Galassia is a 2U CubeSat mission, developed by undergraduate students at NUS (National University of Singapore). As a university program, the main objective is for students to understand space technologies and to gain practical experiences while building, integrating and testing 2U CubeSat bus and payloads.
Galassia carries two scientific payloads. The first payload aims to measure the TEC (Total Electron Count) in the ionosphere; the second payload aims to acquire quantum correlation data in space for the concept verification of quantum-based communication using SPES (Small Photon-Entangling Systems). The life duration of Galassia is expected to be half a year. 1) 2)
Galassia follows a 2U CubeSat design with dimensions of 10 cm x 10 cm x 20 cm and a mass of 2 kg. Besides TEC and SPEQS payloads, the CubeSat bus includes 6 basic hardware subsystems. 3)
Table 1: Spacecraft parameters
Structure: The 2U structure is designed and fabricated using aluminum alloy 5052, as shown in Figure 1. The dimension follows the CubeSat standard and the overall mass is 212 g.
Figure 1: Illustration of the Galassia 2U CubeSat and its subsystems (image credit: NUS)
ADCS (Attitude Determination and Control Subsystem): The ADCS is to stabilize the CubeSat after deployment from the launch vehicle during the detumbling phase, and to maintain a reasonable stable attitude for Galassia throughout its lifespan. There is no pointing requirement from both TEC and SPEQS payloads. A simple PMAC (Passive Magnetic Attitude Control System) is implemented. The PMAC consists of 8 permanent magnets (z axis) and 4 pairs of hysteresis rods (x and y axes). The permanent magnets are used to align the body axis parallel to the magnet dipole axis with the Earth magnetic field vectors. The magnets with a diameter of 1 cm and a height of 4 cm are chosen to be rare Earth magnet grade N42. Hysteresis rods are used to reduce the kinetic energy of the satellite, and to damp the angular velocity of the oscillations during tracking, but only in the plane perpendicular to the magnet axis. The more pairs of hysteresis rods there are, the faster the satellite will become stable after detumbling. Due to the space and mass constraints, after calculations and simulations, 4 pairs of rods were finally determined to be implemented in the design. Figure 2 shows the simulation results of body rate responses under the random initial body rate of 10º/s.
Figure 2: Simulations of Galassia's body rate (image credit: NUS)
OBDH (OBC and On-Board Data Handling): The commercial product, 16 bit dsPIC33, is used as the OBC for Galassia. The OBDH subsystem consists of the OBC, Salvo Real Time Operating System for scheduling the tasks, and an optional flash card for secondary data storage. Salvo was chosen because of its small size, optimized codes and flight heritages.
Table 2: Operation modes of Galassia
To ensure successful data communication between the OBC and other subsystems, the data interfaces between them are through I2C (Inter-Integrated Circuit) buses except SPEQS (Small Photon-Entangling Quantum System), as the I2C protocol can provide a graceful handling of error occurrence during I2C communication. The AX.25 protocol and space package protocol are implemented together to define the data format between the Galassia and the ground station.
EPS (Electrical Power Subsystem): The functions of the EPS are to generate and store power for Galassia's operation, to distribute power to respective loads, and to provide over-current and under-voltage protections of electrical components. The EPS includes a 20 Whr integrated rechargeable Lithium Polymer battery, four sides of GaAs solar panels, and a power control and distribution unit. Figure 3 shows the block diagram of EPS. The fabricated engineering model of solar panels and EPS board are displayed in Figure 4. Many tests were conducted to measure and successfully verify the functions of solar panels, battery charging, and power control and distributions.
Figure 3: EPS block diagram (image credit: NUS)
Figure 4: Engineering models. (a) Solar panel, and (b) EPS (image credit: NUS)
TT&C (Telemetry, Tracking & Command) subsystem: The functions of TT&C are to transmit data received from the OBC to the ground station, to receive data from the ground station and forward it to the OBC, and to broadcast beaconing signals. In this system, the transceiver is designed using ADF7021 and PIC18F47J53, based on software defined radio principles. The uplink is in UHF and the downlink is in VHF. The data rate and modulation scheme for both uplink and downlink are 9.6 kbit/s and FSK (Frequency Shift Key), respectively. Figure 5 illustrates the block diagram of the TT&C subsystem.
Figure 5: Block diagram of the TT&C subsystem (image credit: NUS)
Figure 6: System block diagram (image credit: NUS)
Figure 7: Photo of Galassia in P-POD (Poly-Picosatellite Orbital Deployer) with mounted accelerometers on Shaker Table (image credit: NUS)
Launch: The Galassia nanosatellite was launched as a secondary payload on December 16, 2015 (12:30:00 UTC) on a PSLV-C29 launcher of ISRO from SDSC (Satish Dhawan Space Center) at Sriharikota on the east coast of India. 4) 5) 6)
The primary payload on this flight is TeLEOS-1, a commercial imaging minisatellite (400 kg) of AgilSpace, Singapore. A contract between ST Electronics AgilSpace of Singapore and Antrix Corporation was signed in Feb. 2014. 7)
The secondary payloads on this flight were:
• VELOX-C1, a minisatellite (123 kg) of NTU (Nanyang Technological University), Singapore.
