Samuel Oschin Air and Space Center (a planned addition to the California Science Center). Once moved, it will be permanently displayed in launch configuration, complete with genuine solid rocket boosters and external tank. Crew modules One area of Space Shuttle applications is an expanded crew. Crews of up to eight have been flown in the Orbiter, but it could have held at least a crew of ten. Various proposals for filling the payload bay with additional passengers were also made as early as 1979. One proposal by Rockwell provided seating for 74 passengers in the Orbiter payload bay, with support for three days in Earth orbit. With a smaller 64 seat orbiter, costs for the late 1980s would be around US$1.5 million per seat per launch. The Rockwell passenger module had two decks, four seats across on top and two on the bottom, including a 25-inch (63.5 cm) wide aisle and extra storage space. Another design was Space Habitation Design Associates 1983 proposal for 72 passengers in the Space Shuttle Payload bay. Passengers were located in 6 sections, each with windows and its own loading ramp at launch, and with seats in different configurations for launch and landing. Another proposal was based on the Spacelab habitation modules, which provided 32 seats in the payload bay in addition to those in the cockpit area. There were some efforts to analyze commercial operation of STS. Using the NASA figure for average cost to launch a Space Shuttle as of 2011 at about $450 million per mission, a cost per seat for a 74 seat module envisioned by Rockwell came to less than $6 million, not including the regular crew. Some passenger modules used hardware similar to existing equipment, such as the tunnel, which was also needed for Spacehab and Spacelab Successors During the three decades of operation, various follow-on and replacements for the STS Space Shuttle were partially developed but not finished. Examples of possible future space vehicles to supplement or supplant STS: Advanced Crewed Earth-to-Orbit Vehicle Shuttle II, Johnson Space Center concept for a follow-on, with 2 boosters and 2 tanks mounted on its wings. National Aero-Space Plane (NASP) Rockwell X-30 (not funded) VentureStar, SSTO spacelane concept using an aerospike engine. Lockheed Martin X-33 (cancelled 2001) Ares I (ended with Constellation cancellation) Orbital Space Plane Program One effort in the direction of space transportation was the Reusable Launch Vehicle (RLV) program,