# InnCube--A Wireless Satellite Platform to Demonstrate Innovative Technologies
## 2 Mission
### Scientific and Technical Goals and Payloads  
#### 2.4.1 SKITH (SKIpTheHarness)  
SKITH is the acronym for SKIPheHarness, which is a very compact description of the main idea. Within the InnoCube satellite, a wireless data exchange between all satellite modules, i.e., the onboard computer (OBC), ADCS, power distribution and conditioning unit (PCDU), up-/downlink transceiver and the payload is realized. It is the first time a satellite has been designed following this approach. In this mission we aim to demonstrate the SKITH concept for CubeSats. It features some fundamental advantages over a cabled harness, which will be elaborated in the following.  
The communication between on-board components within conventional satellites is based on a wired harness. Standard concepts used are point to point connections or bus structures e.g., Controller Area Network (CAN). Known issues with cabled connections are the risk of cable failures (due to broken wires or connectors), a high mass (up to 10% of total satellite [12]) and inflexibility to later design changes. The testability of the harness on an integrated satellite requires additional hardware or software effort, to inspect all connections.  
To overcome these issues, the chair for aerospace information technology developed a concept that replaces all internal wired data connection by low power wireless interfaces. Subsequently, all the aforementioned failure risks are obsolete. The satellite integration becomes easier and errors due to inaccurately assembled connections are impossible, at least for data interfaces, as there is still the need for power transmission lines.  
Figure 2: Worst case power simulation.  
Another advantage of a wireless communication concept especially in satellites is the simplified implementation of redundancy. The wireless concept shares some characteristics with a wired bus structure. The common media is not the wire, but the spectral range of the transmission frequency. In a wired bus, the risk of one broken node, blocking the whole bus by shorting the data lines to ground, needs to be handled. A common solution for this is duplicating the bus and dedicated modules.  
In a wireless concept the risk of blocking the communication channel by one broken module is not given, once this module is powered off. Thus, the only need is the ability to separately power off each module, a need that is common on satellites.  
Finally testing of the interfaces can be done without a physical access to the integrated satellite. It is as simple as placing a receiver in the surroundings and analyze the data exchange in the satellite.  
The SKITH interface on InnoCube will be realized by using an EFR32 FG12 microcontroller by Silicon Labs. It is a commercial off the shelf (COTS) component that already includes a 2.4 GHz front end. All external elements needed are an antenna and a tuning circuit. Since the antenna is implemented on a circuit board (PCB) layout, there is only a small inductance that needs to be mounted aside the microcontroller. The HF modulation supported by the front-end is a Gaussian frequency shift keying (GFSK) or quaternary phase shift keying (QPSK). The maximum transmission power is 19 dBm, the receiver sensitivity for a GFSK modulation is \(-94.8\) dBm at a data rate of 1 Mbps [13]. The board layout for a complete SKITH interface, including antenna, needs 25 mm by 30 mm and will be included on all modules. An image showing a PCB carrying two SKITH interfaces is shown in Section 3.5.1.