• VELOX-2, a 13 kg 6U CubeSat of NTU, Singapore. A technology demonstration mission for intersatellite communication.
• Kent Ridge 1, a microsatellite (78 kg) of NUS (National University of Singapore) for Earth observation.
• Galassia, a nanosatellite (2U CubeSat, 2 kg) of NUS, Singapore with the objective to acquire TEC (Total Electron Count) data in the ionosphere. A secondary goal is to demonstrate a SPES scientific experiment in space.
• Athenoxat-1, a 3U CubeSat (technology demonstration) of NTU, Singapore.
Orbit: Near-equatorial orbit, altitude of 550 km, inclination of ~15º, period of ~96 minutes.
• August 2016: Galassia has completed the set of in orbit tests and is beginning to conduct payload experiments. The payload experiments (TEC, SPEQS and ADCS-EP) are always run individually. This approach is adopted to ensure that the power consumption is always within the budget and that unforeseen errors can be mitigated easily. 8)
- Figure 8 shows the preliminary results of the TEC experiment in which the 3 continuous waves (f0-fm, f0, and f0+fm) from Galassia are captured in the ground station. The peaks in Figure 8 have been verified to be coming from the Galassia which also confirms that the TEC payload is functional in space. Currently, the peaks were detected at up to -85 dBm with a sampling noise floor from -105 to -90 dBm. Further optimization is currently being done to get a better signal to noise ratio (SNR) to precisely extract the phase information for calculation of the TEC value.
Figure 8: Three tones from the TEC payload as captured at the ground station (image credit: NUS)
- During the course of operations, in-orbit experiments onboard the SPEQS payload have also been successfully downloaded and sent to the CQT (Center for Quantum Technologies) for analysis. Colleagues at CQT have confirmed that the photon correlations onboard the SPEQS exhibit a contrast of 97% ± 2%, matching ground-based tests. 9) The results have validated the design of both the photon-pair generation and the polarization-measurement system.
Additionally, noise events (dark counts) throughout the SPEQS experiments have been monitored to see the effect from radiation towards the components used in the payload. The compatibility of the in-orbit polarization correlations with baseline measurements proves that the components have not been influenced so far by in-orbit radiation. Further operation will study the long-term performance of the payload, and the results will be used to inform the design of the next iteration of the SPEQS payloads.
- In summary, Galassia has met both its technical as well as educational objectives and is currently in orbit with good health status at the time of this writing. The project has also brought NUS a step forward in designing and building space systems together with the accompanying ground telemetry systems. The next phase of development will be to attain as much in orbit data as possible as well as planning for future missions.
• April 26, 2016: The Galassia nanosatellite and its payloads are operating nominally in the Orbit Test Phase. 10)
- The SPEQS payload mission has been completed successfully. Further experiments will be carried out to monitor the payload performance over time. Work on the TEC payload is still in progress.
- The project made first contact with the satellite on the first pass after launch on December 16, 2015 from the NUS ground station.
• NUS has launched its first two satellites, Galassia and Kent Ridge 1, which were designed and built by its students, researchers and faculty. They were part of six Singapore satellites that were launched in the same operation. Prof. Cher-Hiang Goh, Project Director of the NUS Satellite Program at the NUS Faculty of Engineering, said that the satellites will be able to produce information at a much higher frequency which will be important in cases like disaster monitoring in the region like Southeast Asia. 11)
Sensor complement: (TEC, SPEQS)
TEC (Total Electron Count)
TEC measures the electron content in the ionosphere. The block diagram of the TEC receiving part at the ground station is shown in Figure 2. The TEC payload only works when Galassia is just above the Singapore station to obtain vertical TEC data. There is no data storage required for this instrument. TEC is a measure used to characterize the conductivity of the ionosphere, which consists of ionized layers in the upper atmosphere. The free electrons in the ionosphere affect the propagation of radio waves. Several candidate methodologies that could be used to measure the TEC include pseudorange, carrier phase, and the three frequencies method. After studying and researching on different methods and taking into account the constraints of the CubeSat, the three frequencies method was chosen for implementation in Galassia.
The measurements are based on the transmission of three CWs (Continuous Waves) with center frequencies of f0-fm, f0, and f0+fm. The measurement principle is based on the different delays for the signals with three frequencies. At the ground station, the signals with three frequencies need to be separated.
TEC is comprised of a Local Oscillator generating a 145 MHz frequency that is then sent through three bandpass filter to deliver three distinct continuous wave signals at 144.2, 145.0 and 145.8 MHz. These signals can be received by the ground station and studies of pseudorange, carrier phase, and the three frequencies method can be utilized to calculate the total conductivity of the ionosphere and with that its total electron content. Primarily using the three frequencies method, the ground station will record the delay for the different signals since the total electron abundance in the ionosphere affects signals of different frequency with a different magnitude.
