I_trgb = expected trgb I mag
Orb    = #Orbits
Time   = Time available assumes 2400 secs/orbit  
SN15   = Time to reach I_trgb at S/N=15  
SN10   = Time to reach I_trgb at S/N=10   
T_f814 = I band exptime/#exposures    
SN_I   = I band S/N at I = I_trgb   
T_f606 = V band exptime/#exposures
SN_V   = V band S/N at V = I_trgb - 2

The assumed strategy is 2x1200 sec exposures per orbit and ability 
to split an orbit between V & I as needed.

Example archival program S/N estimates from ETC:

Target       I_trgb  Orb  Time   SN15   SN10   T_f814  SN_I    T_f555  SN_V
---------------------------------------------------------------------------
NGC4258	      25.20    -     -     -       -   2600/2  21.7    5700/2   9.7  
NGC3627/M66   26.20    -     -     -       -   8872/8  17.2    2224/2   2.3
NGC3368/M96   26.20    -     -     -       -   9112/8  17.4    2280/2   2.4

CHP-II targets:

Target       I_trgb  Orb  Time   SN15   SN10   T_f814  SN_I    T_f606  SN_V
----------------------------------------------------------------------------
NGC5457/M101  25.42    3  7200   1760    844   3600/3  21.1    3600/3   7.8

NGC3627/M66   26.20    3  7200   6470   2951   4800/4  12.3    2400/2   3.1
NGC3368/M96   26.20    4  9600   6470   2951   7200/6  15.1    2400/2   3.1

NGC4536       26.92    6 14400  23018  10314  10800/9   9.7    3600/3   2.0
NGC4526	      26.95    6 14400  24288  10879  10800/9   9.4    3600/3   1.9
NGC4424	      26.97    6 14000  25174  11273  10800/9   9.3    3600/3   1.9
 
NGC1448       27.21   11 26400  38757  17311 18000/15   9.6    8400/7   2.3
NGC1365	      27.27   16 38400  43189  19281 24000/20  10.5  14400/12   2.9 
NGC1316	      27.42   16 38400  56646  25262 24000/20   9.2  14400/12   2.6