Lessons from space accidents: the defeat and triumph of "Apollo 13"

In the same April days of 1970, the most dramatic story of everything that happened in space was probably played out. Three astronauts who went to the moon were in mortal danger and were forced to return home for three days, overcoming the various difficulties encountered. This is a very beautiful story about how small changes in the specification can lead to big problems, about the coordinated work of hundreds of people in the MCC in the work-around mode, about courage and professionalism.

Cause

As it often happens in complex technical systems and large projects, the cause of the accident was laid even years before the Apollo 13 flight, and the accident itself was formed from a complex chain of events, and the absence of any link would lead to the absence of an accident.

Design

In order to understand what happened, you need to tell about the design of the Apollo service module:

The energy subsystem of the Apollo service module consisted of two hydrogen tanks, two oxygen tanks and three fuel cells. Fuel cells, consuming hydrogen and oxygen, produced electricity and water, which was consumed by the crew for drinking and cooling equipment. It was a very effective system, better than solar panels, provided that the flight will be no longer than 2-3 weeks.

This is the oxygen tank of the Apollo service module. It is so well insulated that it can store liquid oxygen for years. Liquid oxygen is stored in it in the state of supercritical fluid , and, therefore, it exhibits the properties of both liquid and gas. As you know, with the expansion of the gas temperature decreases. The insulation is so good that liquid oxygen would cool down and lose supercritical properties simply from expansion at normal fuel cell consumption. Therefore, we had to put a special heater to maintain the required temperature and pressure. In zero gravity, liquid oxygen in a supercritical state had the bad habit of splitting into liquid and gaseous layers, which led to incorrect readings of the level sensor. Therefore, we had to put a special impeller for mixing oxygen, and for the crew, the procedure of mixing oxygen in tanks was added to the “housework” kit so that the Houston MCC could obtain correct data on the amount of oxygen on board.

Minor specification change

1965 Before the flight of Apollo 13, another five years, before the first unmanned flight of the AS-201, another year, even the Gemini program only this year made its first manned flight. Active work is underway on the ship "Apollo". Because of the enormity of the work, NASA contractors hire subcontractors to make the necessary elements. The Apollo Service Module did North American Aviation, and the sub-contractor Beech Aircraft did the tanks for it. Since the fuel cells produced 28 volts of voltage, the specification for the tank indicated a working voltage of 28 volts. However, already in the process of developing the service module, it turned out that in preparation for the launch, Apollo will receive electricity from the ground generators of the launch complex, and they have a working voltage of 65 volts (a completely normal situation, when many qualified people make a big project, no jokes) . Therefore, the specification had to be redone. The engineers of Beech Aircraft changed the equipment of the oxygen tank, but forgot to change just one thing for the new voltage - the thermostat contacts. They are designed to open the heater circuit if necessary. Quality control at all levels - Beech Aircraft, North American Aviation and NASA did not notice this error.
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Moving tanks

1968 The tanks, which ended up on the Apollo 13, are installed in the service module, which will become part of the Apollo 10. Since the changes were made to the tanks, after some time it was decided to install the newer tanks on the Apollo 10, and install the existing ones, upgrade and install them on another service module. In the process of removing the tanks, the workers forgot to unscrew one bolt, and the winch, which had already begun to raise the shelf with tanks, stalled and dropped the tanks back to the rack. The height of the fall was ridiculous, only 5 cm, but for space technology it is a serious emergency. The incident was documented, the tank was tested, it was considered to be in good condition and sent for retrofit. Obviously, the modernization was not associated with a serious disassembly of the tank (this is important for understanding the next stage). After modernization, the tanks were installed in the Apollo-13 service module.

The same tank number two in the foreground, photographed after installation.

Cocking

March 27, 1970, two weeks before the start of the Apollo 13. Produced so-called. training prelaunch countdown - complete simulation of the launch with refueling of the ship with working fluids, switching to flight atmosphere, in short, everything except the real “Ignition” command. The simulation was successful with one exception - tank number two refused to empty after the end of the test. In the process of solving the problem, the engineers suggested that the lower drain fitting was damaged when it fell in 1968. Theoretically, this is an emergency, it is necessary to transfer the start and change tanks. But, on the other hand, the lower drain fitting is used only once - during the training prelaunch countdown. In flight, it is not needed, and you can fly with an inoperative choke. Therefore, they proposed to use a heater for oxygen etching, to gasify oxygen, which would evaporate by itself through the upper fitting. The decision was coordinated with the spacecraft commander, astronaut Jim Lovell. Jim signed the documents on the basis of the available data: the proposed solution is the best one that was invented, no other faults were found, the lower fitting is not needed during the flight, and a change of tanks will take forty-five hours, not counting the testing of new tanks, which will disrupt the pre-launch preparation schedule and delay the launch for a month.
When turning on the heater with a ground voltage of 65 volts, the contacts of the thermostat designed for 28 volts welded in the on position, the heater lost the ability to turn off:

A closed contact, a photograph of a full-scale accident replay experiment.

