Hi All

Gary kindly replied to my questions...

Adam asked some questions.

What would the temperature of Galileo's re-entry shockwave peaked at?

The shockwave temperature for the Galileo Probe ranged from the free stream
temperature (undisturbed Jupiter atmosphere) of 150 deg. Kelvin to the shock layer temperature of about 16,000 deg. Kelvin (Water melts at 273.15 deg. Kelvin). A temperature of 16,000 deg. Kelvin is hotter than the Solar photosphere and would vaporize anything, e.g. tungsten. The Galileo orbiter would have completely vaporized long before it reached that temperature.

[Main reason why I asked was to confirm that very fact. Tom Brosz linked to some idiotic ramblings about Galileo's RTGs causing Jupiter to detonate and I wanted to challenge the doom-sayer with some real facts. Like Pu238 not being fissile, hence not a fission-trigger for a fusion blast. But chiefly I compared the vapourisation of Galileo to the vapourisation of Shoemaker-Levy, and made the point that the Pu238 would be spread very far and wide.]

The peak deceleration for the Galileo Probe was 230 G. Had the Galileo orbiter not been vaporized, it would have been crushed.

[Forgot about that... what would the ambient pressure have been? The dynamic pressure would've been huge???]

The peak total unblocked heat flux for the Galileo probe was about 15 kilowatts/cm^2. The probe survived Jupiter entry because of its carbon phenolic heat shield. The outer layer of the heat shield outgassed thus keeping the hot shocklayer plasma away from the probe's outer surface. Also this same gas emitted from the heatshield's surface was mostly an opaque carbon gas that kept the shocklayer radiation from reaching the probe's outer surface. Consequently the probe's outer surface never got much hotter than 3500 deg. Kelvin.

[Wow! That's an amazing heat reduction. Makes me wonder if a dynamic carbon heat-shield wouldn't be possible for a photon drive [U238 plasma radiator temp ~ 25,000 - 50,000 K]]

After completing its mission, the Galileo Probe descended into the Jovian atmosphere which got hotter and hotter as the probe descended deeper (this is due to isentropic compression).

[Jupiter radiates heat too and has lots of cloud layers. I doubt its atmosphere is purely isentropic. If JIMO ever makes it off CAD screens we might get some real details on Jupiter's atmosphere...]

Eventually the ambient temperature of the atmosphere got so hot that the probe vaporized into monoatomic gas.

[Don't know. Doesn't the hydrogen liquefy before it gets that hot? Average density is pretty high down there too. But no doubt Galileo liquefied too...]

[snip...]

Needless to say, designing spacecraft to descend into Jupiter's atmosphere is one of the coolest things that a rocket scientist can do (and they actually pay us to do this as well!).

[I'd have to agree. That sounds so cool. Pity the Grand Tour missions never got launched - they would've been awesome.]

Adam