@Uwe's comment below Parachute material used for the Venera probes to survive 500 °C raises an interesting issue. Venus is really hot, and pyrotechnic actuators (e.g. explosive bolts, frangible nuts etc.) are a staple of spaceflight.

We have many questions here about how various electrical and mechanical cables and even tubes and hoses were cut by pyrotechnic actuators after the Insight landing, the top of the spacecraft is littered with the cut ends of various things.

Temperatures of the atmosphere near the surface of Venus are high. At 50 km where the pressure is already 1 atmosphere the temperature is around 75 °C and by the time it gets to the surface it's 460+ °C. With such a dense, supercritical fluid atmosphere near the surface heat transfer will be rapid and anything on the outside of the spacecraft will be just as hot as the atmosphere itself.

Implicit in my question is the premise that a Venus lander will have at least a parachute or other decelerator that needs to be reliably actuated and later detached, and perhaps several for different pressures regimes, and that pyrotechnic devices will be used to do this as they have in other lander missions on atmospheric worlds.

If my implicit premise is incorrect, then a well-sourced answer explaining why and how it will be avoided will constitute a good answer.

Question: How can/will premature detonation of pyrotechnic devices such as explosive bolts, frangible nuts or explosive cable-cutters on a lander be prevented from exploding prematurely in the hot atmosphere of Venus?

Related; Venus landings or background on the various pyrotechnic devices and their long history of use in spaceflight:

These examples are on Mars, not Venus. Click for larger

Perseverance cut cables for landing Fused picture of rover's top after landing

left: From How were Perseverance's cables "cut" after touching down? in Space Exploration SE right from this answer to How were Perseverance's cables “cut” after touching down?. source: NASA/JPL-Caltech and source: NASA/JPL-Caltech

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    $\begingroup$ Don't know if it helps with the pyros, but Soviet Robots in the Solar System says the entry probe was chilled down to subzero before separation from the bus. $\endgroup$ Commented Jun 13, 2021 at 1:30
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    $\begingroup$ I don't know what (if any) pyros were used, but some high explosives aren't particularly temperature sensitive; for example, you can light C4 on fire and cook over it. $\endgroup$ Commented Jun 13, 2021 at 2:18
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    $\begingroup$ RDX (the primary component of C4) boils at 234ºC, so probably not what was used for hypothetical pyros on Venera. I merely mentioned it as an example of a temperature-stable explosive. $\endgroup$ Commented Jun 13, 2021 at 2:35
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    $\begingroup$ One of the issues with explosives & high temperatures is not issues with detonation but melting. I recall reading an old conference paper many years ago that described blasting practices in the 1960s in a hot region in one of the Mt Isa mines. The rock temperature was >60C, the miners had to wear heat protective clothing & breath oxygen from bottles. They were using nitroglycerine based explosives & they had to charge the holes & detonate the explosives within a very short time frame otherwise the explosives would melt & flow out of the holes. $\endgroup$
    – Fred
    Commented Jun 13, 2021 at 4:47
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    $\begingroup$ The other thing to consider is not just the explosives, but the means of initiation - the detonator (blasting cap). These are the devices that are given an electrical current that causes an explosive compound within them to be ignited that then set off the main explosive. $\endgroup$
    – Fred
    Commented Jun 13, 2021 at 5:38

1 Answer 1

#22 - explosive bolt for opening the top cover

As you can see in the diagram, the explosive bolt (#22) is in a comfortable environment inside the capsule, protected by thermal insulation (#11).



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    $\begingroup$ What is releases by the explosive bolt? $\endgroup$
    – Uwe
    Commented Jun 13, 2021 at 10:57
  • $\begingroup$ It's a beautiful drawing, but can you mention in your answer what it is a drawing of? Thanks! $\endgroup$
    – uhoh
    Commented Jun 13, 2021 at 11:02
  • $\begingroup$ The number of the explosive is 24 in another document you linked. $\endgroup$
    – Uwe
    Commented Jun 13, 2021 at 11:08
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    $\begingroup$ @uhoh VENERA-8. explosive bolts for opening the top cover $\endgroup$
    – A. Rumlin
    Commented Jun 13, 2021 at 17:31

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