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Old 04-29-2016, 06:06 AM
blood63 blood63 is offline
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Apollo 13 question

Why did the other missions not undergo the same disaster that 13 had if all the components were built by the same manufacturer under the same specs?
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Old 04-29-2016, 06:10 AM
jonesj2205 jonesj2205 is online now
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The oxygen tank that exploded had been dropped a couple of inches and the tube to empty the tank was damaged. At one point to purge the tank the heaters were turned on to boil off the oxygen but due to excess voltage the temperature inside the tank got hot enough to melt the insulation on the wiring.
It was a unique set of circumstances that happened to that tank.
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Old 04-29-2016, 07:06 AM
Colophon Colophon is offline
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Originally Posted by blood63 View Post
Why did the other missions not undergo the same disaster that 13 had if all the components were built by the same manufacturer under the same specs?
For the same reason that not all engines on Airbus aircraft shed a fan blade and catch fire. Or that if a wheel falls of one truck, the wheels will fall off all the other trucks made by the same manufacturer. Why on Earth would it?

Same spec and same manufacturer doesn't mean identical product. Otherwise you could time the failure of components to the day. You will always have random variations, even within spec.
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Old 04-29-2016, 07:20 AM
AK84 AK84 is online now
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Incidentally, the tank which exploded had been installed before for an earlier mission and removed before launch and then reused on Apollo 13.

The mission it was removed from? Apollo 10, the dress rehearsal for the Lunar Landing. An accident there would have set the project back months, maybe years.
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Old 04-29-2016, 07:31 AM
Isilder Isilder is offline
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Originally Posted by jonesj2205 View Post
The oxygen tank that exploded had been dropped a couple of inches and the tube to empty the tank was damaged. At one point to purge the tank the heaters were turned on to boil off the oxygen but due to excess voltage the temperature inside the tank got hot enough to melt the insulation on the wiring.
It took another mistake to cause the problem , but the same mistake was probably in earlier Apollo's too though, a bit irrelevant, but since its an engineering philosophy question...

There was a thermometer - but it didn't report temperatures as high as the dangerous range correctly, it was reporting the temperature was the expected temperature , being the maximum of the safe operating range, even though the actual temperate was rising above the designed for range. See , no one had considered what happened above the designed for range.. and the thermometer couldn't even measure that !. Basic idea there.. always have a meter that shows a little beyond the operating range, so that you can see if the operating range is exceeded...or if the meter is defective.

Last edited by Isilder; 04-29-2016 at 07:34 AM.
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Old 04-29-2016, 07:38 AM
Little Nemo Little Nemo is offline
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Originally Posted by Colophon View Post
For the same reason that not all engines on Airbus aircraft shed a fan blade and catch fire. Or that if a wheel falls of one truck, the wheels will fall off all the other trucks made by the same manufacturer. Why on Earth would it?

Same spec and same manufacturer doesn't mean identical product. Otherwise you could time the failure of components to the day. You will always have random variations, even within spec.
Exactly. Engineers generally don't have a problem with an item that fails at a certain point - you can compensate for that. The big problem engineers have is with items which become unpredictable in some circumstances.
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Old 04-29-2016, 07:41 AM
RivkahChaya RivkahChaya is offline
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Why did I run over a nail with a fairly new tire, plug my tire myself, and drive on it for two years, and then suddenly have the plug start to leak, even though there was plenty of tread on the tire? I double plugged it, and it held for eight more months, then I had to replace the tire. It gave me enough time to save money to replace both front tires.

