“Suborbital” is a term you will hear a lot like Sir Richard Branson flies aboard Virgin Galactic’s winged VSS Unity spacecraft and Jeff Bezos flies on board Blue Origin’s new Shepard vehicle touch the limit of space and experience a few minutes of weightlessness.
But what exactly is “suborbital”? Simply put, this means that even though these vehicles will cross the ill-defined limit of space, they won’t go fast enough to stay in space once there.
If a spaceship – or anything else, for that matter – hits a speed of 17,500 mph (28,000 km / h) or more, instead of falling to the ground, it will continually fall around the Earth. This continuous fall is what it means to be in orbit and this is how the satellites and the Moon stay above the Earth.
Anything that launches into space but does not have sufficient horizontal speed to stay in space – like these rockets – returns to Earth and therefore follows a suborbital path.
Why these suborbital flights are important
Although the two spacecraft launched in July 2021 will not reach orbit, the achievement of reaching space in a private spacecraft is a major milestone in human history. Those on board these and all future private sector suborbital flights will be in space for a few minutes, experience a few minutes of exhilarating weightlessness, and absolutely earn their astronaut wings.
A well-pitched baseball
Conceptually, the flights that Branson and Bezos will perform on aren’t much different from a baseball tossed in the air.
The faster you can throw the baseball upwards, the higher it will go and the longer it will stay in the air. If you also throw the ball with a little lateral velocity, it will go further into the range.
Imagine throwing your baseball in an open field. As the ball rises, it slows down, as the kinetic energy inherent in its speed is exchanged for potential energy in the form of an increase in altitude. Eventually, the ball will reach its maximum height and then fall back to the ground.
Now imagine that you could throw the baseball fast enough to reach a height of about 60 miles (97 km). Presto! Baseball has reached space. But when the ball reaches its maximum height, it will have zero vertical speed and will begin to fall back to Earth.
The flight can take several minutes, and for most of that time, the ball would experience a quasi-weightlessness – just like the newly created astronauts aboard these spacecraft. Much like hypothetical baseball, astronauts will reach space but will not enter orbit, so their flights will be suborbital.
This article from John M. Horack, Neil Armstrong Chair and Professor of Mechanical and Aerospace Engineering, Ohio State University is reposted from The conversation under a Creative Commons license. Read it original article.