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Asteroids in Space (was: RE: FT Taskforce and Fleet Actions)

From: "Mark 'Indy' Kochte" <kochte@s...>
Date: Tue, 7 Aug 2001 08:54:36 -0400 (EDT)
Subject: Asteroids in Space (was: RE: FT Taskforce and Fleet Actions)

Greetings, gang,

Below is a write-up I did on asteroids (specifically as they apply to
the
Sol system, but imminently applicable to just about any star system that
vaguely resembles ours - i.e., has a few gas giants and debris orbiting
the parent star) a few years ago in response to some questions about
asteroids on the gaming table. Since that time the number of asteroids
discovered has gone up, though not by a lot, and the number of
*significantly* *sized* asteroids hasn't really increased at all. So for
all intents and purposes, this study is quite valid for gaming in an
asteroid field (you can modify your own asteroid field as you see fit,
however; if you want a super-dense field where you have a dozen
asteroids
on the table, don't let me stop you! you can always call it a localized
phenomenon or something  ;-). I hope the numbers will illustrate why
asteroid fields shouldn't be a big deal for FT craft to fly through. I
don't recall who initiated the question from the FT list. Maybe he is
still out there and will remember this? 

Now in response to Ryan's note about how NASA gets all jittery when one
of
their spacecraft goes through the field, remember that 1) NASA
spacecraft
are fairly autonomous and have extremely limited maneuverability (unlike
FT  ships), 2) they don't have active detection devices (unlike FT
ships),
and 3) stuck here on Earth we haven't had the opportunity, time, or
ability to chart anywhere near the number of asteroids (large or
small) that would be known in the FT Universe.

Note: I get a little tirade going in the write-up. I was suffering from
dealing with Hollywood (and general media) stupidity on things
space-based (I still do, btw  ;-).

Mk
---------- Forwarded message ----------
Subject: asteroids.txt

>Ran a FT combat and decided to try having asteroids on the board. We
got
>into a discussio on how dense an asteroid field should be. I had 1
>asteroid about every 12", they thought there should be a lot more (ie.
>Empire Strikes Back scene with Mil. Falcon). How dense do other players
>on the list place them? Does anyone know about the real life asteroid
>belt: how close are the big asteroids to each other, how big, or small,
>would one have to be to be a hazard, etc.

Hollywood? SF? Dramatic Effect? It's a lot denser. And in NO way bears
any representation to reality (eg, Empire Strikes Back). It's purely for
visual effect.

Reality? Asteroids are really really reeeeaaally far apart from each
other.
If the asteroid field were anywhere NEAR as dense as what you see in
Hollywood,
you could actually SEE the thing as a ring in our solar system. Despite
the
low albedos (light reflectivity) of individual asteroids, combined
together
in such dense proportions would reflect plenty of light.

Want a fight in an Real Asteroid Field? Put one asteroid on the map.
Voila'!
You are in the asteroid field.	:-)  (Okay, okay, so it depends on what
scale
you're talking here; you might put in two)

How big/small are they to be a hazard? Okay, asteroid-education time. 
;-)
To be a hazard, it again depends on your scale, and depends on how fast
you're
travelling in RL. If fast enough, a basketball-sized asteroid could be a
real
bummer.  ;-)   How big? THere ain't too many 'big' asteroids out there.
There
are only 18 that measure 125 kilometers across or larger (the largest is
only
512 km; the second largest is a whopping 277 km, and they go down from
there).
Of those 18, only 4 are greater than 200 km. There are about 4000 or so
which
are 50 km across or larger. You could probably feasibly guess that there
are
4 or so times as many which are only a few kilometers across.

So, now, let's say we're talking 20,000 asteroids here (just a rough
number,
something to work with). That's really not very much in the grand scheme
of
things. You see, it's like this...

The 'width' of the asteroid belt is quite large. Asteroids tend to range
in
bands from ~1.8 AU to ~5.2 AU from the sun (side note: 1 AU
[Astronomical Unit]
is the distance from the sun to Earth; Mars is ~1.5 AU away from the
sun, and
Jupiter is ~5.2 AU away). There are gaps between the bands, called
Kirkwood
Gaps (I will leave it as an exercise for the student to explore the
Kirkwood
Gap phenomenon). Most asteroids are 'concentrated' in a band that ranges
from
2.2 to 3.2 AU That's an area 93 million miles across. And from
186,000,000 to
270,000,000 miles from the sun. This will yield an area of space that
covers
some 1.2 x 10**17 miles (that's 1.2 followed by 17 0's, btw  :).

To replicate, use this simple calculation:

    pi x (270,000,000**2 - 186,000,000**2)

  where 'pi' is ~3.14159

Now...toss 20,000 asteroids in an area measuring 1.2 x 10**17 miles. Oh,
hell,
toss 20,000,000 asteroids in it. You only get 1 asteroid every
6,000,000,000
miles! And now we're talking stuff that's measuring meters across. And
only
18 of them are larger than 125 km.

Okay, for the moment, go back to your map. Remove that one asteroid (or
both
if you put down two). Now you have a blank map with ships. Declare this
is
an asteroid field. You'll be just as right as not.

Now, mind you, I'm only talking 2 dimensions here. I haven't even
tackled
the Z-coordinate (okay, yeah, it won't be *real* far above/below the
plane
of the asteroid 'ring', but it'll be enough to really diffuse an already
tenuous 'field').

I hope this illustrates the point. WHich basically says: Hollywood is
full of
it.

Trivia note: some of you may have noticed that Jupiter is ~5.2 AU from
the sun,
and I indicated some asteroids range out as far as 5.2 AU from the sun;
these
asteroids are part of the Kirkwood Gap phenomenon, and are called Trojan
Asteroids, something some of you may have heard of before, in some dim
faint
distant memory from a basic astronomy class. There are more asteroids
per unit
area in the Trojan region than in the asteroid belt, but the density
numbers
are still phenomenally small, and don't reflect Hollywood's image of
asteroids.

Thus endeth the lesson for today.  :-)

Mk
------------------------------------------------------------------------
-
   o/		      ..     .
  /@		       .  .	      If you insist on reaching for a
  <|\			  .  )	      star, be prepared to take a long,
   |		     /\ 	      hard fall.
   |		    //
   /		 o //*		      Indy - climber, astronomer,
adventurer
  /		<%- /|\ 	      supreme. Have rope, will travel.


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