How do satellites stay in orbit for years without falling?

In one line

The rule

An object in orbit moves forward fast enough that as it falls towards the Earth, the ground curves away beneath it at the same rate, so it keeps missing the Earth and stays in motion around it.

The main formula is: F = G × (M × m) / r²

• F: gravitational force
• G: universal gravitational constant
• M: mass of Earth
• m: mass of satellite
• r: distance from Earth's center

Let's understand it simply

Imagine you are spinning a stone tied to a string above your head. The stone wants to fly away, but the string pulls it in. If you cut the string, the stone flies off in a straight line. Now, think of a satellite as the stone, and Earth's gravity as the string. The satellite is moving sideways very fast. Gravity keeps pulling it towards the Earth, but because the Earth is round, the satellite keeps missing it and goes around and around.

Try this: Roll a football on the ground. It goes straight. But if the ground curved downwards, the ball would keep falling but never hit the bottom—it would keep going around. That’s what happens in space!

How it works

1. A satellite is launched high above the Earth's surface.
2. It is given a very high sideways speed (about 28,000 km/h for low Earth orbit).
3. Gravity pulls the satellite towards the Earth.
4. Because of its speed, as it falls, the Earth curves away beneath it.
5. The satellite keeps falling, but never reaches the ground—it keeps circling the Earth.
6. With no air in space to slow it down, it can keep going for years.

The story behind it

The idea of satellites orbiting the Earth comes from Isaac Newton. In the late 1600s, he imagined firing a cannonball from a high mountain. If it was fast enough, it would keep falling around the Earth instead of hitting the ground. The first real satellite, Sputnik 1, was launched by the Soviet Union in 1957. It proved that objects could stay in orbit for long periods.

Where you see it in real life

• TV satellites: They orbit the Earth, sending signals so you can watch cricket matches live.
• Weather satellites: They circle the Earth, taking photos to help predict the monsoon.
• GPS satellites: They orbit high above, helping your phone show your location in the market.
• ISRO satellites: Used for communication, mapping, and even Chandrayaan missions to the Moon.
• Space stations: Like the International Space Station, where astronauts live and work, orbiting the Earth.
• Spy satellites: Used by countries to watch borders and oceans.

Why it matters

• Satellites help us with communication, TV, and internet.
• They help farmers know about rain and weather.
• They are used in navigation (Google Maps, Ola, Uber).
• Many science and engineering jobs need you to understand orbits.
• Later chapters in physics (gravity, motion, centripetal force) build on this idea.

Worked example

Let’s see how fast a satellite must go to stay in low Earth orbit (about 300 km above the ground):

Given:  r = 6,700 km (Earth's radius + 300 km),  G = 6.67 × 10⁻¹¹ N·m²/kg²,  M = 5.97 × 10²⁴ kg
Step 1: Use the formula for orbital speed:  v = √(G × M / r)
Step 2: Plug in the numbers: v = √(6.67 × 10⁻¹¹ × 5.97 × 10²⁴ / 6.7 × 10⁶)
Step 3: Calculate inside the square root: (6.67 × 10⁻¹¹ × 5.97 × 10²⁴) ≈ 3.985 × 10¹⁴
Step 4: Divide by r: 3.985 × 10¹⁴ / 6.7 × 10⁶ ≈ 5.95 × 10⁷
Step 5: Take the square root: √(5.95 × 10⁷) ≈ 7,715 m/s (about 27,774 km/h)
Answer: The satellite must move at about 7.7 km/s to stay in orbit.

Common mistakes

• Thinking satellites are above gravity: They are always under Earth's gravity; gravity keeps them in orbit.
• Believing satellites need engines to keep moving: Once in orbit, no engine is needed—no air means no friction to slow them down.
• Assuming satellites can stay in any orbit: If they go too slow, they fall back; too fast, they escape into space.
• Forgetting about air drag: Low satellites can lose speed due to thin air and fall after years.

Remember it

A satellite stays in orbit by moving fast enough sideways so that as it falls, it keeps missing the Earth—like running around a well without falling in.