The CEV service module will also be cylindrical. It will cover and protect the heat shield of the CEV capsule while in flight and provide power, propulsion, and attitude control. The service module will be jettisoned prior to re-entry.
Some features of the service module include:
- A single engine propulsion, which will use slightly more efficient methane/oxygen fuel rather than the hypergolic mixture of Apollo SM (hydrazine/nitrogen tetroxide). Methane/oxygen fuel has a greater specific impulse than hydrazine/nitrogen tetroxide, which means a longer burn time for the same mass of propellant and greater velocities. In the future, it may be possible to make methane fuel from components on the moon and Mars to fuel this type of vehicle.
- A larger fuel capacity to make different lunar orbits and landing sites possible.
- Solar panels to generate electricity to supplement the energy from the fuel cells.
- Conduits containing liquid ammonia or water/glycol mixtures to transfer heat to radiators so it can escape into space. In outer space, the difference in temperature between sunlight and shade is about 400 degrees Fahrenheit. This uneven heating causes thermal stress on the metals in the spacecraft's structure. To counter this effect, the Apollo spacecraft rotated on its axis when going to the moon to allow solar radiation to heat the spacecraft evenly (the "barbecue roll maneuver"). The CEV will probably do the same.
- Attitude control with thrusters similar to the Apollo.
The Apollo required a massive launch vehicle (Saturn V) to lift both crew and payload. The shuttle's main engines needed to supply large amounts of thrust to the vehicle for the same reasons. The CEV launch booster, will only lift the crew, not heavy payloads. Because of this, the CEV booster can be smaller than the Apollo and space shuttle boosters.
The first stage of the CEV booster will be a solid rocket booster (SRB) named Ares I, which will be similar to the one on the space shuttle. The second stage will consist of a single space shuttle engine fueled by liquid hydrogen and oxygen tanks. Neither stage will be recovered or re-used (the shuttle SRBs were both recovered and re-used).
Manned space exploration requires placing both astronauts and payloads into orbit. Past vehicles have combined humans and payloads on the same rocket, but the CEV concept has separated these functions. The CLV will lift heavy payloads, like lunar landers, moon transfer stages and space station components. If necessary, the CLV can also be configured to launch humans.
The CLV will consist of two stages:
- The firs t stage will have five main engines fueled by liquid hydrogen and liquid oxygen (named Ares V)
- The second will have either a shuttle main engine or an Apollo J-2 engine, also fueled by liquid hydrogen and liquid oxygen.
Next, we'll look at the future of space exploration.