Shuttle fuel burn

[Peter47]

Sorry this post is about the Saturn V which have studied in more detail than the Space Shuttle.

According to the Apollo 11 press kit the Saturn / Apollo combination burnt 37.2% of its propellent in the first 81 seconds at which stage it has reached 13,220m & 802m/s. (Bear in mind that it started at 409 m/s owing to the earth's rotatation.)

Hr.Min.Sec..Event......................................Altitude....Velocity.... .Range...Time...Velocity....Altitude....Range...Distance......Mass
............................................................ ...............ft............ft/s............nm.........s.........m/s............m.........km..............km.............kg
.....0..00.0..First motion.......................................183....1,341...........0.0.......0.0........409.............56..........0.0...........0.1.......2,938
.....1..21.0..Maximum dynamic pressure........43,365.....2,637.........2.7......81.0........804......13,218..........5.0.........14.1.......1,856
.....2..15.0..Centre engine cutoff..................145,600.....6,505........24.9....135.0.....1,983......44,379........46.1.........64.0.......1,151
.....2..40.8..Outboard engine cutoff..............217,655.....9,031........49.6....160.8.....2,753......66,341........91.9.......113.3.......1,084
.....2..41.6..First stage separation................219,984.....9,065........50.2....161.6.....2,763......67,051........93.0.......114.6..........658
.....2..43.2..Second stage ignition................221,881.....9,059........51.3....163.2.....2,761......67,629........95.0.......116.6
.....3..11.5..Aft interstage jettison.................301,266.....9,679........87.0....191.5.....2,950......91,826......161.1.......185.5
.....3..17.2..LET jettison...............................315,001.....9,778.........94.3....197.2.....2,980.....96,012.......174.6......199.3
.....7..39.8..Centre engine cutoff..................588,152...18,762......600.0.....459.8....5,719...179,269....1,111.2....1,125.6
.....9..11.4..Outboard engine cutoff..............609,759...22,747......885.0.....551.4....6,933...185,855....1,639.0....1,649.5
.....9..12.3..Second stage separation...........609,982...22,757......888.0.....552.3....6,936...185,923....1,644.6....1,655.0..........175
.....9..15.4..Third stage ignition....................610,014...22,757......888.4.....555.4....6,936...185,932....1,645.4....1,655.8
...11..40.1..Third stage first cutoff................617,957...25,562...1,425.2.....700.1....7,791...188,353....2,639.5....2,646.2
...11..50.1..Parking orbit insertion................617,735...25,568...1,463.9.....710.1....7,793...188,286....2,711.1....2,717.7
...44..14.8..Third stage reignition.................650,558...25,554...3,481.9.........0.0....7,789...198,290.....6,448.5...6,451.5
2:50..03.1..Third stage second cutoff.......1,058,809...35,563...2,633.6.....348.3..10,840...322,725.....4,877.4...4,888.1
2:50..13.1..Translunar injection................1,103,215...35,539...2,605.0.....358.3..10,832...336,260.....4,824.5...4,836.2

https://www.hq.nasa.gov/alsj/a11/A11_PressKit.pdf

Does anyone know why the first stage used kerosene rather than liquid hydrogen & oxygen in the way that shuttle does given that the latter has a higher specific impulse so less fuel would have been required? Presumably the rocket would just have been too large or were there other reasons?

[tdracer]

Does anyone know why the first stage used kerosene rather than liquid hydrogen & oxygen in the way that shuttle does given that the latter has a higher specific impulse so less fuel would have been required? Presumably the rocket would just have been too large or were there other reasons?

The Saturn V was really pushing the state of the art - and the F1 first stage engines were several times more powerful than anything previously attempted (1.5+ million pounds of thrust). While H2 engines have a huge specific impulse advantage, kerosene is much easier to deal with since it's not cryogenic and H2 is far less dense that kerosene of the same impulse, so the first stage would have gotten even bigger. Also, the first stage is, as noted, only there for the first 80 seconds. It basically was cheaper, easier, and safer to simply make the first stage heavier and use kerosene, rather than 'optimize' it by using H2. The upper stages, being far more weight critical, used H2 (I don't recall the specific number, but one additional pound on the third stage added something like 20 lbs. of propellant needed to the first stage).
It's basically the same reason they used the Solid Rocket Boosters on the shuttle (solid boosters have worse specific impulse than kerosene).


