Both the Apollo LRV and the space truck were and will be operated by astronauts in space suits. That means lunar exploration is limited by the length of life support the suits provide. Another downside of unpressurized rovers is that they don't protect the astronauts from solar flare events, which can potentially expose them to lethal doses of radiation. But a rover with a pressurized environment would allow astronauts to explore more of the moon and offer an emergency shelter from unexpected solar events.
That's the idea behind NASA's small pressurized rover. The SPR consists of a pressurized habitat module mounted on the lunar truck chassis. From the SPR, astronauts could explore the moon's surface from a cockpit with a wide field of view. They could also equip the module as a field science station. In fact, the SPR can go pretty much anywhere the lunar truck goes.
The rover's habitat module (or living environment) would allow two astronauts -- four in emergencies -- to live and work comfortably in a "shirt-sleeve environment" for up to three days. A shirt-sleeve environment just means one in which the astronauts don't have to wear their space suits. The lunar base is another such environment.
The pressurized module has a small bathroom, a misting showerhead for sponge baths, privacy curtains, cabinets for tools, workbench areas and two crew seats that fold back into beds. The astronauts have to rehydrate food packs because there is no kitchen. All of the features are space-saving. During field tests in Arizona, astronaut Mike Gernhardt reported that it felt comfortable, even like the space shuttle [source: NASA].
Astronauts can enter and exit the module from one shirt-sleeve environment to another by using an airlock docking hatch. They can also exit and enter the rover directly into their space suits through the suitport without having to depressurize the habitat module. That's a feat that Apollo astronauts would envy since they had to depressurize and repressurize the entire lunar module when they exited and re-entered. And unlike Apollo, astronauts wouldn't have to bring their dusty space suits inside, thereby keeping the habitat's inside cleaner. In tests of the suitport, astronauts can don space suits in 10 minutes or less.
Inside any habitat, like the lunar module or space shuttle, the instruments generate heat. To maintain a constant internal temperature, excess heat must be rejected into outer space. The lunar module rejected heat energy by evaporating water. The space shuttle uses radiators. The SPR habitat module rejects internal heat by melting ice in an ice lock around the suitport, which reduces the amount of water that the rover must carry.