We propose large-scale ISOPHT mapping of a bright comet's dust
 tail at 25um, in conjuction with ISOPHOT photometric measurements
 and ISOPHT polarimetery measurements scattered throughout the tail,
 and in parallel with other measurements proposed by astronomers of
 the Guaranteed Time Programme, to perform a dynamical Finson-
 Probstein / Monte Carlo and spectral modeling analysis of the dust
 emitted by the comet. We will determine the emission rate of dust,
 the total mass present in the tail, and the silicate:carbonaceous:
 water ice composition ratio of the dust. We will compare the ISO
 imaging and spectral data to other data obtained by IRAS, COBE/
 DIRBE, IUE, and ground based telescopes for relationships by comet-
 ary age, orbit, color temperature, silicate feature, and trail for-
 mation. The objects to be observed are any any of the following
 periodic comets (in order of preference):

 Spring Launch: P/Koppf, P/Schwassmann-Wachmann 3, P/Encke, P/Honda-
 Mrkos-Padjusakova, P/Borrelly, P/Pons-Winnecke, P/Clark,P/d'Arrest,
 P/Jackson-Neujmin, P/Churyumov-Gerasimenko.

 Fall Launch: P/Koppf, P/Haneda-Campos, P/Wolf-Harrington, P/Taylor,
 P/Hartley 2, P/Temple-Tuttle, P/Wild2, P/Gunn.