BTW, my understanding was not only was the failure of an SRB to light catastrophic, they needed to light within a few milliseconds of each other to avoid catastrophic loads on the shuttle stack. Given how hard it is to light ammonium perchlorate (AP) based propellant, I always thought that a bit scary (we use a very similar AP based propellant in hobby rockets, and 'misfires' (failure to light) are not uncommon).

[joema]

Originally Posted by FLX/MCT

"Were there any contingency scenarios in place for the case that only one booster started successfully?"

No. The maximum survivable L/R SRB ignition differential was about 100 milliseconds -- beyond that and the structure would fail.

The SRBs were originally planned for "thrust termination ports" in the nose which could be blown off and equalize the thrust allowing SRB jettison before solid fuel depletion. Later studies showed it would require 20,000 lbs of additional structural reinforcement, or about 1/3 total payload capacity, so this was dropped.

However the SRBs are best viewed as large pyrotechnic devices. The shuttle and Apollo/Saturn before it had many "criticality 1" pyros that simply had to work. E.g, the Lunar Module ascent and descent stages had no release couplings, they were cut apart with pyros, including a rocket-powered guillotine which cut through the plumbing. There was no backup; it simply had to work.

The often-stated safety measure of shutting down a liquid-fueled engine is less comprehensive than first appears. If the Saturn V had a single engine failure during the first 14 seconds of flight, thrust:weight ratio dropped below 1:1 and it would fall back onto the pad. All five engines had to work perfectly, at least that long.

The shuttle SRBs had sufficient steering authority and thrust to enable a liftoff and abort if all three SSMEs failed, however this was only possible (theoretically) after a structural upgrade in the mid-to-late 1990s.

The shuttle abort options were dramatically improved following STS-51L (Challenger) in 1986. Previously there were long "black zones" during the ascent where no abort was possible due to various structural, aerodynamic or guidance/control factors.

The contingency abort improvments can be seen in figure 7 and 8 in the 2011 AIAA document "Space Shuttle Abort Evolution"(now reproduced in the Wikipedia article Space Shuttle Abort Modes): http://tinyurl.com/jm8zelv

The SRBs themselves were vastly improved from a reliability standpoint after Challenger. The changes were comprehensively discussed in a book by Allan J. McDonald.

Another risk of shutting down a liquid engine is the possibility of sensor-induced spurious shutdown. This happened on STS-51F in 1985 and came within seconds of a second SSME shutdown which would not have been survivable, since that was before they had bailout. A quick-thinking flight controller had them override the redline limits, which placed the SSMEs in "open loop" mode without any safety monitoring. Fortunately they made it to a low orbit; ironically that was also Challenger: https://www.youtube.com/watch?v=0Rz82mf01Yo

[Acrosport II]

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

Nice one,..

Yeah, By that logic, If they had more Irish on the Space Shuttle program, they could have seriously saved some money on their fuel bill!

Employ More Irish!

[PAXfips]

Thanks for the additions on speed, I wasnt really aware of that.

About the return options, just check SFN for the missions and all what joema said.

Just plain power: https://www.youtube.com/watch?v=JBU78AxAm2c

I miss the Shuttle.

[Check Airman]

Interesting series of podcasts on the website Omega Tau:

http://media.libsyn.com/media/omegat...aceShuttle.mp3

http://traffic.libsyn.com/omegataupo...eShuttle-I.mp3

http://traffic.libsyn.com/omegataupo...Shuttle-II.mp3

He does a great job of getting into some technical details with guests who have first hand knowledge. In one part, he discusses contingency plans for problems during launch.

His Concorde interview is highly informational as well.

