Conventional airplanes cannot fly in the mesosphere due to the physics of Earth’s atmosphere. While jet aircraft reach impressive altitudes, they are fundamentally limited by the availability of air molecules. A standard aircraft cannot sustain flight in the mesosphere, which begins far above the maximum ceiling of commercial and military jets. This limitation is caused by the rapidly decreasing atmospheric density at extreme heights, not engine power alone.
Defining the Mesosphere
The mesosphere is the third atmospheric layer above Earth’s surface, situated directly above the stratosphere and below the thermosphere. This region typically spans an altitude range from about 50 kilometers (31 miles) to 85 kilometers (53 miles) above sea level. This layer is characterized by temperatures that dramatically decrease with increasing altitude. Temperatures can plummet to around -90°C (-130°F) near the top of the layer, making the mesopause the coldest point in the entire atmosphere.
The most restrictive characteristic for flight, however, is the extreme drop in atmospheric pressure and density. Air density at the bottom boundary of the mesosphere is already less than one-thousandth of the density found at sea level. By the time the upper boundary is reached, the air is so rarefied that the atmosphere transitions into the thermosphere. This low-density environment is what makes sustained aerodynamic flight impossible here.
The Mechanics of Conventional Flight
Conventional flight depends entirely on four opposing forces: lift, weight, thrust, and drag. For an aircraft to maintain a steady altitude, the upward force of lift must be equal to or greater than the downward force of the aircraft’s weight. Lift is generated by the interaction between the wing’s airfoil shape and the movement of air molecules passing over and under it.
The amount of lift generated is directly proportional to the density of the air and the square of the airspeed. This relationship means that a reduction in air density must be compensated for by a corresponding, and often much larger, increase in speed. At lower altitudes, the high concentration of air molecules allows wings to generate significant lift at relatively low speeds. As an aircraft climbs, the air becomes thinner, requiring the aircraft to fly faster to maintain the same amount of lift.
Why Aircraft Cannot Generate Lift in the Mesosphere
In the mesosphere, the air density is profoundly low, presenting an insurmountable challenge for standard aircraft design. Standard jet engines are designed to compress and ignite oxygen from the surrounding atmosphere. They would quickly cease to function efficiently due to insufficient air mass. Even if an aircraft could somehow achieve the necessary speed, the number of air molecules available to interact with the wing is too small to generate the required lifting force.
The primary limitation is that the speed needed to create lift in the extremely thin air of the mesosphere would cause the aircraft to exceed its maximum operational Mach number. At high altitudes, the margin between the speed at which the wings stall (due to insufficient air density) and the speed at which the airframe suffers structural damage from compressibility effects narrows dramatically. In the mesosphere, this margin disappears entirely. The air is simply too thin for the wings to “grip” and too sparse for the engines to breathe.
Specialized Craft That Traverse the Mesosphere
The mesosphere is not entirely empty of human-made objects, but the craft that operate here do not rely on aerodynamic lift. Research instruments are frequently carried into and through this layer by sounding rockets, which use powerful, self-contained propulsion systems to push their way through the thin air. These rockets rely on momentum and thrust, not wings, and their passage is brief as they are either ascending to space or falling back to Earth.
High-altitude scientific balloons can sometimes reach the stratopause, the boundary just below the mesosphere, but they cannot sustain flotation within the mesosphere itself. The most common objects to interact with this layer are meteors, which begin to burn up from atmospheric friction upon encountering the mesosphere’s upper reaches. These “shooting stars” are a visible demonstration of the air density’s effect. The layer is thick enough to create friction and heat, but too thin to support winged flight.