John A. Christian
SPACECRAFT NAVIGATOR · AUTHOR · PROFESSOR
KATYA VILCHYK
I am a spacecraft navigator.
Even at the furthest reaches of the Solar System, there are clues that can tell us where we are.
I study how spacecraft can navigate far from Earth. Algorithms from my research have helped fly spacecraft around the Moon, land robots on the lunar surface, and traverse interplanetary space. My current focus is on navigation where support from Earth is limited and no local infrastructure exists, so that spacecraft can explore independently.
Independent navigation is an old problem, older than the sextant or the compass, and one whose long history I have spent years studying.
Fundamentals of Spacecraft Optical Navigation
A comprehensive guide to navigating spacecraft with camera images.
Fundamentals of Spacecraft Optical Navigation is a foundations-first textbook for practicing navigators, spacecraft designers and operators, researchers, and students seeking a deeper understanding of optical navigation.
Drawing on techniques from projective geometry, astrometry, planetary science, and aerospace engineering, this book develops the foundations of modern optical navigation systems. Practical solutions are developed from first-principles analysis and illustrated through worked examples using real space mission data.
The book also explores the historical context behind key navigation innovations, showing how modern spacecraft optical navigation emerged from a much older intellectual tradition.
KATYA VILCHYK
The Navigator's Craft
Navigation is the art of observing the world to infer where you are.
RUBEN CHRISTEN / UNSPLASH
Homer’s Odyssey contains one of the oldest surviving accounts of navigation by the stars. The poet tells of Odysseus sailing alone from Calypso's island, maintaining his eastward course by keeping the Great Bear on his left and not “letting sleep fall upon his eyelids.”
For most of human history, a navigator could not afford to be a passive observer. A safe return might depend on recognizing a headland in poor light, noticing a change in the water, observing a familiar star on a clear night, or catching a brief glimpse of the Sun through broken clouds. The world offered only fragments of evidence, and the navigator had to know what to do with them.
Navigation is a practical art. Through apprenticeship and time at sea, the early navigator learned that the sky, sea, wind, and animals all carried information. With time, instruments made observations of these clues more precise, while almanacs and maps made their interpretation more powerful. These advances, however, did not relieve the navigator of their duty to understand the information carried by their surroundings, and to remain capable when conditions were poor or when instruments failed.
There is a particular kind of self-reliance in this tradition. There is confidence, and comfort, in knowing how to read the natural environment and to find the way to your destination. And there is a deep and abiding unease when that ability is surrendered to systems whose operation we do not understand or whose answers cannot be independently checked.
The tradition of classical navigation remains especially strong in space exploration, where we routinely send spacecraft to locations without navigation infrastructure. Spacecraft operating near distant planets, moons, or asteroids cannot assume access to a radionavigation system like GPS. They must operate without familiar landmarks and sometimes with no prior map at all.
While the technology has changed since the Odyssey was first told, the navigator’s craft remains the same today: to observe the world to infer where you are.
JOHN TOWNER / UNSPLASH
My Work
My research develops methods for autonomous spacecraft navigation. I use mathematical models to extract navigation information from camera images, inertial sensors, and other instruments. I also study the natural environment, searching for physical signals that spacecraft can use to navigate when pre-deployed infrastructure is unavailable.
AVA THRASHER
Celestial Navigation
Observations of stars and other celestial bodies may be used to navigate in deep space. Stars are so far away that their directions hardly change within our Solar System, which makes them a reliable reference for estimating a spacecraft's orientation. Planets, moons, and asteroids are nearer, and their apparent direction can change dramatically as the spacecraft moves. The geometry of these changing directions provides the information to estimate the spacecraft's position.
Navigation Algorithms
NASA
Navigation algorithms are the mathematics of finding your way. They combine imperfect measurements, maps, and models into a single best estimate of where a vehicle is and where it is heading, along with a measure of how much that estimate can be trusted.
Terrain Relative Navigation
JOHN CHRISTIAN / NASA
Images of terrain may be used to navigate while orbiting a celestial body or during descent and landing. Some methods match the observed terrain to a known map, while others match to a map that is built on the fly. Still other methods avoid maps altogether and infer relative motion from the apparent movement of unknown terrain from one image to another.
EDWIN DUNKIN, 1879
History of Navigation
The methods we use to navigate spacecraft descend from a long tradition of explorers crossing open seas and unknown land. Many ideas we think of as modern were understood, in some form, long ago.
KATYA VILCHYK
About Me
I am a spacecraft navigator, an author, and a professor. At Georgia Tech, I direct the Space Exploration Analysis Laboratory, where my students and I work on how spacecraft navigate in deep space.
Most of my work is motivated by a simple question: how does a spacecraft know where it is when lives or missions depend on getting the answer right?
Outside of my scholarly work, I enjoy traveling, cartography, horology, star gazing, and spending time with my family.