Space Shuttle Columbia - Prototype Orbiter

Prototype Orbiter

As the second orbiter to be constructed, yet 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. This retention of an 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. Due to Columbia's heavier 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.

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. FSRI once covered almost 25% of the orbiter, though the first upgrade resulted in its removal from many areas, and in later flights 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 FIB's) after their successful use on shuttle Discovery and Atlantis. Originally, Columbia had 32,000 tiles – the upgrade reduced this to 24,300. The AFRSI blankets consist 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 are semi-rigid and can be made as large as 30" by 30". Each blanket can replace as many as 25 tiles and is bonded directly to the orbiter. The direct application of the blankets to the orbiter results in weight reduction, improved producibility and durability, reduced fabrication and installation cost, and reduced installation schedule time. The work was performed during Columbia's first retrofitting and the post-Challenger stand-down.

Despite refinements to the launcher's thermal protection system and other enhancements, 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.

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" afore an American flag on the left wing, and the pre-1998 NASA "worm" logo 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 the letters "USA" on the right wing spaced closer together; Enterprise's markings were modified to match Challenger in 1983.) From its last refit to its destruction, Columbia bore markings identical to those of its operational sister orbiters – the NASA "meatball" logo on the left wing and the American flag afore the orbiter's name on the right; only Columbia's distinctive wing "chines" remained. These black areas on the upper surfaces of the shuttle's forward wing were added because, at first, shuttle designers did not know how reentry heating would affect the craft's upper wing surfaces. The "chines" allowed Columbia to be easily recognized at a distance, as opposed to the subsequent orbiters.

Another unique external feature, termed the "SILTS" pod, was located on the top of Columbia's tailfin, 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 tailfin was later modified to incorporate the drag chute first used on Endeavour in 1992.

Columbia was also originally fitted with Lockheed Martin-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 also the only 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 (at its last refit) with the new MEDS "glass cockpit" display and lightweight seats.

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 Maintenance Down Period, 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, once in 2004, and again in 2005, but no more missions were planned for it again until 2009 when, on STS-144, it would retrieve the Hubble Space Telescope from orbit and bring it back to Earth. Following the Columbia accident, NASA flew the STS-125 mission using Atlantis, combining the planned fourth and fifth servicing missions into one final visit to Hubble. Because of the expected 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 also 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.