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# why do you think to much energy is needed to launch a rocket to orbit the earth?

Why do you think to much energy is needed to launch a rocket to orbit the earth?

• ZeroByte says:

I did some back-of-the-napkin type calculations for another question of this nature some time ago, and cannot find my response, but in a nutshell, the potential and kinetic energy represented in a fully loaded space shuttle on an orbit like the ISS is on the order of megawatts.

That is how much energy must remain in the shuttle for it to orbit. A lot more than the final orbit energy is spent getting it there, though, because the fuel is also being lifted as it burns, the weight of the main tank is being lifted while it is still attached, air resistance is wasting energy, etc.

The formulas for kinetic energy (Ek) and potential energy (Ep) are Ek=1/2mv^2, and Ep = mgh.

v is something on the order of 11000 meters per second. Square that (121,000,000), and multiply by the mass of the shuttle, and divide the result by two. That’s the kinetic energy of the shuttle. Then add to it the potential energy, found by multiplying the mass of the shuttle, g (9.8m/s^2 for rough calculations), and h. I looked up the fully loaded mass of the shuttle, and altitude of the ISS on wikipedia, and voila. That’s a LOT of energy.

The reason it takes this much energy is because of Earth’s gravity. If Earth’s gravity were only half as strong, it would take a lot less energy. It doesn’t show at first glance in these two formulas though. The big savings comes from the lower orbital velocity required. (velocity is squared, remember?)

• quizzard123 says:

Why do we ‘think’ so much energy is needed? That implies it’s a matter of opinion. It’s not, it’s a matter of physics.

To orbit in a low earth orbit, the space shuttle needs to accelerate from zero to about 18,000 mph. That takes a LOT of energy.

• laurahal42 says:

Physics?

The object must be raised to the correct altitude, and must have the correct velocity to achieve orbit. Additionally, it must carry fuel to accelerate, unless it is launched at orbital velocity.

The numbers were understood in Newton’s time. Tsiolkovsky figured out the rocket stuff. This is well understood by all but Yahoo Answers users.

• mental_absence says:

because rockets weight hundreds of tons.
F=ma (newtons law)
big mass (m) means bigger force needed.
work = force x distance so big force means big energy (work)