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  Apollo 13: Cryo stir and the explosion (Page 1)

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Author Topic:   Apollo 13: Cryo stir and the explosion
Max Q
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posted 08-23-2009 05:53 AM     Click Here to See the Profile for Max Q   Click Here to Email Max Q     Edit/Delete Message   Reply w/Quote
Reading through the Apollo 13 time line the other day and I noticed that at 46:40:02 GET when the no. 2 cryogenic oxygen tank was switched on, the gauge indicated "off-scale high" of over 100% for tank quantity just three seconds later. The official time line shows that this was (probably due to short circuit) the first indication of a problem.

Now with the benefit of hindsight, if the problem had been picked up here and the tanks not been stirred again and the explosions not occurred would they have still lost the moon on Apollo 13?

dss65
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posted 08-24-2009 09:23 PM     Click Here to See the Profile for dss65   Click Here to Email dss65     Edit/Delete Message   Reply w/Quote
If memory serves correctly, the cryo stir was necessary in order to get an accurate reading of what was left in the cryo tanks.

I rather doubt that NASA would have proceeded with the mission if the readings would be in doubt — but, hey, they took other risks during Apollo, why not this one?

Max Q
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posted 08-24-2009 10:10 PM     Click Here to See the Profile for Max Q   Click Here to Email Max Q     Edit/Delete Message   Reply w/Quote
Yes, I know that the stir was done to combat stratification in the cryo tanks but hey, who knows what might have been done if they were still a whole ship and not one crippled by this fault.

Obviousman
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posted 08-25-2009 02:23 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
If they had appreciated what the fault was and the consequences, could they have landed?

Certainly.

Would they have? In my opinion, not in a million years. They would have secured that tank, isolated it, and brought the crew back home. Far too much risk that whilst the LM was undocked another "undiscovered" fault in the associated system/s could cause a fatal event.

Proponent
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posted 08-25-2009 11:20 PM     Click Here to See the Profile for Proponent     Edit/Delete Message   Reply w/Quote
Presumably the stir was necessary for the tank to function properly, no? So I would assume that if you decided you couldn't stir the tank, then you'd have to plan on not having as much electrical power available as expected. I would thank that all by itself would lead to an abort.

Here's my question. Presumably, the thermostatic switch in the O2 tank having failed, the tank heaters were drawing current continuously when the heater was switched on rather than intermittently, as would have been the case with a functional thermostatic switch. Could this continuous power draw have been detected?

Lou Chinal
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posted 08-27-2009 04:01 PM     Click Here to See the Profile for Lou Chinal   Click Here to Email Lou Chinal     Edit/Delete Message   Reply w/Quote
Because this is a grand thought experiment, couldn't you intermittently switch the power on and off to the heater in the O2 tank?

Fra Mauro
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posted 11-14-2018 07:50 PM     Click Here to See the Profile for Fra Mauro   Click Here to Email Fra Mauro     Edit/Delete Message   Reply w/Quote
I remember reading in Kranz' book that they turned off a master alarm that measured pressure in a hydrogen tank because it had awakened the crew previously.

Andy Anderson
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posted 11-16-2018 06:45 AM     Click Here to See the Profile for Andy Anderson   Click Here to Email Andy Anderson     Edit/Delete Message   Reply w/Quote
The following extracted from the Cortright Report: Appendix B details the issue relating to the H2 tanks and how the H2 C&W locked out the MC for the increasing O2 pressure;
Hydrogen Low Pressure Master Alarm

The caution and warning system, upon receipt of a malfunction or out-of-tolerance signal, simultaneously identifies the abnormal condition and alerts the crew to its existence. Each signal (both oxygen and hydrogen pressure are on one indicator) will activate the system status indicator, light the master alarm light, and place an audio tone in the crew's headsets. The crew can turn off or reset the master alarm; however, the particular system status malfunction indicators remain lit, blocking further master alarms on this indication, until the malfunction is cleared.

At lift-off, the quantity readings for the hydrogen tanks no. 1 and no. 2 were 91 percent and 93.4 percent, respectively. This was due to initial loading values (98.7 percent for tank no. 1 and 99.4 percent for tank no. 2) and the difference in usage during countdown.

