I was bored this afternoon so I did some googling on the Constellation Program. Specifically the Altair Lunar Lander design.
It's a beast!
Look at the relative size of an Apollo astronaut to a Lunar Module...
Compared to Constellation Program astronauts to the Altair...
Of course, it needs to be a beast. The Lunar Module only needed to land and support 2 astronauts for a few days.
Altair will land 4 astronauts and support them for up to 2 weeks while their empty and automated Orion transport vehicle remains in lunar orbit awaiting their return.
That's a lot of consumables! Air, water, food, equipment, not to mention infrastructure for the permanent lunar bases.
I know I'm geeking out about this so I'll try to keep it (relatively) short.
One of the biggest problems the Apollo astronauts had was lunar dust. On Earth, dust is a soft, fluffy annoyance. On the moon, it is a jagged, abrasive hazard that clings to everything with static electricity and works its way into the deepest crevices and can compromise the integrity of spacesuits and life support equipment.
Altair attempts to solve this problem with a "front porch". It will have its own air lock!
In order to make an Apollo era moonwalk, the astronauts had to don their bulky EVA suits in the Lunar Module, depressurize the Ascent Stage and leave the front door open as they cavorted on the lunar surface.
While working on the lunar surface, they got really, really, dirty!
When they were done, they wore those dirty suits back into the Ascent Stage, repressurized the module and breathed in all of that abrasive lunar dust as it worked it's way into the primitive electronics and life support equipment. It also carried a static charge which posed its own risk to the equipment.
Altair will have an airlock that serves as storage space for the lunar EVA suits and the equipment to be deployed on the lunar surface. All of the dusty EVA stuff gets left in the airlock when the astronauts re-enter the ascent module.
You can see the airlock in the above illustration as the domed cylindrical object just to the right of the Ascent Module. The airlock is actually part of the Descent Module structure and remains on the lunar surface. It gets left behind on the lunar surface as the Ascent Module returns to Lunar Orbit to rendezvous with the Orion return vehicle.
That's a sweet piece of engineering!
Here is a tour of a really rough mock up of Altair where you can see just how big that "front porch" is.
The Altair Lunar Lander is to the Apollo Lunar Module what the Boeing 787 is to the Douglas DC 3.
I just love this shit!