Source: Robert Kurson. Rocket Men - The Daring Odyssey of
Apollo 8 and the Astronauts Who Made Man's First Journey to the Moon (2018)
Apollo 8 and the Astronauts Who Made Man's First Journey to the Moon (2018)
While Borman slept and Anders piloted the spacecraft, Lovell took sextant sightings for navigational purposes. Part of how Apollo 8 kept its attitude (they way in was oriented in space) was by aligning the spacecraft with the stars, and that was part of Lovell’s job as navigator. Lovell selected known stars and then marked their positions using the optics and the onboard sextant. After doing so, Lovell entered the information to the computer, which would then calculate Apollo 8’s attitude based on its relative position to those stars, and then automatically fire the thrusters to keep the spacecraft in the desired orientation in space.
It was important to be pointed to Earth as well as to be properly positioned for reentry.
Lovell had become beyond-expert at navigation using the stars, and he entered the data on the keypad much like a maestro on a piano. Lovell had earned the nickname “Golden Fingers" for his expertise at punching in data on the buttons. However, this time Lovell made a mistake entering the navigational data, in that he accidentally restarted the guidance system. Apollo 8 started to roll, somewhat like Gemini 8 with Armstrong and Scott; the attitude of Apollo 8 was in question.
It was important to be pointed to Earth as well as to be properly positioned for reentry.
Lovell had become beyond-expert at navigation using the stars, and he entered the data on the keypad much like a maestro on a piano. Lovell had earned the nickname “Golden Fingers" for his expertise at punching in data on the buttons. However, this time Lovell made a mistake entering the navigational data, in that he accidentally restarted the guidance system. Apollo 8 started to roll, somewhat like Gemini 8 with Armstrong and Scott; the attitude of Apollo 8 was in question.
Borman awoke and asked what was going on, and Anders stated it was a stuck thruster. The “Eight Ball", the instrument that showed proper attitude, was frozen and useless by that point. Lovell told Borman and Anders that he made a mistake by accidentally resetting the guidance system, which explained the frozen Eight Ball, and which also explained the thruster still firing. Anders started to correct the spacecraft’s roll, using the floating dust in the cabin as a guide. Anders realized that he needed to get the cabin to move in the same direction as the floating dust; when the spacecraft no longer rotated, the interior dust would no longer be rotating in the cabin.
While Apollo 8 once again had a steady attitude, it was unknown which way Apollo 8 was pointing, since the guidance system thought the spacecraft was on the launchpad. Borman took the controls, and everyone was angry: Borman and Anders were angry at Lovell, and Lovell was angry at himself. But all three astronauts had to get past their emotions in order to reorient Apollo 8 - but how to do so? The only real way was to use the stars, and if Lovell could pick out a few known stars, he could restart the process of rebuilding the computer’s idea of where they were in terms of orientation. However, the Sun shown against the darkness, making it impossible to see any stars.
While Apollo 8 once again had a steady attitude, it was unknown which way Apollo 8 was pointing, since the guidance system thought the spacecraft was on the launchpad. Borman took the controls, and everyone was angry: Borman and Anders were angry at Lovell, and Lovell was angry at himself. But all three astronauts had to get past their emotions in order to reorient Apollo 8 - but how to do so? The only real way was to use the stars, and if Lovell could pick out a few known stars, he could restart the process of rebuilding the computer’s idea of where they were in terms of orientation. However, the Sun shown against the darkness, making it impossible to see any stars.
Lovell found help from an old friend, in that looking through the optics system he spotted the Moon. After locating the Earth, he formed a rough idea of the attitude with respect to the 37 stars stored in the computer’s database. CapCom (Collins) relayed procedures from Mission Control that would assist the crew. Mission Control had access to part of the computer’s memory that had been corrupted by Lovell’s mistake, in particular the set of numbers that defined how the guidance system should be aligned with the stars. Once Mission Control uploaded the correct values to Apollo 8, Lovell started the process of reorienting the spacecraft, and after about 30 minutes, Apollo 8’s attitude was back to normal as it closed in on the Earth.
At about 5 pm Houston time on 26 December 1968, Apollo 8 reached the half-way point between the Moon and the Earth, 37 hours after leaving lunar orbit. If all went well, it would be only 20 hours until Apollo 8 splashed down in the Pacific. Apollo 8 had one more television broadcast to do, its sixth of the mission. Anders showed Earth as it appeared 110,000 miles away as Apollo 8 approached. Television viewers saw that there was a storm over South America, and they were able to see Central America and the southern US. After the broadcast, 19 hours remained until Apollo 8 started reentry. When Apollo 8 was 35,000 miles above the Pacific, going 7700 mph, Mission Control determined that no midcourse correction was necessary in terms of trajectory for reentry.
At about 5 pm Houston time on 26 December 1968, Apollo 8 reached the half-way point between the Moon and the Earth, 37 hours after leaving lunar orbit. If all went well, it would be only 20 hours until Apollo 8 splashed down in the Pacific. Apollo 8 had one more television broadcast to do, its sixth of the mission. Anders showed Earth as it appeared 110,000 miles away as Apollo 8 approached. Television viewers saw that there was a storm over South America, and they were able to see Central America and the southern US. After the broadcast, 19 hours remained until Apollo 8 started reentry. When Apollo 8 was 35,000 miles above the Pacific, going 7700 mph, Mission Control determined that no midcourse correction was necessary in terms of trajectory for reentry.
