Complex sentence: Finally, reentry was studied using the nuclear warheads of ballistic missiles, which demonstrated a blunt, Earth-facing heat shield would create a shock wave that would force most the heat generated to flow around the spacecraft.
Split into simpler sentences: Finally, reentry was studied using the nuclear warheads of ballistic missiles. As for reentry, it was proposed a blunt, Earth-facing heat shield would create a shock wave that would force most the heat generated to flow around the spacecraft.