The world’s space agencies do not actively track defunct spacecraft — that is, spacecraft with dead radios — beyond
Earth orbit, though sometimes they can work out where they should be. The problem is, a spacecraft in solar
orbit is almost always too small to observe and things can happen that can change its course. For example, if it includes a pressure vessel — say, a propellant tank — that has not been intentionally depressurized, there’s a good chance it has by now burst or vented. That means it acted like a rocket and changed the spacecraft’s course. Sunlight, solar wind, and even peeling paint can nudge a spacecraft’s course over decades.
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