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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?

#11

Post by vilmosi »

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…

That's still like a couple of degrees (4 full moons) away so not sure how accurate it would be.

Still the thought of seeing literally the same stars on an alien world is blowing my mind. Just imagine the same sky, but different planet... wow

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

#12

Post by jessaustin »

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…

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.

ISTM this would work on the equator too?

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

#13

Post by jwhale »

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 gravity of Mars and (2) Pancam solar images that determine the vector to the Sun."

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

#14

Post by jessaustin »

scott_karana wrote: post #10
msandford wrote: post #6

Earlier quoted context omitted.

Further if you're not looking for realtime direction finding and you're willing to wait a few minutes for a fix, you can get away with far fewer satellites. Putting 6 small satellites in orbit and getting position fixes every hour would still be way better than nothing.

How would the satellites themselves maintain their proper positions relative to Mars, without ground stations to orient against?

We already stipulated that we're landing something on the surface. That could include a stationary transmitter, which satellites could use to periodically update their location and velocity.

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

#15

Post by scott_karana »

jessaustin wrote: post #14
scott_karana wrote: post #10

Earlier quoted context omitted.

How would the satellites themselves maintain their proper positions relative to Mars, without ground stations to orient against?

We already stipulated that we're landing something on the surface. That could include a stationary transmitter, which satellites could use to periodically update their location and velocity.

Yeah, agreed, my comment was meant to politely point out the necessity to the people thinking we could get away with "dropping a few satellites" ;)

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

#18

Post by JoeAltmaier »

FreeFull wrote: post #3
JoeAltmaier wrote: post #2

GPS

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

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

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

#19

Post by afarrell »

scott_karana wrote: post #15
jessaustin wrote: post #14

Earlier quoted context omitted.

We already stipulated that we're landing something on the surface. That could include a stationary transmitter, which satellites could use to periodically update their location and velocity.

Yeah, agreed, my comment was meant to politely point out the necessity to the people thinking we could get away with "dropping a few satellites" ;)

All of these things can be done remotely without any wetware on Mars.

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

#20

Post by DanBC »

vilmosi wrote: post #11
ars wrote: post #9

Earlier quoted context omitted.

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…

That's still like a couple of degrees (4 full moons) away so not sure how accurate it would be. Still the thought of seeing literally the same stars on an alien world is blowing my mind. Just imagine the same sky, but different planet... wow

I wonder if "giant head" enhanced depth perception works across planets?

https://xkcd.com/941/

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