faulty fuel sensor - oh puleeze

How do you "overspool" a rocket engine?

Mike
MU-2


"tony roberts" wrote in message
news:nospam-33EADD.23165714072005@shawnews...
The tanks contain hydrogen and oxygen. A combination of the two power it.
If it runs out of either, it can blow, or overspool the engine - either
would be fatal. So it needs accurate fuel sensors - unless you want to
fly it. Crew safety is paramount - and right now it's compromised.

Tony
C-GICE

In article ,
"Granite" wrote:

Discovery can't take off because of a bad fuel sensor ? Are they kidding
us
? The crew is already strapped in, number one for departure, cocked and
loaded. We just put gas in the thing. I saw the line guys top the tanks
earlier in the day. Stick the tank, placard the gas gauge inop and let's
go
haul the mail ! Now it takes three or four days to replace it ? They
need
to find a new A&P, preferably non-union. We are never going to get
commercial space travel at this rate. I'm sure the FAA is to blame too
...
somehow.




--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

The SSME (like all modern, high performance rocket engines) is a big
turbopump. Big turbines, run from the same fuel source as is being
ignited for use as a rocket. If the turbine is cranking away at full
power and the source of fuel suddenly goes dry, then all that power
being put into maintaining revs suddenly gets put into turbine speed.
Depending on if you're lucky or not, the engine will detect this and
shut off the turbine before it goes dry or before it overspeeds
destructively.

I wonder if these low-fuel sensors are part of the system that shuts
down the SSMEs if there's a fuel starvation issue. I remember a
mission a few years back where MECO (main engine cut-off) was
unexpectedly a few seconds early because of higher then projected fuel
burn or something. Not enough to really impact the mission, but it
showed the safety systems that prevent dry-running SSMEs was working.

Ben Hallert
PP-ASEL and space nut

My recollection was that the turbopump used the engery in the expanding fuel
to pump the fuel. If the fuel runs out doesn't the turbopump stop pumping?

Mike
MU-2


"Ben Hallert" wrote in message
oups.com...
The SSME (like all modern, high performance rocket engines) is a big
turbopump. Big turbines, run from the same fuel source as is being
ignited for use as a rocket. If the turbine is cranking away at full
power and the source of fuel suddenly goes dry, then all that power
being put into maintaining revs suddenly gets put into turbine speed.
Depending on if you're lucky or not, the engine will detect this and
shut off the turbine before it goes dry or before it overspeeds
destructively.

I wonder if these low-fuel sensors are part of the system that shuts
down the SSMEs if there's a fuel starvation issue. I remember a
mission a few years back where MECO (main engine cut-off) was
unexpectedly a few seconds early because of higher then projected fuel
burn or something. Not enough to really impact the mission, but it
showed the safety systems that prevent dry-running SSMEs was working.

Ben Hallert
PP-ASEL and space nut

ALL RIGHT!!!
John I was wondering when someone would give the right reason! You have
won the prize my friend! These fuel sensors cease fuel usage at the
proper time. If these little buggers go bad, well it would be possible to
run out of fuel before getting into outer space...that would not be good. I
think you did a good job of explaining it.

Patrick
student SPL
aircraft structural mech
I stayed in a Holiday Inn last night,
ok ok and old friend is a electrical engineer on the space shuttle


"John" wrote in message
ups.com...
The simple answer is that the sensors are used to shut the engines down
before fuel exhaustion. The Space Shuttle Main Engine uses turbopumps
(that also burn liquid hydrogen and liquid oxygen) to pump sufficient
quantities of propellents to make it all go. The issue is that
turbopumps behave very badly, even destroying themselves if they are
run try, especially if at full power. It is apparently the nature of
the beasts. The sensors cue systems that begin to throttle the engines
back to about 65% power at which point the SSME can be shut down safely
and without damage.

Consider visiting the Science Space Shuttle News Group. Several people
asked the same question and the issue gets explained pretty clearly.
Someone noted that their car's fuel pump had a similar feature so to
protect it from burning itself out from running dry. Just like us, the
astronauts do not have the option of pulling the silly thing over to
the side of the road if something important decides to break.

blue skies to you all

John

tony roberts wrote in
news:nospam-33EADD.23165714072005@shawnews:

The tanks contain hydrogen and oxygen. A combination of the two power
it. If it runs out of either, it can blow, or overspool the engine -
either would be fatal. So it needs accurate fuel sensors - unless you
want to fly it. Crew safety is paramount - and right now it's
compromised.

Tony
C-GICE

In article ,
"Granite" wrote:

Discovery can't take off because of a bad fuel sensor ? Are they
kidding us ? The crew is already strapped in, number one for
departure, cocked and loaded. We just put gas in the thing. I saw
the line guys top the tanks earlier in the day. Stick the tank,
placard the gas gauge inop and let's go haul the mail ! Now it takes
three or four days to replace it ? They need to find a new A&P,
preferably non-union. We are never going to get commercial space
travel at this rate. I'm sure the FAA is to blame too ... somehow.


But the regs say it only has to be accurate when empty!

Backwards, the exhaust of the turbopump is fed into the engine bell,
where the expansion takes place. You may be thinking of a turbo in a
piston engine, which runs parasitically off the exhaust. The pump has
to start before the fuel to get the fuel into the pump, right?
Chicken/Egg thing, there won't be any combustion in the chamber without
fuel being pumped into it.

