Posted on 07/14/2006 10:47:57 PM PDT by raygun
HOUSTON (Reuters) - Astronauts aboard shuttle Discovery prepared to leave the International Space Station on Friday while ground control teams revamped landing plans to handle a small leak in one of the ship's power generators.
Managers believe the leak is inconsequential but because there is not enough proof, they are proceeding cautiously.
[snip]
The shuttle has three power units needed to move the body flaps, speed brakes and other critical landing gear. It can safely land with just one, though two or more make for greater control, Shannon said.
One unit has a tiny leak, about six drops per hour, and NASA plans to test on Sunday whether the unit is safe for landing. If the leak worsens, Shannon wants the crew to dump the unit's hazardous hydrazine fuel -- even though engineers suspect a system using nonhazardous liquid nitrogen is the one leaking...
[snip]
"We don't have enough information to say whether the leak is hydrazine or nitrogen," Shannon said. "If it got bigger, it would be an issue. You just don't want hydrazine in the aft (engine compartment). You don't want it anywhere."
A space shuttle in 1983 returned with a fire in its engine compartment when a spray of hydrazine hit one of it's power units, which can reach temperatures of 500 degrees Fahrenheit.
[snip]
...the key difference between landing with two power units instead of three is that the shuttle's landing gear would be released by firing explosive bolts rather than with hydraulic power...
NASA monitors leaky pipe on space shuttle
(Excerpt) Read more at news.yahoo.com ...
This is the first I heard about a shuttle being on fire while it was landing.
Ruh-roh
ping
"This is the first I heard about a shuttle being on fire while it was landing."
Me too.
Two different articles BTW. Source listed is excerpted, link is to seperate, and more recent, article.
They're going to test on Sunday, and if it fails muster they're going to dump the hydrazine overboard and land with two power-cells (even though the suspicion at present its a nitrogen leak, they say there's no way to tell).
They intimated that 6 drops per hour is 100,000 times less than what is required to start a fire.
It should be pointed out that there are two different kinds of hydrazine on-board: monomethyl-hydrazine (CH3NHNH2) and hydrazine (H2H4). Its unclear which type of hydrazine is leaking.
Shuttle Operational Data Book - structure, systems & components locator cutaway diagrams/schematics
"This is the first I heard about a shuttle being on fire while it was landing."
There have been a lot of 'close calls' which have not been publicized (much), and this is only one.
Isn't it odd that, given how important it seems to be to know which of the two is leaking, they didn't set up the sensors so they could tell?
"100,000 times less than what is required to start a fire."
But the media will hype it like its the damage done to the Titanic.
There is a reason why the shuttle has three APUs when only one is needed.
I bet all three will be used for entry and landing.
Shuttle boss optimistic about Discovery hydraulics issue BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: July 14, 2006
Editor's Note... This story has been updated with the results of today's Mission Management Team meeting to discuss APU landing strategy. MMT Chairman John Shannon provided additional details, but our earlier story is essentially unchanged. Engineers continue to study a variety of options on the assumption hydraulic power system No. 1 has a small hydrazine leak. APU 1 will be fired up during a routine flight control system checkout Sunday. If the leak rate doesn't get worse, the unit likely will be used during entry Monday. If it does worsen, engineers will run the unit until the fuel is exhausted and Discovery will return to Earth with just two operational APUs. Quotes and details from Shannon have been added below.
Observation on TPS damage on Orbiter
Seems to me that before we head off on those lengthy manned missions to places like Mars, they'll need to be some giant leaps in equipment reliability and/or redundancy.
Discovery flew home safe after Challenger, She flew home safe after Columbia, And she will do so again on this mission.
NASA does everything in front of the eyes of the world, takes the risks in front of everyone.
People will likely die on missions to the moon and Mars in the future. People died on sailing vessels exploring our earth. Vessels of discovery sometimes do not return. Risk. That is what these ships jobs are. We pay NASA to take risks for the benefit of us all.
I fly. I am a private pilot. I fly single engine bugsmashers around underneath airliner airspace. Now, there is the old joke about skydivers saying why would you want to jump out of a perfectly good airplane? Well, I have yet to fly a perfect airplane.
Humans are not capable of perfection. But NASA comes damn close. And when you hang it out over the edge as far as NASA does, you will get bit sometimes either by the nature of exploration or our own shortcomings. You manage risk, you plan, you train, you train again, you design it as best you can and make it as redundant as possible. Ships are safe in port, but that is not what ships are for.
We should not panic at every jump of an indicator needle.
If we did, we would never fly again.
Technology has advanced greatly in the last 100 years, and that has extended our reach to new frontiers, the danger of those frontiers is different, but it will always be dangerous. The only way to learn is by doing.
And that is what Discovery is doing now.
After some investigation, the whole nitrogen thing makes absolutely no sense now whatsoever. None. The APU's don't utilize N2, they decompose hydrazine in a catlytic converter (using something similiar to K3[Cu(CN)4]), the resultant decomposed hot gases are piped into a two-stage turbine engine that drives a hyrdaulic pump.
GlobalSecurity.org essay on APU function
I really hope you're happy now that you've thrown the whole issue into utter and complete confusion about what really is going on up there now. The only thing I can speculate is that given the formulas for monomethyl-hydrazine, and plain-jane hydrazine, its evident there's a bit o' N2 in either compound, and from the schematics its plain to see that there's a hefty quantity of nitrogen tetroxide (N2O4 - used by the orbital maneuvering systems - in the same aft-engine area that detection systems capable of differentiating the two components may not be in place (in that they opted to merely detect for the presence of nitrogen). Given the quantity of the leak, it probably wouldn't cause a major impact on flight operations if it was only N2O4 that was leaking (and in either case no noticable pressure drop would be evident in either tanks). Howevever, in the case of a hydrazine leak, whoah...
Hydrazine is a monopropellant rocket fuel. It is also pyrophoric, i.e. it can (and does) ignite spontaneously. Look at the formula, for each mole of hydrazine, if it decomposes, with produce three moles of gas (two of them being pure molecular hydrogen - H2 - can you say Hindenberg?). It probably wouldn't ignite until it well into the re-entry program, but I wouldn't want to be driving a vehicle back to Earth at Mach 25 with pure hydrogen spewing out all over the place in the trunk (that would be bad, now what I mean?
P.S. Oh, and just to be clear, hydrazine is N2H4 (I really mucked that up in post #9).
Of course I didn't suggest we need to attain perfection. There's just a big difference between being able to bring the shuttle out of orbit in a day or two if need be, and being months or years from the nearest safe haven.
I know of the dangers. Before hanging up my spurs I had long since quit keeping track of my total hours. From 65 til 95, I had two tours in the Nam flying choppers, and many more years flying corporate and the airlines. I now look back on 10,000+ accident free hours.
Impressive career! clearly no lecture on risk was necessary, especially from the likes of me. LOL
The moon shall be the training grounds for Mars. Three days from home instead of months. Much can be learned there first. Also technological advancements may bring Mars much closer then we can dream now. Many believe that we may be due for a propulsion breakthrough in the next decade. We have really come very far in such a short time historically speaking, and breakthroughs of all kinds just keep coming. Very eager to see what the future brings.
Sounds like out local schools!!!!
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