How Apollo Astronauts Didn’t Get Lost Going to the Moon

when we drive over to visit a friend we usually have directions with us like it's the third door on the left unfortunately when you're going to the moon you don't have signposts telling you where you are or where you're going so how exactly did Apollo astronauts know where they were in space going to the moon this one is pretty complicated so let's start off with an analogy cutting flying to the moon isn't like cutting you can't just aim at the hole and putt flying to the moon is more like putting across a magical green with hills and valleys that move aiming at a hole that is also moving if you watch the magical green long enough you might be able to see a pattern and put in a way that anticipates all the movements and syncs the ball in which case your brain is doing an incredible amount of calculations to get to that point on Apollo it was a spacecraft's computer brain that did those calculations but constantly and in real time to get astronauts to the moon but let's back up and start this story at the beginning before Apollo 11 even launched in the early 1960s with the inaugural mercury program NASA relied on ground control during the unmanned amande phases of the program the worldwide tracking and telemetry network was thus born when it came to Apollo however there was some fear that the Soviets would Jam any radio signals being sent to a crew on the way to the moon and so NASA decided that onboard navigation was vital this couldn't be tampered with the onboard navigation system required nothing beyond the computers own systems so it could not be tampered with it was the ultimate Cold War failsafe but how did it work solving the navigation problem fell to the instrumentation lab at MIT now known as Draper for its founder dr. Charles stark Draper it was the men and women at this contractor site who figured out the question of deep-space guidance and navigation how Apollo the golf-ball would navigate through the moving hills and valleys of space to reach its target the moving hole that is the moon the basic navigation on board Apollo wasn't much different than dead reckoning on a boat when you're sailing by dead reckoning you use a compass a naught meter and a clock to break the question of navigation into time rate and distance basically you calculate your position at any point on your journey via a previously determined fixed position knowing your speed and how long you've been sailing and in which direction since you last checked your position you can determine where you are by how much your position has changed relative to that fixed spot sailors did this using a log and an hourglass knowing that dead reckoning doesn't account for current steering errors etc they would check it by using a sextant to find their position on the earth by observing the Sun Moon planets or stars that part was once or twice daily if possible except of course when weather obscured the skies sailing the Stars is effectively the same thing only in three dimensions instead of two and thousands of times faster so the instruments are a little more sophisticated instead of a compass a gyro-stabilized stable table kept track of direction instead of an op meter accelerometers on that table tracked every little change in speed the electronic clock ticked a million times a second instead of water currents gravity produced unfelt changes of course so the computer ran the mathematical model of gravity as defined by Isaac Newton embedded in the Apollo command module opposite the hatch were two telescopes the first was a single magnification spotting scope to give the astronaut a wide field of view from that wide field he'd pick a landmark or sometimes a star then he'd move over to the second instrument that was a space sextant a disconsolate apparatus designed to measure angles the sextant had two lines of sight one fixed and one movable the fixed was able to focus on a landmark on earth such as the San Francisco Bay giving it the name landmark line of sight or ll OS this was controlled by adjusting the attitude of the whole spacecraft to Center the landmark on the ll OS when such a landmark wasn't available the spacecraft could put the ll OS on a point of the sunlit horizon on earth or moon just like a sailor doesn't see in space the correct point on that horizon is just one on a line between the star and the center of the earth or moon the movable site called the star line-of-sight or SL OS could be moved as far as 67 degrees from the fixed line of sight what the astronaut did was focus on the star then fiddled with the mirror inside the sextant to bring the image of That star into conjunction with the landmark or horizon in his fixed line of sight when satisfied he punched the mark button at the computer to read the angle between the star and the horizon and note the exact time doing this again with the second star and sometimes a third gave the computer enough data to run it through the navigation program and determine where the spacecraft was now this might seem counterintuitive when you consider that everything in space including the spacecraft is moving but of course engineers figured out a way around that the Apollo spacecraft had an inertial platform on board sometimes called the staple table and this kept a constant eye on how the spacecraft was oriented around the fixed axes of inertial space this sophisticated gyroscope based system allowed the crew to set its orientation with the RCS thrusters and once that orientation was set the spacecraft didn't rotate the other thing engineers and astronauts used to their advantage was that for all intents and purposes the stars are fixed during an Apollo mission there unmoving long enough to take a guidance measurement we also have to remember that even though Apollo 11 was the first mission to land on the moon the crew wasn't going up blind Apollo's 8 and 10 had preceded them but more importantly the engineers and scientists who built the onboard navigation system brought centuries of studying the sky to bear on the problem the computer knew the positions of stars and bodies that would be used for sightings namely the earth and the moon which made real-time navigation calculations a relative cinch so how did all this fit into an Apollo mission navigation is the middle letter in the acronym GNC guidance navigation and control guidance means deciding what changes in velocity are required to make the spacecraft go or you need it to go navigation is what we just discussed determining where the spacecraft is control refers to operating the engine hardware to get the spacecraft where it needs to go on Apollo 11 like all Apollo missions the crew first launched into Earth orbit relying entirely on the Saturn boosters separate computer and inertial guidance to get them there then it came time for the tli burn that would change their trajectory from an earth orbital 1 to 1 that would intersect the moon in three days time it aimed where the moon would be in its orbit when the crew got there but no burn was ever perfect and a tiny error in that burn could translate to a significant deviation a hundred thousand miles down the track so the spacecraft computer combined readings from the inertial measurement unit with mathematical models of gravity to maintain its knowledge of the spacecraft's position and velocity by the time of the Apollo 11 mission the computer software was so reliable the crew only needed to take occasional readings with a sextant to account for drift or as a backup measurement in either case that information allowed the computer to determine whether or not the trajectory had to be adjusted this is guidance guiding the spacecraft to a correction and control controlling the actual course adjustment burn so really the acronym should be NGC but GNC just rolls off the tongue so well thanks to Draper's hack the moon initiative for making this video possible to find out more about Draper's role in getting apollo astronauts to the moon check out we hack the moon comm the site chronicles the engineers and technologies behind the Apollo missions and is full of thousands of never-before-seen images videos and stories about the people who hacked the moon be sure to visit we hack the moon comm and for more vintage space everyday be sure to follow me all across social media if this is your first time seeing vintage space welcome and please do subscribe so you never miss an episode thank you guys so much for watching and I'll see you next time

Channel: The Vintage Space

Views: 219,759

Keywords: Apollo 11, Apollo, History, Space, NASA

Id: X-O3Uu4DuLw

Length: 8min 31sec (511 seconds)

Published: Thu Jun 13 2019