Development of the EXCITE IOD/IOV mission

Over the past twenty years, CubeSats have changed from simple educational tools into spacecraft that can achieve complex mission goals. As widely reported, this quick development has happened due their standardization to established form factors, lower cost per launch, and the rise of a commercial off-the-shelf (COTS) component market [1], [2], [3]. However, the increasing complexity of CubeSat missions has raised the need for new technologies in order to meet the high-performance requirements for the scientific, technological, and commercial goals that used to be achievable only with larger platforms. To prepare the next phase of CubeSat development, which involves on-board propulsion and advanced payloads, dedicated In-Orbit Demonstration missions to test new solutions in space are needed. In this context, the EXCITE mission was conceived to offer a high-performance 12U platform designed for multi-payload in-orbit demonstrations. The EXCITE mission is funded for Phase A and B by the Italian Space Agency in the frame of the ALCOR programme. The consortium involves the University of Pisa as prime-contractor and four Tuscan SMEs: Aerospazio Tecnologie, IngeniArs, MBI, CRM Compositi. The mission aims at the IOD/IOV of five different technologies. These payloads include: • a green monopropellant thruster that uses hydrogen peroxide, which will be demonstrated by performing a series of orbit altitude change maneuvers; • a group of four pulsed plasma thrusters, with a minimum impulse bit of 40 µNs, configured in such a way as to provide torque around the spacecraft longitudinal axis for fine attitude control and translational thrust, to demonstrate the possibility of performing proximity operations; • a reconfigurable S-band antenna, capable of electronically steer the beam and point to the ground station without requiring fine attitude pointing by the platform; • a COTS GPU, which will demonstrate on-board demodulation capabilities of advanced IoT waveforms transmitted from the ground and in-orbit spectral analysis of aggregated interference coming from the Earth; • an innovative passive thermal management system based on pulsating heat pipes designed for heat removal from a body-mounted solar panel. The mission will test the payloads in orbit starting from those which are safer to operate, then moving to the two propulsion systems, which are inherently riskier. In order to achieve these ambitious mission objectives, the design of the platform requires several advancements with respect to conventional Cubesat buses. The presence of on-board propulsion demands for mass optimization to maximise the delta-V capabilities of the platform; thermal transients during firing of the chemical thruster must be handled; and the high-power draw from the payloads requires additional power generation. All this must be integrated smoothly in a relatively small amount of volume dictated by the 12 U form factor. EXCITE addresses these challenges through several innovations aimed at the creation of an advanced bus platform (Fig. 1). First, the structural design will be based on composite materials, since they provide an ideal mix of low weight, high stiffness, and adjustable thermal and mechanical properties. In EXCITE, the main structure includes innovative resin, designed for low outgassing and resistance to microcracking during repeated heating and cooling. These characteristics makes them especially suitable for space, ensuring both strength and lasting size stability. In addition, the deployable solar arrays will use an innovative all-composite honeycomb panel. This design results in high specific stiffness and strength while keeping weight at minimum, resulting in over 30% of mass saving with respect to a standard aluminium-based solution [4]. The resulting power generation from the four deployable solar panels of EXCITE will supply the energy required to operate multiple payloads concurrently, particularly during propulsion and data-intensive experiments. These panels will boost the platform’s power capabilities up to 85 W at BOL. The platform will also have a body-mounted solar panel with an integrated thermal interface that will route the excessive heat to the pulsating heat pipes experiment which will transfer it to the cold side of the spacecraft. Alongside improved structural and power solutions, EXCITE includes high computational capabilities on board thanks to the integration of state-of-the-art microprocessor technologies for the OBC and the IoT-GPU. This feature is becoming ever more important as CubeSats move towards higher degree of autonomy and on-board data processing [5]. This system can manage multiple simultaneous payload operations, process large volumes of raw data, and support flexible mission planning. A commercial imager will be also embarked on the spacecraft to act as data generator and to capture pictures of the Earth. Thanks to its advanced capabilities, the EXCITE CubeSat platform aims not only at the demonstration of its payload but also sets itself as a viable platform for future scientific and commercial missions, including earth observation, supporting a long-term vision by creating the foundation for a new class of high-performance CubeSats. The paper outlines the outcomes of the preliminary design of the mission performed during the first months of the Phase A study, the main architectural choices of the platform and the technical challenges associated with the development of the innovative technologies involved.