The key quantity allowing a satellite to sustain orbit without ongoing thrust is:

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1. **Orbit balance:** A satellite stays in orbit when gravity pulls it inward and its sideways speed keeps it from falling.

2. Set gravitational force equal to centripetal need: $\frac{GMm}{r^{2}}=\frac{mv^{2}}{r}$.

3. Mass $m$ cancels, giving $v=\sqrt{\dfrac{GM}{r}}$, so the required speed depends on $G,M,r$ not the satellite mass.

4. Atmospheric drag or thrust change motion, but the key quantity that lets a satellite remain in orbit without thrust is its orbital velocity.

FINAL_ANSWER: c

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