-Z- (Z@Gundam.Com)
Wed, 29 Dec 1999 17:44:04 -0800


At 20:59 12/28/1999 -0800, you wrote:
>> Additionally, Char
>> said that he would use the nuclear warheads from Luna 2 not only
>> because they would accelerate Axis, but also because they would
>
>Decelerate Axis, in fact. The whole point is to prevent it from
>burning up too much mass when it enters Earth's atmosphere and
>reduce the final impact.

 From a ballistics and orbital dynamics perspective, the point of
decelerating Axis is to get make it fall to Earth in the first place.

As noted i previous posts, one of the counterintuitive aspects of orbital
dynamics is that "higher" orbits are faster than "lower" orbits and that
the speed of the orbit increases with the distance until one achieves
escape velocity and leaves the system entirely. People seem to have a
problem with this even though we can see an analogous situation with
aircraft having to reach a certain speed to become airborne and accelerate
to achieve higher altitudes. (The reasons for this are different, but the
situation speed-wise is the same.)

Axis must be slowed to the degree that its orbit degrades and it falls to
Earth. There's no way to stop it and slowing it further will only make it
fall faster, so the only solution is to accelerate it back into a stable
orbit or, at least, an orbit that won't degrade or later intersect with the
Earth or Moon.

There's actually a fairly narrow window for atmospheric re-entry that
applies to all orbiting bodies (as opposed to solar orbits that intersect
Earth orbit, which is a different case altogether). Axis must be moving at
not less than Mach 34 (40,000 kph = 25,000 mph) and not more than Mach 47
(56,000 kph = 35,000 mph) to enter Earth's atmosphere and impact the surface.

In CCA, the London Bell forces are shown pushing Axis the wrong way. They
should've been trying to push it forward and faster, not backward and slower.

The mass of Axis is enough that atmospheric friction would've been
negligible no matter which end of the speed range it was traveling.

Me, I wouldn't have retarded the orbit it at all. I'd've slingshot it
around the Moon and sent it on an collision course intersecting Earth orbit
at as close to a right angle as I could manage and fired the engines full
bore all the way down. Impact velocity would be close to Mach 100 (120,000
kph = 75,000 mph) with a minimal amount of atmosphere to traverse.

The colony drops in 0079 (target Jaburu, impact Sydney) and 0083 (target
Jaburu, impact Kansas) both started with loops around the Moon, but ended
as degrading near-Earth orbits rather than orbital intersections. The
colony drop technique guarantees that you'll hit the Earth even if you miss
your target, but is easier to deflect. The intersection technique is
almost impossible to deflect but, if it can be, you could miss the Earth
entirely.

-Z-

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