At approximately 32:00 g.e.t., a quantity unbalance of 2.38 percent existed between the hydrogen tanks, and a quantity balancing procedure was conducted to prevent tank no. 1 low-pressure master alarms during the sleep period. In the "auto" mode the tank heaters are turned on and off by pressure switches connected in series. When the pressure in either tank reaches about 260 psi, the heaters in both tanks are switched off. The heaters remain off until the opened pressure switch closes at approximately 225 psi. Since one tank pressure switch normally remains closed, the tank that controls the upper pressure will also control at the lower pressure. During the flight, tank no. 2 was controlling. Tank no. 1 pressure was almost reaching the caution and warning low pressure point (224.2 psia) prior to tank no. 2 reaching its pressure switch activation point of 233.6 psia to turn on the heaters.

Since tank no. 2 had the greater quantity, at 32:00 the tank no. 1 heaters were manually turned off by the crew while tank no. 2 remained in auto. This condition would allow the fuel cells to obtain hydrogen from tank no. 2 because of its higher pressure and in turn reduce its quantity of hydrogen. Several master alarms occurred immediately after this change (33:10, 33:41, 34:01, and 34:32).

At 36:48 the hydrogen tank no. 1 heater was placed back to auto for the sleep period. On the first "down" pressure cycle a master alarm occurred (38:00) due to hydrogen tank no. 1 pressure dropping lower than 224.24 psia, awaking the crew. The crew reset the alarm, and no master alarms occurred through the sleep period although the heaters cycled several times. To obtain a balanced condition for the next sleep period, the ground controllers devised the following plan for the next day's operation:

  1. After crew wakeup, turn hydrogen tank no. 2 heater to off and leave hydrogen tank no. 1 in auto for two to three pressure cycles to determine if this will transfer heater control to tank no. 1 in anticipation of using this configuration for sleep.

  2. If successful, tank no. 1 heaters will be turned off during the day and tank no. 2 heaters left in auto to create a quantity unbalance in favor of tank no. 1.

  3. During the next sleep period, the tanks will be balanced by placing tank no. 1 heaters in auto and tank no. 2 heaters to off.
This plan was executed when the crew awoke the next day. At the time of the accident, tank no. 1 was in off and tank no. 2 was in auto, and the caution and warning master alarm was reset with a low hydrogen pressure indication present at 55:52:30. This hydrogen low pressure indication locked out the master alarm during the time of the increasing pressure in oxygen tank no. 2.
Regarding the initial theme of this thread about continuing the mission, the Mission Rules were very specific;

Except for two circumstance, both tanks were required, although I wonder if the controllers and specialists had at the time formed a complete understanding of the tank condition and completely isolated it electrically, consideration might have been given to completing the lunar landing.

However, even given the more practical review of risk management in those days compared with the "risk aversion" of today, I doubt it.

Terence
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posted 01-15-2015 09:49 AM     Click Here to See the Profile for Terence     Edit/Delete Message   Reply w/Quote
I've often wondered what might have been had the Apollo 13 crew NOT stirred the cryo (oxygen) tank. Was this a critical concern or is it conceivable that it could have been omitted?

I realize that there is no way that with knowledge of a damaged tank the mission would have continued as planned anyway.

Editor's note: Threads merged.

Fra Mauro
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posted 01-15-2015 11:41 AM     Click Here to See the Profile for Fra Mauro   Click Here to Email Fra Mauro     Edit/Delete Message   Reply w/Quote
The tanks were stirred regularly on the Apollo missions, to get accurate readings of how much and to keep the liquid oxygen uniform (without pockets). I've read that it was usually done every 24 hours or so but on the night of the accident it was done early because it was felt that the readings weren't accurate.

AussiePete
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posted 03-15-2015 10:46 PM     Click Here to See the Profile for AussiePete   Click Here to Email AussiePete     Edit/Delete Message   Reply w/Quote
I worked on Aussie P3 Orions for almost two decades. We had an oxygen fire and lost a plane due to what was determined to be a speck of rust within the oxygen pipe work. When the oxygen bottle was connected up and the tap opened things went bad.

