Re: negative light pressure

Wasn't it Gareth Owen who wrote:
>"mensanator@xxxxxxx" <mensanator@xxxxxxx> writes:
>
>> pierre poirier wrote:
>> > Is it possible to construct an optical system such that when put into space,
>> > it would be radially attracted towards the Sun? You're only source of
>> > "energy" is the pressure exerted by light from the Sun.
>> >
>> > Here I must insist that we are concerned about the principle of such a
>> > system, and not about efficiency and whether it would be technologically
>> > possible to make such a system.
>>
>>
>> <- Sun
>>
>> \
>> \
>> \ \
>> >-----------------||||||||=================
>> / /
>> /
>> /
>> solar wind linear mirror
>> collector accelerator
>> powered by
>> light reflected
>> from mirror
>>
>> collected solar wind particles accelerated and ejected
>> out the back through the middle of the mirror
>>
>>
>> force of solar wind and light -->
>> force of accelerated particles <----
>>
>> net force <--
>
>The conservation of linear momentum tells that the only way this can
>work is if the departing particles have more momentum than the
>arriving particles. This requires your "linear accelerator" to do
>work on those particles, and therefore it must rely on an external
>supply of energy.

That's sort of OK that far. The system uses solar energy to accelerate
the particles. But does the amount of energy provided by a photon
outweigh the momentum of the photon? Catching the photon means that its
outward momentum gets added to the momentum of the system.

>
>The question is basically "can I sail upwind", and the answer is "Yes,
>as long as you have an ocean to push against." I've never heard of a
>mechanism by which one can tack through the ether.

You can tack through the solar wind, but it relies on gravity to provide
the force that pulls you towards the Sun. An angled solar sail can
produce a lateral force that can slow down the orbit and allow gravity
to reduce the radius of the orbit.

--
Mike Williams
Gentleman of Leisure
.

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