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mfb
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In general Earth is a small target. If you can avoid a predicted impact it is likely that the object won't be a threat for hundreds of years or longer.
I think this may not be true in all instances. I’m hoping somebody will check my reasoning here, but if the deflection is away from the ecliptic, then only two changes, each of equal magnitude, would be required. I’ll describe the plan and see if it meets with reason:mfb said:To get the object away from Earth permanently you need a much larger trajectory change (~1000 times larger) than a simple impact avoidance maneuver needs. Moving it by a few thousand kilometers vs. moving it by a few million kilometers
What effect would be responsible for increasing the tilt of an elliptical orbit over time?LURCH said:If the initial acceleration is at 90° to the ecliptic plane, then the orbit will become progressively more inclined as time goes by.
Thank you @jbriggs444, that’s exactly the sort of double-checking I was hoping to get. If the tilt were started with a push, would it not continue until another force stopped it? Or would it require continuous thrust to keep going.? My impression is that, once the motion is begun, it will continue until some force makes it cease.jbriggs444 said:What effect would be responsible for increasing the tilt of an elliptical orbit over time?
If such an effect existed, one would expect all of the planets to be orbiting at 90 degrees relative to Jupiter.
Why would the closest approach follow such a pattern? Most likely it will jump around wildly.LURCH said:If a potential impactor is spotted, a slight deflection at an early enough moment will turn a “possible hit” into a “near miss.” On the object’s next approach, probably about three years later, it will miss by a slightly wider margin, and so on for each successive orbit.
Orbits are closed (neglecting three-body interactions and general relativity). A simple push just changes the orientation of the orbit a bit but then it orbits stably in this new orientation.LURCH said:Thank you @jbriggs444, that’s exactly the sort of double-checking I was hoping to get. If the tilt were started with a push, would it not continue until another force stopped it? Or would it require continuous thrust to keep going.? My impression is that, once the motion is begun, it will continue until some force makes it cease.
I was wondering about that too. The orbital period would change a bit but that's all I can imagine happening. If the orbital plane were tilted away from that of the Earth's and then the eccentricity were increased, you could permanently remove the object from danger. But I think that (as with most useful manoeuvres) would require two 'burns'.jbriggs444 said:What effect would be responsible for increasing the tilt of an elliptical orbit over time?
The effect of a force that stops is a change in the orbit -- to a new stable elliptical orbit.LURCH said:If the tilt were started with a push, would it not continue until another force stopped it?
A single burn is adequate. A pair of distinct elliptical orbits about the same primary can intersect in at most two points. With a single burn you can tilt one orbit so that its position near the one intersection point rises up out of the plane and its position near the other intersection point is depressed down out of the plane.sophiecentaur said:But I think that (as with most useful manoeuvres) would require two 'burns'.
I can almost picture that in my mind. The ellipse is narrower than the circle where the planes coincide?jbriggs444 said:With a single burn you can tilt one orbit so that its position near the one intersection point rises up out of the plane and its position near the other intersection point is depressed down out of the plane.
You will have to help me with this one. Doesn't the major axis of the ellipse pass through the Sun - so why isn't there symmetry about that axis? Is it the effect of other bodies?mfb said:The other intersection with the plane of the planets is much farther away from the Sun.
There is no reason for the line that is the intersection of the orbital planes to align with the major axis of either ellipse.sophiecentaur said:You will have to help me with this one. Doesn't the major axis of the ellipse pass through the Sun - so why isn't there symmetry about that axis? Is it the effect of other bodies?