[extropy-chat] Pluto--dissipating energy

[Dan Clemmensen]

It's all about dissipating the energy.

Spike has been trying to educate us, but the real problem is energy 
dissipation.

Most of us just do not think about the total energy, but that is the 
best way to think about
the problem.

Let's start with a completely different problem.  What happens when you 
stretch a Kevlar fiber until it breaks? The experiment is much easier to 
implement than a Pluto probe: just tie one end of the fiber to a truly 
fixed point, wrap the other end of the fiber around a big drum,and then 
turn the drum (using suitable reduction gears) until the fiber breaks.

What happens? Stop at this point and attempt a prediction.


OK, here is what happens. As yo turn the crank, you add energy to the 
system. The energy is stored in the very strong molecular bonds along 
the length of the Kevlar fiber. Since the Kevlar is very strong, the 
amount of energy stored per unit length is very high.

What happens? Stop at this point and attempt another prediction.


What happens is that the energy stored per unit length of the Kevlar is 
higher than the energy needed to vaporize that unit length of Kevlar. 
eventually, The force you apply to the Kevlar exceed the tensile 
strength,and the kevlar breaks at the weakest point along its length.

What happens? Stop at this point and attempt another prediction.


The Kevlar strand breaks. The energy stored in the molecular bonds is 
instantaneously released along the length of The kevlar strand, and the 
kevlar is vaporized along its entire length: The fiber explodes. For me, 
this is an entirely counter-intuitive result, but is is an inevitable 
consequence of the law of conservation of energy.


Transfer to Pluto.
   When the fast spacecraft reaches Pluto, it carries a certain amount 
of kinetic energy. to come to rest relative to Pluto, that energy must 
go somewhere. If you simply smash the spacecraft into the planet, the 
energy WILL vaporize the spacecraft (and a portion of the planet) unless 
you provide a means to transfer the energy to somewhere else.  This is a 
counterintuitive result: you can make the probe out of diamond or out of 
jelly, the result will be the same, since the KE of probe exceeds the 
energy needed to vaporize the probe.

This is why I proposed a dangling filament. the filament will impact the 
planet at an oblique angle and will therefore not decelerate instantly. 
The angle is controllable, from the barest touch to a direct impact.