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Kosmos 482: questions around a failed 1972 Venera lander still orbiting Earth

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Re: Kosmos 482: questions around a failed 1972 Venera lander still orbiting Earth

#71

Post by toss1 »

WalterBright wrote: post #68
eesmith wrote: post #35

Earlier quoted context omitted.

https://en.wikipedia.org/wiki/Celebratory_gunfire lists a few deaths. Given the number of people who celebrate with gunfire, it's indeed not terribly dangerous overall. Nevertheless, "it's still your fault if it kills someone."

"They found that while bullets traveling on a perfectly vertical trajectory tumble on the way down, creating turbulence that reduces terminal velocity below that which would kill, it was very difficult to fire a bullet in this near-ideal vertical trajectory. In practice, bullets were likely to remain spin-stabilized on a ballistic trajectory and fall at a potentially lethal terminal velocity." So I'm not completely w…

Mythbusters found pretty much the same thing - IF (big IF there) you can fire it EXACTLY vertically so that the returning bullet is just like it was dropped from a balloon or something, the terminal velocity is not lethal

However, with any significant angle off-vertical, the bullet still travels in a stable trajectory and orientation, so will impact with a speed much higher than random-orientation terminal velocity, and be potentially lethal, even if passing through some roofing material on the way into your body.

So yeah, don't shoot into the air, and don't be around where anyone does...

Re: Kosmos 482: questions around a failed 1972 Venera lander still orbiting Earth

#72

Post by eesmith »

toss1 wrote: post #71
WalterBright wrote: post #68

Earlier quoted context omitted.

"They found that while bullets traveling on a perfectly vertical trajectory tumble on the way down, creating turbulence that reduces terminal velocity below that which would kill, it was very difficult to fire a bullet in this near-ideal vertical trajectory. In practice, bullets were likely to remain spin-stabilized on a ballistic trajectory and fall at a potentially lethal terminal velocity." So I'm not completely w…

Mythbusters found pretty much the same thing - IF (big IF there) you can fire it EXACTLY vertically so that the returning bullet is just like it was dropped from a balloon or something, the terminal velocity is not lethal However, with any significant angle off-vertical, the bullet still travels in a stable trajectory and orientation, so will impact with a speed much higher than random-orientation terminal velocity,…

WalterBright was quoting the MythBusters section of the linked-to Wikipedia page, at https://en.wikipedia.org/wiki/Celebratory_gunfire#Cultural_r... .

Re: Kosmos 482: questions around a failed 1972 Venera lander still orbiting Earth

#73

Post by WalterBright »

eesmith wrote: post #70
WalterBright wrote: post #68

Earlier quoted context omitted.

"They found that while bullets traveling on a perfectly vertical trajectory tumble on the way down, creating turbulence that reduces terminal velocity below that which would kill, it was very difficult to fire a bullet in this near-ideal vertical trajectory. In practice, bullets were likely to remain spin-stabilized on a ballistic trajectory and fall at a potentially lethal terminal velocity." So I'm not completely w…

My comment wasn't really one of correct or incorrect. It was meant to highlight russellbeattie's propositional logic ("if it kills someone" then "it's still your fault"). I agree with you that it's "not terribly dangerous"[1]. Your comment seemed to have omitted the premise, so I wanted highlight how it was a non-empty set. [2] [1] It's also not terribly dangerous to drive without a seat belt on either. I don't advis…

If you shoot straight up, it will slow to zero, then fall to terminal velocity.

Re: Kosmos 482: questions around a failed 1972 Venera lander still orbiting Earth

#74

Post by eesmith »

WalterBright wrote: post #73
eesmith wrote: post #70

Earlier quoted context omitted.

My comment wasn't really one of correct or incorrect. It was meant to highlight russellbeattie's propositional logic ("if it kills someone" then "it's still your fault"). I agree with you that it's "not terribly dangerous"[1]. Your comment seemed to have omitted the premise, so I wanted highlight how it was a non-empty set. [2] [1] It's also not terribly dangerous to drive without a seat belt on either. I don't advis…

If you shoot straight up, it will slow to zero, then fall to terminal velocity.

Look, I agree with you - celebratory gunfire is pretty safe, and if you want to be safer, shoot straight up. Not only will it slow to zero, but you will be the one most likely to be hurt by it.

That said, just because you shoot straight up doesn't mean it will slow to zero.

The Wikipedia entry lists "October 12, 2003: Wedding guests in Belgrade, Serbia mistakenly shot down a small aircraft", pointing to http://news.bbc.co.uk/2/hi/europe/3185884.stm .

russellbeattie is still right - the person who shot that plane is partially at blame for the damage to the plane and the injuries of the two people onboard.

(I say partially because from what I gather, neither person was a trained pilot and were joyriding.)

Re: Kosmos 482: questions around a failed 1972 Venera lander still orbiting Earth

#75

Post by wcoenen »

ars wrote: post #30

Can anyone explain how it's possible for the apogee to reduce so much, while the perigee barely changes? Wouldn't the air resistance that lowers the apogee also affect the perigee? Or is it specifically because the object is being slowed at perigee, that the apogee lowers, while the perigee doesn't change much because the apogee is in vacuum?

The rule of thumb you can use to make this intuitive:

A change in velocity at a certain point x on an orbit will change the entire orbit, except that orbit will still continue to go through that one point x.

So slowing down at perigee will not alter the perigee. (It is actually the most delta-v efficient way to lower the apogee.)

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