## 1 Introduction  
A CubeSat is a class of satellites with a defined size and form factor. A 1U CubeSat, for example, has dimensions of 10 \(\times\) 10 \(\times\) 11.35 cm\({}^{3}\) and a mass of up to 2 kg, as defined in the CubeSat Design Specifications from California Polytechnic State University (CalPoly) [1]. The document describes the mechanical, electrical, and operational specifications of CubeSats from 1U to 12U. However, it does not cover how the components in a CubeSat, i.e., both the bus and the payload, are interfaced. This lack of such a definition allows CubeSat developers the freedom to choose which interface method to use. More importantly, this aspect could cause incompatibility issues between components, and solving these issues could considerably consume time that could be used for other verification activities to ensure mission success [2]. Furthermore, CubeSat projects can be developed by multiple collaborators, and clearly defining an interface standard between developers during the initial phase could prevent project delays, compatibility issues, and increased costs while improving overall mission success. The first CubeSats developed used the stacking approach, where components were placed on top of each other using a connector. This interfacing method follows the PC/104 specifications [3] employed in embedded computers. The adoption of this specification to CubeSats defines the wiring harness, the printed circuit board (PCB) footprint, and the mechanical mounting of the boards, while the boards are stacked using 104-pin connectors. One of the first developers to employ the PC/104 specification in CubeSat applications is Pumpkin, Inc., who introduced the CubeSat Kit Bus (CSKB) [4]. The CSKB has become the de facto standard in CubeSat design and has been adopted by many commercial CubeSat developers. However, using the PC/104 specification in CubeSats has several issues. According to a survey in [5], 51% of 36 respondents agreed that the size of the connector is too big. Ref. [6] confirmed that the connector occupies up to 20% of the PCB space. This limits the board designers in placing components on the board, resulting in low PCB utilization. The stacking height of the connector is also considerable, making the spacing between boards particularly wide. Another issue is that the number of pins interconnecting the board is often not utilized to its fullest extent. This may increase the risk of human error when assigning pins and mapping during the development and integration phases. Even though there could be many unused pins, a harness is extensively used in stacked systems. Lastly, top boards need to be disassembled if there is a need to take out a middle board, especially during troubleshooting. This leads to additional development and integration time. There have been multiple efforts to resolve issues in using PC/104, specifically in terms of its connector. ISIS, for example, started to consider alternatives to CSKB connectors [7]. The company introduced CSKB Lite, two 28-pin connectors with just enough pins for full utilization. It is also backward-compatible with the standard CSKB connector. In the case of Nagoya University's NUCube satellites, where high-density interfaces are necessary [8], 144-pin connectors were used but with only a 9 mm stack-up height to reduce the volume occupied by the PCBs and a pitch of 0.50 mm to allow more space for components on the boards. This, in turn, made the connector incompatible with CSKB. Lastly, Korea Space University's KAUSAT-5 CubeSat used a flexible flat cable (FFC) connector instead of PC/104 to save volume and mass [6]. Despite these efforts, issues such as extensive use of harnesses and difficulty when assembling and disassembling were not addressed. Another interface method uses a dedicated PCB called a backplane board that provides mechanical and electrical connections between the bus and the payloads.