The temperature sensor inside the tank, made to measure the working temperature in the region of -207 degrees, had an upper measurement limit of +27 degrees. The engineer controlling the work could get only two parameters - “heater on” and “temperature not higher than +27 degrees”. In reality, the constantly on heater quickly evaporated oxygen and, continuing to work in an empty tank, heated to +540 degrees. Somewhere in the huge building complex of the launch pad, there was a recorder fixing a constant current of the heater instead of on-off cycles, but no one looked at its tape before the accident. The heater heated to +540 degrees melted Teflon insulation, and the wires turned into a detonator.
It was impossible to fix the abnormal heating directly - the tank was well insulated, so a fire in the service module could not occur, and the abnormal temperature lasted until pre-start refueling when the new liquid oxygen cooled the inside of the tank.

Characters

The crew of the "Apollo 13"

From left to right: Lovell, Swigert, Haze. Photographed in a hurry because of the replacement in the carriage.

Jim Lovell - the commander, a veteran of the space program, made two flights on Gemini and circled the moon on Apollo 8.
John Swigert is the pilot of the command module. The first flight into space, was in the backup crew, transferred to the main crew a few days before the flight due to the fact that the astronaut of the main crew - Ken Mattingly was in contact with astronaut Charles Duke, who fell ill with rubella, and was not immune to rubella. The first bachelor among astronauts.
Fred Hayes - the pilot of the lunar module. First flight to space.

MCC Houston

Gene Krantz is the head of the “white team”, the main flight shift (there were a total of four shifts), and the lead flight leader.


White Team. Mission unknown.

Crash

55 hours 54 minutes of flight. The next switching on of the tank mixing system (it turned on regularly, more often than once a day) caused a short circuit in tank number two. Teflon insulation caught fire:

Teflon burning in oxygen, a photograph of a full-scale experiment to reproduce the accident.

The burning of Teflon in oxygen caused a sharp heating of the tank and an increase in pressure exceeding the strength limits of the tank. Plucked the top cover of the tank:

Breaking the lid, a photograph of a full-scale experiment to reproduce the accident.

A sharp increase in pressure tore off the sheet covering the section of the service module:

Disruption of the panel, a photograph of the natural experiment to reproduce the accident.

In addition, the shaking from the failure of the tank cover caused abnormal closing of the fuel cell valves 1 and 3, leading to their shutdown after three minutes, and led to a violation of the tightness of the oxygen tank pipelines number one. After 130 minutes, the pressure in the oxygen tank number one dropped to zero - the command module lost water and energy. From the Earth, he was at a distance of 320,000 kilometers.

Photo from the ground telescope.

"Houston, we had a problem here."

Flight pattern

Yes, the phrase-meme sounded in the original exactly like this: "Houston, we've had a problem here." The astronauts and the MCC, of ​​course, did not have complete knowledge of the situation described in the previous paragraph, so for the first minutes people tried to figure out what had happened. In any cosmic incident, first of all it is necessary to establish whether this is a real problem or failure of sensors / telemetry. First, the crew rebooted the computer, reported on the readings of the indicators, connected the fuel cells to different power buses to figure out what was going on. But fifteen minutes later, Jim Lovell reported that he was observing the leakage of some gas from the service module - the problem was clearly very serious, and it was far from over.
At this time, another popular phrase was heard in the MCC - “Guys, let's solve the problem. Let's not make matters worse by conjecture. ”
The initial task was an attempt to save the remaining oxygen in the tank number one. Despite all attempts, the leakage site could not be isolated, the pressure continued to fall. The only possibility was the inclusion of the lunar module, which became a lifeboat. Work had to be done very quickly, simultaneously turning off the command module and turning on the lunar one. The inclusion of the lunar module according to the instructions took about three hours. The leakage rate increased, and when it became clear that the fuel cell would work for less than fifteen minutes, the switching procedure had to be changed on the fly. A separate problem was navigation. It was necessary to rewrite the data of the gyro-stabilized platform of the command module, to recalculate (the corners of the docking of the command and lunar module were not strictly 180 degrees) and enter the data into the gyro-stabilized platform of the lunar module. Complicated procedure was successfully performed. The command module has disconnected, the lunar module has taken control.

