NASA Scrubs Launch Due to Faulty Fuel-Tank Sensor

VUSE g-EE-k writes "NASA has scrubbed Wednesday's launch of Discovery due to a faulty fuel-tank sensor in the external fuel tank. They are going to begin the troubleshooting process. They have not released details as to how long this delay will last. The crew have begun to get off the shuttle. For more information, see the NASA TV site. Drudge Report has some initial coverage of the scrub." Reader adefa adds a link to NASA's Space Shuttle launch page with more info.

Comments

Begin the countdown!

[HyperChicken]

Conspiracy in 5, 4, 3, 2...

Re:Begin the countdown!

[Lumpy]

Rumors were that there were Al Quidea terrorist members hiding inside the engines waiting to strike just before the shuttle left the atmosphere.

Also they found a saddle strapped to the main fuel tank with a note that it was reserved for Lance Bass.

Re:Begin the countdown!

[Scoria]

If you scrutinize a vehicle that is several decades old, it's likely that you'll find a number of unforeseen defects. Even vehicles that are well-maintained suffer from the aging process.

Just to play devil's advocate, a conspiracy theorist might argue that this is one method by which to stop space exploration: Emphasize safety in a medium where safety cannot under any circumstance be guaranteed, scrutinize the aging shuttle until a defect is found, and finally decline the funding required to build a replacement. Repeat. ;-)

Re:Begin the countdown!

[eggoeater]

The external fuel tank burns up in the atmosphere after launch. They are never reused or AFAIK even recovered. The external fuel tank on the pad now, and every part in it, is brand new.

Re:Begin the countdown!

[NeoThermic]

>Why not just put in 10 sensors and as long as 3 or 4 are working then go ahead launch.

They did. There's four fuel sensors, of which one was faulty. You can launch on two, you can use it on just one. Its not a critical system in most respects, but since this fault is a bit odd, they decided to scrub the launch and check it over.

NeoThermic

Re:Begin the countdown!

[Alex P Keaton in da]

Good point- although I wish to take it a step further. Yes any vehicle a few decades old will show some bumps, even if maintained (My grandmother's 78 Caddy, only 32,000 miles, but a few bumps), but even well maintained vehicles (My Pick Up, Used to plow snow for extra money in winter- beat to heck- well maintained though). The severity of what the shuttle goes through is also a huge factor I imagine. Amazing temps and pressures. I don't pretend to have the knowledge about rocket science others here do, but I do know the shuttle goes through some majorly extreme stress and conditions...

It isn't "funny," as nothing that has to do with lefe and death of the crew members is funny, however, I feel like NASA keeps having these setbacks in an almost tragicomic way. I mean, a cover falling off a window and damaging heat tiles? I read that the cover is to prevent dust- so why does it need to be made of something hard that can damage the shuttle? Wouldn't cotton have done as nicely? If someone knows, I really am curious, I am not being a jack-a##

Re:Begin the countdown!

[saigon_from_europe]

Actually, it typically lands in the Indian Ocean (it doesn't completely burn up), but you're correct otherwise.

I believe you mean "it typically oceans in the Indian Ocean"?

Don't worry...

[Loonacy]

I'm still confident they'll launch before DNF or Longhorn are released.

Re:Don't worry...

[m50d]

And debian sarge. Oh, wait. Dammit!

Redundant system

[Fiz Ocelot]

One of four sensors used to detect a low level of hydrogen propellent. They need 2 to work of the four. After they detank, it can be diagnosed, possibly launching tomarrow.

Re:Redundant system

[plover]

Thanks for the explanation.

From the article above, I first read it as "a sensor that detects if the fuel tank is present". That didn't sound too critical, because it's a "look-out-the-window-and-see-if-it's-still-there" kind of problem.

Re:Redundant system

[Aglassis]

They had a fuel low level sensor fail. This was some sort of instrumentation and control equipment or sensor fault. The possible causes could be that the actual sensor failed (which might require replacing the liquid fuel tank) or there was an instrumentation fault. Since they were using a test circuit to simulate a low level (since the tank is actually full), an instrumentation failure could be either a failure in the normal instrumentation circuitry or a failure in the test circuitry. Either of these two cases should be easy to fix.

