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50 years ago today, on April 17, 1970, the Apollo 13 crew arrived home. No danger. Successfully.
The world sighed in collective relief as they watched NASA turn a disaster into one of the most dramatic happy endings ever.
The Apollo 13 flight was unlike any other Apollo mission,
and the final hours of the flight: preparation and implementation of re-entry
to Earth, it was unlike any other, too.
The crew had to run a checklist of more than 500 articles that had been written just hours earlier. They were in constant contact with the Mission Control team to verify each step. The exhausted, cold and dehydrated crew needed to perform multiple unplanned maneuvers, including correcting the emergency trajectory using the Lunar Module (LM) thrusters.
After the final trajectory correction maneuver as the spacecraft headed toward Earth, Earth tracking data showed that the burn had been carried out exactly as expected. However, after that maneuver, the crew had to make sure that they did not fire any further propeller shots, as the LM Reaction Control System fuel supply was approaching a low point where accurate measurements were no longer reliable . Everyone wanted to make sure they had enough fuel for the final leg to Earth.
The crew then had to ensure that they re-powered the systems on the cold command module in the correct sequence, and turned off any additional accessories, such as reflectors, to ensure that the CM batteries would last until reentry. At least one of the three batteries was predicted to fail over the time parachutes needed to deploy. (Read about how the batteries were recharged here.)
And, of course, on a typical Apollo space flight, astronauts would have discarded the LM while they were still in lunar orbit. But the use of the LM Aquarius was necessary until almost the end of the mission, as it was the lifeboat for the astronauts, keeping them alive in place of the paralyzed Command Module, inoperable after the explosion of an oxygen tank in the attached Service. Module.
Therefore, the sequence of reentry events was quite unusual.
The Service Module was actually discarded before the LM. SM’s launch had some
additional drama, in addition to the problems encountered for Apollo 13.
As I wrote in my book “Eight Years for the Moon: The History of the Apollo Missions,” NASA electrical engineer Gary Johnson shared documents that revealed a reentry anomaly had been discovered after the Apollo 11 mission, where the SM was not properly separated from The CM. A series of thruster shots in the SM should have separated the two vehicles, but an incorrect sequence of thruster shots caused the SM to return to the CM, and the Apollo 11 crew reported seeing the SM fly past them. . An investigation revealed that the anomaly had not only occurred on Apollo 11, but also on other previous Apollo flights.
Johnson presented the electronics changes to change the sequence of the propeller firing to the Apollo Program Configuration Control Panel, and he recalls trying to make the engineering changes as soon as possible so that it can start from Apollo 12. But When the research and analysis of how to fix the problem was completed, it was almost time for the Apollo 12 launch, and the Apollo Program made the decision to launch the Apollo 12 without this change being made. The SM Jettison Controller changes were approved and completed for the Apollo 13 flight as well as for subsequent missions.
But the updated separation sequence would not happen on Apollo 13. The Service Module for Apollo 13 was dead, with its propellers inoperable after the explosion. According to the Apollo Flight Journal, this sequence of events was to take place for SM Sep: first, the electrical connections between SM and CM were cut with explosive bolts, and then another explosive guillotine separated the umbilical service module from the command module. Then three loads cut the tension loops that held the Service and Command Modules together, and created a spring action that drives the CM away.
To put as much distance between the SM and the CM and the attached LM, the crew needed to manually fire the LM RCS jets to separate them first, then turn around in a way that allowed the crew to observe and photograph the Service Module.
“And one side of that spaceship is missing,” Jim Lovell radioed to the ground, disbelief in his voice when he saw the abused SM.
When it was time to ditch the LM Aquarius, the crew was in the now-powered Odyssey CM. Odyssey had no maneuverability, no fuel for RCS thrusters. They had to dispose of the LM in such a way that the Lunar Module would not collide with the Command Module or endanger it in any way. NASA engineers had consulted with Barry French of the University of Toronto Institute for Aerospace Studies (UTIAS). French was a pressure wave expert in space, and as detailed in this article published by Fast Company last year, French and his team helped the Mission Control team use pressure in the docking tunnel between the two ships. to act as a spring to push them apart.
