Ground segment
The end-to-end communication scheme with the satellite is a critical element to ensuring mission success.
To this end, the EPFL Spacecraft Team also focuses on the design and development of the Ground Segment, operating in two distinct communication bands: UHF for TT&C (Rx & Tx) and X-band for payload data reception (Rx only).
How we're doing it
The UHF Ground Segment consists of two motorised Yagi-Uda antennas, using Software Defined Radios (SDRs) to enable efficient communication functionalities and strategies. This antenna system currently makes use of readily available, Commercial “Off-The-Shelf” (COTS) components operating in the RA 70cm band.
Furthermore, given the high data rates generated by the payloads on-board the satellite, the mission will make use of an X-band telecommunication scheme for the downlink of the payloads’ data. Given the short wavelength and low signal strength of the space-borne transmitted X-band signals, this requires fine ground tracking precision with a sufficiently high gain parabolic dish antenna system to ensure full signal reception.
Fructuous synergies between the EPFL Spacecraft Team and Callista, the EPFL astronomy association, were exploited; they led to the development a customised Antenna Pointing Mechanism (APM). This tailored antenna system was initially designed to accommodate a recycled 1.9 meter parabolic reflector, or dish, with a receiver tuned at 1420 MHz to detect the Hydrogen-21cm line emission. However, it was quickly decided to enhance the performance of the APM to be able to track Low Earth Orbiting (LEO) satellites as an added functionality. With the aim of maximising the cost-to-performance ratio, the specifications currently allow a 6°/s maximum tracking speed with a target pointing accuracy of less than 1°.
The UHF Ground Segment consists of two motorised Yagi-Uda antennas, using Software Defined Radios (SDRs) to enable efficient communication functionalities and strategies. This antenna system currently makes use of readily available, Commercial “Off-The-Shelf” (COTS) components operating in the RA 70cm band.
Furthermore, given the high data rates generated by the payloads on-board the satellite, the mission will make use of an X-band telecommunication scheme for the downlink of the payloads’ data. Given the short wavelength and low signal strength of the space-borne transmitted X-band signals, this requires fine ground tracking precision with a sufficiently high gain parabolic dish antenna system to ensure full signal reception.
Fructuous synergies between the EPFL Spacecraft Team and Callista, the EPFL astronomy association, were exploited; they led to the development a customised Antenna Pointing Mechanism (APM). This tailored antenna system was initially designed to accommodate a recycled 1.9 meter parabolic reflector, or dish, with a receiver tuned at 1420 MHz to detect the Hydrogen-21cm line emission. However, it was quickly decided to enhance the performance of the APM to be able to track Low Earth Orbiting (LEO) satellites as an added functionality. With the aim of maximising the cost-to-performance ratio, the specifications currently allow a 6°/s maximum tracking speed with a target pointing accuracy of less than 1°.
Objectives
The first academic radio-telescope in Switzerland, designed to detect and map the Hydrogen-21cm distribution throughout the Milky Way
Demonstration of the first LEO satellite tracking mechanism at the EPFL campus
Once this demonstration is validated, it shall be complemented by a custom-designed and built 2.4 meshed dish. The latter is in fact estimated to be ready by Q2-2023, and will enable the reception of space-borne X- band signals, with an estimated gain of 40 dB. A representation of the APM hosting this dish is shown in the next figure.
Naturally, this will be commissioned in due time using SDRs, with the aim of qualifying a student-built X- band Ground Segment to be used for space missions, such as the EPFL Spacecraft Team’s own CHESS mission in 2026, with a sufficient time-frame to adapt to the mission specifications.