We don't live in a mathematically perfect world, and there is a certain amount of randomness.
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Old 04-29-2016, 08:58 AM
Johnny L.A. Johnny L.A. is offline
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Originally Posted by Isilder View Post
See , no one had considered what happened above the designed for range.
That reminds me of a scene in the book Jurassic Park. They're counting dinosaurs to make sure none were missing. The monitor counted the expected 300 animals. But the dinosaurs were breeding, which was a problem. It turns out that since they expected to have 300 dinosaurs, their computer counted to 300 and then stopped counting.
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Old 04-29-2016, 10:20 AM
Francis Vaughan Francis Vaughan is offline
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The failure on Apollo 13 was a Swiss Cheese failure. Lots of things lined up to make it happen. (Similarly, things lined up to get them home again - had it failed after the lunar landing they would not have made it.) The above issues contributed. The tank was dropped a few inches dislodging the fill tube. The subsequent inability to syphon off the LOX after a test led to the decision to boil the LOX off, and it was there that the unfortunate thermometer specification led to failure to notice the real problem. The real problem was that there was a design flaw - one that was the result of a classic problem in design change management. The voltage range for the heater in the tank had been changed. In addition to being powered internally at 28 volts, the systems was redesigned to also be powered from ground based power at 65 volts. No big deal, but a thermostatic switch, rated for use at 28 volts, was missed, and was now operating outside of its design spec. When they boiled the tank dry the switch simply welded itself shut. So the heater never turned off. The heater, sitting in a tank of LOX, managed to get the tank to about 1000F and wreck the insulation. It wasn't that the thermometer should have read a bit higher than they thought, it needed to expose the existence of a massive disaster in the tank. The tank was wrecked before they launched. The third time they did a cryo-stir it set fire to its Teflon insulation. (Which is quite a feat, but being immersed in ready supply pure oxygen is a good start.) It then exploded.

A significant reason the other missions didn't suffer the same (or related) failure was that Apollo 13 did. All the service modules were redesigned with a backup LOX tank, and little issues like the wrongly rated switch were fixed before the next flight.

Last edited by Francis Vaughan; 04-29-2016 at 10:22 AM.
  #10  
Old 04-29-2016, 01:10 PM
Blue Blistering Barnacle Blue Blistering Barnacle is offline
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Originally Posted by Johnny L.A. View Post
That reminds me of a scene in the book Jurassic Park. They're counting dinosaurs to make sure none were missing. The monitor counted the expected 300 animals. But the dinosaurs were breeding, which was a problem. It turns out that since they expected to have 300 dinosaurs, their computer counted to 300 and then stopped counting.
I really liked the book. It was a fun romp.

But I hated the smartass chaos theory mathematician.

All he could say was,
--"It'll never work."
**"Why not."
--" 'Cuz chaos."

LATER, when problems, fun, & hijinx ensue, he's all over the place pointing out flaws in the design.
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Old 04-29-2016, 01:14 PM
AndrewL AndrewL is offline
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The dislodging of the fill tube was itself a swiss cheese failure. Several part of the tube were built right at the edge of their specified tolerances, and they were all just barely in tolerance in the right way to make the entire assembly barely hold in place. Wouldn't have been a problem normally. The entire assembly that the oxygen tank was mounted on was being removed from a service module that it had been temporarily installed in, but the person disconnecting the assembly missed one of the bolts holding it in place. When they tried to lift the assembly out of the service module, the bolt held it in place, the entire module lifted slightly, and then the fixture attaching the crane to the assembly broke and everything dropped back down. Wouldn't have been a problem, but the shock was enough to jar the fill tube loose. The module was inspected, but nobody noticed the loose fill tube because it was buried inside a sealed tank. It was a long chain of minor accidents any of which wouldn't individually have caused a problem.
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Old 04-29-2016, 03:10 PM
blood63 blood63 is offline
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Originally Posted by Colophon View Post
For the same reason that not all engines on Airbus aircraft shed a fan blade and catch fire. Or that if a wheel falls of one truck, the wheels will fall off all the other trucks made by the same manufacturer. Why on Earth would it?

Same spec and same manufacturer doesn't mean identical product. Otherwise you could time the failure of components to the day. You will always have random variations, even within spec.
Yes, but this was a highly specialized electronic component build and inspected very carefully. If a fan blade on a jet engine failed you would be sure that all other fan blades would be checked.
  #13  
Old 04-29-2016, 04:54 PM
Stranger On A Train Stranger On A Train is offline
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Originally Posted by Little Nemo View Post
Exactly. Engineers generally don't have a problem with an item that fails at a certain point - you can compensate for that. The big problem engineers have is with items which become unpredictable in some circumstances.
Every part that is energized or mechanically exercised will fail at some point. The engineer's job is to make sure that the point at which failure occurs (number of operating cycles, or duration against environments, or age, or so forth) will be more/longer than the operational lifetime of the component, with sufficient margin to accommodate parts that are weaker than the mean. However, random failures due to latent (unscreenable) defects, loads or environments that exceed the predicted maximums, or system failures (where a combination of conditions creates a failure condition that isn't exercise in component level testing) are always possible, hence why most critical aerospace systems are designed with as much redundancy as weight and performance will allow.

