The insignia for Extended Duration Orbiter missions.

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.[1]

The first orbiter outfitted with the EDO hardware configuration was Endeavour, during its construction, and its last EDO flight was STS-67, in 1995.[1][2] Endeavour's EDO modifications were removed in 1996 as part of routine maintenance, to reduce the orbiter's weight prior to STS-89.[1] 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.[2][3] 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.[1] The EDO-pallet used in these orbiter configurations was destroyed in the 2003 Columbia disaster.

EDO Pallet

The EDO pallet mounted in the back of Columbia's payload bay

The Extended Duration Orbiter Cryogenic kit (EDO-pallet or CRYO) was a 15-foot-diameter (4.6 m) 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.[1] 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.[4]

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.[1][5]

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.


The EDO tanks stored 368 pounds (167 kg) of liquid hydrogen at −418 degrees Fahrenheit (−250.0 °C), and 3,124 pounds (1,417 kg) of liquid oxygen at −285 degrees Fahrenheit (−176.1 °C). Total empty weight of the system was 3,571 pounds (1,620 kg). When filled with cryogens, the system weight was approximately 7,000 pounds (3.2 t).[1][6]


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.[7] For instance, during STS-80, 5,856 kWh was produced from 3,989 lb of oxygen and 502 lb of hydrogen.[8]: 24  For STS-50, 6,204.7 kWh was generated from 4,367 lb of oxygen and 550 lb of hydrogen.[9]: 12  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.[10]: 20 

Another byproduct of the fuel cell operation was potable water. STS-77 produced 3,091 lb,[10]: 20  while missions utilizing the EDO pallet, such as STS-50 and STS-80, yielded 4,914.6 lb[9]: 12  and 4,492 lb,[8]: 24  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.[7]

The following missions used the EDO pallet:

EDO Flight Shuttle Mission Launch Date Duration Primary Payload(s)
1 Columbia STS-50 June 25, 1992 13 days, 19 hours, 30 minutes, 4 seconds United States Microgravity Laboratory-1[9]: 1 
2 Columbia STS-58 October 18, 1993 14 days, 0 hours, 12 minutes, 32 seconds Spacelab Life Sciences-2
3 Columbia STS-62 March 4, 1994 13 days, 23 hours, 16 minutes, 41 seconds United States Microgravity Payload-2
4 Columbia STS-65 July 8, 1994 14 days, 17 hours, 55 minutes, 1 second International Microgravity Laboratory-2
5 Endeavour STS-67 March 2, 1995 16 days, 15 hours, 8 minutes, 48 seconds ASTRO-2
6 Columbia STS-73 October 20, 1995 15 days, 21 hours, 53 minutes, 16 seconds United States Microgravity Laboratory-2
7 Columbia STS-75 February 22, 1996 15 days, 17 hours, 40 minutes, 22 seconds Tethered Satellite System-1R (reflight of Tethered Satellite System-1 on STS-46)
United States Microgravity Payload-3
8 Columbia STS-78 June 20, 1996 16 days, 21 hours, 48 minutes, 30 seconds Life and Microgravity Spacelab
9 Columbia STS-80 November 19, 1996 17 days, 15 hours, 53 minutes, 18 seconds Wake Shield Facility
10 Columbia STS-83 April 4, 1997 3 days, 23 hours, 13 minutes, 38 seconds Microgravity Science Laboratory-1
(Mission ended early due to a problem with one of Columbia's fuel cells.[11])
11 Columbia STS-94 July 1, 1997 15 days, 16 hours, 45 minutes, 29 seconds Microgravity Science Laboratory-1 (reflight of STS-83)
12 Columbia STS-87 November 19, 1997 15 days, 16 hours, 35 minutes, 1 second United States Microgravity Payload-4
13 Columbia STS-90 April 17, 1998 15 days, 21 hours, 50 minutes, 58 seconds Neurolab
14 Columbia STS-107 January 16, 2003 15 days, 22 hours, 20 minutes, 32 seconds SPACEHAB Research Double Module
FREESTAR, Lost during reentry, Space Shuttle Columbia disaster

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.[12] The project saw its successor in the ISS Medical Project.[13]

Other EDO projects and studies

See also


  1. ^ a b c d e f g Jenkins, Dennis R. (2001). Space Shuttle: The History of the National Space Transportation System. Cape Canaveral, Fla. pp. Pages 393, 437, 438. ISBN 0-9633974-5-1.((cite book)): CS1 maint: location missing publisher (link)
  2. ^ a b NASA PAO (2007). "List of Extended Duration Missions". NASA. Archived from the original on June 23, 2006. Retrieved November 16, 2007.
  3. ^ NASA (1992). "STS-50". National Aeronautics and Space Administration. Retrieved November 16, 2007.
  4. ^ NASA. "Overview of STS–107 Mission and Key Research - FS-2002-06-107-MSFC" (PDF). NASA. Retrieved 2007-11-16.
  5. ^ NASA (1992-03-03). "Artist concept cutaway view of OV-105 docked with Space Station Freedom (SSF)". NASA. Archived from the original on 2009-09-17. Retrieved 2007-11-16.
  6. ^ NASA (2007). "STS-87". NASA. Retrieved November 16, 2007.
  7. ^ a b Evans, Ben (1 April 2015). "Stretching the Shuttle: 25 Years Since the EDO Decision". AmericaSpace. Archived from the original on 3 May 2023. Retrieved 8 September 2023.
  8. ^ a b c STS-80 Space Shuttle Mission Report (PDF) (Technical report). NASA. February 1997. NSTS-37411/TM-112252. Archived (PDF) from the original on 8 September 2023. Retrieved 8 September 2023.
  9. ^ a b c STS-50 Space Shuttle Mission Report (PDF) (Technical report). NASA. August 1992. NSTS-08277/CR-193057. Archived (PDF) from the original on 26 August 2023. Retrieved 8 September 2023.
  10. ^ a b STS-77 Space Shuttle Mission Report (PDF) (Technical report). NASA. June 1996. NSTS-37408/TM-112641. Archived (PDF) from the original on 8 September 2023. Retrieved 8 September 2023.
  11. ^ NASA (2001). "STS-83". NASA. Retrieved December 8, 2007.
  12. ^ Johnson Space Center, NASA. "Extended Duration Orbiter Medical Project (EDOMP)". NASA. Archived from the original on 2008-10-04. Retrieved 2007-11-17.
  13. ^ NASA (July 17, 2007). "ISS Medical Project". NASA. Archived from the original on June 2, 2008. Retrieved 2007-11-17.
  14. ^ NASA. "Manual Apparel Cleaning System for Extended- Duration-Orbiter Shuttle Missions". NASA. Retrieved November 16, 2007.
  15. ^ Rejai, B.; Zeilingold, D.; Rehagen, S. (1992). "28-day extended-duration orbiter automated fault detection, isolation, and recovery concept definition and proof-of-concept development". AIAA Materials Specialist Conference - Coating Technology for Aerospace Systems. Harvard University. Bibcode:1992aiaa.meetZ....R.
  16. ^ a b James E. Atwater (1996). "Life Support Systems: Mercury to Shuttle". Oregon State University. Archived from the original on August 8, 2007. Retrieved November 16, 2007.
  17. ^ NASA POA (June 22, 2001). "International Space Station Waste Collector Subsystem Refurbishment DTO 692". Retrieved 2007-11-17.
  18. ^ NASA. "Bioastronautics Contract: Example Task Orders" (.doc). NASA. Retrieved November 16, 2007.