Apollo 8 Blazed the Future of Navigation


The end of 2018 marked the 50th anniversary of Apollo 8 — the stunning mission to send astronauts around the moon in preparation for the lunar landing seven months later. An excellent documentary on PBS’s NOVA, (based in part on my book Digital Apollo) captured the risky nature of the mission, NASA’s bold decision to leap several steps ahead in the space race (winning it), and the importance of the digital computer as a partner to the crew.

But another dimension of Apollo 8 also deserves commemoration: it pioneered the future of navigation. Apollo 8’s revolutionary digital computer combined readings from onboard navigation sensors with references to features in the external environment, anticipating how Humatics microlocation is enabling today’s robots to navigate our world.

In the 1950s, the MIT Instrumentation Laboratory, under the leadership of Charles Stark “Doc” Draper, developed “inertial” navigation systems, originally for aircraft and ballistic missiles. These systems used gyroscopes and accelerometers to measure precise forces in “inertial space” (that is fixed, with reference to the stars). By mathematically integrating these accelerations, a computer could extract velocity and then integrate again to derive position.

Purely inertial navigation was attractive in a Cold-War environment. It meant that missiles, aircraft, and spacecraft could navigate without any external references and hence did not require any installed infrastructure nor any radio signals, and could not be jammed by hostile forces. Donald MacKenzie, in his excellent book Inventing Accuracy, shows how Draper and his laboratory became ideologically committed to full inertial navigation, with no outside references, and designed the Apollo guidance system to work this way. This devotion is mirrored in some of today’s autonomous vehicle systems, including driverless cars, whose designers believe they must navigate in the ego-centric world of only onboard sensors, with minimal outside references.

Jim Lovell taking star sightings with the Apollo computer during Apollo 8Jim Lovell taking star sightings with the Apollo computer during Apollo 8

As it happened, in addition to this triumph of onboard navigation, Apollo 8 also navigated via radio signals from the ground — the true harbinger of today’s hybrid navigation schemes. Apollo 8 was the moment when the Soviets were no longer a contender in the race to the moon, but already by then, the Cold War had eased to the point that NASA was less worried about Soviet jamming of US Lunar missions. In a kind of earth-based predecessor to today’s GPS, giant radio antennas from the earth bounced radio signals off the Apollo spacecraft, fixing its positions and velocities with unprecedented accuracy.

Giant radio antennas bounced signals off of the Apollo spacecraft to fix its position and velocities with unprecedented accuracy

Gradually over the course of the Apollo program, these radio navigation fixes migrated from secondary to primary — even on Apollo 8, their numbers overwrote those onboard before crucial maneuvers. The inertial system remained essential when the spacecraft was behind the moon, however.

Thus the Apollo system overall enacted what is sure to be the key navigation mode of autonomous systems on earth: measurements to absolute references like radio beacons and stars, combined with onboard inertial and other sensors, all synthesized with sensor fusion software. Some of today’s robotics and driverless car engineers remain committed to an ideology of autonomy completely disconnected from the environment, but like Draper’s ideology of pure onboard navigation, their commitments are likely to yield to more hybrid approaches (they already take advantage of GPS when they can, not to mention the ultimate infrastructure of pre-surveyed HD maps). Navigation is always a systems problem, and when human lives or valuable processes depend on getting it right, a fused approach with a variety of sensors is the only approach that provides the necessary accuracy and robustness.

Humatics microlocation sensors enact exactly this hybrid navigation. Whatever sensors are on a robotic vehicle or car, they are greatly enhanced by simple, inexpensive references to the environment. The future belongs to robotic systems and vehicles that interact with the human world in rich, digital ways — bringing Apollo 8’s robust navigation to its earthly future.