And Francis Vaughan is correct that the crew of Apollo XIII was fortunate that the failure occurred when it did. Had it occurred earlier, before the CSM linked up with the LM, or after the lunar landing, they would not have been able to use the LM as either a lifeboat or a propulsion system for the duration necessary to return to Earth, and they would have been dead. People like to point at Apollo XIII as an example of how astronauts can improvise their way out of a serious anomaly, but in fact nearly all of the methods employed in the recovery had been previously vetted and documented, and the astronauts got very lucky that it happened just so at the best possible time and without damaging the crucial heat shield on the CM. Space is very, very unforgiving, and the notion of working out problems in situ is a deadly way to approach the hazards.

Stranger

Last edited by Stranger On A Train; 04-29-2016 at 04:55 PM.
  #14  
Old 04-29-2016, 06:06 PM
jonesj2205 jonesj2205 is online now
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Quote:
Originally Posted by Stranger On A Train View Post
E

And Francis Vaughan is correct that the crew of Apollo XIII was fortunate that the failure occurred when it did. Had it occurred earlier, before the CSM linked up with the LM, or after the lunar landing, they would not have been able to use the LM as either a lifeboat or a propulsion system for the duration necessary to return to Earth, and they would have been dead.

Stranger
Question for you.
I understand the post-landing issue, but haven't really thought about the beginning of the mission issues. The CSM linked up with the LM 40 minutes after TLI if I'm reading the timeline correctly.
And even if it's post separation from the S-IVB wouldn't it be possible to reconnect and use the S-IVB engine? Would it have had enough thrust left to return to earth orbit?
Alternately it seems they would have had to risk the damaged SM engine, which would have been impossible to control, yes?
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Old 04-29-2016, 07:12 PM
joema joema is offline
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Originally Posted by jonesj2205 View Post
...even if it's post separation from the S-IVB wouldn't it be possible to reconnect and use the S-IVB engine? Would it have had enough thrust left to return to earth orbit? Alternately it seems they would have had to risk the damaged SM engine, which would have been impossible to control, yes?
The S-IVB 3rd stage was expended of propellant -- it was of no help.

The SM engine was feared damaged, and the risk of trying to burn it was judged too great. In fact the engine bell was dented although they did not know this until they took photos of it right before reentry. Most rocket engines use regenerative cooling where many fine pipes circulate the propellent through the nozzle. Normally any small ding or impact risks rupturing the cooling lines and causing a burn though.

However the the SPS engine use ablative cooling, which was simpler. Despite this due to the dent in the engine bell there would have been a risk of a dangerous pressure buildup had the engine been ignited. They didn't even know about that at decision time, and this shows how conservatism was the wise course.

The other main problem was lack of electrical power, without which the SPS engine could not be used. They only had a very short period to get control transferred to the LM before the entire CSM was dead. There just wasn't enough time to try it even had it been safe.

The only other unexplored option would have been to jettison the heavy inert Service Module, thus lightening the remaining vehicle, and immediately burn the LM descent engine almost to depletion. This would also have resulted in an "about face" direct abort, and a much quicker return. However there were several risks with this:

(1) There was only a small time window before they were too far from earth for this to work. They didn't safely have enough time to calculate the trajectory, get the vehicle in the unusual configuration and do the burn.

(2) It would have required virtually all the propellent in the descent stage. If the slightest error was made in guidance, navigation or control during the burn, they would have had no extra propellant to correct this.

(3) It would have exposed the critical CM heat shield to the space environment for long periods of time. It was not designed or tested for this, only for very brief periods after SM jettison before reentry. They didn't have time to run thermal tests to validate this before the decision point came for doing the burn, so they didn't take this path.
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Old 04-29-2016, 07:36 PM
Stranger On A Train Stranger On A Train is offline
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Originally Posted by jonesj2205 View Post
And even if it's post separation from the S-IVB wouldn't it be possible to reconnect and use the S-IVB engine? Would it have had enough thrust left to return to earth orbit?
joema has accurately addressed the questions of the S-IVB having all propellant expended and the potential damage to the Service Module engine, but as far as reconnecting the CSM to the S-IVB, no, it isn't possible. I can't find a good detail on the joints, but this graphic shows the phases of a typical Apollo lunar landing mission. In Step 5 the CSM separates from the S-IVB and forward interstage, and you can see how the interstage "petals" into four pieces to expose the LM so the CSM can dock with it an extract it. (The graphic has an error; they petals don't fly free but actually remain connected to the S-IVB as shown in this picture of the Apollo VII S-IVB post-separation.) At that point, there is neither a mechanical or electrical/control cable connection to the S-IVB, so even if propellant weren't expended it is still not reusable.

