= Notes on Gravity =

== Description ==
(From email 7 September, 2012)

In the gravity folder there is a routine called [[Sgrav]].  It makes a file called [[SGRAV.TXT]] that is like [[SHAPE.TXT]] but with extra columns for surface acceleration, potential and laplacian (just as a check).  This is for a non-rotating body with GM=1.  Then [[Sacc]], [[Spot]], [[Sslp]] and [[Selv]] compute the surface acceleration, potential, slope and elevation (above geoid) for the body with the correct GM and omega.  [[Selv]] also makes the geoid file.

The main subroutine is [[GRAVITY]].  It computes the gravity at any point in space, inside, outside or on the surface.  I used it in my trajectory integration program for landing on Eros.  [[GLATLON]] is a special program I wrote for someone who wanted various information for points on Eros.  You can see how [[GRAVITY]] is used there.  There are five subroutines called by gravity called D1-D5 that subdivide the surface elements if your point of interest is too near to a facet.   Essentially it mimics a recursive call since you can't do that in FORTRAN.

----------