Shuttle Z Credit - © Mark Wade

Shuttle-Z was Shuttle-C on steroids, the ultimate development of the shuttle to be used to put Mars expeditions into orbit. It would use 4 SSME's, and a third stage with 181,000 kg of propellant powered by 1 SSSME. But such designs would require new handling facilities due to the extra height of the vehicle.

LEO Payload: 87,500 kg (192,900 lb). to: 407 km Orbit. at: 28.50 degrees.

• Jenkins, Dennis R,, Space Shuttle: The History of the National Space Transportation System : The First 100 Missions, Third edition, Voyageur Press, 2001. ISBN: 0963397451. Excellent - the most comprehensive account of the design, development, and flights of the space shuttle.Takes the reader from the maze of designs during the first shuttle competition to future plans. More at amazon.com...