Endeavour launch scrubbed again

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Excess hydrogen #

Posted Wednesday 17th June 2009 10:51 GMT

Confused - why is there a potential for needing to remove excess hydrogen? Not possible just to fill 'er up and seal the tank?

I'm happy to have it explained in small words with pictures :-)

Anonymous Coward

Rocket science ain't so hard #

Posted Wednesday 17th June 2009 10:51 GMT

"We're going to step back and figure out what the problem is and go fix it. Once we get it fixed, and we're confident that we have a solution that's going to work and allow us to go fly safely, then we'll proceed forward."

Socrates could not have put it better, except maybe those last two words.

The thing will be in great shape then, so they can launch it, right?

Big Al

Ouch #

Posted Wednesday 17th June 2009 13:56 GMT

Bit rough on the astronauts, doing all that training and psyching themselves up for launch (twice!), only to be let down by some duff mechanical engineering...

Or maybe They are deliberately trying to set back the spaceflight programme...

Hakan

What about LACROSSE? #

Posted Wednesday 17th June 2009 13:56 GMT

Idiots. They delayed the LACROSSE launch just because they felt cocky. Instead they should have tried to really figure out and fix instead of "Let's just retry and see what happens. Other projects? Freck them!".

Andus McCoatover

@Annihilator #

Posted Wednesday 17th June 2009 13:56 GMT

I'd guess (tho' I'm not experienced in Rocket Science - except from lighting the blue paper on Nov. 5) that liquid hydrogen, being bloody cold boils off until the warmer tank itself gets cold. Probably a volume difference of 1000/1. So, the first bit has to be vented. Safely.

Remember the Hindenberg?

So, one might think, cool the tank first. IDEA! Let's use...liquid hydrogen...

I remember filling up superconducting magnets at Nicolet Instruments, outer core used liquid nitrogen. Vapour everywhere, but not particularly dangerous. Only then, when cold enough would we dare to put the liquid helium in. Property of gaseous helium is that it can pass through concrete - and asphyxiate everyone upstairs. BOFH...NOOOOO!!!

Ian Michael Gumby

@Annihilator... #

Posted Wednesday 17th June 2009 13:56 GMT

Didn't your high school science classes teach you a simple formula :

pV=nRT?

Just in case, check out : http://en.wikipedia.org/wiki/Ideal_gas_law

So what happens when the liquid Hydrogen heats up?

(Hint: Look at the formula and if p,n,R are all constant, if T increases, what happens to V?)

Anonymous Coward

@Excess Hydrogen #

Posted Wednesday 17th June 2009 13:56 GMT

The tank's not sealed for the same reason that you don't seal a boiling kettle. Whilst liquid hydrogen is rather cold, it is boiling nevertheless.

Mike Richards

@ Annihilator #

Posted Wednesday 17th June 2009 13:56 GMT

'Confused - why is there a potential for needing to remove excess hydrogen? Not possible just to fill 'er up and seal the tank?'

The LH2 in the external tank is at -252C. Despite having four tonnes of mind-buggeringly good insulation on the tanks, the fuel is still warming up and about 1/2 kilo of liquid hydrogen boils off every hour. If this was allowed to accumulate in the tank it would overpressurise and things would get nasty for a small part of coastal Florida.

A small amount of hydrogen gas is used to pressurise the tank so that fuel can flow to the engines, but the excess is released through a valve and back along an umbilical line to where it can be safely discharged. The umbilical is mounted in the intertank area of the ET which is the ribbed section about two thirds of the way from the bottom.

There's a similar system in place for the liquid oxygen tank which makes up the nosecone of the ET. There, excess gas is vented from the very tip of the tank through a device called the Beanie Cap. You can see it swing free of the Shuttle about two minutes before launch.

Anonymous Coward

Is it me? #

Posted Wednesday 17th June 2009 15:34 GMT

Surely with the experience NASA have this isn't rocket scie... ah, hang on a minute.

Paris, 'cos she can help vent over pressurised pipes.

Andus McCoatover

@Ian Michael Gumby #

Posted Wednesday 17th June 2009 15:45 GMT

Another Keyboard Debt Club member, you B'stard ;-)

From Wikipedia..."pV = nRT (Easy way to remember: Penis goes in Vagina, No Rump Tucking)"

Sodding hell, it ain't Friday yet. Fortunately, only the pub K/B just went to trash...(Er, what's 'rump tucking'?)

Did notice the 'p' is small, and the 'V' is big..Implying like: "Waving a pencil in the Albert Hall" or what??

(Moderatrix - about that snorted keyboard icon. I can send you a few piccies to choose from. Actually, more than a few...)

Anonymous Coward

The stupid bit... #

Posted Wednesday 17th June 2009 18:03 GMT

... is that the USAF requires 48 hours (yeah, TWO DAYS) to switch over the tracking network because it's still made up of bits from the 1950s and they've got to physically walk out and flip switches and re-aim antennas all over the "back 40".

They're doing it in a little over a day by quadrupling the manpower, and you'll notice how quiet they're keeping this.

Anonymous John