this program is given tables of pressure vs eccentric anomaly
for two times.
it outputs an interpolated pressure vector based on sbcor and t.
t -- julian days after the time of the initial conditions
used to generate the tables.
sbcor  --  position and velocity of the spacecraft(au,days)
press(100,3,2) two tables of pressures, with iumax(2) points
and for time time(2).
up(100,2) -- the abscissas, eccentric anomaly, for press
uflag -- when .true. causes a new u to be calculated from sbcor
pvec -- the outputted pressure vector