to withstand reentry forces such as drag, and must reenter at a precise angle of attack to prevent a skip off the surface of the atmosphere or destructively high accelerations. When the reentry capsule comes through the atmosphere the capsule compresses the air in front of it, which heats up to very high temperatures. The surface temperature of a capsule can reach as it descends through the Earth's atmosphere. To prevent this heat from reaching interior structures, capsules are typically equipped with an ablative heat shield that melts and then vaporizes, removing the heat. The Apollo command module reentered with the center of mass offset from the center line; this caused the capsule to assume an angled attitude through the air, providing lift that could be used for directional control. Reaction control system thrusters were used to steer the capsule by rotating the lift vector. Parachutes are used for the final descent, sometimes augmented by braking rockets if the capsule is designed to land on the Earth's surface. Examples of land landing capsules include Vostok, Voskhod, Soyuz, Shenzhou and the Boeing CST-100 Starliner. Other capsules, such as Mercury, Gemini, Apollo, Orion, and Dragon, splash down in the ocean. Aerodynamic heating Capsules are well-suited to high-temperature and dynamic loading reentries. Whereas delta-wing gliders such as the Space Shuttle can reenter from Low Earth Orbit, and lifting bodies are capable of entry from as far away as the Moon, it is rare to find designs for reentry vehicles from Mars that are not capsules. The current RKK Energia design for the Kliper, being capable of flights to Mars, is an exception. Engineers building a reentry capsule must take forces such as gravity and drag into consideration. The capsule must be strong enough to slow down quickly, must endure extremely high or low temperatures, and must survive the landing. When the capsule comes close to a planet's or moon's surface, it has to slow down at a very exact rate. If it slows down too quickly, everything in the capsule will be crushed. If it does not slow down quickly enough, it will crash into the surface and be destroyed. There are additional requirements for atmospheric reentry. If the angle of attack is too shallow, the capsule may skip off the surface of the atmosphere. If the angle of attack is too steep, the deceleration forces may be too high or the heat