Astronaut Steve Robinson will make an unprecedented repair to the belly of the space shuttle Discovery as early as Wednesday, NASA decided on Monday.
Two gap fillers are sticking out from between heat-resistant tiles on the orbiter鈥檚 belly. NASA could not be certain that it would be safe for Discovery to re-enter the atmosphere with the gap fillers protruding, even though they had done so on previous flights.
Advertisement
The space agency is concerned that the protrusions could cause extra heating and add to the already intense temperatures endured by the shuttle during re-entry.
鈥淭he bottom line is there is large uncertainty because nobody has a very good handle on aerodynamics at those altitudes and those speeds,鈥� says NASA鈥檚 deputy shuttle programme manager Wayne Hale. 鈥淭his is the new shuttle programme, the new NASA. If we cannot prove that it鈥檚 safe, then we don鈥檛 want to go there.鈥�
鈥淧rudent action鈥�
The gap fillers are used to prevent the heat shield tiles from rattling together and getting damaged during launch. Two are sticking above the tiles, one by 2.8 centimetres (1.1 inches) and the other by as much as 2.2 cm (0.9 inches) near the front of the orbiter. These protrusions were not the result of foam falling from the external tank during lift-off and hitting the orbiter. They may simply have been jostled loose by the intense vibrations of launch or the adhesive holding the gap fillers to the orbiter may have lost some of its stickiness.
NASA is concerned the protrusions could cause extra heating by disturbing the air flow behind them, creating turbulence. There could be between 10% and 30% more heating, the agency estimates.
鈥淚t was prudent to take action so that we would not have to worry about the worst consequences,鈥� Hale says.
NASA saw the worst consequences on the previous shuttle mission when Columbia was destroyed on re-entry because of a hole punched in its left wing on launch. For Discovery鈥檚 mission, NASA added tools to inspect the orbiter鈥檚 heat shield in space, and this system is what first spotted the gap fillers.
Heavy-duty scissors
The spacewalkers will squeeze the task into their third spacewalk on Wednesday. Robinson should only have to spend about 1.5 hours underneath the orbiter.
Having an astronaut manoeuvre under the orbiter has never been attempted in space. There are no handrails to hold onto, so Robinson will ride on the station鈥檚 robotic arm. Managers say the task is relatively simple.
Hale said Robinson should not need to use much force to tug the gap fillers free with his hands, between 4.4 and 22 newtons if the adhesive has failed and under 310 newtons (the equivalent of lifting a weight of 31 kilograms on Earth) if the glue is still holding the gap filler in place. But if the gap fillers do not come out easily, Robinson could hold the piece steady with forceps and then cut the ceramic-coated fabric strips with a hacksaw or with heavy-duty scissors.
To protect the sensitive tiles, Robinson will be stripped of most of his normal tools so none can float up and hit the tiles, says lead spacewalk officer Cindy Begley.
If he happens to chip a tile while removing a gap filler, he could retrieve an from the airlock to repair the tile. His spacewalking partner, Soichi Noguchi, first tested the tool on their initial spacewalk on Saturday. If these repairs do not work, NASA could attempt a fourth spacewalk.
Space shuttle Atlantis is still standing by at the Kennedy Space Center, ready to make a rescue mission if necessary. Hale says he would release Atlantis from rescue status after a successful gap filler spacewalk.
Click to view videos of spacewalks and .
