# Novel 3U Stand-Alone CubeSat Architecture for Autonomous Near Earth Asteroid Fly-By
## 4 Subsystems Analysis
### On-Board Data Handling  
Depending on the configuration of the satellite, the OBC can have many functions. For the mission discussed in this paper, functions like attitude determination and control, and initial payload image processing are done on separate processors located inside those subsystems. Thus, it is assumed that the main functions of the central OBC is: housekeeping, data processing and storage, autonomous operations, and communication.  
There are several key factors that determine if a specific OBC is compatible with the mission. Important factors like the specific available peripherals and types of storage can be of importance when looking at compatibility with other subsystems. However, for the scope of this paper, this will not be considered. Instead, the focus (and trade-off) will be on--power consumption (PC), volume, mass, clock frequency (CF), and memory storage (MS). Power, mass, and volume are obvious factors due to the 3U design constraint. The clock frequency of the processor in the OBC is of importance as it determines how many computations can be done per second. This (together with other factors like word size) determines what functions are possible to have on the OBC. Especially due to the required autonomy, the navigational aspects of the mission, and the data processing, the computational requirements are relatively high for this mission. Next to the clock frequency, the data storage capabilities are also important. Thus, to increase the scientific output of the mission, a large amount of data needs to be stored on-board during this critical phase. Table 5 reports the characteristics of the most promising COTS OBC available.  
Figure 7: Off-the-shelf X-band antennas data-rate in function of typical NEA fly-by distance from the Earth (assuming 2W of Radio-Frequency (RF) transmitting power).  
The low power usage of the Endurosat OBC, AAC Clyde Space KRYTEN-M3, Hyperion Technologies CP400.85, GomSpace NanoMind A3200, and the ISIS iOBC are immediate advantages over other options. Combining this with data storage capabilities and high clock frequencies, the CP400.85 and ISIS iOBC remain as two of the most promising options.  
The payload section highlighted two main instruments, Hyperion Technologies IM200 and Thoth Argus 2000, that can be used to define the required OBC memory to store data. This is why data can be either downlinked during the scientific phase or after it. This second option clearly requires on-board storage and looks more promising for a low resource CubeSat. On-board stored data will be VIS images from IM200, IR data from Argus 2000 and navigation data from the autonomous GNC system. IM200 data acquisition can be computed around 22 MB/s, while Argus 2000 is approximately around 6 KB/s, and navigation data are negligible in size. This means that the required on-board memory is triggered by IM200 output, and, for example, Hyperion Technologies CP400.85 offers up to 48 min of scientific phase thanks to the 64 GB optional memory. Clearly, to ensure a complete scientific phase, the NEA target characteristics will influence the data acquisition strategy in order to have a larger or smaller scientific phase. The result of the trade-off process showed that for this application, Hyperion Technologies CP400.85 is the best option, especially due to its compact volume, low mass, and large memory storage.