How to pick up a suitable CubeSat ADCS (Attitude Determination and Control System) 
components or an integrated system for your mission?
 

Authored by Thomas Yen, 2021.05.01
Revised by Afan Huang, 2024.09.03

 
In engineering, there is no absolute "best" solution—only the most suitable one. This has led to the current trend of building Attitude Determination and Control Systems (ADCS) by either customizing space components or, in some cases, developing proprietary attitude determination and control components. 

 
As the era of space agency-driven projects comes to a close, commercial clients are increasingly turning to Commercial-Off-The-Shelf (COTS) ADCS components. Additionally, integrated ADCS solutions are now available, offering the benefits of reduced mission development time and costs. 

 
To make informed decisions, it is crucial to understand the specifications, advantages, and disadvantages of these components and systems. This article provides guidelines to help analyze your mission requirements and determine the appropriate pointing accuracy and slew rate for your ADCS.

 

The satellite pointing accuracy is primarily determined by the functional payloads of the satellite, which are typically cameras for remote sensing satellites or antennas for communication satellites. For remote sensing applications, pointing accuracy of up to several hundred arcseconds is frequently required. In contrast, communication satellites typically necessitate pointing accuracy of approximately 1 degree when equipped with S-band or X-band antennas. If the satellite is equipped solely with UHF and VHF antennas, a less precise pointing accuracy of up to 10 degrees may be deemed acceptable, given that these antennas are typically omnidirectional. However, it is important to note that the quality of communication may be compromised if the satellite's attitude drifts.


 
Furthermore, if the satellite incorporates optical payloads, such as nadir-facing cameras or star trackers, the Attitude Determination and Control System (ADCS) is responsible for ensuring that the sun does not enter the field of view (FOV) of these instruments.

 
For solar panels, particularly those designed for deployment, optimal power generation necessitates precise sun-pointing. When utilizing deployable solar panels, it is advised that the pointing accuracy to the sun be maintained within +/- 10 degrees.

 
These are the key factors to consider when determining the pointing accuracy requirements for your mission. Next, we will discuss the slew rate.

 
In most satellite operations, it is generally undesirable for the satellite to exceed an angular velocity of 5 degrees per second (relative to the Earth-centered, Earth-fixed frame). If the satellite rotates faster than this threshold, it is often referred to as "tumbling." Therefore, the ADCS slew rate should typically be set to less than 5 degrees per second. The required slew rate can be determined by considering the number of specific locations your payload needs to target within a given timeframe.

 
It is important to note that integrated ADCS systems, reaction wheels, or magnetorquers may not always specify their slew rate directly. In such cases, you can calculate it using the moment of inertia (MOI) of your satellite and the maximum torque provided by the ADCS.

References

[1] J. R. Wertz, D. F. Everett, and J. J. Puschell. (2011). Space Mission Engineering: The New SMAD. Space Technology Library.

[2] F. L. Markley and J. L. Crassidis. (2014). Fundamentals of Spacecraft Attitude Determination and Control. Space Technology Library.