Sorry, forgot the other half of the problem: limiting rotational
acceleration on the penetrator probe to be dropped, when
it's tethered.
Say that 1000 g, or about 10,000 m/s^2, is the limit for
instruments of interest. At about 1.5e+03 m/s rotational
velocity on the tether (counter-rotating to match speeds
with Europa's surface), you have
a = v^2/r
r = (1.5e+03 m/s)^2 / (1e+04 m/s^2)
or a tether 'radius' (half-length) of about 200 m. I have
no idea whether this is ridiculous or not.
There might be some way to rev it up using Jupiter's
magnetic field and some electrodynamic effect. But that's
beyond my rusty physics, at this point. (In fact, so is
almost all of this discussion -- fooled ya, didn't I? ;-)
-michael turner
[EMAIL PROTECTED]
- Original Message -
From: "Michael Turner" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Saturday, April 17, 2004 5:25 PM
Subject: The tether thing (for the first time?) (was Re: The gun thing again
[Off Topic])
>
>
> I've wondered if you couldn't cancel a lot of a Europa penetrator's
> acceleration by making it a counterweight to a rotating tether
> orbiting very close to Europa. A probe could orbit very
> close - Europa's "atmosphere" is mostly oxygen that (by one
> estimate) collides with other oxygen molecules only about
> 3 times on average before escaping. With "atmospheres" like
> this, who needs vacuum?
>
> For the sake of simplicity, consider what might be
> involved in dropping a probe straight down from
> a low altitude.
>
> Europa surface acceleration due to gravity: 1.3 m/s^2
>
> Counteracting centripetal acceleration achieved at 1.57e+06 m
> from Europa center of gravity (= Europa radius plus a few km)
> would be at orbital velocity given by the equation
>
>a = v^2/r
>
> solving for v:
>
>v = sqrt (ra) = sqrt (1.3 m/s^2 * 1.57e+06 m)
>
> or let's about 1.5 km/s orbital speed, winging just barely above
> Europa's surface features.
>
> So the question is: could a tether hold, with a tip speed
> of 1.5 km/s? Well, flywheel tip speeds are currently in the
> neighborhood of 1 km/s, and that's without fullerene weaves.
> If they crack the fullerene fiber problem, another order of
> magnitude of tensile strength might emerge.
>
> One problem with this approach: the tether, having released
> the penetrator probe, will go flying wildly off somewhere. If,
> however, a counterweight incorporates an ion drive powered by
> flying through Jupiter's magnetic field, maybe it could retrieve itself
> and be reused somehow.
>
> -michael turner
> [EMAIL PROTECTED]
>
>
> - Original Message -
> From: "Gary McMurtry" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Saturday, April 17, 2004 1:30 PM
> Subject: RE: The gun thing again [Off Topic]
>
>
> >
> > A EUROPA penetrator probe will have to survive 20,000 G on impact.
> > Most Mars and Moon probes need only to survive about 2000 G, because
> > there they can use rockets to brake the fall (larger payloads).
> > We've tested a mass spectrometer to 1200 G. They tell me the
> > electronics is not a problem at 2000 G. I think 20,000 G is more of a
> > challenge, but then, I don't know if it is or not. There are folks
> > doing 20,000 G experiments. Maybe you've seen some results on TV
> > over the past year.
> >
> > Gary
> >
> >
> > >Greetings Sir,
> > >Some comments on your post
> > >
> > >At 02:28 PM 4/8/04 -0500, you wrote:
> > >
> > >>One of the problems I encountered was how do you build circuitry to
> > >>survive the launch. The forces involved will destroy most
> > >>electronics as they are now built. Solids state is not very solid
> > >>after 15x gravitational forces.
> > >
> > >Actually, this is probably not a major problem. Gerald Bull put
> > >electronics in shells he launched back in the 1960's. Just packed
> > >them with sand in his shells. JPL sent two penetrator probes into
> > >Mars. The probes did not work, but evidence suggests that it was
> > >problems with the battery supply (i.e. the battery couldn't survive
> > >the long cold and still function) and not the electronics. Also,
> > >combat UAV's can pull (I believe) more that 15g's and they survive
> > >just fine. Crash Black boxes in Indy cars routinely survive probably
> > >50-100 G's in crashs (for extremely short periods of time). So the
> > >electronics will survive.
> > >
> > >>C
