Official OGame Forum - Rules
(http://board.ogame.org/thread.php?threadid=269802):


VI. Moonchances

Free moonshots are allowed but pushing rules apply, a higher ranked
player may not keep a Debris Field created out of a lower ranked
players fleet.

    * Care must be taken that the higher ranked player does not
	obtain a profit in resources out of it.



Note: A GameOperator needs to be informed ONLY if the lower ranked
player intends to transport resources to the higher ranked one.

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OGame Wiki
(http://ogame.wikia.com/wiki/Rules):

Exceptions - Sending weak fleets to a planet without a moon in order
to produce a moon is allowed, so long as the debris field does not
exceed 2 milion resources (a 20% moon chance, the maximum).