Motor Controls in Space

The Challenge of Space Radiation

Spacecraft must operate in the presence of high levels of radiation, including cosmic rays, solar particles, and trapped particles in the Van Allen radiation belts around Earth. These types of radiation can cause serious issues for electronic systems:

1. Single Event Upsets (SEUs): High-energy particles can strike a microcontroller, causing bit flips that may change data values or disrupt instructions.

2. Latch-up: This can occur when charged particles cause parts of an integrated circuit to conduct too much current, potentially leading to system failure or burnout.

3. Total Ionizing Dose (TID): Over time, radiation exposure accumulates, causing degradation in electronic materials and possibly leading to malfunction or failure.

In motor control systems, these radiation-induced effects can have critical consequences. An error or failure could result in a robotic arm malfunction, failure to deploy a solar panel, or rover immobility. These outcomes can jeopardize an entire mission, making reliable electronics paramount.

Radiation-Hardened Microcontrollers: A Solution for Space Motor Controls

Radiation-hardened microcontrollers are specially designed to withstand radiation’s adverse effects. Here’s how they support motor controls in space:

1. Mitigating SEUs and Latch-up
   Radiation-hardened microcontrollers use hardened memory and logic circuits that can absorb or deflect radiation particles, reducing the likelihood of SEUs. Special materials and redundant circuitry are often used to minimize SEU risks. For instance, Triple Modular Redundancy (TMR) is a common technique where operations are repeated across three redundant circuits, and the majority output is accepted, ignoring any errors from a single event upset.
   To address latch-up, radiation-hardened microcontrollers integrate latch-up prevention circuitry and protective design elements. These microcontrollers are often tested rigorously under radiation to ensure their resilience in space conditions.

2. Enhanced Total Ionizing Dose (TID) Tolerance
   Materials and designs in radiation-hardened microcontrollers are chosen to withstand a high total ionizing dose, allowing them to function correctly over extended space missions. Many radiation-hardened microcontrollers specify TID tolerance levels, ensuring they will continue to operate despite prolonged exposure to cosmic radiation.
   In motor control systems, this stability is crucial for long-term functionality. For example, radiation-hardened microcontrollers that control a rover’s wheels must withstand years of radiation exposure without significant degradation, enabling continuous exploration.

3. Redundancy and Fault-Tolerance
   Redundancy is a key feature in space electronics to ensure system reliability. Radiation-hardened microcontrollers often employ on-chip memories with error-correcting codes (ECC), which can automatically detect and correct minor bit errors, and watchdog timers, which help detect system anomalies and initiate recovery procedures.

In motor control applications, fault tolerance allows the system to maintain operation even if a radiation event affects a component. This ensures that critical tasks, like maintaining solar panel orientation, continue uninterrupted.

Key Applications of Radiation-Hardened Motor Controls in Space

Radiation-hardened microcontrollers play a vital role in a variety of space missions. Some examples include:

• Mars Rovers: For planetary exploration, motor controls manage rover movement, robotic arm positioning, and instrument adjustments. Radiation-hardened MCUs help to ensure mobility and functionality despite the harsh environment.

• Space Telescopes and Satellites: Motor controls are used to orient mirrors, lenses, or other instruments. Radiation-hardened microcontrollers keep these instruments stable and correctly aligned.

• Deep-Space Probes: Radiation-hardened motor controls are essential in long-duration missions like Voyager, where microcontrollers control adjustments to the probe's orientation to maintain communication with Earth.

Motor Control Use Case: Reaction Wheels

One specific example where radiation-hardened microcontrollers are critical to supporting motor controls is the case of reaction wheels. Reaction wheels are used for several important aspects of space missions, including:

• Positioning and orienting telescopes, antennas and cameras to precisely target celestial objects or Earth

• Stabilizing spacecraft, keeping them pointed in a fixed direction despite external disturbances, such as solar radiation pressure or gravitational forces from other celestial bodies

• Performing rotations or holding steady orientations without using thrusters, which saves fuel and is critical for extended missions

• Providing fine control for maneuvering, ideal for scientific spacecraft requiring precise positioning for measurements

• Serving as a backup to other attitude control systems, like gyroscopes or thrusters, increasing the reliability of the spacecraft

Each reaction wheel consists of a motor-driven flywheel mounted on a spacecraft. The speed and direction of the flywheel’s rotation are controlled by an onboard computer. Radiation-hardened microcontrollers control the brushless DC motors in reaction wheels, ensuring smooth and precise operation.

Radiation-hardened microcontrollers ensure reliable control and communication with the wheels when spacecraft are exposed to high levels of radiation that can damage or disrupt conventional electronics. They monitor the performance of the reaction wheels, detecting anomalies like excess vibration, power consumption, or motor speed issues. If a wheel fails, the microcontroller reconfigures the system to rely on backup wheels.

Reaction wheels also consume significant power when changing speed. Microcontrollers manage the power supplied to the motors, optimizing efficiency while protecting the spacecraft's power system.

Future Trends: Advancements in Radiation-Hardened Technology

As space missions become more ambitious, new radiation-hardened microcontrollers are being developed to offer greater processing power, enhanced durability, and smaller footprints. This miniaturization and increased power efficiency will allow for more complex motor control systems that can achieve even greater precision and reliability.

Moreover, advancements in software algorithms and machine learning for fault prediction are allowing motor control systems to predict potential issues and self-correct, enhancing mission longevity and success rates.

How VORAGO MCUs Support Motor Control

In space applications, selecting the appropriate processing hardware is crucial for balancing performance, cost, and development time. Radiation-hardened microcontrollers (MCUs), such as VORAGO Technologies' VA41630, offer a cost-effective and efficient solution for critical motor control functions. These MCUs enable rapid prototyping, allowing engineers to implement design iterations in minutes, a significant improvement over the hours or days typically required with Field Programmable Gate Arrays (FPGAs).

While FPGAs provide robust solutions for scenarios demanding higher power or multiple implementations, such high-performance requirements are often unnecessary in space applications. Radiation-hardened MCUs present a more optimal price-performance ratio for tasks such as controlling antennas, reaction wheels, instrument interfaces, and robotic arms. Additionally, these MCUs offer more direct access to fine-tune control settings and reduce CPU load by shifting key functionalities from software-defined to hardware-based implementations.

The VA41630, for instance, is a radiation-hardened Arm® Cortex®-M4 microcontroller featuring 256kB of program memory, 64kB of data memory, an 8-channel ADC, a 2-channel DAC, and interfaces such as Ethernet and SpaceWire. Its high reliability and performance make it well-suited for space-based motor control applications.