For Apollo 8, it was the Pacific Ocean or bust. Apollo 8 had to hit the most narrow of corridors at just the right attitude and trajectory, moving at a speed faster than any humans had ever traveled up to that point. To the crew of Apollo 8, reentry was one of the three maneuvers of the mission of which they were most likely to die, along with the launch at TEI (Trans Earth Injection). Reentry officially started at an altitude of 400,000 feet (75.75 miles), and by that time, the command module had separated itself from the service module. The command module would reenter the Earth’s atmosphere bottom-end-first, since that was where the heat shield was located. The command module would travel 24,500 mph through that narrow corridor, and it would be the computer, not Borman, that would be flying the spacecraft as Apollo 8 reentered the Earth’s atmosphere.
For the astronauts, now strapped back in their seats, they could only endure and trust that everything was a go for splashdown. There was almost no margin for the tiniest of errors, in that if Apollo 8 reentered the atmosphere at too steep an angle it would burn up, and if the trajectory was too shallow, the command module would bounce off the atmosphere into space. The heat shield, to cope with heat of 5000 degrees Fahrenheit at nearly 25,000 mph in the narrow corridor, was made of reinforced phenolic resin that was injected into the fiberglass honeycomb. The heat shield was in layers, and in the extreme heat, each layer was designed to melt away and vaporize, leaving another layer to do the same, etc., all the while keeping the cabin cool. That being said, the astronauts experienced tremendous G-Forces as the atmosphere slowed down the command module. There would be no possibility of communication between Apollo 8 and Mission Control as gasses around the spacecraft ionized from the shock wave, creating a wall where radio/TV signals could not pass through.
For the astronauts, now strapped back in their seats, they could only endure and trust that everything was a go for splashdown. There was almost no margin for the tiniest of errors, in that if Apollo 8 reentered the atmosphere at too steep an angle it would burn up, and if the trajectory was too shallow, the command module would bounce off the atmosphere into space. The heat shield, to cope with heat of 5000 degrees Fahrenheit at nearly 25,000 mph in the narrow corridor, was made of reinforced phenolic resin that was injected into the fiberglass honeycomb. The heat shield was in layers, and in the extreme heat, each layer was designed to melt away and vaporize, leaving another layer to do the same, etc., all the while keeping the cabin cool. That being said, the astronauts experienced tremendous G-Forces as the atmosphere slowed down the command module. There would be no possibility of communication between Apollo 8 and Mission Control as gasses around the spacecraft ionized from the shock wave, creating a wall where radio/TV signals could not pass through.
In order to reduce and cope with the fantastic amount of heat and G-Forces caused by reentry, Apollo 8 would not simply plunge through the atmosphere. The command module was designed to have a slightly off-center weight distribution, which turned the spacecraft into a sort of wing. That design allowed the rapidly descending command module to achieve lift and dip up-and-down, extending its path, shedding velocity, and diffusing the heat as it aimed for splashdown. That process would last five minutes, and if all went well, Apollo 8 would have slowed enough to make its final drop, which then depended on the parachute system working properly, which for an Apollo command module meant three main parachutes. The Navy’s recovery forces that were moving back-and-forth in a specific area of the Pacific near Hawaii were like predators on a hunt.
Before reentry, the crew stowed the remaining loose items in the cabin, and then cut off the oxygen supplied from the service module, which would soon be jettisoned. After separating from the service module, the crew would rely on the small oxygen tanks in the command module. Fifteen minutes before reentry, Borman jettisoned the service module, and with built-in jets, the service module moved away from the command module.
With only six minutes until reentry, the astronauts were not in their spacesuits or helmets, which NASA allowed since the astronauts needed to manually equalize their eardrums as the air pressure rose during the descent. Strapped in their seats, the astronauts were pointed back out into space hurdling back to Earth at more than 20,000 mph. Soon enough, Apollo 8 plunged back to Earth at 24,750 mph, breaking below 100 miles of altitude, and the three astronauts braced themselves for reentry. While Borman and Lovell had experienced reentry during the Gemini Mission Series, they had never reentered the Earth’s atmosphere at this speed . . .
Before reentry, the crew stowed the remaining loose items in the cabin, and then cut off the oxygen supplied from the service module, which would soon be jettisoned. After separating from the service module, the crew would rely on the small oxygen tanks in the command module. Fifteen minutes before reentry, Borman jettisoned the service module, and with built-in jets, the service module moved away from the command module.
With only six minutes until reentry, the astronauts were not in their spacesuits or helmets, which NASA allowed since the astronauts needed to manually equalize their eardrums as the air pressure rose during the descent. Strapped in their seats, the astronauts were pointed back out into space hurdling back to Earth at more than 20,000 mph. Soon enough, Apollo 8 plunged back to Earth at 24,750 mph, breaking below 100 miles of altitude, and the three astronauts braced themselves for reentry. While Borman and Lovell had experienced reentry during the Gemini Mission Series, they had never reentered the Earth’s atmosphere at this speed . . .