NASA Tests Astronaut Vision with Giant Ground Charts on Gemini Flights

NASA, together with partners, devised visual-acuity experiments for the Gemini V and Gemini VII missions after Mercury astronauts described seeing fine details on Earth from 100 miles up. One part used a binocular-like instrument to present rectangles of varying contrast, while the other involved two enormous ground-based eye-charts built by Dow Chemical Corporation, each featuring white rectangles between roughly 150 and 600 feet in size.

The charts were installed on dark soil near Laredo, Texas and near Carnarvon, Australia, and astronauts were asked to state the orientation of the shapes from orbit. Despite cloud cover, window glare, and unfavourable orbital angles, crews occasionally saw the Laredo site and consistently reported being able to spot roads and ship wakes. The experiments demonstrated that astronaut vision remained stable during a two-week flight and confirmed that detailed Earth observation from space was feasible, influencing the development of later Earth-monitoring satellites such as Landsat 1.