As someone who has worked extensively on I&CE operation, maintenance, and repair on nuclear reactors, I fully understand why they scrubbed the launch. Redundancy is for faults in operation, not to compensate for damaged equipment prior to operation. From my experience, it is probably the test circuit that failed. Then the instrumentation circuitry. Then, in the most unlikely case, the sensor itself.

An astronaut on NASA TV explained that the there is a coincidence circuit if two low level alarms trigger that will cause an automatic engine turnoff. If this did not happen and the tank completely emptied, he said that it could cause major damage to the shuttle's main engines. I'm not sure exactly how, perhaps because either without liquid hydrogen, only the oxygen would flow through the engine and no chemical reaction would occur, cooling parts of the engine below their specifications? Or flow characteristics wouldn't be predictable?

Re:Redundant system

[b1t r0t]

Cause the last thing they want is to launch, and then run out of gas while in orbit!

That's pretty close... actually they don't want to run out of gas before reaching orbit. I was watching NASA TV and they mentioned that the purpose of the sensors is that the main engines don't take very well to suddenly running out of fuel when they're going at full throttle. This would allow them to know when fuel was low so that they could throttle back.

Re:Redundant system

[EvilTwinSkippy]

Unlike your car engine, where a loss of fuel simply stops the process, the shuttle actually has to suck in the fuel out of the tank, and then ram the propellent into the nozzel at a pretty high rate of speed.

If you tried to run the engines without any fuel in them, it would be like putting your foot to the floor when the transmission is in neutral. Without a load the engine spins faster and faster until parts start flying off.

On the shuttle, the turbines are large enough that a catostrophic failure would probably destroy most of the equipment in the tail end of the craft. This includes the orbital maneuvering system, the hydrolic system, several fuel cells, and the rearmost parts of the cargo bay. You also run an outside risk of damaging the tail and flight surfaces on the wings.

Not a fun thought at all.

Re:Redundant system

[Anonymous Coward]

From the Shuttle Operational Data Book:

There are eight propellant-depletion sensors, four each for fuel and oxidizer. The fuel-depletion sensors are located in the bottom of the fuel tank. The oxidizer sensors are mounted in the orbiter liquid oxygen feed line manifold downstream of the feed line disconnect. During SSME thrusting, the orbiter general-purpose computers constantly compute the instantaneous mass of the vehicle due to the usage of the propellants. Normally, main engine cutoff is based on a predetermined velocity; however, if any two of the fuel or oxidizer sensors sense a dry condition, the engines will be shut down.

The locations of the liquid oxygen sensors allow the maximum amount of oxidizer to be consumed in the engines, while allowing sufficient time to shut down the engines before the oxidizer pumps cavitate (run dry). In addition, 1,100 pounds of liquid hydrogen are loaded over and above that required by the 6-1 oxidizer/fuel engine mixture ratio. This assures that MECO from the depletion sensors is fuel-rich; oxidizer-rich engine shutdowns can cause burning and severe erosion of engine components.

Re:Redundant system

[Rei]

You run the SSMEs fuel-rich for two main reasons.

* It gives better ISP by reducing the number of atoms in the exhaust stream molecules (H2 vs H2O), thus increasing the amount of directional translational energy compared to rotational and vibrational energy (not because of the lower mass/higher velocity of the output gas, like some sites and even textbooks mistakenly state, because you get less energy output from the reduced reaction rate at the same time and thus over-cancel out the effect)

* It strongly reduces corrosion (not that a mixture containing incredibly hot hydrogen isn't corrosive; it's just less corrosive than a mixture containing incredibly hot oxygen, as far as the combustion chamber and nozzle linings are concerned)

The latter issue is undoubtedly the reason for concern of running out of hydrogen.

Another article link

[JLSigman]

In case others get Slashdotted, Here's CNN.com's article.

Launch window?

[captnitro]

Anybody know how big their launch window is? I was under the impression they had a very small amount of time to be able to meet the ISS.

Re:Launch window?

[MyLongNickName]

I think their launch window broke.

Re:Launch window?

[UMhydrogen]

NASA has through July 31 to launch Discovery or else wait until September 9 due to the need to lift off and separate the external tank in daylight.

Re:Launch window?

[InfiniteWisdom]

There's a daily lauch window of about 10 minutes when the ISS is in the right place. Those 10 minutes occur during the night between July 31st and September 9th.

