clipka <nomail@nomail> wrote:
> Warp <war### [at] tagpovrayorg> wrote:
> >   With this taken into account, can you just go from Earth to the nearest
> > black hole, get an enormous speedup and come back at 100x the speed and
> > slam onto Earth at that speed? From a gravity assist only, I don't think so.
> > I think it would be against conservation of energy. If you were travelling
> > from Earth to another star system, then maybe, but I don't think it works
> > in the closed case.

> It does.

> The trick is that the slingshot affects both bodies: That Huge Planet Over There
> and yout Teeny Weeny Space Machiney.

> Guess which one *seems* to be affected most...

> So if you use a black hole to slingshot you around back home, at the same time
> you sort of slingshot the black hole around your spacecraft into the opposite
> direction... it's just that the black hole won't bother *much*, being the fat
> lazy sucker it is.

  Actually it would work if the black hole was moving towards us. Then
the spacecraft could go there and rob part of this momentum and get a
speed boost back towards Earth.

  If the black hole was moving away from us then it would certainly not
work.

  Think about it as an elastic collision. It's a pretty accurate way of
thinking about it.

> > - If you go so close to a black hole that it will give you a stronger
> > slingshot effect than a regular star would, the tidal forces would
> > probably rip you apart. Not very practical.

> Nah, I don't think so. Would tidal forces rip you apart at the surface of the
> sun? I doubt.

  Remember: When the Shoemaker-Levy was on collision course against Jupiter,
tidal forces broke it in 9 parts well before it reached the surface. And
Jupiter is a lot less massive than the Sun.

  Ok, maybe if your spacecraft is sturdy enough, it might survive a
slingshot from the Sun. However, we are talking about black holes here,
and black holes have several times the mass of the Sun (because stars
as small as the Sun cannot collapse to black holes), and getting very
close to the event horizon (for it to make a difference compared to a
regular star).

> > - The humongous amounts of radiation around a black hole would probably
> > be enough to fry you to ashes in a fraction of a second, no matter what
> > kind of shielding you use, especially if you go so close that you would
> > get a larger speed boost than from a regular star.

> Again, only if there's an accretion disk. Remember: Black holes don't emit
> anything - only their surroundings may ;)

  They don't emit anything, but by their nature as being really massive
objects they surely tend to aggregate lots of nasty stuff orbiting around
them, and this stuff often emits large amounts of radiation by several
means.

  For example one concern about sending probes to orbit Jupiter is the
large amount of radiation there (which could break electronics if not
shielded properly). Jupiter, as a very massive object, gathers tons of it.
And Jupiter is a lot less massive than a normal black hole.

> However, maybe you also want to check the magnetic field of the black hole - I'm
> not sure about the orders of magnitude, but I wouldn't want all my electrons go
> spinning off to the left while the protons go off to the right - not to speak
> of the resulting synchroton radiation ;)

  Yeah, that too.

-- 
                                                          - Warp

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