Satellites don’t Fly, They Fall: The Science of Keeping Objects in Orbit
In the midst of all the awe and wonder surrounding space travel, enthusiasts often ignore one of the greatest marvels of the industry — the underlying science that allows human-made objects to reach outer space and stay there.
Sci-fi movies also tend to sensationalise the earth exploration sphere, focusing more on fiction (that sells more tickets) than scientific principles to advance their plots further. How do satellites dock in Earth’s orbit instead of continuing to fly into outer space? Why don’t satellites fall back onto earth? How does a satellite safely dock with another if it’s travelling at such fast speeds?
How Satellites Reach Space and Stay There
Satellites depend largely on balancing speed and gravity to reach their desired orbit. In short, they maintain their position by locking into speeds that are fast enough to defeat the downward pull of gravity.
To reach outer space, a rocket (the vehicle that carries and drops off a satellite in space) must accelerate to at least 25,039 mph (40,320 kph) to completely escape Earth’s gravity. This amounts to moving at a speed of over 10,000 metres every second! It should be noted, however, that satellites need to maintain a balance in velocity so that they can orbit above the Earth. It is this very balance that prevents them from flying in a straight line off into space or falling back to Earth.
In order to achieve the above, they need to travel at a speed that will facilitate orbital velocity — the term used to describe the balance between gravity’s pull on the satellite and the inertia of the satellite’s motion (the satellite’s tendency to keep going).
A satellite orbiting closer to the Earth, for example, requires more velocity to resist the stronger gravitational pull. This considerably lower speed that satellites travel at is generally around the 17,000 mph (27,359 kph) mark, allowing them to orbit at an altitude of around 150 miles (242 kilometers) from the Earth’s surface.
When Two Satellites Meet
The term space rendezvous is used to describe the process whereby two spacecraft (one of which is often a space station) intentionally approach each other at a very close distance. This requires a precise match in orbital velocities and position vectors of the two objects, allowing for the entities to maintain safe distances.
A space rendezvous is often accompanied by the practice of docking, whereby both entities come into physical contact with each other to create a link. This is an extremely delicate and dangerous procedure with little room for error — due to the high speeds at which satellites travel.
SpaceX leveraged this process in the docking of the Dragon space capsule containing the SpaceChain blockchain hardware payload when it reached the International Space Station (ISS) in early December 2019. The first technological demonstration of blockchain hardware on the ISS, the payload will be used to demonstrate the receipt, authorisation, and retransmission of blockchain transactions.
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