It depends on height: the ISS at about 400 km moves at roughly 7.7 km per second, while a geostationary satellite 36,000 km up moves at about 3.1 km per second.
A satellite cannot pick any speed it likes. For a circular orbit, the height decides the speed. Lower means faster. Higher means slower.
The numbers are large. NASA gives the speed of the International Space Station as about 17,500 miles per hour — roughly 28,000 km/h. At that pace it would cover a 100-metre race track in about one-eightieth of a second.
Satellites a few hundred kilometres up, in low Earth orbit, all travel at about 7.5 to 7.8 km per second. This includes the ISS and India's Earth-imaging satellites.
That speed lets them circle the planet in about an hour and a half. NASA says the ISS makes about 16 orbits in 24 hours.
ISRO gives Cartosat-3's mean altitude as 509 km, with an inclination of 97.5°. To find its speed:
The number 398,600 is Earth's GM — its mass multiplied by the gravitational constant — in km³/s², from NASA's Earth Fact Sheet.
Geostationary satellites sit about 36,000 km above the equator (NASA). Up there, Earth's pull is far weaker, so the speed needed is only about 3.1 km per second. They take 23 hours, 56 minutes and 4 seconds per orbit — the same time Earth takes to spin once — so they appear to hang still over one spot.
On the tracker, a satellite's estimated speed is computed from its public orbital data, the same way as in the example above.
The Velocity card shows the station's estimated speed in km/s; compare it with the 7.67 km/s worked out for a 400 km circular orbit. Open the ISS tracker
For a circular orbit, v = √(GM / r). For any orbit — circle or ellipse — the vis-viva equation gives the speed at distance r:
v² = GM (2/r − 1/a)
where a is the semi-major axis (half the long axis of the ellipse). For a circle, r = a and it reduces to v = √(GM/r).
Circular examples (GM = 398,600 km³/s², equatorial radius 6,378 km):
An elliptical example from India: ISRO's LVM3 placed Chandrayaan-3 in a parking orbit of about 170 × 36,500 km. In distances from Earth's centre, perigee r_p = 6,548 km and apogee r_a = 42,878 km, so a = (6,548 + 42,878) ÷ 2 = 24,713 km.
The same spacecraft moves more than six times faster at the low point than at the high point. A cross-check: r_p × v_p = 6,548 × 10.28 ≈ 67,300 and r_a × v_a = 42,878 × 1.57 ≈ 67,300 — equal, as conservation of angular momentum (Kepler's second law) demands.
Their distances from Earth's centre differ only a little (around 6,700–7,000 km), and orbital speed depends on √(GM/r), so their speeds all fall near 7.5–7.8 km/s.
r = 6,887 km, so v = √(398,600 ÷ 6,887) ≈ 7.61 km/s, about 27,400 km/h.
At perigee, its closest point to Earth. It moves slowest at apogee.