As Jeff Bezos travels onboard Blue Origin’s New Shepard vehicle to touch the edge of space and enjoy a few minutes of weightlessness, you’ll be hearing the phrase “suborbital” a lot.
But what does it mean to be ‘suborbital’? Simply expressed, this means that while these spacecraft will cross the ill-defined space border, they will not be able to stay in space once they there.
Instead of falling back to Earth if a spacecraft – or anything else for that matter – achieves a speed of 28,000 km/h or more, it will continue to orbit the planet. This continual descent is what it means to be in orbit, and it’s how satellites and the Moon stay above the Earth.
Anything that goes into space but doesn’t have enough horizontal velocity to stay there – like these rockets – returns to Earth and follows a suborbital trajectory.
Why are these suborbital flights significant?
The achievement of reaching space in commercial spacecraft is a momentous milestone in humanity’s history, even if the spacecraft launched in July 2021 would not reach orbit. Those on board this and all future private-sector suborbital flights will be in space for a few minutes, experience thrilling weightlessness, and earn his astronaut wings without a doubt.
The flight Bezos will take is conceptually similar to a baseball being tossed into the air. The higher the baseball will travel and the longer it will stay in the air, the faster you can toss it upward. If you toss the ball with some lateral velocity, it will travel further down the field. Consider tossing a baseball into a wide open field. The ball slows down as it climbs because the kinetic energy of its velocity is exchanged for potential energy in the form of greater height. The ball will eventually reach its maximum height before falling to the earth.
Imagine being able to toss the baseball at a speed that would allow you to reach a height of 97 kilometers. Bang! The baseball has made it to the edge of space. The ball, however, will have zero vertical velocity when it reaches its maximum height and will begin to fall back to Earth. The flight might take several minutes, and the ball — as well as the newly appointed astronauts aboard this spacecraft – would be near weightless for the most of that period. The astronauts will reach space but not orbit, thus their flights will be suborbital, similar to the fictional baseball.