Shuttle To Fly Without Safety Revisions

HaloZero writes "In the face of safety concerns, NASA has decided to proceed with launching the Space Shuttle Discovery in July without changes to the external fuel tank. The article states that even though Discovery's last launch shed a huge 1-pound chunk of potentially devastating foam, they're willing to wait to change the spec on the disposable tank. The changes would modify the Ice/Frost Ramp assemblies, which prevent a buildup of ice on fuel lines and cables (as a side effect, they also have a tendency to dislodge large chunks of insulation)."

Comments

Flying without some of the safety changes

[flooey]

The summary is possibly a little misleading. Several safety changes have been made to the foam so far, but there are further changes they'd like to make. It's not like they're flying without any changes whatsoever. That's not to say that I completely agree with the decision, but it's an important point.

Re:Flying without some of the safety changes

[iamlucky13]

Correct. Foam pieces falling from the area in question (the ice ramp) have been observed to be too small to cause major concern, based on their calculations and testing, or will safely clear the orbiter (I forget which). They had been considering replacing the foam in this area with heaters. There has to be some sort of protection or else ice might build up. Ice hitting something at 500 mph is a lot worse than foam. I assume the combination of not wanting to add another active system (which can fail) and needing extra power supplied while sitting on the pad were contributors to this decision.

After the loss of Columbia, NASA removed a foam ramp from the tripod area that holds the external tank in place. This is where the piece that caused the damage came from. In Discovery's last flight (and I believe in some older launch videos), foam was also observed to come off the proturbence air load (PAL) ramp, which is another aerodynamic feature. This was also eliminated. Additionally, NASA is going to be flying a gentler flight profile on remaining missions (listed as "Low Q"). They lose a little bit of load capacity doing this, but the acceleration is lower and their speed is slower in the denser levels of the atmosphere.

Re:Flying without some of the safety changes

[Frequency Domain]

ice hitting something at 500 mph is a lot worse than foam.

You'd think that ice would be more dangerous than foam, but you'd be wrong. I had the pleasure of chatting last December with one of the astronauts who was doing the accident review. According to her the danger is more from relative velocity differences than from mass, since kinetic energy goes up quadratically with velocity and only linearly with mass. The problem with the foam is that it has such a low density that it decelerates very rapidly from aerodynamic drag after breaking loose. Ice, because of its much greater density, retains it's velocity and hits surfaces below at a much lower relative velocity. Given a choice between being hit by a chunk of ice at a few tens of mph, and a chunk of foam with the a tenth of the mass at hundreds of mph, you're better off with the ice.

Re:Go Back to the Old Foam?

[A non-mouse Cow Herd]

You are incorrect. Please read the CAIB report (see chapter 3, part two here http://www.nasa.gov/columbia/caib/PDFS/VOL1/PART01 .PDF). The foam that destroyed Columbia was the old foam. The 'new foam' was only used on machine sprayed areas, while hand formed areas used the old foam.

Furthermore, foam loss was experienced long before the switch, including incidents which caused serious damage. Quoting from the above.

F3.27 Foam loss occurred on more than 80 percent of the 79 missions for which imagery was available to confirm or rule out foam loss. F3.28 Thirty percent of all missions lacked sufficient imagery to determine if foam had been lost.

The new foam did initially suffer from more loss and popcorning, however, it was the old foam that destroyed Columbia.

Re:Stating the OBVIOUS

[iamlucky13]

Two definite factors I can think of are (1) - it's more difficult to apply and to inspect and (2) - The structural volume of the tank would have to be larger, increasing the overall weight.

Two possible factors (I don't know enough about this, but I suspect they would cause problems) are (3) - The foam is porous. If fuel seeped into the foam, it would significantly reduce the insulating value of the foam allowing the fuel to heat up and boil off or ice to form on the outside of the tank as well as reduce the amount of fuel that could be used. (4) - The foam may react with the fuel, causing the enginges to burn inefficiently or even allowing the foam to explode in the liquid oxygen tank (similar to what happened on Apollo 13).

Re:1970's cars more reliable? Pull the other one!

[iminplaya]

Compare this to our new shiney '05 dodge Grand Caravan...

You're comparing a Chevy to a Dodge!?