Issue: There is an optimum angle for safe re-entry for a manned spacecraft. Failure to meet such an angle can result in fatality and destruction.What happens if its coming in too shallow/steep? Other factors that need to be taken into consideration and appropriately treated in order for a safe re-entry are acceleration of the spacecraft, g-forces experienced by the spacecraft and lastly, the heat of the spacecraft.
Heat: The considerable amount of 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 large amount of heat, which must be tolerated and/or minimized. Spacecrafts with a 'blunt nose' produce a shockwave of air in front of them, which allows for a large amount of the frictional heat to be absorbed. Heat can also be tolerated through use of heat shields that use ablating tiles. The ablation layer vaporises or ablates under extreme heats and therefore, dissipates heat during re-entry. Porous Silica tiles are an alternative that can be placed on the exterior of the spacecraft. They dissipate (instead of ablating) large amounts of heat and are extremely good insulators. They are beneficial is that they don't require any excess of fuel in order to be carried, since they are relatively very light (composed of 90% air). Lastly, heat can be minimized by taking a longer period of time to re-enter How do you do this?, thereby lengthening the time over which energy is converted into heat. This essentially allows for an avoidance of any substantial accumulation of heat that can damage the spacecraft and the occupants within it.
Ionisation Blackout: Radio blackouts occur during a period of re-entry. They are caused by overheated air particles ionizing as they collide with the spacecraft. Radio signals are unable to penetrate these air particles and therefore, raises concern if contact is required between the spacecraft and Earth. The issue can only really be avoided or minimized, through planning the mission more carefully such that when they go into that period, the astronauts are self-sufficient and therefore, don't require communication through radio contact.
Decelerating G-Forces: The deceleration of a re-entering spacecraft produces g-forces, which are typically greater than those experienced at launch (~20g). High g-forces can potentially kill occupants and certain procedures are vital for safe re-entry. Such high g-forces are able to be tolerated by reclining the astronaut, such that blood in the body is not forced away from the brain (it also fully supports the body). Such reclining of the body is achieved through the use of a moulded fibreglass couch. G-forces can further be minimised by extending the re-entry, slowing the rate of descent.
