Rocket Equation Homework: Explaining Mass Infinity

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The discussion centers on the Rocket Equation, which relates the mass ratio of a spacecraft to its velocity change and exhaust velocity. Participants express confusion about how the mass of the spacecraft can approach infinity when the ratio ΔV/C is between 2 and 3, questioning whether this refers to the total mass (M+P) or just the dry mass (M). There is also mention of a potential typo in the quoted values for e^2. The exponential relationship indicates that as ΔV/C increases, the total mass grows rapidly, leading to the infinity concept. Clarification is sought on the specifics of the equation and its implications for spacecraft mass.
Biosyn
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Homework Statement



The following equation is known as the "Rocket Equation":

\frac{M+P}{M}= e^{ΔV/C} = mass ratio

M = dry mass
P = mass of propellant
C = exhaust velocity
ΔV = velocity changee^1 = 2.72
e^2 = 2.74
e^3 = 20.4

As ΔV/C goes up, the mass of the spacecraft goes up faster than the exponential, so much so that depending on the lightness of the structural materials and the density of the propellants employed, somewhere between ΔV/C = 2 and ΔV/C = 3 the mass of a single spacecraft will go to infinity! Please explain how and why the mass of the spacecraft will reach infinity?

Homework Equations



\frac{M+P}{M}= e^{ΔV/C}

The Attempt at a Solution

Shouldn't the mass ratio be equal to 1 if the mass is a really huge number?
Or, does the propellant mass have something to do with it. I know that the propellant mass needs to increase along with the dry mass of the rocket.
 
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It's unclear whether the question posed refers to M or M+P. If M is fixed, then M+P goes up exponentially with ΔV/C. But I don't get the bit about going to infinity between 2 and 3. I've no idea where that's coming from. Is this the whole question, or is something left out?
Btw, the quoted value for e^2 is wrong. Looks like a typo.
 
haruspex said:
It's unclear whether the question posed refers to M or M+P. If M is fixed, then M+P goes up exponentially with ΔV/C. But I don't get the bit about going to infinity between 2 and 3. I've no idea where that's coming from. Is this the whole question, or is something left out?
Btw, the quoted value for e^2 is wrong. Looks like a typo.


I think it's the total mass of the spacecraft (M+P). I'm not entirely sure. This is from a USAD Science section study guide.
 
Biosyn said:
I think it's the total mass of the spacecraft (M+P). I'm not entirely sure. This is from a USAD Science section study guide.
Can you provide a link or is it behind a paywall?
 
haruspex said:
Can you provide a link or is it behind a paywall?

It's behind a paywall. :/
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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