Cubesat Communication Board: Space Twitter
The flight unit called “Space Twitter”, conceived under the UDRAGON and MISTRAL projects, leaded by Telespazio, allows telecommunications and telemetry functions at low data rates, with constant coverage of the mission by the ground stations, thanks to an innovative concept of “low cost” ground stations. The unit can also act as “interlink” system between small satellites, exchanging i.e. data for the synchronization of the flight in formation (real-time kinematic RTK positioning: pseudorange, carrier-phase measurements and ancillary data). Space Twitter is an automatic low-speed data communication system for satellites in LEO orbit. It is equipped with a navigation subsystem, one for radio transmission (UHF / VHF) and one for data processing. Thanks to these subsystems and to the onboard software, the Space Twitter is capable of sending Telemetry and receiving remote controls in a completely automatic and independent way from the satellite that hosts it.
Mistral and U-Dragon projects
Euro.Soft collaborated with Telespazio in the development of a functional prototype of the entire TLC subsystem, in the previous MISTRAL and UDRAGON projects. In particular, for the prototype of the on-board unit, the OBC and Radio UHF / VHF cards have been acquired on the market, while the navigation unit has been defined at the breadboard level by Euro.Soft, starting from the Novatel core and integrating new functions. enabling the visibility algorithms of the Space Twitter. A flight unit is ready for flight qualification.
Characterised by the use of new ultra-light alloys, materials and “green” technologies, MISTRAL also integrates health monitoring systems, thanks to sensors inserted in critical parts such as the deployable heat shield, whose opening can be modulated for active control of the re-entry trajectory. In addition, a micro-platform management system called ‘Space Twitter’ allows the capsule in orbit to automatically and continuously send ‘tweets’, i.e. short messages, to communicate its operational status to a series of dedicated ground micro-stations.
The programme was developed by Telespazio, leading a group involving the main industrial and academic players in the sector in Campania, such as OHB Italia, CIRA, Euro.soft University of Naples Federico II, ALI, TSD Space, SAB Aerospace, SRSED, Powerflex, Lead Tech, Antares, CNR, ENEA and University of Naples Parthenope.
The MISTRAL project has been co-financed by the European Union (www.ec.europa.eu), the Italian State and the Campania Region (www.regione.campania.it) within the framework of the POR Campania “FESR 2014-2020” (www.ec.europa.eu). (The project started on 01/10/2015 and ended on 30/11/2020.
Space Twitter design
From the point of view of external interfaces, the connection with the host satellite is highlighted. The Space Twitter is powered by the host satellite through 3 different lines (power) managed by the satellite’s EPS. The satellite can supervise the status of the Space Twitter (Hk line) and control it via a Command line. Two separate lines allow the satellite telemetry (TM packet) to be sent to the ground and to receive remote controls (Send TC). Fault control is a digital input of the Space Twitter that allows the latter to verify the correct functioning of the satellite thanks to the implementation of a watchdog mechanism.
Apart from its use as an “interlink”, as regards communications to the ground, the Space Twitter can be used as:
- simple transponder, Space Twitter is used for tracking purpose. Space twitter communicates its identification code, position, speed and orbit at any passage on the dedicated ground stations, the reception of this telemetry is done by the micro stations, i.e. by the low cost UHF/VHF ground stations.
- automatic communication system in two configurations:
- secondary communication element (in those missions where the primary communication is not frequent enough for the correct transmission of telemetry and reception of remote controls)
- primary transmission element in missions where there is a need to transfer small data but very frequently.
This Operative Mode “Automatic Communication” relates to the use of all Space Twitter functions. In particular:
- all the units are turned on,
- the visibility of the ground stations is automatically calculated
- the TMs are received by the SAT and managed in a temporary buffer.
- Traditional Communications System, This Operative Mode “Traditional Communication” is related at the usage of Space Twitter as a traditional communication board, without using its capability to automatically process the visibility with the Ground Stations.
Automatic Communication function
In the transponder and Automatic Communication operating modes, the Twitter Space performs the processing of the visibility algorithm.
The function determines the “visibility cones” for all the Groud Station. The visibility cones are a function of:
- Satellite Altitude
- Type of Station (antenna, natural obstacles ecc..)
- Range of Station orientation and tracking capability.
The function determines:
- if the Satellite is in visibility with GS
- the time of entry into the visibility cone.
- the time spent in the visibility cone.