A Chinese servicing spacecraft has pumped liquid propellant into one of the satellites of China’s BeiDou navigation system in high Earth orbit. Interesting Engineering reports that the operation took place back in February, though the details are only now coming to light.
Based on the published data, the tanker delivered storable chemical propellant rather than cryogenic fuels such as liquid hydrogen or oxygen. That choice makes life easier for spacecraft. Storable propellants stay liquid for years without complex cooling systems.
Satellites burn propellant for more than just reaching their working orbit. They also need it to correct their trajectory, hold position and orientation, and perform avoidance maneuvers. So a satellite with perfectly healthy electronics, solar panels and other systems can still stop doing its job once the tank runs dry. China has already shown it can upgrade BeiDou without replacing hardware: in August, it modernized all 50 of the system’s satellites in orbit without interrupting navigation.
On-orbit refueling solves the propellant problem without launching a new satellite, but it demands precise maneuvering. The servicer first has to find its target on its own, match speed and trajectory, close in and dock. Then the propellant must be transferred in microgravity without leaks and without disturbing the orientation of either spacecraft.
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If the technology keeps maturing, it could extend the lives of satellites whose main hardware still works but whose fuel is running out. Down the line, a single tanker could service several spacecraft, which could cut the cost of maintaining large constellations.
BeiDou is China’s global satellite navigation system, comparable in purpose to America’s GPS, Europe’s Galileo and Russia’s GLONASS. It serves both civilian navigation and the military. Its satellites carry more than navigation signals, too: in February, China launched an SMS service that runs through them. Satellite messaging on phones has already helped rescue a traveler caught in a landslide in Nepal.
