Question on shuttle fuel usage on liftoff.

I was puzzled by this passage on a web site describing the shuttle:

The Ascent Stage of a Space Shuttle Mission Profile by Jim Cornish.
"It takes five seconds for the shuttle to clear the 85 metre (247 feet)
tower and its 30 metre (100 foot) lightning rod. By the end of the
eighth second, the shuttle has traveled only twice its own length in
distance has already accelerated to 161 kilometers per hour (100 mph.)
During this short time, the orbiter's three main engines and two solid
rocket boosters have consumed more than 680,000 kilograms (1.5 million
pounds) of fuel, about half of its total fuel supply."
http://www.cdli.ca/CITE/sts_ascent.htm

This amount of fuel usage after only 8 seconds does not seem right to
me.


On this page I found the fuel usage of the two SRB's together is about
10,000 kg per second:

Shuttle Fun Facts
"Each of the Shuttle's solid rocket motors burns 5 tons (4,536
kilograms) of propellant per second, a total of 1.1 million pounds
(498,952 kilograms) in 120 seconds."
http://www-pao.ksc.nasa.gov/kscpao/f...s/funfacts.htm

So after 8 seconds this would amount to about 80,000 kg.

And this page allows you compute the fuel usage of the shuttle main
engines:


EXTERNAL TANK.
"The 17-inch-diameter feed line permits liquid oxygen to flow at
approximately 2,787 pounds per second with the SSMEs operating at 104
percent or permits a maximum flow of 17,592 gallons per minute."
....
"The liquid hydrogen feed line flow rate is 465 pounds per second with
the SSMEs at 104 percent or a maximum flow of 47,365 gallons per
minute."
http://science.ksc.nasa.gov/shuttle/...ewsref/et.html

This gives a hydrogen/oxygen burn rate of 1471 kilograms per second,
so after 8 seconds would be 11,768 kg. I know the shuttle remains
latched to the launch pad after the main engines are started for 6 to 7
seconds to get the main engines up nearly to full power, but even this
would still be less than 7*1471
= 10,297 kg.
So the total fuel usage 8 seconds after launch should be less than
80,000 + 11,768 + 10,297 = 102,065 kg, not the 680,000 kg claimed.

Is it correct the shuttle uses only about 100,000 kg total of fuel
during the first 8 seconds after launch?



Bob Clark

In sci.space.policy wrote:
I was puzzled by this passage on a web site describing the shuttle:

The Ascent Stage of a Space Shuttle Mission Profile by Jim Cornish.
"It takes five seconds for the shuttle to clear the 85 metre (247 feet)
tower and its 30 metre (100 foot) lightning rod. By the end of the
eighth second, the shuttle has traveled only twice its own length in
distance has already accelerated to 161 kilometers per hour (100 mph.)
During this short time, the orbiter's three main engines and two solid
rocket boosters have consumed more than 680,000 kilograms (1.5 million
pounds) of fuel, about half of its total fuel supply."
http://www.cdli.ca/CITE/sts_ascent.htm

This amount of fuel usage after only 8 seconds does not seem right to
me.

That's because it's wrong.

In article . com,
wrote:
During this short time, the orbiter's three main engines and two solid
rocket boosters have consumed more than 680,000 kilograms (1.5 million
pounds) of fuel, about half of its total fuel supply."

This amount of fuel usage after only 8 seconds does not seem right to
me.

Especially since it would mean that the shuttle would run out of fuel
roughly another 8 seconds later.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:
In article . com,
wrote:
During this short time, the orbiter's three main engines and two solid
rocket boosters have consumed more than 680,000 kilograms (1.5 million
pounds) of fuel, about half of its total fuel supply."

This amount of fuel usage after only 8 seconds does not seem right to
me.

Especially since it would mean that the shuttle would run out of fuel
roughly another 8 seconds later.

Assuming it wasn't a cloud of debris by then due
to the acceleration loads!

- Ed Kyle