Difficult choice and first trajectory correction

The next task was to choose the mode of return. All the Apollos flew along such a trajectory (the so-called free return trajectory), which allowed the flyby of the moon and the normal landing on Earth. Because of this, all Apollo landings were not far from the lunar equator. At the same time, there were emergency return modes, when a sufficiently long pulse by the engines returned the ship to Earth without flying around the moon:
After a rather tense meeting (another sounded phrase was heard - “Failure is an unacceptable option” ), it was decided to stay on the path of free return. Arguments:

1. The variant with the shooting of the lunar module to reduce the mass that would have to be slowed down, has become impossible.
2. The variant with the use of engines of the lunar module, while there is enough fuel, did not give a noticeable gain in time. A reset of the service module could violate the thermal mode of the heat shield at the bottom of the command module. Damage to the heat shield made landing impossible.
3. According to calculations, consumables (water, electricity) were enough for free return.
4. The main engine of the service module may have been damaged and its use was a great risk.
5. The ship was already close to the moon and emergency return maneuvers were becoming less profitable.

However, Apollo 13 has already left the free return trajectory. A slight deviation was necessary for landing in the selected area. Therefore, I had to make a correction of the landing module of the lunar module, turning it on for 30 seconds. A separate problem was navigation. Pieces of thermal insulation, torn from the destruction of the oxygen tank, scattered in abundance around the ship, becoming false stars. Therefore, I had to use the sun to check the accuracy of orientation. Fortunately, the data was transferred correctly, and the gyro-stabilized platform worked fine, navigation was accurate, and the correction was successful.

PC + 2 maneuver

The free return trajectory also required a little maneuver. It was carried out two hours after perilation (the pericenter of the orbit around the moon), so it was simply called PerUsenium +2 (PC + 2). Thanks to him, the landing point shifted from the Indian to the Pacific Ocean, where the main landing ships were nominally accommodated, and the landing time moved forward by 10 hours. The lunar module landing engine, designed for one switch-on before landing, was turned on a second time, and it worked for 4 minutes and 24 seconds.

Strict savings

The lunar module operated on batteries, not fuel cells. Therefore, on the one hand, oxygen was abundant, because it was used to fill the lunar module after reaching the lunar surface. On the other hand, electricity and water were severely scarce. The lunar module was designed to work two people for a day and a half, but now it had to provide three people for four days. Therefore, after the release of the ship, all possible measures were taken to save electricity and water because of the disk of the moon. Water was consumed by people and spent on cooling equipment. Therefore, in the lunar module everything that was possible was turned off, and people had to endure thirst. While preparing for bed in the command module, the curtains on the windows were drawn out of habit, he quickly cooled down and did not get warm until the landing. In the lunar module, the situation was slightly better, but even there it was so cold that the water was settling with dew on the walls and panels.

Shove the square pin into the round hole

In English, there is an idiom - "square pin in a round hole" - "square peg in a round hole". It means a person in the wrong place. And in the flight of the Apollo 13, the idiom became a reality. Despite the abundance of oxygen in the crew, a breathing problem was brewing. The fact is that the exhaled carbon dioxide must be absorbed by something. More than 15% of carbon dioxide in the inhaled air leads to impaired vision, then consciousness, and, as a result, death. In the lunar module there were round canisters of lithium hydroxide, which absorbed carbon dioxide. But they were not enough. In the command module there were enough canisters of lithium hydroxide, but they were square:

Photo from the film "Apollo 13", but the meaning is very true.

Therefore, the challenge arose to quickly create a way to stick a square pin into a round hole. A special group, taking the same materials as those that were on the Apollo 13, quickly assembled the adapter and wrote the assembly instructions. The idea was quite simple - the canister was placed in a bag into which air was pumped from an air system pump. The bag was taken from the flight suit package, the hose was taken from spacesuits, it was sealed with tape, the bent cover of the flight plan was installed as a spacer for even air distribution, and the staff hole in the canister was closed with a toe and sealed with the same tape.

Assembling the adapter and a working device. Blowing with something subtly dear ...

The instruction was transmitted to the Apollo 13, and the same adapter was assembled in space. The carbon dioxide problem has been solved.

Critical procedure

Parallel to all these cases, extremely hard work was going on to create a procedure for launching a command module. Without the inclusion of the command module landing was impossible. And the inclusion was complicated by the fact that its batteries were already partially discharged, and the procedure for turning on a completely off command module was not only not developed in advance, was not thought about, and was not checked in the simulator. John Aaron, the same “steel-eyed rocket man who saved Apollo 12, led the group to create this procedure. Under conditions of limited time (the command module flew inexorably toward the Earth) they came up with the idea of ​​deploying a power bus that was designed to provide emergency power to the lunar module. Literally several amperes, which were not enough to launch the command module systems, were received from the lunar module, and the procedure was ready on time.

