Orbital and sub-orbital flights are common terms in the space industry. Perhaps the main difference between orbital and sub-orbital flight is the speed at which the vehicle travels. An orbital spacecraft must achieve what is known as orbital velocity, while a sub-orbital missile flies at a lower speed.
According to the American “space” website, the orbital speed is the speed that the body must maintain to remain in orbit around the planet, and a good way to visualize this is to imagine a ball being thrown at ground level at a normal throw speed, the ball moves in an arc through the air before hitting the ground.
But suppose you were to put a small rocket on the ball and make it move so fast that its arc fits perfectly with the curvature of the Earth, at that point, the ball will have reached orbit and will be flying at a constant height above our planet.
Also, to orbit 125 miles (200 km) above Earth, the spacecraft must travel at 17,400 mph (28,000 km/h).
It is this high speed that makes orbital space flight so technically complex and thus expensive. In contrast, suborbital flight requires much lower speeds, but the suborbital missile does not have the ability to reach orbit.
It will fly to a certain altitude that depends on its speed, and then come back down once its engines are turned off. To reach 125 miles above Earth, the suborbital craft needs to fly at 3,700 miles per hour.
At the top of the flight arc, passengers in a semi-orbital craft will still achieve a few minutes of weightlessness, and several private spaceflight companies are vying to take paying customers for orbital or suborbital flights, with Virgin Galactic and Blue Origin vying to achieve semi-orbital flights. Regular orbital in the near future, while SpaceX is sending materials, satellites and astronauts also into orbit.