Small satellites have definitely found their place in today’s space industry. They can deliver new technologies into orbit in a short amount of time for a fraction of the price of larger satellites with more launch opportunities available. New technologies can be demonstrated and evaluated much faster and cheaper by lowering the financial risk involved.
TRISAT is an important step towards internationalization of the Slovenian space industry by gaining higher readiness levels for technology, promoting space engineering and fostering international collaboration. The innovative system miniaturization and new technology demonstration by the TRISAT mission would provide further market competences for new products being developed by Slovenian companies. Despite the fact that TRISAT is actually a constraint driven nano-scale spacecraft by ESA standards, its technology outcome proves the concept of system miniaturization with reasonable application output in terms of obtainable multispectral Earth remote sensing data. Obtained multispectral remote sensing image data will be used for academic research purposes and available to potential users, and radio amateur community.
TRISAT is an educational small satellite mission which aims to establish a mutual cooperation between Slovenian university students and the Slovenian space industry. It would help facilitate a knowledge and technology transfer between the university and the economy through innovations and technologies and with effective support service of entrepreneurship and innovative ecosystem, resulting in a symbiotic relationship between both spheres.
The TRISAT mission is primarily led by the On-Board Data Handling (OBDH) team, which was established in 2009, as part of University of Maribor’s involvement in the European student Moon Orbiter (ESMO) mission from ESA. The team currently combines students from many different fields of expertise. Through the TRISAT mission, they would get a unique and inspirational opportunity which would provide them with valuable and challenging hands-on space project experience. The TRISAT mission would also lower the entry-level for space exploration, which would allow the university to carry out various space-related project activities. This would attract younger students to the OBDH team, expanding the amount of students with experience in space technologies who graduate from the University of Maribor.
The TRISAT mission also contains a technology demonstration aspect, within which we will develop miniaturized flight hardware consisting of the Electrical Power System (EPS) subsystem, the Communication Module (COMM) subsystem and the On-Board Computer (OBC) subsystem. They will form the base of a basic OBDH platform, which will allow different payloads to be delivered into orbit. The development of the subsystems will be performed by university students.
During phase A of the proposed project University of Maribor organized a joint workshop. All partners presented feasibility studies of their subsystems and payloads to the invited technical experts from ESA. Using the valuable feedback received from ESA’s experts all members have refined the basic requirements and constraints of the TRISAT mission. The requirements and constraints were then reconciled between the partners with special attention given to the required size and volume for all on-board subsystems, mass and communication constraints, harness implementation, mission life time and improving the performance of the primary imager payload. This marked the conclusion of phase A.
In addition to the OBDH platform, University of Maribor will provide a complete ground segment for space operations of the TRISAT spacecraft using the Software Defined Ground Station (SDGS) at the Faculty of Electrical Engineering and Computer Science. The SDGS was a result of an already completed ESA project primed by the university.
It will be used to operate the spacecraft and to retrieve and process telemetry and payload data. The ground segment will also be used for testing, verification, validation and demonstrations of the communication subsystems, first on the ground and afterwards in space. This will provide hands-on experience to students on spacecraft operations and also allow us to test new ways of communication, especially different modulation techniques. Highlights of the spacecraft system design are:
- A multispectral SWIR imager with ground sampling distance of 105 m at Nadir and altitude of 700 km, F number of 2, focal length of 100 mm, field of view of 5.5°, Swath of 67 km, estimated SNR up to 50 dB at Nadir, spectral range from 0.95 µm to 1.67 µm using Optec optics and a low-low noise Sofradir sensor with 4 narrow band filters and an additional panchromatic region.
- A CCSDS compatible full-duplex communication module (COMM) with a SoC design approach providing UHF downlink and VHF uplink.
- A CCSDS compatible S-band full-duplex communication module with up to 4 Mbps downlink, up to 4 Mbps uplink.
- An Electrical Power System (EPS) that combines Analog Maximum Power Point Tracking with a Transformer Coupled Charge Sharing battery balancer with a SoC design approach for monitoring and control of the FDIR policy, including basic control of all on-board subsystems and payloads through direct commanding.
- An On-board Computer (OBC) based on a SoC design approach using a fault tolerant PicoSky FT soft-core processor including 128 Mbit of EDAC protected non-volatile in-orbit programmable MRAM memory, 16 Mbit of EDAC protected SRAM memory with data scrubbing, a 512 Gbit EDAC protected mass storage device and a new fault tolerant hardware accelerated task scheduler for hard real time applications and advanced FDIR policies designed for the embedded real time operating system. The OBC also incorporates an additional asynchronous interface for the GNSS module.
The overall system also incorporates:
- An integrated all-in-one ADCS subsystem module with an integrated star tracker, reaction wheels and a full set of attitude control algorithms to provide 3 axis stabilization and pointing accuracy of less than 0.1°, which is required by the primary SWIR imaging instrument.
- A hot redundant on-board CAN bus connecting all subsystems and payloads, which eliminates single point of failures and improves OBDH redundancy.
- LVDS communication channels between the SWIR imaging instrument, the OBC and the high throughput communication module to improve transfer times for large amounts of payload data and minimize their impact on the CAN bus latency.
- SEE mitigation on COTS components with an advanced fault tolerant FPGA SoC design approach, including Latch-up protection on all vulnerable components.
- Non-stackable harness which simplifies the engineering approach coupled with star topology power distribution to simplify the FDIR implementation on the EPS subsystem.
During normal operating conditions the spacecraft will operate in idle mode, where it will point towards the sun, gather energy. The imaging payload and the high throughput communication subsystem will be turned off. The satellite will periodically transmit unsolicited TM data as well as respond to TC requests from the GS. Other modes will be entered via the OBC scheduler, which is synchronized to the GNSS time and location.
The satellite’s CCSDS compatible full-duplex communication module will operate in VHF and UHF radio amateur bands. Extensive telemetry will be provided by the satellite’s on-board data handling as part of the beacon including many house-keeping parameters. A novel Total Ionization Dose sensor value will be included within the beacon telemetry data, which will give useful information about the Total Ionization Dose accumulated during among satellite’s orbit. Furthermore, the telemetry will include satellite’s in-orbit location provided by the on-board GNSS receiver. As part of the radio amateur services the CCSDS compatible full-duplex communication module will act as a digipeater relaying CCSDS compliant data framing, which will be publically available to the radio amateur community. The satellite’s call sing will be S55XTR.
A typical in-orbit operation and demonstration cycle includes two phases, both entered via the scheduler commands. In the first imaging phase, the satellite will point the imager towards the earth’s surface and gather imaging data. Afterwards, it will return to idle mode. The data will then be stored inside the OBC’s mass storage, where thumbnails will also be generated. The second communication phase consists of transmitting the image thumbnails and, if requested, the whole images to the GS. A demonstration of high-speed in-flight on-board software upgrades is also planned. TRISAT is a small spacecraft, capable of capturing short-wavelength infrared spectrum images of the Earth. This remote sensing data could be used, for example, to:
- detect various vegetation patterns (green areas),
- assess damage caused by natural disasters, and
- detect volcanic dust.
The data obtained during the mission will be kept by the University and used for academic research purposes and will be made available to potential users. TRISAT spacecraft will remain operational for a minimum of six years in a day-night sun synchronous orbit with an altitude of 530 km.