[VinRouge]

Interesting also the SS had a self destruct option controlled by the range safety officer.

Not a nice job to flick the switch.

Space Shuttle Destruct Switch - NASA Prepared to Blow Up Discovery

[Toryu]

The SRBs were actually blown up once: During Challenger's final flight, when the SRBs flew unguidedly along after the ET explosion/ Orbiter breakup.

Challenger didn't really explode: It was accelerated away from the collapsing fuel-tank at a rate higher than it's structure could sustain. It broke up under aero-loads.

[joema]

Here is a shuttle abort simulation done around STS-26. The audio is the actual abort; the events are sync'd to video of a successful launch. This simulated abort included a cascade of failures which resulted in inability to RTLS, with ocean ditching the only option:

https://www.youtube.com/watch?v=HGyiLv6mPbg

The simulated failures include:

- AC bus phase 3 failure
- Right engine failure
- MDM (multiplexer/demultiplexer) failure, this is the link between the main computers and secondary computers
- IMU (Inertial Measurement Unit) accelerometer failure. IMUs are the primary on-board navigation method
- Left engine failure
- Center engine failure
- loss of voice communications

Callout terminology used:

"Abort RTLS" -- Return to Launch Site abort, where vehicle pitches around and heads back to Kennedy
"MDM FF2 down at the MDM" -- multiplexer/demultiplexer failure which cuts off communications between computers and other subsystems.
"I/O reset picking up" - Emergency keyboard command, attempt to restore flight avionics after a critical failure
"IMU #1 accelerometer problem" -- Shuttle navigates by three redundant IMUs (Inertial Measurement Units). One failed due to bad accelerometer.
"Deselect/reselect IMU #1" -- try to get IMU back on line by rebooting it.
"Dump in progress" -- emergency firing of the orbital maneuvering engines to lighten the vehicle.
"We're in 601" -- computers are running program 601, designed for RTLS abort
"two engine out blue" -- a procedural call indicating they've lost two engines early in the ascent
"need the pushbuttons" -- automatic engine shutdown upon propellant depletion is unreliable, must manually shut down engines
"any chance of getting this one back?" -- Is shuttle too far downrange for a return to launch, or must it ditch in the ocean
"have you got a predicted IP?" -- Can the ocean landing impact point be calculated?
"602" -- flight computers are running program 602 (RTLS abort subroutine for reentry). RTLS subroutine is used even for a bailout over the ocean.
"need to reduce alpha" -- during reentry the nose is pitched too high, if uncorrected would over-G the vehicle
"He's in the pullout" -- Orbiter is in atmospheric reentry, must pull up, but stay within thermal/G limits.
"Select the lower left antenna" -- Orbiter has several flush-mounted antennas on the upper fuselage which communicate with TDRSS satellites. Request they manually select one to restore comm.

[Dont Hang Up]

The often-stated safety measure of shutting down a liquid-fueled engine is less comprehensive than first appears. If the Saturn V had a single engine failure during the first 14 seconds of flight, thrust:weight ratio dropped below 1:1 and it would fall back onto the pad. All five engines had to work perfectly, at least that long.

However I think Saturn V had much more realistic abort options over the Shuttle. A solid fuel rocket motor was attached directly to the nose cone that contained the command module. The command module could therefore be dragged clear by this (to safe parachute and splashdown height).

Once the emergency escape rocket was jettisoned the vehicle was high enough for the whole Command/Service module to power itself clear of the main structure.

The lunar lander was of course another story. Scarily lacking in any contingency a long long way from home.

[joema]

Originally Posted by Don't Hang Up

"I think Saturn V had much more realistic abort options over the Shuttle. A solid fuel rocket motor was attached directly to the nose cone that contained the command module. The command module could therefore be dragged clear by this (to safe parachute and splashdown height).

Once the emergency escape rocket was jettisoned the vehicle was high enough for the whole Command/Service module to power itself clear of the main structure."

