Monday, August 17, 2015

An idea for a thruster for space exploration

Speculation alert:

The idea of using a VASIMIR for a thruster as opposed to a solar sail got me to thinking about using some other idea besides that one.

This idea comes from the study of the Polywell fusion idea, which confines electrons as opposed to confining positively charged particles, which have a mass over a thousand times greater.  In other words, confining electrons is a lot easier, and can be done in a smaller machine.

Not that I am interested in doing fusion here.  Nope.  The idea is to use electrons for thrust as opposed to positively charged ions as in the Polywell concept for fusion.  The reason being that it would be a lot easier to accelerate the electrons to near relativistic speeds and then eject them for thrust as opposed to ejecting positively charged ions, which are a lot harder to handle due to the heat required.

The mass of an electron is 1/1836 th that of a proton.  To eject that mass at near relativistic speed should yield some thrust, I would say.  Plus the ISP would be quite high, which should yield an interesting little thruster that should be quite economical.

ISP is calculated thusly:

ISP equals average exhaust speed/ gravitation constant

Now, in the FEL design, the effective velocity could be close to the speed of light  ( very close ), which is 299,792,458 m / s , then ISP equals about 1/10th of this since the gravitation constant is about 10 m/s, so
it would be   29979245.8 or  29,979,246!!!

Since thrust is equal to mass flow rate times ISP, then we can calculate the equivalent of 1 mole of hydrogen atoms divided by 1836, which is the mass of an electron, which means dividing by maybe 2 million or so, which yields something like 150 newtons.  I'm not sure if the calcs are right, but the thrust is in the ballpark of what the VASIMIR gets.  Actually, quite a bit more.

In other words, conceptually, it might work if you can put your device into space and get that many electrons moving at that speed.  Of course, that may be an engineering challenge, but I'm not sure about that one either, hence the speculation alert.


I've been thinking about this one a lot today.  It is beginning to appear that this is probably an impractical idea.  Rats.


Running through the rocket equation assuming an ISP of 29 million ( that may be wrong ), the amount of propellant needed would only be 330 grams for 2.1 delta v.  You would need a little over 600 kg of hydrogen from which you would obtain the electrons.  By the way, it would transport 100k pounds at that delta v.  This leaves a payload fraction of 99%!  Great if you can do it.

The machine that accelerate the electrons to near light speed will have to be able to process a LOT of electrons.  It would also take a very long time to thrust before you would see much acceleration.  246k electron volts.  That sounds like it would be too much.


The previous paragraph had to be corrected-- I added a "k" to the "246 electron volts" for clarification.

This method of propulsion has caught my fancy just a bit.  I googled how to accelerate electrons and found an article that says that a new way to do this was found in 2013.  The new way, which uses lasers, may be able to reach new light speed in a table top device.  If so, this may work in a propulsion system.  (Maybe)

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