Improve or prove optimal the covering of the sphere by 20 equal spherical caps

Cover the unit sphere $S^2$ by $N=20$ equal spherical caps so that their common angular radius $r_{20}$ is as small as possible: place 20 cap centers (unit vectors) such that every point of $S^2$ lies within angular distance $r$ of some center, minimizing $r$. This is the covering counterpart of the Tammes packing problem. For $N=20$ the optimal covering radius $r_{20}$ is unknown -- only a best-known (conjectured-optimal) configuration is recorded. Exhibit a covering of $S^2$ by 20 caps of angular radius strictly less than the current best-known $r_{20}$, or prove that the best-known configuration is optimal.

Acceptance. FULLY RESOLVES: a rigorous proof determining $r_{20}$. PARTIAL (improve record): 20 unit vectors (cap centers) and an angular radius $r < r_{20}^{best}$ such that $S^2$ is fully covered; verifier -- the spherical covering radius (maximum over $S^2$ of the angular distance to the nearest center) is $\le r$, checkable exactly by evaluating that maximum at the finite set of candidate 'deepest hole' points (circumcenters of the spherical Delaunay triangles / vertices of the spherical Voronoi diagram of the centers), or via a fine spherical grid with a Lipschitz safety margin. PARTIAL: a certified lower bound on $r_{20}$.