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Compasses don't work on Mars, so how do you navigate?

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Re: Compasses don't work on Mars, so how do you navigate?

#41

Post by mikeash »

gliese1337 wrote: post #32
ars wrote: post #30

Earlier quoted context omitted.

On the equator the sun could be directly overhead - so you have no idea what any directions are, the sun is equally far from all horizons. (Remember the sun does not move on mercury.) If you are on the equator, but not directly under the sun then you can figure things out. I guess I should have said equator on the central meridian. Edit: I was under the mistaken assumption that Mercury is tidally locked. So it would…

The sun does move on Mercury. Mercury is not tidally locked- it has a 3:2 spin-orbit resonance. I.e., it rotates 3 times for every two times it goes around the sun. This means that the two sides of the planet alternate facing the sun at perihelion.

Interesting tidbit about Mercury's rotation: although it's clearly visible to the naked eye and thus has been known since before the dawn of recorded history, and has been observed through telescopes since telescopes were invented, the fact that it is not tidally locked has only been known since 1965.

Re: Compasses don't work on Mars, so how do you navigate?

#42

Post by jeza »

ars wrote: post #9
GregBuchholz wrote: post #8

Celestial navigation plus accurate clocks. I'd think this would be especially good on a planet without clouds (as long as your planet rotates fast enough, so I guess Mercury is out). Anyone know if Mars has any polar stars? https://en.wikipedia.org/wiki/Celestial_navigation

The planet doesn't have to rotate to use celestial navigation. As long as you can see the stars you are fine. So the dark side of mercury would work fine. On the hot side as long as you are not exactly on the equator the sun acts as a fixed direction and you can use that. > Anyone know if Mars has any polar stars? The orbital tilt of Mars is 1.85 degrees (vs 0 for earth) and the Axial tilt is 25.19 vs 23.44 for Earth…

> So Polaris would be pretty close to being a polar star for Mars as well.

Poris is only useful if you're in the northern hemisphere. In the southern hemisphere on earth we use the southern cross. It's a bit trickier if you're using a quadrant because you have to align it with a blank area of sky. Though the 17th century explorers managed it.

Re: Compasses don't work on Mars, so how do you navigate?

#43

Post by cc438 »

stephentmcm wrote: post #23
hybridwebtech wrote: post #7

Already done? More than 40 years ago, but probably still workable: https://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Control_a...

Did you read the article? That's exactly what the author was pointing out. Also this article and wiki have ruined The Martian for me.

Gyroscopes accumulate error with time, they make sense for an application with a short range but they're useless over long periods of time without a reference standard to crosscheck and recalibrate. That's one part of The Martian the author got entirely correct despite the criticism. The mechanical odometer in your car is only accurate to +/-3% of reading and the best mechanical calibration standards are only 0.25% of reading, that puts the trip described in The Martian off by ~90km.

Re: Compasses don't work on Mars, so how do you navigate?

#44

Post by escherplex »

yellowapple wrote: post #36
DanBC wrote: post #20

Earlier quoted context omitted.

I wonder if "giant head" enhanced depth perception works across planets? https://xkcd.com/941/

Just a nitpick, but how could one see the tops of clouds when the two cameras are only negligibly above ground level?

In the flat FL interior during hot summer days with no wind it's common to observe distinct long wide columns of clouds form anvil tops over the space of a few hours in the early afternoon. Sometimes, if you're lucky, a cauldron shape will form which puts on an impressive light show at night. Rather than risking a light Cessna it might be interesting to view formation in exaggerated 3D from the ground.

Re: Compasses don't work on Mars, so how do you navigate?

#45

Post by stephentmcm »

cc438 wrote: post #43
stephentmcm wrote: post #23

Earlier quoted context omitted.

Did you read the article? That's exactly what the author was pointing out. Also this article and wiki have ruined The Martian for me.

Gyroscopes accumulate error with time, they make sense for an application with a short range but they're useless over long periods of time without a reference standard to crosscheck and recalibrate. That's one part of The Martian the author got entirely correct despite the criticism. The mechanical odometer in your car is only accurate to +/-3% of reading and the best mechanical calibration standards are only 0.25% o…

Thanks, I was being mildly sarcastic in my post but having the math laid out is great.

Re: Compasses don't work on Mars, so how do you navigate?

#46

Post by Caer »

CapitalistCartr wrote: post #39
escherplex wrote: post #29

Earlier quoted context omitted.

Fun link. I was planning on similar setup using a couple of remote linked Celestron C8s separated by 5 miles to observe thunderhead cloud formation in SW Florida. Average natural IPD is around 64mm so it should be interesting to see what the occipital lobe does when this is expanded to over 8km. (IPD = InterPupillary Distance; eyeball separation)

IPD?

Interpupillary distance, the distance between the centre of the pupil in one eye to the other.

Re: Compasses don't work on Mars, so how do you navigate?

#47

Post by contingencies »

jwhale wrote: post #13
GregBuchholz wrote: post #8

Celestial navigation plus accurate clocks. I'd think this would be especially good on a planet without clouds (as long as your planet rotates fast enough, so I guess Mercury is out). Anyone know if Mars has any polar stars? https://en.wikipedia.org/wiki/Celestial_navigation

An easier method than creating a star map is to use the brightest star in the sky (the sun) and an accelerometer. This is the method Opportunity uses to calibrate the gyroscopes/wheel encoders. [source pg 4] https://www-robotics.jpl.nasa.gov/publications/Reg_Willson/M... "The attitude of the rover is based on measurements from two vector instruments: (1) accelerometers that determine the vector towards the center of…

Star maps can be downloaded free.

Because you generally only need the brightest subset of stars in any area, you don't even need a comprehensive one.

A star map for Mars would functionally be pretty much equivalent to an earth one, I guess, given the distances involved.

Re: Compasses don't work on Mars, so how do you navigate?

#48

Post by contingencies »

aaron695 wrote: post #16

KRET develops stellar navigation system for Russian strategic bombers http://www.janes.com/article/52661/kret-develops-stellar-nav...

I am seeing a cartoon forming in my head with a Russian strategic bomber pilot, crashed in a kid's bedroom and looking up at a roof covered in those glow in the dark stars and a big red flashing light warning about course deviation.

Re: Compasses don't work on Mars, so how do you navigate?

#49

Post by comrh »

grecy wrote: post #31
FreeFull wrote: post #3

Earlier quoted context omitted.

We haven't put GPS satellites around Mars quite yet. I'm guessing that won't happen until it gets terraformed.

That being said, how many satellites are orbiting Mars right now that could be used to help determine position?

~7

https://en.wikipedia.org/wiki/Category:Artificial_satellites...

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