Shuttle fuel burn
 

I've been quoted a statistic that the Space Shuttle uses 96.2% of its fuel to get enough the first foot off the ground. How true is this?

It takes about eight minutes for the liquid oxygen and liquid hydrogen in the main tank to be used up. The solid rocket boosters have a shorter burn time.

Simple logic suggests the figure you quote is somewhat in error.

Rather 9.6%?
Let alone the SSRBs (sidemounted boosters) ran for some over 90sec providing the majority of thrust and are jettisoned at ~45km over ground.
The main engine operates from the external tank, carrying 600t of LOX and 100t LH2. LOX was pumped at 1200kg/s, LH2 at 200kg/s.

Doesnt count up to 96% for the "first foot" for me.

Besides, if it was true, they would just build the launch site a foot higher. :O

It took around 8 seconds from ingnition of three shuttle engines until liftoff. This time allowed systems check and after start checklist (just kidding) to be done until ingniton of solid boosters. Including first foot of ascent it took 9 seconds at most, which out of 500 total seconds of powered main engines flight represents less than 2% of fuel. Thrust/fuel flow was, excluding few seconds of reduction from 104% to 72% during initial ascent due to max dynamic pressure and last few seconds during which max g load was limited to 3g, constant.

I love it when you talk dirty Dufo :p

The Saturn V (Apollo moon rocket launches) were somewhat different from the Space Shuttle, with very gradual initial acceleration (seen in contemporary footage). Most of the thrust is used to overcome the sheer weight of the rocket, and only once the propellant begins to burn off, does this lead to increasing acceleration (given a constant thrust). This process might be part of the 'myth' that you quote.

The Wikipedia entry for Saturn V rocket data indicates initial acceleration (my calculation) of 2m/s^2 vs 5m/s^2 for the Shuttle.

There is a nice video showing altitude and velocity vs time https://www.youtube.com/watch?v=F0Yd-GxJ_QM for the entire first stage Saturn V burn (less than 3 minutes total), which consumes more than 4/5 of the rocket's launch weight. Just before stage cutoff, the acceleration is around 20 times that at liftoff. The second stage then goes though another period of gradual acceleration as its propellant burns off.

In all gory detail from STS-135:

00...07...30...11:19:16 AM...Orbiter access arm retraction
00...05...00...11:21:46 AM...Launch window opens
00...05...00...11:21:46 AM...Hydraulic power system (APU) start
00...04...55...11:21:51 AM...Terminate LO2 replenish
00...04...00...11:22:46 AM...Purge sequence 4 hydraulic test
00...04...00...11:22:46 AM...IMUs to inertial
00...03...55...11:22:51 AM...Aerosurface profile
00...03...30...11:23:16 AM...Main engine steering test
00...02...55...11:23:51 AM...LO2 tank pressurization
00...02...35...11:24:11 AM...Fuel cells to internal reactants
00...02...30...11:24:16 AM...Clear caution-and-warning memory
00...02...00...11:24:46 AM...Crew closes visors
00...01...57...11:24:49 AM...LH2 tank pressurization
00...00...50...11:25:56 AM...SRB joint heater deactivation
00...00...31...11:26:15 AM...Shuttle GPCs take control of countdown
00...00...21...11:26:25 AM...SRB steering test
00...00...07...11:26:39 AM...Main engine start (T-6.6 seconds)
00...00...00...11:26:46 AM...SRB ignition (LAUNCH)

(last value speed in mph)
11:26:46 AM...T+00:00...LAUNCH
11:26:57 AM...T+00:11...START ROLL MANEUVER.........................927
11:27:04 AM...T+00:18...END ROLL MANEUVER.........................1,002
11:27:18 AM...T+00:32...START THROTTLE DOWN (72%).................1,200
11:27:35 AM...T+00:49...START THROTTLE UP (104.5%)................1,432
11:27:47 AM...T+01:01...MAX Q (744 psf)...........................1,650
11:28:49 AM...T+02:03...SRB STAGING...............................3,627
11:28:59 AM...T+02:13...START OMS ASSIST (1:23 duration)..........3,743

full ascent (and other data along):
Spaceflight Now | STS-135 Shuttle Report | Ascent Timeline

(nt)

:D:)

927mph in 11s - talk about going places! :}

Those figures have to be taken in context:
That mph-value is an inertial speed. It's the speed of the Orbiter's (STS') center of mass rotating around Earth's center. Hence the inertial velocity of 914mph at standstill at T-00s.
Was the launchpad at either pole, the inertial velocity would be 0mph.
It's at maximum at the Equator - for obvious reasons.

The actual (aerodynamic/ relative to Earth's surface) velocities are given in the upper table as "velocity (e)".

That gives us 126mph after T+10s, which is a whole lot more reasonable.

Bare in mind the MPH speed figures quoted at the lower part of PAXfips post are "inertial" speeds. I.E cumulative speed of the vehicle + earth rotational velocity from west to east.
Before launch the vehicle is travelling 914.4 MPH due to the earths rotation.

If you open the link posted by PAXfips and look at the top section, the 6th column from the left will give you the orbiters "local" speed and the 7th column the "inertial" speed. e.g at 10 secs after liftoff "local" speed is 126.8 MPH and after 30 secs speed is 495.7 MPH.

:ok:

Toryu too fast.

An amazing machine through and through and no doubt much missed! :{

As far as I know once the SSRBs were ignited they could no longer be stopped for obvious reasons.
Were there any contingency scenarios in place for the case that only one booster started successfully?

There was a "Circle to Land" procedure if only one booster fired.

I'd love to hear more about this. I understood there was essentially no contingency at all during ascent.

There were a number or runways around the world as alternate if the lift-off does not go according the the plan. However the window of time to be used is very small.

A brief foray into Wikipedia reveals the following

https://en.wikipedia.org/wiki/Space_Shuttle_abort_modes

It would seem that the return to land is only possible after SRBs are jettisoned.

Regarding the original question, I would be prepared to believe that 96.2% of the fuel load is required to carry the fuel load. It is just conceivable that that sort of statistic could be misrepresented by careless journalism as "96.2% just to get the the vehicle off the ground"!

Hmm, if one SRB failed to ignite then I'm pretty certain that could only be a cartwheel to certain total loss of crew and vehicle :eek:

Exactly my thought. Thanks for pre-empting me!

The original quote is an idiomatic metaphorical analogy - to "get off the ground" (i.e. function to achieve the design goal of putting x amount of payload into Earth orbit), the shuttle needed fuel to move the payload, and fuel to move that fuel, and fuel to move the fuel that moves the fuel....to the point that 96.2% of the fuel is used just to move other fuel, over the entire climb and acceleration.

"Tankering" in the extreme.

Yes. It was called 'crash and burn'.

If I remember correctly, the SRBs had three independent igniters, and only needed one to set them alight. So it was one of the less likely failure scenarios, but disastrous if it did happen. The SRBs were bolted to the pad with explosive bolts, but the bolts weren't strong enough to overcome the SRB thrust if the other didn't ignite (that would just introduce another catastrophic failure mode).