John S continued the discussion thus:
> 3. I still think dropcaps will be faster time-
Then surely this wouldn't be unopposed? Gets back to the need to /
reasons for scatter....
[Tomb] Imagine I'm arriving at an outpost and want to attack with
surprise. The attack isn't opposed because the enemy on the ground is mostly
infantry without significant ADE. But if I don't get down there fast, he'll
wake up, dig in, and be a pain to root out. If I get down fast enough, he's
caught in a state of less than full readiness and I have a good chance of
taking the objective. And because dropcaps are "the fast route" to the ground,
I'd figure they'd still be a preferable option here.
> [Tomb] Imagine I'm arriving at an outpost and want to attack with
Thinking on this one, in terms of time to ground, some of it will depend on
propulsion.
A drop cap, fired into the atmosphere of a planet, with no propulsion unit,
will slow up as the atmosphere gets thicker, until it loses the initial
velocity imparted to it. After that, it will fall under gravity, until the
terminal velocity for that planet is reached. This will depend on size,
atmospheric density, initial velocity, etc... (This is a well known process in
meteoritics)
> On 10-Jun-02 at 13:18, John Sowerby (sowerbyj@fiu.edu) wrote:
> Thinking on this one, in terms of time to ground, some of it will
Wheras the dropship will slow up until it loses initial velocity.
It will then fall under gravity+thrust faster than terminal
velocity. At the last safe instant the dropship reverses thrust pulling high
Gs and lands.
Looks to me like a dropship gets them down faster.
> On Mon, Jun 10, 2002 at 12:41:54PM -0400, Tomb wrote:
> From a purely physics point of view:
1. Things do not "drop" out of orbit - the dropship sequence from
Aliens is utter utter crap. You need to deorbit the object. This is not
trivial. Somewhere along the deorbit you have to shed about
10000kmh^-1 of kinetic energy. When the Sulaco lets go of it, the
dropship falls vertically. Erm, so what's holding the Sulaco up? Superman?
Its orbital velocity is holding it up. And, would therefire hold up the
dropship when it was let go of...
Shedding that orbital velocity is no easier than gaining it: the shuttle does
it by slowing slightly (expending fuel) until its orbital velocity is that of
an orbit which is within the atmosphere. At which point air friction will kick
in and it loses the rest of the energy by converting it to quite a lot of
heat. From first deorbit burn to
touchdown the shuttle completes a couple of orbits - far from a
vertical fall.
Now you /could/ do it by simply firing a thruster sideways until your
orbit speed is zero, and which point you'd... well. Drop like a
stone. That's a lot of thrust tho - to /gain/ that velocity, the
shuttle makes a lot of noise and goes through, what is it? 2 gallons a foot of
liquid fuel and a two solid boosters.
2. Unpowered vehicles are not the fastest route to the ground. They
can, at best, fall at g ms^-2. Powered vehicles can (theoretically)
fall faster. You can't catch something you drop out of a plane by diving after
it (modulo air friction) because you can't fall faster
than 1g - the speed the object is falling at. Powered aircraft can
exceed a 1g fall, (although I'm led to believe it induces nausea. Very
quickly.) This is complicated by the aforementioned need to shed
orbital velocity. Powerdiving into a gravity well is /doable/, but
> From a purely physics point of view:
Without mucking around the physics in sci-fi arguement, and sticking
strickly to the rules and fluff as already put out...
> 1. Things do not "drop" out of orbit - the dropship sequence from
You are assuming a ship is orbiting a planet as opposed to a fly by and
drop... Orbiting a planet is kinda like calling your enemy on the telephone to
tell him you're coming for him... He may not know exactly where or when, but
knows you're there and coming. Not likely to get you
surprise.
Other than that, you're dead on.
> Shedding that orbital velocity is no easier than gaining it: the
Given 1. fuel-less systems for thrust (For practicle purposes here at
least) and 2. a system whose thrust "points" makes the shuttle launch like a
stroll in the park... Dumping V. to drop out of orbit at point X within 1
orbit isn't too outrageous. Not something we can truly comprehend right now,
but not physically impossible.
> 2. Unpowered vehicles are not the fastest route to the ground. They
There's another bit here too... Unpowered vehicles need to slow down, unless
you don't mind squashed contents. They usually either need to
retard thier speed the whole way, or do multiple chute-type drops and
sudden decel's.
Now, powered craft need not do so until the absolute last minute, and
depending on the G strain they're willing and able to take, that last moment
can be pretty short. When you then take gravity plates into account, thus
keeping contents from going squish, you can do as high G as you're dropship is
capable of physically withstanding...
"Powerdiving into a gravity well is /doable/, but you'd have to be mad
and have a lot of fuel to waste."
Frankly, two things I've found the military to consistently excel at... Being
mad, and wasting lots of fuel. Seriously. Very serious.