# Why don't they crash?

Discussion in 'Science and Technology' started by QuarkforNagus, Feb 20, 2014.

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Mar 12, 2005
A little from column A, a little from column B...

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But you do have to take into account a star's own motion through the galaxy, in accordance with its proper motion and radial velocity as viewed from Earth.

As you approach a star, you will be seeing it with light that was emitted from it at later and later times along its own trajectory. From your perspective, its position in space will therefore appear to shift as you approach it. Your journey to the star will have to take that into account so that you arrive where the star actually is, instead of where it was.

If you have no FTL sensors, an accurate assessment of the motion of the star is therefore essential. Hypothetical instantaneous FTL sensors would mitigate the problem of unknown factors, by locating the star where it actually is, so to speak, so that you can head directly there (as a good approximation for short travel times; or refined with proper/radial motion for a higher-order correction), which is generally speaking not where the light shows it to be.

3. ### Edit_XYZFleet CaptainFleet Captain

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So - you can either use FTL sensors (even more 'magic' than FTL travel) to see the star or you can calculate the stars' current position by using models we know today.
If you must 'see' where a star is NOW, you can always use its gravitational or electrostatic field to detect it (you need insanely accurate sensors for this, though).

As for 'unknown factors', if at your destination there is something that can substantially alter the trajectory of a star so fast, you're better off mistaking your course.

The challenge is how to get to the stars, not how to determine their position at any given time.

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There's that, plus just run-of-the-mill uncertainty with the margin of error, that generally gets worse the more distant the destination.

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Well, the sun is moving around the galaxy at about 500,000 miles per hour, which sounds like a lot, but it isn't when compared to any FTL travel. At twice the speed of light you'd only have to lead the sun's position by an arc-minute, which means that for some random star that doesn't have a crazy velocity, to hit it you'd have had to been aiming at it from the start with the same accuracy you'd have with a modern off-the-shelf scoped hunting rifle.

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Something tells me that they wouldn't be measuring proper motion with a device of such limited accuracy.

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I don't think so. According to current understanding, gravity also moves at the speed of light. So you'd be no better off than locating it visually and accounting for any velocity.

8. ### Edit_XYZFleet CaptainFleet Captain

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At star's end.
On this issue, what you think is irrelevant.
EM/gravitational waves move at the speed of light.
According to current understanding, static gravitational and electrostatic fields created by inertially moving objects affect distant objects instantaneously. This is even experimentally verified with the sun.

9. ### varekCommanderRed Shirt

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Danville, IN, USA
I thought they had navigational sensors that automatically steered the ship away from large gravity wells.

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