Figure 9: Block diagram of the TEC receiver (image credit: NUS)
Figure 10: Photo of the TEC EM (Engineering Model), image credit: NUS
SPEQS (Small Photon-Entangling Quantum System)
The objective of SPEQS is to acquire quantum correlation data in space for the concept verification of quantum-based communication by NUS/CQT (Center for Quantum Technologies).
The SPEQS experiment assembly was developed by the CQT (Center for Quantum Technologies) in NUS. Polarization-entangled photon pairs are widely used in quantum communications. A compact and efficient system for generating and detecting photon pairs is conducted. The SPEQS experiment utilizes a process called SPDC (Spontaneous Parametric Down Conversion) to generate entangled photon pairs which can be used to establish a quantum communication link between two sites. The generation and detection of photon pairs are performed within the package to check the quality of the entanglement and this is the first step to verify if such communication protocol is feasible in space. This package achieves high entanglement fidelity and enables a quantum light source to be deployed on mobile field communication systems where resources are scarce. 12)
SPEQS conducts the science experiment for a maximum duration of 30 minutes. The SPEQS is designed to operate in three modes which are housekeeping, experiment and data transfer. Table 3 illustrates the power budget.
Table 3: Power budget of SPEQS
Figure 11 illustrates the concept of operation to be adapted by the Galassia OBC (On-Board Computer). The connection between SPEQS and OBC is through an UART (Universal Asynchronous Receiver/Transmitte) bus. The SPEQS data should be stored until they are downloaded to the ground station. A failure of the OBC to transfer data completely to the ground station in a single pass shall not affect the next scheduled SPEQS experiment.
Figure 11: Operation sequence of SPEQS (image credit: NUS)
Figure 12: Photo of the Galassia ground station at NUS (image credit: NUS, Eugene Ee)
Figure 13: Photo of the Galassia Control Room at NUS (image credit: NUS)
1) Luo Sha, Mouthaan Koenraad, Soh Wee Seng, Goh Cher Hiang, Alexander Ling Euk Jin, "Galassia System and Mission," Proceedings of the 28th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 2-7, 2014, paper: SSC14-XI-2, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3089&context=smallsat
2) Goh Cher Hiang, Luo Sha, Eugene Ee Wei Han, "Galassia Nano-Satellite," 2nd Singapore Space Symposium 30 Sept., 2015, URL: http://www.sarc.eee.ntu.edu.sg/NewsnEvents/Documents/GCH.pdf
4) Stephen Clark, "PSLV completes commercial launch with six Singaporean satellites," Spaceflight Now, Dec. 16, 2015, URL: https://spaceflightnow.com/2015/12/16/pslv-set-for-commercial-launch-with-six-singaporean-satellites/
5) "India's PSLV Rocket orbits six Satellite for Singapore in year-closing Mission," Spaceflight 101, Dec. 16, 2015, URL: http://spaceflight101.com/pslv-c29/indias-pslv-rocket-orbits-six-satellite-for-singapore/
6) "India to launch 6 Singaporean satellites," Space Daily, Dec. 11, 2015, URL: http://www.spacedaily.com/reports/India_to_launch_6_Singaporean_satellites-999.html
7) "ST Electronics, Antrix, ATK, Satrec Initiative + SPOT Asia—The TeLEOS-1 Adventure Is Underway (Satellite—Launch Preparations)," Satnews, Feb. 6, 2014, URL: http://www.satnews.com/story.php?number=1002365176
8) Ee Wei Han Eugene, Ajie Nayaka Nikicio, Feng Dan, Harsh Kumar, Hassan Ali Askari, Luo Sha, Zhang Runqi, Goh Cher Hiang, Liaw Hwee Choo, "Design, AIT, Launch & Early-Operations of Galassia Nanosatellite," Proceedings of the 30th Annual AIAA/USU SmallSat Conference, Logan UT, USA, August 6-11, 2016, paper: SSC16-XIII-4, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3418&context=smallsat
9) Zhongkan Tang, Rakhitha Chandrasekara, Yue Chuan Tan, Cliff Cheng, Luo Sha, Goh Cher Hiang, Daniel K. L. Oi, Alexander Ling, "Generation and Analysis of Correlated Pairs of Photons aboard a Nanosatellite," Physical Review Applied, Vol. 5, Published 31 May 2016
10) Information provided by Eugene Wei Han Ee, Galassia Systems Engineer at NUS.
11) "NUS launches first two satellites," NUS News, URL: https://news.nus.edu.sg/news-media/9839-nus-launches-first-two-satellites
12) Rakhitha Chandrasekara, Zhongkan Tan, Yue Chuan Tan, Cliff Cheng, Alexander Ling, "Small Photon Entangling Quantum System for Space Based Quantum Experiments," Proceedings of the 29th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 8-13, 2015, paper: SSC15-X-2, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3229&context=smallsat
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 (firstname.lastname@example.org).