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We all know spacecraft reentry causes extreme heat - plasma, ablator, flaming trail, all that jazz. I'd like to know just what level of heat are we dealing with - could someone throw some numbers, like what's the maximum temperature occurring in the air or on the heatshield surface, or in the hottest place during reentry generally? Just how many Celcius degrees are we dealing with?

SF.
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    Earth only, and crewed spacecraft only? For example the galileo probe that entered Jupiter's atmosphere survived outrageous temperatures and accelerations.... – Andy Apr 28 '16 at 11:20
  • @Andy: The best answer would contain an overview of these. – SF. Apr 28 '16 at 15:14
  • (but yes, Earth only, not necessarily manned.) – SF. Apr 28 '16 at 19:37
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    At atmospheric re-entry speeds, it may not be useful to talk in terms of a single temperature. Non-equilibrium effects in the gas means there may be a translational temperature (what we normally think of as a temperature) as well as vibrational and electronic temperatures, all of which may be different due to the high speeds, high energies, and rarefied air. See this page for a discussion of the different models used. – tpg2114 Apr 28 '16 at 19:39
  • @tpg2114: I was asking this, thinking of non-ablative heat shielding for cargo that is relatively immune to heat (non-burnable raw materials). It seems in all cases tungsten would withstand the reentry. – SF. Apr 29 '16 at 07:50
  • It's not about withstanding the reentry - the problem is protecting the contents. Making a heatshield that survives a few thousand degrees K is easy, but that's not going to help the weak meatbag inside who frowns at mere 300 °K :D The reason we use ablative shielding is because as the shield ablates, it takes the heat with itself. It's the same as cooling something with ice, which really is an low-temperature ablative heatshield :D – Luaan Apr 29 '16 at 09:07
  • @Luaan: I'm well aware of that. I was thinking about raw metals mined from asteroids. If the content melts, no biggie, it will solidify after splashdown. – SF. Apr 29 '16 at 09:11
  • It's still a big deal - it's the difference between getting the pure stuff ready to work and getting ore that needs to be refined. But in any case, there's little reason you'd care I guess. In the end, it's all about your descent profile - if you don't need to lose lots of speed quickly, you don't need "stressful" reentry (though there's limits to how simple unpowered objects can reenter). And don't forget that most stuff changes density with temperature - you wouldn't want your molten metal exploding out of the "spaceship" :D – Luaan Apr 29 '16 at 09:27
  • @Luaan: Considering the delta-V, plus abundance of solar and other energy in space, I believe bringing ore to Earth is a misguided approach. It should be refined in space. OTOH yes, volume changes certainly are a concern, as is structural durability at the moment of impact into sea. – SF. Apr 29 '16 at 09:50
  • If you're talking about landing unprotected raw materials, bear in mind a lot of large meteors break up at altitude from deceleration and possibly thermal stress. So we can't just drop those from orbit. (May be relevant if you're talking about landing raw blocks of rock or anything that's not a processed ingot.) – Andy Apr 29 '16 at 11:58
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    @Andy: I'm exactly thinking about what -minimal- protection would be needed so that it wouldn't happen. – SF. Apr 29 '16 at 12:10
  • Oh, of course. But that's what I'm talking about - as far as we can tell, asteroids are pretty much already refined - the impurities found in ore on Earth are much rarer in space (most notably, oxygen and sulphur). – Luaan Apr 29 '16 at 16:29
  • (Related Topic [http://space.stackexchange.com/questions/15013/requesting-an-in-depth-explanation-of-heat-created-during-atmospheric-reentry/15015?noredirect=1#comment39479_15015]) – Eliot G York Apr 30 '16 at 04:41

5 Answers5

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The Stardust sample return probe had an interesting re-entry to Earth's atmosphere. Returning from a solar orbit the maximum deceleration has been reported as 34g.

Maximum temperatures are estimated at around 3,200 Kelvin or 2900 degrees C at the surface. It should be noted that the entry probe had no re-entry data recording so this measurement was estimated from spectroscopic examination of the heat shield as it descended, which must have been an interesting day's work.

