012, paper: NSS-04-0117
3) M. F. Barschke, F. Baumann, K. Briess, “BEESAT-3: A picosatellite developed by students,” Proceedings of the 61st German Aerospace Congress (61. Deutscher Luft- und Raumfahrtkongress 2012), Berlin, Germany, Sept. 10-12, 2012
4) M. F. Barschke, F. Baumann, K. Briess, C. Nitzschke, “BEESAT-3: Passive Attitude Control for Directed Radio Transmission on a Single-Unit CubeSat,” Proceedings of the UN/Japan Workshop and The 4th Nanosatellite Symposium (NSS), Nagoya, Japan, Oct. 10-13, 2012, Poster
5) Patrick Blau, “Soyuz Launch Success - Bion-M1 & various Passengers safely in Orbit,” Spaceflight 101, April 19, 2013, URL: http://www.spaceflight101.com/bion-m1-mission-updates.html
6) A. N. Kirilin, R.N. Akhmetov, S. I. Tkachenko, “SRP SC “TsSKB-Progress”: Trends and Future Prospects,” 2011, URL: http://www.google.de/url?sa=t&rct=j&q=tsskb%20progress%20of%20samara%2C%20russia&source=web&cd=5&sqi=2&S-_IGoDw&usg=AFQjCNFA4ELDIyJShKf7c4CbUVdnNl4lxg&bvm=bv.45512109,d.Yms&cad=rja
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.