Today oxygen maintenance on the P3 is far more critically overseen.

I would expect our accident filtered right through the P3 environment way back in 1990.

schnappsicle
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posted 03-16-2015 07:18 AM     Click Here to See the Profile for schnappsicle   Click Here to Email schnappsicle     Edit/Delete Message   Reply w/Quote
With all the things that happened to that tank in the two years prior to the flight, it would have exploded eventually. I'm thankful it happened on the way to the moon, and not on the way back home.

No one wanted to see Jim Lovell walk on the moon more than me. Of all the Gemini astronauts, he definitely deserved it. I'm just glad he and the rest of the Apollo 13 crew made it safely back to earth.

What I think is far more plausible is that Ken Mattingly's exposure to measles gave everyone time to step back and delay the launch long enough to replace the faulty tank. That is what should have happened. Everyone knew the tank was faulty, that's why it was removed from Apollo 10 in the first place. However, no one was willing to admit just how faulty it was, or what would happen when it failed. All they were worried about was keeping the program on schedule.

Tykeanaut
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posted 03-16-2015 11:32 AM     Click Here to See the Profile for Tykeanaut   Click Here to Email Tykeanaut     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by schnappsicle:
Everyone knew the tank was faulty
I must admit that's news to me, who knew and why was the mission allowed to go ahead? Surely they must have guessed a problem would arise?

Robert Pearlman
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posted 03-16-2015 12:10 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
The tank was removed from Apollo 10 (SM-106) due to a minor redesign of the service module's oxygen shelf. It was not because the tank was known to be faulty. From the review board report:
Due to electromagnetic interference problems with the vac-ion pumps on cryogenic tank domes in earlier Apollo spacecraft, a modification was introduced and a decision was made to replace the complete oxygen shelf in SM 106. An oxygen shelf with approved modifications was prepared for installation in SM 106. On October 21, 1968, the oxygen shelf was removed from SM 106 for the required modification and installation in a later spacecraft.
It was during that removal, that the tank was dropped:
One shelf bolt was mistakenly left in place during the initial attempt to remove the shelf; and as a consequence, after the front of the shelf was raised about 2-inches, the fixture broke, allowing the shelf to drop back into place. Photographs of the underside of the fuel cell shelf in SM 106 indicate that the closeout cap on the dome of oxygen tank no. 2 may have struck the underside of that shelf during this incident. At the time, however, it was believed that the oxygen shelf had simply dropped back into place and an analysis was performed to calculate the forces resulting from a drop of 2 inches. It now seems likely that the shelf was first accelerated upward and then dropped.
After the shelf was removed, it (including the oxygen tank) was inspected and passed a battery of tests. The same tests were repeated without problem once the shelf was installed in SM-109 (Apollo 13), however...
These tests... would not disclose fill line leakage within oxygen tank no. 2.
Even during the post-flight investigation, the review board found that the chances of the tank being damaged by the drop was low.
The probability of tank damage from this incident, therefore, is now considered to be rather low, although it is possible that a loosely fitting fill tube could have been displaced by the event.
A loose fitting fill tube was suspected during further pre-flight testing at Kennedy Space Center, but it was deemed to not be a concern.
It was decided that if the tank could be filled, the leak in the fill line would not be a problem in flight, since it was felt that even a loose tube resulting in an electrical short between the capacitance plates of the quantity gage would result in an energy level too low to cause any other damage.

Replacement of the oxygen shelf in the CM would have been difficult and would have taken at least 45 hours. In addition, shelf replacement would have had the potential of damaging or degrading other elements of the SM in the course of replacement activity. Therefore, the decision was made to test the ability to fill oxygen tank no. 2 on March 30, 1970, twelve days prior to the scheduled Saturday, April 11, launch, so as to be in a position to decide on shelf replacement well before the launch date.

