Design status of the Delfi-Next nanosatellite project

Delfi-Next is the second project within the Delfi nanosatellite development program of Delft University of Technology. It will provide students hands-on experience, facilitate technology demonstration for innovative miniaturized space technology from the Dutch space sector and allow advancements in satellite bus performance compared to its predecessor Delfi-C3. This paper will describe the mission and provides insight in the design status and trade-offs of each bus subsystem at September 2010. A micropropulsion system from TNO, an in-orbit configurable radio from ISIS BV and amorphous silicon solar cells will be demonstrated onboard Delfi-Next. The electrical power subsystem consists of deployable solar panels, a central power management unit, a battery system and local power regulation units on each printed circuit board. The central power management unit uses redundant maximum power point trackers for each solar panel and distributes the acquired power to a standard system bus on a fixed single supply voltage of 12V, the battery system and a shunt for excessive power. The communication subsystem consists of two redundant radios transmitting a continuous 1.2 9.6 kbps signal on a 145 MHz carrier frequency, a high data rate S-band transmitter, a receiver and a set of deployable antennae in a turnstile configuration. The downlink is received by a global distributed ground station network consisting of several universities and radio amateurs. Onboard data handling is performed by a hot redundant onboard computer, which manages and acquires measurement data from local subsystem microcontrollers by means of an I2C data bus. Because the standard implementation of I2C lacks failure tolerance it is supplemented with bus buffers on each local system which will isolate malfunctioning nodes from the main bus when necessary. A custom designed spacecraft structure optimized for accessibility will provide the basis for all physical subsystems which are made compliant to a standardized form factor. The structure complies with the outer dimensions of a triple-unit CubeSat. Passive thermal control based on heat sinks and optical properties of surface materials will keep components and subsystems within the required thermal range. Attitude determination and control will be performed by a suite of sensors, actuators and processing algorithms to demonstrate active attitude control functionality as a baseline for future Delfi missions. Future Delfi missions to demonstrate formation flying capabilities are foreseen, potentially within the QB-50 network for thermospheric research or demonstration missions for the OLFAR moon-orbiting radio telescope.