I want to get an idea of how long the falcon 9 rocket accelerates and at what g level. Ideally a plot of gs vs time. I see various statistics like specific impulse and thrust and weight, is there a way to calculate average accel from the basic rocket data? I suppose average thrust and weight gives you average accel...
2$\begingroup$ flightclub.io and reddit.com/r/spacex/comments/4e5qw5/… for simulations and reddit.com/r/spacex/comments/4e50mz/crs8_telemetry for captured real telemetry from the webcast. $\endgroup$– jkavalikApr 12, 2016 at 10:33
2$\begingroup$ Average thrust isn't actually very relevant, because each stage drops mass very rapidly as it burns fuel, so acceleration ramps up dramatically. $\endgroup$– Russell BorogoveApr 12, 2016 at 11:47
From the telemetry link mentioned by @jkavalik, someone posted an interesting graph:
The blue line here is the acceleration of the rocket. It ramps up as fuel is consumed. There's a dip from about 55 to 85 seconds where I believe the engines are throttled back in anticipation of "max Q", the point of highest aerodynamic stress. The acceleration then increases continuously until the first stage shuts down and separates. There's a few seconds of free fall before the second stage ignites, and it likewise ramps its acceleration up over time.
I'm not sure what the units are supposed to be; the data the creator was working from was given in kph rather than m/s. The Falcon 9 Manual says that full-weight payloads will take a maximum of 6g axial acceleration. so the peak of the blue line should be something under that, probably in the ballpark of 5g.
$\begingroup$ Note that 100 kph per second is 27.8 m/s^2, or 2.83 gees, and this Quora answer suggests it peaks at about 35 m/s^2 (3.6 gees). So I think the y-axis has to be in km per hour per second. Note that the force experienced by the payload also includes 1 gee for the Earth's gravity at zero acceleration, so the force would peak at 4.6 gees. $\endgroup$ May 11, 2018 at 20:35
$\begingroup$ Wouldn't the plot make more sense in ft/s^2? If you look at the dip after MECO, you'll see the acceleration gets close to the -32.17 you'd expect in those units. And if you look at the max acceleration, you'll also see that you get just over 3 * 32.17. Maybe I'm imagining things, but ft/s^2 is more common than km/hr/s, plus it's an actual standard unit of acceleration whereas km/hr/s is not. $\endgroup$– user36480Aug 31, 2020 at 4:54
1$\begingroup$ @JessRiedel, at the peak of the blue line the rocket is quite horizontal, therefore you have to add only a tiny fraction of gravity force to obtain axial acceleration sustained by the payload. $\endgroup$– gcirianiMar 30 at 2:07