The spectroscopic measurement was taken through the glowing plasma surrounding it, and the range of the measurement will mean that the temperature is an average over the whole shield. As a result this doesn't represent a direct measurement from the hottest point on the heat shield, but it's interesting reading nonetheless.

Andy
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The Space Shuttle thermal protection system is rated for temperatures of up to 1510 °C.
There's a boundary layer of air just above the TPS, outside that temperatures can reach 5500 °C. NASA used HYTHIRM to make thermal images of the orbiter during reentry:

thermal image of STS, showing temperatures of up to 1650 °C on the nose and wing leading edges

Hobbes
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    The shuttle has a really reentry low temperature compare to other spacecrafts. – Antzi Apr 28 '16 at 11:41
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    @Antzi Yes, because it has a huge surface area. Remember, reentry is all about losing speed, it's not inherent to space travel. Slamming into the atmosphere is just still the cheapest way of losing orbital speed. Since the shuttle has a huge surface area, it can afford a less drastic approach. At the same time, it doesn't use ablative shielding, so it must have lower reentry temperatures - the heat is not disposed of, just "stored", and that limits the capacity (compare cooling with liquid water with cooling via evaporation / ice melting). It's all about the reusability. – Luaan Apr 29 '16 at 09:21
  • It also uses its plane-like characteristics to stay up high for longer, reducing the heat flux due to the lower air density. This is not unique to the shuttle (the soyuz does the same thing, to reduce G-forces), but it has a better L/D ratio than capsules. – AI0867 Jan 13 '20 at 21:46
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This article says the recent Orion test experienced 2200 deg C, and this old Apollo fact sheet says 5000 deg F (2760 deg C) on Apollo 4 (a test at lunar return speed).

Organic Marble
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CFD simulations show the air in the bow shock of the stardust probe reached temperatures of around 50,000°K at 71km, falling to 10,000°K at 51km (thin red line). It must be remembered that the air is extremely thin at these altitudes, fortunately resulting in poor heat transfer to the craft.

The surface temperature was much lower, as mentioned in Andy's answer, due to ablative cooling. The surface is designed to burn away, so the surface temperature largely depends on the decomposition temperature of the ablative material.

uhoh
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Level River St
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  • Good figures that remind us our notion of "temperature" (and it's extremes) deviate from our usual senses in more exotic environments. And maybe to subsequently ask about "peak heating" or "peak heat flux" :) – Nick T May 13 '16 at 03:43
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    @uhoh thanks for the edit, but the use of the degree symbol with Kelvin has been incorrect since 1967 https://physics.nist.gov/cuu/Units/kelvin.html https://en.wikipedia.org/wiki/Kelvin The edit is inconsequential so I will not bother to roll it back. – Level River St Aug 26 '17 at 09:40
  • Wow, you are right! I needed the commas to see how big the numbers were because I was born before the degrees symbol for Kelvin was incorrect and the SE font is so small :) I should have stopped after that. It makes sense, K is a unit all by itself so it doesn't need the ° helper. Thanks for the information! – uhoh Aug 26 '17 at 10:20
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"The most difficult atmospheric entry ever attempted" was by the Galileo Probe. Temperature could refer to the plasma temperature or heat-shield temperature, but the latter generally caps out because a) nothing will remain solid past ~4000 °C, and b) many heat shields are designed to ablate, vaporizing in order to absorb some of the thermal energy.

Anyways, the Galileo Probe had to endure a 230-250 g deceleration. Citations claim that it endured "15,500 °C", which I don't quite understand given the above, but it did go on a rapid weight-loss program, shedding 80 kg of mass in about 2 minutes. Some other stats visible on the first page of this pay-walled paper (full paper available through Marcia McNutt's favorite website, though most of it is technical details about how they measured the ever-decreasing thickness of the heat shield) include:

  • 30 kW/cm2 heat flux
    • "300,000 suns" (300k × the solar insolation at Earth's surface)
  • 300 kJ/cm2 heat load
  • Entry speed of Mach 50 (47.4 km/s)
Nick T
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