According to Space.com, orbital and suborbital flight are common terms in the spaceflight industry that sound very similar, but they mean different things.

The main difference between orbital and suborbital flight is the speed at which a vehicle is traveling. An orbital spacecraft must achieve what is known as orbital velocity, whereas a suborbital rocket flies at a speed below that.

Orbital velocity is the speed that an object must maintain to remain in orbit around a planet, according to an explainer from the Austrian private aerospace company Orbspace. A good way to picture this is to imagine a ball being thrown at ground level — at a normal throwing speed, the ball travels in an arc through the air before hitting the ground. But say you were to put a little rocket on the ball that made it travel so fast that its arc shape would perfectly match the curvature of the Earth. At that point, the ball would have achieved orbit and would fly at a consistent height above our planet.

To orbit 125 miles (200 kilometers) above Earth, a spacecraft must travel at a screaming 17,400 mph (28,000 km/h). “It is actually this incredibly high speed which makes orbital space flight technically so complex and therefore expensive,” Orbspace representatives wrote. One of the main reasons airplanes can’t fly in space is that they don’t go fast enough.

Suborbital flight, in contrast, requires much lower speeds. A suborbital rocket doesn’t have the power to achieve orbit. Instead, it will fly up to a certain height that depends on its speed, and then come back down once its engines are shut off. To reach 125 miles above Earth, a suborbital vehicle needs to fly at a relatively sedate 3,700 mph (6,000 km/h), although that’s still much faster than a commercial airplane, which flies at around 575 mph (925 km/h).

At the top of their flight arc, passengers in a suborbital vehicle will still achieve a few minutes of weightlessness. They are, in fact, falling back toward Earth, but they are experiencing freefall, similar to an airplane completing parabolic maneuvers to simulate zero gravity.