Apollo 12: In September 2002, astronomers discovered this asteroid in an unusual orbit around the Earth. This surprised the astronomers because, as far as they knew, the only natural object that orbited the Earth was the moon. Therefore, this strange object couldn’t be an asteroid; it had to be man-made. As it turns out, this was the Saturn V third stage that launched the Apollo 12 astronauts to the moon.
In 1969, this rocket left Earth and went on an unimaginable trip. It came back 30 years later. However, what transpired with this rocket and why did it finish up on such a peculiar journey? Saturn V’s rocket has three stages. The first stage fired for approximately 2.5 minutes and carried them to an altitude of 61 kilometers. The second stage would burn for approximately six minutes, gaining altitude and speed, and then the third and final stage would perform a brief burn to place the spacecraft into orbit.
Once the spacecraft was in a stable orbit, the third stage would again be ignited to perform the translunar injection burn, propelling the rocket and crew toward the moon. Once the Apollo crew had reached the moon safely, the third stage would split and NASA would attempt to dispose of it. On previous Apollo missions, the spacecraft was intended to be placed in an orbit around the sun, where it would remain for tens of thousands of years. NASA intended to meet the moon on its trailing side so that the moon’s gravity would propel the rocket away from Earth and into a solar orbit. This orbit is advantageous for NASA because it ensures that the asteroid will not interfere with future flights, although Apollo 12 was unsuccessful.
In order to dispose of Apollo 12’s third stage, NASA had to direct it to the vicinity of the moon. However, its initial trajectory showed it headed toward this side of the Moon, necessitating a last course correction by the third stage. For this maneuver, the third stage utilized its auxiliary propulsion systems. Two sets of thrusters at the stage’s base provided yaw, pitch, and roll control during flight. Even though the spacecraft had to shift its position by thousands of kilometers, it required very little energy because changing its trajectory so early in the mission would have a significant impact after it reached the Moon. When separation occurred, the third stage was moving at approximately 20,000 kilometers per hour.
In order to alter its course, it had to decelerate by around 140 kilometers per hour. This would cause the spacecraft to arrive on the other side of the Moon. Unbeknownst to NASA, the move did not proceed according to plan. The entire Saturn V rocket was controlled by the instrument unit placed above the third stage. It was also equipped with two c-band transponders that transmitted signals back to ground stations on Earth, providing NASA with more precise trajectory data.
Once the rocket was safely in orbit, NASA could compare this data with the rocket’s own data to determine whether or not it was following the intended flight route. If there was a problem, they could send a command to the rocket to fix it. NASA did not realize that the tracking system was slightly off, which led them to believe the rocket was flying faster than it actually was. As a result, in order to achieve the desired velocity, NASA slowed the rocket too much. They overcorrected by only 40 kilometers per hour, yet this was sufficient to significantly delay the spacecraft’s arrival at the Moon, leading it to miss by thousands of kilometers.
Thus, rather than being launched into a solar orbit, the third stage ended up in a highly elliptical Earth orbit. Throughout the next 15 months, the orbit was stretched and dragged in various directions by the Earth and Moon’s gravity, until it reached large range point one. This is the location between the Earth and the Sun when the gravitational forces of both bodies cancel each other out.
After the third stage crossed this threshold, the sun began to exert a greater influence. Imagine a vehicle attempting to climb a steep hill. If the vehicle lacks sufficient speed to reach the summit, the hill will pull it back down to the bottom. If it has sufficient momentum to pass the top, the opposite side will begin to drag it downward. This is precisely what occurred at the third step. It had just crossed the large range point by one hill and was being pulled into an orbit around the Sun.
In a sense, it eventually accomplished its mission, but its orbit around the sun was far from stable. Instead of being pushed into a solar orbit outside of Earth, it had been retarded into an orbit within Earth’s atmosphere. As a result, the third stage was now completing its revolution around the Sun slightly faster than the Earth. This suggested that it was gradually retreating. It was only a matter of time, though, until the third stage caught up.
This truly occurred in 1986, but it was not close enough to the L1 point to be captured by Earth’s gravity. The third stage continued to race around the Sun for a further 16 years before the inevitable occurred. In 2002, the third stage’s apoapsis coincided with Earth’s arrival on the scene. This time, the third stage passed beyond Earth’s L1 point, marking the first time in 32 years that the Earth exerted a stronger gravitational pull on the object than the Sun. Over the course of two months, the Earth drew the third stage into a similar highly elliptical orbit around the planet as before.
Astronomers had no idea what this object was at this stage, so they conducted spectroscopy studies to identify its composition in order to confirm the object’s identity. Each material reflects light in a somewhat unique manner. Specifically, the amount of light that is reflected at each wavelength will vary. To identify the composition of this object, astronomers measured the third stage’s light at a variety of wavelengths, producing a spectroscopy graph. They may then compare it to other spectroscopic graphs to determine if it matched other substances.
It was discovered that it closely resembled the spectroscopic graph of white titanium oxide paint. Identical to those used on the Saturn V. In addition, astronomers were able to retrace the object’s path and determine that it left Earth’s orbit in 1971. With this knowledge, astronomers may confidently assert that this was really the third and final stage of Apollo 12’s mission. After a year of persistent tracking by astronomers, the orbit was once again propelled into an orbit around the Sun. Astronomers’ calculations indicate that it will return to Earth in the mid-1940s. This item will continue to race through space for many more years, but the laws of physics will always ensure that it eventually comes home.
