12
$\begingroup$

The Space Exploration SE question Premature detonation of explosive bolts when landing on hot Venus? explains the need for and widespread use of pyrotechnic fasteners and cable cutters for Mars landers and elsewhere in spaceflight, and points out that Venus' atmosphere is already 75 °C and 1 atmosphere at an altitude of 50 km and roughly 500 °C and a dense 90 bar supercritical fluid at the surface.

So anything on the outside of a lander is going to get hot during the long descent to the surface in this thick soup.

Questions: What are the chemical and physical constrains on reliable, easily to electrically detonate explosives for pyrotechnic devices that will prevent them from spontaneously detonating at 500 °C when landing on Venus? Are there any realistic, potential candidates?

For example; do we need reactions that are less exothermic? Or a higher barrier between initial and final states? Or a lower density so that below some critical temperature an occasional molecule "exploding" doesn't trigger the next one so easily?

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 there. source: NASA/JPL-Caltech and source: NASA/JPL-Caltech

Improve this question
$\endgroup$
18
  • 1
    $\begingroup$ Out of curiosity, how did the first landing on Venus manage the feat? I ask because it is not clear that what works well on the thin Martian atmosphere would be adaptable for the “thick soup” Venusian atmosphere. $\endgroup$
    – Ed V
    Commented Jun 13, 2021 at 13:47
  • 1
    $\begingroup$ Ah, thanks for the information! I was thinking some sort of insulated internal “shotgun” mechanism, maybe with small shaped charges, could blow the bolts off or out. Seems like that is essentially what was done. So how about using two substances that are thermally stable, but explode on contact? Ram them together at the right locations and take out the bolts. $\endgroup$
    – Ed V
    Commented Jun 13, 2021 at 14:03
  • 1
    $\begingroup$ I suspect NH4NO3 based explosive may work. Per the Texas City disaster, just heating NH4NO3 may not result in an explosion (complex product range as a function temperature, which may be favorable in your situation). Also, N2O dissolved in fuel is an idea where N2O is more electrostatically given to explode than just by heating (but does result in extremely high temperatures on detonating, vaporizing metal). $\endgroup$
    – AJKOER
    Commented Jun 13, 2021 at 16:45
  • 1
    $\begingroup$ Because oil wells reach high temperature at depth, there are special explosives, e.g. freepatentsonline.com/y2010/0006193.html . As you mention, wide-band-gap semiconductors such as SiC first received use in well loggers. Interesting - "As above, so below." $\endgroup$
    – DrMoishe Pippik
    Commented Jun 13, 2021 at 20:02
  • 2
    $\begingroup$ How small could a thermobaric explosive be made? Basically, use a burst of oxygen gas to get flammable particulates suspended in a very small compustion chamber and then use a spark plug to ignite, sending the bolt-cutting ‘piston’ to do its job. Basically just a flour mill explosion in miniature. $\endgroup$
    – Ed V
    Commented Jan 25, 2022 at 17:52

1 Answer 1

Reset to default
1
$\begingroup$

Ionic compounds as a general rule have greater bond strength than covalently bound molecules. This makes them more heat resistant, therefore it seems likely that a binary explosive consisting of an oxidizer salt and a fuel would be the way to go.

Since you don't want the explosive to change phases during the mission, since it could leak or unmix, you'd want a salt with melting temperature above 500 °C, the same goes for fuel.

One possibility would be barium nitrate and powdered aluminium mixture.

Improve this answer
$\endgroup$
3
  • $\begingroup$ The trouble could be safety of their mixture, not to be trigerred prematurely, as 500 °C is a lot. $\endgroup$
    – Poutnik
    Commented Jan 17, 2022 at 9:41
  • $\begingroup$ I don't doubt your answer, is it possible though to add some reference about reactions between barium nitrate and powdered aluminium for completeness? Thanks! $\endgroup$
    – uhoh
    Commented Jan 18, 2022 at 19:28
  • $\begingroup$ I can only provide a link to a video with someone testing it out youtu.be/BB4Nj7ZkUKw $\endgroup$
    – Francis L.
    Commented Jan 19, 2022 at 6:38

Not the answer you're looking for? Browse other questions tagged or ask your own question.