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Old 04-29-2016, 07:58 PM
AndrewL AndrewL is offline
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The Apollo Program really liked to use explosive bolts and cutting charges to disconnect things. Very few parts of the Saturn and Apollo could be reconnected after separating. Only the docking mechanism between the CSM and Apollo was designed for repeated connection/disconnection cycles, and even that had an explosive charge to blow it off the CSM after the last time it was used.
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Old 04-29-2016, 07:59 PM
joema joema is offline
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There was some limited ground control of the S-IVB and it had its own "ullage" thrusters. These were used after spacecraft separation to nudge the trajectory to a lunar impact to obtain seismographic data from instruments previously placed on the surface. However the available delta-V was very low -- far too little to help the Apollo 13 situation.

The other issue is I don't think the S-IVB could even ignite again -- even if it had propellant. Unlike the hypergolic engines in the CSM and LM, it was a cryogenic H2/O2 stage and required a specific start sequence, APU duration, etc. This was all pre-planned for a single earth orbit restart for the trans-lunar injection burn, and that was it.

But that is a non-issue since I believe the S-IVB propellants were burned to physical depletion not to a specific cutoff point. It had a special system to ensure both fuel and oxidizer were simultaneously depleted so there would be no residuals in either tank.
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Old 04-29-2016, 08:14 PM
Dr. Strangelove Dr. Strangelove is offline
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Originally Posted by Stranger On A Train View Post
(The graphic has an error; they petals don't fly free but actually remain connected to the S-IVB as shown in this picture of the Apollo VII S-IVB post-separation.)
According to Wikipedia, which unfortunately lacks a source in this case, the petals flew free for all missions after Apollo 7:

TD&E was performed on all Apollo missions from Apollo 9 onward, as these flights carried the LM. The maneuver was first practiced on the Earth-orbiting Apollo 7 flight, but the S‑IVB utilized a LM fairing adapter that did not separate from the S‑IVB, so the crew could not approach the S‑IVB in fear that the adapter "petals" would strike the Apollo CSM. This was corrected with all flights commencing with Apollo 8 when the fairing "petals" would fall away from the S‑IVB.
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Old 04-29-2016, 08:18 PM
Stranger On A Train Stranger On A Train is offline
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Originally Posted by AndrewL View Post
The Apollo Program really liked to use explosive bolts and cutting charges to disconnect things. Very few parts of the Saturn and Apollo could be reconnected after separating. Only the docking mechanism between the CSM and Apollo was designed for repeated connection/disconnection cycles, and even that had an explosive charge to blow it off the CSM after the last time it was used.
Slight nitpick: while "explosive bolts" are a real ordnance item, they're rarely used on spacecraft except on the ground system for hold down because they generate such a high pyroshock and produce debris. Linear shaped charges are often used for flight termination systems but the high shock makes them unsuited normal stage separation on delicate crewed systems.

Most systems today use a combination of frangible nuts (in which there is a threaded rods with nuts on both sides of the joint which are captured by a cage or lanyard) and separating/frangible rails which have a confined expanding "detonating fuse" charge that essentially pries the joint open (albeit operating in the millisecond range). On occasion a severing bolt cutter will be used, often in conjunction with a Marman/V-band clamp but it can develop a high pyrotechnic shock as well as the released mechanical energy. Of course, SpaceX has gone the route of using all pneumatic non-ordnance devices for separation except for FTS, which has its own challenges in reliability and complexity, but gets away from both the high pyroshock shock environment (just lower frequency mechanical stored energy) and has almost no potential to produce debris under normal operation.

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Old 04-29-2016, 08:22 PM
Stranger On A Train Stranger On A Train is offline
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Originally Posted by Dr. Strangelove View Post
According to Wikipedia, which unfortunately lacks a source in this case, the petals flew free for all missions after Apollo 7:
I stand corrected. Regardless, there was no means of reconnecting the CSM to the S-IVB, and no intention to ever reuse the stage.

