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Comment: Re:No quite yet. (Score 1) 356

by drinkmorejava (#29802837) Attached to: VASIMR Ion Engine Could Cut Mars Trip To 39 Days
I'm not sure what formula you are using. The most simplistic thrust formula you'll see is T=me*Ue+Ae(Pe-Po) where Po is zero in space, m is the time derivative of mass exiting the spacecraft, and Ae is the area of the exit nozzle. This doesn't exactly apply to non-fluid mechanics though.

If you're slowing down the particles and generating a magnetic field, there's not necessarily any momentum transfered to the spacecraft. Kinetic energy can be exchange for a lot of stuff, heat, electric charge, and of course, an opposing force.

Comment: Re:No quite yet. (Score 1) 356

by drinkmorejava (#29802693) Attached to: VASIMR Ion Engine Could Cut Mars Trip To 39 Days
The speed of sound in space is not relevant, only the backpressure (pressure of the outside atmosphere) will matter. Mach 1 at the throat is calculated as sqrt(gamma*R*T) where T is in kelvin if R=287. Gamma will most likely be 1.4 and is pretty constant for ideal gases. T can vary greatly, but 3000K is around the right order of magnitude. Once flow hits the sonic condition, Bernoulli's principal switches, and you'll actually use an expanding nozzle to get a higher exhaust velocity. A cool thing to look out for are the plumes on the shuttle engines as it enters the upper atmosphere. These are due to a lower backpressure, and result in less efficient operation.

Comment: Re:No quite yet. (Score 3, Interesting) 356

by drinkmorejava (#29795129) Attached to: VASIMR Ion Engine Could Cut Mars Trip To 39 Days
Actually, conventional rockets are not limited by the rate of reaction. Momentum is limited by the density of the gas and the cross sectional area at the throat of the nozzle where the flow hits the sonic condition. You could speed up the reaction a million times and increase the pressure in the reaction chamber as much as you wanted, but the flow will absolutely not go any faster than Mach 1 at the throat, period. ...Just saying. And yes, I am a rocket scientist.

Comment: Re:Physical access (Score 1) 1117

by drinkmorejava (#26155989) Attached to: What Restrictions Should Student Laptops Have?

You obviously have not used any remote monitoring tools.

Just to pick one, look at kaseya. Unless everything on the network is locked down, it is going to find a way to connect to the server. Heck, by default it gives you a half dozen ways of remote viewing (mstsc, vnc,..) without manually installing anything beyond the small client package. It's very good software from a management perspective, but using it in a moderate size and diverse environment, it's border-line malicious.

"In matters of principle, stand like a rock; in matters of taste, swim with the current." -- Thomas Jefferson

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