How a Watch Saved the Apollo 13 Mission

Wednesday, 29 November 2017 - 11:18AM
Space
NASA
Astrophysics
Wednesday, 29 November 2017 - 11:18AM
How a Watch Saved the Apollo 13 Mission
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Image credit: NASA

Everyone remembers "the scene." Ever since Apollo 13 hit theaters in 1995, everyone remembers the moment when the team has to fire the engines at precisely the right time to change their course and make sure they enter Earth's atmosphere at the right angle. If they had fired those engines for a second more or less, it could have been a disaster.

So how did they time those burns so perfectly? An Omega Speedmaster watch.

Sixty years after it was first created to withstand the intense vibrations and shocks of race cars, every astronaut since the Apollo 11 mission has gone up equipped with the Speedmaster. The only NASA-certified flight watch and chronograph, it's what made the difference between landing the astronauts in the ocean and sending them hurtling into space. 

The Manual Burn


When the oxygen tank exploded on the service module of the Apollo 13 capsule, they were already 205,000 miles from Earth and 55 hours into their mission to land on the Moon. Apart from losing one of their sources of breathable air, the navigational and targeting computers were all inoperative—the computers relied on fuel cells that needed oxygen to create power, and all the oxygen in the service module's tanks was leaking into space. The astronauts couldn't rely on their computers to calculate their engine burn, so they would have to do it manually. This was where the watches came in.

In order to precisely time the burns, the team had to use the Earth as a reference point and the chronographs on their Speedmasters, which acted as super-accurate timers.



Like in the movie, Jim Lovell had to line up the spacecraft with the Earth's terminator and control the yaw of the ship, while Haise managed its pitch and Swigert used his Speedmaster to time the burn. The burn, which lasted four minutes and 24 seconds, was so accurate that only two small mid-course corrections were needed for the rest of the mission.

According to Lovell, the commander of the Apollo 13 mission, the consequences of mistiming the burn (and hitting the Earth's atmosphere at the wrong angle) would have been catastrophic:

Opening quote
"In order to reenter Earth's atmosphere safely, Apollo 13 had to approach at an inclination no shallower than 5.3 degrees, and no steeper than 7.7 degrees. Come in at 5.2 degrees or below, and the blunt-ended command module would skip off the top of the atmosphere and boing straight back into space, entering a permanent orbit around the sun. Come in at a 7.8 degree or above, and the spacecraft would be able to reenter all right, but at so steep an angle and with such a high g-force that the crew would probably be crushed well before they ever hit the water."
Closing quote


The Silver Snoopy


After the crew finally splashed down in the Pacific Ocean, there were a lot of congrats to go around—to the TRW contractor who created the terminator guide solution, to the NASA staff members who created the C02-filtering "mailbox" contraption, and to Flight Director Gene Kranz, who made the decision to loop around the Moon rather than go for a direct abort. There's a special award NASA gives to people who make a huge difference in a mission, called the Silver Snoopy, and one went to the makers of the Speedmaster, Omega. Now, 47 years later, the Speedmaster is celebrating its 60th anniversary with a limited edition version that hearkens back to the original design.   

For an expanded view, please click on the infographic.

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