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Yes, ok I understand your confusion to my comment as I had forgotten that terminal velocity applies to atmospheric based objects?

But I haven’t thought about specific impulse much, so I am very naïve (but curious)

So, what, if any, does the mass of the object being pushed by an engine with the 5.4 Newton’s of energy have of the ability of the engine to push it?

If you push a 1-ton thing with 5.4, and a 100-ton thing with 5.4 Newtons will they reach mars at the same time? And what will be the fuel consumption diff?



> ability of the engine to push it

Acceleration. For equal mass a more powerful engine would make the object go faster, faster.

> If you push a 1-ton thing with 5.4, and a 100-ton thing with 5.4 Newtons will they reach mars at the same time?

    Force = Mass * Acceleration
    Acceleration = Force / Mass
    a: 5.4 / 1000 =    0.0054m/ss
    b: 5.4 / 100 000 = 0.000054m/ss
As the space-crow flies, the 100 ton thing would take longer - it's accelerating 100 times slower. You also have to factor in the mass of the fuel, both starting weight and consumption. As the engine depletes the fuel reserves it gets lighter and therefore accelerates faster (increased Jerk[1]). So if the 100 ton engine was a chemical engine the situation might be different.

The following would be the same time: "assuming reactionless drives, if you push a 1-ton thing with 5.4N, and a 100-ton thing with 540N."

[1]: https://en.wikipedia.org/wiki/Jerk_(physics)


Awesome, so the next question is to know the fuel consumption per engine vs the acceleration of the mass... basically their efficiency.

So if we smack 4 engines on 100 tons, assuming the same fuel... how far do we get.

I’d love to get these numbers.

But I noticed you had a stated m/s - so is there a constant of Newtons of thrust to acceleration of 1ton of mass in space?

(Sorry I don’t know how to word that question better)


I dont know why - but I was under some weird impression that mass is less affected in space due to lack of drag.... Stupid thing to think.

I guess that this is why the slingshot method is so important.


> mass is less affected in space due to lack of drag

Your intuition is closer to correct than many might think. It's harder to move massive things than non-massive things in space. This is because of inertia. Inertia may be more fundamental to physics than mass [1], and could be thought of as matter "dragging" against the gluon (and possibly other) fields [2].

[1] https://www.princeton.edu/~pear/pdfs/2001-inertial-mass-quan...

[2] http://web.mit.edu/physics/news/physicsatmit/physicsatmit_03...


> Stupid thing to think.

There's a difference between stupid and unaware. We live in an environment that is vastly different to space. You have to know quite a bit of Newtonian mechanics before it really starts making intuitive sense. Asking questions is how you get there.


Living in the small town of Newton NC, my car broke down and I took it into the exclusive dealership and shop I got it from - the only place I know - but It wouldn’t budge after I got there. Completely motionless.

I asked the guy to fix it and he exclaimed “oh, sorry can’t help you there - all of these cars are dead. We can’t work on any of these! It will tend to just stay!”

Just then, another car of the exact same model and color drove out of the lot, right by us!

I said “what! That’s the same freaking car! Same color and body style and everything!”

And he said, well you can find another person to try to work on it, but that body tends to stay in motion, this one... not so much...

Clearly I don’t know enough Newtonian mechanics!




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