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Discovery may have been hit by debris

发布时间:2019-03-01 05:06:04来源:未知点击:

By Kelly Young, Johnson Space Centre (Image: NASA) (Image: NASA) (Image: NASA) A piece of foam insulation from space shuttle Discovery’s external tank may have struck the orbiter’s right wing, NASA officials said on Thursday. However, there is no evidence of damage to the craft. A new photo has revealed that an area of foam measuring 18 by 5 centimetres (7 by 2 inches) was missing from the tank near an ice-frost ramp that covers a hydrogen pressurisation line. That piece of foam debris appears to have broken into three pieces before hitting the orbiter. Based on radar tracking data, one of those pieces changed the direction of its fall near the wing, indicating it may have hit it. However, inspections have so far revealed no damage to the wing and the debris may have just been deflected by air currents near the wing. “This is the closest to a potential hit that we have out of all the data we’ve got,” said deputy shuttle program manager Wayne Hale. Falling foam is of critical concern to NASA as a chunk hit shuttle Columbia during launch and ultimately led to its destruction in February 2003. But Discovery’s launch was the most closely watched shuttle launch ever, and observers have pointed out that the more you look, the more you find. The foam fell late in the launch, when the shuttle was high in the atmosphere, and that makes it less hazardous. Engineers estimate that the maximum force that the foam could have struck the wing with was just one-tenth of the energy needed to cause damage. “When all is said and done we’re very confident that we’re going to have a very clean vehicle that’s safe to re-enter” the atmosphere, said orbiter project manager Steve Poulos, on the third day of Discovery’s 12-day mission. A larger piece of foam that came off the external tank’s hydrogen Protuberance Air Load ramp did not strike the vehicle, NASA managers say. But that foam shedding prompted NASA to ground all other shuttles until the problem is solved. Hale says he sent an email to Discovery’s crew to discuss the recent foam loss. “I told them frankly I was absolutely mortified at the performance of the external tank foam and that we were not going to fly again until we fix it,” Hale says. New sensors embedded in the front part of the wings indicate there were four areas that may have been struck by foam or ice. But photo inspections have not found any serious damage in that area, just a few scuffs. “I expect on flight day 6 we’re going to get approval to fly as is,” Hale says. NASA officials pointed out that Discovery is estimated to have 80% fewer impact sites than previous missions. Based on the best-ever images used for these checks – resolving details as small as 1.25 cm – NASA says it has seen 26 separate impact sites on Discovery’s heat shield. Historically, the average number of heat shield dings per flight is 150. New photos of the orbiter also showed a thermal blanket on the upper side of the orbiter that has come loose. But this area only reaches the relatively cool temperature of 315°C during re-entry, not nearly as hot as the underside of Discovery. Another anomaly spotted in images is a protruding gap filler used to buffer tiles during launch. NASA is concerned that the added bump on the underside of the shuttle could cause extra heating during re-entry through the atmosphere. But the shuttles have flown with protruding gap fillers at least twice before. “At this point we’re not overly concerned about this,” Poulos says. Meanwhile, the crews of the International Space Station and Discovery will spend Friday hauling gear from the station to the shuttle. NASA may also choose to do a more focused inspection of Discovery with the robotic arm. One of the candidate inspection sites is the nose landing-gear door that had a piece of tile come off during launch. Then on Saturday, astronauts Steve Robinson and Soichi Noguchi will embark on the first of three spacewalks. Discovery,