# How do engineers measure satellite drag, and how do they track it over time?

I’ve been slowly getting myself familiar with astrodynamics and understanding satellite orbits. I’m familiarizing myself with the concept of drag experienced by the satellites. I am curious about how do GNC teams measure it and then respond to it?

Specifically:

• Do gnc teams / astrodynamicists monitor drag on their missions continuously? If so, how do they monitor it?
• How does the change in drag get tracked by the team? For example, drag today in comparison to what it was same time yesterday?
• If there is a sudden change in drag due to changes in the atmosphere, is there a certain limit that the engineer waits until acting on the information? e.g. if there is a space weather event (like during spacex launch in 2022), where there is a loss in altitude, do they wait until the event passes before acting or will they start boosting the satellite as soon as they see the drag has changed significantly? Or do they take preemptive action and bump it up even before the drag has changed?
• I assume that there is a whole classification of phenomena, accumulated experience and instructions, according to which specialists act in this or that case. If these are atmospheric changes (by the Sun, the magnetic field, or something else), then predictive models can probably be used that estimate the main forces acting on the spacecraft.
– ayr
Commented Jun 18, 2023 at 5:48
• Surely there are some databases on the largest and most risky objects in the atmosphere (garbage or something else) that a spacecraft can collide with, and their orbits are most likely also modeled. Ideally, there should be an additional system (controls + sensors) that will allow the spacecraft to be corrected in the event of complexly modeled or unpredictable phenomena.
– ayr
Commented Jun 18, 2023 at 5:48
• This is a really interesting proposition - though modeling of the thermosphere and its reaction to solar activity combined with aggregate tracking data and modeling of satellites in similar-altitude orbits, and a given satellite's current attitude, one could presumably pick up a change in the drag coefficient of a given satellite over time if it was pretty large. I wouldn't be surprised if that was actually done in some cases - especially for high-value satellites in LEO (e.g. spy, crewed stations...)
– uhoh
Commented Jun 18, 2023 at 6:55