Question about direction

  • #1
If I understand correctly, direction in space is all relative to the observer (north, south, east, and west). Anyway, suppose we're looking at the earth from a distance, where the north and south poles are located as on a globe.

My question is: when we send probes and shuttles into space, we seem to be going sideways for travel, but do we ever launch straight up from either of the poles and continue our exploration in other directions?

I do feel that I may not be understanding something, or missing something entirely. Any explanation or resources would be greatly appreciated.

Answers and Replies

  • #2
Science Advisor
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The plane of the solar system roughly corresponds to the plane of the equator of the Earth, this is why we launch things going out "sideways". If we launched something going "straight out of the poles" it wouldn't hit anything interesting for quite a long time as it would just be going away from the plane of the solar system and not towards other planets, etc. In addition, most of the people on Earth are located closer to the equator. There are no people at the poles, so it would be pretty hard to build launch sites there.
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  • #3
Science Advisor
The issue here is with the energy cost of sending anything into space in directions not coinciding with the rotation/revolution planes.

When you send a satellite into Earth orbit in the equatorial plane (the East-West plane) you can use the rotation of the planet to boost the satellite and save fuel.
The savings in terms of delta-V (the velocity required for a maneuver) are in the vicinity of 500m/s iirc. Compare with ~7 km/s required for a low-Earth circular orbit. It's not a whole lot, but still a substantial saving due to the way rockets work (you need extra fuel to move extra fuel and so on). But since it's not prohibitive either, we do sometimes send satellites into polar orbits.

With the solar system travel, the savings from the orbital velocity of Earth when sending probes in the ecliptic (orbital) plane amount to ~30km/s. Compare to about 45km/s required to escape the solar system from the distance of Earth's orbit. It's much, much easier to send stuff close to the plane of the ecliptic (which differs from equatiorial plane by 23.5 degrees by the way) and then try and alter the orbit with slingshot maneuvers.

But besides, almost everything in the solar sytem apart from some rare rocks lies within relatively few degrees from the ecliptic, so it's not like there's much reason to send stuff away in any other plane.
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  • #4
Thank you both for the explanations, very helpful with imagining this and understanding why we launch along the ecliptic.

I was trying to think of any follow up questions, but it seems you both covered everything that I could think of at the moment :p