A major result of the IRAS mission was that the infrared spectral energy 
distributions (SEDs) of many young stars can be explained by protoplanetary 
disks.  Recent images from the repaired Hubble Space Telescope have now 
directly verified the presence of disks in a few cases.  One of the most 
important of these is the nearby object HH 30, where an optically thick 
circumstellar absorption disk, 450 AU in diameter, is seen nearly edge-on.  
HH 30 is now the best-resolved (7 AU per pixel) astrophysical accretion disk 
system of any type, and the first where the disk's vertical structure is 
clearly visible.  Model fitting of the HST images constrains the disk density
and temperature distributions to a family of solutions corresponding to a
wide range of possible infrared spectral energy distributions.  Obtaining new 
SED measurements is therefore critically important to a full understanding 
of the disk's internal structure, for determining the source luminosity, 
and for placing HH 30 in proper context with other objects already studied 
by ISO and IRAS.  We propose ISOCAM and ISOPHOT observations to measure the 
spectral energy distribution of HH 30 between 5-90 microns.  These data will 
be combined with the unique geometrical information available to firmly 
establish the relationship between temperature and vertical thickness for a 
young stellar object disk.  The results should provide unique insights into 
protoplanetary environments, and a strong test of accretion disk theories 
which are widely applied in astrophysics.