Keys toward precise attitude control

Authored by Austin Chang, 2021.05
Revised by Afan Huang, 2025.09

Failures of the attitude control system

In the complex world of satellite engineering, the Attitude Determination and Control System (ADCS) plays a crucial role in maintaining a satellite's orientation and stability. However, ADCS failures can manifest in various ways, from steady-state errors and prolonged response times to divergent control outcomes. While improper calibration of attitude sensors and actuators, along with misalignment between sensor, actuator, and system reference frames, are often culprits, two significant factors often fly under the radar: inaccurate mass properties and insufficient tuning of the attitude control system.  

The Practical Role of Attitude Control in Space Missions

Before diving into the technical challenges, it's essential to understand why precise attitude control matters across different space applications. For communication satellites, maintaining exact orientation ensures optimal signal strength and coverage areas, directly impacting data transmission quality and service reliability. Earth observation satellites require milliarcsecond-level pointing accuracy to capture high-resolution imagery and maintain consistent ground track coverage for monitoring applications such as climate change, agricultural monitoring, and disaster response. 

Two Critical Factors Affecting Attitude Control

Typically, engineers obtain mass properties through simulations using sophisticated Computer-Aided Design (CAD) tools like SolidWorks or Autodesk. However, the transition from simulation to reality is not always smooth. Two types of errors can emerge in practice: variations in mass properties over time and discrepancies between simulation results and the physically integrated hardware. 

Simulation-Reality Gap

First, we encounter variations in mass properties over time. These changes can stem from factors such as thermal variation, which causes satellite deformation due to differing thermal expansion coefficients across materials. Additionally, flexible components like solar panels can significantly alter mass properties during a satellite's operational life. The second type of error manifests as discrepancies between simulation results and the physically integrated hardware. This gap arises from a multitude of factors: inconsistencies in material densities, machining tolerances, assembly errors, and other unpredictable elements. These variables can cause the actual moment of inertia and center of mass to deviate significantly from CAD-based calculations. 

Variations in Mass Properties over Time

To address these challenges, a two-pronged approach is necessary. For the second issue – the simulation-reality gap – obtaining accurate measurements of your assembled satellite's mass properties is crucial. This data provides a real-world baseline that can dramatically improve the accuracy of attitude control systems. Dealing with the first issue – temporal variations – often requires embedding robust control techniques into the satellite's control logic. Interestingly, our experience suggests that this issue becomes truly significant only for larger satellites, where the characteristics of flexible bodies dominate the spacecraft's behavior. 

Factors for the failure of the attitude control system

Underpinning these issues lie the satellite's mass properties - critical mechanical characteristics that include total mass, center of mass (COM), moment of inertia (MOI), and product of inertia (POI). These properties, particularly the combination of MOI and POI forming the "inertia matrix" or "inertia tensor," are fundamental to effective attitude control. This concept is so central to our work that it inspired our company's name. When developing or integrating an ADCS, accurately defining these parameters is not just beneficial - it's essential. They form the backbone of proper attitude control algorithm propagation, ensuring that the satellite can maintain its intended orientation with precision. 

The mass of satellites in five categories
(The mini and medium satellites are categorized as small satellites.)
Source : What is a CubeSat. (2018). Canada.Ca. https://www.asc-csa.gc.ca/eng/satellites/cubesat/what-is-a-cubesat.asp

Tensor Tech’s Approach to Small Satellite Attitude Control

Recognizing the critical need for accurate mass property measurements, especially for smaller spacecraft, Tensor Tech has developed the TensorTestBed, an attitude determination and control system testbed. The TensorTestBed stands out in a market where most mass property measurement instruments are calibrated for objects weighing over 30kg. Our focus on nano-satellites fills a crucial gap in the industry, providing precise measurements for these increasingly popular smaller spacecraft. 

Learn More

Want to explore Tensor Tech’s ADCS TestBed System?  
〈Related Reading：What is a TestBed? Practical Application in Satellite ADCS〉

TensorTestBed, the satellite mass properties measurement and attitude control testing facility developed by Tensor Tech
 

Conclusion

Precise attitude control remains one of the most challenging aspects of satellite engineering, with mass property accuracy and proper system tuning serving as critical success factors. The TensorTestBed offers an effective solution for both our clients and internal teams to test the performance of their attitude control systems. Featured with a hemispherical air-bearing platform, the TensorTestBed provides one of the most accurate ways to simulate attitude control in a near zero-gravity environment on Earth. Without access to such specialized equipment, many struggle to properly tune their attitude control systems, resulting in suboptimal performance.Contact Us.