Low Level Fuel Sensor

Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and it
doesnt even have a sensor!

Walter

"Walter L. Preuninger II" wrote:

Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and it
doesnt even have a sensor!

Your lawn mower won't eat itself when it runs out of fuel.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Walter L. Preuninger II wrote:
Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and it
doesnt even have a sensor!

Walter



Your lawn mower does not (to the best of my knowledge, anyhow) have
separate supplies of fuel and highly reactive oxidizer --- the latter of
which would be pleased to help consume various parts of the engine
itself given the absence of the fuel.

Thanks for clearing up my confusion as to why it is really bad to use up
just 1 component of the fuel.

Walter

"Justa Lurker" wrote in message
...
Walter L. Preuninger II wrote:
Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank
and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and
it
doesnt even have a sensor!

Walter



Your lawn mower does not (to the best of my knowledge, anyhow) have
separate supplies of fuel and highly reactive oxidizer --- the latter of
which would be pleased to help consume various parts of the engine
itself given the absence of the fuel.

"Walter L. Preuninger II" wrote in message
...
Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank
and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and it
doesnt even have a sensor!

Walter


The space shuttle has 3 engines and for a bunch of reasons too technical to
explain here, they want them to

a. All shut down at the same time.
b. Shut down in an orderly manner. This means closing valves in a certain
order, and shutting down turbopumps so that the engine is not damaged and
can be re-used again on a future flight.

JD

What I don't understand is why there aren't redundant sensors for this
if it is critical.
What if the sensor failed in flight? If this sensor is considerd so
critical it doesn't make sense to only have one, or are there multiple
sensors being called one to simplify things for the public?

If there is really only one sensor my confidence in NASA's orbiter
program is going down a notch. How many other critical things are they
cutting corners on?

-McDaniel

wrote:

What I don't understand is why there aren't redundant sensors for this
if it is critical.

There are.
There are 4 sensors, one of which may not have been functioning. (or
the self-test may have broken).
If two more failed on the way up, AIUI, the engines would shut off
prematurely.
Depending on when this happened, the effect varies from the shuttle not
reaching the orbit designed, to everyone dying.

And if you've already got 1 failure on the pad, then given that
all of the three other channels are probably identical, then unless
you've got a very, very compelling reason to know why that particular
sensor is faulty, launching anyway is a bad idea.

In article ,
"Walter L. Preuninger II" wrote:

Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and it
doesnt even have a sensor!

Yes...but your lawnmower will not have a multi-million dollar
turbo pump destroy itself when it runs out of gas. They don't
want any of the engine components to run dry. Under normal
circumstances, the shuttle launches with quite a bit of extra
fuel, so they would never get into a low fuel situation unless
something unusual has already happened in the flight.

-john-

--
================================================== ====================
John A. Weeks III 952-432-2708
Newave Communications http://www.johnweeks.com
================================================== ====================

On Thu, 14 Jul 2005 06:42:15 -0500, John A. Weeks III wrote:

In article ,
"Walter L. Preuninger II" wrote:

Quote from cnn.com

"The sensor monitors the amount of super-cold hydrogen fuel in the tank and
tells the orbiter's engines to shut down if there's not enough fuel."

Hmmm, when my lawn mower does not have enough fuel, it shuts down, and it
doesnt even have a sensor!

Yes...but your lawnmower will not have a multi-million dollar
turbo pump destroy itself when it runs out of gas. They don't
want any of the engine components to run dry. Under normal
circumstances, the shuttle launches with quite a bit of extra
fuel, so they would never get into a low fuel situation unless
something unusual has already happened in the flight.


When you think about how the turbopump works, the liquid fuel enters the
compressor first, then is turned into gas at high pressure, then flows
thru the turbine. When it runs out of fuel, the compressor will run out of
fuel first, while the turbine is still at full power. The compressor
has nothing to compress other than a little bit of gaseous fuel. So, the
power from the turbine has to go somewhere. That somewhere is a faster
spinning turbine and compressor, limited only by the inertia of the
turbine and compressor (well there still is that little bit of gaseous
fuel too), which isn't much.

So as you might imagine, as the turbopump accelerates, at some point it's
going to go above it's structural limits and break, sending out high
speed debris in the plane of the pump. It would probably shred the aft
end of the vehicle.

--
Craig Fink
Courtesy E-Mail Welcome @

On 2005-07-14, wrote:

What I don't understand is why there aren't redundant sensors for this
if it is critical.
What if the sensor failed in flight? If this sensor is considerd so
critical it doesn't make sense to only have one, or are there multiple
sensors being called one to simplify things for the public?

There are four sensors. The problem is that having one fail on the pad
for unknown reasons means that:

a) You only have three working sensors, so you have less "safety margin"
in case they fail
b) *You don't know why it failed*

The second is critical - it's possible that whatever caused it to fail
is a problem suffered by all "copies" of the sensor, namely something
intrinsic to the design... and, if so, then you don't know if any of the
other three will just start randomly failing whilst in flight.

If it had broken after launch, it'd have been worrying but not critical
- however, before launch, they can try and solve the problem in case it
manifests again.

--
-Andrew Gray