IRAZU CubeSat Mission
The Central American Association of Aeronautics and Space (ACAE : Asociación Centroamericana de Aeronáutica y del Espacio), in partnership with academy, industry and the government, have identified the promotion of the aerospace as a very promising strategy for economic, scientific and technological development in Costa Rica. Several studies have identified actions to enable the development of the aerospace sector in the country. Among them, a practical demonstration of the technical capabilities to develop a space engineering project is considered mandatory.
The Irazú project is an innovative mission taking place in Costa Rica, which aims to launch the first Central American satellite in orbit by 2018. This mission, declared of national interest by the president of the country, is being led by ACAE and ITCR (Costa Rica Institute of Technology). This project has two main objectives: going through the space project lifecycle and demonstrating a platform to measure the effects of climate change in Costa Rican rainforests, amid the efforts of this country to become the first carbon-neutral nation in the world. 1)
Costa Rica has played a leading role in the conservation of natural resources. Recent evidence of this includes the country's continuing reforestation, increasing its forest coverage from 40.8% in 1986 to 51.4% in 2010, and its ambitious objective to become a carbon neutral country by 2021. The ITCR (Instituto Tecnológico de Costa Rica) School of Forest Engineering, located in Cartago, Costa Rica [also referred to as TEC (Tecnológico de Costa Rica)] has been actively monitoring rainforests to study properties such as water level, biomass growth and meteorological variables, among other things. Researchers have faced severe difficulties accessing remote forest locations for data extraction, and when accessible, valuable resources must be allocated to the manual collection of this data. Project Irazú is a proof of concept which aims to demonstrate a data relay system to transmit daily measurements acquired by ground sensors in remote areas to a data processing center. The project is a joint effort between the ACAE and ITCR. 2) 3)
The Irazú project has two main objectives, which are:
1) To demonstrate the capability to develop and operate an aerospace engineering project in Costa Rica.
2) To develop a scientific mission that will allow Costa Rican scientists to collect data related to the country's rainforests.
Science: The scientific component aims to contribute to ongoing studies to determine the growth of biomass of a tree planting and study the influence of environmental variables. This is important for assessing the environmental services of these ecosystems that fix carbon from the atmosphere. The forest plantations grow evenly, and this condition allows accurate estimates of biomass growth and total carbon fixing. Because the satellite's lifetime will only be 6 months, the scientific team decided to concentrate all their efforts for this mission on the monitoring of growth of tree plantations and to emphasize other aspects, such as to study and understand the hydrology-climate-soil-growth relationships, of the selected species.
This mission will provide the foundation for future development of new proposals on reforestation that offsets carbon emissions. Furthermore, this mission aims to impact directly in the short term the promotion of Costa Rica's forestry sector and to encourage reforestation with commercial timber species.
The general science objective can be formulated in the following fashion: To monitor the environmental service of a forest plantation by carbon sequestration and studying the dynamics of biomass growth and its relationship with environmental variables.
Some background: On March 16, 2016, officials at the Costa Rica-based Central American Association for Aeronautics and Space (ACAE) announced they will launch a crowdfunding campaign to raise $75,000 needed to orbit the first Costa Rican satellite, a small 1U CubeSat. This small device called Irazú, of size 10 cm x 10 cm x 10 cm and a mass of about 1 kg, is expected to be launched to the ISS (International Space Station) and to be deployed into space at some later time from the station. The project takes its name from Costa Rica's highest volcano (Irazú with an elevation of 3,432 m), located in the province of Cartago. 4)
Project Manager Marco Gómez said, the research consists of real-time measurements of temperature, humidity and carbon dioxide fixation. Data will be collected in a forest in Los Chiles, a mountainous area near Costa Rica's border with Nicaragua, and will be used to evaluate climate change effects on forests.
The Irazú project involves student and faculty involvement from the university; they will be responsible for processing, analyzing and preparing visualizations with daily data obtained at the forest as well as from the satellite mission. Data will be used by researchers from various TEC faculties in projects ranging from climate effects to numerical weather prediction. Information collected will also be shared on a website as open data so it can be used by investigators and students all over the world.
The 1U CubeSat standard was selected for this project since it has been used successfully for various Earth observation missions by universities around the world. Most subsystem were purchased from GomSpace to reduce risk due to their flight heritage.