Battery explosion

At 97 hours of flight time, an explosion occurred in one of the batteries of the lunar module. Hydrogen and oxygen, normally released during battery operation, accumulated in the compartment of one of the batteries and a random spark led to an explosion. Fortunately, this explosion did not bring any special problems, three batteries worked as well, the fourth one had a slightly reduced charge.

Problem out of nowhere

All the time the ship returned from the moon, a problem was accumulating, the cause of which no one could identify. For a normal landing, the ship must be in a fairly narrow range of angles of entry into the atmosphere. Too small angle - and the ship will bounce off the atmosphere like a flat stone from water, too large an angle, and the ship will burn due to too much heat when braking. And the unknown force during the flight led to the fact that the angle of entry slowly but steadily decreased. It seems that all the forces acting on the ship were taken into account. Even the discharge of urine overboard was forbidden so that the reactive force would not spoil the trajectory, but all in vain - the angle went beyond the permissible limits. Another correction was needed. To save electricity, it was conducted manually, not including a computer. The lunar module landing engine turned on for 14 seconds at 10% thrust,for the third time. Time was also measured manually by a wristwatch. The correction was satisfactory, the angle of entry into the atmosphere was within acceptable limits, but later another correction will be required.
Already after the flight, it was established that the reactive force was created by water evaporating from the cooling system of the lunar module. Prior to this, the lunar module had never been in free flight so long that this small force became noticeable.

Another correction

At 108 hours of flight there was a rupture of the safety membrane of the pressurization tank. Helium, designed for one-time work before landing on the moon, was warmed up even before the first correction after the accident. The pressure in the tank was constantly growing, and a breakthrough of the safety membrane was inevitable. The loss of gas boost meant that the landing engine of the lunar module could no longer be started. But another correction was needed. I had to use the engines of the orientation of the lunar module. Fortunately, the impulse needed a small, only 22 seconds of much less powerful orientation engines, and the correction for 137 hours of flight was successful.

Landing

Before landing, it was necessary to perform many operations. First, it was necessary to transfer ballast to the command module — unnecessary things that would replace 45 kilograms of moonstones. This became the ballast of the camera, other small things, and the plate that was planned to leave on the Moon - Lovell decided to take it as a souvenir.
Secondly, it was necessary to turn on the command module, and, given the several days of downtime and the abundance of moisture on the walls, this was an exciting moment. Fortunately, the procedure was developed correctly, and the module for a short battery life returned to service. Then the service module was undocked. It was moving away, spinning slowly, and the astronauts looked with amazement at what great damage was caused by the accident - the whole panel was torn down:


Thirdly, it was necessary to undock the lunar module. The astronauts sadly escorted the module, which did not deliver them to the moon, but saved life.
And fourthly, it was necessary to check the correctness of the command module orientation. Since the final part of the flight took place in the shadow of the Earth, the time when the Moon was covered by the Earth was measured. Time coincided with the calculations of the MCC, the orientation was correct, and then computers worked.

The cooling of the lunar module again managed to reduce the angle of entry into the atmosphere, so the ship took longer than usual the dense layers of the atmosphere without communication, which certainly made people jittery. And after the connection was restored, the last intrigue remained - whether the parachutes will work. Fortunately, they worked, and live the whole planet could be glad for the successful return of the astronauts home.

Lessons

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Epilogue and notes

This is a post from the cycle “lessons of cosmic incidents”. The first post of this cycle for those interested.
I understand perfectly well that in this post there is a lot of technology, very little about people, and much is left overs. Compensate for this imbalance by watching the film Apollo 13, it is worth seeing, even if you are not particularly keen on astronautics.

Information sources:

1. Wikipedia and the sources specified in its articles.
2. Lovell Jim and Kluger Jeffrey, "Lost Moon: The Perilous Voyage of Apollo 13". There is a translation of Khartikov, but it is very uneven, often difficult passages are transferred correctly, and then some kind of mistake is there. If there are no other translations, it is recommended to read. There is an audiobook in English.
3. "Moon Machines", Science Channel, serial, 2008, episode "Lunar Module".
4. “When We Left Earth”, Discovery Channel, TV series, 2008, fourth series.
5. “From the Earth to the Moon”, HBO, TV series, 1998.
6. JSC Digital Image collection - photographic materials.
7. Apollo Expeditions To The Moon .
8. "" Failure from the list of opportunities EXCLUDE! " " - NK, 2006.

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