How Do Satellites Stay in Orbit?

Orbit is controlled falling

LEO, MEO, and GEO

How satellites get to orbit

import math

mu = 3.986004418e14  # Earth's gravitational parameter, m^3/s^2
r = 6_371_000 + 400_000
v = math.sqrt(mu / r)
print(round(v, 1), 'm/s')

Keeping satellites alive in orbit

note

Orbital maintenance

Satellites need periodic corrections because real space is messy.

Main disturbances

Atmospheric drag in low Earth orbit, solar radiation pressure, lunar and solar gravity, and Earth’s nonuniform gravity field.

Real example

The International Space Station, at roughly 420 km altitude, regularly needs reboosts to stay in orbit.

illustration

diagram

note

Why fuel matters

Every correction uses propellant. When fuel runs out, a satellite may drift, fail to keep its slot, or be moved to a disposal orbit.

Space debris and orbital cleanup

Transcript

Welcome to Slate. Today we're looking at How Do Satellites Stay in Orbit?. We'll cover Why orbiting is really just falling and missing the ground, LEO, MEO, GEO: different altitudes for different purposes, How satellites are launched, positioned, and maintained, and Space debris: the growing problem of orbital junk. Let's get into it.

Picture a ball thrown sideways from a mountain. Throw it faster, and it lands farther away. Throw it fast enough, and Earth curves away beneath it as the ball falls. That is orbit. A satellite is always falling toward Earth, but it keeps missing because it has enough sideways speed. The diagram shows this balance as gravity pulling inward while motion carries the craft forward. Isaac Newton described this idea in the 1680s. His cannonball thought experiment is still the cleanest way to see it. A low Earth orbit satellite moves about 7.8 kilometers per second. At that speed, it circles Earth in about 90 minutes. Gravity at 400 kilometers up is still strong, about 90 percent of the surface value, so orbit is not a place with weak gravity. It is a place where the satellite is moving fast enough that falling becomes a loop. Think of a car on a track banked just right. The track keeps it from sliding inward. In orbit, gravity is the track. If the speed is too low, the satellite drops. If the speed is too high, it escapes. The exact path depends on altitude, speed, and direction, which is why orbital mechanics is really the art of balancing motion and gravity.

Different missions need different orbital neighborhoods. Low Earth orbit, or L-E-O, sits roughly from 160 to 2,000 kilometers above Earth. It is close, so communication delay is small and images are sharp. The International Space Station orbits at about 420 kilometers. Earth observation satellites, many internet constellations, and crewed missions use this region. Medium Earth orbit, or M-E-O, is farther out, around 2,000 to 35,786 kilometers. The best-known residents are navigation satellites like G-P-S, which orbit at about 20,200 kilometers. They trade a little more delay for broad coverage and stable timing. Geostationary orbit, or G-E-O, sits at 35,786 kilometers above the equator. There a satellite circles Earth once every sidereal day, 23 hours, 56 minutes, and 4 seconds, so it appears fixed over one point on the ground. That is why weather satellites and many television relays live there. Here’s the key tradeoff: lower orbits give faster links and finer detail, but they move quickly across the sky and need constellations. Higher orbits cover more ground with fewer satellites, but signals take longer to travel. The map-like diagram makes this easy to compare.

A rocket does not fly a satellite to orbit the way a plane flies to another city. It builds speed in stages. First, it climbs through the thick lower atmosphere, where drag is intense. Then it pitches over to build horizontal velocity. That sideways speed is the real prize. A satellite in low Earth orbit needs about 7.8 km/s of orbital speed, and the rocket must also overcome gravity losses and air drag. The launch vehicle usually leaves the satellite in a transfer orbit, not the final one. From there, the satellite uses its own propulsion to circularize, raise altitude, or change plane. The diagram shows the sequence: launch, staging, coast, burn, and insertion. A common example is a geostationary satellite. Rockets often place it into a highly elliptical transfer orbit. The satellite then fires an apogee motor or electric thrusters near the high point to raise the low point and settle into GEO. This is like climbing a hill in steps rather than trying to jump straight to the top. Once in orbit, satellites do not stay perfectly placed on their own. Small nudges called station-keeping burns correct drift caused by lunar gravity, solar pressure, and Earth’s uneven gravity field. Without those corrections, a GEO satellite would slowly wander.

A satellite’s job is never finished after launch. It must survive temperature swings, radiation, and the slow drag of the upper atmosphere. In low Earth orbit, the atmosphere is thin but not zero. At around 400 kilometers, drag is enough to pull the International Space Station downward, so it needs regular reboosts. The station loses altitude over time and must be pushed back up by visiting spacecraft or its own propulsion system. In even lower orbits, satellites can reenter naturally in weeks to years if they are not raised. Higher up, drag is tiny, so other forces matter more. Sunlight exerts pressure, and the Moon and Sun tug on the orbit. Earth’s gravity is not perfectly round either; it bulges at the equator, which shifts orbital paths. The visual here helps show that “stable” does not mean “unchanging.” Engineers track position with radar, optical telescopes, and onboard GPS receivers. They plan maneuvers to avoid collisions and to keep antennas, solar panels, and sensors pointed correctly. A satellite is a machine in a very precise dance. It needs fuel, software, and constant navigation to keep the steps clean.

Every satellite, rocket stage, paint chip, and fragment of metal can become debris. In orbit, even a small object is dangerous because impact speed is enormous. Two objects meeting head-on in low Earth orbit can strike at about 10 kilometers per second or more. At that speed, a one-centimeter fragment can disable a spacecraft. The debris population grew quickly after decades of launches, explosions, and collisions. The 2009 collision between the active Iridium 33 satellite and the defunct Russian satellite Cosmos 2251 showed how one crash can create thousands of fragments. The 2007 Chinese anti-satellite test added many more. Here’s the problem: more debris raises the chance of more collisions, and more collisions create more debris. That loop is called the Kessler syndrome, named after NASA scientist Donald J. Kessler, who described it in 1978. Engineers reduce the risk with passivation, which removes leftover energy from tanks and batteries, with controlled reentry for low-orbit satellites, and with graveyard orbits for GEO spacecraft. The final diagram shows the chain clearly: launch, operations, failure, fragments, and future collision risk. Keeping orbit usable is now part of satellite design, not an afterthought.