An Introduction to GNSS

A primer in using Global Navigation Satellite Systems for positioning and autonomy


Dr. Robert Thirsk
Dr. Robert Thirsk

The urge to explore is innate — and space presents humanity with a boundless frontier to be explored. For myself, the notion of space exploration was planted in my mind when I was a child. Growing up in the 1960s, I followed the exploits of the early astronauts who boldly went where no one had gone before. What courage!

I watched in awe as Armstrong and Aldrin guided their spiderly lunar module down to a pin-point landing on the Moon and then, a few hours later, bounded about its magnificently desolate surface. Their “we-do-it-not-because-it-is-easy-but-because-it-is-hard” attitude inspired me. In later years, I jumped through all the academic and career hoops that might someday help me realise my own dream of spaceflight.

Beyond this self-indulgent motivation to explore the great unknown, the development of space over the past decades has brought about pragmatic and untold benefits to society at large. We take for granted that many everyday services are enabled by space technology — how we communicate, how we know whether to grab an umbrella as we step out the door in the morning, even how we’re entertained. Space even affords a unique laboratory setting to advance research in ways that aren’t possible on Earth.

During both my forays into space, I relied upon positioning and automation technologies to complete my missions. During ascent of the shuttle, for example, data from the vehicle’s three inertial measurement units were fed to the flight software steering the engine gimbals so that we arrived in space at a targeted position and velocity.

On orbit, I worked with science teams on the ground to conduct a host of international investigations — from medical science to fluid physics to robotics. Whether crystalising a large protein molecule associated with a debilitating congenital illness — impossible to do on Earth due to gravity — to testing control algorithms for satellite systems using free-flying robots, every experiment provided new insights. Knowing that the data we collected would be applied to social needs on the ground brought a feeling of satisfaction and gratitude for the opportunity to serve. And the view out the spacecraft window wasn’t too bad either!

What unfolds over the next decades will be even more exciting. We will watch in wonder as the next generation of astronauts ventures farther into the solar system.

Enterprising industrialists will develop novel means to harness resources from the Sun and near-Earth asteroids to support the needs of civilization. Enhancements of existing space technologies will improve sustainability of life on Earth. In particular, new applications of autonomy and positioning technologies will transform how we grow our food, monitor the environment, manage our natural resources and transport goods about the global supply chain.

Which brings me to the subject of this book. Global Navigation Satellite Systems (GNSS) are at the heart of answering the questions: where am I and how do I get to my destination? The answers lie in precision positioning, navigation and timing (PNT) capabilities enabled by GNSS. The accuracy and speed of the technologies detailed in this book have advanced to the point where cars, ships, planes and spacecraft can know their locations in real-time with unprecedented precision. Their ready adoption across applications like mining and autonomous vehicles has been enabled by the integration of advanced sensors and increasingly sophisticated positioning solutions.

What does this have to do with sustainability? Greater efficiencies and reduced costs are achieved through autonomous operations, from self-driving transport trucks that shave hours off shipping times and enable unmanned ore transport in mining operations, to agricultural positioning technologies that ensure year-after-year repeatability in crop production.

Although I’m no longer an active astronaut, my passion for innovation guides my continuing mission to make our world a better place. One way I do that is by encouraging today’s young explorers to work outside of their comfort zones, to participate in collaborative, team-oriented ventures and to pursue audacious dreams. The realisation of such dreams will only be possible when built upon a foundation of lifelong learning and advanced skills.

If you’re reading this book, you’ve already launched on the right trajectory to this bright and sustainable future!

–Dr. Robert Thirsk

Table of contents

  1. Overview
  2. Basic concepts
  3. GNSS constellations
  4. GNSS error sources
  5. Resolving errors
  6. Sensor fusion
  7. GNSS threats
  8. Autonomy
  9. GNSS applications and equipment