 Complete the following phrase:  The orbiter was protected from heat during reentry by the thermal protection system TPS, a thermal soaking protective layer around the orbiter. In contrast with previous US spacecraft, which had used ablative heat shields, the reusability of the orbiter required a multi-use heat shield. During reentry, the TPS experienced temperatures up to , but had to keep the orbiter vehicles aluminum skin temperature below . The TPS primarily consisted of four types of tiles. The nose cone and leading edges of the wings experienced temperatures above , and were protected by reinforced carbon-carbon tiles RCC. Thicker RCC tiles were developed and installed in 1998 to prevent damage from micrometeoroid and orbital debris, and were further improved after RCC damage caused in the 