SCIENTIFIC ABSTRACT
Comets comprise the most primitive material in the solar system. Observations
of their composition are diagnostic of the environment during their formation.
Phenomena to be studied are bare cometary nuclei and onset of activity at large
heliocentric distances and gas and dust emissions in the inner solar system.
Objectives of observations of gas and dust are to characterize the physical
parameters of the dust (total production, sizes and surface properties) and to
analyze the chemical composition of both volatile and refractory constituents
with special emphasis on organic compounds. The first priority target, P/Kopff,
is most productive among the here proposed comets: not only in dust, but also
in gas production (OH up to 5x10^28). Also, a cometary trail of this comet was
observed by IRAS. Results from this observational programme have to be compared
with the results from the programme "Properties of Solar System Dust" and other
CP-comet observations by CAM, SWS and LWS.

OBSERVATION SUMMARY
Observations of active comets (P/Kopff and P/Churyumov-Gerasimenko or P/Wild 2)
should be made through 4 apertures (13.8 to 120 arcsec at three wavelengths
between 12.8 and 25 microns) centered on maximum brightness and through 9
filters (3.6 to 160 microns) to obtain thermal energy spectrum of the dust
emission. Spectra in the 2-12 micron range will be obtained with PHT-S, in
order to determine the strength and shape of features due to organic grains,
silicate grains and various molecular species (H2CO, CO, CO2, CH-X, etc.).
Observations of cometary nuclei and onset of activity (Chiron and
P/Schwassmann-Wachmann 1) should be made in several sets of flux measurements
from 25 to 160 microns with PHT-P and PHT-C. Observations through 3 different
apertures (52 to 99 arcsec) with the 60 micron filter may allow separation of
a dust coma from the nucleus.

LINKED OBSERVATIONS:
Active comets have high proper motion. They are tracked in the solar system
objects mode. No ephemeris are given here. The astrometric observation of the
target objects shortly before launch and during the ISO operation should be
used for ephemeris improvement. Background is determined by a subsequent (a few
days later) staring observation at the mid-term position of the previous
observation ("shadow" object). Targets for observations of bare nuclei are in
the outer solar system and hence have slow proper motion (< 0.1'/h). They are
observed as solar system objects with staring mode. In order to determine the
background, the method of "shadow" object is also used.

FIXED TIME OBSERVATIONS: The active comet observations are time-critical
(within a few days) because of the time-variable activity. It is planned to
specify the accurate observation time after the exact ephemeris are known and
an analysis of the background has been made. For planning purposes the
following time periods are given (S = spectro-photometry, P = photometry):
autumn launch:
	1. P/Kopff: Jan. 1996 (S)
	2. P/Kopff: Mar. 1996 (S)
	3. P/Kopff: Nov. 1996 (S)
spring launch:
	1. P/Kopff: begin Nov. 1996 (S)
	2. P/Kopff: mid Nov. 1996 (S)
	3. P/Kopff: Dec. 1996 (S)
The two Chiron observations are separated by about one-half the rotation period
(2.5 to 3 hours).

CONCATENATION:
Each comet observation starts with a peaking-up of the tracked comet. For
time-economy this is done only once per observation which includes several
filters-, apertures- and one spectrometer-observation. In addition the 3.6
micron observation has to be concatenated with the PHT-S observation in order
to provide absolute calibration of the spectra.