This is basically true, but the presumed safety factor of launch abort can be misleading. The launch escape tower is jettisoned early in the 2nd stage, which leaves the only a "mode II" abort option of separating CSM, which had a meager 0.32-to-1 thrust-to-weight ratio. The separation would have been very slow.

This almost happened on Apollo 13, when a severe longitudinal oscillation happened on the center engine of the 2nd stage. This was briefly shown in the movie. In the actual mission, later analysis showed the vibration was so severe it nearly caused structural failure. The center engine was vibrating with a fore/aft stroke of 3 inches -- and it's mounted on a large metal cruciform beam, similar to a skyscraper I-beam.

13 Things That Saved Apollo 13, Part 5: Unexplained Shutdown of the Saturn V Center Engine - Universe Today

Saturn V Also Suffered Engine Launch Anomalies : Discovery News

Instrumentation revealed the engine vibration peaked at 68 g. The cutoff was essentially a lucky event that probably saved the vehicle and possibly the crew. Had the 2nd stage broken up it's unclear if the sluggish CSM could have accelerated away safely.

While Apollo 13 was the only manned mission of that series that experienced a significant booster anomaly, the unmanned Apollo 6 also had severe pogo problems that would have probably triggered an abort. In that case it happened on stage 1, so they theoretically could have used launch escape, although it was at a very high dynamic pressure.

On the Skylab Saturn V launch, pyros failed to separate the interstage skirt between stage 1 and 2. On a manned mission this was officially an abort scenario since the additional weight would have prevented reaching orbit. Officially this would have been a tower abort, although I'm not sure a 12g abort would have been needed in that more gradual situation.

A non-obvious criteria governing Apollo abort rules is the reentry heating and g load must be survivable. The CM had a L/D ratio of about 0.3:1, so while it had some lift to modulate g and heat loads, there were otherwise possible abort trajectories that exceeded g or thermal limits. The goal was avoid these but I vaguely recollect there were conditions where abort initiation was possible but it was not survivable.

The Apollo Launch Escape System weighed about 8,000 lbs, vs the CM roughly 13,000 lbs -- 62% of vehicle weight. At a significant payload cost, it did provide an abort option over the first 25% of the ascent until it was jettisoned.

[MG23]

Originally Posted by Dont Hang Up

The lunar lander was of course another story. Scarily lacking in any contingency a long long way from home.

It was basically designed to minimize the risk of failure, rather than to have backups if it did fail. The ascent stage engine, for example, was about as simple as you can make a rocket engine; if I remember correctly, it was pressure-fed and hypergolic, so just a couple of tanks, a couple of valves, and a rocket nozzle.

NASA actually did propose to carry an emergency backup for the LEM ascent stage on later missions which would stay on the Moon for longer periods with a greater risk of failure. Basically just a rocket engine, a couple of fuel tanks that would be filled with enough fuel from the LEM to reach low orbit, and space for two astronauts to stand in their space suits.

[joema]

Originally Posted by MG23

"It was basically designed to minimize the risk of failure, rather than to have backups if it did fail. The ascent stage engine, for example, was about as simple as you can make a rocket engine; if I remember correctly, it was pressure-fed and hypergolic, so just a couple of tanks, a couple of valves, and a rocket nozzle."

That is correct, and I would not describe the LM as lacking contingencies. The design philosophy was extreme reliability through simplicity -- even at a significant cost of performance.

The LM used batteries instead of fuel cells to improve reliability, the engines had no turbopumps, no ignitors, no engine gimbal in the ascent stage, no regenerative cooling -- it was as simple as could be made. The propellant valves were double redundant and the plumbing had multiple contingency paths.

The LM was the first digital fly-by-wire vehicle, and like modern aircraft, flight control was critical. The LM had dual-redundant fly-by-wire guidance & navigation computers hand-built and tested with extreme rigor, and the backup computer had independent software developed by a separate company to avoid a generic failure.

If both LM flight control computers failed, there was a manual reversion mode including a non-computerized analog pathway from the hand controller to separate redundant solenoid propellent actuators on each RCS thruster. Activating this required only a full deflection "hard over" on the hand controller to trigger the alternate path.

