Escape Velocity

In 1977, NASA launched the Voyager 1 spacecraft on a journey that would make history. To break free of Earth's gravitational pull, the probe had to reach what physicists call escape velocity — roughly 11. 2 kilometers per second, or about 25,000 miles per hour. Anything less, and Earth draws it back. No matter how spectacular the launch, falling short of that threshold means falling back down.…