NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Paul Dolkas
Date: 2013 Sep 3, 20:58 -0700
Greg-
They don’t. On the moon, there is no atmosphere, so the correction for bending light as you take sights close to the horizon doesn’t exist. Same for Mars, pretty much – atmos pressure is about 1% of earth’s on the surface. The rovers don’t use the hoizon to determine vertical – they use an electronic inclinometer, so they are esentially using a high tech version of a bubble sextant. There’s no dip to figure in.
-Paul
p.s. Incidentally, the first use of CN on the moon was a simple solar compass that the Apollo astronauts used on their lunar rover. The rover had a gyrocompass, since the moon lacks a magnetic field, but to conserve battery power, it was only turned on once they unloded the rover on the moon. So the question was: which way is north? The instrument panel was equipped with a sundial like gizmo, and they would relay it’s reading, along with the tilt of the rover to mission control, who would use the info to calculate the bearing to north. Somebody in NavList probably has the smarts to resurect the algorithm they used to do this – it’s way above my head.
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Greg Rudzinski
Sent: Tuesday, September 03, 2013 5:26 AM
To: paul@dolkas.net
Subject: [NavList] Re: The Future of Celestial Navigation: A British Viewpoint
Paul,
How do rover vehicles keep track of altitude on a planet or moon which doesn't have an atmosphere or ocean ?
Greg Rudzinski
From: Paul Dolkas
Date: 2013 Sep 2, 22:13 -0700
And while we are on the subject, let’s not forget that only one planet has GPS, and there is a whole lot of exploration that is, and will be going on in places not quite so well equipped.
A few examples: the two Mars rovers currently use their cameras to take “sextant” shots to periodically update what is essentially a dead reckoning (gyrocompass + odometer) navigation system. If/when manned trips to the Moon & Mars take place, surface vehicles will need a celestial navigation system (automated or not) for the same reason. Unless somebody invents an inexpensive GPS constellation system, replicating our current capability on a distant planet will not be in the cards, Remember – the only reason we now have a GPS system was that the U.S. military needed one, and was quite willing to spend the tens of billions it took to put one in place.
A personal note – space exploration was what got me interested in CN in the first place. One of my master’s degree classes in optical sciences involved designing our own optical system, and I chose to design a “Mars Sextant”, not really knowing much about such devices at the time. I had no idea what a bubble sextant is, and ended up re-inventing the wheel with a sextant that was equipped with a pendulum-based artificial horizon.
Paul Dolkas
----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------
