If you are interested in space travel, like me, you might have noticed that during the Apollo missions, the lunar orbit was measured in nautical miles instead of kilometers or miles. If you didn’t notice, your a better person than I and probably have more exciting hobbies.
The nautical mile is the standard unit of measurement for global navigation distance in most countries(excluding China and Russia). The knot is also the accepted standard of the International Civil Aviation Organization(ICAO) for distance, and knots are used for military pilots. Hence, NASA astronauts are less likely to make mistakes using Knots as opposed to Kilometers or Miles.
As a submariner(in the distant past), talking about knots and nautical miles was second nature and converted that speed to MPH when talking to non-navy friends. In this article, I’ll let you know what I discovered about space travel and knots.
Does NASA Use Knots for Everything?
NASA, and space travel, is a complicated business. One of these many complications is how NASA used a mixture of the metric system and the British/Imperial units for space missions.
The Apollo guidance computer performed all its calculations in metric, and then the output was converted to Standard(feet per second, pounds) for the convenience of the astronauts. To add to this, they used nautical miles to describe the lunar orbit for apollo missions.
NASA started to use metric units for many of its missions earlier than the rest of the US aerospace industry to simplify international collaboration. Contractors did not change over. One consequence of this was the loss of the Mars Climate Orbiter due to the contractor writing the landing software in standard British units instead of metric, which the contract specified.
The original reason for using nautical miles for navigation is that it makes reading charts and navigating faster. If you are going from one point on a map to another, using longitude and latitude, you can quickly figure out how long it will take to get there(traveling 20 knots for 72 hours as an example). Astronauts, who were mostly military pilots, did these calculations with very little extra thought, making the job less complicated.
How Long is a Nautical Mile?
A nautical mile is 1.852 Kilometers, which is exactly one minute of latitude on earth. A Knot, which is how boats and aircraft measure speed, equals one nautical mile per hour.
| Measurement | Feet Per Hour |
|---|---|
| 1 KNOT | 6076 |
| 1 MPH | 5280 |
How Many Nautical Miles is it to the Moon?
The moons sphere of influence, which is where something will go into orbit around the moon, is within 33,000 nautical miles (or 37,950 standard miles)
| Miles | Kilometers | Nautical Miles | |
|---|---|---|---|
| Apogee | 252,088 | 405,696 | 289,901 |
| Perigree | 225,623 | 363,104 | 259,466 |