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Why Rockets Love the Equator and How Tall Your Hill Needs to Be to Woo Them

Hello, space enthusiasts! Today, we’re diving into a fun topic: why rockets are like sunbathers 🌞 – they both love the equator! And if you’ve ever wondered how tall a hill would need to be to make rockets forget about the equator, you’re in for a treat.

Rockets and the Equator: A Love Story

Old fashioned rocket starting from a man made hill with erupting flames in comic book style.
Denis × DALL·E Human & AI

First things first, why do rockets have a thing for the equator? It’s all about the Earth’s rotation. Our planet spins on its axis, and at the equator, this rotation is at its fastest. When a rocket is launched from the equator, it gets a little “boost” from Earth’s rotation. Think of it like a running start before a long jump. This boost means rockets need less fuel to reach orbit, which saves money and makes engineers (and accountants) very happy.

The Hill Hypothesis

Now, let’s get to the fun part. If we can’t launch from the equator, could we build a massive hill or mountain to give our rockets a boost? The idea is that launching from a higher altitude reduces the amount of atmosphere the rocket has to push through, which can save on fuel.

But how tall would this hill need to be to match the equatorial advantage?

The Formula

Let’s derive a fun formula for this. The rotational speed \( v \) of a point on the Earth’s surface due to the Earth’s rotation is given by:

v = R × ω × cos ( Φ )

Where:

  • \( R \) is the Earth’s radius (about 6371 km).
  • \( \omega \) is the angular speed of Earth’s rotation (about \( 7.27 \times 10^{-5} \) rad/s).
  • \( \phi \) is the latitude.

The boost at the equator is \( v_{eq} = R \times \omega \).

The difference in speed between the equator and a given latitude is:

Δ v = v eq v

Now, the potential energy gained by a rocket when it’s on top of a hill of height \( h \) is \( m \times g \times h \), where \( m \) is the rocket’s mass and \( g \) is the acceleration due to gravity. This energy can be converted to kinetic energy, giving the rocket a speed boost of:

Δ v hill = 2 g h

For the hill to compensate for the lack of rotational speed, we set \( \Delta v = \Delta v_{hill} \):

R × ω ( 1 cos ( Φ ) ) = 2 g h

Solving for \( h \):

h = ( R × ω ( 1 cos ( Φ ) ) ) 2 2 g

Conclusion

So, next time someone asks you why we don’t just build a massive hill to launch rockets, you can whip out this formula and explain why. Spoiler: the hill would need to be ridiculously tall, especially as you move further from the equator. But hey, it’s a fun thought experiment!

Remember, rockets are a bit picky. They love the equator, and while a hill might woo them a little, there’s nothing like that equatorial charm. Until next time, keep looking up!

(Note: This is a simplified explanation and doesn’t account for many other factors that influence rocket launches, such as aerodynamics, temperature, and more. Always consult with a rocket scientist before building your hill! ⛰)