Ben Hallert
PP-ASEL

My recollection was that the turbopump used the engery in the expanding fuel
to pump the fuel. If the fuel runs out doesn't the turbopump stop pumping?

Mike
MU-2

There are a number of differnet ways that turbopumps
on rockets can be powered, what you are describing is an expander cycle,
the SSME is a staged combustion pump.

The pump is preburinign some small amount of fule to spin the turbine,
if I recall it's about 150,000 HP per pump per engine.
This is a lot of power.

I enjoyed the initial post in the original thread, taking it in the
spirit of a moderately clever kind of aviation-related standup comedy
routine.

And certainly no one has any desire to see the current Shuttle program
be terminated at the cost of, or as the result above, one more set of
crew fatalities.

But the bottom line here is surely that the whole manned space flight
effort and focus at NASA not only should be terminated as fast as
possible, but should have been terminated several decades ago, for at
least two major reasons.

First of all, manned space flight at this point in time is just too
difficult, dangerous, and expensive to be worth pursuing. It's a matter
of the laws of physics versus the currently available or currently
foreseeable level of technology, not the competence or the culture of
NASA. Maybe some future breakthrough in technology will make manned
space flight a much more reasonable goal; maybe not.

But by far the more compelling reason is that there are really zero
useful things, much less compelling needs, that we can or might want to
accomplish in space that are not better done with unmanned rather than
manned missions.

Something like two-thirds of NASA's budget for the past several decades
has gone into manned space flight efforts. Yet, essentially ALL of the
useful scientific and technological accomplishments in space to date --
space probes, planetary missions, space observatories, communications
satellites, gps systems, earth and environmental observatories,
surveillance satellites -- have come totally from UNmanned satellites;
and essentially ZERO significant results have come from manned space
flights.

Think about it: If you go into any moderately well equipped research or
manufacturing facility of any kind in any field these days, you don't
find scientists and technicians standing there turning knobs, watching
meters, and writing results in lab notebooks. You find instead either
highly automated, computer-controlled instruments and sample
manipulation equipment, along with similar observation, measurement, or
manufacturing apparatus, sitting there taking data, manipulating
samples, or modifying things, in many cases 24/7, while feeding data and
results back to hard disks and computers outside the lab, with maybe
occasional reprogramming from a scientist or tech at a keyboard in their
office or elsewhere outside the lab.

If you want to measure or observe or do anything in space, you put the
measurement and observation hardware in space, and keep the scientists
and engineers in shirt-sleeve comfort and safety on the ground -- and
you do this not just as as a matter of cost and safety, although these
are compelling reasons, but also because the observational and recording
capabilities of hardware these days far exceed the observational
capabilities of humans in any case.

Finally, just for the record, none of the above is to say we should not
have done the Apollo Project as we did it when we did it. That was a
much different era; Apollo was a proud and admirable accomplishment; it
was worth doing.

But now that we've come to understand a lot better what we really can do
and want to do in space using unmanned missions, and how unbelievably
much more it costs and how little we can really accomplish with manned
missions, we've just got to get over this astronaut hero worship phase
and start using our space efforts and resources much more intelligently.

Finally, just for the record, none of the above is to say we should not
have done the Apollo Project as we did it when we did it. That was a
much different era; Apollo was a proud and admirable accomplishment; it
was worth doing.

Why?

Earlier on you said

First of all, manned space flight at this point in time is just too
difficult, dangerous, and expensive to be worth pursuing.

Well, it was even more difficult, dangerous, and expensive in the Apollo
days. Most of your post seems to be that we should wait until space
travel is easy, safe, and cheap before we pursue it. You complain that
manned space research isn't impersonal enough (comparing it with
manufacturing facilities on earth), but then you single out the Apollo
program as being "a proud and admirable accomplishment" that was "worth
doing".

What's the difference?

I would posit the opposite. Manned space travel isn't bold, daring, and
audacious enough to capture our imagination and inspire mankind to do
better than blow up people who hold the wrong opinions. The space
shuttle has been, as NASA wanted it to be, "just a truck". Using the
shuttle to replace rockets was an error given the lack of anything
better than chemical rocket engines to power it. Instead we should have
(and should now) use expendable rockets to put stuff into orbit, and a
space station based fleet of mini-shuttles to do stuff with them once
the heavy lifting is done. Another fleet of mini-shuttles would be used
to carry people up and down - they would be the size of a lear jet and
have enough payload capability for six people and little else.

But the focus of our space program should be going to Mars and onward.

Because it's there.

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

"Jose" wrote in message
m...
better than chemical rocket engines to power it. Instead we should have
(and should now) use expendable rockets to put stuff into orbit, and a
space station based fleet of mini-shuttles to do stuff with them once the
heavy lifting is done. Another fleet of mini-shuttles would be used to
carry people up and down - they would be the size of a lear jet and have
enough payload capability for six people and little else.

But the focus of our space program should be going to Mars and onward.

Because it's there.

Jose

Funny you should say that. There is a company in Oklahoma that plans on
taking a stripped Lear 25 fuselage, bolting it to a basic wing, adding
turbofan engines and a re-useable rocket engine. Take-off and climb to
30,000 feet of the turbofans, light the rocket and climb to 158,000 feet,
then coast to about 330,000 feet before gliding back to earth. All in a half
hour flight. www.rocketplane.com

Allen