re: How hard would to build a rocket to go to the moon?

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And is it legal?

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Luna 2 was the first rocket to reach the moon. It weighed around 850 pounds and had a payload of around 350 pounds for reference.

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A rule of thumb is that 90% of the mass of a typical rocket is propellant. We can take a look at Tsiolkovsky's Rocket Equation to find out if that is about right.

?v=velnmom1?v=veln?mom1

delta v is the velocity change of the rocket
ve is the exhaust velocity of the rocket
mo is the original mass of the rocket
m1 is the final mass of the rocket

If we don't know the exhaust velocity, we can use the Isp (specific impulse) to figure it out.

ve=Ispg0ve=Ispg0

Let's say we want to get the rocket to LEO, at about the altitude of the ISS. That would require an orbital velocity of 7800 m/s, so we'll use that as our delta v. Isp varies per rocket. Let's use an Isp of about 340. That's about right for midsize rockets like a Soyuz rocket or Falcon 9. For our final mass, we'll use 1 kg, for simplicity.

So, let's plug those in and rewrite the equation to dispose of the natural log to isolate Mo.

m0=m1e?vIspg0=(1kg)e7800m/s(340s)(9.8m/s2)m0=m1e?vIspg0=(1kg)e7800m/s(340s)(9.8m/s2)

That gives us an initial mass of the rocket of 10.39 kg

So, if our imaginary rocket with a final mass of 1 kg started off at 10.39 kg, then 90.3% of the mass of the rocket was propellant. Our rule of thumb was pretty darn close.

I did that in metric and you asked for pounds, but the answer will be the same - to propel 1 pound of mass would require 9.39 pounds of propellant.

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