[Physics] How does the decaying orbit of a satellite maintain its orbit as it descends, as opposed to crashing straight back to Earth

orbital-motionsatellitesspace

I understand that as a satellite in low-Earth orbit experiences atmospheric drag, it is slowed down. Therefore it no longer has the velocity to maintain its orbit at that point, as per the orbital velocity formula.

However, what I don't understand is, how does it maintain an orbit as it descends? The orbital velocity increases as the orbital radius decreases, meaning it needs a higher linear orbital velocity, not a lower one, to maintain its orbit. The drag also increases as the satellite descends.

I'd have thought that it simply crashes straight down.

Best Answer

Consider this an orbit of a satellite.

Angular momentum $\vec{L}=\vec{r} \times \vec{p}$ where $\vec{r}$ and $\vec{p}$ are vectors.

angmom

Angular momentum is a conserved quantity. In a satellite with a decaying orbit due to atmospheric drag , as $r$ becomes smaller by the loss of energy, conservation of angular momentum means that $p$ has to increase and therefor the velocity, since $\vec{p}=m \vec{v}$.

It cannot fall straight down because conservation of angular momentum would be violated.

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