A spherical tank for storing liquid oxygen on the space shuttle is to be made from stainless steel of $0.80-\mathrm{m}$ outer diameter and 5 -mm wall thickness. The boiling point and latent heat of vaporization of liquid oxygen are $90 \mathrm{~K}$ and $213 \mathrm{~kJ} / \mathrm{kg}$, respectively. The tank is to be installed in a large compartment whose temperature is to be maintained at $240 \mathrm{~K}$. Design a thermal insulation system that will maintain oxygen losses due to boiling below $1 \mathrm{~kg} /$ day.