4.1 Bathysphere cable

Issue: The bathysphere is a metal ball with thick walls which is lowered to great depths suspended from a cable. The problem is that the heavy bathysphere and heavy weight of the long cable require use of a very strong cable. In the 60s, the then best steel was used to manufacture cables, but the risk of staying at the bottom was too great.

Question: How can the bathysphere cable be reliability improved?