The statement most closely aligning with why there are no aircraft or spacecraft flying or orbiting in the mesosphere is:
Aircraft are not powerful to reach the mesosphere and spacecraft can't orbit that low.
Explanation:
-
Aircraft: Commercial and military aircraft are designed to operate at altitudes usually between about 30,000 to 40,000 feet, or around 9 to 12 kilometers, which is well below the mesosphere. The mesosphere extends from approximately 50 km to 85 km above Earth. At these higher altitudes, the air is too thin for conventional aircraft to generate sufficient lift.
-
Spacecraft: Spacecraft that operate outside the atmosphere are designed to reach much higher altitudes (above 100 km for low Earth orbit). They do not operate in the mesosphere, as it's not a stable region for orbiting; the drag from the atmosphere at those altitudes would cause a spacecraft to lose altitude quickly.
-
Meteor Strikes: While there is a higher density of meteoric activity in the mesosphere (where many meteors burn up), this is not the primary reason why vehicles do not operate there.
-
Heat and Burn-up: Spacecraft will burn up if they return from orbital speeds, but this does not pertain to missions that simply wish to fly through or operate specifically within the mesosphere, as typical spacecraft do not operate in that layer.
-
Radio Communication: The ionosphere (higher than the mesosphere) can affect radio communications, but this is more of a concern for radio signals traveling through the upper atmosphere rather than the most immediate reasons for absence at altitudes we define as the mesosphere.
In summary, aircraft cannot operate effectively in the mesosphere due to insufficient lift in thin air, and spacecraft do not orbit there due to the unsuitability of the altitude for stable orbits.