# Meteor shower falls from Halley’s Comet on Saturday

Professional and amateur astronomers will have their eyes on the skies this weekend, watching for the annual Orionids meteor show as our planet passes through the tail of Halley’s Comet. The annual show lasts around a week and reaches its peak this weekend, when the Earth and Moon pass through the cone of debris left by Halley …

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#### How is 1:2000 calculated?

If there's a 1:2000 chance the German spacejunk will hit someone, is there a 1:2000 x c.7,000,000,000 probability it will hit a particular person? Does that equate to a one in fourteen trillion risk?

I'll stick to the lottery (not)

#### Easy

They know roughly where it'll land (within a few degrees of latitude, but limited idea of longitude, just due to it's orbit), what proportion of that area is land and what the population of that area of land is. So your chances of being hit are actually variable on where you are on the planet. In Blighty for example, there is zero chance.

Unless it takes a big fluke ricochet off a 747 on the way down or something...

I doubt it would so much ricochet off a 747 as go straight through it and out the other side. ;-)

#### 1 in 2000?

So equally, 1 person in my small local town is at risk, 8 in the next largest town, 25 in our local important town, not to mention *hundreds* in Paris, London, Tokyo, Berlin...

Where's it planned to come down, anyways?

Nop, it means that if that sattelite comes down 2000 times, 1 of those times it will hit someone

#### Also a weather forcast then.

For cloud, thick black clouds as thats all we get in blighty when there is some interesting astronomical event happening...

Yup, it's a royal decree or somesuch.

#### heh...

Cloud, thick black clouds as that you always get in blighty :)

Mine is the one with the sunglasses in october...

#### German satellite

Shouldn't there be a self-destruct mode so if nothing else it comes down in small bits. Don't particularly want a satelite landing on my head.

If you blow it up before it comes down, congratulations, you've just made a shitload of space debris.

If you try to blow it up on the way down, tough titties, you're out of radio contact.

A timer might work, I suppose, halfway through re-entry. But at those speeds, the sharp change in angle caused by an explosion could increase the possible impact area many hundreds of times.

Besides, anything that comes into the atmosphere without heat shielding will not exactly be intact by the time it hits the ground. Not satellites, broken shuttles, European supply pods, whales or potted plants. You'd have to be bloody unlucky to get hit.

#### Space Debris

I'm no expert on this, but I understand there's already tons of space debris up there already.

And I had to laugh at your comment about whales coming down from space. It would save barbequing it after it came through the stratosphere. I wonder (prior to coming back to earth) it thought, I can hardly breath - oh hang on, I've got a little hole above my head - that will help.

The main thing that is likely to survive re-entry intact is the primary mirror assembly. Weighs in at about a ton, and is unlikely to be destroyed. Also its too massive for any reasonable demolition charge to break up (demo charges are heavy, and satellites are mass-constrained).

"I'm no expert on this, but I understand there's already tons of space debris up there already."

Exactly - we don't want to make it worse! The Chinese blew up a satellite a while back and tracking stations all over the world are still following bits of it.

#### Sensors

I'm sure that a combination of an accelerometer and a heat or ionization detector could trigger self-destruct of a satellite only after its re-entry. Making that fail-safe (in other words, reducing the odds of a premature explosion to the infinitessimal) is surely no harder than making a reliable satellite and its (potentially explosive) launcher in the first place. Although you would need some interesting studies to make sure that multi-year exposure to space and space radiation didn't degrade the explosive into instability (studies that I'd wager have already been done by the military, and the results filed "secret" or above).

The problem is economics. This plan would make the satellite quite a few kilogrammes heavier (the weight of a sufficient quantity of explosive). This would increase the launch cost very considerably and/or reduce the available mass for the useful payload. Better to rely on favorable statistics, and pay out compensation to any very unlucky person (or their heirs), at least until death by falling satellite happens for the first time.

#### and to complete the reference

Whale: Oh! What is this thing coming at me??? I wonder if it will be my friend??

Potted Plant: Oh no, not again!

probably paraphrased, as it has been a bit since I read Doug Adams

Worlds Unluckiest man head for Pole to avoid satellite impact - gets eaten by penguin.

#### Ye Gods !.!

she was walking all alone

down the street in the alley

her name was sally

she never saw it

when she was hit by space junk

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