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Author
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Topic: Apollo: Use of metric in communications
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yotlu
Member Posts: 37
From: Austria
Registered: Apr 2017
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posted 06-27-2018 06:25 PM
   
Lately I was watching the Apollo 16 landing from PDI to touchdown on YouTube. After touchdown Young takes a guess on where they landed: 104:30:23 Young: Okay. We're forward and to the north of Double Spot. I would guess about 200 meters to the north and maybe 150 meters to the west. (Pause) Since most European countries use the metric system, I was surprised to hear a familiar unit instead of inches, feet and miles.I turned to the Lunar Surface Journal to find other examples (from PDI to touchdown). During descent to the lunar surface, only Shepard refered one time to meters. 108:12:44 Shepard: About 60 meters (south of track); that's where we're going. By browsing the journal I found other examples of the use of metric units while on the lunar surface.I am bad at guessing distances and the size of objects. Doing it in imperial units would hurt my brain. So my question is, why did the Apollo astronauts sometimes used the metric system instead of the more familiar imperial? |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 06-28-2018 11:01 AM
Meters or yards, no real difference when it comes to estimating distances. |
David C
Member Posts: 1039
From: Lausanne
Registered: Apr 2012
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posted 06-28-2018 12:50 PM
Purely from memory, if I recall correctly, use of metric units came from geology training. But yes, for visual assessment there is no difference between yards and meters. |
oly
Member Posts: 971
From: Perth, Western Australia
Registered: Apr 2015
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posted 06-28-2018 10:22 PM
There is an explanation for the use of the metric and imperial systems with the guidance computer here. While it was agreed in 2007 that the moon officially uses the metric system, NASA has also lost a climate orbiter following confusion between the use of the two systems in 1999. I am now curious why the metric system crept into the astronauts vocabulary, as most astronauts of Apollo were pilots familiar with the imperial system used in US aviation, I suspect that the scientific community (geology, photography and astronomy) influences may have rubbed off during training. Additional research required. |
YankeeClipper
Member Posts: 622
From: Dublin, Ireland
Registered: Mar 2011
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posted 06-29-2018 01:05 PM
NASA published a case study on the 1999 loss of the Mars Climate Orbiter (MCO) - System Failure Case Study - Lost in TranslationThe MCO Mishap Phase I Report can be read here. |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 06-30-2018 06:52 AM
The MCO incident is unrelated to this topic. |
YankeeClipper
Member Posts: 622
From: Dublin, Ireland
Registered: Mar 2011
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posted 06-30-2018 11:30 AM
Don Eyles 2004 paper on the LM Guidance Computer (LGC) (referenced by oly) has this passage:With respect to units, the LGC was eclectic. Inside the computer we used metric units, at least in the case of powered-flight navigation and guidance. At the operational level NASA, and especially the astronauts, preferred English units. This meant that before being displayed, altitude and altitude-rate (for example) were calculated from the metric state vector maintained by navigation, and then were converted to feet and ft/sec. It would have felt weird to speak of spacecraft altitude in meters, and both thrust and mass were commonly expressed in pounds. Because part of the point of this paper is to show how things were called in this era of spaceflight, I shall usually express quantities in the units that it would have felt natural to use at the time. oly referred to the MCO incident as an example of the potential risks / consequences of miscalculation associated with conversions between International System (SI) and Imperial (English) Units. I merely added reference links for those interested in further study. |
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