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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?

#61

Post by comboy »

creshal wrote: post #51
gliese1337 wrote: post #34

I am surprised that no one has yet mentioned the Gyrocompass: https://en.wikipedia.org/wiki/Gyrocompass The post mentions manually-set directional gyroscopes, but gyrocompasses are a step ahead of that; on any sufficiently-quickly-rotating planet, a gyrocompass will point you towards the geographic poles by noting the axis of precession of a gyroscope with arbitrary orientation. That's even better than a magnetic com…

How maintenance intensive are they, though? Moving parts in or near vacuum tend to be a bit iffy (e.g. lubrication), especially for multi-year (or multi-decade) robotic missions.

I would assume that once you establish direction you can just put some 3 beacons and have a local navigation system based on that.

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

#62

Post by JoeAltmaier »

yellowapple wrote: post #40
JoeAltmaier wrote: post #18

Earlier quoted context omitted.

It could be set up years ahead of any significant ground presence, at a fairly small cost.

Existing GPS satellites orient themselves by ground stations, so we'd need at least some ground presence. Said presence doesn't have to be manned, though.

Or they could orient by celestial navigation. Or have their position measured remotely and updated from Earth.

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

#63

Post by hamiltonkibbe »

darkmighty wrote: post #59
avian wrote: post #56

Earlier quoted context omitted.

Grandparent is talking about gyrocompasses, not ordinary gryoscopes though. I haven't heard of a laser-ring gyrocompass. Not sure it if that is even possible.

The gyrocompass orientation should, in principle, be obtainable by properly integrating gyroscope readings (and accelerometer? not sure if required).

You still need a way of determining the initial position/pose

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

#64

Post by adekok »

stephengillie wrote: post #27
adekok wrote: post #22

Earlier quoted context omitted.

Mars doesn't have hydrogen because at temperatures where water is liquid, the speed of hydrogen atoms due to temperature is greater than the escape velocity from Mars.

I thought it was just pressure - the more dense molecules push the Hydrogen out of the way as gravity pulls at them.

Pressure is the collective action of the molecules / atoms flying around and smashing into things.

At "normal" temperature on Mars, hydrogen atoms have a thermal velocity [1]. That velocity is greater than the escape velocity from Mars.

A lone hydrogen atom will typically bounce around a lot in the lower atmosphere. It eventually works it's way (via random scattering) to the upper layers of the atmosphere. Once the atom reaches the upper atmosphere... it's gone. It flies away, never to return.

Keep that up for a billion years, and Mars loses most of the hydrogen it started off with.

Oxygen is heaver, so it's thermal velocity is smaller than the escape velocity.

[1] https://en.wikipedia.org/wiki/Thermal_velocity

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

#65

Post by JoeAltmaier »

adekok wrote: post #64
stephengillie wrote: post #27

Earlier quoted context omitted.

I thought it was just pressure - the more dense molecules push the Hydrogen out of the way as gravity pulls at them.

Pressure is the collective action of the molecules / atoms flying around and smashing into things. At "normal" temperature on Mars, hydrogen atoms have a thermal velocity [1]. That velocity is greater than the escape velocity from Mars. A lone hydrogen atom will typically bounce around a lot in the lower atmosphere. It eventually works it's way (via random scattering) to the upper layers of the atmosphere. Once the a…

So the Mars atmosphere is a distillation column for gasses!

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

#66

Post by lmm »

mikeash wrote: post #41
gliese1337 wrote: post #32

Earlier quoted context omitted.

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.

Mercury is pretty featureless, right? It's not like Jupiter where you could see the rotation just by keeping track of the Great Red Spot.

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

#67

Post by lmm »

JoeAltmaier wrote: post #65
adekok wrote: post #64

Earlier quoted context omitted.

Pressure is the collective action of the molecules / atoms flying around and smashing into things. At "normal" temperature on Mars, hydrogen atoms have a thermal velocity [1]. That velocity is greater than the escape velocity from Mars. A lone hydrogen atom will typically bounce around a lot in the lower atmosphere. It eventually works it's way (via random scattering) to the upper layers of the atmosphere. Once the a…

So the Mars atmosphere is a distillation column for gasses!

Every atmosphere is a distillation column for gasses. Oxygen and Nitrogen are similar enough that they don't separate (also Earth's atmosphere moves enough to mix), but you definitely find that e.g. Radon will sink to the floor, and lighter gasses like Helium will float up to high altitude.

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

#68

Post by lmm »

comrh wrote: post #49
grecy wrote: post #31

Earlier quoted context omitted.

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...

Looks like 5 of those are active rather than proposed.

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

#69

Post by gshubert17 »

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…

The pole star of a planet is in the direction of its axis of rotation. The orbits of Earth and Mars around the sun are in similar planes, and their axial tilts are similar, but they point in different directions. According to this

http://abaaonline.blogspot.com/2013/07/pole-star-on-differen...

Mars north pole points near Deneb. The reference also gives pole stars for other planets.

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

#70

Post by jameshart »

yellowapple wrote: post #35
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

Doesn't Mars have clouds, though?

Dust clouds, maybe. Water clouds, no, not at all.
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