Orbit Calculator: Speed and Time Around Earth at Any Height

How the orbit calculator works

An orbit is a kind of endless fall. A satellite is always being pulled towards Earth, but it is also moving sideways so fast that the ground curves away beneath it as quickly as it drops. The result is a path that keeps going round instead of coming down.

The calculator adds your chosen height to Earth's mean radius of 6,371 km to find the distance from Earth's centre. It then works out the one speed at which gravity's pull at that distance bends the path into a perfect circle. Divide the length of that circle by the speed and you have the time for one orbit. Divide a day by that time and you have orbits per day.

Why higher orbits are slower

Gravity weakens with distance. Twice as far from Earth's centre, the pull is only a quarter as strong, so a satellite needs less speed to stay on a circular path. That is why the International Space Station, about 400 km up, races along at about 7.7 km/s, while a geostationary satellite moves at less than half that pace.

Higher orbits are also longer journeys. A slower speed on a bigger circle adds up quickly: the station completes a lap in roughly 92 minutes, navigation satellites around 20,000 km up take about half a day, and a geostationary satellite takes 23 hours and 56 minutes. Try sliding from the lowest setting to the highest and watch the orbit time stretch.

What each preset orbit is used for

The four presets show some of the busiest neighbourhoods around Earth, each chosen because the height suits a particular job.

• International Space Station, about 400 km: a laboratory in low Earth orbit, continuously crewed since November 2000 and circling about 16 times a day.
• Earth observation, about 700 km: satellites that photograph and measure the planet, helping with farming, forests, water, weather, maps and disaster response.
• Satellite navigation, about 20,200 km: in medium Earth orbit, each satellite circles about twice a day, sending precise timing signals that phones, ships and tractors use to work out where they are.
• Geostationary, 35,786 km: above the equator, one orbit takes as long as Earth takes to spin once, so the satellite appears fixed in the sky. Weather satellites and satellite television dishes rely on this.

What the calculator leaves out

The calculator keeps things simple on purpose, so it is best read as a very good first guide rather than a planning tool for real satellites. Three things in particular make real orbits messier than a neat circle.

• Air drag: in very low orbits, a thin trace of atmosphere slowly saps a satellite's speed, so it sinks unless it is boosted. The International Space Station needs regular boosts for this reason.
• Elliptical orbits: many orbits are stretched ovals, and a satellite moves fastest at its closest point to Earth and slowest at its farthest.
• Earth's shape: the planet bulges slightly at the equator, and that uneven pull, along with tugs from the Moon and the Sun, gradually shifts orbits over time.

Orbits as infrastructure

Seen from the ground, satellites behave less like gadgets and more like roads, power lines or water pipes. They are built once, relied on every day and mostly noticed only when they are missing. The guide to satellites and orbits shows how much of daily life, from forecasts to maps, depends on them.

That is also why space interests long-term investors. Satellites take years to design, build and launch, they carry technical uncertainty, and they need licences and careful planning to share orbits safely. The plain-English guide to the future of investing in space looks at how investors think about these long time horizons, and the space economy explorer maps where satellites fit among everything else.

Keeping busy orbits tidy is part of the picture too. Software that predicts close approaches between satellites and plans small avoiding moves is one of the places where AI meets the space economy.

Nicole Junkermann's perspective

Nicole Junkermann has long argued that patient capital matters for deep technology, and orbits are a good illustration. A constellation of satellites may take many years to come together, yet once it works it can quietly support farmers, forecasters and emergency teams for a long time.

In her view, the systems most worth building are the ones people can rely on without thinking about them. As she puts it on her website, "I invest in infrastructure that builds trust". She tends to ask the same question of satellites as of AI: who on the ground benefits, and can they trust what it tells them?

To keep exploring, try the signal delay calculator to see how long messages take to cross space, or work out your weight and age on other planets.