Delfi-n3Xt Structure, Mechanisms & Thermal Control
The structural subsystem (STS) has an outer structure which complies with the standard triple-unit CubeSat dimensions. This was one of the main constraints originating from the mission statement. A larger satellite would introduce a higher launch cost, but more importantly, could reduces our focus in miniaturization. A smaller satellite would limit the amount of technologies we could take aboard and is very difficult with our single-point-failure tollerant design philosophy.
The outer structure consists of two detachable L-shaped side panels, a CNC-milled top and bottom panel (TOP & BOP) and a stack of Printed Circuit Boards (PCBs) held in place with rods and distance tubes.Detachable L-shaped side panels are chosen to provide easy access and mounting, while keeping manufacturing relatively simple. Midplane standoffs connecting the rods to the side panels provides additional stiffness.
The inner structure consists of a stack of PCBs on rods, which are distanced with tubes. However, as the standard system bus for Delfi-n3Xt deviates from the PC/104 standard used in the majority of CubeSat systems also a slightly different PCB lay-out is chosen which provides more space for electrical circuits on the PCB and is fully symmetric.
Delfi-n3Xt has deployment mechanisms for the solar panels and VHF/UHF antennae. The system is based on Delfi-C3 heritage, which had 12 of these systems of which all were deployed successfully. The concept is rather simple; a restraining wire holds the solar panel or lid of the Modular Antenna Boxes (MABs) in place and is burned by a redundant low power thermal knife. The antenna inside the MABs is made of measuring tape, which shows a springiness behaviour when the lid is opened. After deployment, the lid with optical tape on top closes again to prevent high local thermal influx. The solar panels have a hinge with deployments stops and two springs, which keep the solar panel at the desired angle once deployed. For all deployment mechanisms a power of 1.92 W is required for between 3 and 12 seconds.
The thermal control of Delfi-n3Xt is passive. With heat radiators, heat sinks and thermal isolation inside the satellite and optical tapes on the outer structure of the satellite, all systems will be kept within their nominal operating temperatures. A thermal finite element analysis has been performed providing insight in the thermal issues which needed to be dealt with. The items which have been identified as critical are the (dis-)charging of the battery system which should be above 0 ºC and the ignition of a cold gas generator of the micropropulsion payload which should be above 10 ºC. As ignition for the T³µPS can take place in a large time window the system does not need to be above this temperature all the time. For the batteries, the combination of some insulation, their thermal capacity and optical tapes surrounding the battery system keeps the temperatures in the required range. The rest of the satellite is optimized for a thermal range which centers around ambient temperatures.