Airplanes are amazing feats of human ingenuity. Thanks to the power and speed of these machines, trips that used to take humans many months now take less than a day to complete. But are these bird-like hunks of metal able to enter space?
So, can an airplane fly into space? No, an airplane cannot fly into space. As exciting as the prospect sounds, the earth’s gravitational pull is much too strong for an airplane to leave earth and enter space.
There are some fundamental physics here that need to be covered to make this clearer for you. And to truly understand the answer to this question, you also need to know where “space” actually begins relative to the earth’s atmosphere. We’ll discuss all of this in the following sections.
Table of Contents
How do airplanes fly?
To understand why airplanes cannot fly into space, you first need to understand how it is that an airplane can fly at all. After all, it does seem like a miracle for an object made of metal to fly high up in the air.
Airplanes are able to stay in the air because of a force known as lift. Lift is the mechanical aerodynamic force that every part of the airplane (especially the wings) helps generate to keep it afloat.
Lift is a vector quantity, which means that it has a magnitude and a direction. Its direction is perpendicular to the direction of motion of the airplane, which is how it opposes the downward gravitational pull experienced by the plane, helping it stay in the air.
Any solid object that deflects or turns the flow of a gas will generate lift. The lift is generated as per Newton’s third law: For every action, there is an equal and opposite reaction.
Since air flows in one direction, there is a consequential force that arises in the opposite direction. All parts of the airplane’s exterior are designed to help generate this lift, especially its wings. Both the upper and the lower surface of the wings contribute to generating lift.
Add the propeller or the propulsion engine of the plane to this equation, and you can see the whole picture. The propeller helps the plane move forward, thus splitting the flow of the air in two, which in turn helps generate lift and helps the plane take flight.
Where does space start?
Now that you know how an airplane stays in the air let’s examine where it is exactly that Space starts.
Most airplanes never fly above a height of around 50,000 feet. That is approximately 15 kilometers or 9.5 miles: far below the height where space starts.
There is an arbitrarily defined line known as the Kármán line encircling the earth. This line lies at a distance of around 100 km (60 miles) from the earth’s surface. This is where we say that space starts. Of course, the earth’s atmosphere doesn’t quite end there. In fact, low orbit satellites flying as high as 160 km (100 miles) can still experience the effects of the atmosphere.
So there is no physical line that separates the earth’s atmosphere from space. Instead, the earth’s atmosphere gradually thins out until, eventually, you reach a point where there is none. The Kármán line is just an arbitrary definition that makes it easier to quantify the beginning of space.
Why can’t airplanes fly into space?
Now that we’ve covered some fundamentals, it will be easier to discuss why it is that airplanes cannot fly into space. There are a few important reasons here, some of which you might have already deciphered from the previous sections.
The first and the most fundamental reason why an airplane can’t fly into space is that there is no air in space.
Airplanes require air for two reasons:
- The plane needs to split the flow of a gas (the air) to generate lift. Since there is no air in space, there is no gas to deflect and generate lift.
- Even if there were some air (as we’ve discussed in the section about the Kármán line), there isn’t enough oxygen at that height for the propulsion engine of the plane to burn the fuel and generate the forward motion that in turn would help generate lift.
Let’s say that, hypothetically, you were able to create an airplane that could successfully reach the Kármán line. As far fetched as that sounds, that would still not be the same as flying “into space,” as it would still be almost impossible for the tiny airplane to escape the earth’s massive gravitational pull.
How rockets fly into space
The second reason why airplanes (or any other object for that matter) can’t penetrate space is because of the gravitational pull that it experiences from the earth.
The cause of this is a factor known as escape velocity. This is the velocity with which an object would have to be propelled upwards for it to escape the planet/object’s gravitational pull. The escape velocity for the earth is about 25,000 mph or 7 miles per second (40,000 km/h).
The earth’s gravity is the reason why a rock thrown up in the air will reach a certain height before falling back down. Fortunately for an airplane, the lift helps it stay up in the air. But the force required for it to escape the earth’s gravity altogether would be immense.
Newton’s first law states that an object in motion will stay in motion in that same direction unless interfered by an external force. What that means is that it wasn’t for the gravitational pull of the planet, planes that were lifted into space would technically be able to fly out into space.
Rockets, however, are able to fly into space despite the earth’s gravity. And that is precisely because their propulsion engine can generate enough force to propel them upwards at a velocity that is higher than the escape velocity.
In essence, the rocket’s propulsion engine is a more powerful form of a jet engine. They can move upward at such a high rate of speed by firing hot exhaust gas in a downward direction. This gas comes from the burning of rocket propellant, which can come in a variety of different formats, including solid chemical propellants, liquid chemical propellants, and hybrid propellants.
Below is a nice video that explains the things covered above and more:
So there you have it. Hopefully, it has become more apparent to you now why airplanes can’t fly into space.
Conclusion
By definition, space starts at the height of 100 kilometers (around 60 miles) from the earth’s surface. This arbitrarily defined starting point is called the Kármán line. Most airplanes, however, never fly above a height of 50,000 feet (15 kilometers or 9.5 miles).
Airplanes can’t fly into space. And this includes powerful airplanes like fighter jets and commercial planes. In fact, not even the fastest fighter jet can fly at a speed that’s even close to the escape velocity of 25,000 miles per hour (or 40,000 km/h) that an object requires to escape earth’s gravitational pull.
But that’s not the only reason why an airplane can’t fly into space.
Rockets can fly into space because they can beat the escape velocity of the earth. And their upwards flying mechanism is nothing like the lift-driven flight mechanism of a typical airplane. An airplane can fly by manipulating the flow of the air around its body, generating a force called “lift” that can counter its weight. Since there is no air in space, this mechanism fails.
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