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  Compass use during Apollo surface ops

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Author Topic:   Compass use during Apollo surface ops
Max Q
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Posts: 399
From: Whyalla South Australia
Registered: Mar 2007

posted 08-24-2007 10:24 PM     Click Here to See the Profile for Max Q   Click Here to Email Max Q     Edit/Delete Message   Reply w/Quote
I am reading "A Man on the Moon" and the section about Apollo 15 where Dave Scott removed the top hatch of Falcon and stood on the ascent stage cover and had a look around. Now the book mentions several features and their directions given as compass like from the lunar module:
Immediately, he spotted familiar features. To the northeast, a slender crescent of sunlight delineated the ridge crest of Mount Hadley, almost 3 miles high, the bulk of the great mountain still cloaked in shadow. Due east, beneath the sun's obliterating glare stood the hills he and Irwin had christened Swann Ridge.
M understanding is that compasses don't function properly on the moon given that the moon has a very weak and patchy magnetic field. Were these directions given as artistic license by the author, or was a direction designated north on Falcon for ease of explanation?

Jay Chladek
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Posts: 2272
From: Bellevue, NE, USA
Registered: Aug 2007

posted 08-24-2007 11:56 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
I would say that given the photos of the region prior to the flight and the orientation of Falcon after touchdown that Dave would have had a very good idea what direction "North" was on the moon since they were in a spot between a canyon area and a set of mountains.

A compass might not work, but the lunar module used other navigation equipment which didn't need it. And the astronauts needed to have a good idea of where they were so that they wouldn't go off in the wrong direction on the first day of EVA activities.

Obviousman
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Posts: 438
From: NSW, Australia
Registered: May 2005

posted 08-25-2007 05:58 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
A compass wouldn't work. The directions quoted were based on known directions upon landing. They always faced east on approach, with the sun behind them, so the LM shadow would help with movement and depth perception.

Max Q
Member

Posts: 399
From: Whyalla South Australia
Registered: Mar 2007

posted 08-25-2007 06:24 AM     Click Here to See the Profile for Max Q   Click Here to Email Max Q     Edit/Delete Message   Reply w/Quote
But east would still be a relative Earth term I guess.

Blackarrow
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Posts: 3393
From: Belfast, United Kingdom
Registered: Feb 2002

posted 08-25-2007 01:23 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
Actually, they always faced west on the landing approach.

Michael Davis
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Posts: 545
From: Houston, Texas
Registered: Aug 2002

posted 08-25-2007 04:37 PM     Click Here to See the Profile for Michael Davis   Click Here to Email Michael Davis     Edit/Delete Message   Reply w/Quote
In the lunar rover, I recall that there was a compass of sorts. It was not magnetic of course, but rather used the know sun angle to give an indication of direction.

I don't believe that this system was used for the initial EVA to survey the landscape. Since the LM always faced west shortly after lunar sunrise, and the crews had trained for months on the details of the landing site, and they typically landed within a few hundred meters of their intended target, determining directions would have been easy.

Obviousman
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Posts: 438
From: NSW, Australia
Registered: May 2005

posted 08-27-2007 04:29 AM     Click Here to See the Profile for Obviousman   Click Here to Email Obviousman     Edit/Delete Message   Reply w/Quote
Ooops - that why I should check my facts. I thought that north was to the left of the lunar module ladder.

Yes, the terms east, west, etc., are or earthly origin. In navigation terms, east is defined as the direction in which the Earth rotates.

We tidy it up for geographic north, etc.

BMckay
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Posts: 3719
From: MA, USA
Registered: Sep 2002

posted 01-11-2022 01:07 PM     Click Here to See the Profile for BMckay   Click Here to Email BMckay     Edit/Delete Message   Reply w/Quote
On Apollo 17, did they not use a sun compass?

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