A space system consists of a space and a ground segment. The space segment is the satellite, or a group of satellites, put into orbit by a launch vehicle and performing tasks in space. The ground segment consists of all the supporting infrastructure on Earth, including the radio station used to exchange data with the space segment and the team operating the entire system.


Overall architecture

The architecture of the mission is comprised of two segments: a space segment (the satellite) and a ground segment (the ground station and mission control). Together they create the system which includes all the processes related satellite functions, mission control and data handling.

Space segment

Efir’s space segment consists of a single 1U CubeSat placed in Low Earth Orbit (LEO) at an altitude of 400 kilometers and an inclination of 51.6 degrees. With this orbit, Efir will stay in LEO for a little more than a year, overflying southern Europe, most of Asia, all of Africa, all but the extreme southern tip of South America, all of Australia and most of North America.

This will allow us to observe, measure and compare light pollution in the most densely populated urban areas globally using two payloads: a wide field of view camera and a set of bright LEDs. The latter will emit specific signals over designated areas of both high and low light pollution, allowing citizen scientists – or just about anyone with a smartphone – to visually observe the satellite from the ground and measure light pollution levels or read Morse code messages using a dedicated app.

Payload

Camera: An off-the-shelf commercial camera with a very wide field of view will allow Efir to observe the world’s largest urban agglomerations at night. Spacial resolution is not critical for this mission, but light sensitivity will be significantly improved in order to measure illumination levels and airglow outside urban areas. The wide field of view will allow the satellite so observe a very wide swathe of Earth when pointing at nadir, collecting data on light pollution with each passing.

High-power LEDs: A set of light emitting diodes (LEDs) powerful enough to provide a visible magnitude to Earth observers. Depending on the visible magnitude, observers will be able to determine the amount of light pollution: the less visible the satellite, the more polluted their local sky is. Additionally, the light emitted from the LEDs will be analyzed through spectrometers to determine the atmospheric composition in areas with high levels of light pollution.

Minor Universal Tasks (MUTs): MUTs refers to a variety of small payloads that increase the scientific output of the satellite. In this case, a miniature spectroscope will be targeted with a ground-based laser beam and provide basic data on the composition of the atmosphere.

Nadir side of Efir, showcasing the LEDs and sensors. Copyright SAT-1 Initiative.  Nadir side of Efir, showcasing the LEDs and sensors with deployed antennas. Copyright SAT-1 Initiative.  Another view of the satellite. Copyright SAT-1 Initiative.


Platform

The payloads will be supported by a standardized set of subsystems, including power management, attitude determination and control (ADC), communications, a navigation sensor, an on-board computer and a structure with a thermal management system. Uplink-downlink will be carried out in the UHF band, allowing amateur radio operators across the world to receive data packets. A set of magnetometers and magnetorquers will provide 3-axis attitude determination and control, respectively. Like all CubeSats, power will be supplied by solar panels with 27% efficiency and a set of batteries.

Ground segment

The ground segment consists of a transceiver station, a data processing facility and a mission control and operations center. Three possible sites are being studied to situate the station:
Sofia, preferably a university campus site, allowing easy access for both Initiative operators and student trainees and good infrastructural availability.
Plana region, where Bulgaria’s principal satellite communications facility is currently located. The region is surrounded by low mountains, which isolate it from stray emissions from cities, while having the least rainfall in the country and generally in an excellent location to send and receive satellite transmissions.
Kondofrey, a small village some 60 km southwest of Sofia. Kondofrey bears the same geographic benefits as Plana, however it was a secondary location for the satellite communications center and thus it never hosted a large installation.

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