[extropy-chat] Pluto New Horizons launch -getting ready

[Robert Bradbury]

On 2/17/06, spike <spike66 at comcast.net> wrote:
>
> Above a certain velocity, the mass of the projectile did not result in
> significant change in the diameter of the hole.  The length of the
> projectile is directly proportional to the depth of the hole and the
> projectile velocity is directly proportional to the diameter of the hole.


It sounds like the  velocity, which determines the kinetic energy of the
"first impacting" atoms is transferred down and to the sides (of course it
can't get transferred "down" very far because the atoms in the rest of the
planet are only going to compress just so much and no more.  The only place
the compression can get transferred to is outward and ultimately upward
(which is why the walls of the crater rise up above the initial surface
plane at the point of impact).  Of course some of the atoms gain enough
energy to move into the gas/plasma state and may settle out someplace far
from the crater or go into orbit.  Now the length effect is fairly easy to
explain as the front portion of the probe keeps getting vaporized and pushes
material out of the way the portion behind it keeps penetrating deeper and
deeper into the surface.  Sounds like one doesn't need nuclear weapons for
"bunker busters".  Sounds like one needs really long narrow cone shaped
weapons coming in at extremely hypersonic velocities.

Now, to return to the question at hand...  I don't care if all of this
material is getting vaporized and if the vaporization wave is proceeding
through the shield at the speed of sound.  Light travels a foot in a
nanosecond. I believe we are now timing things down to femtoseconds or even
attoseconds. Given a velocity of 14 km/sec it looks like you have ~70 msec
in the last km of descent to decide what to do.  To me this sounds like a
rather significant amount of time before the nanosecond of impact.

If we are impacting Pluto at 14 km/sec all I have to do is get the lander
going at a speed of ~ -14.XX km/sec to put enough distance between it and
the impact conflagration to allow it to survive and make a nice soft landing
elsewhere.  So long as the net negative velocity is somewhat greater than
the impact velocity and less than the escape velocity from Pluto one should
be ok.  So what it looks like is that one wants to launch the probe away
from the impactor at a few tens of meters per second some number of seconds
shortly before impact.  Mind you if you were *really* clever you would
launch it in a somewhat horizontal direction that could put it into orbit so
you could survey the entire planet.

Now it looks like high speed bullets max out around 1.5 km/sec. But various
explosives used in nuclear weapon detonations can manage ~5-9 km/sec [1].
So some set of nesting bullets (e.g. Matrioshka Bullets) containing the
"probe" (or mini-probe-components) should be able to do the trick.  While
"normal" rail guns only manage 2.5 km/sec [2] this doesn't appear to be a
hard limit as Sandia's Z machine can accelerate objects to velocities to
13-34 km/sec [3,4] in less than a second.  As the speed of sound in solids,
e.g. steel, is ~5 km/sec if you can manage about -20 km/sec at the precise
moment of impact you could negate both your forward velocity and avoid the
back propagating pressure wave.  So this *isn't* impossible.  And you've got
all that time from Jupiter to Pluto to store up the electricity from the RTG
to produce the power required.  (Mind you you are going to need some large
capacitors to store it in but perhaps that is where nanotech comes in --
nanotubes appear to have the capability of making great capacitors).

It should be noted that the acceleration in rail guns can reach 250,000 g
and in the Z machine reaches a billion g's *without* destroying the object
being accelerated.  So very high deceleration rates can be tolerated.  The
problem is to slow the propagation of the energy of impact from nanoseconds
to seconds so the probe contents can remain in a functional state.

I would lay odds that the simulations Spike mentions did not try to
structure the impactor so the maximum amount of energy was transferred to
the surrounding planetary material rather than the impactor itself because
that long ago I don't think we had the supercomputer power required to do
atomic level simulations of materials engineered to reflect IR & vibrational
energy.

Robert

1. http://nuclearweaponarchive.org/Nwfaq/Nfaq4-1.html
2. http://www.military.com/soldiertech/0,14632,Soldiertech_RailGuns,,00.html
3. http://www.geocities.com/Area51/Shadowlands/6583/project459.html
4.
http://www.sandia.gov/news-center/news-releases/2005/nuclear-power/z-saturn.html
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