Gouge Found on Shuttle Endeavour's Underside

SonicSpike writes " NASA has discovered a chunk missing from the underside of the space shuttle Endeavour. It was discovered after the shuttle docked with the ISS earlier today. Technicians theorize it may have been caused by ice ripping free of a fuel take during takeoff. From the article:'The gouge — about 3 inches square — was spotted in zoom-in photography taken by the space station crew shortly before Endeavour delivered teacher-astronaut Barbara Morgan and her six crewmates to the orbiting outpost ... On Sunday, the astronauts will inspect the area, using Endeavour's 100-foot robot arm and extension beam. Lasers on the end of the beam will gauge the exact size and depth of the gouge, Shannon said, and then engineering analyses will determine whether the damage is severe enough to warrant repairs. Radar images show a white spray or streak coming off Endeavour 58 seconds after liftoff. Engineers theorize that if the debris was ice, it pierced the tile and then broke up, scraping the area downwind. Pictures from Friday's photo inspection show downwind scrapes."

Re:Can't be the First Time

[AKAImBatman]

I'm sure it did, but there were several other issues as detailed in this Space.com article [space.com]:

Foam coming off the tank because of improper application; deficiencies in the materials used; degradation during its transport to the Cape; the loading of supercold fuels; and the violent ride to space. Florida Today reported earlier this year that foam came off the tank on at least 71 flights to date, but NASA did not consider the resulting damage to the heat shield a safety issue.

Requirements and specifications not being followed in testing and manufacturing of the external tank.

Loss of institutional knowledge and experience at NASA and the Michoud plant because of "lots of old-timers retiring or taking buyouts" as the shuttle program reduced its workforce throughout the latter half of the 1990s.

NASA's limited insight into changes vendors had made with materials used in making the tanks.

Environmental requirements requiring removal of freon from the process for spraying the foam insulation onto the tank. NASA has said that the freon-free application method resulted in foam that initially did not adhere to the tank as well, but changes were later made to strengthen the bond of the environmentally friendly foam.

On top of all that, the shuttles themselves are just getting *old*. I imagine that leads to all sorts of maintenance and structural issues. They may still be within engineering tolerances, but engineering tolerances for the Shuttle predicted a 1 in 100,000 flight failure. A figure which Richard Feynman challenged [fotuva.org] and reduced to somewhere between 1 in 50 and 1 in 100.

So far we're on target for Dr. Feynman's predictions. :-/

More reading

[Anonymous Coward]

Here's a non-sensationalist summary of the situation that's not just yanked from AP:

http://www.nasaspaceflight.com/content/?cid=5195 [nasaspaceflight.com]

The damage is likely minor, but the media loves jumping on these things.

Re:It's curtains for them

[Anonymous Coward]

Actually it depends a lot on the shape and mass of the piece of debris. When the piece of debris separates from the fuel tank it has the same velocity as the shuttle. Then it interacts with the atmosphere. For a piece of foam, it will slow down extremely rapidly in the lower atmosphere so that there is a large difference in velocity when the Shuttle rams it. In the upper atmosphere which is much more diffuse the difference in velocity will be much slower. For a piece of ice which will have a high mass and possibly a streamlined shape, it would not slow down nearly as much as a piece of foam. But the ice might have a greater mass. Depending upon the situation the kinetic energy (1/2*mv^2) may be higher for the foam due to the square of the velocity term.

For these reasons a loss of foam in the upper atmosphere when the Shuttle is traveling Mach 15 (for example) is not as serious as a loss of foam in the lower atmosphere when the Shuttle is traveling Mach 1. The point of maximum damage for a piece of foam or ice will occur when the slowing down of the debris relative to the speed of the shuttle is at a maximum. The piece that doomed Columbia broke off when Columbia was traveling roughly 1700 mph at about 80,000 ft. It was estimated that the piece struck with a difference in velocity of about 530 mph. This is relatively close to Max Q. Any impact within about 30 seconds of Max Q is very dangerous.

Re:Perseid meteor shower

[florescent_beige]

Lucky for you my young padawan I have no life.

Does anyone know how/if NASA handles things like micrometeorites?

Dunno exactly, how's that for a start? I do know the shuttle's glazings are replaced [nasa.gov] about once every 10 flights due to impact, mostly with man made stuff like paint chips from exploded satellites. Just guessing here and don't quote me, but the way they deal with this is probably with stats. As in, if a chip of paint can ding a window, I guess a gram-sized piece of debris can poke two holes in the orbiter (an in and an out). Although, that might not be fatal if it doesn't pass through someone's body, the little hole can probably be patched with, you know, the space shuttle hole patch kit they must have.

The Orbiter is maneuvered [nap.edu] to avoid known space debris, but that only goes down to about tens [esa.int] of centimeters. So stuff smaller than that has to be handled with stats.

Re:It's curtains for them

[Anonymous Coward]

That is NOT a sacrifice, I would gladly take the risk of death for the chance to experience a trip to space.

Re:Can't be the First Time

[Anonymous Coward]

The Shuttle rolls over as a proactive measure to facilitate an aborted launch.

Re:Where's the 250 Foot Robot?

[Anonymous Coward]

But it comes in handy if you have any trouble with angels.

Re:Geography

[Xolotl]

The Atlantic is much bigger than the desert areas and much less populated, so there is even more of a safety margin if something comes down. More significantly though, it is close to the equator, where the velocity boost from the rotation of the Earth is greater, so larger payloads can be carried. This is more significant than the slightly thinner air in the high desert.