From FRASER GORDON
Your Star Trek correspondent Robert Erck is mistaken in his understanding
of the solar sail article by Colin McInnes (Letters, 23 February). The sail
is not in a Keplerian orbit, so normal results for orbital mechanics do
not apply-the sail can move inward or outward in the Solar System by orientating
the sail appropriately; as explained in the article. An increase in sail
velocity is quite feasible.
Fraser Gordon University of Essex, Colchester
