Closest non solar planet

[mistermack]

It occurs to me that there may be non solar planets much closer but not attached to a star? perhaps just outside the solar system there a planet which was jettisoned from it's native solar system some time ago?

That is possible. I seem to remember reading about lone planets recently. Not that they've found them, but they seem to consider it very possible.
They would be hard to find though. And incredibly cold, unless they had an inner heat source.

The trouble is that the space between the stars is so vast, they would be incredibly remote. And we would have no way of finding them, without incredible luck.
edit.
I'm trying to wear out the word incredible.

[Blind groper]

Mistermack

A very, very efficient fusion drive might, and I repeat might, be able to achieve what a linear accelerator drive could do. Probably more thrust, but the final velocity would be no better.

Scrumple,

If you are not too worried about the 'non solar' bit, there are probably hundreds of objects in the Kuiper belt the size of our moon or bigger, which could almost be called non solar planets. They would be horrendously cold, of course.

[pErvinalia]

Interesting thread! Regarding the slowing down bit at the other end, I would of thought you'd need less fuel to decelerate compared to the acceleration phase, as a space craft could use the gravity well of the destination star to strip speed off. Essentially get trapped in orbit around that star. Although, perhaps with the speeds involved (fractions of c) it would require going so close to the star to strip that speed off that both the solar radiation and g-forces involved would be too high.

[Gawdzilla Sama]

Interesting thread! Regarding the slowing down bit at the other end, I would of thought you'd need less fuel to decelerate compared to the acceleration phase, as a space craft could use the gravity well of the destination star to strip speed off. Essentially get trapped in orbit around that star. Although, perhaps with the speeds involved (fractions of c) it would require going so close to the star to strip that speed off that both the solar radiation and g-forces involved would be too high.

The gravity well would speed it up. You'd have to overshoot and let it pull you back to get any deceleration, and the acceleration of diving past the sun would nullify that.

I think.

[Blind groper]

The best braking system when approaching another system would be a solar sail.

However, due to the inverse square law, it would have little effect until you were well inside the system, and if you were still going at a reasonable fraction of light speed, you would just keep going and zip out the other side. You need to be decelerating from well short of the target.

[Gawdzilla Sama]

The best braking system when approaching another system would be a solar sail.

However, due to the inverse square law, it would have little effect until you were well inside the system, and if you were still going at a reasonable fraction of light speed, you would just keep going and zip out the other side. You need to be decelerating from well short of the target.

You can't tack either.

[pErvinalia]

Interesting thread! Regarding the slowing down bit at the other end, I would of thought you'd need less fuel to decelerate compared to the acceleration phase, as a space craft could use the gravity well of the destination star to strip speed off. Essentially get trapped in orbit around that star. Although, perhaps with the speeds involved (fractions of c) it would require going so close to the star to strip that speed off that both the solar radiation and g-forces involved would be too high.

The gravity well would speed it up. You'd have to overshoot and let it pull you back to get any deceleration,

Yeah, that's what I mean.

and the acceleration of diving past the sun would nullify that.

Not sure that is correct. You don't need to accelerate past the sun. You only need to travel past it. No need to be accelerating when going past it.

[Blind groper]

Not sure that is correct. You don't need to accelerate past the sun. You only need to travel past it. No need to be accelerating when going past it.

Since space is vacuum, there is no frictional braking, and the acceleration from gravity while diving towards the sun would exactly equal deceleration when moving away from the sun. In other words, no net braking. If you were travelling at a goodly percentage of light speed, you would pass right through that stellar system and just keep right on going. That is why the space ship needs to be able to decelerate. A bit more than half the fuel to accelerate and a bit less than half to decelerate.

[pErvinalia]

Well you're assuming that the trajectory past the star would be straight in the sense that no correction to the orbit would be performed. What I was thinking was that at some point a correction (or multiple corrections) would be performed that would mean that the acceleration on approach wouldn't necessarily equal the deceleration on passing. I should say, while I have no idea of the validity of the physics of this, I've pinched the idea from an Arthur C Clarke book (the "Rama" series). But while I suspect the physics of this are sound, the reality would involve such a close approach to the star that solar radiation and then subsequent massive deceleration g-forces would mean in a practicle sense it would be non-viable. Although maybe for robot technology it might not be the case.

[Blind groper]

rEvolutionist

Gravity deceleration is accomplished by throwing a vehicle into a trajectory that bypasses a star or planet in the opposite direction to the rotation of that star or planet. The vehicle slows the spin by an infinitesimal amount, and it is slowed in its movement. However, that will be such a tiny effect on a vehicle travelling at more than (say) 5% of light speed, that it could be discounted. It can be used in the current generation of space craft since they are moving so slowly that the counter-rotation effect is significant. Not so for a high speed interstellar craft.

[cronus]

Space isn't a absolute vacuum and you's only need to hit a grain of salt at close to light speed....and that is game over. Making the probe thin and long might reduce the risk?

[Blind groper]

Scrumple,
The space craft will not be going near light speed inside any star system. That is what acceleration and deceleration is about. It will be going at a fraction of light speed (0.1 to 0.2c) in interstellar space, where the chances of hitting anything bigger than a hydrogen atom is almost zero.

[JimC]

I have read speculation about using intense magnetic fields to gather the charged particles in the interstellar medium. If the field was big and effective enough, perhaps the gathered particles could be used as reaction mass... As a side benefit, they aren't crashing into the spacecraft...

[mistermack]

I have read speculation about using intense magnetic fields to gather the charged particles in the interstellar medium. If the field was big and effective enough, perhaps the gathered particles could be used as reaction mass... As a side benefit, they aren't crashing into the spacecraft...

You could do that. But you would be building up a charge, unless you collected an equal amount of positive and negative. I'm not sure what kind of field could collect both.
And if you collected a significant mass, that would put the brakes on a bit, as their change of momentum would have to be supplied by the ship.

I just made that up, by the way, so it's probably wrong.

I don't think there is any possibility of using a planet or even a star's gravity to slow a ship.

You just couldn't go that close, at 0.1c. You would be sure to hit some particle big enough to destroy the ship.

[Gawdzilla Sama]

Interesting thread! Regarding the slowing down bit at the other end, I would of thought you'd need less fuel to decelerate compared to the acceleration phase, as a space craft could use the gravity well of the destination star to strip speed off. Essentially get trapped in orbit around that star. Although, perhaps with the speeds involved (fractions of c) it would require going so close to the star to strip that speed off that both the solar radiation and g-forces involved would be too high.

The gravity well would speed it up. You'd have to overshoot and let it pull you back to get any deceleration,

Yeah, that's what I mean.

and the acceleration of diving past the sun would nullify that.

Not sure that is correct. You don't need to accelerate past the sun. You only need to travel past it. No need to be accelerating when going past it.

You don't get a choice in that. Orbital mechanics says you will speed up as the sun's gravitational attraction increases.