Account for the orbital decay of satellites in low Earth orbit

Orbital decay of satellites in low Earth orbit

- A satellite I a stable orbit around the Earth possesses a certain amount of mechanical energy, which is the sum of its kinetic energy (due to high speed) and its gravitational energy (due to altitude). The lower the altitude of the orbit, the lower the total mechanical energy is.

- Satellites in low Earth orbit are subject to friction with the sparse outer fringes of the atmosphere. This friction results in a loss of energy. Loss of energy means that this orbit is not longer viable and the satellite drops down to an altitude that corresponds with its new, lower energy. Ironically, the satellite will be moving faster than before (recall that lower orbits require faster orbital velocities) however the extra kinetic energy is derived from the lost potential energy.

- Process of orbital decay, its cyclic, as the satellites new lower orbit r4esides in slightly denser atmosphere, which leads to further friction and loss of energy. The process is not only continuous but speeds up as time goes on.

Issues associated with safe re-entry for a manned spacecraft into Earth's Atmosphere and landing.

- Heat: Considerable kinetic and potential energy possessed by an orbiting spacecraft must be lost during re-entry. Atmosphere decelerates the spacecraft, the energy is converted into a great deal of heat. Heat must be tolerated and/or insulation surfaces. Heat can be minimized by taking longer to re-enter, thereby lengthening the time over which the energy is converted to heat.

- g forces: Deceleration of re-entering spacecraft also produces g forces, typically great than those experience during launch. High g forces can be better tolerated by reclining the astronaut, so that blood is not force away from the brain, and by fully supporting the body. The g forces can be minimized by extending the re-entry, slowing the rate of descent.

- For a time during re-entry, radio blackout caused by overheated air particles ionizing as they collide with the spacecraft. May be a safety issue if contact is need between the spacecraft and earth at this phase of its flight.

- Reaching the surface: Surviving the issues listed above, the spacecraft must touch down softly onto the surface of the Earth. Several solutions to this problem have been employed, such as first using parachutes and then splashing onto ocean, or using many parachutes before crunching onto the ground, or by landing on an air strip.