Letter from Thomas Gold to Dr Wilmot Hess, National Aeronautics and Space Administration [NASA], Manned Spacecraft Center, Houston, Texas Says that 'Now that there is no reasonable doubt left that the lunar surface is almost everywhere covered with a thick layer of a slightly cohesive, very fine powder, it seems appropriate once more for me to urge that this information be integrated as far as possible in the Apollo planning. As I have experimented very much with such substances (under NASA grants), I feel an obligation to assist with such work and to offer various suggestions how it can economically be done'. Goes on to give suggestions. Talks about astronaut exercises in a vacuum chamber. Also talks about the simulation of optical properties. 5 January 1968