At some point in your life, you've probably watched a rocket launch straight up into the sky. You may have even watched Artemis II's Orion spacecraft quickly reach space , kicking off NASA's most important mission in decades. However, you may have also noticed that, after lift off, the rocket doesn't stay vertical. As the spacecraft gets higher, it begins to curve, even appearing to fly horizontally, parallel to the Earth. That may seem counterproductive for something headed out of the atmosphere and into outer space, but it's actually an essential part of a rocket's journey. And it involves fuel. Rockets, like other flying machines, are working against gravity. It needs as much thrust as possible for its initial liftoff, which is why they start out vertical. However, that also consumes a massive amount of fuel. Staying that way for too long would burn through its supply and send it plunging back down to Earth.…