The lowest Heaven or firmament as understood is refering to our Universe, as there are multiple Universes. The Stars spoken of, which are Suns, are used as missles or projectiles for the Shaytaans which can be refering evil human beings or Jinns as Allah theatens them both.
I don't see much revelance in the fact both jinn and humans(travel 4.3 light years!!!??) are vunerable to these missiles, the fact is these missiles are a physical reality. If the stars are in the lowest heaven then how do you explain these verses?
071.015
YUSUFALI: "'See ye not how Allah has created the seven heavens one above another,
PICKTHAL: See ye not how Allah hath created seven heavens in harmony,
SHAKIR: Do you not see how Allah has created the seven heavens ,~ one above another,
071.016
YUSUFALI: "'And made the moon a light in their midst, and made the sun as a (Glorious) Lamp?
PICKTHAL: And hath made the moon a light therein, and made the sun a lamp?
SHAKIR: And made the moon therein a light, and made the sun a lamp?
The Koran clearly states moon and sun are both a light and lamp within the seaven heavens. If the lowest heaven is only our universe then the sun and lamp can't in the midst of the seven heavens can they?
The verse explicitly says a flame from fire and copper will be sent against them both ie Human and Jinns who try to pass beyond the zones of the Heavens.
As I said before talking about mankind is irrelevant anyway how is man supposed to reach the lowest heaven when the nerest star is 4.3 light years away. Impossible!!
What is relevant is that the stars are clearly a protection from the evil spirits, Jinn or whatever you want to call them. This along with the fact they are pursued by flaming fire.
037.006
YUSUFALI: We have indeed decked the lower heaven with beauty (in) the stars,-
PICKTHAL: Lo! We have adorned the lowest heaven with an ornament, the planets;
SHAKIR: Surely We have adorned the nearest heaven with an adornment, the stars,
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YUSUFALI: (For beauty) and for guard against all obstinate rebellious evil spirits,
PICKTHAL: With security from every froward devil.
SHAKIR: And (there is) a safeguard against every rebellious Shaitan.
037.008
YUSUFALI: (So) they should not strain their ears in the direction of the Exalted Assembly but be cast away from every side,
PICKTHAL: They cannot listen to the Highest Chiefs for they are pelted from every side,
SHAKIR: They cannot listen to the exalted assembly and they are thrown at from every side,
037.010
YUSUFALI: Except such as snatch away something by stealth, and they are pursued by a flaming fire, of piercing brightness.
PICKTHAL: Save him who snatcheth a fragment, and there pursueth him a piercing flame.
SHAKIR: Except him who snatches off but once, then there follows him a brightly shining flame.
These verses make it quite clear that the stars protect the lowest heavens with the stars. The way these verses unfold suggest that the stars are what cause this flaming fire. As for jinns being vunerable to fire, one would think they would be just as vunerable to fire on earth as they in space. Although clearly this is just speculation.