I was reading about the Galileo Probe, but suddenly my imagination struck an obstacle.

The probe was slowed from its arrival speed of about 47 kilometers per second to subsonic speed in less than two minutes. The rapid flight through the atmosphere heated the heat shield to around 15,500 °C. At the time, this was by far the most difficult atmospheric entry ever attempted; the probe entered at Mach 50 and had to withstand a peak deceleration of 228 g.

Excuse me?

... 47 kilometers per second... a peak deceleration of 228 g.

Holy smokes.

I'm having a difficult time imagining this, and I don't think these animations do the entry much justice. (Actually, the first one is rather nice, but the second does zero justice.) So, I'd like to make my own animation. It won't be nearly as pretty and artistic as those two (I'll use simple line graphics, maybe some sprites if I'm really feeling it), but it will help me visualize this thing's hilariously rapid journey.

To make a half-way decent, half-way realistic simulation of what happened, I'll need data in a form I can use, or in a form I can transform for use. I doubt that the probe was transmitting on its firey way down, but there must have been some way to infer its altitude or perhaps speed during entry, if it hadn't already stored that data during entry and transmitted it during its slow descent. (For example, we have its peak gee-load.) What I'm really looking for are altitude and speed (or gee-load) readings; a table or a list of relevant values I can plugin. If none exist, then maybe a way to infer them?

Do there exist data on the altitude and speed (or gee-load) of the Galileo Probe during and after its atmospheric entry into Jupiter?

  • 1
    $\begingroup$ ssd.jpl.nasa.gov/horizons.cgi#results recognizes the Galileo probe (as NAIF id -344) so you might be able to get something from there. I believe HORIZONS supports sub-second resolution, but, again, I was too lazy to research further. The results here will almost definitely be calculated, not measured. $\endgroup$
    – user7073
    Commented Dec 2, 2019 at 16:15

1 Answer 1


Data for planetary missions is stored in the Planetary Data System.

This has an entry for the Galileo probe. Within the data files for the tmospheric Structure Instrument (ASI), there's a file called accel.txt which describes several files that contain acceleration data.

Data in these files, e03z1.dat, e03z2.dat, e03an.dat, contain data
for all of the Entry sequence acceleration measurements. The data in
file asi_z1 contains all data from the primary axial sensor. The data
in file asi_z2 contains all data from the secondary axial sensor. The
data in file asi_an contains all data from the lateral sensors.

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    $\begingroup$ Wow, great! This can definitely help me. Should be easy to plug in the magnitude data and get a 3d graph of acceleration. Change in velocity and position should also be available with this. Resolution of the acceleration is submillimeter, which is better than what I was expecting. Knowing its altitude at the start of descent (data available probably somewhere) should help with a rough simulation. It'll be interesting to see what comes out of this, thank you. $\endgroup$
    – BMF
    Commented Dec 3, 2019 at 19:53
  • $\begingroup$ @BMFForMonica if there's some interesting result or cool plot you'd like to share, please feel free to post an additional answer! $\endgroup$
    – uhoh
    Commented Dec 4, 2019 at 4:47

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