The Space Shuttle Program has recently embarked on a program which will lengthen the on-orbit stay time of the Space Shuttle. In its current configuration, the orbiter is limited to a maximum of 10 days by Environmental Control and Life Support System (ECLSS) consumables, stowage constraints, and the fuel cell reactants.The capabilities of the Extended Duration Orbiter (EDO) will permit longer duration Spacelab, Spacehab, and Commercially Developed Space Facility (CDSF) missions. Additionally, the EDO may be required for Space Station Freedom assembly operations in the late 1990's. Of the National Aeronautics and Space Administration's (NASA) fleet, both Columbia (OV-102) and Endeavour (OV-105) will be modified to accomplish extended missions of up to 16 days. As a logical follow-on, NASA is currently pursuing approval of a 28-day Extended Duration Orbiter program. Endeavour, which is presently in production, is being manufactured so as not to preclude subsequent modifications which would provide the capability to achieve a 28-day mission. As compared to the current orbiter, the EDO will consist of an improved carbon dioxide removal system for the cabin to reduce the amount of stowed lithium hydroxide, a redesigned waste collection system to replace the existing unit, extra gaseous nitrogen for the crew cabin atmosphere, increased stowage volume in the middeck for food and personal effects, a new trash compactor to minimize waste volume, and additional cryogenic oxygen and hydrogen to maintain necessary power levels. The first EDO flight is scheduled for March 1992 with the United States Microgravity Lab as the payload.