The tanking test was conducted without any sign of a problem. What the engineers had not taken into consideration was the potential for damage due to extended operation of heaters and fans during the tests.
Further [post-flight investigation] tests have shown that the temperatures on the heater tube may have reached as much as 1000 degrees F during the detanking. This temperature will cause serious damage to adjacent Teflon insulation, and such damage almost certainly occurred.

None of the above, however, was known at the time and, after extensive consideration was given to all possibilities of damage from a loose fill tube, it was decided to leave the oxygen shelf and oxygen tank no. 2 in the SM and to proceed with preparations for the launch of Apollo 13.

David Carey
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posted 03-16-2015 08:42 PM     Click Here to See the Profile for David Carey   Click Here to Email David Carey     Edit/Delete Message   Reply w/Quote
The mis-rated thermostat (28 Volts vs 65 Volts) of the heater installed in the tank was a notable, but overlooked, factor as well.

Along with the summary from Robert and referenced Review Board Report, a good accounting of the cascading problems can be found here.

Peter downunder
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posted 03-22-2015 12:28 AM     Click Here to See the Profile for Peter downunder   Click Here to Email Peter downunder     Edit/Delete Message   Reply w/Quote
Was there a problem with emptying the tank after testing? That required boiling off the contents, which caused the wiring damage?

Even though the process wasn't going to be required during a flight, if the tank didn't operate the way it was designed (ability to empty) why didn't that cause concern?

moorouge
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posted 03-24-2015 10:49 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Because it was a recognised back-up procedure for speeding up a tank empty during countdown simulations.

Spacepsycho
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posted 11-05-2020 12:32 PM     Click Here to See the Profile for Spacepsycho   Click Here to Email Spacepsycho     Edit/Delete Message   Reply w/Quote
I've read the books, spoken to a few NAA engineers who built the command and service modules and while watching the movie, I had a question that I've never seen answered.

Stirring the O2 tanks was done to mix the stratified oxygen slush in order to get an accurate reading and wasn't critical to the operation of the spacecraft. The thermostat fused closed and reached an internal tank temp of at least 1,000f immediately after the spacecraft was powered up on the pad.

So nothing happened to the O2 tanks for one to two days while on the pad before launch, they endured the launch, lunar orbit insertion (LOI) and only became a problem after the mixing paddles were turned on. So my question is, would the Apollo 13 mission been successful if the O2 tanks were left alone and never stirred? It's not like stirring the O2 tanks had any effect on O2 levels or how O2 was supplied to the CM.

Editor's note: Threads merged.

damnyankee36
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posted 11-05-2020 01:22 PM     Click Here to See the Profile for damnyankee36   Click Here to Email damnyankee36     Edit/Delete Message   Reply w/Quote
I would imagine nothing. But, I'd like to take the question a step further.

Suppose NASA had known, or at least suspected, of the fused contacts and the burned insulation. Would they have risked continuing with the mission on the assumption that if no future stirring were to occur there would be no chance of an explosion?

I would like to say they would have aborted the mission. But when I look at the fix to hopefully prevent a landing abort on Apollo 14 makes me wonder. IIRC, there was a point that an abort would have been extremely dangerous. Had an unexpected abort happen at that point then I can only imagine the result.

garymilgrom
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posted 11-05-2020 01:24 PM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
Interesting question!

SpaceAholic
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posted 11-05-2020 05:25 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Spacepsycho:
...and wasn't critical to the operation of the spacecraft.
Doesn't seem correct. Phase state change of cryo oxygen from a liquid to partial solid/liquid mix (slush) had potential to obstruct/alter reactant flow rate through the feed tubes to the fuel cells. How was this not an issue?

garymilgrom
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posted 11-05-2020 06:11 PM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
Scott, as I understand it, it is an issue if accurate fuel quantities are desired. However that measurement in itself is not mission critical. I could be wrong.

oly
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posted 11-06-2020 04:34 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by damnyankee36:
I'd like to take the question a step further.

At what point in the mission does NASA determine that the "damage" exist?