Normally, the two spaceships were separated using an explosive
load because the tunnel would have been depressurized before separation. But with
the tunnel is still pressurized, shock waves from explosives could endanger Odyssey
They hatch and put astronauts at risk during re-entry. French and his team
determined that 2 PSI of pressure in the tunnel was enough to push the mole
modulus of distance at approximately 2 feet per second, approximately 1.5 mph.
His plan worked perfectly. Capcom Joe Kerwin poignantly broadcast from Mission Control: “Goodbye Aquarius, and we thank you.”
Then the crew made their final preparations to make that final, fiery leg back home. All anyone could do now was hope that every last minute procedure and calculation had been correct.
When the crew collapsed through Earth’s atmosphere,
Communications with Mission Control were impossible. During the Apollo era, the
the radio blackout was a normal part of the reentry, caused by the ionized air surrounding
the CM during its overheated reentry through the atmosphere, which interfered
with radio waves For practically every re-entry from Mercury to Apollo 12,
The timing of the radio blackout was predictable, almost a second. However,
The Apollo 13 radio blackout period was very long: it spanned
Approximately 87 seconds longer than expected.
Five years ago, in an earlier series of “13 Things,” we discussed possible reasons why the blackout period was unbearably long. The most likely explanation was that the spacecraft was reaching a shallower trajectory than expected. This would result in a longer period in the upper atmosphere where there was less deceleration of the spacecraft. In turn, the reduced rate of deceleration lengthened the time that the heat of the reentry produced the ionized gases that would block communications.
But why was the trajectory shallower than expected? POT
Engineers and flight controllers have been asking that question for 50 years. A
group led by Apollo Flight Dynamics Officer (FIDO) Dave Reed, Refurbishment Officer (RETRO) Chuck Deiterich and Electricity, Environment and Communication
Systems (EECOM) John Aaron recently conducted a comprehensive review of the data,
and he used computer modeling to recreate every detail of the events leading up to the reentry.
Your conclusion? Blame the excess ventilation of a cooling system on the LM.
“Our model was quite complex,” Reed told Universe Today,
“With many adjustable variables, such as passive thermal control (PTC)
true bearing and velocity, path relationship with PTC bearing,
sublimator ventilation diagram and photos, estimates of the propulsion percentage of
“Non-propulsive” vents, O2 ventilation contributions, hydrogen leakage potential,
velocity effects on the input angle at various input distances, helium
ventilation, hot and cold side sublimation physics, and duration of ventilation. “
Reed said that after studying all the identified possibilities
and modeling its ventilation drive of various systems, “it is evident that
the delta velocity necessary to cause the observed path to drop from the
The CSM LM stack was primarily from the Lunar Module cooling system, ”he said. “Additional
However, leak sources were present from both the SM hydrogen tanks located
underneath the damaged O2 tanks, and the remaining O2 tank as well. “
Reed, Deiterich and Aaron wrote that their findings are consistent with the mission’s real-time data, and are supported by “a series of crew transmissions reporting again, again, relief and ‘sparks’ from the CSM ( which could have been activated by the PTC cold-heat cycles) and by the calculations of the maximum moment that the LM cooling system could generate, as well as any ventilation of the SM hydrogen and oxygen tanks. “
In this video, you can feel the palpable concern in Mission
Control over the long communications blackout. And contrary to the final
scenes in the movie “Apollo 13” flight controllers, flight directors and
everyone present at Mission Control didn’t start celebrating until
parachutes were deployed and the crew splashed slowly and surely in the south
Pacific Ocean.
“During the blackout,” Reed recalled, “I clearly remember looking at Chuck (Deiterich) with the clear realization that if we, Chuck and I, had used a wandering vector to calculate the last half-course, and that if the crew had not Don’t survive …… only the two of us would have been responsible. I can tell you that during those 90 seconds of blackout, all the gravity in Houston was under our feet. Celebrate hell. I have no way of expressing the horror of those seconds, nor my relief when I saw the crew on the ramps. “
Our thanks to NASA engineer Jerry Woodfill for his insights and ideas for our entire series of articles on Apollo 13 that start with “13 Things That Saved Apollo 13” and then “13 MORE Things That Saved Apollo 13”.
Additional thanks to NASA engineers Norm Chaffee and Gary Johnson and flight controllers Dave Reed and Chuck Deiterich for their ideas and memories of this current series:
Part 1: The BBQ Roll, and Part 2: Charging the Batteries.
