> US intelligence, surveillance and reconnaissance (ISR) satellites orbit at about 800 km (500 mi) high and move at 7.5 km/s (4.7 mi/s), so a Chinese Intermediate-range ballistic missile would need to compensate for 1350 km (840 mi) of movement in the three minutes it takes to boost to that altitude. Even if an ISR satellite is knocked out, the US possesses an extensive array of manned and unmanned ISR aircraft that could perform missions at standoff ranges from Chinese land-based air defences, making them somewhat higher priority targets that would consume fewer resources to better engage.
> The Global Positioning System and communications satellites orbit at higher altitudes of 20000 km (12000 mi) and 36000 km (22000 mi) respectively, putting them out of range of solid-fuelled Intercontinental ballistic missiles. Liquid-fuelled space launch vehicles could reach those altitudes, but they are more time-consuming to launch and could be attacked on the ground before being able to launch in rapid succession. The constellation of 30 GPS satellites provides redundancy where at least four satellites can be received in six orbital planes at any one time, so an attacker would need to disable at least six satellites to disrupt the network.
