The Pluto Perspective

Posted on July 9, 2020

Memories of an Amazing Encounter

Aiming for Pluto

Derek Nelson

New Horizons optical navigation engineer


As an optical navigation engineer, my role on New Horizons was to analyze images of Pluto and its moons as they were downlinked from the spacecraft during the early morning hours. The team used these images to determine where New Horizons was relative to the Pluto system, and to decide if we needed to adjust the spacecraft's course. On critical days, this image downlink and optical navigation process would kick off an extensive chain of events across multiple teams to ensure the spacecraft could point and steer itself to the intended aimpoint for the Pluto flyby. I tend to think of optical navigation as analogous to "the eyes of a spacecraft," or a lookout perched upon the crow's nest of a ship.

Sipping freshly brewed coffee in a yet-bustling room at the Johns Hopkins Applied Physics Laboratory endearingly nicknamed "The Bullpen," my colleague and I sat at our laptops, constantly refreshing our image-download program. Downlinking many high-resolution images from a distance of over 3.2 billion miles is shockingly fast yet terribly slow by terrestrial standards. As the data trickled in over a few hours, we would watch line-by-line as the pixels revealed a unique view of worlds never seen at such resolution and clarity. We knew that each passing image was itself a new discovery – providing the most critical navigation information while faintly tinting the previous day's glamour.

Along with other early-bird colleagues, we'd peer out laptop windows morning after morning and watch Pluto, its "heart" and its moons grow larger, revealing greater detail. We would analyze each new image, calculate the most recent prediction for the spacecraft's trajectory, and point New Horizons in the right direction. After weeks of our team iterating and addressing each day's challenges, New Horizons hit its intended aimpoint on July 14, 2015, just seconds off the intended time.

The New Horizons team used hundreds of optical navigation images, like those in this sequence, to deliver the spacecraft to the right place at the right time for the Pluto flyby. (Credit: NASA/Johns Hopkins APL/Southwest Research Institute)

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