I agree that a capsule is the best approach for the OSP (we need to get something up there ASAP). However there is a subtle problem with the thermal protection. If they go with an ablator then (by definition) the heat shield is not reusable. That means the heat shield needs to be unbolted or scrapped off after every mission. An alternative is to go with insulated tiles like what is on the shuttle. However the problem with insulation type thermal protection is the heat pulse does eventually work its way through the tiles and get to the structure. With the Shuttle, they have this rig that drives up next to the shuttle immediately after it lands to pump a liquid coolant (freon?) into the Shuttle's structure. That coolant takes care of the heat pulse before it gets into the structure and causes damage. Unfortunately a good capsule design can not assume it will land next to a coolant pumping rig. Using sprayed water for cooling is a no starter. The heating experienced on a reentering spacecraft is very nonuniform. If a cooling system was like a liquid rocket motor fuel injector then too much water would spray out where there was relatively little heating while not enough water would spray where it was really needed. A modern ablating thermal protection system is really quite elegant. For example, SIRCA is a light silica foam that is impregnated with resin. The resin absorbs heat by turning into gas and carbon char (this is called "pyrolysis"). The silica foam is quite porous so the gas from ablation jets out from the surface to blow the shock layer's hot plasma away from the vehicle's surface. The hotter the plasma, the greater the blowing which causes the plasma to be further separated from the vehicle's surface. SIRCA is also a good insulator, so it provides good protection for the regions where there is no pyrolysis. This is an important issue. For example, carbon phenolic has excellent ablation properties but is a marginal insulator. A payload might cook if it had a carbon phenolic heat shield that never achieved pyrolysis. However a SIRCA heat shield would vaporized in a flash if it was exposed to a heat pulse that was appropriate for carbon phenolic.

Gary