Since 1966, NASA has been landing the unmanned Surveyor probes onto the surface of the moon to collect data. In December 1968, NASA managed to get a manned spacecraft into lunar orbit with the Apollo 8 mission. The next goal to accomplish was to combine these feats in order to land a crewed spaceship onto the moon’s surface.
The Lunar Module seen from the Command Module. Credit: NASA
The first step was to find a suitable landing site. The Lunar Module would need to have a flat surface with no craters nearby. Additionally, the area would need to be well-lit enough at the time of landing. The approach would have to be clear so that the landing radar could work at its best. Finally, it would need to be at a location where landing and liftoff would use as little fuel as possible to make the return journey to orbit possible. Using images taken from the Lunar Orbiter satellites, the Apollo 8, and the Apollo 10 missions NASA narrowed down the number of possible landing sites to 5. After further investigation, the final landing site was chosen: The Sea of Tranquility.
Once Apollo 11 was in orbit around the moon, the Lunar Module detached from the Command Module and fired its engine to begin deorbiting. As it slowed its horizontal and vertical velocity, the Lunar Module used small thrusters to adjust its trajectory until it was hovering above the landing site. Then it slowly descended until it finally landed softly onto the lunar soil.
After the Apollo 11 mission, five other lunar landings occurred each more successful than the last. These missions helped build the foundation for NASA’s accomplishments over the past 50 years. Without the scientific and engineering breakthroughs of the Apollo program, our understanding of the universe would be vastly less.
During the 1960s, NASA had the daunting task of landing a person on the moon. When John F. Kennedy announced the goal to put a man on the moon by the end of the decade, they had only recently sent Alan Shepard into space for the first time. It would be another nine months before John Glenn would become the first American to orbit the Earth. NASA would need to perfect every step in just 8 short years. The first step is to reach the altitude of the moon. In order to get there efficiently, we must perform a maneuver known as a “Hohmann Transfer.” Designed to minimize fuel consumption, it allows us to build lighter, cheaper spacecrafts.
But once the spacecraft is headed to the moon, it will be going too fast to be fully captured by the moon’s gravity. At this speed, it will slingshot around it and head back to Earth. To insert itself into lunar orbit, the spaceship needs to slow down. The only way it can do this is by burning its rocket in the direction it’s flying. Once it’s burned for long enough, the speed of the rocket is low enough to establish a lunar orbit.
Both the US and the USSR had been trying to refine this technique since the late 1950s, with little success. Both nations had succeeded in getting impactors and landers onto the moon, but it wasn’t until November 1966 when NASA successfully put an unmanned craft into orbit. In December 1968, Apollo 8 would become the first manned spaceship to orbit the Earth.
Getting to lunar orbit was tricky, but once NASA engineers could consistently make the calculations correctly, they advanced to the next challenge – getting a manned lander onto the surface of the moon.
Getting to space is not a difficult task, but staying in space is an entirely different challenge. At the altitude of the International Space Station — 250 miles — a spacecraft must have a horizontal velocity of about 5 miles per second. That’s roughly 17,000 mph. As the mass of the object or vehicle being delivered to space increases, the necessary power of the rocket also increases.
Image Credit: NASA/STS-132 Crew
In October 1957, the USSR launched and successfully orbited the artificial satellite Sputnik 1. A month later, a second Sputnik satellite was launched. These events triggered the Space Race between the Russians and the United States to become the first country to put a human into space.
The rockets required to achieve this feat would be huge marvels of engineering. Instead of going straight up, they would require building horizontal speed almost immediately after launch. This is done by a “gravity turn” maneuver while the ascending rocket is still in the atmosphere. Traveling more at a diagonal angle, the rocket would continue to climb towards space while also beginning to get to the necessary speeds for orbit. Once in space, it would continue to build speed until it was going so fast that every time it fell back towards the Earth, it would miss.
The USSR won this race in April 1961, when Yuri Gagarin became not only the first human to orbit the Earth, but also the first to reach outer space. Less than a month later, the US launched Alan Shepard on a sub-orbital flight, but the US didn’t achieve orbit until February 1962 when John Glenn piloted the Friendship 7 for three full orbits around the Earth.
But this was only the beginning. Even before the United States had made it to orbit, President John F. Kennedy addressed Congress on May 25, 1961, declaring NASA’s next mission: getting humankind to the moon.
We can’t take our eyes off it, it helps control our tides, and wolves howl at it; can you name what “it” is? You probably guessed correctly, it’s Luna, also known as the moon! The moon is the largest satellite of Earth, and one of the only natural satellites. This means that there may be other satellites out there orbiting around Earth (thanks to space junk and our cell phone providers), but it is by far the largest and amongst the only that came from space to orbit our home planet. Our moon is also the brightest object in our night sky, so bright in fact that you can sometimes see it during the day. However, the moon seems to be constantly changing. How can that be possible?
To demonstrate what is happening, you can do an easy experiment at home. All you need is a single light source (representing the sun), your face (representing Earth), and a ball or your fist (modeling the moon).
Earth’s gravity has the moon tidally locked, meaning the same half of the moon is always facing Earth, and the other half is always facing away (the dark side of the moon). Since it is tidally locked, your model of the moon does not need to spin. All you have to do now is put your moon between your face and model of the sun and start to rotate counterclockwise (the same direction that Earth spins).
When the moon is between the sun and the Earth, light from the sun cannot reflect from the moon to Earth. This phase is called a “New Moon”. As you keep rotating you will first see a waxing crescent, then: the first quarter, waxing gibbous, full moon (Earth is between the moon and the sun), waning gibbous, third quarter, waning crescent, then back to New Moon. If you keep rotating the cycle will continue on and on. For our real moon this cycle will take about 29 days to be completed.
You can easily keep track of this cycle on your own as well. All you need to do is step outside each night and make some observations. Take note of what the day and time is, and what the moon looks like to you. Once you have done this for a couple of weeks you should be able to predict what you will see next! So go ahead, give it a try for yourself and have fun.
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