Landing on the Moon.
You are into the 104th hour of your mission. You have traveled the 240,000 miles of space between the Earth and the Moon, and you are now in orbit around the moon.
You are in an lopsided elliptical orbit around the moon. The high altitude of this orbit is 60 miles. The low altitude of this orbit is about 9 miles, a mere 50,000 feet! At the low point of this orbit, you look out the CM window. What you see are mountains that surround your landing site. As you watch, the landing site goes whizzing by at 3,730 miles per hour. You are so close to the surface you instinctively close your eyes and lift your feet!
You see a small valley surrounded by mountains. The mountains rise above the lunar surface by 20,000 feet. Inside the valley are craters and many other odd features. These odd features interested the scientists back home enough to decide to land your Lunar Module (LM) here. You realize that in the next four hours you will either land in this valley, crash in this valley, or be forced to abort your landing.
You say "see you later" to the Command Module Pilot (CMP), because he stays behind in lunar orbit. You enter the LM spacecraft, with the Lunar Module Pilot (LMP), through a tunnel that connects the two vehicles. You close the hatch tightly behind you.
You assume the control station at the left side of the vehicle. As the commander of this mission you will be in control of the LM all the way down to the surface. Your primary job is to choose a landing area smooth enough to safely land the LM. The last 2 minutes of the landing require the LM will be in a manual control mode. You will be in complete control of where the vehicle finally sets down on the lunar surface.
Your LMP assumes the right control station in the LM. His primary job is to watch the instruments and verbally inform you of the altitude and velocity of the vehicle as you approach the landing site. He is also responsible for updating the rendezvous radar and other instruments in case you must abort the landing.
Both of you don your helmets and pressurize your space suits to 3.7 pounds per square inch at 100% pure oxygen. You check each other for leaks in your suites.
You both connect cable restraints to hasps around your spacesuit waist. The cabin of the LM has no seats. You will control the spacecraft standing on your feet. The cable restraints are like seat belts in your car. Normal movement is allowed, but if there is a sudden jolt the cable restraints will lock and hold you in place. You each have one window to look through. Because you are standing, your face is very close to the glass. This position gives you an excellent view of where your craft is going.
You operate the controls to disconnect the LM from the Command Module, and the LM is free to fly on its own. You use the LM thrusters to precisely back away from the CM by 50 feet and stop. You push a button to release and lock the four landing legs of the LM. These legs have been in a folded position during transport from Earth. The CM pilot looks out his window and confirms, by radio, the landing legs are in the correct position and locked in place. You and your LMP are ready to land!
At this time, both vehicles are at the high point in your lopsided orbit which is 60 miles. Both vehicles are now plunging down to the low point of the orbit, which is only 50,000 feet above the surface of the moon.
12 minutes before you reach the low point in your orbit the navigation computer will start the LM decent rocket engine. The rocket thrust will be in the opposite direction of your travel, so you will begin to slow down and eventually impact the lunar surface. Two minutes short of impact, you will take manual control of the LM and gently set it down in the center of the valley. You will throttle the decent rocket engine and hover the LM until you find a suitable landing site. That’s your plan anyway.
The CM will continue to orbit the moon as before. Eventually the CM will establish a more circular orbit of 60 miles by 60 miles, and wait for your return rendezvous in three days.
In a perfect landing you will set down 12 minutes after the decent engine starts. The decent stage of your vehicle holds 14 minutes of fuel for landing. This means you only have 2 minutes of extra fuel to hover and find a smooth landing surface. You think to yourself, no problem. That’s plenty of time right?
You and your LMP are in a horizontal position in the LM. You are essentially flat on your back looking out your window into the blackness of space. You cannot see the moons’ surface. You have this attitude because the decent rocket engine is below your feet and must provide deceleration thrust opposite of your direction of travel.
12 minutes before you reach the low point of your orbit, the navigation computer starts the decent engine. The engine comes up to 10% thrust for 30 seconds and the engine nozzle gimbals around to find the exact center of gravity of the LM. The engine then increase thrust to 92.8%, which is considered full power. Your body feels the deceleration and your restraining cables keep your feet on the floor of the vehicle. For the next 9 minutes not much happens until you notice the peaks of the mountains fill the left side of your window. You realize you are about 20,000 feet above the surface of the moon. You still are in a horizontal position and cannot see where you are going. You can only see the mountains fill the side of your window as you lose velocity and descend downward.
The LM landing radar locks on to the surface and the computer now updates your altitude and velocity accurately. This is a great relief, because if the landing radar does not work you would have to abort the landing.
When the LM is at 7,000 feet, small thrusters on the vehicle fire to pitch the LM upright in a vertical position. You can now see exactly where you are headed and have a clear view of the landing site.
When the LM is at 1,000 feet you code the computer for manual control of the vehicle. A light illuminates on the control console, and your LMP notifies you that 12 minutes have elapsed. You now have 2 minutes of fuel to hover and land. No pressure.
You realize if you stay on this course you will land in a large bolder field. You reduce your downward velocity and increase your horizontal velocity to move to another location. You see a smooth area ahead and commit to land there.
You then increase your downward velocity so you can land quickly, while slowing your forward motion to almost nothing. You are now falling straight down. Your LMP calls out 200 feet and dust fills your window and reduces your visibility. Your LMP calls out your altitude at 100 feet, and you realize you are totally on instruments, because you can see nothing but dust outside.
There are 6 foot metal probes on the bottom of the landing pads of the LM. When any one of them touches the lunar surface they signal the LMP of surface contact. Your LMP calls out "contact" and you push a button to shut down the decent rocket engine.
Your vehicle free falls the last 6 feet to the surface. You feel the shock absorbers on the landing legs cushion the fall in the lower gravity of the moon. Instantly all the lunar dust outside your vehicle falls, and the view out your window is absolutely crystal clear. You have landed on the moon!