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How would a U.S. Space Shuttle's atmospheric entry on Venus differ from reentry on Earth? Say there's a Space Shuttle in a low Venus orbit performing a (re-)entry burn. How would the following atmospheric entry and flight differ from the one on Earth, given the different composition and density of the Venerean atmosphere and the a bit lower gravity, as well as the acid rain? What impact would it have on the shuttle and, if something fails, on the crew?

  • I wonder how the atmospheric entry and in-atmosphere flight would be different from that of Earth down to Venus' 1 atm level (which is ~33 miles above the surface)
  • and how much lower into Venus' atmosphere a Space Shuttle could get before something fails and what would fail (first) and for what reason (extreme pressure/heat/weather?)

Note: a similar question could be asked on Mars but since both planets have an almost entirely carbon dioxide atmosphere the only major difference would be in their gravities. Other than that, down to Venus' 0.006 atm level the entry would be about the same as if a shuttle entered Mars' atmosphere.

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    $\begingroup$ Somewhere at about 5-10km heigh, where the external temperature grows to 100-200C, the electronics stops working. The loss of trajectory control makes the flight controlled only by the aerodynamical forces. Fortunately, there the atmosphere is already enough dense to stabilize it, and at that point, it is already enough slow to remain in a single piece. I think it would arrive in a single piece. As the atmosphere becomes more and more dense, its terminal velocity might be enough slow to even survive the splashdown. Of course at this point, the astronauts in it already faced a painful death. $\endgroup$
    – peterh
    Commented Dec 14, 2020 at 13:17
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    $\begingroup$ The remaining nitrogen tetroxide fuel of the orbital maneuvering engines would likely explode. It will be a glowing wreck. $\endgroup$
    – peterh
    Commented Dec 14, 2020 at 13:23
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    $\begingroup$ @CarlWitthoft Aha, then it will be a glowing wreck with empty OMS fuel tanks. Glow will happen because the 400C surface temperature is enough for things to glow. $\endgroup$
    – peterh
    Commented Dec 14, 2020 at 13:56
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    $\begingroup$ @peterh is right about the cooling but not the stabilization. The orbiter was fly-by-wire; as soon as the cooling and the flight control system failed it would tumble and break up. If the crew wasn't killed by the lack of cooling they would be by the breakup. $\endgroup$
    – Organic Marble
    Commented Dec 14, 2020 at 14:12
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    $\begingroup$ Adding this as half-comment half-prompt to read some great science comedy. No answer on flight on Venus is complete without referencing Randall Monroe's "Interplantary Cessna" article at what-if.xkcd.com/30. Highlights include: "The upshot is: Your plane would fly pretty well, except it would be on fire the whole time, and then it would stop flying, and then stop being a plane." $\endgroup$
    – almcnicoll
    Commented Dec 16, 2020 at 14:40

3 Answers 3

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Can't speak to the trajectory aspects but the Orbiter crew compartment was very intolerant of crush pressure loading.

The two negative pressure relief valves protect the crew compartment from being crushed if ambient pressure rises above the pressure in the cabin. These negative pressure relief valves will crack when ambient pressure is 0.2 psid greater than cabin pressure. The negative pressure relief valves are located below the side hatch. Caps are provided as a redundant seal to prevent leakage overboard (Figure 2-8). When the pressure outside the cabin increases above cabin pressure, the relief valves will crack, the caps will pop off, and air will flow into the cabin to equalize the pressure.

enter image description here

So as soon as the ambient pressure got higher than ~1 bar, the hot unbreathable atmosphere would start flowing into the crew compartment.

