Technical requirements¶

Functional requirements¶

Functional requirements define what functions need to be done to accomplish the objectives of the mission. In this way, the following requirements are defined:

• The satellite shall send one RF beacon regularly with a period time equal to 60 seconds = 1 minute.
• The satellite may send its GPS coordinates information inside the beacon frame.
• The satellite may send system state information (like temperature) inside the beacon frame.
• A ground station situated at the Télécom SatLab (Toulouse, France) shall be inside the satellite footprint at least twice a day.

Performance requirements¶

Performance requirements define how well the system needs to perform the functions previously defined. Also they determine quantitative parameters that will set bases for the later technical measures specification. These concepts lead us to the performance requirements shown below:

• The beacon signal shall comply RTTY specifications.
• The communication time with the ground station shall be long enough in order to assure that one complete beacon frame can be received.
• The RF emitter device may be implemented with the low cost, 434 MHz, 2-FSK transmitter, available at the lab. Product information: Aurel, TX-4MAVPF10.
• If on board GPS reception is implemented, the device shall be accurate enough in order to assure, for each coordinate (latitude, longitude and attitude), an absolute error smaller than 50 m.

Interface requirements¶

Once the system components are defined, a block diagram showing the main subsystems, their interconnections, and the external interfaces is a powerful tool to define the interfaces and interactions. By this way, the nodes represent each subsystem and the links represent each interface. There are two types of interfaces, internal and external. The internal interfaces are the links representing the interactions between all the subsystems. By the other hand, the external interfaces are the links representing the interactions between the main system and the rest of the world, outside the product boundaries. There are different types of interfaces: mechanical, electrical, data protocol, etc.

System/subsystems interactions block diagram.
!!

The interface requirements are the set of specifications that both linked nodes need to meet in order to have a proper and coherent system behaviour and interactions.