The spacecraft, features 6 subsystems; the first five (structure, thermal, electrical power system (EPS), onboard computer (OBC) and communication) are essential for any CubeSat mission, while the payload is usually reserved for the scientific component. Since the Irazú project has its scientific component on the ground, the payload was used for educational purposes. A secondary OBC is being developed by Costa Rican engineers to act as an IMU (Inertial Measurement Unit), but mainly to provide these engineers the experience of designing, manufacturing, testing and operating a spacecraft component. One notable absence in the design is an ACS (Attitude Control Subsystem). Since the spacecraft has an antenna with a omnidirectional pattern and since it lacks a scientific payload with pointing requirements, then an ACS is not necessary for spacecraft operations.
The architecture of the CubeSat is presented in Figure 1. It follows a decentralized approach that comes standard in the GomSpace CubeSat platforms. Each subsystem has its own microprocessor that connects to the bus using either I2C or CAN (for the Irazú spacecraft, I2C will be implemented). Additionally, the GomSpace SDK (Software Development Kit) and mission libraries will allow the team to program the spacecraft functions. These will be used in order to ensure rapid development of the subsystems and to lower risk, since they have already been used to successfully develop other GomSpace CubeSats.
Figure 1: Irazú CubeSat architecture (image credit: GomSpace)
The Irazú CubeSat design is similar to the 1U platform offered by GomSpace with the following differences:
• The CubeSat structure is manufactured in Costa Rica.
• The payload is a secondary OBC which acts as an IMU.
• An aluminum plate is placed on one of the sides of the CubeSat and another one inside of the spacecraft for fund-raising purposes.
An exploded view of the spacecraft is presented in Figure 2. The GomSpace subsystems were selected since they satisfied all the requirements that were defined in project Irazú's SRR (System Requirements Review). Furthermore, only one supplier was selected for the critical electronic components to facilitate the integration process.
Figure 2: Exploded view of the Irazú CubeSat (image credit: ITCR)
EPS (Electrical Power Subsystem): The EPS consists of 5 solar panels, that can generate up to 2.3 W in LEO, and the power supply, consisting of a 7.4 V battery. These are designs that have already been tested in space by the provider to reduce the risks. The provider selected was GomSpace, with its "NanoPower P31u" as a power source, in combination with the "NanoPower P110" solar cells. The source of energy consists of two power buses with voltages of 3.3 V and 5 V, which are compatible with the requirements of all the other subsystems. — As an essential component of the CDR (Critical Design Review), it was proven that enough power would be generated with only five solar cells (Ref. 2), even under worst-case scenario lighting conditions. The EPS system was tested and verified up to August 2017, and after verifying its working specifications compared to the CDR calculations, it is ready for integration in September 2017.
OBC (On-Board Computer): The OBC is one of the core subsystems of the Irazu satellite. It is in charge of receiving commands from both the ground station and the remote transmitter. Then, the computer decodes and executes these commands, together with other satellite subsystems like EPS and Communication. The OBC for the Irazu project is based on the GomSpace NanoMind A3200. This computer features a high performance microcontroller that is based on the AVR32 MCU architecture. It has 512 KB of built-in Flash memory, 32KB of FRAM for parameter configuration, real time clock and calendar capabilities, and on-board temperature sensors. For communication with other subsystems, the Irazu OBC makes use of the CSP over an I2C bus.
Figure 3: Project Irazú onboard computer architecture (image credit: GomSpace, ITCR)
The GomSpace OBC includes an AVR32 MCU and an attitude determination system, consisting of 3-axis magneto resistive sensor and 3-axis gyroscope. The other subsystems included in the spacecraft are thermal and structural. For these, an extensive analysis had to be performed in order to conclude whether the CubeSat will survive the launch and operating environment.
RF Comms: The RF communication system is half-duplex operating in UHF with an omnidirectional canted turnstile antenna. It consists primarily of a half-duplex, software configurable transceiver: the NanoCom AX100. It is responsible for sending the telemetry and receiving the commands for the uplink/downlink of the scientific data.
The telemetry data are obtained from the following subsystems: EPS for battery charge, the OBC for timestamp and gyroscope, and COMMS for the RSSI (Relative Received Signal Strength). In the main operation mode of the CubeSat, the scientific data for downlink will be obtained from the OBC and, for the uplink, data will be obtained from the Remote Ground Station, so the CS&F can be performed. Operators in the ground segment (mission control) can access the other operating modes.
The antenna coupled to the transceiver operates in the ultrahigh frequency (UHF), and it is circular polarized with an omnidirectional radiation pattern. The highest gain is 1.4 dBi (along the Z-axis of the CubeSat). The lowest gains are 0.6 to -0.3 dBi (along the X- and Y-axes), Figure 4.
