alternative ion drive?

[YT2095]

I`m familiar with the current type of ion drive we have that uses Xenon gas that get charged etc...

 

if a very large but lightweight and rigid plate where in space and one side covered with a thin layer of some powerfull Alpha emitter isotope, wouldn`t there be a gentle push also on this plate propelling it forwards slowly due to newtonian motion?

 

I only use the Alpha emitter as an example as IIRC, the paticles of alpha are quite large and heavy.

[[Tycho?]]

Yup, that could work. I kinda doubt that would be more efficient than other ion drives though.

[5614]

Yep, that works.

 

You know that momentum is always conserved.

 

So if the alpha particles are released into space with a velocity (and thus a momentum) a negative momentum (or momentum in the opposite direction) must also be given to something. In this case it would be the plate.

 

Which radiation particle to chose is a point too. I think that alpha particles are best choice because they have the biggest mass (momentum = mass * velocity), so even though beta particles would move faster (and gamma faster still) alpha probably remains the best option as it is significantly heavier than the others.

 

I don't know how good this propulsion system would be though. You'd need something with a quick decay rate to give a thrust, but to sustain this thurst you'd need a lot of the radioactive substance which would weigh the plate down.

 

It's an interesting idea and certainly works well in theory.

[YT2095]

well I go to thinking about solar sails and ion drives and that they would eventualy either be "out of range" or run out of gas (Xenon), whereas a "Paint" made from a mixture of fast and slow decaying alpha emitters, would still continue to operate long after the gas ran out on a conventional or a solar sail ducked behind a planet or was out of range or indeed wanted to travel Against the "tide".

 

I realise the push would be very very gentle indeed, maybe only a miligram or so for a reasonable sized frame, but it all mounts up

[Klaynos]

It'd be quite difficult to alter whilst in use :\

[insane_alien]

For a type of throttle you could fold up the sheet. decrease the surface area, decrease the thrust. probably more difficult than it sounds.

[Sisyphus]

well I go to thinking about solar sails and ion drives and that they would eventualy either be "out of range" or run out of gas (Xenon)' date=' whereas a "Paint" made from a mixture of fast and slow decaying alpha emitters, would still continue to operate long after the gas ran out on a conventional or a solar sail ducked behind a planet or was out of range or indeed wanted to travel Against the "tide".

 

I realise the push would be very very gentle indeed, maybe only a miligram or so for a reasonable sized frame, but it all mounts up [/quote']

 

Why would it operate longer than an ion drive? And why would that be better, seeing as how it would necessarily have a exponentially decreasing thrust? And why a mix of fast and slow decayers? Wouldn't that just mean a rapid decrease of most of the thrust, followed by a slow decrease of the remainder? And even if you could simulate a "throttle" by say, folding portions of the sheet in the opposite direction, you'd still drain "fuel" at the same rate.

 

Also, any data on the relative velocities of the xenon ions and and alpha particles?

[5614]

The chances are that xenon will weigh less than an alpha emitting radioactive sample, seeing as Xe is a gas.

 

The suggestions of using a mixture of fast and slow decaying alpha emitters is at first a good idea, or so I thought! But then it doesn't work so well if you think about it. The fast emitter will give the ship some speed and then be all used, then the slow emitter whilst it will still be emitting would be too slow and weak to accelerate, and maybe even too weak to overcome the resistive forces acting on the plate or ship.

 

Maybe a combination of very fast emitting (for the initial acceleration) and then fast (but not as fast) alpha emitting particles to sustain the motion. Whilst as you say Xe runs out, as does fuel in current rockets, I think the weight to thrust/force ratio is working against you. And that is assuming a very light weight ship.

[Klaynos]

The chances are that xenon will weigh less than an alpha emitting radioactive sample, seeing as Xe is a gas.

 

But ion engines rely on removing mass from an object, so a comparison of "weight" is kinda silly. You could say that more the the Xe can be used than alpha emittors so more mass will remain on the craft as waste...

[5614]

But as we want the aircraft to lift off the ground it will need to overcome any forces which happen to be acting downwards, aka weight. Hence I said weight.

 

Your point still holds, kinda, but I had (IMO) a good reason for saying weight.

 

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Also a light source which fires photons away from an object will give the object a momentum. With photons the momentum is very very small, but if you could get enough of them. Although this is totaly impractical because of huge amount of energy which would be required to produce that many photons.

[Norman Albers]

In 1968 I worked 20 hrs/wk as a research assistant for NASA, and my prof showed me how to do fourth-order Runge-Kutta numeric integration to optimize a low-thrust rocket simply going from Earth orbit to a "far" orbit such as Saturn. To my continued amazement the Lagrangian quantity told you when to shut off your thruster! Optimal is to fire at first to change momentum, then you see the "L" goes through zero and you coast for the middle journey, then "L" comes back through zero and you turn back on to insert in the far orbit. THIS IS MATHEMATICAL MAGIC and I still wonder at it. Norm Albers