Why does the Orion program need a command and service module

Question

During the Apollo missions, it made sense to have a command and servie module so you didn't have to land all the resources to get to the Moon and back (fuel, oxygen, food, etc) plus you only landed two of the three astronauts. On Orion, the ratio of resources to get the Moon vs the resources to stay on the Moon will be much different since they will be staying for up to 180 days on the surface while only 6 days will be spent getting to the Moon and back. Plus the command module will not be occupied while the lander is on the surface, everyone lands. It seems like a command and service module isn't really needed with this senario and it would enable you to add more oxygen, food, fuel to the lunar module where most of the time will be spent.

Answer 1

Like the Apollo spacecraft, the Orion will be divided into a "capsule" shaped Command Module (CM), which reenters the atmosphere, and a Service Module (SM) containing the main propulsion, avionics and consumables, which is discarded after use.

    The Orion CM will be larger than the Apollo CM (5.5 meters, or 16.5 feet, in diameter), with 2.5 times the internal volume, weighing about 50,000 pounds. The craft will carry 6 astronauts for Earth-orbit missions, and 4 for lunar missions.

Orion will descend by parachute to a dry land recovery site (with ocean splashdown as a backup); the landing will be softened by a rocket and airbags.

    The Orion Service Module will differ from the Apollo SM by using solar panels, rather than fuel cells, for electric power.

There are to be four versions of the Orion CEV:

    Block 1A: for transferring crew and cargo to and from the International Space Station.

    Block 1B: a pressurized but unmanned version for transferring cargo to and from the ISS.

    Block 2: for lunar landing missions, in conjunction with a Lunar Surface Access Module.

    Block 3: Earth reentry vehicle for Mars landing missions, in conjunction with an as yet unspecified Mars Transit Vehicle.

    A unmanned, unpressurized Cargo Delivery Vehicle (CDV) is also to be developed to transport unpressurized cargo to the ISS, using the same Service Module propulsion and avionics system as the Orion CEV.

    Each Orion Command Module is to be reusable up to 10 times. Orion development is managed by the Johnson Space Center. Orion CEV Fact Sheet 1.5MB .pdf

Answer 2

You still don't want to land all that stuff on the Moon.  Both landing and takeoff are expensive in fuel.  Remember, all that fuel has to be launched into low Earth orbit, at $10,000 a pound.  So saving thousands of pounds is saving millions of dollars.

Think about where computers are today compared to 1969.  The microprocessor chip came out in 1972.  Today's pocket computer is 1986's $16 million dollar supercomputer, except that the pocket computer has more memory and disk. So the service module can take care of itself (I'm sorry, Dave, I can't do that.)

Answer 3

it's a whole bunch better to have your ride home waiting for you.