First operational orbiter

Weightedit

As the second orbiter to be constructed, and the first able to fly into space, Columbia was roughly 8,000 lb (3,600 kg) heavier than subsequent orbiters such as Endeavour, which were of a slightly different design, and had benefited from advances in materials technology. In part, this was due to heavier wing and fuselage spars, the weight of early test instrumentation that remained fitted to the avionics suite, and an internal airlock that, originally fitted into the other orbiters, was later removed in favor of an external airlock to facilitate Shuttle/Mir and Shuttle/International Space Station dockings. Due to its weight, Columbia could not have used the planned Centaur-G booster (canceled after the loss of Challenger). The retention of the internal airlock allowed NASA to use Columbia for the STS-109 Hubble Space Telescope servicing mission, along with the Spacehab double module used on STS-107.citation needed Due to Columbia's higher weight, it was less ideal for NASA to use it for missions to the International Space Station, though modifications were made to the Shuttle during its last refit in case the spacecraft was needed for such tasks.

Thermal protection systemedit

Externally, Columbia was the first orbiter in the fleet whose surface was mostly covered with High & Low Temperature Reusable Surface Insulation (HRSI/LRSI) tiles as its main thermal protection system (TPS), with white silicone rubber-painted Nomex – known as Felt Reusable Surface Insulation (FRSI) blankets – in some areas on the wings, fuselage, and payload bay doors. FRSI once covered almost 25% of the orbiter; the first upgrade resulted in its removal from many areas, and in later flights, it was only used on the upper section of the payload bay doors and inboard sections of the upper wing surfaces. The upgrade also involved replacing many of the white LRSI tiles on the upper surfaces with Advanced Flexible Reusable Surface Insulation (AFRSI) blankets (also known as Fibrous Insulation Blankets, or FIBs) that had been used on Discovery and Atlantis. Originally, Columbia had 32,000 tiles – the upgrade reduced this to 24,300. The AFRSI blankets consisted of layers of pure silica felt sandwiched between a layer of silica fabric on the outside and S-Glass fabric on the inside, stitched together using pure silica thread in a 1-inch grid, then coated with a high-purity silica coating. The blankets were semi-rigid and could be made as large as 30" by 30". Each blanket replaced as many as 25 tiles and was bonded directly to the orbiter. The direct application of the blankets to the orbiter resulted in weight reduction, improved durability, reduced fabrication, and installation cost, and reduced installation schedule time. All of this work was performed during Columbia's first retrofitting and the post-Challenger stand-down.

Though the orbiter's thermal protection system and other enhancements had been refined, Columbia would never weigh as little unloaded as the other orbiters in the fleet. The next-oldest shuttle, Challenger, was also relatively heavy, although 2,200 lb (1,000 kg) lighter than Columbia.

Markings and insigniaedit

Columbia was the only operational orbiter with black chines. These were added because at first, shuttle designers did not know how reentry heating would affect the craft's upper wing surfaces.citation needed The chines allowed Columbia to be easily recognized at a distance, unlike the subsequent orbiters. The chines were added after Columbia arrived at KSC in 1979. The only other orbiter with black chines was Pathfinder, but it was a cosmetic test article and only gained it when was refurbished.

Additionally, until its last refit, Columbia was the only operational orbiter with wing markings consisting of an American flag on the port (left) wing and the letters "USA" on the starboard (right) wing. Challenger, Discovery, Atlantis, and Endeavour all, until 1998, bore markings consisting of the letters "USA" above an American flag on the left-wing, and the pre-1998 NASA "worm" logotype afore the respective orbiter's name on the right-wing. Enterprise, the test vehicle which was the prototype for Columbia, originally had the same wing markings as Columbia but with white chines and the "USA" letters on the right-wing spaced closer together. Enterprise's markings were modified to match Challenger in 1983. The name of the orbiter was originally placed on the payload bay doors much like Enterprise but was placed on the crew cabin after the Challenger disaster so that the orbiter could be easily identified while in orbit.

From its last refit to its destruction, Columbia bore markings identical to those of its operational sister orbiters – the NASA "meatball" insignia on the left-wing and the American flag afore the orbiter's name on the right-wing.

SILTS podedit

Another unique external feature, termed the "SILTS" pod (Shuttle Infrared Leeside Temperature Sensing), was located on the top of Columbia's vertical stabilizer, and was installed after STS-9 to acquire infrared and other thermal data. Though the pod's equipment was removed after initial tests, NASA decided to leave it in place, mainly to save costs, along with the agency's plans to use it for future experiments. The vertical stabilizer was later modified to incorporate the drag chute first used on Endeavour in 1992.

OEX/MADS "black box"edit

One unique feature that permanently stayed on Columbia from STS-1 to STS-107 was the OEX (Orbiter Experiments) box or MADS (Modular Auxiliary Data System) recorder. On March 19, 2003 this "black box" was found slightly damaged but fully intact by the U.S. Forest Service in San Augustine County in Texas after weeks of search and recovery after the Space Shuttle Columbia disaster. The OEX/MADS was not designed to survive a catastrophic loss like an airplane black box.

Other upgradesedit

Columbia was originally fitted with Lockheed-built ejection seats identical to those found on the SR-71 Blackbird. These were active for the four orbital test flights, but deactivated after STS-4, and removed entirely after STS-9. Columbia was the only spaceworthy orbiter not delivered with head-up displays for the Commander and Pilot, although these were incorporated after STS-9. Like its sister ships, Columbia was eventually retrofitted with the new MEDS "glass cockpit" display and lightweight seats.

Planned futureedit

Had Columbia not been destroyed, it would have been fitted with the external airlock/docking adapter for STS-118, an International Space Station assembly mission, originally planned for November 2003. Columbia was scheduled for this mission due to Discovery being out of service for its Orbital Major Modification, and because the ISS assembly schedule could not be adhered to with only Endeavour and Atlantis.

Columbia's career would have started to wind down after STS-118. It was to service the Hubble Space Telescope two more times between 2004 and 2005. Following the Columbia accident, NASA flew the STS-125 mission using Atlantis, combining the planned fourth and fifth servicing missions into one final mission to Hubble. Because of the retirement of the Space Shuttle fleet, the batteries and gyroscopes that keep the telescope pointed will eventually fail, which would result in its reentry and break-up in Earth's atmosphere. A "Soft Capture Docking Mechanism", based on the docking adapter that was to be used on the Orion spacecraft, was installed during the last servicing mission in anticipation of this event.

Columbia was scheduled to launch the X-38 V-201 Crew Return Vehicle prototype as the next mission after STS-118, until the cancellation of the project in 2002.self-published source?