I've noticed that most re-usable heat shield designs are not developed enough to be useful in the near future. The re-usable shields I've seen used in the past all use the "thermal soak" method, which adds a lot of weight and in the Space Shuttle's case, is unreliable. Other concepts that have been proposed but not used involve liquid cooling, but this adds a lot of weight and complexity.
The only truly reliable heat shields that I've seen proposed/used are ablative shields, but these degrade with use by design, especially with the high velocities that come from atmospheric re-entry when returning from the Moon or Mars. Are there any other heat shield designs I've missed that are both re-usable and practical? Are there improvements being made to thermal soak and liquid-cooled shields that could make them usable in the future?