Figure 4: Radiation pattern of UHF antenna: NanoCom Ant430 (GomSpace)
All scientific data sent to the ground stations is encoded into an AX.25 protocol by the transceiver. This data frame includes the AX.25 header, the data field, and a 16 bit CRC (Cyclic Redundancy Check) for error detection. The software in the AX.25 header configures a call sign with SSID, for destination and source. In the AX.25 Data Field, an encoded header is added for the CSP (CubeSat Space Protocol), which contains the destination/ source node, ports, and priority, so the packets can be routed correctly in the communications architecture.
CS&F (CubeSat Store and Forward) system: The Store and Forward protocol is a technique used in telecommunications that consists of sending data to a node, storing it and transmitting it to another node after a given period. 5) It was created in the 1970's to manage networks that had low bandwidth connections and basic transmitters (these had very low memory, which led to frequent saturation). The Store and Forward protocol was useful for these networks, because the transmitter stored the incoming data and waited until there were other "free" transmitters to forward the information and avoid saturation.
When the networks became more sophisticated, the technique became obsolete until the early 1990's, with the growth in popularity of small satellites, that were in the range of 100 – 500 kg. The design of Irazú shows that a 1 kg satellite can fulfill the same function as the satellites of the 90's, thanks to advances in microelectronics. This concept will be tested for the first time using a 1U CubeSat in 2018, with the operation of the Irazú satellite.
A CS&F (CubeSat Store and Forward) system consists of at least three components: the remote station, the satellite, and the communication station (Figure 1). The remote station is an autonomous communication station that collects scientific data from sensors that are located in an area with difficult access and limited signal. Once the satellite is in the line of sight of this station, the data is transmitted and stored in its internal memory. The communication station then sends a signal to collect the scientific data and pre-analyze it. The simplest CS&F consists of a unit of each component but it could be developed with more remote stations, satellites and communication stations, which would result in a transmission system of real-time scientific data around the world using cost efficient spacecraft and ground stations.
Figure 5: Architecture of the CubeSat Store and Forward System (image credit: ITCR)
Table 1: Accomplished and future Phases of the project Irazú and deliverables (Ref. 3)
Launch: A launch of the Irazú CubeSat as a secondary payload on a service flight to the ISS is scheduled for the spring of 2018. The launch provider is JAXA.
Orbit: Near-circular orbit, altitude of ~ 400 km, inclination = 51.6º.
Sensor complement: (SOBC)
SOBC (Secondary Onboard Computer)
The SOBC is being built by Imagine XYZ of San José, Costa Rica, a spinoff of the Costa Rica Institute of Technology specializing in electronics research and development. The objective of SOBC is to measure the angular velocity, and linear acceleration of the satellite, as well as the magnetic field surrounding the satellite by implementing integrated arrays of sensors which include: gyroscopes, accelerometers, and magnetometers. This array configuration will generate information that shall be used by an embedded computer to determine and correct noise and drift.
Figure 6: Prototype SOBC mounted on a 3D printed structure (image credit: ITCR)
The ground segment is the final component of the Irazú mission. Its functions are tracking the satellite, monitoring its health, uploading commands and most importantly downloading the data that originated from the forest sensors. The ground station was designed by the Radio Club of Costa Rica, using recommendations from M2 Antenna Systems Inc., which offers solutions for amateur radio satellite ground stations. The main objective was to create a low-cost station for operations in the UHF band. This can be accomplished by using COTS (Commercial off-the-Shelf Components).
The ground station component relates to the actual hardware required to contact the spacecraft, while mission control focuses more on the software needed to operate the mission. The final element of the ground segment is used to turn the raw data acquired by the ground sensors to produce scientific imagery that will be attractive to the public and raise interest in the mission. Figure 7 displays the block diagram of the ground segment.
Table 2 presents the components of the ground station, the selected models for the design and the distributors that sell them. The Radio Club of Costa Rica suggested M2 Inc. as the main distributor since they have purchased and operated their products and have had good experience with this company in terms of delivery and product support. The Yaesu rotator control model was selected due to its ease of use over the one offered by M2 Inc. Furthermore, the Kenwood TS-2000 transceiver was selected since it has a built-in TNC (Terminal Node Controller) and power amplifier, among other features.
Table 2 Stakeholders of the Irazú project
Figure 7: Block diagram of Irazú ground segment (image credit: ITCR)
Figure 8: Irazú project concept of operations (image credit: ITCR)
Ground stations (Ref. 3):
Except for the customized software modem, all ground station hardware is COTS amateur radio hardware. This hardware was selected to meet the requirements that were imposed by the uplink and downlink budgets.
