Celestial Navigation On USS Patriot
by U.S. Navy Lt. j.g. Alexander Fairbanks
August 23, 2020

Sailors aboard mine countermeasures ship USS Patriot (MCM 7) used celestial bodies to navigate an 1,100 mile voyage back home off the coast of western Japan on July 24, 2020.

The ancient art of celestial navigation met the power and speed of modern naval technology as sailors took measurements with a century’s old tool and inputted those measurements into a complex computer program to accurately pinpoint their position on the planet.

"This is a core competency as a professional mariner and as a warfighter," said Lt. Cmdr. Jonathan Volkle, Patriot’s commanding officer. "Celestial navigation does not receive a lot of attention, it is briefly taught in school to junior quartermasters and navigators but is rarely practiced at sea.”

This voyage allowed the crew to put the concepts of celestial navigation into practice and improve their mariner skills as they utilized various technology to find their latitude and longitude.

The sextant, a tool dating back to the 18th century, has not changed much to what sailors use today.

Patriot sailors used their sextant to take measurements of the angular distance between the horizon and the sun, moon, planets, and stars, in order to calculate latitude and longitude. A critical measurement in celestial navigation is taking latitude at noon.

“When the sun is at its highest point of the day, you can do quick math and figure out your latitude, this is called latitude at noon or local apparent noon,” said Chief Quartermaster Scott Lopez, from Mine Countermeasures Squadron Seven, who embarked in Patriot for the voyage. “Another way to utilize the sun is through the use of sun lines. This is done by taking three measurements of the sun every hour to find your position. However, with sun lines you can only accurately figure out where you are every three hours. Other sextant measurements are taken before the sun rises and just after the sun sets. You can take multiple measurements on stars and planets and then input that data to calculate your position with very little time delay.”

These measurements taken with the sextant are manually typed into a computer containing a program called System to Estimate Latitude and Longitude Astronomically (STELLA).

STELLA contains astrological data including the Nautical Almanac. The Nautical Almanac, a publication also originally starting in the 18th century, details the calculated positions of the sun, moon, and planets in our solar system such as Venus and Mars; and of 57 particular stars such as Acamar and Zuben’ubi relative to the first point of the constellation Aries, every whole hour. A mariner can reference this publication to find their position. In the past when a measurement was taken with the sextant, the mariner would have to apply long-form math problems in reference to the Nautical Almanac to find their position. With STELLA, those math problems are calculated instantly. Navigators aboard U.S. Naval ships are required to learn this system in conjunction with a brief lesson in celestial navigation.

“In navigation school they just give us the problems, the sextant measurements, and we input the data into STELLA to solve for our location,” said Lt. Ben Pederson, Patriot’s navigator. “In real life, the problems are not set-up, making the process more challenging as the solutions are not always perfect.”

Another system for navigation that has improved is the accurate keeping of time. In the past it was very difficult to keep an accurate account of time due to clocks constantly developing errors at sea. It was not until the invention of a very accurate chronometer (clock), yet another device from the 18th century, by John Harrison, that precise keeping of time at sea was possible. This tracking of time is needed to accurately calculate longitude. Today, sailors utilize extremely accurate digital clocks to keep track of time.

The final piece in the navigational puzzle is a compass. Rather than relying fully on a magnetic compass, which direction indicator error needs to be corrected for, modern naval ships utilize a gyrocompass, which is more accurate and easier to use. This helps determine direction, as opposed to position.

The combination of repeatedly inputting sextant measurements, the course and speed of the ship, and time into STELLA, provides an accurate fix of the ship’s position. This fix is then plotted onto a chart, but in the modern Navy a digital chart is utilized instead of a paper chart. This allows sailors to see where they are, while the compass allows them to know where they are going.

The crew of the Patriot was successful on their voyage, but it did come with challenges.

“Sometimes there would be an overcast and we could not get sun lines or on a cloudy night we were unable to get the star fixes we needed,” said Quartermaster 2nd class Justin Ladrillono. “The weather was a big challenge, so we had to rely on other means such as dead reckoning while we waited for the weather to improve.”

Dead reckoning utilizes the ship’s last known position, course, and speed to make an estimated calculation about the ship’s current location. It does not account for the effects of wind and current on your position, potentially making the calculation of your position less accurate.

While the navigation team on the bridge were using only celestial navigation, Combat Information Center (CIC) watch standers provided back-up. CIC kept track of the ship’s location by the standard means of Global Positioning System (GPS) in addition to other radars and systems. If they felt the navigation team was maneuvering the ship into danger they could provide the navigation team with informed and accurate guidance.

“In the beginning I was concerned if we would be able to navigate effectively,” said Ladrillono. “But knowing CIC was there for back-up allowed me and the rest of the team to focus and succeed.”

The navigation team on the bridge consisted of quartermasters, junior officers, and the navigator. They collectively took sextant measurements, fixes, inputted and plotted data. As the voyage progressed the bridge team became more confident in the methods of celestial navigation.

“I was apprehensive before we began, because it was something new,” said Pederson. “I have never solely relied on celestial navigation, but as we progressed I was assured by the professionalism of the team. It really proved that celestial navigation can be accurate.”

As the navigation team honed their celestial navigation skills they became better mariners and more effective warfighters. Celestial navigation is important with respect to warfighting because GPS systems are not guaranteed.

“There is a lot of discussion about operating in contested environments,” said Volkle. “Some of our adversaries have the capability to disrupt our GPS, so we need to be ready if that kind of scenario comes to befall us.”

If an adversary destroyed a GPS satellite or utilized electronic warfare to disrupt the satellite or the ability for the ship to communicate with the satellite, the ship would be unable to navigate by GPS entirely. There is also the unlikely possibility of a degradation or malfunction into the ship’s GPS. In either scenario, navigation teams trained in celestial navigation would still arrive where needed to accomplish the mission.

Although the ability to celestially navigate is important, it can be demanding on a portion of the crew. It requires numerous watch standers to repeatedly obtain celestial measurements or fixes and facilitate all the transfer of data and plotting. Despite the challenges, the navigation team on Patriot was able to successfully travel down the majority of the western coast of Japan using celestial navigation. Once in the piloting waters towards Sasebo the team switched to more standard means of navigation due to the congested waterway and weather conditions.

“In today’s Navy modern technology has made it easier when it comes to navigation. With improved GPS and updated navigation systems, watch standers can just look at a screen and know where they are,” said Lopez. “This may not always be the case. It is nice to have a captain who cares enough to push his watch standers out of their comfort zones and make them better sailors.”

U.S. Navy | U.S. Navy Gifts | U.S. Department of Defense

Our Valiant Troops | Veterans | Citizens Like Us