Gravity is weaker farther from Earth, so a higher satellite needs less sideways speed to keep curving around the planet — and it also has a longer loop to travel.
NASA states the rule plainly: the higher a satellite's orbit, the slower it moves. Closer to Earth the pull of gravity is stronger, so a satellite there must move faster to avoid being pulled down.
This surprises many people, because rockets work hard to get satellites high. Getting high takes energy. Staying high takes less speed.
A higher satellite is slower and has a bigger circle to go round. Both stretch the time for one orbit.
The geostationary circle is about six times bigger than the ISS's, yet its period is about 15 times longer.
Measure both from Earth's centre. The ISS is about 6,778 km out; a geostationary satellite is about 42,164 km out. That is 6.2 times farther.
Here is the strange part. To raise an orbit, a satellite fires its thruster forward along its direction of travel. NASA notes that such a boost increases the altitude — and that slows the orbital speed.
So a satellite that speeds up briefly ends up higher and slower. Raising an orbit this way, step by step, is called orbit-raising.
Compare the Velocity card for a NavIC satellite, tens of thousands of kilometres up, with the ISS tracker's 7.66 km/s — the higher satellite is far slower. Open the NavIC tracker
Two power laws do all the work. For a circular orbit of radius r:
v = √(GM / r) so v ∝ r^(−1/2) T = 2πr / v = 2π √(r³ / GM) so T ∝ r^(3/2)
Take the ISS (r₁ = 6,778 km, v₁ = 7.67 km/s, T₁ = 92.6 min) and a geostationary satellite (r₂ = 42,164 km). The ratio r₂/r₁ = 6.221.
Why does a faster satellite end up slower after a forward burn? Look at energy. The specific orbital energy (per kilogram) of a circular orbit is
ε = v²/2 − GM/r = −GM / (2r)
It is negative and gets closer to zero as r grows, so higher orbits hold more energy even though their kinetic part, GM/(2r), is smaller. A forward burn adds energy; the satellite rises; on the way up it trades kinetic energy for potential energy and arrives slower than it started.
Numbers for the ISS: ε = −398,600 ÷ 13,556 ≈ −29.4 km²/s² (MJ/kg). For geostationary: ε = −398,600 ÷ 84,328 ≈ −4.7 MJ/kg. Moving one kilogram from the first circle to the second needs about 24.7 MJ of orbital energy, even though the final speed is less than half the initial speed.
This is also why, in orbital rendezvous, a spacecraft trying to catch one ahead of it drops to a lower, faster orbit rather than simply speeding up.
Speed falls by √4 = 2, so it halves. The period grows by 4^(3/2) = 8 times.
A higher orbit has more total energy. The rocket must lift the satellite against gravity, and that potential energy outweighs the kinetic energy saved by the lower orbital speed.
The one at 400 km. The ISS takes about 92 minutes, while Aqua at about 705 km takes about 99 minutes.