As Jeff Bezos heads for his trip on a rocket, fellow billionaire and space entrepreneur Elon Musk indicated that he has noted the flight is going to be a suborbital one. That is, the Amazon founder will not be zooming into space but just touching its edge before he drops right back to Earth. So, technically there is space involved but there is a big difference between suborbital and orbital flights. Here’s what you need to know.

Where Is Bezos Headed?

Sitting in the capsule perched atop his space company Blue Origin’s rocket, Bezos and his three co-flyers will be headed just across the Karman line, the imaginary point about 100km above the Earth where its atmosphere ends and space begins. According to the US National Oceanic and Atmospheric Administration (NOAA), “once this 100km line is crossed, the atmosphere becomes too thin to provide enough lift for conventional aircraft to maintain flight”. Which means that if the speed is not high enough to escape Earth’s gravity, the aircraft will just fall back to Earth.

The four passengers flying to suborbital space on board Blue Origin’s Alan Shepard system
But then there is the US military and its space agency Nasa’s definition, which holds that space starts about 80km above the Earth’s surface. NOAA says that “pilots, mission specialists and civilians who cross this boundary are officially deemed astronauts”. By that definition, Bezos would have touched space as the Alan Shepard suborbital spaceflight system will be taking him to a height of 100km above the Earth’s surface. Richard Branson, the Virgin Galactic founder who went on his own space trip last week, flew about 86km above Earth on his supersonic plane.

Why Is There A Debate?

Commenting on suborbital flights in the context of the trips that billionaires Branson and Bezos are making, American scientist Neil deGrasse Tyson told CNN that what the duo is doing with their respective companies is not really going to space, but just reaching higher than most flying objects can. “I see it not as ‘oh, we’re going into space’. No, you’re getting a nice view of the Earth,” deGrasse Tyson told CNN.

In fact, deGrasse Tyson also questioned whether a suborbital flight can even offer a view of the Earth’s curvature — as the Branson and Bezos companies are claiming a trip on board their machines would do — given that the relative height above Earth is minor.

“…I don’t even know if you’re going to see the curvature (on a suborbital trip). I did some calculations and I’m thinking they’re not. But national boundaries disappear. It’s an overview effect that you will get a little bit of even at 50 miles up,” deGrasse Tyson added.

What’s The Difference Between Orbital And Suborbital Flight?

It’s literally rocket science, but the main distinction is in the speed at which you’re going. According to US space agency Nasa, a sub-orbital spaceflight is one in which “the spacecraft reaches space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it does not complete one orbital revolution”.

Remember we’ve talked about how a conventional aircraft would fall back to the Earth’s surface after it leaves its atmosphere. Well, to not fall back, a vessel would need to attain what is known as escape velocity, ‘escape’ here implying the ability to throw off the Earth’s gravitational pull. Without going into the complex physics behind it, what you must remember is that a rocket can do that only when it attains a speed of 28,000 kmph.

For a suborbital flight though such high speeds are not needed. A suborbital rocket requires just about enough speed to be able to fly to about 100km above Earth’s surface. Once there, it can just shut off its engines and fall back to Earth. The speed required is more modest, about 3,700 kmph. But scientists say that at the highest point of a suborbital flight one can experience weightlessness although the vessel itself is not floating in space but is in the process of dropping back to Earth.