There was a practiced contingency procedure to ascend from the lunar surface and achieve orbit using no computers and no inertial platform whatsoever. It involved using charts, a stopwatch and making stepped pitch changes to align window etchings with the lunar horizon. Astronaut Gene Cernan said he achieved this in the simulator and felt it was possible.

[Amadis of Gaul]

Originally Posted by VinRouge

Interesting also the SS had a self destruct option controlled by the range safety officer.

I wonder what research they did to conclude that a Space Shuttle heading for "populated areas" in a million flaming pieces would do less damage than if it were still in more or less one piece.

[Max Angle]

I wonder what research they did to conclude that a Space Shuttle heading for "populated areas" in a million flaming pieces would do less damage than if it were still in more or less one piece.

It would have been destroyed well before it started pointing anywhere other than out to sea, as someone pointed out above the Range Safety Officer has an unenviable job in the event of a launch going badly off course.

[Jwscud]

Mike Mullane's excellent autobiography touched on this. RSOs did not socialise with astronauts to avoid clouding their judgement.

I thoroughly recommend "Riding Rockets" to anyone interested in the shuttle or aviation in general.

[AC560]

Originally Posted by Jwscud

Mike Mullane's excellent autobiography touched on this. RSOs did not socialise with astronauts to avoid clouding their judgement.

I thoroughly recommend "Riding Rockets" to anyone interested in the shuttle or aviation in general.

Interesting to note that originally there was a caution light in the shuttle showing when the RSO armed the self destruct. This was to indicate they should eject, when they took the seats out of the Columbia after the first four flights they left the light in (and in subsequent versions). Not a warning light you would like to see go off I imagine.

[bratschewurst]

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 first stage of the Saturn V generated around 7.6 million lbs of thrust at lift-off, with a total stack weight of around 6.8 million lbs (figures varied slightly from Apollo 9 to 17). The STS SRBs generated 5.6 million lbs thrust and the three SSME's generated another 1.2 million lbs, pushing a total stack mass of around 4.5 million lbs. So it's not surprising that the STS was accelerating much more smartly at lift-off; its thrust-to-weight ratio was quite a bit better at launch.

On the other hand, toward the end of the Saturn V first-stage burn, the center engine would be cut in order to limit acceleration to under 4Gs. By this point the vehicle had burnt off close to 4.5 million lbs; ie it was less that half the weight it had been at lift-off 2.5 minutes previously.

[bratschewurst]

It was basically designed to minimize the risk of failure, rather than to have backups if it did fail. The ascent stage engine, for example, was about as simple as you can make a rocket engine; if I remember correctly, it was pressure-fed and hypergolic, so just a couple of tanks, a couple of valves, and a rocket nozzle.

It was also the only stage of the Saturn stack that had a non-gimbaling engine, making it even simpler; all directional control was done by the reaction control system, which was almost as simple and, of course, had been tested on the descent.

On the other hand, IIRC it was also the only engine in the Saturn stack that couldn't be tested before launch, as the fuels were so corrosive that the engine could only be used once before needing extensive rebuilding. So lighting it was always a bit of a nail-biter; unlike every other engine in the vehicle, if it didn't work the first time, the astronauts died.

[bratschewurst]

This almost happened on Apollo 13, when a severe longitudinal oscillation happened on the center engine of the 2nd stage. This was briefly shown in the movie. In the actual mission, later analysis showed the vibration was so severe it nearly caused structural failure.

The second stage thrust structure was apparently rated to 15Gs, which was somewhere between 1/2 and 1/4 of what it experienced during Apollo 13. It's entirely possible that this was actually the closest the Apollo program came to losing a crew after the Apollo 1 fire.

Prior to this flight, POGO was viewed as more of a problem for astronaut comfort and their ability to function than as a potential structural failure issue, which is why the Saturn engineers were willing to live with it. After Apollo 13, they put it a POGO suppressor and the problem did not re-occur. The Shuttle was designed with POGO suppression from the get-go.