If it was pre-launch, I believe that there would be a scrub or delay until the fault could be rectified.

oly
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posted 11-06-2020 08:59 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Spacepsycho:
So nothing happened to the O2 tanks for one to two days while on the pad before launch, they endured the launch, lunar orbit insertion (LOI) and only became a problem after the mixing paddles were turned on.
There may have been two previous cryo stirs conducted without an explosion, and the spacecraft was in the trans lunar coast stage when the failure occurred, it did not reach LOI.
quote:
Originally posted by garymilgrom:
However that measurement in itself is not mission critical.
Knowing the mass of the vehicle is a critical part for calculating ΔV so that navigation and orbital burn calculations can be done, stirring the cryo tank so that accurate content measurement can be gauged may be considered a critical requirement by some, hence the engineering and weight incorporation of a cryo tank fan system.

Espace
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posted 11-07-2020 08:56 AM     Click Here to See the Profile for Espace   Click Here to Email Espace     Edit/Delete Message   Reply w/Quote
For info, in the Apollo 13 mission transcript there is a discussion at just after 23 hours, 20 minutes GET regarding the specifics of a cryo stir of both sets of tanks.

So there was definitely at least one stir prior to the fateful one.

Headshot
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posted 11-07-2020 10:03 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
How was the post-explosion mass determined to calculate the burn to place the stack on a free-return trajectory, and eventually the course corrections that followed?

I mean Houston had little to no idea of the extent of the damage to the tanks and, at the time, they did not know that a whole panel of the service module was gone. Has anyone ever read a determination of how much mass Apollo 13 lost as a result of the explosion?

Espace
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posted 11-08-2020 03:00 AM     Click Here to See the Profile for Espace   Click Here to Email Espace     Edit/Delete Message   Reply w/Quote
Surely the important thing during any burn is the attitude and required delta V, which during any normal burn was usually monitored by the inertial system or other more "simple" sources (I'm thinking in the generic case something like the command Module's EMS). Knowing an exact mass is in some ways irrelevant unless you want to have a handle on the burn time for cross checking or as a back up.

As I recall it (I'll admit haven't gone back to back sources such as transcripts this morning, so I'm probably wrong) on Apollo 13 they had the PGNS available for at least the first burn post the explosion.

Mass however would have been was more critical on the last mid course when they didn't have a platform so "mark 1 eyeball" for attitude and a timed burn, but by that time they had done at least one "measured burns" and that might have enabled people to get a handle on the mass.

oly
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posted 11-08-2020 05:11 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
Yes, there are additional references to O2 cryo tank stir request prior to the failure, including a discussion at 02:03:07:08:
Because of the 02 tank 2 quantity sensor drop out, EECOM wants to keep a little closer track of the cryo quantities, and he's going to be asking you to stir all the cryo tanks at slightly more frequent intervals than had been planned, and the first time is now, and we will be calling you probably every 5 or 6 hours.

Jim Behling
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posted 11-08-2020 11:06 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Espace:
Knowing an exact mass is in some ways irrelevant unless you want to have a handle on the burn time for cross checking or as a back up.
Knowing the mass of the vehicle is needed for planning purposes and to determine how much propellant will be needed for each burn.

Headshot
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posted 11-08-2020 11:28 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
Considering that the explosion occurred in a single sector (4) of the Service Module and all the mass was lost from that area, I would believe that the center of gravity of the stack would have shifted away from its calculated location.

In Apollo 13's case, since the stack included the LM and all its fuel, the shift might have been small (depending on exactly how much mass was lost), but not necessarily insignificant for course corrections. It probably contributed, along with the venting gas, to holding the proper attitude for lengthy trajectory burns very difficult.

Espace
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posted 11-08-2020 12:31 PM     Click Here to See the Profile for Espace   Click Here to Email Espace     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jim Behling:
Knowing the mass of the vehicle is needed for planning purposes and to determine how much propellant will be needed for each burn.
I understand that, especially for a nominal mission.

Maybe Headshot can clarify their question because as I read it he/she was wondering if an accurate knowledge of vehicle mass was essential to establish a target duration for the DPS burns. In my opinion, it would sure have been a nice thing to have, but not absolutely essential because it was the delta V, which could be measured on board if a platform or similar was available, that really mattered.

