Extended Duration Orbiter

The Extended Duration Orbiter (EDO) program was a project by NASA to prepare for long-term (months) microgravity research aboard Space Station Freedom, which later evolved into the International Space Station. Scientists and NASA needed practical experience in managing progressively longer times for their experiments. The original Space Shuttle configuration usually provided a week to ten days of spaceflight. Several research projects and hardware components were part of the project, of which the EDO-pallet was one of the most visible, contracted by Rockwell International.

The first orbiter outfitted with the EDO hardware configuration was Endeavour, during its construction, and its last EDO flight was STS-67, in 1995. Endeavour's EDO modifications were removed in 1996 as part of routine maintenance, to reduce the orbiter's weight prior to STS-89. Columbia was outfitted for EDO flight during its maintenance period from August 10, 1991, through February 9, 1992, prior to STS-50, which was the first EDO flight. From 1992, through 1994, Atlantis went through a maintenance period, during which Atlantis was modified to have the provisions needed for EDO capability, but NASA chose not to proceed with the final modifications, and Atlantis never had EDO capability. The EDO-pallet used in these orbiter configurations was destroyed in the 2003 Columbia disaster.

EDO Pallet
The Extended Duration Orbiter Cryogenic kit (EDO-pallet or CRYO) was a 15 ft equipment assembly which attached vertically to the payload bay rear bulkhead of an orbiter, and allowed the orbiter to support a flight of up to 16 days duration. The equipment included cryogenic tanks, associated control panels, and avionics equipment. Although Atlantis was partially upgraded to accommodate the EDO, only Columbia and Endeavour actually flew with the pallet. The pallet made its debut on STS-50, and was lost on STS-107 in 2003.

Initially, NASA considered adding a second EDO pallet to Endeavour, placed in front of the first, for a total of thirteen tank sets, that would have allowed an orbiter to remain in space for 28 days, but managers decided against it when the International Space Station assembly began, and instead removed the EDO capability from the orbiter, to reduce its weight and allow it to carry more cargo to the ISS.

No replacement for the pallet was planned, since the Station-to-Shuttle Power Transfer System provided much of the same abilities, and the 2011 retirement of the shuttle fleet made it redundant.

Specifications
The EDO tanks stored 368 lb of liquid hydrogen at -418 °F, and 3,124 lb of liquid oxygen at -285 °F. Total empty weight of the system was 3,571 lb. When filled with cryogens, the system weight was approximately 7,000 pounds (3.2 t).

Use
The EDO pallet was designed to augment the orbiter's endurance for prolonged missions by supplying additional hydrogen and oxygen for its fuel cells. These fuel cells, in turn, converted hydrogen and oxygen into electrical energy essential for the orbiter's operations. For instance, during STS-80, 5,856 kWh was produced from 3,989 lb of oxygen and 502 lb of hydrogen. For STS-50, 6,204.7 kWh was generated from 4,367 lb of oxygen and 550 lb of hydrogen. In comparison, STS-77, a mission without the EDO pallet, yielded 3,924 kWh from 2,745 lb of oxygen and 346 lb of hydrogen.

Another byproduct of the fuel cell operation was potable water. STS-77 produced 3,091 lb, while missions utilizing the EDO pallet, such as STS-50 and STS-80, yielded 4,914.6 lb  and 4,492 lb,  respectively.

Missions incorporating the EDO pallet provided extended opportunities for scientific research. They enabled detailed studies in areas like microgravity, life sciences, terrestrial observations, and astronomical observations. They also facilitated an understanding of human adaptability in reduced gravity conditions.

The following missions used the EDO pallet:

EDO medical project
Prior to the EDO project, no shuttle had flown a mission longer than 10 days. Since space travelers may faint when they stand up (orthostatic intolerance) after returning to normal gravity even after short flights, and muscle strength may be reduced, the EDOMP project focused on ensuring that the crew could land the orbiter, and exit from it without help after a 16-day flight. Astronauts on 40 shuttle flights (STS-32 through STS-72) participated in 36 EDOMP investigations. The results of these investigations were used to make rules and recommendations for 16-day flights. Several types of exercise devices (i.e. a treadmill, a cycle ergometer, and a rower) were among the devices and procedures developed to prevent the de-conditioning of the body that occurs during space flight. The crew transport vehicles, in which astronauts were transported after landing, were built to enhance medical capabilities at the landing site, as well as crew comfort and safety. A database of 125 formal publications, and 299 abstracts, technical papers, and presentations, also resulted from the EDOMP. The project saw its successor in the ISS Medical Project.

Other EDO projects and studies

 * Manual Apparel Cleaning System - A system for laundering selected items of clothing.
 * An automated Fault Detection, Isolation, and Reconfiguration-system (FDIR) that would support the shuttles for up to 28 days.
 * Extended Duration Orbiter Waste Collection System. A similar system was later added to ISS as the ISS Waste Collector Subsystem.
 * Extended Duration Orbiter Regenerable CO2 Removal System.
 * Medical Extended Medical Enterprise (MEME).