NASA has been asked to build a space habitat for astronauts going to Mars. The Orion capsule itself may be to small to entertain astronauts for months on their way to the red planet. NASA worked on something like this in the 90s, called TransHab. When they weren’t allowed to continue developing this habitat the rights to the patents were sold to Bigelow Aerospace that developed their Bigelow Expandable Activity Module (BEAM). We’re expecting to see that sent to the ISS later this year. Maybe most of the requested Deep Space Habitat already exists?
Popular Science: Congress wants NASA to create a Deep Space Habitat by 2018
Digital Trends: Congress wants NASA to build a Deep Space Habitat
Space.com: BEAM Ready for Space Station Trip
Bigelow Aerospace: BEAM