Andy Anderson
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posted 11-10-2020 03:03 AM     Click Here to See the Profile for Andy Anderson   Click Here to Email Andy Anderson     Edit/Delete Message   Reply w/Quote
Looking at the merged posts from 2009, 2015, 2018 and the latest ones, here are some thoughts I trawled out of the available documentation and websites.
quote:
Originally posted by damnyyankee36:
Suppose NASA had known, or at least suspected, of the fused contacts and the burned insulation. Would they have risked continuing with the mission on the assumption that if no future stirring were to occur there would be no chance of an explosion?
A chronology of events, considerations and actions determined in the subsequent investigation is listed in the A13 Incident Investigation - Vol II Section 3.3 - pages 38 to 58.

For NASA to have known or suspected there was a possible problem would have entailed a more extensive review of the data of the detanking procedure used which may have occurred if the "shelf" incident had been remembered and reported and if a detailed consideration of the 8 hour heater operation had been made shortly after the CDDT detanking, indicating that there had been no overheat protection by the thermostats.

If that had occurred and the findings recognized as indicating possible damage inside the tank then the launch would have been surely delayed and the vehicle returned to the VAB for replacement of the O2 tank as had been considered but not thought necessary.

Also, refer to the Cortright Report - Appendix E, pages E7- E10 and E80-83.

As was summarized on Page E83 of that report:

Any consideration of whether management decisions would have been different if the correct data had been provided is highly speculative. However, it is likely that requests for additional tests or data may have been considered during the discussions if the correct information had been available
You can find these documents here in the High Resolution section.

The O2 tank problem, which was not considered a flight issue, was not the only issue confronting the engineers and management — the LM She tank leak rate was another one, which ultimately had an indirect impact on the subsequent recovery from the incident at GET 55.55 and of course, another issue was the crew swap.

The second "opportunity" to consider the state of the O2 tank was when the O2 Tank 2 quantity gauge failed and the prelaunch problem could have been revisited again but this was very unlikely given the decisions already made prior to that occuring.

The gauge failure at GET 46:40:10 was actually not totally unexpected as MCC controllers were aware of the detanking problems at the KSC and it was thought that possibly teflon parts of the fill tube could end up short circuiting the capacitance gauge. (It was later determined that also, melted solder from the high tank temperature during detanking could have also caused this).

At the time, EECOM Charlie Dumis, the SSR ECS specialist, George Conway and Shelby Owens in the MER discussed the problem in great detail.

There was doubt over whether it was due to a short or an open circuit as initially both cases could cause the observed off-scale high reading.

Later, SPAN (I believe Arnie Aldrich) called Sy Liebergot with more details but it was not determined which of the two possibilities was correct. (During the later investigation it was determined at the time of the O2 tank failure, the characteristics of a short were observed).

In any case, to enable correlation of the O2 tank quantities, it was then decided to actually conduct more frequent cryo stirs, and this was done at GET46:42 and at GET 48:00, when the O2 Tank 2 fans were actually run for 6 minutes to see if this would "blow that tube out of there".

The normal schedule was for a one minute cryo stir to be done "pre" and "post" sleep and any SIVB or SPS ΔV manoeuvre.

Sy came on shift and he and the SSR then decided to do stirs at GET 51, 56 and 60 hours on all four cryo tanks as in addition to the O2 tank 2 quantity gauge problem, there was also an issue with a H2 tank imbalance and transducer shift that was causing nuisance Caution and Warning alerts and in fact was thought to be more of an issue as it affected crew rest (see my 2018 post above).

As the data began showing little difference in the readouts between the increased stirring during these additional stirs and also would not be as effective at lower quantities, Sy advised Gene Kranz, that he was considering reducing the stir frequency.

In any event, it was concluded to do a four tank stir after the TV show at GET 55:50 — the seventh O2 tank stir — as it could be tied in with the termination of a Battery B charge.

And then "it" happened, somewhat fortuitously at that specific time for reasons that have been mentioned previously elsewhere.

Additionally, because of the She tank issue, the entry into the LM had been brought forward and so the IVT stuff had been completed to open the hatch and also a plan for a short DPS burn had been worked out in case it was necessary to relieve the She tank pressure.

