>> Deorbiting anything to fall into the Sun is expensive.
>
>I don't understand this - if you've left Earth orbit
>(which takes accelerating to escape velocity and costs
>the same whichever way you go, I believe) if you do it
>in a Sunwards direction, it will get there, surely?
>Where does the extra energy (expense) come into it?

An object that escapes the gravity well of earth still has the energy
associated with the earth's orbit in the gravity well of the sun (it has
less if it escapes 'backwards' wrt earth orbit motion). To go 'in' it has
to lose energy until its perihelion is tangent to the sun's 'atmosphere'
(low enough that it is slowed down and its next apohelion is safely lower
than earth's orbit). If it is not tangent it will come back to haunt you
(or your distant offspring) in the form of a comet/asteroid and if it is
well built it will not break up as asteroids do and eventually
impact/reenter earth with a great probability. Aditionally, shooting the
sun is much harder than shooting the moon so whatever you send out will
have to be instrumented and working well for a few years at least, carry
fuel, respond to remote control, be able to maneouver etc.

Peter

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