USA 4

USA 4 is an active satellite operated by United States, launched on 1984-08-28 from Vandenberg SFB, California. With over 42 years in orbit, it has far exceeded many satellites’ design lifetimes. It orbits in Medium Earth Orbit (MEO) at altitudes between 2,807 km and 37,515 km with an inclination of 63.0°. It travels at approximately 13,954 km/h (3.88 km/s), completing one full orbit every 11 hours 57 minutes — that’s roughly 2.01 orbits per day. Its orbital eccentricity of 0.6541 gives it a noticeably elliptical path, with significant altitude variation between perigee and apogee. It is part of the Geo Protected Plus constellation group. Orbital Radar tracks USA 4 in real time using the latest two-line element set (TLE) data, providing live position, altitude, speed and orbital path updated continuously.

USA 4 operates in Medium Earth Orbit (MEO), the region between LEO and GEO spanning roughly 2,000 to 35,786 km altitude. MEO is home to navigation constellations (GPS at ~20,200 km, Galileo at ~23,222 km, GLONASS at ~19,130 km) and some communications systems. The higher altitude gives each satellite a much larger ground footprint than LEO, meaning fewer satellites are needed for global coverage, but signal latency is higher and radiation exposure — particularly from the Van Allen belts — is a significant design challenge.