The immediate accessibility to the LM for the subsequent "lifeboat" mode activation and the procedures to some extent, for a free return DPS burn were to hand.

quote:
Originally posted by Spacepsycho:
Stirring the O2 tanks was done to mix the stratified oxygen slush in order to get an accurate reading and wasn't critical to the operation of the spacecraft
After the investigation, a third O2 tank was added (already planned for the "J" missions) and the tanks were redesigned with O2 fans removed as it was determined that would be satisfactory for cryo operations plus other refinements at much cost - much to Bob Gilruth and Chris Kraft annoyance.

Here for a bit of "light" reading, are a few reports relevant to the discussion on cryo designs and characteristics:

quote:
Originally posted by Headshot:
How was the post-explosion mass determined to calculate the burn to place the stack on a free-return trajectory, and eventually the course corrections that followed? I mean Houston had little to no idea of the extent of the damage to the tanks and, at the time, they did not know that a whole panel of the service module was gone. Has anyone ever read a determination of how much mass Apollo 13 lost as a result of the explosion?
Good question, but for a start, the amount of O2 lost from sector 4 could be calculated.

At the time of the explosion, according to the TM, there was 252.4 lbs in tank 1 and 260 lbs in tank 2 for a total of approximately 512 lbs.

The bay door weighed 98.8 lbs but I suppose when the total vehicle mass was determined by RETRO later at GET58:32, as CSM=63367 lbs and LM=33499 lbs, that fact was unknown, but was probably insignificant as it was only .1% of the total.

The condition of the O2 Tank 2 was of course, unknown or if in fact it was still there, so that would not have been a consideration, mass wise, at the time.

It was later determined that the tank was relatively intact except for the failure in the dome area that led to the rapid release of O2 which immediately "exploded" in Sector 4 and expelled the sector door - fortunately, as the CM could have been nudged of the Service module which would have complicated things even further.

I have also wondered if the sudden release of this "atmosphere" may have contributed to the loudness of the bang the crew heard.

oly
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posted 11-10-2020 05:57 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
Great information Andy, thank you for the in depth assessment.

I too have wondered about the "bang" and believe that the sound may have been generated by the sudden release of pressure acting upon the CM heat shield/lower surface. The sound being generated by a percussive shock or drumming of the spacecraft.

As sound does not travel through a vacuum, and the contact area between the CM and SM were minimal, I can't imagine another explanation.

Jim Behling
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posted 11-10-2020 07:46 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
Has nothing to do with the gas release. The panel breaking off with fasteners (stored energy) and welds breaking would send shocks through the structure.
quote:
Originally posted by Andy Anderson:
...much to Bob Gilruth and Chris Kraft annoyance.
What do you mean "annoyance"? They (especially Kraft) did not deal with Apollo spacecraft costs. That would be the Apollo Program and the Apollo Spacecraft Project.

Kraft was not part of that (he was only flight ops and not part of the Apollo Program). And even though the Apollo Spacecraft Project was based at MSC, it did not directly report to Gilruth for funding and direction.

Headshot
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posted 11-10-2020 11:20 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
Very good and comprehensive post by Andy Anderson. Thank you.

I am curious where Mr. Anderson discovered the mass of 98.8 pounds for the panel that was blown away. The mass for the SIM Bay door ejected on the J-Series missions was given in the Apollo Flight Journal as 170 pounds. That sector 1 door and the sector 4 panel blown off of Apollo 13 were both 50 degree sectors, so I would have thought that their masses should have been more comparable. I must be missing something.

Andy Anderson
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posted 11-10-2020 06:37 PM     Click Here to See the Profile for Andy Anderson   Click Here to Email Andy Anderson     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jim Behling:
What do you mean "annoyance"?
Well "annoyance" might not be the right word but I gleaned that from what he wrote in his autobiography, "Flight," page 339.
Ed Cortright was now at the Houston center, working for Max Faget's engineers on understanding all of this. He hadn't bothered making his manners to Bob Gilruth, or even giving us an update on his conclusions. So Bob made the move and invited him up to the ninth floor.

