[Lex Computer & Tech Group/LCTG] NASA thrusters

Wed Oct 11 18:59:38 PDT 2023

 But there is a disadvantage. Hall Effect thrusters can't push out the volume (mass) of propellant chemical thrusters push out, by orders of magnitude. This is why chemical thrusters are used in spacecraft liftoff from Earth. 
-- Bob Primak 

    On Wednesday, October 11, 2023 at 09:16:04 PM EDT, Ted Kochanski via LCTG <lctg at lists.toku.us> wrote:  

 John, et al
The basic are simple the Hall Effect is a bit more complicated

Fundamentally the rocket equation [it is rocket science] is that you throw mass out the back and that makes you accelerate forward [Newton Law of Action/Reaction and F=ma]
So you start with the mass of your total system [rocket structure + propellent] M0 and its initial velocity V0  -- -this gives you the initial momentum of the rocket After ejecting the increment of propellent out the rear nozzle -- you will achieve a new mass of the rocket M1= (M0-dM) where dM=M0-M1 is the reduction in the mass of the rocket] and where [dm is the mass of the propellant expelled out the nozzle at  velocity VpThere is also a new velocity of the rocket V1 where dV = V1-V0

Now of course you need to put everything into the same frame of reference [in Newton's View the Fixed stars] so the velocity of the expelled propellent is only Vp referenced to the rocket -- to the fixed stars the velocity of the expelled propellant is V of the rocket relative to the fixed stars minus the propellent ejection velocity
Conservation of the total momentum of the systemallows you to compute the change in the rocket's momentum after the expulsion of the small amount of mass dm is thenM0dV=dmdv+dmvNote the dmdV term is the result of the resultant change in propellant velocity relative to the fixed stars but since this is multiplied by the minute change in mass -- the term can essentially be ignored especially for a rocket whose mass is much more than the propellent [e.g. for an ionic thruster]
dV=−Vp dm/M0
if you want to see what happens for a continuing "thruster firing" all you need to do is to Integrate from the initial mass M0 to the final mass Mf of the rocket to get the overall change in velocity of the rocket ΔV
This results in the famous logarithmic relationship with mass due to the Russian physicist Konstantin Tsiolkovsky in 1897. It gives us the change of velocity that the rocket obtains from burning a mass of fuel that decreases the total rocket mass from  M0 to Mf
ΔV=Vpln(M0/Mf)
This result is called the rocket equation. It was originally derived by the Soviet physicist Konstantin Tsiolkovsky in 1897. It gives us the change of velocity that the rocket obtains from burning a mass of fuel that decreases the total rocket mass from M0 down to Mf. As expected, the relationship between ΔV and the change of mass of the rocket is nonlinear.
So the key to ionic and fission/fusion thermal drives is that you can achieve much higher Vp than you can with chemical combustion.  The other advantage is that you can use much less propellent to achieve the same ΔV
Ted
PS: check out the following for even more information on such mattershttps://www.nasa.gov/smallsat-institute/sst-soa/in-space_propulsion/

On Wed, Oct 11, 2023 at 4:28 PM John Rudy via LCTG <lctg at lists.toku.us> wrote:

I just read this 3 times and still don’t understand it.  Of course there is a sentence in the middle that reminds me of my high school teacher’s “the proof will be left to the reader”.

John

==================================================     

Sci-fi propulsion is now a reality

David Oh, chief engineer for operations at NASA's Jet Propulsion Laboratory says this will be the first-ever mission to use Hall Effect thrusters in interplanetary space. What does that mean? Well basically, Hall Effect thrusters use electricity to ionize xenon gas — ionization refers to removing or adding one or two electrons from the atoms that make up a substance. In this case, the substance is a gas. 

Upon ionization, those atoms gain a charge. (Regular old atoms have neutral charges because their positive proton count and negative electron count are equal. Remove some electrons, for instance, and you lose some negativity.) The result? Ions. Then, those charged ions form an electric field which can, through a series of complicated steps, propel an object. In this case, that's the Psyche spacecraft. 

"They come out of the thruster going at 15 kilometers per second, or nine miles per second," Oh said. "That's five times faster than the speed of the fuel coming out of a regular chemical rocket."

John Rudy

781-861-0402

781-718-8334  cell

13 Hawthorne Lane

Bedford MA

jjrudy1 at comcast.net

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