this subroutine uses equation 3 of jpl
tm 391-240 of c christensen to find the
effective area of the panels of the mvm
s/c.  the panel angle is stored in
phit(i) for the time span tphi(i)
to tphi(i+1), where time is j.date
past t0.  for times when phi is
changing quickly, a linear interpolation
is provided.  its use is indicated by ipa==
iphi(bit2)=1.  for times when the
s/c was in free roll, ap(1)=ap(2)=0,
and ipb==iphi(bit1)=1.

epochs
1 -  2 start to tcm1
3 -  5 tcm1 to tcm2
6 -  7 tcm2 to tcm3 venus encounter
8 - 11 tcm3 to tcm5 superior conjunction
12 - 18 tcm5 to tcm8
19 - 22 tcm8 to eom mercury (3) encount