GPS Orbits – Typical altitude of NAVSTAR satellites What is the normal (nominal) altitude of a GPS (NAVSTAR) satellite above Earth's surface?

Introduction / Context:
GPS satellites occupy medium Earth orbits (MEO), chosen to balance global coverage, signal strength, and orbital perturbations. Knowing their altitude supports link budget estimates and timing/geometry calculations in surveying.

Given Data / Assumptions:

• GPS (NAVSTAR) system.
• Nominal design orbit, not geostationary or LEO.

Concept / Approach:
GPS satellites orbit at a semi-major axis of ~26,560 km from Earth’s centre, corresponding to a nominal altitude of ~20,200 km above mean sea level, with 55° inclination and ~12-hour orbital period (sidereal).

Step-by-Step Solution:
Recall standard GPS altitude ≈ 20,200 km.Reject LEO (~400–1200 km) and GEO (~35,786 km) values.

Verification / Alternative check:
Period ~11 h 58 min, consistent with MEO altitude and constellation geometry.

Why Other Options Are Wrong:

• 16,200/24,400 km: not standard GPS altitudes.
• 36,100 km: close to GEO; GPS is not geostationary.
• 10,400 km: too low for NAVSTAR.

Common Pitfalls:
Confusing GLONASS, Galileo, or geostationary altitudes with GPS values.

Final Answer:
20,200 km