Bite the orbit

Bite the orbit
Astronaut during a spacewalk.


  • How do Satellites orbit the planet?
  • How do astronauts experience zero-g?
  • How Newton’s one thought experiment led to the orbits we have today?
  • This week in Invisible History: Howe vs Singer. Domain: Household inventions.

It was 2009, and I had gotten a computer with an internet connection in my house for the first time. The first thing that I googled that time was “space station.” Space always fascinated me. I used to wait for National geographic magazines to be delivered at our doorsteps. I used to read a lot of these magazines and try to make sense of such marvels by humans. One of such wonders is the international space station.

I went on youtube for the first time and saw Don Pettit in space doing various science experiments. It fascinated me. The weightlessness enthralled me, and I thought, how does he float in space in that station? I read that gravity pulls on all the objects with the same acceleration. Then why can’t I float and he could? This was counterintuitive to what I had read. So I did some digging, and my mind was blown. Let’s get into it.

Oh, gravity, thou art a heartless b*tch.

First things first, the international space station moves at a speed of 27000 kilometres per hour. In other words, it travels 7.67 km per second. So to understand how this works, let's talk about gravity. Gravity is what keeps us grounded to the earth. Simple? Well yeah, that's it. But ironically it also holds the satellites out there in their orbits. Gravity pulls on all the objects with the same acceleration. If you are at the sea level, then it pulls you at a rate of 9.81 m/s2. Now, as we increase the distance from the centre of the earth, the force of gravity decreases on us. This can be seen from the following equation.

F = (GxM1xM2)/r2

The m1 and m2 are the masses of the bodies in consideration
r is the distance between them
G is the gravitational constant.

Earth and Moon
The Moon orbiting the earth.

If we increase 'r' or the distance between us and the earth, the force exerted by gravity is decreased. This reduction is a factor of a square. So technically, if you climb a mountain, you will be lighter.

Newton’s brain

If we combine what we understand from the previous section and combine it with Newtonian mechanics, we can realise Newton's thought experiment. This classic experiment is concerned with the cannonball on a mountain top. We know if we shoot a cannonball off a cannon, it will follow a traditional arc trajectory. Similar to angry birds. Now imagine this cannon on an absurdly tall mountain, the ball will fall farther. This is because it has the curvature of the earth to pull down the other side of the planet. In addition to this, this ball will be lighter. (Due to the distance from the centre of the earth.) Now if this cannonball is shot to a speed of 8000 m/s, the ball will always have enough momentum to avoid earth while being pulled by the planet. Gravity will pull it back and slingshot it to the starting point. This is what an orbit is.

OrbitThe orbital speed with the distance from the centre.

And just like that, you have a satellite orbiting the earth. A satellite is technically anything that orbits the celestial body. For instance, the earth is a satellite of the sun, and the moon is a satellite of the earth. It's also important to note that: the lower your orbit, the faster you have to go to overcompensate for that increased gravity, which is precisely why the international space station has to travel at more than 27,000 kilometres per hour.

The zero-g

If you're paying close attention to Newton's cannonball thought experiment, you'll notice that I mentioned that the cannonball is still under the influence of earth's gravity. But if you've ever watched any footage inside the international space station, you'll notice that the astronauts are in what appears to be zero-g or zero gravity. If we do the math, then they are experiencing 91% of the gravitational force of what we experience here on the surface. So how do they float?

zero g
Zero-G plane working on the same concept of weightlessness to simulate ISS for trainers.

The answer is the same reason that the characters in the movie inception experience weightlessness when the van drives off of the bridge. When you're in free fall, your body feels weightless. This is because gravity is the only force acting on you, and there's no reaction force pushing in the opposite direction. And it's for this reason that Joseph Gordon Levitt's character could experience weightlessness.

Your Turn now

The curiosity of doing experiments in space and putting a satellite out there led to one megastructure that revolves around the earth 16 times a day. It revolves with ridiculous tangential speed and is home to around ten astronauts. They are carrying experiments to see how life can be hauled away from earth. Such can be used to see if we can colonise the moon or mars. Satellites like these are paving the way for human beings to inhabit other worlds. It really is the ultimate spacecraft until someone builds an even bigger one.

This week in Invisible history.

Last week's clue was exciting as many people guessed the answers nearly right. Out of all the people, only two gave the right answer. They are Shubham Jain (LinkedIn) and Bucketsu (Reddit.) Last week's clue was "The Submersible Turtle." This clue related to the first U.S. submarine built for wartime use, the American Turtle. On 7th September 1776, the American Turtle was used in New York harbour to attach explosives to the hull of the Eagle, Admiral Howe's flagship. Known as a "torpedo" the weapon was a cask with 150 lbs of black powder and a clockwork time fuse. Because it separated from the ship before it exploded, little damage was done. The submarine, just large enough for one occupant, was operated by Ezra Lee, turning a 24-in diameter two-bladed wooden propeller giving up to 3 knots speed. It was built by David Bushnell of Saybrook, Conn., who provided it with a rudder and a second propeller for vertical movement. Water taken in as ballast to submerge was expelled by hand-pump to resurface.

The Submersible Turtle
The Submersible turtle.

The clue for the next week is “Howe vs Singer,” and the domain is household inventions. If you guess the answer, you will guess the next week’s article. You can write the answers to me in the comment section or on social media. I have left the links down below. If you give the right answer, your name will be mentioned in the next week’s article.

Thank you for making it to the end of the article. I hope you enjoyed it and want to read more articles like this. If not, then let me know what should be improved. What do you think about the satellites and how they affected us? Let me know your thoughts on social media with links down below. Let’s stay curious and learn every day.

See you next Saturday!

  1. Reddit:r/theinvisiblegenius
  2. Instagram: @theinvisiblegenius
  3. Twitter: @notnitinchopra

Reference links

  1. How many satellites are orbiting the Earth in 2018? | Pixalytics Ltd
  2. International Space Station Facts and Figures | NASA
  3. 50th anniversary of first U.S. satellite launch celebrated
  4. Wayback Machine | On orbit elements


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