Nasa engineers on Monday pored over new imagery of the space shuttle Endeavour‘s underbelly to decide if its damaged heat shield needed repair, as astronauts prepared for the mission’s second spacewalk.
The three-dimensional images of a gouge in the shield were taken on Sunday by a camera, and measured by a laser, both of which were trained on the shuttle’s protective surface.
The examination took about three hours as the imaging devices atop a 30m-long robotic arm coupled with the Orbiter Boom Sensory System (OBSS) scanned five areas on the shuttle underside that may have been damaged during Wednesday’s launch from Cape Canaveral, Florida, the National Aeronautics and Space Administration said.
The gouge, 30,5 x 25,5 millimetres — smaller than initially reported — and 28,5 millimetres deep, was made near a landing gear hatch by a piece of foam, possibly covered with ice, that broke off the shuttle’s external fuel tank shortly after blast-off.
Mission management team chairperson John Shannon said an exact mould of the gash will be reproduced in thermal tiles and tested in a laboratory that simulates the extreme heat and friction the shuttle encounters on re-entry to Earth.
Nasa engineers will be able to ”do a thermo analysis model … to understand what the actual heating impact of re-entry will be for a damage of this type”, he told a press conference.
The tests, to be carried out ”in the next 24 to 48 hours”, should provide engineers enough data to determine whether repairs are needed to the damaged heat shield before the shuttle undocks from the International Space Station (ISS) on August 20, he said.
”If it comes back that a repair is desirable to do,” he added, ”we have three different methods of doing that. I don’t have an idea right now whether a repair will be required or which kind of repair” will be used.
The available repair options include heat reflecting paint, a paste to fill in the hole and a metal plate to completely cover the damaged thermal tile.
”We are really prepared for exactly this case since Columbia,” Shannon said, referring to the February 2003 disaster of the shuttle Columbia that killed seven astronauts.
The foam came off the shuttle’s fuel tank, which holds super-cold liquid hydrogen fuel for the take-off and is jettisoned before orbit is reached. An insulation layer on the tanks is supposed to prevent icing.
Nasa keeps a watchful eye on the shuttle’s thermal shield since the Columbia disaster.
Columbia‘s protective heat shield was pierced by a piece of insulating foam that peeled off its external fuel tank during lift-off. The breach resulted in the shuttle disintegrating as it re-entered Earth’s atmosphere, killing all seven astronauts on board.
Also, space officials decided on Sunday to extend the mission by three days, which means that Endeavour, launched on Wednesday from Cape Canaveral, will now return to Earth on August 22, a Nasa spokesperson said.
The extra time will allow a fourth, additional spacewalk to the mission to continue construction work on the International Space Station (ISS). On Saturday the ISS was expanded with a new truss segment attached by two astronauts.
Endeavour‘s tour was initially planned for 11 days, with three space walks. Nasa however said from the start it would extend the mission after testing a new system that transfers electricity from the ISS to the shuttle.
The system, which prolongs the life of the shuttle’s batteries and allows it to remain aloft longer, was tested successfully on Sunday.
Also on Sunday, preparations began for the mission’s second spacewalk, due to start at 15.31pm GMT on Monday, during which astronauts Dave Williams and Rick Mastracchio will replace a faulty gyroscope aboard the ISS.
The space station has four gyroscopes that are used to control its attitude.
On Saturday, Mastracchio, of the United States and Canadian Dave Williams spent six hours and 17 minutes installing and activating a new, 1,58-tonne segment for the ISS the Endeavour brought up. – AFP
