21. However, heat shields are required for this, which add mass and constrain spacecraft geometry. 22. Space craft have heat shields to ensure a safe re-entry. 23. The crater is located approximately south of the heat shield and Heat Shield Rock. 24. The heat shield increases the mass, possibly by 15 %. 25. Phenolic resins have been commonly used in ablative heat shields . 26. The tension ties were stainless steel straps bolted to the CM's aft heat shield . 27. The Columbia Accident Investigation Board conducted the heat shield tests recently in San Antonio. 28. However, during re-entry, the Elsa's heat shield begins to disintegrate. 29. Then the relatively small ablative heat shield and finally a parachute does the rest. 30. The crater is located approximately south of the heat shield and Heat Shield Rock.