Reference: Shuttle ECLSS training manual

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    $\begingroup$ To be fair, one would expect NASA to modify these valves for a Venus mission, or include enough Terran atmosphere in pressure tanks to equalize upon entry into Venusian atmosphere. $\endgroup$
    – Carl Witthoft
    Commented Dec 15, 2020 at 12:34
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    $\begingroup$ @CarlWitthoft no one in the real world would ever seriously consider flying an unmodified orbiter into Venus, but the question was what would happen if one did. If one did the required mods, it would no longer be a shuttle orbiter. $\endgroup$
    – Organic Marble
    Commented Dec 15, 2020 at 15:41
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In very rough terms, based on data from Wikipedia and NASA sites:

An empty Space Shuttle is around 165 000 pounds (74 843 kg). Height, 56.1 m (184 ft 1 in). Diameter, 8.7 m (28 ft 7 in). So, a density of about 22.5 $\frac{\text{kg}}{\text{m}^3}$, while Venus' atmosphere at ground level is 67 $\frac{\text{kg}}{\text{m}^3}$, so the Shuttle would float somewhere around 15 km altitude. Or a bit lower if you add a few thousand kg of people and payload.

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    $\begingroup$ Wow, right! But can it withstand some atm of external pressure? And, I think only the cabin is sealed, so only its volume counts as hydrostatic buoyant. $\endgroup$
    – peterh
    Commented Dec 14, 2020 at 13:57
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    $\begingroup$ @peterh is correct; the majority of the orbiter volume was vented to ambient. $\endgroup$
    – Organic Marble
    Commented Dec 14, 2020 at 14:08
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    $\begingroup$ Re shuttle payload by not working as a lighter than air blimp space.stackexchange.com/a/39523/26356 $\endgroup$
    – GremlinWranger
    Commented Dec 14, 2020 at 14:16
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    $\begingroup$ @peterh-ReinstateMonica yeah, we might have to rebuild the hull out of unobtanium, or purchase a General Products hull. $\endgroup$
    – Carl Witthoft
    Commented Dec 14, 2020 at 15:34
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    $\begingroup$ The dimensions are not right. I think they are for the full stack on the launch pad. The orbiter is only 37 meters long, and the diameter is smaller too. $\endgroup$
    – Neith
    Commented Dec 16, 2020 at 14:46
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It's going to be a very rough landing.

I'm going to handwave the descent and approach phases, and focus on the landing.

The Shuttle Landing Facility is a runway 4600 m long, 91 m wide, and 40 cm thick. The Space Shuttle needed most to all of the runway for landings, even with drag chutes.

This Venus Shuttle would require a similar prepared runway for landing, if not even longer. This runway and its foundation would have to be made of materials that can take Venus-standard temperature, pressure, and corrosive atmosphere. Without that, the craft will be attempting a rough-field landing, and would almost certainly require extensive maintenance and repairs afterwards.

That isn't even the hard part - getting back to space will be difficult! Making the launch system, stacking the shuttle, and refueling it is left as an exercise for the advanced student.

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    $\begingroup$ Ok, but the density of the atmosphere is half of sea water. The freefall speed of the shuttle is probably not enough for a crash, I think it will arrive softly. $\endgroup$
    – peterh
    Commented Dec 15, 2020 at 16:30
  • $\begingroup$ It's still a rough field landing for a vehicle designed for a very long runway. So I'm willing to revise my answer to "hard landing needing repairs". $\endgroup$
    – Codes with Hammer
    Commented Dec 15, 2020 at 16:52
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    $\begingroup$ Even if the electronics would not destroyed by the landing, probably its control constants are not designed for such dense atmosphere. And it is aerodynamically unstable, fly-by-wire, requiring continuous electronical control. If its control can handle this, then it will arrive with head. If not, it will arrive like a thrown dice. $\endgroup$
    – peterh
    Commented Dec 15, 2020 at 16:56
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    $\begingroup$ Note, the 450C temperature probably quickly burns all the 1. painting, 2. gears, and 3., most important: cables. Burned cables cause short circuits. $\endgroup$
    – peterh
    Commented Dec 15, 2020 at 16:58
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    $\begingroup$ @peterh-ReinstateMonica: That makes getting back into space even more difficult. $\endgroup$
    – Codes with Hammer
    Commented Jan 6, 2021 at 13:54

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