Re:Launch window?

[saider]

Actually, yes.

The ascent path to the ISS will be partially or completely dark for the next few months after the window. This is because of the mechanics of the ISS orbit. Basically they have to make sure that the ISS passes reasonably close to the launch pad and that that pass occurs early enough in the day, so that it is still daylight a few thousand miles downrange.

Better safe than sorry

[ravenspear]

Hopefully they will get the issue fixed soon.

They have until July 31st in the current launch window if I recall correctly.

Fuel sensor

[MyLongNickName]

I have a faulty fuel sensor in my car. My solution: just fill up every few days to make sure I don't run out of gas. Why can't these "genius" rocket scientist just have the crew stop off and get gas half way up, and again when they come back down?

Dammit, *I* should be in charge of NASA.

(please note, that this post is as insightful as most of the other Slashdot 'advice' to NASA. please mod accordingly)

Drudge - WTF?!?

[RealityMogul]

Why link to Drudge??? WHY!?!?

Just so you all know - here's the "initial coverage" he has which was just a link to an AP blurb on Yahoo:

"KENNEDY SPACE CENTER - Today's launch of the space shuttle "Discovery" has been scrubbed. The launch was called off because of a faulty fuel-tank sensor. Discovery was supposed to take off for the first shuttle flight since the "Columbia" disaster of two and a-half years ago."

Re:Drudge - WTF?!?

[victor_the_cleaner]

Probably because that's the echo chamber that the origianl poster gets all his/her news from.

I had to laugh though... Drudge Report had some initial coverage

I have a few friends that work in the Public Information/Media Relations department at KSC. I'll check to see if Drudge was issued a press credential.

Drudge Report, where I go for all my hard-hitting science news.

Re:Drudge - WTF?!?

[Good Sumerian]

I totally read that as Kentucky Space Chicken.

Troubleshooting to begin shortly

[Alizarin Erythrosin]

NASA engineers are waiting for the astronauts to disembark so they can troubleshoot the sensor while the tank is still full. The way they were discussing it on NASA TV, the tank will be defueled at some point, so they wanted to run some tests before that.

Troubleshooting process?

[savagedome]

They are going to begin the troubleshooting process

Trouleshooting prcocess??? Alright. In words of George Carlin:

Whole thing starts when you get to the gate. First announcement, "We would like to begin the boarding process." Extra word, "process", not necessary. Boarding is enough, "We'd like to begin the boarding." Simple! Tells the story...

People add extra words when they want things to sound more important than they really are. "Boarding Process" sounds important.... It isn't! It's just a bunch of people getting on an airplane. People like to sound important. Weather men on television talk about shower activity, sounds more important than showers. I even heard one guy on CNN talk about a rain event. Swear to god. He said, "Louisiana is expecting a rain event." I thought HOLY SHIT I hope I can get tickets to that!

Re:Troubleshooting process?

[timster]

Of course, this being NASA, "process" means PROCESS. There is a big complicated manual somewhere describing what is to be done and how and by whom.

It's sort of like if the people boarding the airplane had to play trumpets in perfect harmony or else they would fall down, catch fire, and die.

Re:Troubleshooting process?

[TrippTDF]

About this time someone says "get on the shuttle, get on the shuttle"

I say "FUCK YOU I'm getting IN the Shuttle! Let Lance Bass ride ON the shuttle."

Amazing

[CompressedAir]

I've never heard every engineer at JSC say "Doh!" at the same time before.

not a surprise

[falcon5768]

even if they hadnt for the sensor, they where likely going to scrub it for weather. They only had a 40% chance of launching today.

In related news

[A beautiful mind]

In a shock announcement today, Roland Piquepaquille announced that he has purchased the majority (51%) of the well known news syndication site, Drudge Report.

Orlando Sentinel shuttle blog

[kingrat]

Here.

Risk averse society?

[isotope23]

Are we becoming so risk averse that we will significantly slow or stop the tide of exploration?

How the heck did NASA put men on the moon in a decade? They did not have a bunch of high tech crap that they have now, it was the ability to take risks.

Perhaps Nasa should take a lesson from Henry Ford. Forget multi-billion dollar boondoggles (with quadruple backups out the wazzoo) like the shuttle. build a freaking factory to mass produce a SIMPLE, STANDARDIZED rocket.

