The Role Of Oscillators In Satellites And Satellite Systems

By John Oncea, Editor

Oscillators, is there anything they can’t do? Well, of course there are. But what they can do – especially in space as part of a satellite system – is pretty cool.

Oscillators are mechanical or electronic devices that work on the principle of oscillation, generating a periodic fluctuation between two things based on energy changes. A simple type of mechanical oscillator is a clock pendulum, and a more complex example is an atomic clock – the most accurate timepiece in the world – which keeps time according to the oscillation within atoms.

Beyond their use in timekeeping, oscillators are commonly used in radio receivers, television sets, computers, cell phones, and more. They even used audio equipment such as synthesizers.

They are also a vital part of satellites, serving as the core of its navigation and communication systems, and in satellite systems, where they are used to syncronize signals between satellites that make up said system.

What Are Oscillators

Oscillators are essential for timing and syncronization in electronic systems, providing clock signals for digital devices and carrier waves for communication systems. According to TechTarget, “There are many types of electronic oscillators, but they all operate according to the same basic principle: an oscillator always employs a sensitive amplifier whose output is fed back to the input in phase. Thus, the signal regenerates and sustains itself. This is known as positive feedback. It is the same process that sometimes causes unwanted ‘howling’ in public address systems.”

How Stuff Works adds there are two main types of oscillators:

• Linear or harmonic oscillators, which produce a sinusoidal output and rely on the principle of resonance, where an LC (inductor-capacitor) or RC (resistor-capacitor) circuit is used to determine the frequency of oscillation. The Colpitts, Hartley, and RC Phase Shift oscillators are the most common types of linear oscillators.
• Relaxation oscillators, which generate a non-sinusoidal output such as a square or sawtooth wave. These types of oscillators work by charging and discharging a capacitor through a resistor at a rate determined by the RC time constant. Examples of relaxation oscillators include the unijunction transistor (UJT) oscillator and the 555 timer in astable mode.

Oscillators can produce signals from very low frequencies (below 20 Hz) to extremely high frequencies (up to several gigahertz) and their operation depends on three key components, starting with an amplifier to provide the necessary gain to ensure that the loop gain criteria are met for sustained oscillation.

Next is the feedback network – these can be LC or RC oscillators, or crystal circuits – that determines the frequency of oscillation and ensures the phase shift criteria are met. Finally, the power supply provides the energy the oscillator needs to function.

Oscillators function as essential rhythm generators for various systems and devices by utilizing amplification and feedback principles to produce periodic signals. These signals are crucial for tasks such as timekeeping in digital circuits and facilitating long-distance communication.

The Role Of Oscillators In Satellites

The parts of a satellite vary depending on its purpose, notes Space Foundation, but all satellites share some basic components. These include:

• Antennas: Satellite antenna systems are used to receive and transmit signals to and from Earth.
• Command and Data Handling: The operational heart of a satellite, command and control systems monitor every aspect of the satellite and receive commands from Earth for operation.
• Guidance and Stabilization: Sensors monitor the satellite’s position to ensure it remains in the correct orbit and is oriented toward the correct target. If necessary, thrusters and other maneuvers allow a satellite to fine-tune its position and orientation.
• Housing: Constructed from strong materials that can withstand the harsh space environment.
• Power: Most satellites rely on a solar array to convert sunlight into energy.
• Thermal Control: Guards satellite equipment against extreme temperature changes.
• Transponders: Uplink and downlink signals arrive and depart at different frequencies. Transponders convert uplinked frequencies to downlink frequencies and then amplify the converted transmission for sending to Earth.

Most satellites, especially those involved in navigation, communication, and timing applications, incorporate oscillators as essential components, but not all satellites necessarily use the same type or quality of oscillators. Quartz crystal oscillators are commonly used in satellites due to their reliability and precision, and atomic clocks, which use quartz crystals in conjunction with atoms like cesium, hydrogen, or rubidium, are employed in applications requiring extremely high precision, such as GPS satellites.

Space-qualified oscillators must be designed to withstand the harsh radiation environment of space, writes SAE. They also need to perform reliably across the wide temperature ranges experienced in orbit, as well as manage phase noise and jitter. Some of the benefits provided by oscillators include:

• Frequency generation and control: Oscillators produce stable and precise frequencies essential for various satellite operations. They generate carrier signals for communication, timing signals for data transmission, and reference frequencies for other satellite components.
• Clock generation: Oscillators act as clock generators in digital systems within satellites, providing timing signals to syncronize operations and facilitate data processing.
• Long-term stability: Ultrastable oscillators minimize frequency drift over time, which is critical for maintaining accurate satellite operations throughout their lifespan.
• Environmental compensation: Some oscillators, like TCXOs, incorporate circuits that adjust frequency to compensate for temperature-induced changes, maintaining stable output in the varying space environment.

Oscillators And Satellite Systems

A satellite system consists of both space-based and ground-based components that work together to enable communication and fulfill the satellite’s mission. The key components of a satellite system include satellites, the space-based component, typically consisting of the satellite bus – the main structure housing critical systems – and the payload – mission-specific equipment such as communication transponders, cameras and sensors, scientific instruments, and navigation equipment.

Other components that make up a satellite system include ground stations, user terminals, satellite phones, control centers, tracking, telemetry, and control (TT&C) systems, and network operations centers. These components work together to enable various satellite applications, from communications and Earth observation to navigation and scientific research. The specific configuration and capabilities of each component depend on the satellite’s intended purpose and mission requirements.

The precision and stability of oscillators are paramount in satellite systems, as even small frequency deviations can lead to significant errors in communication, navigation, and other satellite functions. This is why satellite manufacturers often use high-quality quartz crystal oscillators and other advanced oscillator technologies to ensure optimal performance in the challenging space environment.

Oscillators play several critical roles in satellite systems, writes APL Technical Digest. These include:

• Signal processing: Oscillators, specifically local oscillators (LOs), are used in both uplink and downlink signal paths. In the uplink, LOs help with upconversion, converting lower-frequency data signals to higher frequencies for transmission. In the downlink, LOs are used for downconversion, converting higher-frequency received signals to lower intermediate frequencies for processing.
• Navigation and positioning: Highly stable oscillators like Temperature Compensated Crystal Oscillators (TCXOs) and Oven Controlled Crystal Oscillators (OCXOs) are crucial for satellite navigation systems like GPS, providing precise timing necessary for accurate positioning.
• Telemetry and control: Oscillators are used in tracking, telemetry, and control (TT&C) systems, ensuring accurate communication between satellites and ground stations.

The stability, accuracy, and low phase noise characteristics of oscillators are critical for the overall performance and reliability of satellite communication systems, enabling precise frequency control, timing, and signal processing necessary for effective satellite-to-ground and satellite-to-satellite communications.