TIM FURNISS / LONDON & GRAHAM WARWICK / WASHINGTON DC
Agency hopes development of inspection and repair methods will pave way for spacecraft to return to flight
NASA engineers will report this month on potential methods of on-orbit inspection and repair of the Space Shuttle orbiter thermal-protection system (TPS). The Columbia Accident Investigation Board (CAIB) has recommended that a capability to inspect and make emergency repairs to thermal-protection tiles and reinforced carbon-carbon panels be developed before the Shuttle returns to flight, possibly in April next year.
The board has recommended developing a practical means of inspecting and repairing an orbiter while it is docked at the International Space Station (ISS), as well as a comprehensive autonomous capability to repair the widest practicable range of damage on non-Station missions, such as flights servicing the Hubble space telescope. The CAIB wants on-orbit TPS inspections to be performed early in all Shuttle missions.
NASA says inspection methods under study include crew spacewalks using small manned manoeuvring units, and use of the remote manipulator system robotic arm fitted with cameras. Issues such as the shape of the damage and the ability of materials to adhere in orbit complicate on-orbit repair, says NASA. "There is no definitive solution, or leading candidate."
Past efforts to develop repair schemes did not succeed, but the CAIB says advances in imaging and inspection capability, materials technology and the presence of the ISS "have greatly improved the prospects for deploying the capability". NASA has already accepted the CAIB's recommendation that Shuttles be routinely imaged in orbit by US reconnaissance satellites to check for damage.
The board believes the lack of on-orbit repair capability may have influenced NASA's decision not to request imaging of Columbia in orbit to check for damage after foam insulation shed by the external tank was observed hitting the orbiter soon after lift-off. The foam strike is believed to have damaged the wing leading-edge TPS, resulting in a thermal breach during re-entry that led to Columbia breaking up.
The CAIB's fourth and latest interim recommendation is to improve imaging of the Shuttle launch and ascent. The board wants NASA to upgrade the imaging system to provide a minimum of three useful views of the Shuttle from lift-off to at least solid rocket booster separation, along any expected ascent azimuth. Only two ground-based, long-range camera sites provided usable images of the Columbia launch, and were "inadequate" to provide engineering data needed to assess debris impacts on the orbiter.
Source: Flight International