Instead of a compass, astronauts relied on a gyro-stabilized “stable table” to keep track of direction. Going to the Moon is the same thing, but in three dimensions … and also thousands of times faster! So the instruments are a little more sophisticated. Knowing that dead reckoning doesn’t account for variables like currents or steering errors, sailors would check their position by a sextant, using the Sun, Moon, planets or stars. Sailors would do this check as often as every hour.
Knowing your speed, 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. You can calculate your position at any point on your journey via a previously determined fixed position. When you’re sailing by dead reckoning, you use a compass, a knotmeter, and a clock to break the question of navigation into time, rate, and distance.
Let’s start with dead reckoning on a boat, because that’s the easiest comparison to understand. For those of you who, like me, need to read things to really grasp it, here’s a more detailed look at what’s in that video.
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