why heatshield is not required for going to karman line and coming back
The Kármán line, which is often considered the boundary between Earth's atmosphere and space, is located approximately 100 kilometers (62 miles) above the Earth's surface. When suborbital spacecraft, like those used for space tourism or research missions that reach the Kármán line, go up and then return relatively quickly, they typically do not require a heat shield for reentry.
There are several reasons for this.
-
Speed and Duration: Suborbital flights (like Virgin Galactic's unity flight or blueorigin flight) do not achieve the high velocities required to enter orbit around the Earth. Instead, they follow a ballistic trajectory, going up and then coming back down relatively quickly. This means they do not experience the extreme speeds associated with orbital reentry, which generate significant heat.
-
Atmospheric Density: The density of the Earth's atmosphere at the Kármán line is very low, and there is not enough material in the atmosphere to generate the kind of heat that spacecraft experience during orbital reentry. A heat shield is designed to dissipate the tremendous kinetic energy generated by high-speed orbital reentry.
-
Shallow Reentry Angle: Suborbital spacecraft typically follow a shallow reentry trajectory. This means they reenter the atmosphere at a less steep angle compared to spacecraft returning from orbital missions. A shallow reentry angle generates less heat.
-
Short Duration: Suborbital flights are relatively short in duration. The spacecraft spends only a brief amount of time in space and reenters the Earth's atmosphere relatively soon after reaching the Kármán line. This limited exposure to the space environment reduces the heat buildup.
In contrast, spacecraft (e.g. Space shuttle) returning from orbital missions experience much higher speeds and need to dissipate the significant kinetic energy generated during reentry. This requires a heat shield to protect the spacecraft from the intense heat and friction generated as it passes through the denser layers of the Earth's atmosphere.