NASA has selected Lockheed Martin to design and build the Orion. Main systems (such as power, navigation, life support, communications, and computers) will be more advanced versions of those on the Apollo and the space shuttle.
The CEV will consist of three basic parts:
- A capsule to hold the crew.
- A service module to hold the main propulsion system, power systems, and attitude controls. Attitude refers to how the spacecraft is oriented in space (x, y, and z directions or pitch, roll, yaw axes). Apollo used four units of four thrusters mounted on the service module for this task, while the shuttle uses reaction control thrusters located on the nose and aft sections.
- A booster to lift the CEV into Earth orbit.
For lunar landing missions, there will be a special module.
The capsule will be cone-shaped like the Apollo command module, because it is more aerodynamic than the shuttle. Instead of re-entering the atmosphere of Earth orbit at 8 kilometers per second (like the shuttle), the CEV will re-enter the atmosphere from the higher velocities of lunar travel, at 11 kilometers per second.
Besides shape, the CEV crew capsule has several other things in common with the Apollo, along with a few differences:
- The larger diameter (16.5 feet, or 5 meters, instead of 3.9 feet) will hold more crew and cargo.
- The CEV aft heat shield will be ablative, meaning that it will boil away. Apollo used a single, multi-layered aft heat shield made of aluminum and epoxy resin that ablated as it absorbed the heat of re-entry. (It was designed to be used only once, just like the rest of the command module.) The shuttle uses ceramic thermal tiles, thermal blankets, and reinforced carbon resins to absorb the heat. However, this concept has proven to be more difficult to service than its theoretical design. The CEV heat shield will be replaceable up to 10 times and last the design life of the vehicle.
- Air bags on the CEV will enable both land recoveries and sea recoveries. All of the Apollo's recoveries were ocean splashdowns.
- The CEV's position atop the launch booster puts it out of the way of falling debris like pieces of foam or ice.
- An escape tower -- a small rocket that lifts the command module off the booster in the event of a launch failure -- is one of the CEV's unique features. This mechanism is safer than the shuttle's abort procedures.
In the next section, we'll explore the service module and the booster.