The Remote Ground Station is formed by a Kenwood TM-D710G Radio (46.9 dBm), a Microset UHF power amplifier RU 2-45 (46.5 dBm) and an omnidirectional circular polarized UHF antenna (5.5 dBi). The computer that runs the CSP application is a Raspberry Pi 3 model b+, running in Raspbian (Debian) as shown in Figure 9.
Figure 9: M2 Inc. EB-432 antenna and Kenwood TM-D710G used to run the ground station for Project Irazú (image credit: ITCR)
Scientific data is collected from sensors wirelessly, using the radio frequency module: RFM69HCW (Figure 10). After all data is obtained from the network of sensors and stored in the Raspberry, each data frame is encoded with the same AX.25 data frame used with the AX100 transceiver.
Both uplink and downlink are performed at a baud rate of 9600 bit/s. 1200 bit/s was originally intended to be used, but after testing between both radios, better performance was identified at 9600 bit/s. This change was made with the intention of reducing risks in transmitting the scientific data by using a higher baud rate.
The CSP protocol implements interfaces and drivers, to transmit data over different protocols to conserve the CSP (CubeSat Space Protocol) structure. A KISS interface is already carried out in the CSP GitHub, for serial communication.
The approach of the KISS (keep it simple, stupid) interface is to send data to the CubeSat radio and/or OBC over a USB-Serial converter. In case the AX100 is in AX.25 mode, the AX.25 header is added by its microcontroller. Therefore, the AX.25 header is not included in either the KISS CSP interface or the Kenwood in KISS mode. To include the AX.25 Header and the correct CRC (Cyclic Redundancy Check), a "Kenwood" interface was developed inside the CSP protocol that was based on the KISS interface.
The main problem faced with the link was the modulation incompatibility between radios. The AX100 uses G3RUH FSK modulation and the TM-D710G uses FM modulation with two-tone AFSK (Amplitude Frequency Shift Keying) encoding that is generated by its built-in TNC (Terminal Node Controller).
Figure 10: Raspberry Pi 3 and RFM69HCW module used to collect scientific data (image credit: ITCR)
1) Marco Gómez Jenkins, Julio Calvo Alvarado, Ana Julieta Calvo, Adolfo Chaves Jiménez, j, Johan Carvajal Godíneze, Alfredo Valverde Salazar, Julio Ramirez Molina, Carlos Alvarado Briceño, Arys Carrasquilla Batistai, "Irazú: CubeSat, Mission, Architecture and Development ," Proceedings of the 67th IAC (International Astronautical Congress), Guadalajara, Mexico, Sept. 26-30, 2016, paper: IAC-16-B4,1,8 ,URL available at ResearchGate: https://www.researchgate.net/profile/Julio_Calvo-Alvarado-publication/308804145_Irazu_CubeSat-Mission_Architecture-and_Development/
2) Marco Gómez Jenkins, Julio Calvo Alvarado, Ana Julieta Calvo, Adolfo Chaves Jiménez, Johan Carvajal Godínez, Alfredo Valverde Salazar, Julio Ramirez Molina, Arys Carrasquilla Batista, Luis Diego Monge Solano, "Monitoring of Carbon Fixation in Costa Rican Rainforests through the use of CubeSat Technology," Proceedings of the 11th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 24-28, 2017, paper: IAA-B11-0906P
3) Marco Gómez Jenkins, Julio Calvo Alvarado, Ana Julieta Calvo, Adolfo Chaves Jiménez, Johan Carvajal Godínez, Alfredo Valverde Salazar, Julio Ramirez Molina, Luis Carlos Rosales, Esteban Martinez, Arys Carrasquilla Batista, Luis Diego Monge, Carlos Alvarado Briceño, Juan José Rojas, Marcos Hernandez, "Project Irazú: Advances of a Store & Forward CubeSat Mission for Environmental Monitoring in Costa Rica," Proceedings of the 68th IAC (International Astronautical Congress), Adelaide, Australia, 25-29 Sept. 2017, paper: IAC-17-B4.1.11
5) Trevor Koritza, John M. Bellardo, "Increasing CubeSat downlink capacity with store-and-forward routing and data mules," IASTED International Conference on Wireless Communications, Alberta, Canada. July 2010, URL: http://users.csc.calpoly.edu/~bellardo/pubs/wc10.pdf
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).