By Liz White, editor
Cape Kennedy, Florida - Although the insulation foam which came off the external tank of space shuttle Endeavour during the 15 July take off of the STS 127 mission caused some concern initially, mission experts at NASA are now sure no damage to the vehicle's protective heat shield occurred.
In a 16 July mission briefing shown on NASA TV, John Shannon, shuttle programme manager said, "What we saw here was strips of the foam covering the intertank structure (the stringers) [that] peeled off the primer layer on the metal." This foam shedding mostly occurred more than three minutes after lift off, a stage when damage is unlikely as the foam's velocity is limited.
The insulating polyurethane foam, used to keep the fuel tanks of liquid oxygen and hydrogen tanks at the right temperature, and prevent ice formation, is only about half an inch (12 cm) thick in the intertank region, Shannon said. Little sheets came off in 7-8 different areas, he added.
Shannon indicated that it "looks like the primer is not holding the foam on," and said the team doesn't understand why, and needs to for the next mission.
Foam loss is a high concern on shuttle missions since the disastrous break up of the Columbia shuttle on re-entry 1 Feb 2003, killing all seven crew members, was shown to be caused by damage to the heat shield from a large piece of foam which broke off the external tank during lift-off.
For the current mission all the inspections of the tiles on the shuttle have indicated only minor superficial damage, none of which would cause any problems, and Endeavour's heat shield has been cleared for re-entry.
In the 17 July briefing, after further inspections, Mike Moses, chair of the mission management team, said there were about "16 dings in forward chine area," of the shuttle, which he classified as little scuff marks. One was a little deeper, but there are "No real worries with any of these areas."
Shannon, the previous day, also pointed out what he called "good news." On the liquid hydrogen tank "where problematic foam loss occurred previously, the foam looks to be "in outstanding shape. All of the modifications we have done to the ice frost ramps, the feed line," and other areas, "all looked like they performed extremely well," Shannon said.
Meanwhile, inspections continue on the foam on the tank destined for the next shuttle mission, STS 128, which is on site at the Kennedy Space Center, in Florida.
As Shannon pointed out, NASA can bore into the foam, glue a probe on, and pull it out, to see how it is performing and assess whether there are material or process issues with the foam.
Press reports on 23 July said engineers at KSC had carried out 26 of these foam adhesion tests on the intertank area, pulling out small cores of foam to see if the sprayed-on insulation is bonded to the tank structure.
PIC: Plug-pull tests being performed on foam at the intertank area of ET 132 at KSC: photo NASA/Tim Jacobs.