We listened to him summarize what he knew. We'd heard it all from Max already, so there were no surprises. The obvious solution was to replace the switch as previously ordered.

"I'm recommending that we design and build a new tank," Cortright said, and we were astounded.

"Why would you do that?" Gilruth asked.

"That tank is perfectly sound," I said. "We've got hundreds of test hours and flight hours on it. A new tank loses us all that experience."

"I have my reputation to worry about," Cortright said. "I can't recommend anything less."

What he meant was that a simple solution was just too easy. If it didn't look difficult, he didn't look good. We argued, but Cortright wouldn't budge. Vanity overcame his common sense. In the next weeks, Gilruth and I fought all the way through NASA headquarters. The bosses took the political way out and ratified Cortright's recommendation.

That new design costs $40 million...

By the way, I seem to vaguely remember reading that prior to Apollo 13, thermostats were not fitted to the O2 tanks for Apollo 14 and thereafter so Apollo 13 was the last mission to have this feature.

I also believe that a mod to the engines in the SII stage for (AS-508) Apollo 13 would have prevented the pogo problems that cause the early shut down of the center engine but it was decided not to install it until the next mission.

quote:
originianlly posted by Headshot:
...discovered the mass of 98.8 pounds for the panel that was blown away.
I got that from Simulation And Analysis Of Panel Separation From The Apollo 13 Service Module, bottom of page 12.
Panel Mass ... The actual weight of a full scale panel is 98.8 lbs.

Headshot
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posted 11-10-2020 07:05 PM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
Thank you Andy. Looks like both our figures come from good sources. Nonetheless, it is very puzzling that there should be such a significant difference in mass between the sector 1 door and the sector 4 panel given that their dimensions should be close.

Space Cadet Carl
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posted 11-12-2020 08:37 AM     Click Here to See the Profile for Space Cadet Carl   Click Here to Email Space Cadet Carl     Edit/Delete Message   Reply w/Quote
This has been a very informative topic and I appreciate everyone's input. I'm just surprised a cryogenic stir wasn't necessary until 46 hours into the mission. I'm guessing during the first two days of the mission it really wasn't a required task.

Andy Anderson
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posted 11-12-2020 06:59 PM     Click Here to See the Profile for Andy Anderson   Click Here to Email Andy Anderson     Edit/Delete Message   Reply w/Quote
The 46 hour stir after the O2 tank 2 gauge failed was additional to the routine stirs that were scheduled as part of the pre- and post-sleep checklists and also prior to burning of the SPS and the S-IVB (once for that I guess) as listed in the CSM Systems Checklist.

At the time of the stir immediately prior to the problem at GET 55:55 there had been a total of seven stirs.

I have done a bit more digging and from the S/N 1001 copy of the two flown CSM Systems checklists, it seems that Ken (I presume) had made a pen entry that seems to modify that schedule, however, it appears they stuck to the checklist as written, because at GET 23:20 post rest, there was talk between the crew and Capcom confirming that a stir had been done:

oly
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posted 11-13-2020 12:22 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
There appears to be an assumption that the O2 tank failure occurred because of the cryo stir event.

The post-flight investigation determined that the reasoning for the tank rupture may have been attributed to overheated wiring insulation, however, there may have possibly been other factors at play.

In the manufacturing and test history of the O2 tank, the investigation determined that:

The installation procedures for heater, fan, and probe wiring were found to be critical, with several areas where routing damage would not be visible on the assembled product. (While mating a fan with the heater probe, the demonstrator ab raided the fan wiring at the motor exit point. This area was not visible with the fan completely installed.)
This indicated that potential manufacturing defects may have existed without detection. Additionally, the tank had experienced fan motor problems during testing that required the replacement of the units with improved design units. While this was considered to have no bearing on the flight failure, the possibility exists that there was another fault involved with the tank failure.

Without having the failed tank or the service module available to investigate the failure, the investigation team could only use the available data to determine probable cause.

While several modifications were carried out to improve system reliability, there is no doubt that the Apollo 13 event resulted in nervous management and political minds that contributed to the demise of the Apollo program.


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