Weird idea/vision of space travel.

[Titan]

Ok, I will be there first to admidt that I am a programmer, not an astrophysict, but I occasionally get random ideas based on what I know and wonder about them. I did get an A in freshman physics (mechanics) and it was a subject I had much interest in. So here goes.

I understand that ion drives work by the law of conservation of momentum, being that we fire a very lightweight particle at very high speed in the opposite direction we wish to travel, and we get a resultant velocity, much slower because of a large mass.

My question relates to impulse. I remember from physics class that when blades on old fashioned water wheels were changed from flat to cup-shaped, they resulted in more momentum change because the incoming water hits the blade, then effectively "bounces" out and this bounce increases the forward momentum. I used to theorize that if a martial artist were strong and fast enough, he could improve the power of his punch (say breaking boards) if he recoils quickly from the force of the boards hitting back, restulting in the boards recieving more force from impulse. But the real reason martial artists are told to snap a punch is for minimal impulse, and it's stupid to leave your arm out there.

But in regards to space travel, Imagine a ship with an ion drive at the rear, with a large dish-shaped, well, dish on the rear as well, that is highly reflective to incoming ions. My basic idea would be to have 2 ships, going in opposite directions so when one ion travels from one ship, it hits the other ship with added impulse, then bounces (ideally) back and forth, allowing for a steady build-up of acceleration, theorhetically better than just one ship with an ion drive. Plus this conserves fuel.

Now obviously this acceleration wouldn't be constant, nor would it increase, it actually would decrease as the distance of the ships increased, and perfect reflection would not happen, and ions may interfere with each other, but the potential of contructing a space travel system that relies on 2-directional reflection could be effecient and beneficial. So transit leaving mars would be going to earth, and jupiter. Perhaps ships could launch disposable dishes and send them aimlessley into space. Or perhaps, we could have a stationed reflector that recieves equal ion reflections from both sides.

Does this sounds like a good idea, has it already been considered and publicly discussed, or do I watch to much star trek?

 

[DrPizza]

Good analogy to this is 2 people on ice (frictionless). If they throw a basketball back and forth, they will both make it to the edge of the ice (eventually).

Now, add to this analogy that there are lateral forces acting on the ball while it's in the air (wind). The ball will no longer travel in a straight line, but its path will be curved away from the straight line. When the people are close together, the ball will still make it to each other. But, when they're farther away, it will no longer travel in a straight enough line to reach the other person.

In your concept, the ions would be influenced by gravity. So, at first they make it back and forth between the ships, but eventually, once the distance was great enough, the forces acting on the ions during the trip would redirect them enough so they wouldn't make it to the other ship.

 

[Titan]

While it is true gravity would alter the path of the ions, I do not believe it would do so like wind would affect a ball, as wind is random and gravity is more constant, or at least predictable. This may require complicated computing to measure and predict all surrounding gravitational influences, but that're hardly unreasonable. I assume if a technology like this were implemented, it would have a way to target the other ship and correct for gravitational forces, perhaps by using a laser-transmission to predict the ions course. I will concede that once distance gets too great, this would become incalculably difficult. But what would be defined as too far would be judged by innovative implementation.

Perhaps the perfect and constant reflection approach isn't the real abstract goal though, I'm thinking along the lines of fuel and energy conservation. Tailoring our travel habits to the goal of energy conservation. The same result would be achieved if both ships could absorb the ion and store it for future use (catch the ball instead of trying to bounce it off your head). If it were done right, 2 ships could get to one planet with only one ion (if they had to), and with some other fuels for stopping, one arriving early, and the other waiting for the planet's orbit to get to it. Of course that is simplistic and sounds dumb, but I am envisioning complicated networks and chain reactions of travel, the absorbing feature would work better, as an incoming ship reached a planet, a departing ship would unleash a stream of ions from the opposite direction, necessarily slowing the incoming ship, while propelling itself away. It may not be good for long-distance travel, but maybe for short distances?

I'm not talking warp drive here, but with better technology could this work to explore the scope of a solar system?

 

[DrPizza]

I really doubt this would work. It seems you're looking at the solar system as a more or less static place, and you're underestimating the force exerted on particles by massive objects such as the sun and the other planets and moons and asteroids and... Consider how fast a comet is moving, yet its path is far from linear. I thought for a few minutes about non-linear paths, but it really doesn't matter. The orbits of the planets in the solar system are chaotic. As much as you may think gravity is predictable, I don't believe it is to the scale you're talking about.

 

[silverpig]

It's sort of a good idea. The main problem with your solution to the gravitation problem would be that in order for me to shoot my ions around jupiter to you, I would have to shoot them at a different angle than in which I wanted to travel. So we'd both have to fire our ions all over space to keep ourselves in line.

Second, ion drives are EXTREMELY weak. As in they produce the same amount of thrust as you holding up a piece of paper. In order to get anywhere you'd need to have the drive in operation for a really long time.

On the other hand, a solar sail works in sort of the same way you have said. You can either have an absorbing sail (black) or a reflecting sail (like a mirror). The mirror sail will give you twice as much thrust as you get that added impulse from bouncing the photon back.

 

[JediJeb]

Another problem with this is that traveling in space is done in curved paths, no where near a straight line. The thrust used to move in space is simply altering your orbit around the sun or planet you are near. The ions would move in a fairly straight line compared to the curved line the ship is following. Think of it in terms of vector addition, in the example of the people on ice throwing the ball, if they were moving to their left ( the orbit direction) and have the added rearward force of the ball, they dont move straight rearward but at an angle, if the ball pushes them as fast reward and they are moving to the left, they end up moving at a 45degree angle across the ice.

Also since both ships would be orbiting the sun to start with, and moving in opposite directions they would eventually pass each other going around the sun in opposite directions.