Either that or let free enterprise take over...

Re:Risk averse society?

[Bemopolis]

How the heck did NASA put men on the moon in a decade? They did not have a bunch of high tech crap that they have now, it was the ability to take risks.

Well, they did chicken-fry three astronauts on the ground, which led to significant delay in the Apollo program, including (surprise) Congressional hearings. The accident was largely the result of the cowboy risk-taking you endorse. Do that a few times and public support would evaporate like, well, those very astronauts. Oh wait, we did -- NASA cowboyed the Challenger launch over the heads of the engineers who BUILT the damn SRBs, and the scattering of Columbia over my high school in East Texas was at least in part attributable to the same mindset.
In short, there's "risk" and then there's "pointless risk". Often hard to tell apart until the inquest.

As for "free" enterprise, if they could do it they'd do it already -- and have the taxpayers subsidize it AND insure it for them. And then they'd be chicken-frying citiesworth of people at no risk to them. After all, why do you think they call it "free" enterprise?

Bemopolis

Re:Risk averse society?

[isotope23]

Risk-taking is a part of life. If airplanes had been invented under the current regulatory climate noone would get off the ground.

NASA cowboyed the Challenger launch over the heads of the engineers who BUILT the damn SRBs

If the engineers who built the things say "its not safe" and you ignore them that is pointless risk.

However what is acceptable risk? Assume they had 12 fuel sensors, needed 2, but only 11 worked. I bet they'd STILL delay the launch...

Another thing to think about, how is it that we can have a couple thousand ICBM's ready to launch hot molten death on a few minutes notice,
but don't have a space program capable of launching humans every few days?

Re:Horrible Quality

[srw]

> What ever happened to the days when everything NASA was super high quality?

Two things... My roomate's old beater car is three years newer than the Space Shuttle. There's no way in hell you'd catch me trying to drive that thing at mach whatever (if it would even do it.)

Second, (and somewhat more seriously) this was one of four fuel sensors that have to work at -400 degrees (I don't recall if NASA TV said C or F... I would guess C) in liquid hydrogen. That's not a trivial task. Of course, that's why they design redundant systems. They really only need two of the four sensors to work... and they only need them in the case where another failure causes a low fuel situation (which should never happen.) This sensor was part of a backup system to a backup system. So, really, they probably could have gone ahead in full safety. It's just that on this launch, no one wants to screw up.

I'm sure the quality is fine... they're just being super cautious this time.

Re:Horrible Quality

[jridley]

True, back in the 60's in the Apollo days, they tested the bejezus out of everything; that's because they were pushing stuff to almost beyond what technology of the time would do, and they had to have the best of the best to have a chance in hell of pulling off the mission.

They just don't have the budget for that now. I think they just ignored a lot of stuff and got lucky most of the time. They are going to be super-careful this time; they can NOT afford a failure on this launch.

Remember when the air force told NASA to expect something like 1 in 20 missions to blow up, because that was their record with SRBs? NASA has been doing WAY better than that.

These days they're scrubbing when they notice something outside of nominal. I'm happy they are. The Challenger was lost when they were operating outside of nominal and figured they could get away with it. After that event, investigations showed that they were ignoring a WHOLE LOT of stuff. I keep hoping they'll stop ignoring their own rules; we'll see.

Drudge "Report"

[courtarro]

I think it's best not to reference "news sources" that announce "SEN. MCCAIN STARS IN BOOB RAUNCH FEST" in 20-point text concerning his participation in Wedding Crashers, with a tiny link at the top to NASA information.

Re:My Nissan has the same problem...

[HyperChicken]

Face it, if you're not screwing the gas cap on correctly, there is a high probability that your careless disregard for the gas cap has caused a band of squirrels to take refuge in your fuel line.

Re:Horrible Quality

[timster]

I would hope F, as there is no such thing as -400 C.

Re:Horrible Quality

[j0e_average]

Don't feel bad....NASA gets the whole C/F thing mixed up too!

Re:Launch to coincide

[EvilTwinSkippy]

Launch to coincide ... with the release of Duke Nukem Forever.

Duke Nukem is going to be released in tiny peices over Texas?

/I'm going to hell for that one.