ISO Mobility Profiles

In order to classify the ability of thousands of different builds of spacecraft, the ISO determined to classify air and spacecraft by their ability to travel in various environments and conditions.

\* TWR = Thrust-to-Weight Ratio. The ability of a ship's engines to overcome the weight of the craft under standard Earth gravity. A value of 1 means the engines output exactly as much force as the ship's weight. A value between 0 and 1 means the engines cannot lift the ship. A value greater than 1 means the engines are capable of accelerating a ship out of the earth's gravity well.

\*\* LWR = Lift-to-Weight Ratio. The ability of a ship to fly in air at least as dense as 1 Earth atmosphere. A value of 1 or greater means the aircraft's hull generates enough lift to keep the craft at a constant altitude. A value between 0 and 1 means the craft does not generate enough lift to counter the effect of gravity

ATM-(O): Atmosphere Only, meaning craft incapable of self-propulsion above the Earth Pressure-Altitude of FL1000. This includes all aircraft, as long as the service ceiling is at or below FL1000. These craft are prohibited in Class S airspace and above.

ATM-(E): Atmospheric Extended, describing any craft capable of high-altitude operations due to a low-thrust hybrid engine or monopropellant systems. Ceilings may be above FL1000 but aircraft lack Delta-V or thrust for entering orbit. Often describes shuttles to Low-Orbital Platforms. Prohibited in uncontrolled space.

ATM-(T): Atmospheric Transitional, describing a craft capable of operating beyond the atmosphere but lacking the EM drives or high-impulse engines for extended space travel. Have a positive lift-to-weight ratio at or above Earth sea-level pressure. Usually equipped with hybrid chemical engines with a airbreathing/oxidizer switch. Applies to any spacecraft which can enter orbits within a star system, but with no sensible interstellar capabilities. Prohibited in dark space.

(H)YB: True Hybrid, describing craft equipped with airbreathing/air-friendly engines and interstellar drives and engines. Have a positive lift-to-weight ratio (LWR) at or above sea-level in standard Earth air pressure, but usually even at higher altitudes. Describes the majority of privately-owned spacecraft.

VAC-(A): Vacuum Atmospheric, describing spacecraft equipped with airbreathing/air-friendly engines and interstellar drives and engines. These craft have a limited, and perhaps non-existent lift profile, and have a lift-to-weight ratio at sea-level between 0 and 1. While they may still have control surfaces for stability, they rely on directed thrust to maintain positive vertical speed en-atmo.

VAC-(S): Vacuum Stabilized, describing spacecraft with no airbreathing/air-friendly engines, but having engines or thrusters that can maintain a positive Thrust-to-Weight (TWR) ratio on Earth. The LWR will always be less than 1.

VAC-(G): Vacuum Glider, describing spacecraft with no air-friendly engines, but having an aerodynamic profile allowing for a greater-than-one LWR at sea-level earth pressure.. TWR will always be less than one.

VAC-(N): Vacuum Native, describing spacecraft with no airbreathing engines, and TWR and LWR less than one. Due to safety, only excessively large spacecraft are built with the inability to make planetary landings. Even these are built with fail-safe features or momentum-arresting systems to soften the blow of unplanned planetary landings.