discuss issues associated with safe re-entry for a manned spacecraft into the Earths atmosphere and landing on the Earths surface.
1.
Heat: The considerable kinetic and potential energy possessed by an orbiting spacecraft must be lost during re-entry. As the atmosphere decelerates the spacecraft, the energy is converted into a great deal of heat. This heat must be tolerated and/or minimised. The heat can be tolerated by using heat shields that use ablating surfaces (as used on Apollo capsules) or insulating surfaces (as used on the space shuttle). The heat can be minimised by taking longer to re-enter, thereby lengthening the time over which the energy is converted to heat. The space shuttle uses this technique.
2.
g forces: The deceleration of a re-entering spacecraft also produces g forces, typically greater than those experienced during launch. High g forces can be better tolerated by reclining the astronaut, so that blood is not forced away from the brain, and by fully supporting the body. The g forces can be minimised by extending the re-entry, slowing the rate of descent. This strategy is employed by the space shuttle.
3. For a time during re-entry, there is a radio blackout caused by overheated air particles ionising as they collide with the spacecraft. This may be a safety issue if contact is needed between the spacecraft and earth at this phase of its flight.
4. Reaching the surface: Even after 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 into ocean, or using many parachutes before crunching onto the ground, or by landing on an air strip (as performed by the space shuttle).
identify that there is an optimum angle for re-entry into the Earths atmosphere and the consequences of failing to achieve this angle.
- For any given spacecraft wishing to re-enter safely, an optimum angle of re-entry exists. For Apollo capsules this angle was between 5.2 and 7.2, although this would differ for other spacecraft.
- If the angle is too shallow then the spacecraft will rebound, due to compression of the atmosphere beneath it.
- If the angle is too steep then the spacecraft will decelerate too quickly, creating too much heat and burning up the spacecraft.
Taken from
HSC - Charles Sturt University
http://www.hsc.csu.edu.au/physics/core/space/9_2_2/922net.html#net23
http://www.hsc.csu.edu.au