There were proposals for various on-orbit tugs and Lunar shuttles that would take command vehicles to and from the Moon but always remain in space, but as far as I'm aware these all used some variation of the Apollo Docking Mechanism. There was also a proposal (or actually several) for the use of an up-sized Gemini ('Big Gemini) for various orbital operations including the Air Force Manned Orbiting Laboratory (MOL) but nothing ever went past the study phase.

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Old 04-29-2016, 10:43 PM
AK84 AK84 is online now
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If the TLI burn did not get the CSM-LM stack to a high enough orbit to get caught by the moon's gravity, what was the point (if any) where the SPS could get them there
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Old 04-29-2016, 11:41 PM
Stranger On A Train Stranger On A Train is offline
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I'm not sure I understand the question. Are you asking whether the Service Module main propulsion system could perform translunar injection? No, it didn't have nearly enough impulse to send the CSM-LM to Lunar orbit. It barely had enough to inject and circularize a near equatorial Lunar orbit, and then send the CSM back to Earth intercept with a few minor correction burns if necessary.

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Old 04-30-2016, 12:15 AM
AK84 AK84 is online now
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Originally Posted by Stranger On A Train View Post
I'm not sure I understand the question. Are you asking whether the Service Module main propulsion system could perform translunar injection? No, it didn't have nearly enough impulse to send the CSM-LM to Lunar orbit. It barely had enough to inject and circularize a near equatorial Lunar orbit, and then send the CSM back to Earth intercept with a few minor correction burns if necessary.

Stranger
Sorry, I was not clear, I am aware that without the SIV-B they were not going anywhere out of Earth orbit.

Per Apollo abort modes, if the SIVB failed during launch, the SM engine could still burn and get them into Earth orbit, I was wondering that if the SIVB failed during TLI, was there any possibility of them using the SPS to get to the moon? Maybe contingents on when exactly did it fail (say three-quarters of the way through the burn as opposed to almost immediately ) or if they were placed in a lower than expected orbit after TLI.

Last edited by AK84; 04-30-2016 at 12:17 AM.
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Old 04-30-2016, 12:25 AM
Stranger On A Train Stranger On A Train is offline
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I guess it would depend on when and how the S-IVB failed. By dumping the LM they might have enough impulse to make a roundabout to the Moon, but remember, it isn't just the distance they have to cover; they also have to be able to return to the Earth in the right position and at the right vector in order to reenter. Without running a trajectory simulation I can't say for certain, but my off-the-cuff answer is that it is unlikely they could get to the moon and return on a trajectory that would be within the operational life of the CSM.

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Old 04-30-2016, 01:07 AM
AK84 AK84 is online now
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So if it fails during the burn or.gets into a lower than expected orbit they are in trouble. Would they be able to return to Earth.
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Old 04-30-2016, 01:11 AM
Stranger On A Train Stranger On A Train is offline
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There is no way to answer that without specifics of the trajectory. If it failed before TLI, I think it is very likely. After, it's not so good. And if the S-IVB explodes or ruptures and damages the Service Module, they may be SOLregardless.

Stranger

Last edited by Stranger On A Train; 04-30-2016 at 01:14 AM.
  #28  
Old 04-30-2016, 07:25 AM
joema joema is offline
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So if it fails during the burn or.gets into a lower than expected orbit they are in trouble. Would they be able to return to Earth.
In general there was always an available abort trajectory for all Apollo mission phases, except for the trans-earth injection burn to return home. Even for the lunar ascent there were some limited abort options where the CSM could dip to a low orbit to rescue a LM which had a premature engine cutoff.

On the TLI burn if the S-IVB shut down early or late it would be a mission abort, the only question is what mode. The CSM did not have enough delta V to complete the normal mission without a full duration S-IVB burn.

The CSM had about 2,804 meter per sec total delta V. The S-IVB trans-lunar injection burn was about 3,100 meters per second.

For an S-IVB shutdown early in the TLI burn, the SPS could do a direct abort, cancel that velocity and come back. For a shutdown late in the TLI burn, a direct abort was not possible using the main SPS engine so the CSM would do a short burn to change trajectory to an Apollo-13-style slingshot around the moon and come back.

In theory a direct abort might have been possible at any point after TLI by sequentially burning both SPS then the LM descent stage. I think the 2,804 m/s delta V figure was the CSM by itself; if they kept the LM attached the velocity change would be lower but the total delta V from burning both engines was probably higher. I don't know if that was a practiced contingency.
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